Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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34118 Publications

Nanostructuring Ge Surfaces by Ion Irradiation

Facsko, S.; Fritzsche, M.; Ou, X.; Keller, A.

Low energy ion irradiation induces the formation of periodic surface patterns. These struc-tured surfaces exhibit periodicities in the range of a few tens to hundreds of nanometers and are promising templates for producing nanostructured thin films. Periodic ripple patterns with wave vector parallel to the ion beam direction are observed frequently for ion irradiation at incidence angles between 50° and 70° to the surface normal. At normal incidence dot or hole patterns with hexagonal symmetry are observed only under special irradiation conditions.
The formation of hexagonally arranged hole patterns on Ge(001) surfaces induced by irradia-tion at normal incidence was studied with a scanned focused Ga+ ion beam (FIB). Hole pat-terns with characteristic length of about 50 nm are observed in a narrow energy range of 4 - 6 keV. Hole patterns induced by FIB irradiations were compared to broad beam Ga+ and Ge+ irradiations with the same ion energy. No differences were found demonstrating that FIB irra-diations with a large overlap of the scanned beam are identical to conventional broad beam irradiations.
Furthermore, ion the formation of checkerboard patterns on Ge surfaces was observed dur-ing 1 keV Ar+ irradiation at normal incidence and higher substrate temperature. Similar to the case of ion irradiated crystalline metal surfaces on the crystalline Ge surface a new instability appears at temperatures above the recrystallization temperature due to the Ehrlich-Schwoebel barrier. In this case, we observe regular checkerboard or hole patterns with the symmetry of the patterns reflecting the crystal structure of the irradiated surface.

Keywords: ion irradiation; surface patterning; Ge; nanostructures

  • Lecture (Conference)
    18th International Conference on Surface Modification of Materials by Ion Beams (SMMIB 2013), 15.-20.09.2013, Kusadasi, Türkiye

Publ.-Id: 19765

Reverse epitaxy: patterns on crystalline Ge surfaces

Facsko, S.; Ou, X.; Keller, A.

Low energy ion irradiation induces the formation of periodic surface patterns. These structured surfaces exhibit periodicities in the range of a few tens to hundreds of nanometers and are promising templates for producing nanostructured thin films. Periodic ripple patterns with wave vector parallel to the ion beam direction are observed frequently for ion irradiation at incidence angles between 50° and 70° to the surface normal. At normal incidence dot or hole patterns with hexagonal symmetry are observed only under special irradiation conditions.
At room temperature semiconductor surfaces are amorphized by ion irradiation. However, at temperatures higher than the recrystallization temperature the surface remains crystalline and novel ion induced patterns appear with the symmetry of the crystal structure of the material. We present pattern formation on Ge surfaces during 1 keV Ar+ ion irradiation under normal incidence at temperature above the recrystallization temperature of Ge. Similar to the case of ion irradiated crystalline metal surfaces on the crystalline Ge surface a new instability appears at higher temperature due to the Ehrlich-Schwoebel barrier. In this case, regular checkerboard or hole patterns with the symmetry of the patterns reflecting the crystal structure of the irradiated surface are observed.

Keywords: ion irradiation; surface patterning; homoepitaxy

  • Lecture (Conference)
    Symposium on „Nanoscale Pattern Formation at Surfaces“, 26.-30.05.2013, Copenhagen, Danmark

Publ.-Id: 19764

Ion Irradiation of Ge: From Sponge-Like Structures to Periodic Patterns

Böttger, R.; Ou, X.; Fritzsche, M.; Keller, A.; Heinig, K. H.; Bischoff, L.; Liedke, B.; Facsko, S.

Ion irradiation of Ge surfaces leads to a variety of different morphologies depending on the irradiation conditions. In the energy range of few MeV down to a few tens of keV swelling and the formation of sponge like structures are observed. When lowering the energy these porous structures turn into self-organized periodic surface patterns: at off-normal incidence angles well-known ripple patterns with wave vector parallel or perpendicular to the ion beam direction appear, whereas at normal incidence angles hexagonally ordered dot or hole patterns can be formed. The structure size of the patterns is in the range of 10 to 100 nm and, occa-sionally, a high degree of ordering is achieved.
On materials which turn amorphous during ion irradiation the formation of periodic patterns relies on at least two inter-playing processes: surface roughening due to local variation of ero-sion rate and smoothing via diffusional processes. In addition, atomic relocations on the sur-face and in the bulk resulting from the collision cascade have been identified as equally im-portant or even dominating. At the atomic level the creation of surface and bulk defects, sput-tering, and the influence of the ion beam on surface diffusion processes play a decisive role in the morphology evolution.
At high temperature, when amorphization of the Ge surface is prevented by recrystallization, novel surface patterns are developing during ion irradiation. Similar to the case of ion irradia-tions of crystalline metal surfaces a new instability appears on the crystalline Ge surface due to a Ehrlich-Schwoebel barrier for ascending ion induced vacancies. In this case, regular checkerboard patterns are evolving on the Ge (001) surface with structures oriented along the <100> direction.
Moreover, a new mechanism for pattern formation on Ge has been discovered recently: by polyatomic Bi ion irradiation or monoatomic Bi ion irradiation of hot Ge melt pools are in-duced at the Ge surface by the incident ions. These melt pools can also lead to a surface insta-bility and thus to the formation of periodic dot patterns at normal incidence.
We will present an overview of the different morphologies induced by ion irradiation on Ge surfaces and analyze the dominant formation mechanism.

Keywords: ion irradiation; surface patterning; vacancy diffusion

  • Lecture (Conference)
    Workshop on "Particle - surface interactions: from surface analysis to materials processing" (PASI 2013), 03.-5.05.2013, Luxembourg, Luxembourg

Publ.-Id: 19763

Interaction of highly charged ions with surfaces

Facsko, S.

Highly charged ions (HCI) release a large amount of potential energy during their neutralization when interacting with solid surfaces. This energy is mostly retained in the solid leading to local phase transformations on a nanometer scale. The study of modifications on surfaces and thin foils as a function of potential and kinetic energy gives insight into the interaction of HCIs with surfaces as well as into phase transformations under these non-equilibrium conditions.

Keywords: Highly charge ions; surfaces; nanostructures

  • Invited lecture (Conferences)
    11th European Conference on Atoms, Molecules and Photons, 24.-28.06.2013, Aarhus, Danmark

Publ.-Id: 19762

Spin Nernst Angle: Definition and qualitative Estimation for Cu Alloys

Zahn, P.; Gemming, S.

The spin Nernst effect describes the occurrence of a spin current perpendicular to an applied thermal gradient and the spin quantization axis in a non-magnetic material. To quantify the effect, the spin Nernst angle will be defined in a more general way than in ref. [1]. This allows for a clear separation of the transverse spin current into two opposite contributions proportional to the spin Hall angle and the spin Nernst angle, respectively. Qualitative trends for Cu alloys with 3d, 4d and 5d defects extending a resonant scattering model by Fert and Levy [2] will be presented.
The work was partially supported by the Initiative and Networking Fund of the German Helmholtz Association, Helmholtz Virtual Institute MEMRIOX (VH-VI-442) and the DFG Priority Program 'Nanostructured Thermoelectrics' (ZA264/3-2).
[1] K. Tauber et al., Phys. Rev. Lett. 109, 026601 (2012)
[2] A. Fert and P.M. Levy, Phys. Rev. Lett. 106, 157208 (2011)

  • Poster
    550. WE-Heraeus-Seminar 'Spin Transport beyond Boltzmann', 08.-10.01.2014, Bad Honnef, Deutschland

Publ.-Id: 19761

Memory Effects in Resistive Ion-beam Modified Oxides

Zahn, P.; Gemming, S.; Potzger, K.; Schmidt, H.; Mikolajick, T.; Slesazeck, S.; Stöcker, H.; Abendroth, B.; Meyer, D. C.; Dittmann, R.; Rana, V.; Waser, R.; Ronning, C.; Spaldin, N. A.; Basov, D.

The Virtual Institute MEMRIOX establishes a joint research initiative in the field of ion-tailored oxide-based memristive elements, to be pursued within a novel and unique combination of core competences from the Helmholtz centers Dresden-Rossendorf and Jülich and their university partners in Dresden, Freiberg, Jena, San Diego, and Zürich.
A nanoscale memristive element may prove the concept of the ultimate future non-volatile memory cell with a resistance set directly by electric currents. The Virtual Institute aims at stepping beyond the established layer-by-layer control of intrinsic defects during the synthesis of memristive elements. The project is financed by the Initiative and Networking Funds of the Helmholtz Association (VH-VI-442).

  • Poster
    E-MRS Spring Meeting, 27.-31.05.2013, Strasbourg, France

Publ.-Id: 19760

Gelatin-based biomaterials with tailorable mechanical properties as promising matrices for soft-tissue replacement

Ullm, S.; Tondera, C.; Gebauer, T.; Neffe, A. T.; Lendlein, A.; Pietzsch, J.

Gelatin-based hydrogels are promising degradable materials for soft tissue regeneration. Our approach aims at biopolymer-based polymer networks with tailorable elastic properties and degradation behavior due to different degrees of crosslinking with lysine diisocyanate ethyl ester. Two gelatin-based hydrogel films were compared regarding their influence on vitality, adhesion and proinflammatory activation of both endothelial cells and human macrophages, to investigate representative cells being responsible for tissue integration and degradation of the material.
Materials & methods
10 wt% gelatin solutions were crosslinked with three- (G10LNCO3) or eight-fold (G10LNCO8) excess of isocyanate groups, resulting in hydrogels with tailored Young’s moduli (13 and 55 kPa), swelling (1200 and 350 vol%) and degradation time [1]. For experiments on cell vitality, human leukemia HL-60 cells differentiated to macrophages (MΦ), and primary human aortic endothelial cells (HAEC) were incubated with material eluates for 24 and 48 h. Furthermore, these cells were seeded directly on swollen hydrogels for adhesion assays at 2 or 4 h, as well as for microscopic studies on their infiltration ability into the hydrogels after 48 h and 7 days. In order to characterize the ability of hydrogels to induce proinflammatory effects in cells, expression of COX-2 and the receptor for advanced glycation endproducts was quantified by western blotting after 48 h.
MΦ showed a higher vitality and HAEC showed a lower vitality after incubation with material eluates, which can only be related to fragments formed by partial degradation. Interestingly, the strong difference in degradation rate, with G10LNCO3 showing a mass loss of 60 wt% within 6 days, while G10LNCO8 showed only 5–10 wt% mass loss, did not have an influence on the vitality. The adhesion ability of MΦ to swollen hydrogels was significantly decreased to 30% (p<0.05, ANOVA) for G10LNCO3 and to 38% for G10LNCO8, respectively, when compared with adhesion on normal cell culture plastic. By contrast, HAEC in part showed enhanced adhesion to the materials (116% for G10LNCO3, n.s.; 145% for G10LNCO8, p<0.05). This suggests that gelatin offers adhesion sequences for HAEC, but not for MΦ. A higher degree of crosslinking resulted in higher adhesion of both cell types. Additionally, both cell types infiltrated the materials within 4 days, which highlights the degradability of the material, putatively supported by cell-mediated mechanisms. Direct contact with the materials resulted in an increment of COX-2 expression in both cell lines, with a higher degree of hydrogel crosslinking leading to elevated COX-2 expression. Receptor for advanced glycation endproducts synthesis remained unaffected in both MΦ and HAEC.
The hydrogels provide both a surface preventing adhesion of macrophages and supporting adhesion of endothelial cells, which might lead to good tissue integration. However, the materials or their degradation products induced proinflammatory effects on MΦ depending on the degree of crosslinking. In further studies, these hydrogel films will be studied in animal models concerning their initial interaction with the organism after implantation and their degradation.
Financial & competing interests disclosure
This work is part of a research initiative within the Helmholtz-Portfoliotheme “Technologie und Medizin - Multimodale Bildgebung zur Aufklaerung des In vivo -Verhaltens von polymeren Biomaterialien”.
1 Tronci G, Neffe AT, Piercea BF, Lendlein A. An entropy–elastic gelatin-based hydrogel system. J. Mater. Chem. 20, 8875–8884

  • Abstract in refereed journal
    Regenerative Medicine 8(2013), S201
  • Poster
    World Conference on Regenerative Medicine, 23.-25.10.2013, Leipzig, Deutschland

Publ.-Id: 19759

Radiosynthesis of 5-(2-[18[F]fluoroethyl)-sunitinib as inhibitor of VEGFR-2 – first results

Kniess, T.; Kuchar, M.; Bergmann, R.; Steinbach, J.; Pietzsch, J.

