Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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31984 Publications
Structure and chemistry of surface-doped Pt:SnO2 gas sensing materials
Degler, D.; Pereira De Carvalho, H. W.; Kvashnina, K.; Grunwaldt, J.-D.; Barsan, U. W. N.;
Surface-doped Pt:SnO2 was synthesized by impregnation of calcined SnO2 made by an aqueous sol-gel route. The structure of the introduced Pt-dopant and its behaviour during gas exposure were examined by in-situ and operando X-ray absorption spectroscopy. The results reveal that Pt forms a nano-sized PtO2 phase, which was not found for bulk and surface doped materials, studied previously. In a comparative investigation of undoped and Pt-doped SnO2 gas sensors the performance and the surface chemistry were investigated, the latter one using operando FT-IR spectroscopy. The results prove a strong influence of the different Pt structures on the surface chemistry of SnO2, providing the basis for an understanding on the varying sensor performance of differently synthesized Pt:SnO2 gas sensing materials

Publ.-Id: 23006 - Permalink


Crystal-field and covalency effects in uranates: x-ray spectroscopic study
Butorin, S.; Kvashnina, K.; Smith, A.; Popa, K.; Martin, P.;
The electronic structure of U(V) and U(VI) containing uranates NaUO3 and Pb3UO6 was studied using an advanced technique, namely x-ray absorption spectroscopy (XAS) in the high-energyresolution uorescence-detection (HERFD) mode. Thanks to a significant reduction of the core-hole lifetime broadening, the crystal-field splitting of the 5f shell were probed directly in the HERFDXAS spectra collected at the U 3d edge, which is not possible with conventional XAS. In addition, the charge-transfer satellites resulting from the U 5f-O 2p hybridization were clearly resolved. The crystal-field parameters, 5f occupancy, and degree of covalency of the chemical bonding in these uranates were estimated using the Anderson impurity model by calculating the U 3d HERFD-XAS, conventional XAS, core-to-core (U 4f-to-3d transitions) resonant inelastic x-ray scattering (RIXS) and U 4f x-ray photoelectron spectra, respectively. The crystal field was found to be strong in these systems, while the 5f occupancy was determined to be 1.32 and 0.84 electrons in the ground state for NaUO3 and Pb3UO6, respectively, thus indicating a significant covalent character for these compounds.

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  • Secondary publication expected

Publ.-Id: 23005 - Permalink


High-resolution x-ray absorption spectroscopy as a probe of crystal-field and covalency effects in actinide compounds
Butorin, S. M.; Kvashnina, K.; Vegelius, J. R.; Meyer, D.; Shuh, D. K.;
Applying the high-energy-resolution uorescence-detection (HERFD) mode of x-ray absorption spectroscopy (XAS) we were able for the first time to probe the crystalline electric field (CEF) splittings of the 5f shell directly in the HERFD-XAS spectra of actinides. Using ThO2 as an example, the data measured at the Th 3d edge were interpreted within framework of the Anderson impurity model. Since the charge-transfer satellites were also resolved in the HERFD-XAS spectra, their analysis revealed that ThO2 is not an ionic compound as previously believed. The Th 6d occupancy in the ground state was estimated to be as twice as much compared to that for the Th 5f states. We demonstrate that HERFD-XAS now allows for characterization of the CEF interaction and degree of covalency in the ground state of actinide compounds as it is extensively done for 3d transition metal systems.
  • Open Access LogoProceedings of the National Academy of Sciences of the United States of America 113(2016)29, 8093-8097
    DOI: 10.1073/pnas.1601741113

Publ.-Id: 23004 - Permalink


Valence fluctuations of europium in the boride Eu4Pd29+xB8
Gumeniuk, R.; Schnelle, W.; Ahmida, M.; Abd-Elmeguid, M.; Kvashnina, K.; Tsirlin, A.; Leithe-Jasper, A.; Geibel, C.;
We synthesized a high quality sample of the boride Eu4Pd29+xB8 (x = 0.76) and studied its structural and physical properties. Its tetragonal structure was solved by direct methods and confirmed to belong to the Eu4Pd29B8 type. All studied physical properties indicate a valence fluctuating Eu state, with a valence decreasing continuously from about 2.9 at 5 K to 2.7 at 300 K. Maxima in the T dependence of the susceptibility and thermopower at around 135 K and 120 K, respectively, indicate a valence fluctuation energy scale on the order of 300 K. Analysis of the susceptibility evidences some inconsistencies when using the ionic interconfigurational fluctuation (ICF) model, thus suggesting a stronger relevance of hybridization between 4f and valence electrons compared to standard valence-fluctuating Eu systems.

Publ.-Id: 23003 - Permalink


Kondo effect and thermoelectric transport in CePd3Bex
Gumeniuk, R.; Schnelle, W.; Kvashnina, K.; Leithe-Jasper, A.;
The physical properties of the series CePd3Bex (0 ≤ x ≤ 0.47) have been studied. Introducing Be into CePd3 results in a drastic reduction of the Seebeck coefficient from 100 μV K−1 at 300 K to -2 μV K−1, respectively. Paramagnetism of Ce3+ free ions and metallic conduction dominate the physical properties. A structural transition at x = 0.25 is accompanied by a significant lowering of the Kondo temperature and leads to a successive suppression of the thermoelectric performance of CePd3Bex with increasing x.
Keywords: crystal structure, Kondo effect, thermoelectric properties, XAS

Publ.-Id: 23002 - Permalink


Creating and imaging nanosized magnets using HIM and TEM holography
Hlawacek, G.; Röder, F.; Bali, R.; Wintz, S.; Hübner, R.; Bischoff, L.; Lichte, H.; Potzger, K.; Lindner, J.; Fassbender, J.ORC
Besides imaging, gas field ion source (GFIS) based microscopes [1] are used for materials modification. This usually is based on the use of high fluence to either mill the sample material or implant Nobel gas ions into the target material [2]. Here, we present a novel route utilizing a Helium Ion Microscope (HIM) to form nano–sized magnets of arbitrary shape using very low fluences (6 × 1014 cm−2) of 20 keV–25 keV Neon ions. The fine Neon beam available in the HIM is used to locally switch 40nm thin Fe60Al40 films from the well ordered paramagnetic B2 structure into the ferromagnetic A2 structure [3, 4]. Planar structures potentially useful for applications such as spin valves or other spin–transport devices have been formed this way. Kerr Microscopy and off–axis TEM holography has been used to analyze the resulting magnetic nano–structures. Results on the energy depended depth of magnetization as well as on the lateral definition of the magnetic structures due to scattering are presented.
  • Lecture (Conference)
    62nd AVS meeting, 18.-23.10.2015, San Jose, USA

Publ.-Id: 23000 - Permalink


High resolution surface patterning with the Helium Ion Microscope
Hlawacek, G.;
In the past years Helium Ion Microscopy (HIM) [1] has become a mature imaging and nano-modification technique. The method is best known for its high resolution imaging capabilities. In addition it provides excellent charge compensation capabilities and a high surface sensitivity [2]. With the introduction of Ne as an working gas for the used Gas Field Ion Source (GFIS) also fast and high resolution nanomachining has become possible. In the following I would like to give a brief introduction of the technique. Subsequently, I will present examples of materials modification with a highly focused Helium or Neon beam.
  • Invited lecture (Conferences)
    XXII International Conference on Ion-Surface Interactions, 20.-24.08.2015, Moskau, Russia

Publ.-Id: 22999 - Permalink


Application of Helium Ion Microscopy to surface science problems
Hlawacek, G.; Veligura, V.; Jankowski, M.; van Gastel, R.; Wormeester, R.; Zandvliet, H. J. W.; Poelsema, B.;
Helium Ion Microscopy (HIM) is well known for its high lateral resolution and unique nanomachining capabilities. In addition it is a very surface sensitive technique and therefore ideally suited to answer scientific questions in surface and interface science. I will give a brief introduction of the technique followed by a selection of problems related to surface and interface science.
The high surface sensitivity of HIM allowed us to measure the thickness of thin carbon layers present on gold nanorods. On the other hand one can use back scattered helium (BSHe) particles to reveal buried interfaces such as the diffusion front of a Pd2Si layer covered by more than 100 nm of SiO2.
The orientation of a sample can be determined using channeling. I will show that with a simple geometrical model channeling directions can be predicted with sufficient accuracy to align the He beam parallel to low index directions. Exploiting channeling into a crystalline sample the background from the substrate can be suppressed, thus enhancing the surface sensitivity even further. This has been used in a recent study of the surface reconstruction observed in the case of a few ML of Ag deposited on Pt(111). Based on a change of the work function of 25meV across the atomically flat terraces we can distinguish Pt rich from Pt poor areas and visualize the single atomic layer high steps between the terraces. Utilizing channeling/dechanneling and the exceptional surface sensitivity of the HIM we can measure the periodicity of the hcp/fcc pattern formed in the 2 ML thick Ag alloy layer. A periodicity of 6.65 nm along the <-1-12> surface direction has been measured. In terms of crystallography a hcp domain is obtained through a lateral displacement of a part of the outermost layer by 1/√3 of a nearest neighbor spacing along <-1-12>.
  • Invited lecture (Conferences)
    1st International Conference on Applied Surface Science, 27.-30.07.2015, Shanghai, China

Publ.-Id: 22998 - Permalink


On the way to a quantitative analytical ion microscopy
Klingner, N.; Hlawacek, G.; Heller, R.; Facsko, S.;
Analytical Ion Micrsocope
  • Lecture (Conference)
    Gas Ion Microscopy User Group Meeting 2015, 13.07.2015, Dublin, Ireland

Publ.-Id: 22997 - Permalink


Helium Ion Microscopy
Hlawacek, G.;
In the past years Helium Ion Microscopy (HIM) [1] has become a mature imaging and nano-modification technique. The method is best known for its high resolution imaging capabilities. In addition it provides excellent charge compensation capabilities and high surface
sensitivity [2]. With the introduction of Ne as an working gas for the used gas field ion source (GFIS) also fast high resolution nanomachining has become possible. In the following I would like to give a brief introduction to the technique. Subsequently I want to highlight the
importance of channeling to achieve the best possible imaging conditions and maximize the surface sensitivity. Finally I want to present selected results on high and low fluence He and Ne milling and implantation.
  • Invited lecture (Conferences)
    mmc2015, 29.06.-02.07.2015, Manchester, United Kingdom

Publ.-Id: 22996 - Permalink


Materials analysis using channeling and ionoluminescence in a helium ion microscope
Hlawacek, G.;
Helium ion Microscopy1 is a versatile microscopy technique that provides high resolution imaging and nano-machining in combination with a high surface sensitivity and large depth of focus. It utilizes a narrow beam of He+ ions to achieve a lateral resolution of less than 0.5 nm. Backscattered Helium ions (BSHe) and secondary electrons (SE) can be used to obtain an image of the specimen.
When using crystalline samples channeling of the particles can occur. This effect can be exploited in several ways in the HIM. First of all it is possible to map out the different channeling directions and intensities and thus obtain information on the crystal structure of the sample. A simple geometrical model is introduced that can predict the channeling directions and relative intensities observed in the HIM2. By exploiting channeling and making use of the dechanneling contrast thin surface layers can be made visible in SE as well BSHe images3. We used this to observe composition and structural changes in a 2 ML thin silver layer on Pt(111). Work function differences as small as 40 meV between Ag and Pt rich areas on the surface reveal the position of mono—atomic surface steps. A regular arrangement of areas with reduces the channeling probability reveals the surface reconstruction of the top 2—3 ML which has a periodicity of only 5.8 nm.
Ionoluminescence on the other hand allows to obtain information on defects in the bulk of the material. I will show results obtained for a variety of materials including semiconductors4, rare earth containing perovskites and ionic crystals. The types of defects were identified and the influence of the scanning conditions on the IL signal has been investigated5. We used IL to map out the interaction volume of the beam in NaCl, and demonstrate the possibility of subsurface patterning. In our setup using a 35 keV He+ beam and NaCl only 3 vac/nm-2 are needed to obtain a detectable IL signal6.
  • Invited lecture (Conferences)
    IBA2015, 14.-19.06.2015, Opatija, Croatia

Publ.-Id: 22995 - Permalink


Helium Ion Microscopy of atomic steps and surface reconstruction
Hlawacek, G.; Jankowski, M.; van Gastel, R.; Wormeester, H.; Zandvliet, H.; Poelsema, B.;
Helium Ion Microscopy (HIM) [1] is well known for its exceptional imaging and nanofabrication capabilities. HIM has an unprecedented surface sensitivity, and channeling can be utilized to maximise the signal to noise ratio. We demonstrate the resolving power of the technique using a thin (2 ML) silver layer on Pt(111). The obtained HIM results are compared to results obtained by low energy electron microscopy, spot profile analysis low energy electron diffraction (SPA-LEED), and atomic force microscopy phase contrast. In HIM single atom layer high steps can be visualized as a result of a work function change—across the otherwise atomically flat terraces—of only ~20 meV. By utilizing the dechanneling contrast mechanism [2] also the surface reconstruction of this thin surface layer can be revealed. We find a threefold periodic structure of channeling (fcc stacking) and dechanneling (hcp stacking) areas.
The periodicity—measured along the h112i surface direction—of this structure is 5.8 nm. This is in excellent agreement with values obtained by SPA-LEED [3].
  • Lecture (Conference)
    Physics Boat, 09.-11.06.2015, Helsinki, Stockholm, Finland, Sweden

Publ.-Id: 22994 - Permalink


He-ion Microscopy
Hlawacek, G.;
Tutorial on Helium Ion Microscopy
  • Invited lecture (Conferences)
    Physics boat 2015, 08.06.2015, Helsinki, Finland

Publ.-Id: 22993 - Permalink


Relaxation dynamics in graphene: Surprising Coulomb scattering effects
Winnerl, S.;
We report on Coulomb scattering effects in graphene and Landau-quantized graphene.
  • Lecture (others)
    3rd Workshop of the SPP "Graphene", 17.-20.05.2015, Kremmen, Deutschland

Publ.-Id: 22992 - Permalink


Relaxation dynamics in graphene studied by THz radiation from the free-electron laser FELBE
Winnerl, S.;
The free-electron laser FELBE, which is operated as a user facility, provides tunable radiation in the mid infrared and terahertz spectral range (wavelength: 4 – 230 µm) in form of ps pulses. It is driven by a superconducting accelerator that enables continuous pulsing operation at a repetition rate of 13 MHz, making it highly attractive for many experiments. We briefly review a few types of experiments including non-perturbative nonlinear spectroscopy and near-field microscopy on systems like excitons in semiconductor quantum wells or electrons confined in quantum dots. Mainly we discuss time-resolved spectroscopy on graphene and in particular Landau quantized graphene. Here evidence for extremely efficient Auger scattering is found that can actually deplete a level that at the same time is optically pumped.
Keywords: Graphene, ultrafast dynamics, FEL
  • Lecture (others)
    Semninar an der Uni Manchester, 25.11.2015, Manchester, United Kingdom

Publ.-Id: 22991 - Permalink


Coulomb scattering in the vicinity of the Dirac point in graphene
Winnerl, S.;
After a brief introduction into time-resolved spectroscopy we focus on polarization-resolved pump-probe experiments at different infrared photon energies. Here an anisotropy induced by the polarization of the pump beam is observed. For photon energies below the optical photon energy (~200 meV) the relaxation dynamics is dominated by Coulomb scattering. The experiments show directly that non-collinear scattering, which leads to an isotropic distribution, is remarkably slow at low fluences, namely on a timescale of 5 ps. The findings are in good agreement with microscopic theory. The timescale of this thermalization is very attractive for applications where hot carriers in graphene are exploited in detectors or modulators of infrared radiation.
Keywords: Graphene, ultrafast dynamics, Coulomb scattering
  • Invited lecture (Conferences)
    International workshop on many-body phenomena in graphene, 26.-27.10.2015, Gothenburg, Schweden

Publ.-Id: 22990 - Permalink


Coulomb Scattering in Graphene
Winnerl, S.; Mittendorff, M.; Otto, J.; Wendler, F.; Winzer, T.; Malic, E.; Knorr, A.; Schneider, H.; Helm, M.;
Coulomb interaction is the main mechanism that transforms a nonequilibrium carrier distribution in graphene into a hot Fermi-Dirac distribution. In many experiments carriers are assumed to be thermalized on a timescale well below 100 fs. However, we have recently observed that the carrier distribution is strongly anisotropic in k-space when graphene is excited with near infrared pulses (photon energy 1.5 eV, duration 30 fs). The anisotropy induced by the polarization of light vanishes on a timescale of 150 fs due to scattering with optical phonons [1]. Exciting with photon energies of 75 meV, i.e. well below the optical phonon energy (~200 meV), strongly quenches the scattering via phonons and allows one to study pure Coulomb scattering in the vicinity of the Dirac point. At low fluences the transition from the anisotropic distribution to an isotropic one is very slow (~5 ps at 10 K) since Coulomb scattering is predominantly collinear and thus preserves the anisotropic distribution. At higher fluences the strength of Coulomb scattering increases, resulting in a faster decay of the anisotropy. In a second experiment we study the relaxation dynamics in Landau quantized graphene [2].
By applying circularly polarized radiation in the pump-probe experiments individual low-index Landau level transitions can be addressed. Here a surprising effect is revealed, namely a change in sign of a pump-probe signal with respect to the expectation considering single-particle interactions only (cf.Fig.1). This is caused by strong Auger scattering that depletes the zeroth Landau level even though it is optically pumped at the same time.

[1] M. Mittendorff. et al. Nano Lett., 14 2014, 1504
[2] M. Mittendorff. et al. Nature Phys., 11 2015, 75
Keywords: Graphene, ultrafast spectroscopy, carrier dynamics, Coulomb scattering, Landau quantization
  • Lecture (Conference)
    Nanospectroscopy for two-dimensional materials, 08.-10.09.2015, Chemnitz, Deutschland

Publ.-Id: 22989 - Permalink


Strong Auger scattering in Landau-quantized graphene
Winnerl, S.; Mittendorff, M.; Wendler, F.; Malic, E.; Knorr, A.; Schneider, H.; Helm, M.;
While the carrier dynamics in graphene in absence of magnetic fields is well researched in a large spectral range ranging from UV to THz, the dynamics in Landau quantized graphene is almost unexplored. We investigate the carrier dynamics within the system of Landau levels (LLs) of index n = -1, n = 0 and n = 1 by pump-probe experiments complemented by microscopic modelling. Using circularly polarized mid-infrared radiation (photon energy 75 meV) allows one to selectively excite the two energetically degenerate transitions LL-1 → LL0 and LL-1 → LL0, respectively. Surprisingly, induced transmission is observed in one configuration of pumping and probing with opposite configuration (cf. Fig 1 (c) and (d)). Considering single particle Pauli blocking, one would expect induced absorption in this case. The sign change indicates that LL0 is depleted by strong Auger scattering, even though it is optically pumped at the same time.
We discuss the role of carrier-carrier and carrier-phonon scattering in Landau quantized graphene and provide an outlook on the application potential of this system for tunable THz lasers.

References
[1] M. Mittendorff, F. Wendler, E. Malic, A. Knorr, M. Orlita, M. Potemski, C. Berger, W. A. de Heer, H. Schneider, M. Helm, and S. Winnerl, " Nature Phys. 11, 75 (2015).
Keywords: Graphene, Landau quantization, Auger scattering, Terahertz
  • Lecture (Conference)
    Graphene Week 2015, 22.-26.06.2015, Manchester, United Kingdom

Publ.-Id: 22988 - Permalink


Einblick in die Relaxationsdynamik von Graphen mittels Infrarot-Kurzzeitspektroskopie: überraschende Coulomb-Streueffekte
Winnerl, S.;
Graphen, ein zweidimensionaler Kohlenstoffkristall weist eine Bandstruktur ohne Bandlücke auf. Im Bereich kleiner Energien ist die Dispersion linear und Elektronen und Löcher verhalten sich perfekt symmetrisch. Ihr Verhalten entspricht masselosen Dirac-Fermionen. Nach einem kurzen Überblick über grundlegende Eigenschaften von Graphen und dem Anwendungspotential dieses Materials stellen wir einige unserer Experimente zur Ladungsträgerdynamik vor.
Wird Graphen mit kurzen, linear polarisierten nahinfraroten Lichtpulsen angeregt, so beobachten wir eine im k-Raum anisotrope Ladungsträgerverteilung. Erstaunlicher Weise bleibt diese Anisotropie für 150 fs erhalten, obwohl die Elektron-Elektron Streuzeit in dem System viel kürzer ist. Wir zeigen, dass Energie- und Impulserhaltung für diese Anisotropie-erhaltende Wirkung der Coulomb-Streuung verantwortlich sind und eine isotrope Ladungsträgerverteilung durch Elektron-Phonon-Streuung erreicht wird. Verwenden wir zur Anregung Strahlung mit Photonenergie kleiner als die optische Phonon-Energie, so bleibt die Anisotropie auf der Skala von 1 – 10 ps erhalten. Für diese Experimente dient der Freie-Elektronenlaser FELBE als Strahlungsquelle.
Schließlich diskutieren wir die Ladungsträgerdynamik zwischen Landau-Niveaus von Graphen im Magnetfeld. Hierfür wurde zirkular polarisierte Infrarotstrahlung von FELBE eingesetzt. Hier gibt es aufgrund der Coulomb-Wechselwirkung einen sehr verblüffenden Effekt, nämlich dass ein Landauniveau entvölkert wird, obwohl es durch optisches Pumpen mit Ladungsträgern befüllt wird.
Zusammenfassend zeigen unsere Experimente, dass man mit Licht unterschiedlicher Wellenlänge und unterschiedlicher Polarisationszustände tiefe Einblicke in die Dynamik stark Coulomb-wechselwirkenden Elektronen in Graphen erhalten kann.
Keywords: Graphen, Relaxationsdynamik, Kurzzeit-Spektroskopie
  • Invited lecture (Conferences)
    26. Edgar Lüscher Seminar 2015, 07.02.2015-13.01.2016, Klosters, Schweiz

Publ.-Id: 22987 - Permalink


Terahertz spectroscopy at HZDR
Schneider, H.;
There is no abstract.
  • Invited lecture (Conferences)
    International consortium on terahertz photonics and optoelectronics conference, 16.-17.12.2015, Moskau, Russland

Publ.-Id: 22986 - Permalink


Applications of Helium Ion Microscopy
Hlawacek, G.;
HIM is well known for its exceptional imaging and nanofabrication capabilities. After a brief introduction of the gas field ion source and the ion microscope, I will present a wide range of results obtained with either the Twente UHV Orion+ or the NanoFab at the HZDR in Dresden. Special emphasis will be given to the use of channeling and the role of defects created by the energetic ion beam. Ionoluminescence is used to obtain information on the latter. Helium Ion Microscopy has an unprecedented surface sensitivity. Recent results obtained on thin silver layers on Pt(111) demonstrate that work function differences as small as ~20 meV as well as surface reconstructions can be visualized. Finally, some preliminary results of Neon based materials modification and cross section preparation will be presented.
  • Invited lecture (Conferences)
    49th Annual Meeting of the Israel Society for Microscopy, 17.-18.05.2015, Bar Ilan, Israel

Publ.-Id: 22985 - Permalink


Microscopy of (electronic) materials
Hlawacek, G.;
Microscopy of (electronic) materials
  • Invited lecture (Conferences)
    Festveranstaltung 30 Jahre Werkstoffe der Elektronik, 25.03.2015, Leoben, Österreich

Publ.-Id: 22984 - Permalink


Exploiting channelling in Helium Ion Microscopy
Hlawacek, G.;
Helium ion Microscopy1⁠ is a versatile microscopy technique that provides high resolution imaging and nano-machining in combination with a high surface sensitivity and large depth of focus. It utilizes a narrow beam of He+ ions to achieve a lateral resolution of less than 0.5 nm. Backscattered Helium ions (BSHe) and secondary electrons (SE) can be used to obtain an image of the specimen. While the first one will provide information of the bulk the latter is extremely surface sensitive2⁠.
When using crystalline samples channeling of the particles can occur. This effect can be exploited in several ways in the HIM. First of all it is possible to map out the different channeling directions and intensities and thus obtain information on the crystal structure of the sample. A simple geometrical model is introduced that can predict the channeling directions and relative intensities observed in the HIM. Such a map of the channeling directions for a fcc metal is presented in figure 13⁠. Channeling is also important for many imaging applications. The contrast on thin surface layers in SE mode can be enhanced when channeling is considered. For BSHe images the situation is more complicated as the signal is dominated by the bulk. Only heavy element adlayers on light element substrates can easily be imaged in BSHe mode. However, the dechanneling contrast also allows the visualization of light elements on heavy element substrates4⁠. In figure 2 a thin organic layer on a silicon wafer is made visible in SE and BSHe mode. By exploiting channeling and making use of the dechanneling contrast thin surface adlayers can be made visible in SE as well BSHe images5⁠.
  • Invited lecture (Conferences)
    EBSD 2015, 30.-31.03.2015, Glasgow, United Kingdom

Publ.-Id: 22983 - Permalink


Mechanisms of metal induced crystallization analyzed by in situ Rutherford Backscattering Spectroscopy
Wenisch, R.; Hanf, D.; Lungwitz, F.; Heller, R.; Hübner, R.; Gemming, S.; Krause, M.;
Metal induced crystallization (MIC) is a promising technique for low temperature thin film transistor fabrication and graphene synthesis. In MIC, a transition metal acts as seed for the crystallization of an amorphous group IV element. Bond screening near the interface and facilitation of nucleation are recently discussed as mechanisms for MIC. So far, in situ studies have been performed using X-ray diffraction, which is sensitive to the degree of crystallinity but lacks depth resolution. A better insight into the MIC mechanisms requires depth resolved in situ studies in order to determine the concentration profiles of the diffusing components.

Here, the Si/Ag and C/Ni bilayer systems are studied. They are annealed at temperatures of up to 750 °C. Simultaneously, the layer composition and the compositional profiles are investigated with in situ Rutherford backscattering spectroscopy revealing the diffusion kinetics of the components. Both, the quick initial nucleation and the ensuing growth processes are investigated. Further characterization is performed employing in vacuo Raman spectroscopy revealing the phase structure of the resulting films and scanning electron microscopy to investigate the surface structure.
  • Poster
    DPG Frühjahrstagung, 15.-20.03.2015, Berlin, Deutschland

Publ.-Id: 22982 - Permalink


In situ Study of Metal Induced Crystallization Processes for Low-Dimensional Materials Synthesis
Wenisch, R.; Heller, R.; Hanf, D.; Hübner, R.; Lungwitz, F.; Schumann, E.; Gemming, S.; Krause, M.;
Metal induced crystallization (MIC) is a promising technique for thin film transistor fabrication and graphene synthesis. In MIC, a transition metal catalyzes the crystallization of the amorphous phase of a group IV element by bond screening near the interface and facilitation of nucleation. So far, in situ studies have been performed using X-ray diffraction which is sensitive to the degree of crystallinity. However this technique lacks depth resolution and is therefore unable to track diffusion and layer exchange.
Here, the Si/Ag and C/Ni bilayer systems are studied. The samples are annealed at temperatures of up to 750 °C. Simultaneously, depth profiles of the elements are investigated by in situ Rutherford backscattering spectroscopy revealing the diffusion kinetics. The changes in the phase structure are explored by in situ Raman spectroscopy. Both the quick initial nucleation and ensuing growth processes are investigated. Scanning electron microscopy provides insight to the surface morphology.
  • Poster
    International Winterschool on Electronic Properties of Novel Materials, 08.-13.03.2015, Kirchberg in Tirol, Österreich

Publ.-Id: 22981 - Permalink


Ion Beam Analysis in the Helium Ion Microscope
Heller, R.; Klingner, N.; Facsko, S.; von Borany, J.; Gnauck, P.; Hlawacek, G.;
Helium ion microscopes (HIM) have turned into a frequently used imaging device in several laboratories around the world. Beside a sub nano-meter resolution and its high field of depth the latest generation of HIM devices (Zeiss Orion NanoFab) offers the ability to make use of Neon ions enabling additional opportunities in terms of surface modifications on the nm scale [1].

While the image generation in a HIM is based on evaluating the amount of secondary electrons the information carried by the back-scattered He/Ne projectiles (BSP) is not taken into consideration at the moment. Thus the HIM offers excellent topographic imaging capabilities but chemical information (in terms of elemental composition) of the surface is not accessible. Nevertheless back-scattered particles carry that information and may be used to provide additional contrast mechanism(s). First attempts to measure BSP energy spectra were done by Sijbrandij et al. [2] and gave evidence for the general feasibility but also revealed that a quantitative chemical analysis of thin layers would require development of more sophisticated detection concepts than those used in their experiments (silicon surface barrier detector).

In the present contribution we show the development and the implementation of a Time-of-Flight back-scattering spectrometry (ToF-BS) technique within our HIM. Pulsing the primary ion beam by using the existing beam blanker with a customized pulsing electronics enables us to generate pulses as short as below 10ns. BSP detection is done by means of a micro channel plate detector. Our measurements demonstrate that this technique is capable to achieve an energy resolution as good as 2keV (for 30keV He incident ions) by simultaneously keeping the spatial resolution in the order of a few 100nm. We further show that with some slight modification the presented setup can be utilized to acquire ToF spectra of sputtered particles as well, thus enabling lateral resolved ToF-SIMs within the HIM.

[1] G. Hlawacek, V. Veligura, R. van Gastel, and B. Poelsema, J. Vac. Sci. Technol. B 32(2), 2014, 020801.
[2] S. Sijbrandij, B. Thompson, J. Notte, B. W. Ward and N. P. Economou, J. Vac. Sci. Technol. B, 26(6), 2008, 2103-2106
  • Lecture (Conference)
    22nd International Conference on Ion Beam Analysis, 16.06.2015, Opatija, Croatia

Publ.-Id: 22980 - Permalink


KMC simulation of irradiation-induced nanostructure evolution in Oxide Dispersion Strengthened Fe-Cr alloys
Liedke, B.; Posselt, M.; Murali, D.; Abdou, J. M.; Claisse, A.; Olsson, P.;
Oxide Dispersion Strengthened (ODS) steels are considered as one of the most promising candidates for structural materials in next generation nuclear fusion reactors and future nuclear fission reactors [1]. The ODS materials consist of a ferritic or ferritic/martensitic Fe-Cr matrix filled with yttria-based oxide particles and is fabricated during mechanical alloying and hot consolidation processes. It is well known that their extraordinary properties such as high-temperature creep strength as well as high dose ion/neutron irradiation resistance are due to formation of small Y-Ti-O clusters with a size of few nanometers. Besides their significant effect on reduction of dislocations and grain-boundaries mobility, the nanoclusters also act as traps for point defects like vacancies, interstitials and helium, which may be typically generated in a nuclear reactor. It is still under debate what the formation mechanisms of the nanoclusters are and why they prove such high temperature and radiation damage stability.
Experimental methods typically applied to investigate the issues stated above cannot fully reflect the atomic-scale of the nanoclusters, as well as the mechanisms related to their formation, evolution and destruction upon radiation damage. Therefore, atomistic computer experiments can significantly contribute to a general understanding.
In this work, kinetic Monte Carlo (KMC) technique is applied to study evolution of Y-Ti-O nanoclusters in a bcc-Fe and FeCr matrix. Starting from a uniform distribution of O, Y, Ti atoms in the matrix at first a stationary state is produced by high temperature annealing. Such a state is characterized by a certain population of Y-Ti-O nanoclusters. Then vacancies and interstitials are introduced in order to simulate ion and neutron irradiation taking into account realistic conditions, and the evolution of the nanostructure is studied. The parameters for the atomic interactions used in KMC were obtained recently by first-principle Density-Functional-Theory calculations and applied in Metropolis Monte Carlo simulations on energetics, structure and composition of the Y-Ti-O nanoclusters [2].
1. G. R. Odette, M. J. Alinger, B. D. Wirth, Annu. Rev. Mater. Res. 38, 471 (2008)
2. M. Posselt, D. Murali, B. K. Panigrahi, Modelling Simul. Mater. Sci. Eng. 22, 085003 (2014)
Keywords: Oxide Dispersion Strengthened steels, ODS, kinetic Monte-Carlo, density functional theory
  • Lecture (Conference)
    Advances in Materials and Processing Technologies (AMPT), 14.-17.12.2015, Madird, Spain

Publ.-Id: 22979 - Permalink


Development of a new radiofluorinated quinoline analog for PET imaging of phosphodiesterase 5 (PDE5) in brain.
Liu, J.; Wenzel, B.; Dukic-Stefanovic, S.; Teodoro, R.; Ludwig, F.-A.; Deuther-Conrad, W.; Schröder, S.; Chezal, J.-M.; Moreau, E.; Brust, P.; Maisonial-Besset, A.;
Phosphodiesterases (PDEs) are enzymes that play a major role in cell signalling by hydrolysing the second messengers cyclic adenosine monophosphate (cAMP) and/or cyclic guanosine monophosphate (cGMP) throughout the body and brain. Altered cyclic nucleotide-mediated signalling has been associated with a wide array of disorders, including neurodegenerative disorders. Recently, PDE5 has been shown to be involved in neurodegenerative disorders such as Alzheimer's disease but its precise role has not been elucidated yet. To visualize and quantify the expression of this enzyme in brain, we developed a radiotracer for specific PET imaging of PDE5. A quinoline based lead compound has been structurally modified resulting in the fluoroethoxymethyl derivative ICF24027 with high inhibitory activity towards PDE5 (IC50 = 1.89 nM). Radiolabelling with fluorine-18 was performed by a one-step nucleophilic substitution reaction using a tosylate precursor (RCY(EOB) = 12.9 ± 1.8%; RCP >99%; SA(EOS) = 70-126 GBq/µmol). In vitro autoradiographic studies of [18F]ICF24027 on different mouse tissue as well as on porcine brain slices demonstrated a moderate specific binding to PDE5. In vivo studies in mice revealed that [18F]ICF24027 was metabolized under formation of brain penetrable radiometabolites making the radiotracer not suitable for PET imaging of PDE5 in brain.
Keywords: PDE5; PET imaging; Fluorine-18; quinoline; Micellar chromatography

Publ.-Id: 22978 - Permalink


NMR shift and relaxation measurements in pulsed high-field magnets up to 58 T
Kohlrautz, J.; Reichardt, S.; Green, E. L.; Kühne, H.; Wosnitza, J.; Haase, J.;
Nuclear magnetic resonance (NMR) experiments at fields up to 58 T in pulsed magnets at the Dresden High Magnetic Field Laboratory are reported. The challenge to resolve NMR shifts in these timedependent fields is addressed for the first time, and it is shown that this can indeed be accomplished with high precision with an internal reference. As a result, signal averaging is possible during a single magnetic field pulse, but also for multiple pulses. Thus, even very weak signals can in principle be recorded and their shifts can be determined. In a second set of experiments, the measurement of nuclear relaxation is investigated. Using adiabatic inversion with the inherent time dependence of the magnetic field and small-angle inspection, it is shown that relaxation measurements are possible, as well. The shift experiments were performed with 27Al NMR on a mixture of aluminum metal and a Linde type A zeolite. For the relaxation studies, 27Al NMR and 69Ga NMR on the metals aluminum and gallium were preformed, respectively.

Publ.-Id: 22977 - Permalink


Electron spin resonance modes in a strong-leg ladder in the Tomonaga-Luttinger liquid phase
Ozerov, M.; Maksymenko, M.; Wosnitza, J.; Honecker, A.; Landee, C. P.; Turnbull, M. M.; Furuya, S. C.; Giamarchi, T.; Zvyagin, S.;
Magnetic excitations in the strong-leg quantum spin ladder compound (C7H10N)2CuBr4 (known as DIMPY) in the field-induced Tomonaga-Luttinger spin-liquid phase are studied by means of high-field electron spin resonance (ESR) spectroscopy. The presence of a gapped ESR mode with unusual nonlinear frequency-field dependence is revealed experimentally. Using a combination of analytic and exact-diagonalization methods, we compute the dynamical structure factor and identify this mode with longitudinal excitations in the antisymmetric channel. We argue that these excitations constitute a fingerprint of the spin dynamics in a strong-leg spin-1/2 Heisenberg antiferromagnetic ladder and owe their ESR observability to the uniform Dzyaloshinskii-Moriya
interaction.

Publ.-Id: 22976 - Permalink


Subcritical transition to turbulence of a precessing flow in a cylindrical vessel
Herault, J.; Gundrum, T.; Giesecke, A.; Stefani, F.;
The transition to turbulence in a precessing cylindrical vessel is experimentally investigated. Our measurements are performed for a nearly resonant configuration with an initially laminar flow dominated by an inertial mode with azimuthal wave number m = 1 superimposed on a solid body rotation. By increasing the precession ratio, we observe a transition from the laminar to a non-linear regime, which then breakdowns to turbulence for larger precession ratio. Our measurements show that the transition to turbulence is subcritical, with a discontinuity of the wall-pressure and the power consumption at the threshold ϵLT. The turbulence is self-sustained below this threshold, describing a bifurcation diagram with a hysteresis. In this range of the control parameters, the turbulent flows can suddenly collapse after a finite duration, leading to a definitive relaminarization of the flow. The average lifetime 〈τ〉 of the turbulence increases rapidly when ϵ tends to ϵLT.
Keywords: DRESDYN precession turbulence transition bifurcation

Publ.-Id: 22975 - Permalink


Magneto-elastic coupling across the first-order transition in the distorted kagome lattice antiferromagnet Dy3Ru4Al12
Henriques, M. S.; Gorbunov, D. I.; Kriegner, D.; Valiska, M.; Andreev, A. V.; Matej, Z.;
Structural changes through the first-order paramagnetic–antiferromagnetic phase transition of Dy3Ru4Al12 at 7 K have been studied by means of X-ray diffraction and thermal expansion measurements. The compound crystallizes in a hexagonal crystal structure of Gd3Ru4Al12 type (P63/mmc space group), and no structural phase transition has been found in the temperature interval between 2.5 and 300 K. Nevertheless, due to the spin-lattice coupling the crystal volume undergoes a small orthorhombic distortion of the order of 2 x 10-5 as the compound enters the antiferromagnetic state. We propose that the first-order phase transition is not driven by the structural changes but rather by the exchange interactions present in the system.