Radiolabeled inhibitors of receptor tyrosine kinases (RTK) might be suitable probes for monitoring pathophysiological situations related to enhanced expression of the vascular endothelial growth factor receptor (VEGFR). Imaging of
angiogenesis with PET could facilitate for the individual patient the evaluation of e.g. the success of corresponding anti-angiogenic chemotherapy or monitoring the stimulation of the endogenous adaptive vessel growth after implantation of
bioMaterials. For this purpose we developed an 18F-radiolabeled probe, 5-(2-[18F]fluoroethyl)-sunitinib basing on the lead structure of sunitinib®, a multi-kinase inhibitor selective to VEGFR-2.

Materials and Methods:
The non-radioactive reference compound 5-(2-fluoroethyl)-sunitinib was synthesized by Knoevenagel condensation of 5-(2-fluoroethyl)-indoline-2-one with N-[2-(diethylamino)ethyl]-2,4-dimethyl-5-formyl-1H-pyrrole-3-carboxamide. Two suitable precursors for radiolabeling, A and B were obtained by reacting a 5-(2-bromoethyl)-substituted sunitinib derivative with silver 4-toluenesulfonate and silver methanesulfonate, respectively. [18F]Fluoride was produced by the 18O(p,n)18F reaction from [18O]H2O in a 18/9 cyclotron (IBA), separated by an anion exchange cartridge (QMA, Waters) and activated by azeotropic drying with acetonitrile in a stream of nitrogen before use. In a set of radiolabeling experiments 4 mg of precursor A or B were reacted with [18F]fluoride in 500μL of solvent at a scheduled temperature regime for 20 min. The yield of 5-(2-[18F]fluoroethyl)-sunitinib was determined by radio-TLC (silicagel, THF/TEA=9/1).

The non-radioactive 5-(2-fluoroethyl)-sunitinib was investigated in a competition binding assay against VEGFR-2; a Kd value of 9 nM is justifying its classification as specific inhibitor. The radiolabeling reaction of the precursors A and B was performed at temperatures varying from 60, 90, and 120°C in one of the following solvents: acetonitrile, DMF, and DMSO. As result it turned out that for both precursors in DMF and DMSO only poor labeling yields about 2% could be achieved, whereas by using acetonitrile at 90°C the yield of 5-(2-[18F]fluoroethyl)-sunitinib increased to 7-9%. Reaction temperatures higher than 90°C lead to fast and complete decomposition of the precursors as monitored by several non-radioactive by-products on TLC. Notably no difference in yield was observed by using the methanesulfonyl- or the 4-toluenesulfonyl-precursor.

The new VEGFR-2 targeted radiolabeled probe 5-(2-[18F]fluoroethyl)-sunitinib was successfully synthesized by radiofluorination of the corresponding methanesulfonyl- or 4-toluenesulfonyl-substituted precursor with [18F]fluoride. First attempts to transfer the labeling method to a remote-controlled system were successful. By now a procedure for the purification of the radiotracer by semi-preparative HPLC and SPE is under development to enable the radiopharmacological evaluation.

  • Poster
    Annual Congress of the European Association of Nuclear Medicine, 19.-23.10.2013, Lyon, France
  • Abstract in refereed journal
    European Journal of Nuclear Medicine and Molecular Imaging 40(2013)Suppl. 2, S316
    DOI: 10.1007/s00259-013-2535-3

Publ.-Id: 19758

Pulmonary Blood Flow Increases in Damaged Regions Directly after Acid Aspiration in Rats

Richter, T.; Bergmann, R.; Knels, L.; Hofheinz, F.; Kasper, M.; Deile, M.; Pietzsch, J.; Ragaller, M.; Koch, T.

Background: After gastric aspiration events, patients are at risk of pulmonary dysfunction and the development of severe acute lung injury and acute respiratory distress syndrome, which may contribute to the development of an inflammatory reaction. The authors' aim in the current study was to investigate the role of the spatial distribution of pulmonary blood flow in the pathogenesis of pulmonary dysfunction during the early stages after acid aspiration.
Methods: The authors analyzed the pulmonary distribution of radiolabeled microspheres in normal (n = 6) and injured (n = 12) anesthetized rat lungs using positron emission tomography, computed tomography, and histological examination.
Results: Injured regions demonstrate increased pulmonary blood flow in association with reduced arterial pressure and the deterioration of arterial oxygenation. After acid aspiration, computed tomography scans revealed that lung density had increased in the injured regions and that these regions colocalized with areas of increased blood flow. The acid was instilled into the middle and basal regions of the lungs. The blood flow was significantly increased to these regions compared with the blood flow to uninjured lungs in the control animals (middle region: 1.23 [1.1; 1.4] (median [25%; 75%]) vs. 1.04 [1.0; 1.1] and basal region: 1.25 [1.2; 1.3] vs. 1.02 [1.0; 1.05], respectively). The increase in blood flow did not seem to be due to vascular leakage into these injured areas.
Conclusions: The data suggest that 10 min after acid aspiration, damaged areas are characterized by increased pulmonary blood flow. The results may impact further treatment strategies, such as drug targeting.

Publ.-Id: 19757

Neutronics diagnostics for European ITER TBMs: Activation foil spectrometer for short measurement cycles

Klix, A.; Domula, A.; Fischer, U.; Gehre, D.; Pereslavtsev, P.; Rovni, I.

An important aim of neutronics Test Blanket Module (TBM) experiments in ITER will be to check the prediction accuracy of nuclear responses in an environment closer to a future fusion power reactor than so far provided by existing facilities. The development of measurement methods suitable for the harsh environment in an ITER TBM has been addressed in several recent R&D programs supported by Euratom. Within this framework, KIT is developing an activation foil spectrometer for the measurement of local neutron flux densities in the TBM. We intend to establish a measurement method which allows to record the induced activities in small packages of activation foils simultaneously and to calculate the corre- sponding spectral neutron flux densities with moderate time resolution of tens of seconds immediately after extraction from the TBM. In the present work we propose a candidate set of activation foil materials which cover the neutron energy range from thermal to 14 MeV. In order to assess their basic suitability for such measurements, we have computed induced gamma-ray activities in the foils using a calculated neutron spectrum in a representative position in the European HCPB TBM assuming a short irradiation time of 30 s. In a further step we have investigated pulse height spectra which would be obtained in a typical gamma-ray measurement arrangement in a HPGe detector and concluded that the proposed set of activation foils should be basically suitable for such a measurement system but require improvement of relevant cross sections uncertainties.

Keywords: Neutron flux density; Activation foil; Neutron flux spectrometer; Test Blanket Module

Publ.-Id: 19756

Intersublevel dephasing in InAs/GaAs quantum dots below the Reststrahlen band

Teich, M.; Stephan, D. R.; Winnerl, S.; Schneider, H.; Wilson, L. R.; Helm, M.

Using transient four-wave mixing in the terahertz range, we have measured the s-p inter-sublevel dephasing time in self-assembled InAs/GaAs quantum dots for transition energies below the Reststrahlen band. Dephasing times of up to 600 ps at a photon energy of 18 meV have been determined. By comparing pump-probe and four-wave mixing measurements, we show that there is no significant influence of any pure dephasing process at low temperature. The linear temperature dependence is consistent with acoustic phonon scattering.

Keywords: quantum dots; THz; FEL; dephasing

Publ.-Id: 19755

Status of Development of the Reactor Dynamics Code DYN3D

Rohde, U.; Kliem, S.; Duerigen, S.; Bilodid, Y.

The reactor dynamics code DYN3D has been developed in HZDR and its predecessor organizations over more than 20 years. Originally, the code was developed for the analysis of reactivity-initiated transients and accidents in Russian VVER type reactors and recommended by the IAEA as a reference code for the VVER-440/V213 reactor. In the meantime, the code became an advanced simulation tool for transients in Light Water Reactors with 16 users in 7 countries.
The DYN3D code comprises neutron statics and kinetics calculations, thermal hydraulics of the reactor core and modeling of transient fuel rod behavior. In the paper, an outline on the basic models is given.
3D neutronics is based on nodal expansion methods for hexagonal, square and trigonal geometry of the fuel assemblies. With respect to neutron energy resolution, two-group and multi-group versions are available. Besides of standard diffusion approximation, simplified P3 (SP3) transport approach for square and trigonal lattices is implemented. Neutronic calculations can be performed with resolution on fuel assembly or pin-wise level.
Neutronics is coupled to thermal hydraulics, where the reactor core is modeled by parallel coolant channels. One- and two-phase flow in the channels is described based on a four-equations model. The code comprises a simplified thermo-mechanical model of the transient fuel behavior.
Macroscopic neutronic cross section libraries containing the dependence of cross sections from fuel burn-up and thermal hydraulics feedback parameters like fuel temperature, moderator density and temperature or boron concentration can be linked to the code through various data interfaces.
Besides of the basic models, the code disposes of various special features like:
• Zone-wise inner-nodal neutron flux reconstruction at pin level
• Reactor poisson dynamics
• Consideration of history effects in burn-up
• Decay heat model with consideration of the power history before shut down
• Calculation of steady states with external source
Comprehensive efforts have been made on verification and validation of DYN3D against numerical benchmarks, dedicated experiments on neutron kinetics and thermal hydraulics as well as real plant data. Some examples for verification of new models like history effects and SP3 method on trigonal lattice will be given.
Last but not least, examples on the application of DYN3D for the simulation of reactivity initiated accidents like control rod ejection will be shown. An advanced graphical tools for the visualization of the results of calculations will be demonstrated.

Keywords: reactor dynamics; transient simulation; neutron kinetics; thermo-hydraulics model; reactivity initiated accidents; computer code; VVER type reactors

  • Lecture (Conference)
    The 8th International Scientific and Technical Conference “Safety Assurance of NPP with WWER”, 28.-31.05.2013, Podolsk, Russia

Publ.-Id: 19754

Sensitivity Analysis o the Ranking of Input Uncertainties withe Respect to Peak Cladding temperature Uncertainty in a PWR LBLOCA Analysis

Rohde, U.; Kozmenkov, Y.

An uncertainty analysis of a large break loss-of-coolant accident (LBLOCA) for a German PWR Konvoi was performed using a statistical method, which is based on the Wilks’ theory. The evaluated output parameter is the peak cladding temperature (PCT). The primary goal of this paper is a ranking of the input uncertainties, according to their contributions to the PCT uncertainty in the ATHLET simulation of PWR LBLOCA, by performing a sensitivity analysis. It was shown, that the starting (extended) set of varied parameters can be considerably reduced without any statistically significant influence on the uncertainty analysis results.
The statistical t-test was used to minimize the number of varied parameters. A set of uncertainty parameters with significant impact on the uncertainty of the PCT was identified. The main contribution to the uncertainty of the first cladding temperature maximum during the blowdown phase of the accident is produced by the core parameters that affect the fuel’s stored energy at the beginning of the accident. However, the major contributors to the uncertainty of the second PCT maximum are the uncertainties in the code models, and first of all the uncertainties in the heat transfer coefficients for dispersed and pure steam flows.

Keywords: statistical uncertainty analysis; sensitivity analysis; Large Break LOCA; peak cladding temperature

  • Lecture (Conference)
    23rd Symposium of AER on VVER Reactor Physics and Reactor Safety, 30.09.-04.10.2013, Strbske Pleso, Slovakia
  • Contribution to proceedings
    23rd Symposium of AER on VVER Reactor Physics and Reactor Safety, 30.09.-04.10.2013, Strbske Pleso, Slovakia
    Proceedings of the 23rd Symposium of AER on VVER Reactor Physics and Reactor Safety, Budapest: MTA Energoatom, 978-963-7351-21-1, 501-512

Publ.-Id: 19753

Current status and future perspectives of the COBRA experiment

Ebert, J.; Fritts, M.; Gößling, C.; Goepfert, T.; Gehre, D.; Hagner, C.; Heidrich, N.; Koettig, T.; Neddermann, T.; Oldorf, C.; Quante, T.; Rajek, S.; Reinicke, O.; Schulz, O.; Tebruegge, J.; Timm, J.; Wonsak, B.; Zuber, K.

The aim of the COBRA experiment is to prove the existence of neutrinoless double-beta-decay (0v𝛽𝛽-decay) and to measure its half-life. For this purpose a detector array made of cadmium-zinc-telluride (CdZnTe) semiconductor detectors is operated at the Gran Sasso Underground Laboratory (LNGS) in Italy. This setup is used to investigate the experimental issues of operating CdZnTe detectors in low-background mode and to identify potential background components, whilst additional studies are proceeding in surface laboratories. The experiment currently consists of monolithic, calorimetric detectors of coplanar grid design (CPG detectors). These detectors are 1 × 1 × 1 cm3 and are arranged in 4 × 4 detector layers. Ultimately four layers will be installed by the end of 2013, of which two are currently operating. To date 82.3 kg⋅days of data have been collected. In the region of interest for 116 Cd around 2.8 MeV, the median energy resolution is 1.5% FWHM, and a background level near 1 counts/keV/kg/y has been reached. This paper gives an overview of the current status of the experiment and future perspectives.

Keywords: CZT COBRA double beta decay neutrino

Publ.-Id: 19752

First Experimental Results on the Azimuthal Magnetorotational Instability

Seilmayer, M.

More than 50 years ago, Velikhov and Chandrasekhar discovered a hydromagnetic instability which was later coined magnetorotational instability (MRI). For an ideal fluid it implies that a Couette flow between two corotating cylinders in the presence of a magnetic field is only stable as long the angular velocity increases outwards, quite in contrast to Rayleigh's hydrodynamic stability condition which demands the angular momentum to increase outwards.
The experimental verification of the standard version of MRI, with only an axial field being applied, is difficult since it requires both the magnetic Reynolds and the Lundquist number to be in the order of 1. The helical version of MRI, with an azimuthal field applied in addition to the axial one, is much easier to investigate since it requires only a Reynolds number in the order of 1000 and a Hartmann number in the order of 10. Very similar requirements apply to the so-called azimuthal MRI (AMRI), a non-axisymmetric (m=1) version that occurs for purely or strongly dominant azimuthal magnetic fields.
We present first experimental results on the AMRI obtained at the PROMISE facility with an enhanced power supply which can deliver currents up to 20 kA. For this system, we discuss the elaborate measures that were needed to obtaine a reasonable signal-to-noise ratio of the ultrasonic measurement system. In dependence on various parameter variations, some typical features of the observed instability, such as the energy content, the wavelength, and the frequency are analysed and compared with theoretical predictions.

Keywords: AMRI; magnetorotational instability

  • Lecture (Conference)
    eGdR Symposium, 08.-12.07.2013, Ascona, Schweiz

Publ.-Id: 19751

Detecting Supernova Dust on the Earth's Sea Floor with AMS

Feige, J.; Wallner, A.; Breitschwerdt, D.; Fifield, L. K.; Korschinek, G.; Merchel, S.; Rugel, G.; Steier, P.; Tims, S.; Winkler, S. R.; Golser, R.

An 60Fe anomaly was detected with accelerator mass spectrometry (AMS) - a very sensitive method to measure extremely low isotopic ratios - in a 2 Myr old layer of a ferromanganese crust (Knie et al., 2004). This signal is assumed to be of supernova origin and might be linked to the observation of our solar system being located in a Region of thin, hot interstellar medium. This region, called the Local Bubble, was presumably formed by multiple supernova explosions starting 14 Myr ago. Calculations suggest that at least one of these supernovae occured close enough to the solar system to leave a detectable 60Fe trace on Earth.
New AMS measurements are performed in deep-sea sediments from the Pacific Ocean. An international collaboration of different AMS facilities searches for signatures of the long-lived radionuclides 26Al, 53Mn, and 60Fe in a time range from 1.7 to 3.1 Myr. Magnetostratigraphic dating of the samples is confirmed by measurements of the cosmogenic radionuclide 10Be. All 10Be and 26Al measurements are finished, 53Mn and 60Fe is in progress. First results will be presented and discussed.

Keywords: accelerator mass spectrometry; AMS; supernova; cosmogenic radionuclide

  • Lecture (Conference)
    Symposium "Fathoming Stellar Evolution with Laboratory Precision", DPG Frühjahrstagung des Arbeitskreises Atome, Moleküle, Quantenoptik und Plasmen (AMOP), 17.-21.03.2014, Berlin, Deutschland

Publ.-Id: 19750

Evaluation of the Survey 2011/12 amongest doctoral student within the Helmholtz Association

Seilmayer, M.; Jose, D.; Thonicker, I.; Schmidt, L.

The Helmholtz Juniors are the PhD students Network of the German Helmholtz-Association (Helmholtz-Gemeinschaft Deutscher Forschungszentren, HGF). Their main effort is an intensive collaboration between the PhD students of the different Helmholtz research centers and an improvement of the PhD education. They consist of elected or delegated members of the PhD representative teams of each center.
In order to represent the interest of the PhD 1 students to the Helmholtz Association, we need to have precise and up-to-date knowledge about the working conditions, problems and wishes of PhDs. This survey is a crucial basis therefore. After 2008 and 2010, this report refers to the third wave of the Helmholtz wide phd survey. Its results technically enable us to even describe developments over the last 4 years, which should be the aim of a separate, comprehensive report in the near future.
Within the Helmholtz-Juniors, the working group PhD-Survey developed, conducted, analyzed, and reported the survey and its data. The raw data is hold by the working group. The report is free to be used by the Helmholtz Centers as well as its PhDs. In the report, the centers are coded by a random number, while each center is told its own number only.
In the report, firstly we provide information about the background of the participants. Secondly we address four main topics of interest, namely PhD project planning, the income situation of PhD students, conditions for starting a family during the time as PhD student and the situation of students of foreign nationalities within the HGF. And thirdly we report results regarding the Helmholtz graduate schools. We do neither refer to every question in the survey nor do we present cross tables or indepth information. If one is interested in further analysis, she may contact the members of this working group. The complete questionnaire is appended.

Keywords: PhD Representation; Helmholtz Juniors; Survey; HeJu

  • Article, self-published (no contribution to HZDR-Annual report)
    Forschungszentrum Rossendorf 2013
    33 Seiten
    ISSN: 2191-8708, eISSN: 2191-8716

Publ.-Id: 19749

Historical Aspects of Subsecond Thermal Processing

Voelskow, M.; Yankov, R. A.; Skorupa, W.

From atom bomb simulation to advanced semiconductor processing - what a bellicose - to peaceful bottom - up approach this research field experienced

Keywords: historical aspects; subsecond thermal processing

  • Book chapter
    Wolfgang Skorupa, Heidemarie Schmidt: Subsecond Annealing of Advanced Materials: Annealing by Lasers, Flash Lamps and Swift Heavy Ions (Springer Series in Materials Science), Switzerland: Springer, 2014, 978-3-319-03130-9, 1-13
    DOI: 10.1007/978-3-319-03131-6_1

Publ.-Id: 19748

Entwicklung szintillatorbasierter Echtzeit-Detektoren für laserbeschleunigte Protonen

Metzkes, J.; Karsch, L.; Kraft, S. D.; Pawelke, J.; Richter, C.; Schürer, M.; Sobiella, M.; Stiller, N.; Zeil, K.; Schramm, U.

  • Poster
    44. Jahrestagung der Deutschen Gesellschaft für Medizinische Physik, 18.-21.09.2013, Köln, Deutschland

Publ.-Id: 19747

Reflective Optical Probing of the Critical Density Surface in Laser-Produced Plasmas

Metzkes, J.; Zeil, K.; Kraft, S. D.; Kluge, T.; Schramm, U.; Mondal, S.; Ravindra Kumar, G.

  • Lecture (Conference)
    Meeting Prof. G. Ravindra Kumar Tata Institute of Fundamental Research 2013, 30.08.2013, Mumbai, India

Publ.-Id: 19746

III-V Quantum Dots in Dielectrics Made by Ion Implantation and Flash Lamp Annealing

Prucnal, S.; Turek, M.; Gao, K.; Zhou, S.; Pyszniak, K.; Drozdziel, A.; Zuk, J.; Skorupa, W.

Different semiconductor nanocrystals synthesized in dielectrics on silicon are very interesting for applications in non-volatile memories and photovoltaics. In this paper we present an overview of microstructural and opto-electronic properties of different III-V quantum dots embedded in SiO2 and Si3N4 made by sequential ion implantation and millisecond range flash lamp annealing. It is shown that within 20 ms post-implantation annealing high quality crystalline III-V quantum dots can be formed in different matrices. Formation of crystalline III-V quantum dots was confirmed by cross-section transmission electron microscopy, photoluminescence and mu-Raman spectroscopy. Flash lamp annealing is essentially a single-flash-single-wafer technique whose main attributes are the ease and control of processing over large wafer batches.

Keywords: III-V; quantum dots; silicon; FLA; ion implantation

Publ.-Id: 19745

Conductivity type and crystal orientation of GaAs nanocrystals fabricated in silicon by ion implantation and flash lamp annealing

Prucnal, S.; Liedke, M. O.; Zhou, S.; Voelskow, M.; Mucklich, A.; Turek, M.; Zuk, J.; Skorupa, W.

The integration of III-V semiconductor material within silicon technology is crucial for performance of advanced electronic devices. This paper presents the investigations of microstructural and opto-electronic properties of GaAs quantum dots (QDs) formed in silicon by means of sequential ion implantation and flash lamp annealing (FLA). Formation of crystalline GaAs QDs with well-defined crystal orientation and conductivity type was confirmed by high resolution transmission electron microscopy and mu-Raman spectroscopy. The influence of the post implantation millisecond-range annealing on the evolution of the nanoparticles size, shape, crystallographic orientation and doping type of GaAs QDs is discussed.

Keywords: GaAs; Quantum dots; Ion implantation; Flash lamp annealing; Silicon

Publ.-Id: 19744

Short time thermal processing and defects: history and ideology

Skorupa, W.