Publ.-Id: 22974 - Permalink


High-resolution gamma-ray tomography for two-phase flow investigations in centrifugal pumps
Bieberle, A.; Schäfer, T.; Neumann, M.; Hampel, U.;
This article presents high-resolution gamma-ray computed tomography (HireCT) measurement technique for quantitative investigations of two-phase flow in authentically operated centrifugal pumps. For instance in nuclear power plants single liquid phase designed centrifugal pumps are used for the emergency cooling in a hypothetic accident scenario. Thus, their operation is essential to keep the reactor under control. This contribution includes the determination of measurement accuracy and selected results of two-phase flow studies in a commercially available industrial centrifugal pump. The HireCT scanner uses 137Cs as isotopic source emitting high energy gamma photons of 662 keV. This offers imaging as well as quantitative investigations in technical devices with dense walls, such as centrifugal pumps. CT scans have been applied especially in the impeller region of the operating industrial centrifugal pump. To observe gas-liquid phase distributions within a sharply mapped impeller wheel, which rotates with nominal speed of 1480 rpm, time-averaging rotation-synchronized computed tomography has been applied. Therefore, data projections of the entire radiation detector arc are continuously acquired with a sampling rate of 22 kHz. The detector contains 320 single scintillation detectors with an active area of 2 mm in width and 4 mm in height as well as a detection efficiency of about 75% for 662 keV gamma photons. The measuring accuracy was evaluated by a sophisticated mockup. For measurement intervals of 5 min a measuring accuracy of ±1% absolute could be provided. Identified phase fraction distributions in measurements at an authentically operated centrifugal pump at various inlet gas fractions offered gas phase buffering areas within the impeller chambers that apparently interfere the hydrodynamic processes and, thus, the transport of the liquid. Eventually, the HireCT have been proven as a suitable tool for two-phase flow investigations in rapidly rotating objects.
Keywords: Centrifugal pumps, gamma-ray computed tomography, two-phase flow
  • Contribution to proceedings
    Specialist Workshop on Advanced Instrumentation and Measurement Techniques for Nuclear Reactor Thermal Hydraulics (SWINTH), 15.-17.06.2016, Livorno, Italien
  • Lecture (Conference)
    Specialist Workshop on Advanced Instrumentation and Measurement Techniques for Nuclear Reactor Thermal Hydraulics (SWINTH), 15.-17.06.2016, Livorno, Italien

Publ.-Id: 22973 - Permalink


Active optical metasurfaces based on defect-engineered phase-transition materials
Rensberg, J.; Zhang, S.; Zhou, Y.; Mcleod, A. S.; Schwarz, C.; Goldflam, M.; Liu, M.; Kerbusch, J.; Nawrodt, R.; Ramanathan, S.; Basov, D. N.; Capasso, F.; Ronning, C.; Kats, M.;
Active, widely tunable optical materials, such as phase-transition materials, have enabled rapid advances in photonics and optoelectronics, especially in the emerging field of meta-surfaces and meta-devices. Here, we demonstrate that spatially selective defect engineering on the nanometer scale can transform phase-transition materials into optical metasurfaces. Using ion irradiation through nanometer-scale masks, we selectively defect-engineered the insulator-metal transition of vanadium dioxide, a prototypical correlated phase-transition material whose optical properties change dramatically depending on its state. Using this robust technique, we demonstrated several optical metasurfaces, including tunable absorbers with artificially induced phase co-existence and tunable polarizers based on thermally triggered dichroism. Spatially selective nanoscale defect engineering represents a new paradigm for active photonic structures and devices.
Keywords: metasurfaces, metamaterials, meta-devices, defect engineering, phase-transition materials

Publ.-Id: 22972 - Permalink


Tailored magnetic fields for controlling the electrochemical deposition of metal
Mutschke, G.; Mühlenhoff, S.; Yang, X.; Eckert, K.; Tschulik, K.; Uhlemann, M.; Fröhlich, J.; Bund, A.;
The contribution will give an overview of recent results regarding the influence of magnetic fields on the electrochemical deposition of metal. Magnetic fields give rise to forces on the electrolyte which, if properly applied, can be useful. Lorentz forces have been known long-since for causing convection of the electrolyte, and thus, to affect mass transfer. Magnetic gradient forces are well established for the purpose of magnetic particle separation and also influence electrolytes that consist of para- or diamagnetic ions and molecules. The presentation will mainly discuss two different ways of controlling the metal deposition by tailored magnetic fields. First it will be shown that Lorentz forces originating from specific inhomogeneous magnetic field configurations can be utilized for improving the uniformity of the metal deposit at vertical electrodes, despite of the influence of buoyancy [1].
On the contrary, magnetic fields can also be beneficial for obtaining a desired non-uniform deposition at length scales down to the micrometer range. Here, the Kelvin force resulting from small-scale gradient fields can be utilized. Depending on the electrolyte composition, structured deposits of paramagnetic and also of diamagnetic metal ions can be obtained, despite of the small modulus of the magnetic susceptibility of the latter. In both examples, analytical reasoning, simulations and experimental results of lab-scale electrochemical systems will be presented which elucidate the interplay of forces, the electrolyte flow and the effect on mass transfer [2-3].

References:
[1] S. Mühlenhoff et al.; On the homogenization of the thickness of Cu deposits by means of MHD convection within small dimension cells. Electrochem. Comm. 36 (2013) 80–83.
[2] G. Mutschke et al.; Comment on "Magnetic Structuring of Electrodeposits". Phys. Rev. Lett. 109 (2012) 229401.
[3] M. Uhlemann et al.; Structured Electrodeposition in Magnetic Gradient Fields. Eur. Phys. J. Spec. Top. 220 (2013) 287-302.
Keywords: electrochemistry, electrolysis, metal deposition, magnetic field, Lorentz force, Kelvin force, buoyancy, convection
  • Invited lecture (Conferences)
    2015 International Chemical Congress of Pacific Basin Societies (PACIFICHEM 2015), 15.-20.12.2015, Honolulu, USA

Publ.-Id: 22971 - Permalink


Multi-isotope comparison of 3He, 21Ne, and 36Cl moraine ages from the high-altitude central Puna Plateau, NW Argentina (24°S)
Luna, L.; Bookhagen, B.; Niedermann, S.; Merchel, S.; Rugel, G.; Scharf, A.; Strecker, M.;
Glacial deposits on the high-altitude, arid Puna Plateau of northwestern Argentina document past changes in climate, but the associated geomorphic features have never been directly dated. The plateau is situated in the “Arid Diagonal,” the hyper-arid transition zone between the Westerlies precipitation dominated southern Andes, and the South American Summer Monsoon controlled central Andes. Despite the climatically critical position of the Puna Plateau, paleoclimate data for the region is extremely sparse. This study provides direct age control of glacial moraine deposits from the central Puna Plateau (24°S) at elevations of 4500-5000 m through cosmogenic surface exposure dating. The volcanic lithologies of the deposits additionally allow for comparison of production rates from multiple cosmogenic isotope systems at low latitude and high elevation. Moraine boulders were dated using cosmogenic 3He from pyroxene, 21Ne from quartz, and 36Cl from feldspars. Preliminary data suggests that the most extensive glaciation occurred more than 80 ka ago, and that an additional prominent advance occurred at ~39 ka. In addition, comparison of isotope production ratios from low latitude and high elevation will contribute to better constrained production rates, particularly for 36Cl, for which global production rate estimates are highly variable. This study documents Quaternary climate changes on the Puna Plateau, while at the same time improving production rate agreement between multiple cosmogenic isotope systems.
Keywords: AMS, TCN, cosmogenic dating, paleoclimate, feldspars, quartz, pyroxene
  • Poster
    European Geosciences Union (EGU) General Assembly, 17.-22.04.2016, Vienna, Österreich

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Publ.-Id: 22970 - Permalink


Radiative particle-in-cell simulations - plasma based light sources and synthetic spectroscopy
Pausch, R.; Debus, A.; Huebl, A.; Steiniger, K.; Widera, R.; Bussmann, M.;
We present simulated far field radiation spectra from plasma based light sources such as high harmonics generation (HHG) during laser foil irradiation and betatron oscillation during laser-wakefield-acceleration (LWFA). The synthetic spectra allow quantifying both total radiation flux of these light sources and the occurring radiation background. We also present applications of far field radiation as spectroscopic diagnostic of the plasma dynamics occurring during LWFA and a variety of plasma instabilities, such as Kelvin-Helmholtz and the Rayleight-Taylor instability. This so-called synthetic diagnostic allows probing the electron dynamics by predicting the emitted radiation spectra thus emulating real experiments.

In order to obtain these results, we developed an in-situ method to compute spectrally and angularly resolved far field radiation based on Liénard-Wiechert potentials. By computing radiation concurrently to simulating the plasma dynamics, using the particle-in-cell code PIConGPU, we are able to take into account all $sim10^{10}$ electrons simulated, thus allowing to quantify both coherent and incoherent radiation. Furthermore, spectra can be computed for thousand of observation directions and frequencies simultaneously. We show that the code’s capability of resolving radiation processes temporally is an indispensable tool for linking the evolution of the plasma dynamics to the emitted radiation.
Keywords: PIConGPU, LWFA, HHG, KHI, radiation, spectra, synthetic diagnostics
  • Poster
    Novel Light Sources from Laser-Plasma Interactions, 20.-24.04.2015, Dresden, Deutschland

Publ.-Id: 22969 - Permalink


Silicon photomultiplier readout of a monolithic 270×5×5 cm3 plastic scintillator bar for time of flight applications
Reinhardt, T. P.; Gohl, S.; Reinicke, S.; Bemmerer, D.; Cowan, T. E.; Heidel, K.; Röder, M.; Stach, D.; Wagner, A.; Weinberger, D.; Zuber, K.;
The detection of 200-1000MeV neutrons requires large amounts, ∼100 cm, of detector material because of the long nuclear interaction length of these particles. In the example of the NeuLAND neutron time-of-flight detector at FAIR, this is accomplished by using 3000 monolithic scintillator bars of 270×5×5 cm3 size made of a fast plastic. Each bar is read out on the two long ends, and the needed time resolution of sigma_t < 150 ps is reached using fast timing photomultipliers. In the present work, it is investigated whether silicon photomultiplier (SiPM) photosensors can be used instead. Experiments with a picosecond laser system were conducted to determine the timing response of the SiPM-preamplifier assembly. The response of the full system including the scintillator was studied using 30MeV single electrons provided by the ELBE superconducting electron linac. The ELBE data were matched by a simple Monte Carlo simulation, and they were found to obey an inverse-square-root scaling law. In the electron beam tests, a time resolution of sigma_t = 136 ps was reached with a pure SiPM readout, well within the design parameters for NeuLAND.
Keywords: Time of flight detector Neutron detector FAIR Nuclear Astrophysics Silicon Photomultiplier Avalanche Photodiode Picosecond laser system Photomultiplier

Publ.-Id: 22968 - Permalink


Liquid metal batteries
Weber, N.;
Liquid metal batteries consist of a stable density stratification of two liquid metals, separated by a likewise liquid salt, which is working as electrolyte. A potentially very long lifetime, extreme current densities and a low price are just a few advantages of such cells, making them a promising candidate for stationary energy storage. Simulations of the fluid flow in liquid metal batteries are presented.
  • Poster
    International Summer School Storage 4 Energy S4E 2015, 05.-10.10.2015, Dresden, Deutschland

Publ.-Id: 22967 - Permalink


Synthetic in situ radiation diagnostics in particle-in-cell codes – from the lab to the stars with a GPU-accelerated code
Pausch, R.; Debus, A.; Steiniger, K.; Huebl, A.; Widera, R.; Schramm, U.; Bussmann, M.;
We present the synthetic in situ radiation diagnostic included in the 3D3V particle-in- cell code PIConGPU. It provides spectrally and angularly resolved far field radiation and thus translates the simulated plasma dynamics to radiation observables accessible in experiments.
Our radiation diagnostics algorithm based on Liénard-Wiechert potentials is capable of predicting non-linear Thomson scattering of both sub-relativistic and relativistic electrons in plasmas. The multi-GPU-based implementation and its direct integration into the particle-in-cell code PIConGPU not only results in high processing speeds - up to 7.2 Peta FLOPS on TITAN - but also enables to compute the radiation for all ~10^10 simulated macro particles, thousands of frequencies and hundreds of observation directions. Such performance permits to cover spectral ranges from infrared to X-ray with virtual radiation detectors covering an entire “skymap”, whereas taking into account all particles allows us to make quantitative predictions of the emitted radiation power for both coherent and incoherent plasma radiation occurring simultaneously. We discuss in detail how our multi-GPU-based implementation overcomes bandwidth, processing speed and disk space constraints seen in CPU- based radiation codes by replacing the offline fast Fourier transform over several tens of Petabytes of particle trajectories with an in situ Fourier transform.
We demonstrate PIConGPU’s capabilities using simulated spectra of plasma based light sources and accelerators, realized in laboratories today, and instabilities, occurring in astrophysical jets. As examples, we show a quantitative analysis for high harmonics generation (HHG) during laser foil irradiation, an explorative search for spectral signatures of laser wakefield acceleration (LWFA) and a time-dependent study of Kelvin-Helmholtz instability (KHI) spectra.
Keywords: PIConGPU, radiation, LWFA, KHI, HHG, spectra, sky map
  • Poster
    ICNSP 2015 - International Conference on Numerical Simulation of Plasmas, 12.-14.08.2015, Golden, USA
  • Poster
    HZDR PhD Seminar 2015, 02.-04.11.2015, Altenberg, Deutschland

Publ.-Id: 22966 - Permalink


Energy filter for tailoring depth profiles in semiconductor doping application
Csato, C.; Krippendorf, F.; Akhmadaliev, S.; von Borany, J.; Han, W.; Siefke, T.; Zowalla, A.; Rüb, M.;
This work presents the physics and technology of a micromechanically fabricated ‘‘energy filter’’ for doping applications. This energy filter is capable of producing pre-defined tailored doping profiles by a single monoenergetic ion implantation. The functional principle of the energy filter is explained using a simple model. Pattern transfer is being investigated for two different filter-substrate distances. Different aspects of the filter’s temperature behavior during irradiation are discussed. Finally, the results of an entire wafer area implantation are presented and discussed.
Keywords: Implantation, Ion, Energy filter, Silicon carbide, Doping homogeneity

Publ.-Id: 22965 - Permalink


Synthesis and radiofluorination of 4-(6-fluoro-fluoren-9-on-2-yl)-1,4-diazabicyclo[3.2.2]nonane for imaging of alpha-7 nicotinic acetylcholine receptor (α7 nAChR) by PET
Scheunemann, M.; Teodoro, R.; Wenzel, B.; Deuther-Conrad, W.; Brust, P.;
Aim: Until now, the two fluorinated dibenzothiophene sulfones [18F]ASEM(1) and its para fluorinated isomer [18F]DBT10(2) have been developed from a novel class of α7 nicotinic acetylcholine receptor (nAChR) ligands based on the antiviral drug tilorone. The aim of this study is to investigate the effect of substituting the SO2 by a CO linkage on the radiofluorination efficiency of the corresponding fluoren-9-one analogues and on radioligand parameters.
Methods: FLN-19 was prepared from 3-nitro-fluoren-9-one via bromination, fluorodenitration and Pd catalyzed cross coupling in 25% overall yield. A precursor with a nitro leaving group for radiolabelling was similarly obtained. Binding affinity for human nAChRs was evaluated in vitro by radioligand displacement experiments. [18F]FLN-19 was obtained via nucleophilic aromatic substitution. In vitro autoradiography of [18F]FLN-19 on pig brain slices was performed.
Results: FLN-19 binds with high affinity and selectivity to α7 nAChR (Ki = 1.18 nM, 288 nM, and 64.0 nM for α7, α4β2, and α3β4 nAChR, respectively). The highest nitro-to-fluoro conversion was obtained in DMF under microwave assisted heating (labeling yields ≈ 90%), and [18F]FLN-19 was prepared in ≥ 97% radiochemical purity. Binding of [18F]FLN-19 on pig brain slices was significantly reduced by α7 nAChR-specific ligands.
Conclusions: With [18F]FLN-19, a first fluorenone derived α7 nAChR radioligand was readily prepared, efficiently radiolabelled and successfully tested in first in vitro studies.

References

1. Horti A. G. et al. J Nucl. Med., 2014, 55, 672-677.
2. Teodoro R. et al. Molecules, 2015, 20, 18387-18421.
  • Lecture (Conference)
    Nuklearmedizin2016, 54. Jahrestagung der DGN, 20.-23.04.2016, Dresden, Deutschland

Publ.-Id: 22964 - Permalink


Theoretical investigation of in situ k-restore processes for damaged ultra-low-k dielectrics
Förster, A.; Wagner, C.; Schuster, J.; Gemming, S.;
Ultra-low-k (ULK) materials are essential for today's production of integrated circuits (ICs). However, during the manufacturing process, the ULK's low dielectric constant (k-value) increases due to the replacement of hydrophobic species with hydrophilic groups. We investigate the use of plasma enhanced fragmented silylation precursors to repair this damage. The fragmentation of the silylation precursors octamethylcyclotetrasiloxane (OMCTS) and bis(dimethylamino)-dimethylsilane (DMADMS) and their possible repair reactions are studied using density functional theory (DFT) and molecular dynamics (MD) simulations.
Keywords: k-Restore; Low-k materials; DFT; MD; Plasma repair

Publ.-Id: 22963 - Permalink


Radiosynthesis and biological evaluation of the new PDE10A radioligand [18F]AQ28A
Wagner, S.; Teodoro, R.; Deuther-Conrad, W.; Kranz, M.; Scheunemann, M.; Fischer, S.; Wenzel, B.; Egerland, U.; Hoefgen, N.; Steinbach, J.; Brust, P.;
Cyclic nucleotide phosphodiesterase 10A (PDE10A) regulates the level of the second messengers cAMP and cGMP in particular in brain regions assumed to be associated with neurodegenerative and psychiatric diseases. A better understanding of the pathophysiological role of the expression of PDE10A could be obtained by quantitative imaging of the enzyme by positron emission tomography (PET). Thus, in this study we developed, radiolabeled and evaluated a new PDE10A radioligand, 8-bromo-1-(6-[18F]fluoropyridin-3-yl)-3,4-dimethylimidazo[1,5-a]quinoxaline ([18F]AQ28A). [18F]AQ28A was radiolabeled by both nucleophilic bromo-to-fluoro or nitro-to-fluoro exchange using K[18F]F-K2.2.2-carbonate complex with different yields. Using the superior nitro precursor, we developed an automated synthesis on a Tracerlab FX F-N module and obtained [18F]AQ28A with high radiochemical yields (33±6%) and specific activities (96-145 GBq/µmol) for further evaluation. Initially, we investigated the binding of [18F]AQ28A to the brain of different species by autoradiography and observed the highest density of binding sites in striatum, the brain region with the highest PDE10A expression. Subsequent dynamic PET studies in mice revealed a region-specific accumulation of [18F]AQ28A in this region, which could be blocked by pre-injection of the selective PDE10A ligand MP-10. In conclusion, the data suggest [18F]AQ28A is a suitable candidate for imaging of PDE10A in rodent brain by PET.
Keywords: PDE10 radioligand, 18F-labeled radioligand, automated synthesis, nitro precursor, bromo precursor, Animal PET/MR
  • Open Access LogoJournal of Labelled Compounds and Radiopharmaceuticals 60(2017)1, 36-48
    DOI: 10.1002/jlcr.3471

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Publ.-Id: 22962 - Permalink


Synthesis of fluorine-containing PDE10A-Inhibitors as potential Ligands for Positron Emission Tomography (PET).
Franz, L.; Scheunemann, M.; Wagner, S.; Lang, M.; Brust, P.; Briel, V.;
Phosphodiesterases (PDE ́s) are second messenger hydrolysing enzymes and important regulators of signal transduction mediated by these molecules. PDE10A, a cAMP and cGMP sensitive hydrolase, is primarily expressed in the striatum and was identified as drug target for the therapy of diverse disorders in the central nervous system (CNS) [1] like schizophrenia or chorea huntington [2]. Recently, 1-arylimidazo[1,5-a]quinoxalines have been reported to be potent and selective inhibitors of PDE10A [3]. In terms of a potential use as 18F-labelled PET imaging agent new substituted derivatives were synthesized. It has been shown that the methoxy substituted inhibitors are prone to metabolic oxidation, which leads to a loss of inhibitory potency or ability to cross the blood brain barrier [3,4].
To improve the metabolic stability of inhibitors the methoxy function in position 6 was exchanged by chlorine. In the first synthesis step chlorine was introduced at position 6 by electrophilic aromatic substitution. An electron deficient system was generated in step 2 by oxidation of the amine to a nitro function to allow the nucleophilic aromatic substitution of fluorine by 4-methylimidazole in step 3. Afterwards, the amine was recovered by acidic reduction with elementary iron in step 4 and acetylated in step 5. Cyclisation in step 6 was realized by a Bischler-Napieralski reaction. The derivatization of the 1-arylimidazo[1,5-a]quinoxaline was focused on position 1 and 8. Finally, the fluoro-pyridinyl-group was introduced by Suzuki-coupling with the corresponding boronic acid at the brominated positions to afford the mono- or disubstituted pyridinyl derivatives. All compounds were characterized by high performance liquid chromatography, nuclear magnetic resonance spectroscopy and mass spectrometry. It is expected that the new chlorinated derivatives have the same pharmaceutical effects as their methoxy analogues.
  • Poster
    Annual Meeting of the German Pharmaceutical Society - DPhG, 23.-25.09.2015, Düsseldorf, Deutschland

Publ.-Id: 22961 - Permalink


Quantifying the interaction of seismicity and gas transport in fractured hard rock at earthquake focal depth (DAFGAS-II)
Lippmann-Pipke, J.; Erzinger, J.;
Es ist kein Abstract vorhanden.
  • Other report
    Potsdam: GFZ, 2015
    13 Seiten

Publ.-Id: 22960 - Permalink


Alles im Fluss
Helm, M.; Michel, P.; Gensch, M.; Wagner, A.;
Der supraleitende Elektronenbeschleuniger ELBE erzeugt als Sekundärstrahlung auch Infrarot- und THz-Photonen, Positronen, Neutronen und MeV-Röntgenquanten.
Keywords: ELBE, Beschleuniger, Freie-Elektronenlaser, Positronen
  • Physik Journal 15(2016)1, 29-34

Publ.-Id: 22959 - Permalink


Regular flow reversals in Rayleigh-Benard convection in a horizontal magnetic field
Tasaka, Y.; Igaki, K.; Yanagisawa, T.; Vogt, T.; Zuerner, T.; Eckert, S.;
MHD Rayleigh-Benard convection was studied experimentally using a liquid metal inside a box with square horizontal cross section and aspect ratio five. Systematic flow measurements were performed by means of ultrasonic velocity profiling that can capture time variations of instantaneous velocity profiles. Applying a horizontal magnetic field organizes the convective motion into a flow pattern of quasi-two dimensional rolls arranged parallel to the magnetic field. The number of rolls has the tendency to decrease with increasing Rayleigh number Ra and to increase with increasing Chandrasekhar number Q. We explored convection regimes in a parameter range, at 2x10^3 < Q < 10^4 and 5x10^3 < Ra < 3x10^5, thus extending the regime diagram provided by Yanagisawa et al. (Physical Review E, 2013). Three new regimes were identified, whereas the regime of regular flow reversals in which five rolls periodically change the direction of their circulation with gradual skew of the roll axes can be considered as the most remarkable one. The regime appears around a range of Ra=Q = 10, where irregular flow reversals were observed in Yanagisawa et al. (2013). We performed the POD analysis on the spatio-temporal velocity distribution and detected that the regular flow reversals can be interpreted as a periodic emergence of a 4-rolls state in a dominant 5-rolls state. The POD analysis
Keywords: Rayleigh-Benard convection

Publ.-Id: 22958 - Permalink


Ge nanoparticle formation in ZrO2/Ge and SiN/Ge superlattices by flash lamp annealing
Rebohle, L.; Seidel, S.; Wutzler, R.; Prucnal, S.; Hübner, R.; Helm, M.; Skorupa, W.; Lehninger, D.; Heitmann, J.; Klemm, V.; Rafaja, D.;
Semiconductor nanocrystals in dielectric matrices are of great interest for a broad range of applications, especially in the field of photon management in solar cells and for non-volatile memories. In this work we investigate the formation of crystalline Ge nanoparticles in superlattice stacks by flash lamp annealing. In detail, amorphous ZrO2/Ge and SiN/Ge superlattices confined by two SiO2 layers on Si were produced by magnetron-sputtering and plasma-enhanced chemical vapor deposition, respectively. Raman and TEM investigations reveal that, depending on the original Ge layer thickness, crystalline Ge nanoparticles with different aspect ratios will be formed under annealing. As shown by electrical measurements, these layers feature large charge trapping capabilities. We compare these two types of layer systems with regard to the formation process of the Ge nanoparticles, the trapped charge density, the memory window and the retention. Finally, the perspectives for non-volatile memories are discussed, if these layer stacks are downscaled to current device dimensions.
Keywords: Ge nanoparticles, amorphous ZrO2, flash lamp annealing, non-volatile memory
  • Lecture (Conference)
    EMRS Spring Meeting 2015, 11.-15.05.2015, Lille, France

Publ.-Id: 22957 - Permalink


Probleme der SUV-Quantifizierung in der Positronenemissionstomografie und mögliche Lösungswege/Problems of SUV Quantification in Positron Emission Tomography and Possible Solutions
van den Hoff, J.; Hofheinz, F.;
Die Genauigkeit und Reproduzierbarkeit des Standardized Uptake Value (SUV) zur quantitativen Auswertung von Ganzkörper-PET/CT-Untersuchungen wird von messtechnischen und biologischen Faktoren beeinflusst, welche die Aussagekraft des SUV einschränken, insbesondere seine Eignung als Surrogat des Glukosemetabolismus in der FDG-PET. In messtechnischer Hinsicht wird der SUV unmittelbar von der Güte der Kreuzkalibrierung zwischen PET-Gerät und Dosiskalibrator wie auch von der Genauigkeit des Patientengewichts beeinflusst. Adäquate Qualitätskontrolle vorausgesetzt können diese Einflussgrößen aber beherrscht werden. Eine grundsätzliche Beschränkung bei kleinen Läsionen stellen Partialvolumeneffekte dar, welche sich gar nicht oder nur mit ungenügender Verlässlichkeit korrigieren lassen. Bei Läsionsgrößen unterhalb etwa des 3-Fachen der räumlichen Auflösung ist eine sinnvolle SUV-Bestimmung nur noch sehr bedingt möglich. Neben messtechnischen Faktoren beeinflussen 2 biologische Effekte maßgeblich die Verlässlichkeit der SUV-Bestimmung, zum einen die nicht unbeträchtliche Zeitabhängigkeit des SUV, zum anderen die Tatsache, dass der SUV sich proportional zum gegebenen Tracerangebot im arteriellen Blut ändert, wobei Letzteres selbst nach Normierung auf SUV-Einheiten eine beträchtliche Variabilität zwischen verschiedenen Untersuchungen aufweist. Diese biologischen Faktoren führen zu einer schlechten Test/Retest-Stabilität des SUV, was insbesondere nachteilig für Verlaufsuntersuchungen oder die schwellwertbasierte Unterscheidung zwischen benignen und malignen Läsionen ist. Beide Effekte können durch den Übergang vom SUV zum Tumor-zu-Blut Standard Uptake Ratio (SUR) eliminiert werden. Der SUR ist bildgestützt leicht zu bestimmen, sofern ein großes Gefäß (Aorta, Herzventrikel) in der Untersuchung miterfasst wird. Der Scanzeit-korrigierte SUR weist eine im Vergleich zum SUV deutlich verbesserte lineare Korrelation zur metabolischen Umsatzrate auf, wodurch sich die diagnostische Aussagekraft der PET erhöht, wie erste klinische Studien belegen.

Abstract
Accuracy and reproducibility of the Standardized Uptake Value (SUV) for quantitative evaluation of whole body PET/CT investigations is influenced by technical and biological factors which limit its value, notably suitability of the SUV as a surrogate of glucose metabolism in FDG PET. On the technical side the SUV is directly influenced by the quality of the cross calibration between the PET system and the dose calibrator as well as by accuracy of the assumed patient weight. Given adequate quality control these factors can be handled. A principal limitation in small lesions are partial volume effects, which cannot be corrected at all or only with insufficient reliability. For lesion sizes below approximately three times the given spatial resolution a meaningful SUV determination is only possible with substantial reservations. Beside the technical factors, 2 biological factors strongly influence the reliability of SUV determination, the notable time dependency of the SUV on the one hand and on the other hand the fact that the SUV changes in proportion to the given tracer supply in the arterial blood, where the latter exhibits substantial variability even after normalization to SUV units. These biological factors lead to poor test/retest stability of the SUV which is especially disadvantageous for follow-up investigations or threshold based discrimination between benign and malign lesions. Both effects can be eliminated by a transition from SUV to the tumor to blood Standard Uptake Ratio (SUR). Image-based determination of the SUR is easy, provided a large vessel (aorta, heart ventricle) is covered by the investigation. In comparison to SUV, the scantime corrected SUR exhibits a distinctly improved linear correlation to the metabolic uptake rate which increases the diagnostic power of PET as could be demonstrated in first clinical studies.
Keywords: Positronenemissionstomografie - PET/CT - Standard Uptake Value - SUV - Standard Uptake Ratio - SUR/positron emission tomography - PET/CT - Standard Uptake Value - SUV - Standard Uptake Ratio - SUR

Publ.-Id: 22956 - Permalink


Shallow Boron Emitters in Crystalline Silicon through in-Diffusion by Flash Lamp Annealing
Riise, H. N.; Schumann, T.; Azarov, A.; Hübner, R.; Skorupa, W.; Svensson, B. G.; Monakhov, E.;
Flash Lamp Annealing (FLA) is a technique in which Si can be heated to temperatures close to and above its melting point within a few milliseconds [1, 2] and it has been shown to be suitable for annealing of implantation-induced damage [2, 3] and for activation of implanted dopants [4]. Recently, FLA was also proved to be effective in forming shallow Phosphorous (P) emitters in Si through diffusion from a P surface source deposited by spin coating [5].
In this work, it is demonstrated that shallow Boron (B) emitters can be formed in crystalline Silicon (Si) by spin coating and subsequent in-diffusion using FLA. A 300 μm Float Zone mono-crystalline Si wafer was spin-coated at 6000 rpm for 30 seconds by a polyboron spin-on diffusant (Filmtronics B155 SOD) before being processed with FLA. After heat treatment by FLA, the film was oxidized in HNO3:H2SO4 (1:1) before being removed by HF. Secondary Ion Mass Spectrometry (SIMS), sheet resistance measurements and Transmission Electron Microscopy (TEM) analysis were performed to determine the B diffusion profile, the sheet resistance and crystal quality of the samples, respectively.
Annealing for 10 and 20 ms with an energy density of 93-105 J/cm2 leads to B emitter depths of 140- 200 nm and peak B concentrations of 1-3·1020cm−3. Sheet resistance values below 200 Ω/ indicate high dopant activation. These values are well suited for e.g. emitters in crystalline Si solar cells as the shallow emitters will only absorb photons with a wavelength below 420 nm [6] and most of the available sunlight will be absorbed in the base of the cell while the low sheet resistance gives a low series resistance. High-resolution TEM images of the surface and junction regions did not show any crystal defects demonstrating that the FLA treatment does not induce high defect concentrations in the samples. TEM did however reveal a rough surface resulting from the etching treatment to remove the SOD.
Annealing for 10 and 20 ms with energy densities below 90 J/cm2 produce even shallower profiles with a maximum B extension of <100 nm while the peak concentration still remains above 1·1020cm−3 whilst the sheet resistance increases to 300-3000 Ω/. In conclusion, spin-coating with subsequent in- diffusion by FLA is thus a versatile technique with possibility to tailor the emitter depth in Si while still keeping the peak concentration high.
References
[1] H. A. Bomke, H. L. Berkowitz, M. Harmatz, S. Kronenberg, R. Lux, Applied Physics Letters 33, 955 (1978).
[2] J. T. Lue, Applied Physics Letters 36, 73 (1980).
[3] R. Klabes, et al., Physica Status Solidi A: Applications and Materials Science 66, 261 (1981).
[4] T. Ito, et al., Japanese Journal of Applied Physics, Part 1: Regular Papers, Brief Communications & Review Papers 41, 2394 (2002).
[5] H. B. Normann, et al., Applied Physics Letters 102, 132108 (2013).
[6] M. A. Green, Solar Energy Materials & Solar Cells 92, 1305 (2008).
  • Poster
    2015 MRS Spring Meeting & Exhibit, 06.-10.04.2015, San Francisco, CA, USA

Publ.-Id: 22955 - Permalink


Nanoripple patterning under medium energy implantation using metal foreign atoms
Redondo-Cubero, A.; Palomares, F. J.; Lorenz, K.; Mücklich, A.; Hübner, R.; Vázquez, L.;
Ion beam sputtering (IBS) is a universal phenomenon that can be used for the production of nanopatterns in a wide range of materials and scales. Many semiconductor systems are suitable for this kind of processing, but Si is certainly the most studied one due to its technological relevance and mono-elemental nature [1]. In the last years, the key role of metal impurities for the initial formation of the pattern has been clearly established [2], changing the field in a significant way. Still, several questions remain open, such as the segregation effect of metal silicides [3], the relevance of preferential sputtering for the different metal species [4], or the threshold metal concentration needed for nanopatterning at given experimental conditions. Most of these works are restricted to low energetic beams (0.5-5 keV) produced with conventional ion guns and different set-ups to induce indirect metal codeposition [5]. However, in order to have an appropriate control of the metal species more dedicated systems, where metal could be also directly incorporated, are becoming essential. In this communication, we will present our recent experimental works on IBS nanopatterning of Si at medium energies (40 keV) with simultaneous metal incorporation [6]. In order to understand the influence of the metal on the pattern formation we study three different experimental systems produced with (a) direct metal implantation, (b) indirect metal co-deposition, i.e., with simultaneous irradiation of a metallic plate adjacent to the target, and (c) with non-metal implantation (used as a reference). In all cases, irradiation was carried out in a high-flux ion implanter using an incidence angle of 60º with respect to the target surface normal and for different ion fluences. The dynamics of the pattern is studied using atomic force microscopy (AFM) to characterize the pattern morphology, and particularly to quantify the surface roughness and pattern wavelength. Metal content was determined with Rutherford backscattering spectrometry and the formation of silicides mapped with X-ray photoelectron spectroscopy. In addition, we performed current sensing AFM as well as transmission electron microscopy analysis of the metal containing samples in order to disclose the formation of any compositional pattern and its eventual correlation with the morphological one. We will discuss the main differences arising from the different metal incorporation paths, paying special attention to effects such as geometrical shadowing, the threshold contents required to trigger the pattern in every case and the formation of metal silicides. [1] J. Muñoz-García et al., Mater. Sci. Eng. R-Rep. 86, 1 (2014) [2] C. Madi et al., Phys. Rev. Lett. 101, 246102 (2008) [3] M. Engler et al., Nanotechnology 25, 115303 (2014) [4] R. Gago et al., Nanotechnology 25, 415301 (2014) [5] K. Zhang et al., Nanotechnology 25, 085301 (2014) [6] A. Redondo-Cubero et al. Phys. Rev. B 86, 085436 (2012)
  • Invited lecture (Conferences)
    2015 MRS Spring Meeting & Exhibit, 06.-10.04.2015, San Francisco, CA, USA

Publ.-Id: 22954 - Permalink


TEM investigation of barrier-like anodic oxide films on aluminium
Schneider, M.; Lämmel, C.; Hübner, R.; Michaelis, A.;
In a previous work, the authors investigated the formation of thin barrier-like oxide films on aluminium using pulse anodizing [1]. The electrochemical experiments have shown differences in the properties and behaviour of the anodic films depending on the pulse frequency. Furthermore, the results suggest a relationship to the microstructure (e.g. thickness or composition) of the oxide films. Therefore, the authors have completed the former investigation by new research using transmission electron microscopy (TEM) and ellipsometry. All results were compared with electrochemical measurements. Again, the anodic films were formed at 3VAg/AgCl with various pulse frequencies in an acetate buffer solution (pH5.9). The aluminium was chemical vapour deposited on silicon wafers to get a smooth and well-defined surface which is favourable for subsequent analytical analysis (TEM, ellipsometry). The TEM investigation confirms the tendency that the oxide thickness decreases with increasing pulse frequency. The film thicknesses determined by coulometry and microscopy fit very well assuming a native oxide layer of approximately 1nm. Additionally, the Al:O ratio across the film thickness clearly depends on the pulse frequency. A model concept explaining this fact will be presented. Furthermore, there are no indications to the formation of crystalline domains within the oxide layers deposited at various pulse frequencies.
[1] M. Schneider, C. Lämmel, C. Heubner, A. Michaelis: Surface and Interface Analysis 45 (2013) 1497-1502
  • Lecture (Conference)
    VII Aluminium Surface Science & Technology Conference, 17.-21.05.2015, Madeira Island, Portugal

Publ.-Id: 22953 - Permalink


Three-Dimensional Hydrodynamic Numerical Simulations of Gas-Liquid Flows in Reactor with Ceramic Foams as Internals.
Subramanian, K.; Baldota, R. D.; Zalucky, J.; Schubert, M.; Lucas, D.; Hampel, U.;
Ceramic foams are promising alternatives for packing internals used in chemical engineering processes due to their high porosity and high specific surface area, which results in low pressure drop and high catalytic utilization of the packing. The application of solid foam packings as catalyst carriers, particularly for gasliquid systems, are not yet well understood. Due to their highly porous nature, it is very tough to understand the interplay between hydrodynamic behaviour and process performance [1]. The aim of this work is to perform three-dimensional Computational Fluid Dynamics (CFD) simulations of the evolving gas-liquid flow patterns considering ceramic foams as column internals and to validate them with experimental X-ray tomographic studies The closures applied for trickle bed simulation studies are modified according to the hydraulic/geometric properties of the ceramic foam considering the flow domain as porous. The influence of the liquid and gas drag is taken into consideration via Relative Permeability approach [2] and added as external source term to the liquid and gas momentum equations separately. The influence of dispersion forces are further included inorder to steady the liquid spreading and liquid saturation. The geometrical parameters of the ceramic foam packing are estimated using µCT image analysis. Empirical correlations proposed in earlier experimental studies are included in 3D CFD models. Initial results of trickle bed reactor simulations were presented earlier [3]. In this work, the validation of CFD simulation with X-ray tomographic experimental studies will be presented and discussed in detail.