In this talk I will treat the fascinating world of defect engineering from the viewpoint of short time thermal processing in the millisecond range. Special focus will be devoted to ion implantation-related issues.

Keywords: millisecond range thermal processing; flash lamp annealing

  • Invited lecture (Conferences)
    International Symposium on Semiconductors: Defects, Doping and Diffusion (IS2D3), 24.-25.10.2013, Oslo, Norway

Publ.-Id: 19743

Nanocrystalline approaches to electronic materials using subsecond thermal processing

Skorupa, W.

This talk reviews the advances that subsecond thermal processing in the millisecond range using xenon-filled flash lamps brings to the processing of the most advanced semiconductor materials, thus enabling the fabrication of novel electronic structures and materials. It will be demonstrated how such developments can translate into important practical applications leading to a wide range of technological benefits. An important issue of our work was the formation and characterization of Si-based light electroluminescence from MOS structures with group-IV- and rare earth-containing dielectric layers. Recently we could demonstrate that germanium and silicon exhibit superconductivity at ambient pressure. Regarding photovoltaic applications, we dealt with the ion beam doping and thermal processing of PV silicon demonstrating a distinct improvement of the minority carrier diffusion length compared to RTP and furnace treatments. Whereas these examples base on solid phase processing the more sophisticated approach regards on working with the liquid phase at the surface of solid substrates. A recent example is the controlled formation of III-V nanocrystals (InAs, GaAs) in silicon after ion beam synthesis (NanoLett. 11, 2814 (2011)).
Moreover, a new approach of forming compound semiconductor nanocrystals inside a silicon nanowire will be demonstrated.

Keywords: Milliscond range annealing; flash lamp annealing; photovoltaics; electroluminescence; III-V nanocrystals; liquid phase processing; silicon nanowire

  • Invited lecture (Conferences)
    223rd ECS Meeting, Symposium E3: Nanocrystal Embedded Dielectrics for Electronic and Photonic Devices, 12.-17.05.2013, Toronto, Canada

Publ.-Id: 19742

Single particle resuspension experiments in turbulent channel flows

Barth, T.; Preuß, J.; Müller, G.; Hampel, U.

The resuspension of a monolayer of spherical glass and polypropylene particles from a channel floor by a dry and turbulent airflow was investigated. Special attention was given to the influence of the particle size, the particle and wall material, the wall surface roughness and the critical friction velocity. The experiments were performed in an air-driven small-scale test facility and the channel floor was made of interchangeable glass and steel wall segments. The turbulent channel flow was recorded using a planar Particle Image Velocimetry system. Prior to the experiments the spherical particles were classified using Scanning Electron Microscopy techniques. The particles on the channel floor were detected and classified by means of an optical microscope combined with a digital camera. A statistically sufficient particle monolayer was generated on the channel floor by dispersing the particles into the flow during a pure deposition regime. Afterwards, particle resuspension was induced by stepwise increase of the fluid velocity. The resuspension was quantified by the fraction of remaining particles against the friction velocity for a particle diameter range between 3 µm and 45 µm. It was found that particles instantly resuspend once a critical friction velocity is exceeded. Larger particles require lower fluid velocities for the removal than smaller particles. The wall surface roughness seems to scatter the resuspension process with respect to the friction velocity.

Keywords: aerosol particle; turbulent flow; resuspension

Publ.-Id: 19741

Enhanced feedback effects in sodium cooled fast reactors using moderating material – the effect of the plutonium content in the fuel

Merk, B.

The use of fine distributed moderating material to enhance the negative feedback effects and to reduce the sodium void effecting sodium cooled fast reactor cores is described. The influence of the moderating material on the neutron spectrum is given and evaluated in comparison with the capture cross sections of major materials (U-238, Pu-239, and Pu-240). The influence of the variation of the Pu content on the efficiency of the enhancement of the Doppler effect and on the reduction of the positive coolant and sodium void effect in a representative SFR fuel assembly configuration is analyzed. Additionally the influence of the moderating material combined with the variation of the Pu content on the infinite multiplication factor is studied.

Keywords: Enhanced feedback effects; Fast reactor; SFR; Sodium void effect; Yttrium hydride; Varying PU content

  • Contribution to proceedings
    PHYSOR 2014, 28.09.-03.10.2014, Kyoto, Japan
    PHYSOR 2014 – The Role of Reactor Physics Toward a Sustainable Future
  • Lecture (Conference)
    PHYSOR 2014, 28.09.-03.10.2014, Kyoto, Japan

Publ.-Id: 19740

Phosphorus in-diffusion from a surface source by millisecond flash lamp annealing for shallow emitter solar cells

Normann, H. B.; Vines, L.; Privitera, V.; Skorupa, W.; Schumann, T.; Svensson, B. G.; Monakhov, E. V.

We have investigated in-diffusion of phosphorus into monocrystalline silicon by depositing a phosphorus source on the surface followed by millisecond flash lamp annealing (FLA) to form shallow emitters for solar cells. By varying both the energy density of a 20 ms flash in the range from 62 to 132 J/cm(2) and the sample preheating, it is observed that FLA treatments can in-diffuse a high concentration of phosphorus atoms becoming electrically active. The most promising emitters are obtained after FLA in the energy range from 110 to 128 J/cm(2) including preheating at 300 degrees C with a peak concentration of 4 - 6 x 10(20) cm(-3). The emitter junction depth for these treatments is in the range of 100 nm to 200 nm, respectively.

Keywords: photovoltaics; solar cell; flash lamp annealing; millisecond annealing; doping; phosphorus; electrical activation

Publ.-Id: 19738

New insights into the nuclear structure in neutron-rich 112,114,115,116,117,118Pd

Luo, Y.; Rasmussen, J.; Hamilton, J.; Ramayya, A.; Frauendorf, S.; Hwang, J.; Stone, N.; Zhu, S.; Brewer, N.; Wang, E.; Lee, I.; Liu, S.; Terakopian, G.; Daniel, A.; Oganessian, Y.; Stoyer, M.; Donangelo, R.; Ma, W.; Cole, J.; Shi, Y.; Xu, F.

New level schemes of Pd-112,Pd-114,Pd-115,Pd-116,Pd-117,Pd-118 are established by means of gamma-gamma-gamma, gamma-gamma-gamma-gamma and gamma-gamma(theta) measurements of prompt fission gamma rays from Cf-252 using the Gammasphere multi-detector array. Spins/parities were assigned to levels based on gamma-gamma angular correlation measurements, level systematics and decay patterns. In the even-N isotopes Pd-112,Pd-114,Pd-116, two sets of odd-parity bands were identified and extended with spins measured in each band. The odd-parity bands with large level staggerings were interpreted as disturbed chirality with less pronounced triaxial deformations in the Pd isotopes than observed in the chiral symmetry breaking Ru-110,Ru-112 with maximum triaxiality.
Onset of wobbling motion was identified from the sign of the signature splitting in the gamma band of even-even Pd-114, and probably also in Pd-116, as first seen in the N = 68 isotone Ru-112. Maximal triaxiality in Ru and Pd isotopes is found to be reached for N = 68, Ru-112 and Pd-114, 4 neutrons more than predicted in the theoretical calculations.
The new data and TRS calculations allowed a systematic study of the band crossings in the even-N Pd-112,Pd-114,Pd-116 and odd-N Pd-115,Pd-117 isotopes. Now we find a new overall, more complex shape evolution than previously proposed from triaxial prolate in Pd-110 via triaxial oblate in Pd-112 to nearly oblate in Pd-114,Pd-116 with a large change of the triaxial deformation parameter gamma toward nearly oblate in the (pi
g(9/2))(2) alignment in Pd-114,Pd-115,Pd-116,Pd-117,Pd-118, and triaxial-prolate-triaxial-oblate shape coexisting bands in Pd-115.

Publ.-Id: 19737

Hot electron effect on charge formation in SiO2 layer enriched by rare-earth based nanoclusters

Nazarov, A. N.; Tiagulskyi, S. I.; Tygulskyy, I. P.; Lysenko, V. S.; Rebohle, L.; Skorupa, W.

Fowler-Nordheim (FN) hot electron injection in dielectгics is often used as a method which is alternative to x-ray irradiation. In this work charge trapping during FN еlесtrоп injection in SiO2 implanted bу various rаre-еаrth (RE) impurities (Се, Еu, Gd, Тb, Еr, Тm) with following high tеmреrаturе annealing is considered. Implanted doses correspond to a RE atomic concentration from 0.1 to 1.5 at. %. The charge trapping in Al-SiO2(RE)-n-Si struсturеs is mеаsurеd bу high-frequency (100 kHz) capacitance-voltage (C-V) characteristics and changing of the voltage applied to the structure during еlесtгоп injection at constant current regime. The RE impurity distribution and nanocluster formation in the Sio2 layer after high-temperature annealing (from 900 to 1100°C) are studied bу Rutherford buck sсаttеring (RBS) method and high-resolution transmission electron microscopy (HRTEM) correspondingly. Сhаrgе trаррing раrаmеtеrs (type of charge, capture cross-section, trapped charge concentration) аrе determined at hot electron injection frоm 10E14 to 10E21 e/cm2.

It was shown that at medium electron injection (from 10E15 to 10E18 е/сm2) for аll types of RE impurities negative charge trapping was observed. It was found that mахimum negative сhаrge trapping took place iп Eu implanted dielectrics which demonstrated mахimum size of the formed nanoclusters. A shell model of the defect generation and negative charge trapping around the nanoclusters was proposed. Qualitative calculations of dangling bonds, arоund the RE oxide nanoclusters were performed which confirmеd the obtained ехрегimепtаl results.

Keywords: rare earth; ion implantation; charge trapping MOS structure; electroluminescence

  • Poster
    17th International conference on radiation effects in insulators, 30.06.-05.07.2013, Helsinki, Finland

Publ.-Id: 19736

Dipole strength of 181Ta for the evaluation of the 180Ta stellar neutron capture rate

Makinaga, A.; Massarczyk, R.; Schwengner, R.; Beard, M.; Dönau, F.; Anders, M.; Bemmerer, D.; Beyer, R.; Hannaske, R.; Junghans, A. R.; Kempe, M.; Kögler, T.; Röder, M.; Schmidt, K.; Wagner, A.

The photoabsorption cross section of 181Ta up to the neutron-separation energy is deduced using bremsstrahlung produced with an electron beam of 9.6 MeV energy. The analysis of the measured gamma-ray spectra includes the quasicontinuum of levels at high energy. Simulations of gamma-ray cascades are performed to estimate intensities of inelastic transitions and branching ratios of the ground-state transitions. The resulting photoabsorption cross section shows enhanced dipole strength in the energy range from 5 to 8 MeV, which may be related to a pygmy dipole resonance. The results of the present experiment are compared with predictions of a quasiparticle-random phase approximation in a deformed basis. A combination of the present experimental data and (gamma,n) data is used as an input to the statistical code TALYS applied to calculate cross sections and reaction rates of
photonuclear reactions that are important for the nucleosynthesis of 180mTa.

Keywords: Nuclear resonance fluorescence; photon scattering; photoabsorption cross section; dipole strength function; astrophysical reaction rates; statistical reaction model; quasiparticle random phase approximation; nuclear deformation

Publ.-Id: 19735

Development and first experimental tests of Faraday cup array

Prokůpek, J.; Kaufman, J.; Margarone, D.; Krůs, M.; Velyhan, A.; Krása, J.; Burris-Mog, T.; Busold, S.; Deppert, O.; Cowan, T. E.; Korn, G.

A new type of Faraday cup, capable of detecting high energy charged particles produced in a high intensity laser-matter interaction environment, has recently been developed and demonstrated as a real-time detector based on the time-of-flight technique. An array of these Faraday cups was designed and constructed to cover different observation angles with respect to the target normal direction. Thus, it allows reconstruction of the spatial distribution of ion current density in the subcritical plasma region and the ability to visualise its time evolution through time-of-flight measurements, which cannot be achieved with standard laser optical interferometry. This is a unique method for two-dimensional visualisation of ion currents from laser-generated plasmas. A technical description of the new type of Faraday cup is introduced along with an ad hoc data analysis procedure. Experimental results obtained during campaigns at the Petawatt High-Energy Laser forHeavy Ion Experiments (GSI, Darmstadt) and at the Prague Asterix Laser System (AS CR) are presented. Advantages and limitations of the used diagnostic system are discussed.

Publ.-Id: 19734

Internal characterisation of fresh agricultural products using traditional and ultrafast electron beam X-ray computed tomography imaging

Donis Gonzalez, I. R.; Guyer, D. E.; Pease, A.; Barthel, F.

Currently, destructive techniques can be employed to evaluate the internal attributes of fresh fruits, vegetables and nuts. However, clearly not all produce can be evaluated. Thus, there is a need to develop an in vivo non-destructive technique able to assess fresh agricultural commodity internal components, especially disorders. In this study, medical grade computed tomography (CT) was used to obtain transversal two-dimensional (2D) Images from several fresh agricultural product phenomena. CT scanning was performed by placing and securing numbered samples onto a whole polyethylene sheet, placed on the CT scanner table. Phenomena included the internal decay of chestnuts (Castanea spp.), internal defects in pickling cucumbers (Cucumis sativus), translucency disorder in pineapples (Ananas comosus), pit presence in tart cherries (Prunus cerasus var. Montmorency) and plum curculio (Conotrachelus nenuphar ) infestation of tart cherries.
In addition, an ultrafast X-ray CT scanner was also used to visualise internal characteristics of fresh chestnuts. Chestnuts were labelled and packed in a thin plastic hose, which was pulled through the scanning plane. The 2D CT X-ray images and post-processing three-dimensional CT image recon-struction indicate that CT can be used as an accurate in vivo insight of fresh intact agri-cultural products. Results suggest that there is a potential for non-destructive inline sorting of the internal quality of several agricultural products.
The long-term objective is that the fresh and processing product industries will then be able to detect internal quality attributes of fresh agricultural commodities, at a relatively early stage, after validation under commercial conditions.

Publ.-Id: 19733

Temperature dependence of ion-beam mixing in crystalline and amorphous germanium isotope multilayer structures

Radek, M.; Bracht, H.; Posselt, M.; Liedke, B.; Schmidt, B.; Bougeard, D.

Self-atom mixing induced by 310 keV gallium (Ga) ion implantation in crystalline and preamorphized germanium (Ge) at temperatures between 164 K and 623 K and a dose of 1x1015 cm-2 is investigated using isotopic multilayer structures of alternating 70Ge and natGe layers grown by molecular beam epitaxy. The distribution of the implanted Ga atoms and the ion-beam induced depth-dependent self-atom mixing was determined by means of secondary ion mass spectrometry. Three different temperature regimes of self-atom mixing, i.e., low-, intermediate-, and high-temperature regimes are observed. At temperatures up to 423 K, the mixing is independent of the initial structure, whereas at 523 K, the intermixing of the preamorphized Ge structure is about twice as high as that of crystalline Ge. At 623 K, the intermixing of the initially amorphous Ge structure is strongly reduced and approaches the mixing of the crystalline material. The temperature dependence of ion-beam mixing is described by competitive amorphization and recrystallization processes.

Keywords: germanium; isotope multilayer; ion-beam mixing; thermal spike model

Publ.-Id: 19732

A spectroscopic study of uranyl hydrolysis

Drobot, B.

Short overview of a time resolved laser induced fluorescence spectroscopy (TRLFS) study and mathematical analyzis (PARAFAC).

Keywords: U(VI); Uranium; TRLFS; spectroscopy; PARAFAC

  • Lecture (others)
    Annual PhD seminar, 07.-09.10.2013, Bautzen, Germany

Publ.-Id: 19731

Aspects of Fermiology in correlated metals

Wosnitza, J.

es hat kein Abstract vorgelegen

  • Invited lecture (Conferences)
    Sino-German (International) Workshop On Kondo and Mott Physics in Correlated Matter, 13.-17.10.2013, Hangzhou, China

Publ.-Id: 19730

World Record Race - Research at High Magnetis Fields

Wosnitza, J.

  • Invited lecture (Conferences)
    Symposium "10 Jahre Mikroaktorik", 11.10.2013, Freiburg, Deutschland

Publ.-Id: 19729

The Dresden High Magnetic Field Laboratory - Recent Research Results

Wosnitza, J.

es hat kein Abstract vorgelegen

  • Invited lecture (Conferences)
    Seminar at Niigata University, 12.08.2013, Niigata, Japan

Publ.-Id: 19728

Titration curves, column experiments, and reactive transport models

Britz, S. M.; Noseck, U.; Brendler, V.; Stockmann, M.

Surface reactions related to e.g. transport and retardation processes in groundwater systems are correlated with geochemical conditions that vary in time and space. For longterm safety analysis of radioactive waste repositories it is of great interest to better understand and to realistically assess these geochemically driven surface and transport reactions, since they might strongly impact radiation exposure. To get an advanced insight into these processes column experiments are conducted and subsequently modeled with the geochemical speciation code PhreeqC, Version 2.18 (coupled with UCODE_2005). In order to set-up realistic reactive transport models so-called surface complexation parameters (SCP) such as surface site density, specific surface area, and protolysis constants need to be derived from titration experiments of relevant mineral phases. Two different titration techniques are conducted for muscovite and orthoclase: continuous and batch titration. Derived results are compared offering an insight into pHinfluencing reactions that contribute to surface reactions but also to cation exchange and mineral dissolution. In column experiments diffent solids are applied: natural sediments from the Gorleben site, Germany and pure mineral phases (orthoclase, muscovite, quartz). Parameters such as pH, ligands, ionic strength, and cation concentrations are varied in each experiment to reflect realistic enviromental conditions. Moreover, transient pH conditions are applied in selected columns.
Both types of experiments (titration, column experiments) including each geochemical variation provide data to model reactive transport processes of hazardous pollutants more realistically in groundwater-flow driven environments with PhreeqC. Calculations will be conducted and first results offered for discussion.
This project is funded by the German Federal Ministry of Economics and Technology (BMWi) under contract no. 02 E 11072A and 02 E 11072B.

  • Poster
    Goldschmidt 2013, 25.-30.08.2013, Florence, Italy

Publ.-Id: 19727

Technischer Zwischenbericht: Partikelentstehung und –transport im Kern von Druckwasserreaktoren

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

Im borsäurehaltigen Kühlmittelreislauf von Druckwasserreaktoren können nach einem postulierten Kühlmittelverluststörfall während des Sumpfumwälzbetriebs signifikante Konzentrationen an gelöstem Zink auftreten, welche durch Korrosion feuerverzinkter Einbauten des Containments verursacht werden. Bedingt durch die in Batch-Experimenten nachgewiesene abnehmende Löslichkeit der Zink-Korrosionsprodukte (Zink-Borate) mit zunehmender Temperatur ist eine Ausscheidung fester Korrosionsprodukte in heißen Zonen nicht auszuschließen. Die physikochemischen und thermofluiddynamischen Mechanismen der Korrosionsprodukt-Abscheidung wurden am HZDR im Labormaßstab bzw. an der Hochschule Zittau/Görlitz an halbtechnischen Versuchsanlagen untersucht.
Der Beitrag gibt einen Überblick über die bisher im BMWi-Verbundvorhaben „Partikelentstehung und –transport im Kern von Druckwasserreaktoren“ durchgeführten Untersuchungen, die erzielten Ergebnisse sowie die geplanten Arbeiten zur Modellierung der Korrosions- und Ablagerungsprozesse und zu Präventivmaßnahmen.

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

  • Other report
    Dresden: HZDR, 2013
  • Lecture (others)
    Sitzung des Projektkomitees „Transienten und Unfallabläufe“, 26.09.2013, Köln, Deutschland

Publ.-Id: 19726

Partikelentstehung und –transport im Kern von Druckwasserreaktoren

Kryk, H.; Kästner, W.

Im borsäurehaltigen Kühlmittelreislauf von Druckwasserreaktoren können nach einem postulierten Kühlmittelverluststörfall während des Sumpfumwälzbetriebs signifikante Konzentrationen an gelöstem Zink auftreten, welche durch Korrosion feuerverzinkter Einbauten des Containments verursacht werden. Bedingt durch die in Batch-Experimenten nachgewiesene abnehmende Löslichkeit der Zink-Korrosionsprodukte (Zink-Borate) mit zunehmender Temperatur ist eine Ausscheidung fester Korrosionsprodukte in heißen Zonen nicht auszuschließen. Die physikochemischen und fluiddynamischen Mechanismen der Korrosionsprodukt-Abscheidung wurden am HZDR im Labormaßstab bzw. an der Hochschule Zittau/Görlitz an halbtechnischen Versuchsanlagen untersucht.
Der Vortrag gibt einen Überblick über die bisher im BMWi-Verbundvorhaben „Partikelentstehung und –transport im Kern von Druckwasserreaktoren“ erzielten Ergebnisse als Unterstützung für Sicherheitsbewertungen durch die Reaktor-Sicherheitskommission und entsprechende Behörden.

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

  • Invited lecture (Conferences)
    RSK-Ausschuss Anlagen- und Systemtechnik, 28.11.2013, Bonn, Deutschland

Publ.-Id: 19725

The effect of dual Fe+/He+ ion beam irradiation on microstructural changes in FeCrAl ODS alloys

Chen, C.; Richter, A.; Kögler, R.

Nanostructured ferritic oxide dispersion strengthened (ODS) alloys contain a high density of Y-Al-Ti-O nanoparticles, high dislocation densities and fine grains. Structural analysis with HRTEM shows that the composition of the initial Y2O3 oxide is modified to perovskite YAlO3 (YAP), Y2Al5O12 garnet (YAG) and Y4Al2O9 monoclinic (YAM) particles.
Irradiation of these alloys was performed with a dual beam implantation of 2.5 MeV Fe+ and 350 keV He+, either simultaneously or sequentially.
Additionally, the He+ concentration was varied between 18 and 72 appm/dpa. Irradiation causes atomic displacements resulting in vacancy and self-interstitial lattice defects and dislocation loops. A clear hardness increase in the irradiated area is observed by nanoindentation in every ion implantation regime. Hardness ratios of irradiated relative to non-irradiated ODS materials and the appearance of hardness maxima close to the surface region are discussed in detail. The irradiation induced hardening effect is stronger for a heat treated HT-ODS alloy than for an as-received one. The large difference in the hardness data of as-received ODS for simultaneous and sequential implantation can be explained by point defect recombination at dislocations and grain boundaries occurring for sequential irradiation.

Publ.-Id: 19724

Visualisierung neurodegenerativer Veränderungen in einem neuen Mausmodell der Alzheimer Erkrankung mittels (+)-[18F]flubatine.

Ullmann, C.

Es ist kein Abstract vorhanden.