Reference 1 :: S. Calvo., d. Beugre.,m.Crine., a. Leonard., p. Marchot.,d.Toye.,phase distribution measurements in metallic foam packing using x-ray radiography and micro-tomography, chemical engineering and processing, 48, 1030–1039 (2009).
Reference 2 :: A.E. Saez,, R.G.Carbonell, Hydrodynamic parameters for gas-liquid cocurrent flow in packed beds,AIChE Journal, Vol. 31, No.1, 52-62 (1985).
Reference 3 :: K.Subramanian, M. Schubert, D. Lucas, U. Hampel, Closures for simulation of gas-liquid flows in solid foam structures, ISCRE23 & APCRE7, Sep 7 – 10 2014, Bangkok, Thailand.
Keywords: CFD, Foam, Multiphase , Porous media
  • Lecture (Conference)
    10th European Congress of Chemical Engineering, 27.09.-01.10.2015, Nice, France

Publ.-Id: 22952 - Permalink


36Cl and 129I at ASTER and DREAMS
Rugel, G.; ASTER-Team; Braucher, R.; Merchel, S.; Pavetich, S.; Scharf, A.; Ziegenrücker, R.;
At ASTER (Accélérateur pour les Sciences de la Terre, Environnement, Risques) and DREAMS (DREsden Accelerator Mass Spectrometry) sophisticated ion sources are used for 36Cl and 129I. Both facilities have dedicated 36Cl chemistry labs. At DREAMS it is also used for storage and pressing of AgCl in sample holders (SHs). Most 36Cl-AMS labs, reduce the isobar 36S from the SH by a labor-intensive AgBr-backing. Though, at ASTER and DREAMS only ultrapure Ni and Cu is used, respectively. To find out the pros and cons of the two materials, we have (a) exposed AgCl pressed in Ni and Cu to air (in the dark). After 2 h only, cauliflower-type NiCl2 (analysed by EDX) has been formed from AgCl and Ni preventing any later AMS, whereas AgCl in Cu after 3 days looks unweathered and is still measurable. (b) compared S-decline in AgCl pressed in Ni and Cu (ASTER SHs). After ∼5 min S decreases by a factor of ∼5 for both reaching the same low S-rate after 20 min. However, S is higher at 5-20 min in Cu showing that Cu is contaminated at the surface. High S is not seen at all at DREAMS for DREAMS Cu SHs. Thus, chemical etching and controlled storage of Cu SHs might be a cheaper and better alternative for 36Cl-AMS.
For 129I AMS a sophisticated tuning strategy is minimising sputtering of any iodine containing material at DREAMS.
Keywords: AMS, cross-contamination, ASTER, sulphur, sulfur
  • Poster
    DPG Frühjahrstagung des Arbeitskreises Atome, Moleküle, Quantenoptik und Plasmen (AMOP), 29.02.-04.03.2016, Hannover, Deutschland

Publ.-Id: 22950 - Permalink


Time-Resolved Two Million Year Old Supernova Activity Discovered in the Earth’s Microfossil Record
Bishop, S.; Ludwig, P.; Egli, R.; Chernenko, V.; Deveva, B.; Faestermann, T.; Famulok, N.; Fimiani, L.; Gomez, J.; Hain, K.; Korschinek, G.; Hanzlik, M.; Merchel, S.; Rugel, G.;
Using accelerator mass spectrometry, we have conducted a search for live, supernova-produced, 60Fe atoms within biogenically produced magnetite (Fe3O4)crystals contained in two Pacific Ocean sediment cores. We have found a time-resolved 60Fe signal in both sediment cores, above background, centered at approximately 2.1 Myr ago and spanning approximately 800 kyr duration (full width half maximum). The onset of this signal coincides with a known marine extinction event at the Pleiocene/Pleistocene boundary, and its shape will require eventual astrophysical interpretation to understand.
Keywords: AMS, supernova, magneto-fossil
  • Lecture (Conference)
    DPG Frühjahrstagung des Fachverbandes Physik der Hadronen und Kerne und des Arbeitskreises Beschleunigerphysik, 14.-18.03.2016, Darmstadt, Deutschland
  • Invited lecture (Conferences)
    Max-Planck-Institute for Physics (MPP) Colloquium, 17.05.2016, München, Deutschland
  • Invited lecture (Conferences)
    Seminar Geophysics Faculty of the Kazan Federal University, 22.03.2016, Kazan, Tatarstan, Russia
  • Invited lecture (Conferences)
    Summer Institute Using Particle Physics to understand and image the Earth Geoneutrinos, Muography, Cosmogenic Nuclides, 11.-21.07.2016, L’Aquila, Italy

Publ.-Id: 22949 - Permalink


Alternative fabrication routes towards oxide dispersion strengthened (ODS) steels and model alloys
Bergner, F.;
The talk is focussed on fabrication, in particular non-standard or alternative fabrication routes towards ODS steels. There is a natural reference for that, namely state-of-the-art ODS steels produced by the ‘classical’ PM route, which consists of the production of a pre-alloy, gas atomization, mechanical alloying, consolidation and thermal, mechanical or thermo-mechanical treatment. The motivation to consider alternative routes is derived from problems such as the multi-step/multi-parameter character of the PM process and the resulting high production costs, limited throughput and limited reproducibility. These problems can be addressed by way of improving, simplifying, skipping or combining individual steps, by way of reconsidering alloy fabrication from the melt or by looking for hybrid routes. It is demonstrated that there is a wide and fascinating potential for alternative fabrication routes towards ODS steels. For this to be achieved, each of the steps involved in the classical PM route has to be carefully reconsidered. Moreover, the liquid metal route and hybrid routes composed of PM and LM elements have to be taken into account. Significant progress has been made on particular process steps. These include substitution of mechanical alloying, scaling up of SPS and the contactless excitation of cavitation.
Keywords: ODS steels, Fabrication
  • Lecture (Conference)
    Advances in Materials and Processing Technologies (AMPT 2015), 14.-17.12.2015, Madrid, Spain

Publ.-Id: 22948 - Permalink


Late Pleistocene outburst floods from Issyk Kul, Kyrgyzstan?
Rosenwinkel, S.; Landgraf, A.; Korup, O.; Schwanghart, W.; Volkmer, F.; Dzhumabaeva, A.; Merchel, S.; Rugel, G.; Preusser, F.;
Elevated shorelines and lake sediments surrounding Issyk Kul, the world’s second largest mountain lake, record fluctuating lake levels during Quaternary times. Together with bathymetric and geochemical data, these markers document alternating phases of lake closure and external drainage in the Late Pleistocene. The uppermost level of lake sediments requires a former blockage of the lake’s western outlet through the Boam gorge. Previous studies hypothesised that failures of Pleistocene ice or landslide dams in the gorge generated partial outburst floods of Issyk Kul. We test this hypothesis by exploring possible links between late Quaternary lake levels and outbursts. We dated stranded shorelines using 14C in shells, snails, and plant detritus, as well as sand lenses in delta and river sediments using Infrared Stimulated Luminescence. Our dates are consistent with lake levels expanding into Boam gorge between ~46 ka and 22 ka. Cosmogenic 10Be and 26Al exposure ages of fan terraces containing erratic boulders downstream of the gorge constrain the timing of possible outburst floods to 22-24 ka, postdating a highstand of Issyk Kul. A flow competence analysis gives a peak discharge of >104 m3 s–1 for entraining and transporting these boulders. Palaeoflood modelling, however, shows that naturally dammed lakes unconnected to Issyk Kul could have produced such high discharges upon sudden emptying. Hence, although our data are consistent with hypotheses of catastrophic outburst flooding, we caution against directly these to Pleistocene lake levels of Issyk Kul. Average lake-level changes of up to 90 mm yr–1 in the past 150 years were highly variable without any outburst event, so that attributing catastrophic lake-level drops to dam breaks is ambiguous using sedimentary archives alone. Nevertheless, the Pleistocene flood events that we reconstruct are among the largest reported for the Tien Shan mountains, and motivate further research into the palaeoflood hydrology in Central Asia.
Keywords: outburst flood, lake-level changes, palaeoflood, Issyk Kul, Kyrgyzstan, cosmogenic nuclide, exposure age, AMS
  • Earth Surface Processes and Landforms 42(2017), 1535-1548
    DOI: 10.1002/esp.4109

Publ.-Id: 22947 - Permalink


Effect of neutron flux on the characteristics of irradiation-induced nanofeatures and hardening in pressure vessel steels
Wagner, A.; Bergner, F.; Chaouadi, R.; Hein, H.; Hernández-Mayoral, M.; Serrano, M.; Ulbricht, A.; Altstadt, E.;
Effects of neutron flux (or dose rate) on the characteristics of irradiation-induced nanofeatures in neutron-irradiated pressure vessel steels were occasionally reported. Such effects let one expect that the mechanical properties mediated by the operation of the nanofeatures as dislocation obstacles would also depend on flux. However, there are controversial views on the presence of flux effects on mechanical properties. The present approach is based on the investigation of pairs of samples from the same batch of material for a number of RPV steels including different levels of Cu as well as base and weld materials. The samples of each pair were irradiated at about the same temperature but different fluxes up to about the same fluence, thus automatically revealing potential flux effects. Small-angle neutron scattering and Vickers hardness testing were applied to characterize the nm-scale solute clusters and the resulting irradiation hardening. A number of analytic models of cluster evolution, namely deterministic growth and coarsening, and hardening as well as combinations thereof were applied to interpret the trends extracted from the experimental results. It is found that there are indeed trends of the cluster size and volume fraction as functions of flux but no resolvable trend for hardening. The absence of a flux effect on hardening can be rationalized in terms of size and number density of solute clusters that enter the hardening expressions. Size and number density depend on flux in opposite directions and, therefore, partly cancel out. Flux effects for the whole set of experimental data including low- and high-Cu base metals and welds can be consistently described by a combination of deterministic growth and dispersed barrier hardening using a unique value of the obstacle strength of solute clusters.
Keywords: Pressure vessel steel, Neutron flux, SANS, Microstructure, Hardening

Publ.-Id: 22946 - Permalink


Experimental characterisation of a novel, compact high-field beamline for application in laser-driven ion beam therapy
Kroll, F.; Karsch, L.; Masood, U.; Pawelke, J.; Schürer, M.; Schramm, U.;
Introduction:
Compact laser-driven ion accelerators are a potential alternative to complex, large and expensive conventional accelerators. High-power short-pulse lasers, impinging on e.g. thin metal foils enable multi-MeV ion acceleration on µm length and ps time scale. The generated ion bunches (typically protons) show unique beam properties, like ultra-high pulse dose. Nevertheless, laser accelerators still require substantial development in reliable beam generation and transport. We present first experimental results on a beamline prototype based on high-field magnet technology specifically designed for capture and transport of laser-accelerated particles.

Material and methods:
Since the mid-1950s, pulsed high-field magnets serve as versatile research tools for solid state physics and material research. Recently developed pulsed magnet technology, specifically designed to meet the demands of laser acceleration [1], open up new research opportunities: We present a pulsed solenoid for effective collection and focusing of laser-accelerated ions which could function as a first component in a laser-driven gantry system [2]; furthermore, we present a dipole magnet for beam deflection and energy dispersion. The magnets were combined to form a first, pulsed high-field beamline and are powered by portable pulse. Characterization of both magnets has been carried out using a 10 MeV proton beam from a conventional Tandetron accelerator at Helmholtz-Zentrum Dresden – Rossendorf (HZDR). The transported beam was detected by means of radiochromic film and scintillator.

Result:
The transport experiments clearly show the functionality of both magnets: The solenoid focuses the large, divergent ion beam to a millimeter-sized spot showing no aberration. The dipole deflects the protons by a 45° angle and can be used as energy selection device via energy dispersion. For the several 10 µs long proton bunches no effect of the time structure of the magnetic pulse (~ several 100 µs) was observed thus making the magnets well suited for even shorter, laser-driven ion bunches. The beam position accuracy, after passing the beamline, was measured to be of the same order as the beam position fluctuations itself, showing the precision of the installed beamline. The maximum magnetic field strength achieved was 20 T for the solenoid and 5 T for the dipole. For operation at higher proton energies, i.e. above 200 MeV, an increase by a factor of only 1.5 – 2 is requested.

Summary:
Our experimental results show that compact high-field magnets can be used to precisely guide charged particle bunches. The pulsed nature of laser-accelerated particles is matched by the magnet technology. The maximum field strengths reached are sufficient for experiments with protons of several 10 MeV kinetic energy. For clinically relevant energies above 200 MeV, however, a slight increase is required. Experimental studies at a laser-accelerator are scheduled.
References
[1] T. Burris-Mog, et al., Laser accelerated protons captured and transported by a pulse power solenoid, PRSTAB 14, 121301 (2011)
[2] U. Masood, et al., A compact solution for ion beam therapy with laser accelerated protons, Appl. Phys. B 117, 41 (2014)
Keywords: ion beam therapy, beamline, pulsed magnet, laser acceleration
  • Lecture (Conference)
    46. Jahrestagung der Deutschen Gesellschaft für Medizinische Physik (DGMP) e. V., 09.-12.09.2015, Marburg, Deutschland
  • Open Access LogoContribution to proceedings
    46. Jahrestagung der Deutschen Gesellschaft für Medizinische Physik (DGMP) e. V., 09.-12.09.2015, Marburg, Deutschland
    46. Jahrestagung der Deutschen Gesellschaft für Medizinische Physik (DGMP) e. V. - Abstractband, 978-3-9816508-8-4

Publ.-Id: 22945 - Permalink


Nanostructured BN–Mg composites: features of interface bonding and mechanical properties
Kvashnin, D. G.; Krasheninnikov, A. V.; Shtansky, D.; Golberg, P. B. S. D.;
Magnesium (Mg) is one of the lightest industrially used metals. However, wide applications of Mg-based components require a substantial enhancement of their mechanical characteristics. This can be achieved by introducing small particles or fibers into the metal matrix. Using first-principles calculations, we investigate the stability and mechanical properties of a nanocomposite made of magnesium reinforced with boron nitride (BN) nanostructures (BN nanotubes and BN monolayers). We show that boron vacancies at the BN/Mg interface lead to a substantial increase in BN/Mg bonding establishing an efficient route towards the development of BN/Mg composite materials with enhanced mechanical properties.
Keywords: BN nanotubes, composite materials

Publ.-Id: 22944 - Permalink


Silicon and silicon-nitrogen impurities in graphene: Structure, energetics, and effects on electronic transport
Ervasti, M. M.; Fan, Z.; Uppstu, A.; Krasheninnikov, A. V.; Harju, A.;
We theoretically study the atomic structure and energetics of silicon and silicon-nitrogen impurities in graphene. Using density-functional theory, we get insight into the atomic structures of the impurities, evaluate their formation energies and assess their abundance in realistic samples. We find that nitrogen, as well as oxygen and hydrogen, are trapped at silicon impurities, considerably altering the electronic properties of the system. Furthermore, we show that nitrogen doping can induce local magnetic moments resulting in spin-dependent transport properties, even though neither silicon nor nitrogen impurities are magnetic by themselves. To simulate large systems with many randomly distributed impurities, we derive tight-binding models that describe the effects of the impurities on graphene π electron structure. Then by using the linear-scaling real-space Kubo-Greenwood method, we evaluate the transport properties of large-scale systems with random distribution of impurities, and find the fingerprintlike scattering cross sections for each impurity type. The transport properties vary widely, and our results indicate that some of the impurities can even induce strong localization in realistic graphene samples.
Keywords: graphene, defects, electronic transport

Publ.-Id: 22943 - Permalink


Evaluation and Improvement of MR-based Attenuation Correction for PET/MR
Schramm, G.;
This chapter is an introduction to the fields of Positron Emission Tomography (PET), hybrid Positron Emission Tomography and Magnetic Resonance Imaging (PET/MR), attenuation correction (AC), and MRI-based attenuation correction (MRAC). Since this work represents a cumulative dissertation, the aim of this chapter is to provide the required background to understand the intentions and the context of the three publications [Schramm et al., 2013a,b, 2014] dealing with the evaluation and improvement of MRAC. These publications are included in chapter 3 of this work.
  • Doctoral thesis
    TU Dresden, 2015
    Mentor: Prof. Jörg van den Hoff
    107 Seiten

Publ.-Id: 22942 - Permalink


Super-Resonant Infrared Near-Field Microscopy
Lang, D.; Uhlig, T.; Kehr, S. C.; Eng, L. M.; Helm, M.;
Scattering-type scanning near-field optical microscopy (s-SNOM) is an AFM-based technique for achieving nanoscale resolution even at infrared wavelengths [1]. s-SNOM thus is of valuable impact when investigating low-dimensional conductors or semiconductors. Nevertheless, the scattered near-field signal strongly depends on the dielectric function of both tip and sample. In order to enhance this signal strength we face two options, by either tuning the tip or sample into resonance using appropriate or tunable laser light sources, and resonant tip materials.


In this work we use a CO2-laser with a tunable center wavelength from 9.7 µm to 11.3 µm as an infrared excitation source in combination with self-prepared AFM particle-tips as probes [2]. The tip particles consist of spherical silicon carbide (SiC), silicon nitride (Si3N4) or silicon oxide (SiO2) nanoparticles with a diameter of ~ 60 nm. Those materials show phonon resonances in or around the CO2-laser wavelength range and thus enhance the signal significantly. We explored here the scenario when using both resonant tips AND samples, hence resulting in a tip-sample coupled super-resonance where both the tip and the sample contribute to the signal-enhancement. Accordingly, a significantly increased near-field image contrast and resolution is expected in this case.

References:

[1] S.C. Kehr et al., Nat. Commun. 2, 249 (2011).

[2] M.T. Wenzel et al., Optics Express 16 (16), 12302-12312 (2008).
Keywords: CO2-laser, near-field infrared microscopy, phonon resonance
  • Poster
    79. DPG-Jahrestagung und DPG-Frühjahrstagung, 15.-20.03.2015, Berlin, Deutschland
  • Poster
    German THz Conference 2015, 08.-10.06.2015, Dresden, Deutschland

Publ.-Id: 22941 - Permalink


AMS measurements of 10Be, 26Al and 41Ca at DREAMS
Scharf, A.; Akhmadaliev, S.; Arnold, M.; Bohleber, P.; Leya, I.; Merchel, S.; Rugel, G.; Smith, T.; Ziegenrücker, R.; Zipf, L.;
DREAMS, the DREsden AMS-facility, is performing routine accelerator mass spectrometry for the isotopes 10Be, 26Al, 36Cl, 41Ca and 129I. Sample ratios of 10Be/9Be as low as 8 x 10-15 (background-corrected) have been measured and an exposure age of about 330 years of a boulder of 3000 t in Nepal could be determined [1]. We could demonstrate that a by-product of ice core drilling, so-called drilling chips, are also suitable for 10Be analysis of ice cores, instead of using valuable ice core samples. A set of several in-house 26Al and 41Ca standards has been made traceable to primary standards by cross-calibration [2]. Numerous 26Al and 41Ca concentrations of meteorites could be determined, but for marine sediments there is still a need for a low-level (10-13) 26Al standard. ICP-MS measurements have shown that the steel pins used to fix the CaF2 sample material in the cathodes have high K-concentrations of (44.6 ± 2.2) μg/g. By replacing the steel pins with copper pins the 41K background during 41Ca measurements could be lowered by a factor of three.
Ref. : [1] W. Schwanghart et al., Science (2015), DOI:10.1126/ science.
aac9865. [2] G. Rugel et al., Nucl. Instr. Meth.B (2015), in review.
Keywords: AMS, DREAMS, exposure age, ice cores, meteorites
  • Poster
    DPG-Frühjahrstagung 2016, Sektion AMOP, 29.02.-04.03.2016, Hannover, Deutschland

Publ.-Id: 22940 - Permalink


Entwicklung der targetspezifischen Komponente eines Tumor-Pretargeting Systems auf der Basis L-konfigurierter Oligonukleotide
Schubert, M.;
Fortschritte auf dem Gebiet der Molekularbiologie haben im letzten Jahrzehnt etablierte wissenschaftliche Ansichten über die Entstehung von Tumorerkrankungen wesentlich verändert. Im Gegensatz zur früheren Sichtweise, dass Tumore einzig eine Ansammlung relativ homogener Krebszellen sind, verweisen die Erkenntnisse der letzten Jahre auf deren sehr komplexe Biologie. Dabei sind Krebszellen in nicht entartete Zellverbände, bestehend aus Fibroblasten, Pericyten, Endothelzellen sowie entzündungsauslösende Immunzellen eingebettet, die maßgeblich an der Bildung des Tumormikromilieus beteiligt sind, welches insbesondere bei der Tumorgenese und Metastasierung eine entscheidende Rolle spielt. Hanahan und Weinberg entwickelten ein Konzept zur Klassifizierung sogenannter "Hallmarks of Cancer" die das komplexe Zusammenspiel auf wenige grundlegende und allgemeingültige Organisationsprinzipien zurückführen. Die Verbesserung des Verhältnisses von Tumorerkrankungen soll dazu beitragen neue und effektivere Strategien für deren Therapie zu entwickeln. Besonders die Entwicklung weg vom standardisiertenTherapieverfahren hin zu einer zielgerichteten und auf den jeweiligen Patienten zugeschnittenen "individualisierten" Behandlung gewinnt in der Pharmazie zunehmend an Bedeutung. Von großem Interesse hierbei sind, Molekülstrukturen, die basierend auf supramolekularen Bindungsmotiven mit einer hohen Spezifität und Selektivität an Zielstrukturen im entarteten Gewebe binden. Eine Substanzklasse, die dabei im Fokus des pharmazeutischen Interesses steht, sind monoklonale Antikörper (mAk). Angesichts ihrer hohen Affinität gegenüber bestimmten Epitopen tumorassoziierter Antigene sind sie unter anderem in der Lage, tumorspezifische Signalwege zu beeinflussen und so das Tumorwachstum zu hemmen.

Als erste klinisch zugelassene Radioimmuntherapeutika werden die beiden radioaktiv markierten Antikörperpräparate Zevalin ([90Y]Y-ibritumomab tiuxetan) und Bexxar ([131I]I-tositumomab) bereits mit großem Erfolg zur ergänzenden Behandlung von Non-Hodgkin's Lymphomen angewandt. Mittels ionisierender Strahlung hervorgerufene DNA-Doppelstrangbrüche stellen dabei das eigentliche zellinaktivierende Ereignis dar. Der Vorteil einer solchen Radioimmuntherapie besteht vor allem darin, metastasierende Tumorerkrankungen zu behandeln, welche mit den klassischen Verfahren wie Chirurgie oder externer Bestrahlung nur schwer zu erfassen sind. Dennoch ist der Einsatz radioaktiv markierter monoklonaler Antikörper vor allem bei der Behandlung strahlenresistenter solider Tumore, trotz ihrer hervorragenden Bindungseigenschaften, limitiert. Ein weiterer Nachteil besteht darin, dass aufgrund ihrer hohen Blutverweildauer und nur langsamen Anreicherung im Zielgewebe, bedingt durch ihre Molekülgröße, der gesamte Organismus einer hohen Strahlenbelastung ausgesetzt wird.

Eine Alternative dazu stellt die Strategie des Pretargeting von Tumoren dar. Wie schematisch in Abbildung 1 am Konzept komplementärer Oligonukleotid-Bausteine gezeigt, besteht die Intention dieses Prinzips darin, mittels einer mehrstufigen Applikationsfolge die Injektion eines targetspezifischen Antikörper-Konjugates und einer kleinen radioaktiv markierten Verbindung zu trennen, welche zueinander ein komplementäres System bilden. Aufgrund der hohen Blutverweildauer wird das Antikörper-Konjugat zur Anreicherung im Tumorgewebe bereits einige Tage vor der eigentlichen Radionuklidanwendung appliziert. Nicht am Antigen gebundene Antikörper-Konjugate werden innerhalb der Wartezeit aus der Blutbahn eliminiert. Erst dann erfolgt in einem zweiten Schritt die Injektion der radioaktiv markierten komplementären Verbindung, welche nach kurzer Verteilungsphase am im Tumor lokalisierten Antikörper-Konjugat hybridisiert. Für eine möglichst geringe Strahlenbelastung sollte sich die radioaktiv markierte Verbindung durch eine schnelle Verteilung im Organismus, einer vorwiegend renalen Ausscheidungscharakteristik sowie einer sehr hohen Affinität und schnellen Bindungskinetik zum im Zielgewebe lokalisierten Antikörper-Konjugat auszeichnen. Besonders die schnelle renale Elimination solch kleiner Moleküle ist die Hauptursache für die deutlich geringere Strahlenbelastung des Gesamtorganismus gegenüber der konventionellen Radioimmuntherapie.
  • Doctoral thesis
    TU Dresden, 2015
    Mentor: Prof. Jörg Steinbach
    214 Seiten

Publ.-Id: 22939 - Permalink


Sensitivity of electromagnetic method for gas bubble detection in liquid metal flows
Andreew, O.; Gundrum, T.; Wondrak, T.; Eckert, S.; Gerbeth, G.;
Electromagnetic induction (EMI) is known as a technique which is very sensitive to variation of electrical conductivity of materials. In the present study we simulate numerically the work of electromagnetic sensor which consists of two differential coils. Such a detector rejects the basic signal and monitors the perturbations of electromagnetic field caused by the heterogeneity of electrical conductivity. We investigate the capability of this method for detecting non-metallic inclusions, such as gas bubbles in liquid metal (GaInSn) and sensitivity of differential detector to variation of its configuration.
Keywords: electromagnetic induction technique, two-phase flow, bubble detection, liquid metal
  • Poster
    8th International Congress on Electromagnetic Processing of Materials (EPM2015), 12.-16.10.2015, Cannes, France
  • Contribution to proceedings
    8th International Congress on Electromagnetic Processing of Materials (EPM2015), 12.-16.10.2015, Cannes, France, 531-536

Publ.-Id: 22938 - Permalink


Contactless inductive flow tomography for a thermally driven convection problem
Wondrak, T.; Pal, J.; Stefani, F.; Galindo, V.; Eckert, S.;
The contactless inductive flow tomography (CIFT) allows to visualize the mean flow structure in liquid metals by measuring the flow induced magnetic field perturbations under the influence of one, or several, applied magnetic fields. The reliable measurement of these very small field changes, and the involved mathematics to solve the inverse problem, are the main challenges for this flow diagnostic method. We present preliminary results of CIFT applied to a thermally driven flow within a setup showing some similarity to Czochralski silicon crystal growth. As working fluid GaInSn was used. Due to the low velocities in the order of 1 cm/s, the dynamic range of the measurement system has to be enhanced to 5 orders of magnitude which set high demands on the stability of the installation and the current source. Large efforts were made to adapt CIFT to the experimental setup in order to compensate thermal expansion during the measurement. Typical features of the thermally driven turbulent flow could be detected in the magnetic field measurements and were verified by simultaneous temperature measurements recorded by thermocouples placed in the vicinity of the rim of the heat sink.
Keywords: flow measurement, contactless inductive flow tomography, temperature driven convection, liquid metal
  • Poster
    8th International Congress on Electromagnetic Processing of Materials (EPM2015), 12.-16.10.2015, Cannes, France
  • Contribution to proceedings
    8th International Congress on Electromagnetic Processing of Materials (EPM2015), 12.-16.10.2015, Cannes, France, 527-530

Publ.-Id: 22937 - Permalink


Recent progress on contactless inductive flow tomography for continuous casting in the presence of strong static magnetic fields
Wondrak, T.; Ratajczak, M.; Timmel, K.; Stefani, F.; Eckert, S.;
The flow structure of liquid steel in the mold of a continuous caster has huge impact on the quality of the produced steel. In order to influence the flow during the casting process electromagnetic brakes (EMBr) are used. Even a rough knowledge of the flow field would be highly desirable. The contactless inductive flow tomography is a technique for reconstructing the velocity field in electrically conducting melts from externally measured induced magnetic fields. For a physical model of a mold with a cross section of 140 mm × 35 mm we present preliminary measurements of the flow field in the mold in the presence of a magnetic brake. In addition, we show first reconstructions of the flow field in a mold with the cross section of 400 mm × 100 mm, demonstrating the upward scalability of CIFT.
Keywords: flow measurement, contactless inductive flow tomography, continuous casting, liquid metal
  • Lecture (Conference)
    8th International Congress on Electromagnetic Processing of Materials (EPM2015), 12.-16.10.2015, Cannes, France
  • Contribution to proceedings
    8th International Congress on Electromagnetic Processing of Materials (EPM2015), 12.-16.10.2015, Cannes, France, 491-494

Publ.-Id: 22936 - Permalink


Synthese und radiopharmakologische Charakterisierung von radiomarkierten, EGFR-spezifischen Oligopeptiden zur Theragnostik von Krebserkrankungen
Starke, F.;
Die vorliegende Arbeit wurde beginnend am 01.01.2011 am Institut für Radiopharmazeutische Krebsforschung des Helmholtz-Zentrums Dresden-Rossendorf (HZDR) durchgeführt. Sie ist in den Forschungsbereich „Gesundheit“ und hier speziell in das Programm „Strahlungsbasierte Theragnostik in der Onkologie“ der Helmholtz-Gemeinschaft einzuordnen. Am HZDR arbeiten Forscher aus unterschiedlichsten Bereichen zusammen, um Fortschritte im Kampf gegen Krebserkrankungen zu erzielen. Der Fokus liegt hierbei auf der Entwicklung neuer, innovativer Verfahren zur onkologischen Bildgebung, der Optimierung einer individualisierten Strahlentherapie, sowie der Erforschung neuartiger Therapiebeschleuniger auf Basis von Laser-Technologien. Die am HZDR durchgeführte Tumorforschung erfolgt dabei stets translational - die Erkenntnisse aus der Forschung sollen zum Nutzen des Patienten in die klinische Anwendung transferiert werden.

In Deutschland stellt Krebs schon seit vielen Jahren die zweithäufigste Todesursache dar. Es wird angenommen, dass maligne Tumore bis Mitte des Jahrhunderts zur häufigsten Todesursache in den Industrienationen aufsteigen werden. Vor dem Hintergrund dieser Zahlen wird deutlich, dass die Diagnose und Therapie von malignen Erkrankungen eine der größten medizinischen Herausforderungen des 21. Jahrhunderts sein wird.

Bei der Behandlung von Tumorerkrankungen ist es essentiell, diese so früh wie möglich diagnostizieren und anschließend möglichst zuverlässig und nebenwirkungsarm therapieren zu können. Neue radiopharmazeutische und nuklearmedizinische Methoden haben dabei das Potential, einen wesentlichen Beitrag zur Bewältigung dieser Problematik zu liefern. Das Prinzip der Radiopharmazie beruht dabei auf der Verwendung radioaktiver Substanzen zur Diagnose und Therapie verschiedener Erkrankungen, die mit Veränderungen des zellulären Stoffwechsels einhergehen. Bei jeder möglichen Anwendung ist es essentiell, dass sich die in den Körper eingebrachte radioaktive Substanz möglichst selektiv und schnell im gewünschten Zielgewebe oder Zielorgan anreichert. Dort kann diese dann in Abhängigkeit des eingesetzten Radionuklides entweder zur Diagnostik mittels Positronen-Emissions-Tomographie (PET) beziehungsweise Einzelphotonen-Emissions-Computertomographie (SPECT) oder zur Zerstörung des Tumorgewebes eingesetzt werden.

Krebszellen besitzen häufig bestimmte Moleküle auf ihrer Oberfläche, durch die sie sich von gesunden Zellen unterscheiden. Ein Beispiel für ein solches Molekül ist der epidermale Wachstumsfaktor-Rezeptor (EGF-Rezeptor). Der EGF-Rezeptor reguliert unter anderem das Zellwachstum und den apoptotischen Zelltod. In geringer Zahl ist er auf der Oberfläche aller menschlichen Zellen vorhanden. Bei einer Vielzahl maligner Tumore befindet sich aber eine stark erhöhte Zahl des EGF-Rezeptors auf der Zelloberfläche. Diese Überexpression korreliert mit der Bildung von Metastasen und einer häufigeren Therapieresistenz - und damit mit deutlich schlechteren
Heilungsaussichten für den Patienten. Aus diesem Grund ist der EGF-Rezeptor eine äußerst bedeutsame Zielstruktur für die Entwicklung neuer, vielversprechender pharmazeutischer und radiopharmazeutischer Wirkstoffe. [1]
Das übergeordnete Ziel der vorliegenden Arbeit war deshalb die Entwicklung eines neuen Radiotracers zur ‚Theragnostik‘ von EGFR-überexprimierenden Krebserkrankungen.
  • Doctoral thesis
    TU Dresden, 2015
    Mentor: Prof. Jörg Steinbach
    161 Seiten

Publ.-Id: 22935 - Permalink


New possibilities in the self-catalyzed growth of GaAs nanowires using a modification of migration-enhanced epitaxy
Balaghi, L.; Tauchnitz, T.; Bischoff, L.; Hübner, R.; Schneider, H.; Helm, M.; Dimakis, E.;
The self-catalyzed (or Ga-induced) growth of vertical GaAs nanowires on Si(111) by molecular beam epitaxy has offered the possibility to obtain nanowires with fairly good control of the structural polytypism (especially in favor of the zinc-blende phase), without the risk of contamination by foreign elements like Au. The growth is typically performed close to the congruent temperature of GaAs (580-630 °C) in combination with relatively high V/III ratios. Those conditions ensure the efficient surface diffusion of Ga adatoms from the substrate and the nanowire side-walls to the apex of the nanowires, and suppress the thermal decomposition of the {110} side-walls. Nevertheless, the specific growth conditions impose several limitations: 1) the growth temperature exceeds largely the thermal budget limit of the Si-CMOS technology, rendering the future integration of the two material technologies impossible; 2) the interruption of the axial growth cannot be abrupt because of the long shut-off transient of the As-flux, which is typically accompanied by the formation of a segment that is rich in stacking faults below the Ga droplet; 3) significant inter-diffusion at high temperatures will deteriorate the compositional/doping profile of axial heterostructures; 4) it is difficult to avoid the unintentional radial (shell) growth, which is undesirable in axial heterostructures.
Aiming to surmount the inherent limitations of the conventional self-catalyzed growth mode, we developed a new growth scheme that expanded successfully the growth window to temperatures as low as 450 °C, minimized the radial growth, and allowed for accurate and defect-free interruptions of the axial growth. Our scheme is inspired by the migration-enhanced epitaxy of GaAs thin films, where the Ga and As fluxes are supplied alternately and in doses comparable to the atom sheet-density of the growth interface. In the case of nanowires, though, we adapted the alternate supply of Ga and As to achieve targeted delivery of the Ga atoms to the apex of the nanowires, minimizing in that way the radial growth. This work did not concern the nucleation stage, thus nanowires grown in a conventional way were used as templates for all experiments.
The results of our study include quantitative descriptions of the Ga adatom migration kinetics, the incorporation efficiency of As through the Ga droplet, and the dependence of both on the growth temperature. Having constructed a complete picture of the growth kinetics, we were able to identify the optimal growth conditions and beam-shutter sequence for different growth temperatures, covering the range from 550 to 450 °C. The structural analysis of our nanowires by transmission electron microscopy showed a zinc-blende structure with a small number of twin defects (Fig. 1). However, the spacing between the twins is irregular and does not correlate with the periodic beam-shutter sequence. The success of our growth scheme is interpreted on the basis of the atomic arrangement of the non-reconstructed {110} side-facets.
Ongoing work concerns the nucleation stage at 450 °C, as well as the fine tuning of the growth scheme parameters in order to eliminate the formation of twin defects.
  • Lecture (Conference)
    Nanowire growth workshop and Nanowires workshop 2015, 26.-30.10.2015, Barcelona, Espana

Publ.-Id: 22934 - Permalink


Sensitivity of liquid metal gas bubble differential EMI detector
Andreew, O.; Gundrum, T.; Wondrak, T.; Eckert, S.; Gerbeth, G.;
Electromagnetic induction (EMI) is known as a technique which is very sensitive to variation of electrical conductivity of materials. In this paper, we investigate capability of this method for detecting non-metallic inclusions, such as gas bubbles in liquid metal (GaInSn). We make both numerical simulation and experiment in order to build the sensitivity map for the interior of a rectangular column filled with liquid metal. The electromagnetic sensor consists of two differential coils. Such a detector rejects the basic signal and monitors the perturbations of electromagnetic field caused by heterogeneity of electrical conductivity. Theoretical results are used for validation of measured signals. The method is capable of detecting spherical target we used instead of real gas bubbles and produce a good agreement with numerical data.
Keywords: electromagnetic induction technique, two-phase flow, liquid metal
  • Lecture (Conference)
    7th International Symposium on Process Tomography, 01.-3.9.2015, Dresden, Germany
  • Contribution to proceedings
    7th International Symposium on Process Tomography, 01.-3.9.2015, Dresden, Germany

Publ.-Id: 22933 - Permalink


New developments on contactless inductive flow tomography
Wondrak, T.; Ratajczak, M.; Timmel, K.; Pal, J.; Stefani, F.; Galindo, V.; Eckert, S.;
The contactless inductive flow tomography (CIFT) allows to visualize the mean flow structure in liquid metals by measuring the flow induced magnetic field perturbations under the influence of one, or several, applied magnetic fields. The reliable measurement of these very small field changes, and the involved mathematics to solve the inverse problem, are the main challenges for this flow inference method. We demonstrate the applicability of CIFT for various model experiments devoted to the continuous casting process, by employing a new measurement system using induction coils and AC excitation. This enables the determination of the flow structure even in the presence of a strong static magnetic brake field which is often used in continuous casting for controlling the flow in the mold. Additionally, we present preliminary results of CIFT applied to a thermally driven flow with some similarity to Czochralski silicon crystal growth. Due to the low velocities in the order of 1 cm/s, the dynamic range of the measurement system has to be enhanced by about one order of magnitude in comparison with the continuous casting application.
Keywords: liquid metal, flow measurement, contactless inductive flow tomography, continuous casting, temperature driven convection
  • Lecture (Conference)
    7th International Symposium on Process Tomography, 01.-3.9.2015, Dresden, Germany
  • Contribution to proceedings
    7th International Symposium on Process Tomography, 01.-3.9.2015, Dresden, Germany

Publ.-Id: 22932 - Permalink


Correlation of electrical and structural properties of single as-grown GaAs nanowires on Si (111) substrates
Bussone, G.; Schäfer-Eberwein, H.; Dimakis, E.; Biermanns, A.; Carbone, D.; Tahraoui, A.; Geelhaar, L.; Haring Bolívar, P.; Schülli, T. U.; Pietsch, U.;
We present the results of the study of the correlation between the electrical and structural properties of individual GaAs nanowires measured in their as-grown geometry. The resistance and the effective charge carrier mobility were extracted for several nanowires, and subsequently, the same nano-objects were investigated using X-ray nanodiffraction. This revealed a number of perfectly stacked zincblende and twinned zincblende units separated by axial interfaces. Our results suggest a correlation between the electrical parameters and the number of intrinsic interfaces.
Keywords: single GaAs nanowires, electrical characterization, X-ray nanodiffraction, correlation, plastic deformation, axial interfaces

Downloads:

Publ.-Id: 22931 - Permalink


Increasing electromagnetic compatibility of contactless inductive flow tomography
Wondrak, T.; Ratajczak, M.; Gundrum, T.; Stefani, F.; Krauthäuser, H. G.; Jacobs, R. T.;
In many metallurgical and silicon crystal growth applications the knowledge about the flow field of the respective liquid metals is vital for proper process management. The high temperatures and the opaqueness of those melts set severe restrictions on the applicable flow measurement methods. The Contactless Inductive Flow Tomography (CIFT) is able to reconstruct the mean flow structure of liquid metals by measuring the flow induced perturbation of an applied magnetic field outside the melt. Typically, these perturbations are about 4 orders of magnitude smaller than the applied magnetic field. Therefore, special care has to be taken to ensure a very high dynamic range of the utilized magnetic field sensors and to minimize the effect of electromagnetic interferences. In this paper we give a short overview on CIFT and delineate some methods to increase its electromagnetic compatibility.
Keywords: contactless inductive flow tomography, liquid metal, electromagnetic compatibility
  • Lecture (Conference)
    Joint IEEE International Symposium on Electromagnetic Compatibility and EMC Europe (EMC 2015), 16.-22.8.2015, Dresden, Germany
  • Contribution to proceedings
    Joint IEEE International Symposium on Electromagnetic Compatibility and EMC Europe (EMC 2015), 16.-22.8.2015, Dresden, Germany, 978-1-4799-6615-8, 306-311
    DOI: 10.1109/ISEMC.2015.7256177

Publ.-Id: 22930 - Permalink


Simplified method for electromagnetic detection of gas bubbles in liquid metals
Andreev, O.; Wondrak, T.; Gundrum, T.; Eckert, S.;
The AC electromagnetic induction is the most appropriate mechanism for monitoring of metallic objects and media with inhomogeneous distribution of electrical conductivity. In particular, the liquid metal flows with gas bubbles inside can be controlled by this method. In the present work we show a particular case when the series of 1D measurements can be applied for definition of position of a single gas bubble in y and z directions. The numerical experiment was made within a rectangular column filled with the liquid metal as it is shown in Figure (a). The basic AC (100 Hz) magnetic field was generated by a rectangular excitation coil. Typical distribution of the amplitude value of secondary magnetic field caused by a single bubble (5 mm) is shown in Fig.(c). The wall of measurement is opposite to the excitation coil. The shown normal component of magnetic field can generate an electrical signal in a measuring coil applied to the wall. In our experiment we use a system of rectangular coils stretched in horizontal and vertical directions (Fig. a,c).
A detector of such configuration averages the value of magnetic field flux within the long direction of the coil. Vice versa, a number of detectors can give the detailed information about distribution of magnetic field along the short sides of the coils. So far as the secondary magnetic field is presented by a dipolar structure (Fig. c) where the central singular point corresponds to position of the bubble, the signal collected from the series of coils has a zero point situated between two extremes (Fig. b, c). This zero point indicates position of the bubble. Thus, using a system of vertical and horizontal coils placed on the rear walls (Fig. a,c), one can estimate position of a single bubble in y and z directions according to two 1D distributions of the signal. In our numerical experiment a single bubble moves in vertical direction by a spiral trajectory (Fig. d). In Figure (e) we reconstruct the y and z coordinates of the bubble (red circles). The real positions of the bubble are marked by the small blue circles in this figure.
Keywords: liquid metal, two-phase flows, inductive method, bubble detection
  • Poster
    3rd International Workshop on Measuring Techniques for Liquid Metal Flows (MTLM2015), 15.-17.4.2015, Dresden, Germany