  • Master thesis
    Universität Leipzig, 2013
    102 Seiten

Publ.-Id: 19723

Search for supernova-produced 60Fe in the microfossil record

Ludwig, P.; Bishop, S.; Egli, R.; Chernenko, V.; Faestermann, T.; Famulok, N.; Fimiani, L.; Frederichs, T.; Gomez, J.; Hain, K.; Hanzlik, M.; Korschinek, G.; Merchel, S.; Rugel, G.

Material distributed into the interstellar medium by supernova explosions can be incorporated into terrestrial archives. After the discovery of live 60Fe atoms in 2-3 Myr old layers of a Pacifc Ocean ferromanganese crust (Knie et al., 2004), a confirmation of this signal, as well as a mapping of the signal with high time-resolution is desireable. Another reservoir in which the 60Fe signature should have been incorporated in are the fossils of magnetotactic bacteria in ocean sediment. To this end, two sediment cores from the Eastern Equatorial Pacifc were obtained, iron was chemically extracted with high selectivity towards biogenic magnetite, and the extraction procedure was characterized using novel magnetic measurements. The samples were then measured with accelerator mass spectrometry in Garching. Preliminary results for both sediment cores will be reported.

Keywords: accelerator mass spectrometry; AMS; supernova; astrophysics

  • Lecture (Conference)
    DPG-Frühjahrstagung der Sektion AMOP (SAMOP), 17.-21.03.2014, Berlin, Deutschland

Publ.-Id: 19722

Investigation of heavy metals sorption behavior of isolated bacterial cell wall components of Gram-positive bacteria using ICP-MS and TRLFS

Viacava Romo, K. E.

Attention for heavy metal removal and recovery has been increasing as their demand and scarcity increase. The property of certain types of biomass to remove heavy metals from the environment has encouraged the search of novel biosorbents for technology development. In this work the heavy metal biosorption of two Gram-positive bacteria strains Lysinibacillus sphaericus bacterial (JG-A12 and JG-B53) isolated from the uranium mining waste pile Haberland (Johanngeorgenstadt, Saxony) has been investigated. The metal binding capacities of the isolated main three cell wall components (peptidoglycan, lipids and surface-layer proteins) and the heavy metal uptake of the intact bacteria have been studied for eight different heavy metals (palladium, cadmium, platinum, gold, lead, europium and uranium). Lysinibacillus sphaericus JG-B53 probed to have higher heavy metal binding capacities and uptakes. The best biosorbent for both strains was the peptidoglycan and the higher binding capacities were observed for uranium, lead and europium. Finally in order to elucidate the mechanisms involved in the biosorption of metal ions, the Eu3+ was used as a fluorescent probe and investigated with time-resolved laser-induced fluorescence spectroscopy (TRLFS) as it interacted with the different biosorbents. The results although complexed to interpreted due to the inherent complexity of the biosorbents showed clearly the Eu3+-biosorbent binding and are an important basis for further complexation studies.

Keywords: Bacteria; sorption; heavy metals; S-layer; cell wall; lipids; peptidoglycan; ICP-MS; TRLFS

  • Master thesis
    TU Dresden, 2013
    120 Seiten

Publ.-Id: 19721

Direct Observation of Binary Vortex Core States in Magnetic Mutlilayers

Wintz, S.; Im, M.-Y.; Banholzer, A.; Weigand, M.; Raabe, J.; Mattheis, R.; Fischer, P.; Erbe, A.; Fassbender, J.

Topological spin textures such as skyrmions or vortices are attracting significant attention because of their fundamentally interesting magnetostatic and dynamic properties. In particular, magnetic vortices have been studied intensively during the past decade. As shown in Fig. 1(a), such a spin vortex consists of a planar, flux-closing magnetization curl that tilts out of the plane in the central core. Vortices are typically found as the ground state of micron sized ferromagnetic thin film elements, whi- le their nanoscopic cores are being much smaller, with diameters on the order of 10 nm only. Along with fundamental investigations, proposals were also made to apply vortices for memory cells, or as oscillators in data communication devices. In this view, stacking of vortices via nonferromagnetic interlayers [cf. Fig. 1(b)] is an important issue to address, since such geometries allow for the exploitation of GMR/TMR as well as spin-torque effects.

Keywords: magnetic vortex core multilayer x-ray microscopy

  • Poster
    IEEE International Magnetics Conference 2014, 04.-08.05.2014, Dresden, Deutschland

Publ.-Id: 19720

Synthesis and biological evaluation of a novel non-peptidic brain-penetrant F-18-labeled oxytocin receptor ligand

Wenzel, B.; Mollitor, J.; Kranz, M.; Deuther-Conrad, W.; Günther, R.; Teodoro, R.; Fischer, S.; Ludwig, F.-A.; Smits, R.; Steinbach, J.; Hoepping, A.; Brust, P.

1. Introduction
Oxytocin is a neurohypophysial peptide hormone, synthesized in the hypothalamus and stored in the posterior pituitary gland for release into the bloodstream. It acts as neurotransmitter and neuromodulator to regulate a diverse range of CNS functions including emotional, parental, and sexual behaviors. Its receptor (OTR) is expressed in peripheral organs as well as in specific brain areas related to cognitive function and psychiatric diseases such as schizophrenia and depression. So far, investigation of the distribution of OTR in brain in vivo is hampered by the lack of suitable radiotracers. Thus, the development of a brain-penetrant PET ligand with high affinity and selectivity to the OTR would promote the development of non-invasive and quantitative imaging of OTR expression in healthy and diseased brain. Therefore, we synthesized a series of fluorinated non-peptidic OTR ligands and performed radiofluorination of one selected candidate to investigate its in vivo properties by organ distribution and dynamic PET imaging studies in mice and pigs.

2. Materials & Methods
Binding affinities of the novel compounds to the human OTR were determined by radioligand displacement studies using stably transfected hOTR-HEK293 cells and [3H]oxytocin. The radiosynthesis of the selected candidate [18F]ABX163 was performed in a two-step procedure using the methoxymethyl (MOM)-protected tosylate precursor ABX185. 18F was incorporated using K[18F]F-Kryptofix 222-carbonate complex at 90°C in ACN within 15 min followed by removal of the two MOM protecting groups with 1M HCl at 90°C within 15 min. The radiotracer was isolated by semi-preparative HPLC (Reprosil-Pur AQ column, 250x10mm), ACN/aqu. 20 mM NH4OAc) followed by final purification with a Sep-Pak C18 Plus light cartridge and formulation in isotonic saline containing 10% ethanol. Specific binding of [18F]ABX163 was assessed by in vitro autoradiography on mouse brain slices. Metabolism and organ distribution of the radiotracer were studied in female CD-1 mice at 30 and 60 min p.i. Dynamic PET scans were performed in mice (animal PET/MR; 60 min) and in one female piglet (PET; 120 min), the latter one accompanied by chromatographic analysis of plasma radio-metabolites.

3. Results
Based on the biphenyl-benzopyrrolodiazepine derivative WAY-162720, described as OTR selective and brain-penetrant ligand [1], three fluoro-containing reference compounds were synthesized which retained high affinity towards the OTR (Ki=14-22 nM). Radiolabeling of the selected candidate [18F]ABX163 was obtained in a two-step radiosynthesis with a RCY(DC) of 20-25%, radiochemical purity >98%, and specific activity of 35-133 GBq/µmol.[18F]ABX163 was stable for at least 60 min in saline, PBS, and pig plasma at 37°C. A logDoctanol/PBS value of 2.9 ± 0.2 (n=3) was determined by shake flask method.
Both organ distribution and dynamic PET imaging studies revealed limited uptake of the radiotracer in mouse brain (mean SUV value of 0.04). Besides, significant uptake in the pituitary gland was observed (SUV=0.85 at 55 min p.i.), which indicates target-specific binding of [18F]ABX163. By a dynamic PET study in one piglet, a mean SUV of 0.43 was estimated for whole brain at 120 min p.i. Most remarkable was the elevated uptake in the olfactory bulb with SUV120=0.73, a region with high expression of OTR. Metabolite analysis of pig plasma by radio-HPLC demonstrated moderate metabolism of [18F]ABX163 with non-metabolized tracer accounting for 44% of total radioactivity at 30 min p.i.

4. Discussion & Conclusion
Radiofluorination of a novel non-peptidic oxytocin receptor ligand [18F]ABX163 was achieved with appropriate radiochemical yield and specific activity. Evidence was obtained, that uptake of [18F]ABX163 in the pituitary gland of mouse brain and olfactory bulb of pig brain reflects target-specific binding. Differences in brain uptake between mice and pigs may be caused by species-specific expression of efflux transporters in the blood-brain barrier. With the development and evaluation of [18F]ABX163 we could demonstrate for the first time the potential of non-peptidic oxytocin receptor ligands for imaging of OTR in brain by PET. To further improve brain uptake, we are currently working on structural modifications of [18F]ABX163.

[1] Ring RH, Malberg JE, Potestio L, Ping J, Boikess S, Luo B, Schechter LE, Rosenzweig-Lipson S, [2006] Psychopharmacology 218-225.

  • Lecture (Conference)
    ESRR'2014 - 17th European Symposium on Radiopharmacy and Radiopharmaceuticals, 24.-27.04.2014, Pamplona, Spain

Publ.-Id: 19719

Comparative evaluation of two novel fluorine-18 PET radiotracers for the alpha7 nicotinic acetylcholine receptor (α7nAChR)

Teodoro, R.; Deuther-Conrad, W.; Rötering, S.; Scheunemann, M.; Patt, M.; Donat, C. K.; Wenzel, B.; Peters, D.; Sabri, O.; Brust, P.

Objectives :
The α7nAChR plays an important role in mediating cholinergic transmission, and is considered as biomarker for inflammatory processes and certain types of cancer. [18F]NS14490 (1), and [18F]DBT10 (2) showed high in vitro binding affinity and selectivity (Ki,α7= 2.5 and 0.3 nM, Ki,α3β4= 102 and 5000 nM, respectively, and Ki,α3β2both > 800 nM). Here, we report automated radiosyntheses and in vivo PET evaluation in pigs of 1 and 2.

Methods : Syntheses of 1 and 2 were performed in one-step procedure using OTs and NO2 precursors, respectively, in automated module (Tracerlab FX F-N). Dynamic PET studies (4 h) were performed in anesthetized female juvenile pigs after injection with ~300-400 MBq of 1 or 2 (n=6 each). Blocking studies were performed in 3 pigs each by bolus injection/constant infusion of NS6740 (7 mg/kg), a highly selective α7nAChR ligand. Metabolite-corrected plasma input functions were used for 2-tissue-compartment modeling (2TCM) to determine binding parameters of 1 and 2 in 24 brain regions.

Results : 1 and 2 were synthesized in high radiochemical purities (>92%, >95%), and high specific activities (> 150 GBq/μmol, EOS) with a RCY of 24-36% and 45-50%, respectively. Maximum brain SUVs of 1 (0.54) and 2 (1.89) were reached at 3 and 11.5 min p.i., respectively. Metabolism of 1 and 2 is comparable. At 60 min p.i. about 25% of 1 and 24% of 2 accounted for total radioactivity in plasma. 2TCM of 1 and 2 allowed reliable estimates of k3 of 1 (-46%) and BP, respectively (Table). NS6740 significantly reduced (* p<0.05) mean k3 of 1 (-46%) and mean BP of 2 (-75%).

Conclusions : 1 and 2 are promising PET tracers for imaging α7nAChR. Because of higher affinity, brain uptake and specific binding [18F]DBT10 (2) is selected for further evaluation to obtain approval for translational clinical validation in human beings.