Publ.-Id: 22929 - Permalink


2D velocity measurement using local Lorentz force velocimetry
Hernández, D.; Wondrak, T.; Schleichert, J.; Karcher, C.; Thess, A.;
Local velocity measurement of liquid metals continues to be an unsolved issue. Contact or even contactless measurement techniques cannot be used due to the fact that metal melts, like liquid steel, are usually at high temperatures, aggressive and opaque. Fortunately, there is a contactless velocity measurement technique called Lorentz force velocimetry in which a static magnetic field is applied on the electrically conductive metal stream. This static magnetic field is produced by permanent magnets, and if their size is smaller in comparison with the cross-section of the flow, a localized magnetic field distribution on the liquid metal is achieved. As a result and according to the principles of magnetohydrodynamics, eddy currents are generated within the liquid giving rise to a localized flow-breaking Lorentz force. Additionally and owing to Newtons third law, a force of the same magnitude but in the streamwise direction acts on the permanent magnet system which is connected to an optical interference force measurement device, giving access to local velocity information. This paper presents the results of local Lorentz force velocimetry at the mini-Limmcast facility at Helmholtz-Zentrum Dresden - Rosendorf using a 10mm cubic magnet and having as test fluid Galinstan in eutectic composition. In addition, partial results of Lorentz LFV using a multi-degree-of-freedom force/torque sensor are presented.
Keywords: Lorentz force velocimetry, liquid metal, flow measurement
  • Lecture (Conference)
    3rd International Workshop on Measuring Techniques for Liquid Metal Flows (MTLM2015), 15.-17.4.2015, Dresden, Germany

Publ.-Id: 22928 - Permalink


Recent developments on the contactless inductive flow tomography
Wondrak, T.; Ratajczak, M.; Stefani, F.; Gundrum, T.; Timmel, K.; Pal, J.; Eckert, S.;
The Contactless Inductive Flow Tomography (CIFT) allows the reconstruction of the mean three dimensional flow structure in conducting liquids [1]. Exposing the liquid to one or multiple applied magnetic fields and measuring the flow induced magnetic field around the fluid volume, it is possible to infer the velocity field by solving a linear inverse problem with appropriate regularization techniques. One challenge is the reliable detection of the tiny flow induced perturbation of the applied magnetic field. Typically, the flow induced magnetic field is about 3 to 5 orders of magnitude smaller than the applied magnetic field, so that a measurement system with a high dynamic range is required.
We start with a short overview of the first demonstration experiment of CIFT [1]. In a cylindrical vessel filled with GaInSn a propeller generates a three dimensional flow structure with a maximum velocity of 1 m/s. The flow induced magnetic field is about 3 orders of magnitude smaller than the applied magnetic field.
One promising application for CIFT is the continuous casting of steel in which the flow structure in the mould is very important for the quality of the produced steel. For a model of a continuous slab caster operated with GaInSn we developed a measurement system consisting of one excitation coil around the mould and 14 magnetic field sensors [2]. In this industrially relevant setup the flow induced magnetic field is about 4 orders of magnitude smaller than the applied magnetic field. We were able to reconstruct different flow transitions in the mould in case that Argon was injected into the submerged entry nozzle (SEN) [3], and various effects of an electromagnetic stirrer at the SEN on the flow in the mould [3]. Recent developments concerned the reconstruction of the flow in the mould in the presence of a strong static magnetic field. Additionally, we show preliminary measurements at a modified Rayleigh-Bénard setup operated with GaInSn demonstrating the applicability of CIFT for thermally driven convection systems with velocities in the order of 0.01 m/s. Typical features of the thermally driven turbulent flow could be detected in the magnetic field measurements and were verified by simultaneous temperature measurements recorded by small thermocouples.

References
1. F. Stefani et al., Physical Review E, 70 (2004), 056306
2. T. Wondrak et al., Measurement Science & Technology 21 (2010), 045402
3. T. Wondrak et al., Metallurgical and Materials Transactions B 42 (2011), 1201-1210
Keywords: contactless inductive flow tomography, liquid metal, flow measurement, continuous casting
  • Lecture (Conference)
    3rd International Workshop on Measuring Techniques for Liquid Metal Flows (MTLM2015), 15.-17.4.2015, Dresden, Germany

Publ.-Id: 22927 - Permalink


Electromagnetic interaction of a small magnet and liquid metal flow in a pipe with insulating or conducting walls
Kazak, O.; Heinicke, C.; Wondrak, T.; Boeck, T.;
We study the effects of electrically conducting walls on the interaction between a permanent magnet and a liquid-metal flow in a cylindrical pipe using experiments and numerical simulation. The problem is motivated by Lorentz force velocimetry, where the drag force on the magnet due to the induced eddy currents in the flow is used for flow measurement. Compared with insulating walls, the conducting walls lead to an increased drag force on the magnet. Except for low distances, the experimental results are satisfactorily reproduced in simulations using two different approximations of the magnetic field distribution.
Keywords: Lorentz force velocimetry, liquid metal, flow measurement
  • Magnetohydrodynamics 51(2015), 579-588

Publ.-Id: 22926 - Permalink


Origin of Cu-Ni-PGE mineralization at the Manchego Prospect, West Musgrave Province, Western Australia
Karykowski, B. T.; Polito, P. A.; Maier, W. D.; Gutzmer, J.;
The late Mesoproterozoic Giles Complex of the West Musgrave province hosts one of the largest concentrations of mafic-ultramafic layered intrusions on Earth. Therefore, the area is highly prospective for hosting significant Ni-Cu and platinum-group element (PGE) mineralization, especially following the discovery of a large magmatic sulfide deposit at Nebo-Babel in 2000. More recently, a significant occurrence of massive to disseminated sulfide mineralization reaching up to 0.62 wt % Cu, 0.47 wt % Ni, and 1 ppm Pt + Pd was identified at the Manchego prospect. The magmatic sulfide mineralization at Manchego is hosted by a range of gabbronoritic rock types situated below a linear magnetic anomaly interpreted to be a magnetite layer belonging to the layered mafic-ultramafic Jameson Range intrusion, which predates the Manchego intrusion. The principal ore minerals comprise massive to disseminated pyrrhotite, chalcopyrite, pentlandite, magnetite, and ilmenite. The presence of several geochemically distinct gabbronoritic lithotypes and an abundance of xenoliths strongly indicate a dynamic magmatic plumbing system, such as a conduit-type environment. Whole-rock samples of sulfide-rich gabbronoritic lithologies have δ34S values ranging from -11.8 to -8.4%, which clearly demonstrates the addition of crustal sulfur at Manchego and therefore the availability of crustal sulfur in the West Musgrave province. In comparison to Nebo-Babel, the lithologies intersected at Manchego geochemically resemble the high Ti basaltic NB-4 dikes described by Godel et al. (2011), which are compositionally distinct from the proposed parental magma for the Nebo-Babel intrusion. Therefore, the Manchego prospect provides evidence for the prospectivity of intrusions derived from high Ti basalts in the area, such as the Alcurra Dolerite. Manchego shares many genetic similarities with the Pants Lake intrusion in northern Labrador; both are situated in a magma conduit-type system and assimilated crustal sulfur. However, neither intrusion was sufficiently dynamic to allow the emplacement of chalcophile-undepleted magma pulses, which could have led to an upgrading of metals. Based on present knowledge, this very important step in the formation of economic sulfide deposits is seemingly missing at Manchego; however, exploration is at an early stage.
Keywords: Natural resources exploration; Nickel, platinum group elements, layered intrusions, Western Australia

Publ.-Id: 22925 - Permalink


Heavy ions at the DREAMS facility
Pavetich, S.; Fifield, K.; Fröhlich, M.; Hotchkis, M.; Merchel, S.; Rugel, G.; Wallner, A.; Ziegenrücker, R.;
The Dresden Accelerator Mass Spectrometry (DREAMS) facility is designed for the measurement of 10Be, 26Al, 36Cl, 41Ca and 129I [1]. The actual goal is to extend the measurement capabilities to actinides. For this purpose, a time-of-flight system was designed and is currently under construction. The system is based on a 1.5 m long flight path and thin carbon foils with Micro Channel Plates as start and stop detectors. For an optimal tuning of the system with low currents, special beam diagnostic elements are planned. In order to characterize the existing system, first measurements of actinide samples have been performed in collaboration with the ANU and ANSTO, using an ionization chamber as detector. Measurements of Pu-isotopes in the 3+ and the 5+ charge state have been conducted.

[1] S. Akhmadaliev et al., NIMB 294 (2013) 5.
Keywords: AMS, actinides, time-of-flight
  • Poster
    DPG-Frühjahrstagung der Sektion AMOP (SAMOP), 23.-27.03.2015, Heidelberg, Deutschland

Publ.-Id: 22924 - Permalink


Determination of the Maxwellian averaged cross-section of the reaction 35Cl(n,γ)36Cl
Pavetich, S.; Akhmadaliev, S.; Dillmann, I.; Halfon, S.; Heftrich, T.; Käppeler, F.; Lederer, C.; Martschini, M.; Merchel, S.; Paul, M.; Reifarth, R.; Rugel, G.; Steier, P.; Tessler, M.; Wallner, A.; Weigand, M.; Weissman, L.;
Routine measurements of 36Cl at the Dresden Accelerator Mass Spectrometry (DREAMS) facility have resulted in an astrophysical application: the determination of the Maxwellian averaged cross-section (MACS) of the reaction 35Cl(n,γ)36Cl. As 35Cl acts as a neutron poison in the nucleosynthesis processes during later burning phases of stars, the reaction is important for astrophysical calculations of elemental abundances. The neutron irradiations with a quasi Maxwell Boltzmann spectrum for the production of 36Cl were performed at the Karlsruhe Institute of Technology and the Soreq Applied Research Accelerator Facility. AMS measurements were performed at VERA and DREAMS and are planned at the Australian National University in 2015. Acknowledgement: Alberto Mengoni, CERN.
Keywords: Accelerator Mass Spectrometry, DREAMS, astrophysics, 36Cl
  • Lecture (Conference)
    DPG-Frühjahrstagung der Sektion AMOP (SAMOP), 23.-27.03.2015, Heidelberg, Deutschland

Publ.-Id: 22923 - Permalink


A study of two-phase flow in monoliths using ultrafast single-slice X-ray computed tomography
Schäfer, T.; Meitzner, C.; Lange, R.; Hampel, U.;
Running chemical reactions in monolithic structures is being considered as highly promising for intensifying industrial reaction processes. A potential pitfall of such structures is the difficulty to achieve homogeneous and well defined gas/liquid distributions patterns with economically feasible distribution mechanisms. Experimental studies on gas/liquid distribution in monoliths are often hampered by missing measurement and visualization technique to disclose the two-phase flow inside the narrow and opaque channels.
This paper presents results of a study carried out with ultrafast single-slice X-ray tomography, a novel imaging techniques , which can overcome these limitations. We investigated two-phase flow in two different types of square-channel monolith structures, one with high cell density of 400 cpsi and one with low cell density of 39 cpsi. Our study discloses in-channel flooding and draining behavior via extraction of characteristic distribution parameters, such as averaged and channel-linked liquid holdup, two-phase flow patterns and liquid maldistribution from X-ray images using advanced image processing techniques.
Keywords: ultrafast X-ray tomography; two-phase flow; monolith; holdup; maldistribution; flow pattern; flow visualization

Publ.-Id: 22922 - Permalink


Image reconstruction for hard field tomography
Hampel, U.;
Computed tomography requires the solution of an inverse problem, that is, the reconstruction of an object distribution from measurement data. In hard field tomography this problem can be more specifically referred to as the reconstruction of an object distribution from its line integrals. A first solution to the mathematical problem was given by Johann Radon in 1917 long before anyone thought about computed tomography. The transformation of an object distribution into the space of its line integrals is hence today called the Radon transformation. With the development of computed tomography technology later quite powerful algorithms basing on analytic and algebraic inversion schemes for the Radon transform were developed. This chapter shall introduce the mathematical fundamentals of the forward and inverse problem of hard field computed tomography, the discretization of the problem and further discuss some distinct features and specialties of image reconstruction, such as 3D inversion approaches and concepts for limited and local tomography.
Keywords: Image reconstruction, Radon transformation, inverse problem, analytic reconstruction, algebraic reconstruction, cone-beam reconstruction, limited data tomography
  • Book chapter
    Mi Wang: Industrial Tomography: Systems and Applications, Amsterdam: Woodhead Publishing, 2015, 1782421181, 347-376

Publ.-Id: 22921 - Permalink


Actinide AMS at DREAMS
B. Khojasteh, N.; Merchel, S.; Pavetich, S.; Rugel, G.; Scharf, A.; Ziegenrücker, R.;
Radionuclides such as 236U and 239Pu were introduced into the environment by atmospheric nuclear weapon tests, reactor accidents (Chernobyl, Fukushima), releases from nuclear reprocessing facilities (Sellafield, La Hague), radioactive waste disposal, and accidents with nuclear devices (Palomares, Thule) [1]. Accelerator Mass Spectrometry (AMS) is the most sensitive method to measure these actinides.
The DREsden AMS (DREAMS) facility is located at a 6 MV accelerator, which is shared with ion beam analytics and implantation users, preventing major modifications of the accelerator and magnetic analyzers. DREAMS was originally designed for 10Be, 26Al, 36Cl, 41Ca, and 129I [2,3]. To modify the system for actinide AMS, a Time-of-Flight (TOF) beamline at the high-energy side has been installed and performance tests are on-going. Ion beam and detector simulations are performed to design a moveable ionization chamber. Especially, the detector window and anode dimensions have to be optimized. This ionization chamber will act as an energy detector of the system and its installation is planned as closely as possible to the stop detector of the TOF beamline for highest detection efficiency.
[1] Srncik et al., J. Environ. Radioact. 132 (2014) 108. [2] Akhmadaliev et al., Nucl. Instr. Meth. B. 294 (2013) 5. [3] Rugel et al., under review in Nucl. Instr. Meth. B.
Keywords: AMS, DREAMS, actinides, ionization chamber
  • Poster
    DPG-Frühjahrstagung der Sektion AMOP (SAMOP), 29.02.-04.03.2016, Hannover, Deutschland

Publ.-Id: 22920 - Permalink


X-ray computed tomography
Hampel, U.;
Computed tomography with X-rays is widely used in medicine and non-destructive testing today. In process applications X-ray tomography is, however, until now more seldom used, which is obviously due to its high complexity and costs. Nonetheless, particularly in laboratory studies it has frequently proven its superior capability to measure multiphase flow parameters, such as local phase fractions in pipes, vessels or other process system components, with high resolution and accuracy. Most recently different technologies were presented, which allow faster tomographic imaging of flows with X-ray CT, which now opens the door for a wider application of this technique in process analysis, monitoring and control. The chapter gives a concise overview over basic principles and hardware of X-ray CT with particular respect to process applications and provides state-of-the-art examples of its application in multiphase flow analysis.
Keywords: X-ray tomography
  • Book chapter
    Mi Wang: Industrial Tomography: Systems and Applications, Amsterdam: Woodhead Publishing, 2015, 1782421181, 175-196

Publ.-Id: 22919 - Permalink


Funktionelle Charakterisierung der Wechselwirkungen zwischen neuartigen polymeren Biomaterialien und dem Organismus
Ullm, S.;
Die funktionelle Wiederherstellung geschädigter Zellen, Gewebe oder Organe ist das Hauptziel der regenerativen Medizin. Der Einsatz innovativer Biomaterialien, die mit dem Organismus positiv interagieren, gilt als besonders aussichtsreicher Ansatz zur Realisierung dieses Ziels. Aus diesem Grund sind die Entwicklung neuartiger Biomaterialkonzepte und die Verbesserung des Verständnisses der Wechselwirkungen zwischen Biomaterial und Organismus Kernthemen der aktuellen Biomaterialforschung.
Die vorliegende Arbeit wurde im Kontex des von der Helmholtz-Gemeinschaft geförderten Portfoliothemas "Technologie und Medizin - Multimodale Bildgebung zur Aufklärung des in-vivo-Verhaltens von polymeren Biomaterialien" angefertigt. Die Aufgabe der beteiligten Helmholtz-Zentren und Universitäten besteht in der Entwicklung und Optimierung multiskaliger und multimodaler Bildgebungsverfahren zur Untersuchung des Verhaltens polymerer Biomaterialien im Körper. Das Hauptaugenmerk soll dabei auf der Aufklärung der auftretenden Wechelwirkungen zwischen Biomaterial und Organismus sowie der Identifizierung der Abbauprodukte des jeweiligen Biomaterials liegen, mit dem Ziel, dessen in-vivo-Verhalten besser vorhersagen zu können und so die Entwicklungszeiten erheblich zu verkürzen.
Gegenstand der vorliegenden Arbeit war es, eine Gruppe vielversprechender polymerer Biomaterialien auf der Basis von Gelantine hinsichtlich ihrer Wechselwirkungen mit ausgewählten Zelltypen und dem gesamten Organismus eingehend zu charakterisieren. Die zu untersuchenden Gelantine-basierten Hydrogele wurden im Rahmen des oben genannten Helmholtz-Portfoliothemas von der Arbeitsgruppe um Dr. Axel Neffe am Helmholtz-Zentrum Geesthacht, Institut für Biomaterialforschung Teltow, synthetisiert sowie hinsichtlich ihrer Materialeigenschaften charakterisiert und ersten in-vitro-Experimenten mit murinen Fibroblasten und mesenchymalen Stammzellen eingesetzt. In der vorliegenden Arbeit sollte die Reaktion verschiedener humaner Zellsysteme, die Schlüsselrollen während der Gewebereaktion und Neovaskularisierung einnehmen, auf die Hydrogele und deren Abbauprodukte untersucht werden. Darüber hinaus sollte das In-vivo-Verhalten der Hydrogele in einem subkutanen Implantationsmodell in immunkompetenen Mäusen analysiert werden. Im Ergebnis sollte die vorliegende Dissertation einerseits dazu beitragen das Anwendungspotential der untersuchten Hydrogele zu beurteilen und andererseits das allgemeine Verständnis der Biomaterial-Gewebe-Interaktion zu erweitern.
  • Doctoral thesis
    TU Dresden, 2015
    Mentor: Prof. Jens Pietzsch
    155 Seiten

Publ.-Id: 22918 - Permalink


Analysis of intermittent flow patterns of water-steam flow in solar thermal power plants with direct steam generation
Hoffmann, A.; Hirsch, T.; Schleicher, E.; Pitz-Paal, R.;
Solar thermal power plants that use parabolic troughs for direct steam generation depict a commercially available technology for a renewable electricity production. The once-through operation mode is the most cost-effective approach for this type of power plant and, consequently, is mainly considered in the current research. This operation mode preheats and evaporates water and superheats steam within one continuous pipe. Hence, all mass qualities are passed along the pipe and various flow patterns are present. It is presumed that intermittent flow pattern influence the position of the mixture-vapor transition point at the end of evaporation and lead to undesired thermal stresses in the receiver pipe. In order to get an insight in the two-phase flow a numerical analysis is performed with ATHLET. This code provides a one-dimensional mass, momentum and energy balance for both phases water and steam, respectively. The applicability of ATHLET on intermittent flows is discussed and confirmed. In the result an intermittent flow is numerically determined at specific void fraction ranges in the design of the DISS test facility at the Plataforma Solar de Almería, Spain. The occurrence of these unsteady flow pattern diminishes at a pressure P > 60 bar. Furthermore, it is shown that the oscillating nature of the two-phase flow effects the position of the mixture-vapor transition point. For the validation of the numerical results an experiment with a wire-mesh sensor is designed. The obtained results deliver a substantial contribution to understand the two-phase flow behavior in the direct steam generation process.
Keywords: Direct steam generation, ATHLET, flow pattern
  • Contribution to proceedings
    ICMF-2016 - 9th International Conference on Multiphase Flow, 22.-27.05.2016, Firenze, Italy
  • Lecture (Conference)
    ICMF-2016 - 9th International Conference on Multiphase Flow, 22.-27.05.2016, Firenze, Italy

Publ.-Id: 22916 - Permalink


The HZDR reactor dynamics code DYN3D
Kliem, S.;
The presentation gives an overview on the code DYN3D which is a three-dimensional core model for steady-state, dynamic and depletion calculations in reactor cores with quadratic or hexagonal fuel assembly geometry being developed by the Helmholtz-Zentrum Dresden-Rossendorf for more than 20 years. An overview on the basic DYN3D models and the available code couplings is given. The verification and validation status is shortly outlined.
  • Invited lecture (Conferences)
    1st Sino-German Symposium on Fundamentals of Advanced Nuclear Safety Technology, 09.-12.03.2015, Shanghai, China

Publ.-Id: 22915 - Permalink


Synthese und kinetische Charakterisierung von Endopeptidase-Substraten des Cathepsin B
Behring, L.;
Das Leben sämtlicher Orgnismen beruht auf einem vielschichtigen, feinabgestimmten System enzymatischer Reaktionen, die ein komplexes Regulationssystem erfordern. Da sich die meisten Erkrankungen auf Fehlfunktionen verschiedener Enzyme zurückführen lassen, ist es ein wichtiges Anliegen der Forschung, diese enzymatischen Prozesse zu verstehen und beeinflussen zu lernen.