Research Support: DFG (DE 1165/2-1)

  • Poster
    SNMMI 2014 Annual Meeting, 07.-11.06.2014, St. Louis, Missouri, USA
  • Abstract in refereed journal
    Journal of Nuclear Medicine 55(2014)1, 1099


Publ.-Id: 19718

Materials research at the Dresden High Magnetic Field Laboratory

Wosnitza, J.

es hat kein Abstract vorgelegen

  • Invited lecture (Conferences)
    Seminar at the Départment de Physique, Université de Montréal, 22.07.2013, Montreal, Canada

Publ.-Id: 19717

Recent developments in superconductivity in organic materials

Wosnitza, J.

es hat kein Abstract vorgelegen

  • Invited lecture (Conferences)
    10th International Symposium on Crystalline Organic Metals, Superconductors and Magnets (ISCOM 2013), 14.-19.06.2013, Montreal, Canada

Publ.-Id: 19716

Die Jagd nach dem Weltrekord - Materialforschung an der Grenze des Machbaren

Wosnitza, J.

es hat kein Abstract vorgelegen

  • Invited lecture (Conferences)
    Dresdner Lange Nacht der Wissenschaften, 05.07.2013, Dresden, Deutschland

Publ.-Id: 19715

Materials research at high magnetic fields

Wosnitza, J.

es hat kein Abstract vorgelegen

  • Invited lecture (Conferences)
    Kick Off Meeting for the Helmholtz International Beamline for Extreme Fields (HIBEF), 02.-05.06.2013, Hamburg, Deutschland

Publ.-Id: 19714

The Fulde-Ferrell-Larkin-Ovchinnikov state in quasi-two-dimensional organic superconductors

Wosnitza, J.

es hat kein Abstract vorgelegen

  • Invited lecture (Conferences)
    IV International Symposium on Strong Nonlinear Vibronic and Electronic Interactions in Solids, 01.-03.05.2013, Tartu, Estonia

Publ.-Id: 19713

Probing magnetic exchange interactions in rare-earth intermetallic compounds by high-field measurments

Wosnitza, J.

es hat kein Abstract vorgelegen

  • Invited lecture (Conferences)
    International Conference on Rare-Earth Materials: Advances in Synthesis, Studies and Applications, 26.-28.04.2013, Wroclaw, Poland

Publ.-Id: 19712

High-magnetic-field properties of frustrated magnets

Wosnitza, J.

es hat kein Abstract vorgelegen

  • Invited lecture (Conferences)
    Kick-off meeting of the Helmholtz Virtual Institute "New States of Matter and their Excitations", 22.-24.04.2013, Berlin, Deutschland

Publ.-Id: 19711

Infrared images of single electrons

Winnerl, S.; Helm, M.

Scattering-type near-field optical microscopy (s-SNOM) is a powerful technique to image nano objects. It can be employed in a broad spectral range, namely the complete infrared region spanning from the terahertz range up to the visible range. In this article we describe a system which utilizes a free-electron laser as a spectrally narrow and widely tunable source of infrared radiation. This system was employed to study electrons confined in self-assembled InAs quantum dots. We spatially resolved single quantum dots upon resonant excitation of transitions between discrete energy levels of the confined electrons.

Keywords: near-field microscopy; terahertz nano-spectroscopy; single quantum dots

  • Open Access Logo Imaging & Microscopy 15(2013)1, 40-42

Publ.-Id: 19709

The novel fluorine-18 PET radiotracer [18F]NS14490 allows in vivo investigation of alpha7 nicotinic acetylcholine receptor (α7-nAChR) expression on brain vasculature

Bucerius, J.; Rötering, S.; Deuther-Conrad, W.; Donat, C. K.; Fischer, S.; Xiong, G.; Mottaghy, F. M.; Wildberger, J. E.; Cumming, P.; Brust, P.

Objectives :
The α7nAChR plays an important role in the pathophysiology of atherosclerosis, where it is known to mediate the deleterious effects of nicotine. Recently, [18F]NS14490 was described as radioligand with high in vitro binding affinity and selectivity towards α7nAChR (Ki, α7=2.5), Ki, α3β4=102, Ki, α4β2>800 nM) [BMC 21(2013), 2635]. Here, we report in vivo investigation of α7nAChR in brain blood vessels of pigs using [F]NS14490 and PET.

Methods : The synthesis of [18F]NS14490 and pig studies were performed as reported [Teodoro et al. this volume]. Baseline (n=3) and blocking studies with NS6740 (n=3) were done. Volumes of interest for the left carotid artery (LCA) and Circle of Willis (CW) were drawn with reference to T1-weighed MR images aligned to a summed PET image. Metabolite-corrected plasma input functions were used for 2-tissue-compartment (2TC) modelling to determine receptor parameters. Parametric maps of the distribution volumes (VT) were calculated for baseline and blocking conditions.

Results : Reduction of VT on brain vasculature was clearly visible in parametric maps of [18F]NS14490.
Maximum SUV in LCA (1.4±0.2) and CW (1.3±0.2) was reached at 4 and 2 min p.i., respectively. At 4 h after blockade, the SUV in LCA was reduced by 36%, with lesser declines in CW. Using an 2TC irreversible binding model, we found a [18F]NS14490 k3 of 0.0023 min-1 in LCA, which was 40% blocked by NS6740.

Conclusions :
The study provides first evidence for the detection of α7nAChRs by PET in the pig brain vasculature, notably in the LCA. This further elucidates the feasibility of PET to non-invasively image vascular image vascular α7nAChRs.

Research Support: Support from DFG (DE 1165/2-1, Dan Peters (DanPET AB) and Matthias Scheunemann is gratefully acknowledged.
References: 1.Rötering S., Scheunemann M., Fischer S. et al. (2013) Radiosynthesis and first evaluation in mice of [(18)F]NS14490 for molecular imaging of α7 nicotinic acetylcholine receptors. Bioorg Med Chem 21, 2635
2. Teodoro R, Deuther-Conrad W, Rötering S, et al. (2013) Comparative evaluation of two novel fluorine-18 PET radiotracers for the alpha7 nicotinic acetylcholine receptor (α7nAChR), submitted

  • Poster
    SNMMI 2014 Annual Meeting, 07.-11.06.2014, St. Louis, Missouri, USA
  • Abstract in refereed journal
    Journal of Nuclear Medicine 55(2014)1, 1695


Publ.-Id: 19708

Broadband fast terahertz detector based on graphene

Mittendorff, M.; Winnerl, S.; Kamann, J.; Eroms, J.; Weiss, D.; Schneider, H.; Helm, M.

Some sources of pulsed intense terahertz radiation such as free-electron lasers and gas lasers pumped by high-pressure CO2 lasers exist already for relatively long time. More recent developments like THz-generation via nonlinear processes in plasmas or lithiumniobate crystals as well as novel accelerator-based sources for coherent synchrotron radiation have greatly advanced the field of nonlinear terahertz optics [1,2]. Robust, simple and fast detectors are highly desirable for experiments at these sources, in particular if they are not naturally synchronized to a pulsed near-infrared laser. We present a graphene-based detector operated at room temperature featuring a rise time of 50 ps. It was tested at the free-electron laser FELBE in the frequency range from 1.3 THz to 38 THz.
The detector is based on an exfoliated graphene flake on Si/SiO2 coupled to a broadband logarithmic periodic antenna. The temporal resolution of the detector (rise time ~50 ps) is limited by the electronic circuitry. We show that high-resistive substrates are of crucial importance to keep RC-time constants short. The responsivity is about 5 nA/W in the investigated spectral range. While a linear dependence of the detector signal was found for small pulse energies, significant saturation occurred for larger pulse energies. We demonstrate that the nonlinearity provided by the saturation can be exploited in autocorrelation measurements. In this type of measurement the detector response is limited by the intrinsic carrier relaxation time but not by the electronic circuit, resulting in a temporal Resolution below 10 ps [3]. The high temporal resolution combined with room-temperature operation and high damage threshold makes the detector attractive for pulse diagnostics of intense THz sources. Furthermore the broadband response, which possibly can be extended towards the visible and UV spectral region by using different substrate materials, is ideal for characterizing the timing of pulses in multicolor experiments.
[1] M. C. Hoffmann and J. A. Fülöp, J. Phys. D: Appl. Phys. 44, 083001 (2011).
[2] H. Hirori, Hideki and K. Tanaka, IEEE J. Sel. Top. Quantum Electron. 19, 8401110 (2013).
[3] M. Mittendorff, S. Winnerl, J. Kamann, J. Eroms, D. Weiss, H. Schneider, and M. Helm, Appl. Phys. Lett. 103, 021113 (2013).

Keywords: fast detector; terahertz

  • Lecture (Conference)
    6th Workshop on Terahertz Technology and Applications 2014, 11.-12.03.2014, Kaiserslautern, Deutschland

Publ.-Id: 19707

Longitudinal fields in focused terahertz beams

Winnerl, S.; Hubrich, R.; Mittendorff, M.; Schneider, H.; Helm, M.

In textbooks electromagnetic waves are often described as infinitely extended plane waves, which are of purely transverse character. For beams of finite size, however, also longitudinal fields are expected. In case of focused radially polarized beams, the longitudinal fields can actually be stronger as compared to the transverse components. This has been found in experiments recording the intensity of near-infrared beams. In our study we directly record the electric field of single cycle terahertz pulses of radial and linear polarization. This enables us to reveal the phase relation between longitudinal and transverse fields. The obtained value of pi/2 is of universal nature as it does not depend on the type of mode, frequency or focusing condition. Additionally we demonstrate that the longitudinal components of radially polarized beams exhibit superior focusing properties.

Keywords: radially polarized fields; longitudinal electromagnetic fields; terahertz radiation

  • Lecture (Conference)
    DPG-Frühjahrstagung, 10.-15.03.2013, Regensburg, Deutschland

Publ.-Id: 19706

Relaxation dynamics in graphene close to the Dirac point

Winnerl, S.

The carrier relaxation in graphene is of strong interest for understanding carrier-carrier and carrier-phonon interactions in this fascinating material as well as for optoelectronic applications such as detectors, and saturable absorbers. Here we give an overview on our investigations on the dynamics in the energetic vicinity of the Dirac point, which is explored by pump-probe experiments with mid-infrared and terahertz radiation [1]. We compare our experimental results with microscopic theory and discuss the role of optical phonons, acoustic phonons and carrier-carrier scattering. For excitations slightly above and below the Fermi edge an interesting change in sign of the pump-probe signals is observed, which can be explained by an interplay of intraband and interband excitation. Furthermore we present recent results on the dynamics in Landau quantized graphene, where a strong dependence of the pump-probe signals on the state of circular polarization of both pump and probe radiation is found. The results indicate the importance of Auger-type processes in this regime.
S. Winnerl et al., Phys. Rev. Lett. 107, 237401 (2011).

Keywords: graphene; carrier dynamics; ultrafast spectroscopy

  • Invited lecture (Conferences)
    DPG-Frühjahrstagung, 10.-15.03.2013, Regensburg, Deutschland

Publ.-Id: 19705

Relaxation dynamics in graphene in the terahertz spectral range

Winnerl, S.

The relacation dynamics in graphene in the infrared spectral range is reviewed. In particular the range of terahertz energies, i.e. excitation in proximity of the Dirac point, is discussed.

  • Lecture (others)
    SFB Kolloquium, 14.11.2013, Konstanz, Deutschland

Publ.-Id: 19704

Graphene investigated in the THz range: ultrafast dynamics and device perspectives

Winnerl, S.; Mittendorff, M.; Schneider, H.; Helm, M.; Winzer, T.; Wendler, F.; Malic, E.; Knorr, A.