Aufgrund des engen Zusammenspiels verschiedener Prozesse ist für das Verständnis der Rolle unterschiedlicher Enzyme an Krankheitsbildern wie Krebs die Beobachtung der in vivo stattfindenden Reaktionen nötig. Dafür stehen verschiedene Bildgebungsverfahren zur Verfügung. Besonders geeignet sind hierbei PET (Positronenemissionstomographie) und SPECT (single photon emission computed tomography). Beide Verfahren sind nichtinvasiv, beeinflussen den untersuchten Organismus minimal und können mit hoher Sensitivität funktionelle Informationen geben.

Die Suche nach geeigneten Targeting-Strategien und die Entwicklung problemspezifischer Tracer sind daher wichtige Schritte auf dem Weg zu einem besseren Verständnis der Prozesse, die verschiedenen Krankheitsbildern zugrunde liegen und damit auch auf dem Weg zur Heilung dieser Erkrankungen.
  • Master thesis
    TU Dresden, 2015
    Mentor: Prof. Jens Pietzsch
    169 Seiten

Publ.-Id: 22914 - Permalink


Challenges and Solutions on the Major and Trace Element Analysis of Eudialyte Group Minerals with the Electron Microprobe
Krause, J.; Atanasova, P.; Möckel, R.; Osbahr, I.; Rudolph, M.; Gutzmer, J.;
Alkaline complexes containing eudialyte group minerals (EGM) comprise one of the most promising sources for future rare earth element (REE) supply. The accurate quantification of the chemical composition of EGM is complicated by both mineralogical and X-ray-specific challenges. These include:
1) structural and chemical variability of EGM composition (e.g., [1-3]);
2) mutual interferences of X-ray lines from major and trace elements, in particular REEs [4];
3) the diffusive volatility of light anions as F and Cl and cations such as K and Na;
4) particular instability of EGM under the electron beam.
A novel analytical approach has been developed to account for the above-mentioned analytical challenges. Additionally, loss on ignition and differential scanning calorimetry data has been applied to constrain the content and composition of volatiles in the EGM structure. The influence of the electron beam on the structure of EGM has been explored with Raman spectroscopy. All correction for the overlapping of X-ray lines is processed offline. For comparison a subset of samples was analysed with Laser Ablation Inductively Coupled Plasma Mass Spectrometry. The results demonstrate that the abovementioned parameters need to be considered and carefully optimized to perform accurate quantitative analyses on the chemical composition of EGM with the electron microprobe.
  • Open Access LogoContribution to proceedings
    Goldschmidt 2015, 16.-21.08.2015, Prag, Tschechische Republik
    Goldschmidt2015 Abstracts: Cambridge Publications, 1688-1688
  • Poster
    Goldschmidt 2015, 16.-21.08.2015, Prag, Tschechische Republik

Publ.-Id: 22913 - Permalink


Petrographie der SEE-Th-Gänge von Lehmi Pass in Idaho und Montana
Hüttel, S. P.;
Diese Bachelorarbeit befasst sich mit der Petrographie den Seltenerdelement-Thorium-Gängen von Lemhi Pass in Idaho und Montana. Im Rahmen des Projektes sollen die Seltenerdgehalte der Gänge, über die bisher nur wenig bekannt ist, untersucht und eine Wertung der Seltenerdelement-Gehalte gegeben werden.
  • Bachelor thesis
    TU Bergakademie Freiberg, 2015
    Mentor: Bernhard Schulz, Petya Atanasova
    90 Seiten

Publ.-Id: 22912 - Permalink


Petrographie der SEE-Karbonate von Sheep Creek in Ravalli County, Montana
Meumann, J.;
Bei den metamorphen Karbonaten von Sheep Creek, Montana handelt es sich ursprünglich entweder um flachmarine Sedimentite oder kabonatitische Gänge. Diese wurden durch LREE-reiche (light rare earth elements), metamorph mobilisierte Wässer wenigstens partiell vererzt. Sie stehen als linsen- bis bandförmige Strukturen mit maximal 2,40 m Mächtigkeit in Wechsellagerung mit Amphiboliten an. Diese Abfolge ist wiederum in 2,7 Ga alten und somit neoarchaischen Gneisen eingeschaltet. Die bearbeiteten Proben konnten wie folgt gruppiert werden: In Allanit-Monazit-Calcit-, allanitreiche Karbonat-Silikat-, Ankerit-Magnetit-Ilmenit-, Ankerit-Calcit-Ferrosilit-, Enstatit-Calcit- und massive Ilmenit-Magnetit-Gesteine.
Als wesentliche SEE-Minerale sind in den Marmoren Monazit und Allanit vertreten. Es sind allerdings auch andere potentiell ökonomisch relevante Minerale in Form von Ilmenit, Magnetit, Titanit, Apatit und Baryt partiell angereichert. Monazit und Allanit machen insgesamt stellenweise mehr als 80 wt-% der Gesteine aus, wobei hauptsächlich leichte Elemente angereichert sind. In den Monaziten sind 11 wt-% bis 53 wt-% an leichten SEE in Form von Cer, Lanthan und Neodym eingebaut.
Bei den Allaniten fallen die Gehalte mit insgesamt 11 wt-% bis 26 wt-% Cer, Lanthan und Neodym geringer aus. Eine Verwachsung mit radioaktiven Mineralen wie z.B. Thorit ist hier praktisch bedeutungslos.
In einer Probe sind Ilmenitgehalte von ~ 66 wt-% anzutreffen, Magnetit ist dagegen mit Massenanteilen von stets weniger als 10 wt-% nur untergeordnet anzutreffen. Selbiges gilt für Titanit mit maximal ~ 2,5 wt-% und für Apatit mit generell < 5 wt-%. Baryt ist dafür stellenweise mit bis zu ~ 17 wt-% angereichert.
  • Bachelor thesis
    TU Bergakademie Freiberg, 2015
    Mentor: Bernhard Schulz, Petya Atanasova
    109 Seiten

Publ.-Id: 22911 - Permalink


Euler-Euler Modeling of Poly-Dispersed Bubbly Flows
Rzehak, R.;
CFD simulations of bubbly flow on the scale of technical equipment become feasible within the Eulerian two-fluid framework of interpenetrating continua. For practical applications suitable closure relations are required which describe the interfacial exchange processes. To facilitate predictive simulations a reference set of closure relations has been defined for bubble forces and bubble-induced turbulence including numerical values for all parameters. Models for bubble coalescence and breakup are not yet included at present due to their lacking maturity. This means that the bubble size distribution must still be estimated by other means or treated as a parameter in a sensitivity study. Using measured bubbles sizes the validity of model predictions for gas fraction, mean velocities of gas and liquid, and liquid turbulent kinetic energy have been validated over a range of conditions. These include both pipe flows and bubble columns and circular and rectangular cross sections. The bubble size is limited to the range of 1 to 10 mm and the gas fraction to at most 10 to 20 %. The present report gives a brief but complete description of the model, a few validation examples, and references for further study.
Keywords: fluid dynamics, dispersed gas liquid multiphase flow, Euler-Euler two-fluid model, closure relations, CFD simulation, model validation
  • Book chapter
    Guan Heng Yeoh: Handbook of Multiphase Flow Science and Technology, Singapore: Springer, 2017, 978-981-4585-86-6
    DOI: 10.1007/978-981-4585-86-6_4-1

Publ.-Id: 22910 - Permalink


The formation of silver metal nanoparticles by ion implantation in silicate glasses
Vytykacova, S.; Svecova, B.; Nekvindova, P.; Spirkova, J.; Mackova, A.; Miksova, R.; Böttger, R.;
It has been shown that glasses containing silver metal nanoparticles are promising photonics materials for the fabrication of all-optical components. The resulting optical properties of the nanocomposite glasses depend on the composition and structure of the glass, as well as on the type of metal ion implanted and the experimental procedures involved. The main aim of this article was to study the influence of the conditions of the ion implantation and the composition of the glass on the formation of metal nanoparticles in such glasses.

Four various types of silicate glasses were implanted with Ag+ ions with different energy (330 keV, 1.2 MeV and 1.7 MeV), with the fluence being kept constant (1 × 1016 ions cm−2). The as-implanted samples were annealed at 600 °C for 1 h. The samples were characterised in terms of: the nucleation of metal nanoparticles (linear optical absorption), the migration of silver through the glass matrix during the implantation and post-implantation annealing (Rutherford backscattering spectroscopy), and the oxidation state of silver (photoluminescence in the visible region).
Keywords: Silicate glasses; Silver nanoparticles; Ion implantation

Publ.-Id: 22909 - Permalink


The structural and optical properties of metal ion-implanted GaN
Macková, A.; Malinský, P.; Sofer, Z.; Šimek, P.; Sedmidubský, D.; Veselý, M.; Böttger, R.;
The practical development of novel optoelectronic materials with appropriate optical properties is strongly connected to the structural properties of the prepared doped structures. We present GaN layers oriented along the (0 0 0 1) crystallographic direction that have been grown by low-pressure metal–organic vapour-phase epitaxy (MOVPE) on sapphire substrates implanted with 200 keV Co+, Fe+ and Ni+ ions. The structural properties of the ion-implanted layers have been characterised by RBS-channelling and Raman spectroscopy to obtain a comprehensive insight into the structural modification of implanted GaN layers and to study the subsequent influence of annealing on crystalline-matrix recovery. Photoluminescence was measured to control the desired optical properties. The post-implantation annealing induced the structural recovery of the modified GaN layer depending on the introduced disorder level, e.g. depending on the ion implantation fluence, which was followed by structural characterisation and by the study of the surface morphology by AFM.
Keywords: RBS channelling; Metal-implanted GaN; Structural changes

Publ.-Id: 22908 - Permalink


Ultrafast nonlinear response of GaAs under high pressures
Braun, J. M.; Schneider, H.; Helm, M.; Pashkin, A.;
Applying hydrostatic pressure leads to dramatic changes in the band structure of semiconductors. In particular, it enables a continuous tuning of the bandgap energy of a given sample. Here we study ultrafast carrier dynamics in gallium arsenide (GaAs) at pressures up to 3 GPa. The optical pump-probe spectroscopy traces the nonlinear response in the vicinity of the bandgap. Thus, we are able to observe the changes in the ultrafast response caused by tuning the bandgap energy across the spectrum of the femtosecond probe pulse.
Our setup employs a femtosecond Ti:sapphire laser which provides pulses with the spectrum centered around 1.55 eV and a FWHM of ~0.1 eV. The experiment is performed in a non-collinear reflection geometry (fig. 1) where the pump and probe beams are focused by an all-reflective Schwarzschild objective to a ~5μm spot on the sample. Pressure is applied in a diamond anvil cell (DAC) with CsI used as pressure transmitting medium in order to ensure a good contact between the sample and diamond anvil. The sample studied is a semi-insulating GaAs crystal with thickness of about 50μm. The pump pulse with energy of 0.03 nJ induces changes in the optical reflectivity of the sample which is probed by the delayed weaker probe pulse.
In agreement with a previous study at ambient and low pressures, pumping induces an increase in reflectivity which decays on a timescale of hundred picoseconds and is assigned to the recombination of the photogenerated charge carriers [1]. With pressure increase, this relaxation becomes slower as shown in fig. 2. Finally, for pressures above 2 GPa, the pump-probe signal changes its sign and the relaxation components vanish completely. The nonlinear response appears only around zero pump-probe delay and probably originates from the negative real part of the thirdorder susceptibility of GaAs [2]. We interpret this phenomenon as a shifting of the bandgap energy above the excitation spectrum of our experiment. This assumption is in good agreement with the known bandgap pressure coefficient of 0.11 eV/GPa in GaAs leading to a complete transparency of the sample for pump and probe pulses at pressures above 2 GPa [3].
[1] D. G. McLean, M. G. Roe, A. I. D’Souza, P. E. Wigen, Appl. Phys. Lett. 48, 992 (1986).
[2] A. A. Said, M. Sheik-Bahae, D. J. Hagan, T. H. Wei, J. Wang, J. Young, E. W. Van Stryland, J. Opt. Soc. Am. B 9, 405 (1992).
[3] A. R. Goñi, K. Strössner, K. Syassen, M. Cardona, Phys. Rev. B 36, 1581 (1987).
Keywords: pump-probe spectroscopy, recombination dynamics, high pressure, diamond anvil cell, gallium arsenide, GaAs
  • Poster
    Joint AIRAPT-25th & EHPRG-53rd International Conference on High Pressure Science and Technology, 30.08.-04.09.2015, Madrid, Spain

Publ.-Id: 22907 - Permalink


Ultrafast nonlinear response of GaAs under high pressures
Braun, J. M.; Schneider, H.; Helm, M.; Pashkin, A.;
Applying hydrostatic pressure leads to dramatic changes in the band structure of semiconductors. In particular, it enables continuous tuning of the bandgap energy. Thus, optical pump-probe spectroscopy under high pressures allows the study of nonlinear optical response in the vicinity of the interband resonance.
Here, we study ultrafast carrier dynamics in gallium arsenide (GaAs) at pressures up to 3 GPa. Our setup employs a femtosecond Ti:sapphire laser which provides pulses with the spectrum centered around 1.55 eV with a FWHM of ~0.1 eV. The experiment is performed in a non-collinear reflection geometry (fig. 1) where the pump and probe beams are focused by an all-reflective Schwarzschild objective to a ~5µm spot on the sample. Pressure is applied in a diamond anvil cell with CsI used as pressure transmitting medium. The studied sample is a semi-insulating GaAs crystal with thickness of about 50µm. The pump pulse with energy of 0.03 nJ induces changes in the optical reflectivity of the sample which is probed by the delayed weaker probe pulse.
In agreement with a previous study at ambient pressure, pumping induces an increase in reflectivity which decays on a timescale of hundred picoseconds and is assigned to the recombination of the photogenerated charge carriers [1]. With increasing pressure this relaxation becomes slower as demonstrated in fig. 2. Finally, for pressures above 2 GPa, the pump-probe signal changes its sign and the relaxation component vanishes completely. The nonlinear response appears only around zero pump-probe delay and its origin is attributed to the negative real part of the third-order susceptibility of GaAs [2]. We interpret this phenomenon as a shifting of the bandgap energy above the excitation spectrum of our experiment. This assignment is in good consistency with the known bandgap pressure coefficient of 0.11 eV/GPa in GaAs leading to a complete transparency of the sample for pump and probe pulses at pressures above 2 GPa [3].
In the future we plan to study the response of the photoexcited electron-hole plasma in GaAs using optical pump / THz probe spectroscopy under pressure. The all-reflective optics of our experimental setup enables us to couple coherent THz radiation pulses from the free-electron laser at the HZDR into a diamond anvil cell.
[1] D. G. McLean, M. G. Roe, A. I. D’Souza, P. E. Wigen, Appl. Phys. Lett. 48, 992 (1986).
[2] A. A. Said, M. Sheik-Bahae, D. J. Hagan, T. H. Wei, J. Wang, J. Young, E. W. Van Stryland, J. Opt. Soc. Am. B 9, 405 (1992).
[3] A. R. Goñi, K. Strössner, K. Syassen, M. Cardona, Phys. Rev. B 36, 1581 (1987).
Keywords: pump-probe spectroscopy, recombination dynamics, high pressure, diamond anvil cell, gallium arsenide, GaAs
  • Poster
    German THz Conference 2015, 08.-10.06.2015, Dresden, Deutschland

Publ.-Id: 22906 - Permalink


Gouy phase shift of a tightly focused, radially polarized beam
Kaltenecker, K. J.; König-Otto, J. C.; Mittendorff, M.; Winnerl, S.; Schneider, H.; Helm, M.; Helm, H.; Walther, M.; Fischer, B. M.;
Radially polarized beams represent an important member of the family of vector beams, in particular due to the possibility of using them to create strong and tightly focused longitudinal fields, a fundamental property that has been exploited by applications ranging from microscopy to particle acceleration. Since the properties of such a focused beam are intimately related to the Gouy phase shift, proper knowledge of its behavior is crucial. Terahertz microscopic imaging is used to extract the Gouy phase shift of the transverse and longitudinal field components of a tightly focused, radially polarized beam. Since the applied terahertz time-domain approach is capable of mapping the amplitude and phase of an electromagnetic wave in space, we are able to directly trace the evolution of the geometric phase as the wave propagates through the focus. We observe a Gouy phase shift of 2π for the transverse and of π for the longitudinal component. Our experimental procedure is universal and may be applied to determine the geometric phase of other vector beams, such as optical vortices, or even arbitrarily shaped and polarized propagating waves.
Keywords: Gouy phase, EOS, THz

Publ.-Id: 22905 - Permalink


Metallurgical infrastructure: a key enabler of a circular economy
Reuter, M. A.;
Base metals such as copper, lead, nickel, cobalt, zinc etc. form the basic crucial carrier metals for a sustainable society – the Web of Metals. This paper discusses the special and crucial role these metals have in acting as enablers in any recycling efforts as they carry and release important and vital minor elements at the heart of high-tech applications and products. Through examination of the rising needs for such carriers, this paper examines the approach and technologies which need to be considered by any producer of base metals. Attention is paid to the limits and extent of this carrier role in the typical processing of materials.
Examples of specialised technology and flowsheet needs are presented with consideration given to a “whole of chain” or Systems-Integrated Metal Production (SIMP) approach as a cornerstone of a circular economy. Also outlined are the challenges facing not only producers, but legislators who need to consider the balance between providing our societal needs with baseline technology infrastructure requirements for valuable metals extraction. In summary, the message of this paper states simply that not only is the criticality of metals important but the criticality of the infrastructure (Infrastructure Criticality) that can recover metals from complex designed “mineral” mixtures. Base metals are at the heart of a Circular Economy, therefore key enablers of the Internet-of-Metallurgical-Things.
Keywords: Resource efficiency base metals, Recycling, System integration, Design for Recycling (DfR)
  • Invited lecture (Conferences)
    On metal by-products recovery, 12.-13.11.2015, Brüssel, Belgien
  • Invited lecture (Conferences)
    Cleantech Innovations in Mineral Production, 10.09.2015, Helsinki, Finland

Publ.-Id: 22904 - Permalink


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