The carrier relaxation dynamics in graphene in energetic proximity to the Dirac point is studied. In particular we discuss the role of optical phonon scattering and the interplay of interband and intraband excitations. The potential to make use of the ultrafast dynamics of graphene, in particular under terahertz excitation, in saturable absorbers and fast detectors is highlighted. A room-temperature operated ultra-broadband graphene-based detector is presented.

  • Invited lecture (Conferences)
    21st International Conference on Applied Electromagnetics and Communications, 14.-16.10.2013, Dubrovnik, Croatia

Publ.-Id: 19703

Relaxation dynamics of graphene investigated in the mid-infrared and THz spectral range

Winnerl, S.; Mittendorff, M.; Winzer, T.; Wendler, F.; Malic, E.; Knorr, A.; Orlita, M.; Potemski, M.; Berger, C.; de Heer, W. A.; Schneider, H.; Helm, M.

The unique band structure of graphene results in optical properties, which are promising with respect to graphene applications in detectors, saturable absorbers and frequency mixers. For these applications the knowledge of the carrier dynamics is essential. However, while the relaxation dynamics in graphene is extensively studied in pump-probe experiments involving pumping with near-infrared photons, only few studies exist for pumping in the mid-infrared and THz spectral range [1,2]. Here we present results of single-color pump probe experiments on epitaxial graphene on SiC studied in a wide range of photon energies (8 – 245 meV). A significant slowing down of the carrier relaxation is observed when the photon energy is reduced to values below the optical phonon energy of ~200 meV. For photon energies below twice the value of the Fermi energy (Ef ≈ -13 meV) negative pump-probe signals, i.e. induced absorption is observed. This is associated with intraband absorption contributions at energies, where interband absorption is initially not possible. Our experimental results are compared to microscopic calculations based on the density matrix formalism. Comparison of experiment and theory reveals the role of scattering via optical and acoustic phonons as well as contributions from Auger scattering processes. Applying a magnetic field perpendicular to the graphene layers leads to a not equidistant Landau-level splitting. Using circularly polarized radiation for pump-probe experiments allows one to selectively measure individual Landau-level transitions. The pump-probe signals exhibit a strong dependence on the polarization state of both pump and probe radiation.
[1] S. Winnerl et al. Phys. Rev. Lett. 107, 237401 (2011).
[2] S. Tani, F. Blanchard, and K. Tanaka, Phys. Rev. Lett. 109, 166603 (2012).

Keywords: graphene; carrier dynamics; ultrafast spectroscopy

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

Publ.-Id: 19702

Longitudinal THz fields and their phase relation with respect to transverse fields

Winnerl, S.; Hubrich, R.; Mittendorff, M.; Schneider, H.; Helm, M.

Radiation with significant longitudinal components of the electric field is of interest for excitation of systems with a dipole moment in the direction of propagation of the radiation. Another special feature of longitudinal fields occurring in the focus of radially polarized radiation is their superior focusing property as compared to transverse fields of linearly polarized beams. In contrast to previous studies in the near infrared spectral range, where the intensity distribution was recorded, our terahertz study provides direct access to the electric field. Consequently, the phase relation between longitudinal and transverse field components can be addressed. We present results for the field distribution in the focal plane for both radially and linearly polarized single cycle THz pulses generated by photoconductive emitters. In both cases a phase shift of pi/2 between transverse and longitudinal field components is found. We show that this phase shift is of universal nature as it does not depend on the type of mode, the focussing condition and the frequency [1]. The universal phase shift is a fundamental consequence Maxwell’s law div E = 0 and symmetry properties of the beams. We also show that the longitudinal field components of a radially polarized beam can be focussed to a smaller spot as compared to the transverse components of linearly polarized radiation. This is valid even for moderate focusing conditions, where the transverse fields are stronger than the longitudinal field components. Implications of the findings for imaging applications and for studies of light-matter interaction in case of vanishing Poynting vector will be discussed.
[1] S. Winnerl, R. Hubrich, M. Mittendorff, H. Schneider, and M. Helm, New J. Physics 14, 103049 (2012).

Keywords: vector beams; Bessel-Gauss beams; terahertz radiation

  • Lecture (Conference)
    International Workshop on Terahertz Science and Technology, 01.-05.04.2013, Kyoto, Japan

Publ.-Id: 19701

Ultrafast graphene-based terahertz detector

Winnerl, S.; Mittendorff, M.; Kamann, J.; Eroms, J.; Weiss, D.; Schneider, H.; Helm, M.

The gapless band structure, universal interband absorption and considerably strong intraband absorption make graphene attractive for applications in the terahertz frequency range [1]. Furthermore the high mobility and fast carrier relaxation [2] enable a fast response when graphene is used a material for terahertz detection. Graphene-based fast bolometers [3] and rectifying transistors [4] have been reported recently. We demonstrate an ultrafast broadband detector operated at room temperature. Response times of 50 ps are observed in the wavelength range from 30 µm to 220 µm.
The detector is based on an exfoliated graphene flake on Si/SiO2, which is coupled to a logarithmic-periodic planar antenna. In the center of the antenna interdigitated electrodes provide the electrical contacts between the antenna arms and the graphene flake (cf. Fig. 1). The response of the detector to picosecond terahertz radiation pulses from a free-electron laser was studied. A responsivity of ~5 nA/W and a signal rise time of 50 ps was found for the spectral range from 30 µm to 220 µm. The linear detection range is followed by region of saturation for high pulse powers. The characteristic pulse energy E_sat for the onset of saturation is ~10 nJ for lamda = 220 µm. With decreasing wavelength the saturation regime shifts towards higher pulse energies (E_sat ≈ 150 nJ for lamda = 30 µm). Comparing detectors fabricated on either intrinsic or doped silicon we find that a high substrate resistivity is crucial for the short response time. We attribute this to large RC time constants occurring for the conductive substrates.
These easy-to-use detectors are well suited for monitoring the timing of terahertz pulses. We will discuss several physical mechanisms, which may be involved in the detection process. As an outlook we suggest that the detector principle allows one to produce detectors covering an even larger spectral range, namely from the UV to THz range. To this end appropriate non-absorbing substrates have to be used.

[1] B. Sensale-Rodriguez, R. Yan, M. M. Kelly, K. Tahy, W. S. Hwang, D. Jena, L. Liu, and H. G. Xing, Nature Commun. 3 (2012) 780.
[2] S. Winnerl, M. Orlita, P. Plochocka, P. Kossacki, M. Potemski, T. Winzer, E. AMlic, A. Knorr, M. Sprinkle, C. Berger, W. A. de Heer, H. Schneider, and M. Helm, Phys. Rev. Lett. 107 (2011) 237401.
[3] J. Yan, M.-H. Kim, J. A. Elle, A. B. Shukov, G. S. Jenkins, H. M. Milchberg, M. S. Fuhrer, and H. D. Drew, Nat. Nanotechnol. 7 (2012) 472.
[4] L. Vicarelli, M. S. Vitiello, D. Coquillat, A. Lombardo, A. C. Ferrari, W. Knap, M. Poloni, V. Pellegrini, and A. Tredicussi, Nat. AMterials 11 (2012) 865.

Keywords: terahertz detection; ultrafast detector; metal-graphene-metal device

  • Poster
    Graphene Week, 02.-07.06.2013, Chemnitz, Deutschland

Publ.-Id: 19700

Carrier dynamics in graphene near the Dirac point

Winnerl, S.

The relaxation dynamics of charge carriers in graphene is characterized by interesting properties such as impact ionization resulting in carrier multiplication [1,2]. Apart from the fundamental interest, knowledge about the carrier dynamics is important for the development of graphene-based electronic and optoelectronic devices. In our study we apply picosecond mid-infrared and terahertz pulses to explore the carrier dynamics in the vicinity of the Dirac point. In particular the role of carrier-phonon and carrier-carrier scattering is discussed. The carrier dynamics was studied in single-color pump-probe experiments in a wide spectral range (photon energies: 10 meV – 245 meV). A significant increase of the relaxation time was observed as the photon energy was decreased to values below the optical phonon energy of about 200 meV [3]. Microscopic modelling based on the density matrix formalism revealed a suppression of optical-phonon scattering for low photon energies, however, this process is still more efficient than scattering via acoustic phonon [3,4].
The pump-probe study was extended to graphene in magnetic fields (B = 4.2 T, photon energy 75 meV), where the Landau level (LL) transitions LL-1 -> LL0 and LL0 -> LL1 were resonantly excited. Applying circularly polarized radiation allows one to distinguish between these energetically degenerate transitions. Pump-probe signals for all four different combinations of left- and right-circularly polarized radiation are characterized by complex dynamics involving positive and negative signals as well as fast and slow components. An analysis of the results indicates that the carrier occupation of the three LLs is strongly influenced by Auger-type scattering processes. In particular situations the population change by Auger scattering even dominates over the change induced by optical pumping. In summary the role of carrier-phonon scattering in graphene in the energetic vicinity of the Dirac point is clarified by a joint experiment-theory study. Furthermore we report strong evidence for efficient Auger-type scattering in Landau-quantized graphene. M. Mittendorff, H. Schneider, M. Helm, M. Orlita, and M. Potemski planned and performed the experiments, T. Winzer, F. Wendler, E. Malic, and A. Knorr carried out the microscopic modelling. The samples were grown by M. Sprinkle, C. Berger, and W. A. de Heer.

Keywords: graphene; relaxation dynamics; ultrafast spectroscopy

  • Invited lecture (Conferences)
    The 18th International Conference on Electron Dynamics in Semiconductors, Optoelectronics and Nanostructures, 22.-26.07.2013, Matsue, Japan

Publ.-Id: 19699

Longitudinal fields in focused terahertz beams

Winnerl, S.; Hubrich, R.; Mittendorff, M.; Schneider, H.; Helm, M.

We measure transverse as well as longitudinal terahertz field components in the focus of both radially and linearly polarized beams. A phase shift of pi/2 between the transverse and longitudinal field contributions is found in both cases for all frequency components. Furthermore tighter focusing of the longitudinal components of the radially polarized beam as compared to the transverse components of the linearly polarized beam is demonstrated.

Keywords: terahertz; vector beams; radial polarization

  • Lecture (Conference)
    38th International Conference on Infrared, Millimeter and Terahertz Waves, 01.-06.09.2013, Mainz, Deutschland
  • Contribution to proceedings
    38th International Conference on Infrared, Millimeter and Terahertz Waves, 01.-06.09.2013, Mainz, Deutschland
    DOI: 10.1109/IRMMW-THz.2013.6665517

Publ.-Id: 19698

One-Group Cross Sections Generation for Monte Carlo Burnup Codes

Kotlyar, D.; Shwageraus, E.; Fridman, E.

Allowing Monte Carlo (MC) codes to perform fuel cycle calculations requires coupling to a point depletion solver. In order to perform depletion calculations, one-group (1-g) cross sections must be provided in advance. This paper focuses on generating accurate 1-g cross section values that are necessary for evaluation of nuclide densities as a function of burnup. The proposed method is an alternative to the conventional direct reaction rate tally approach, which is more computationally expensive. The method presented here is based on the multi-group (MG) approach(1), in which pre-generated MG sets are collapsed with MC calculated flux. In our previous studies(2), we showed that generating accurate 1-g cross sections requires their tabulation against the background cross-section (σ0) to account for the self-shielding effect. However, in previous studies, the model that was used to calculate σ0 was simplified by fixing Bell and Dancoff factors. This work demonstrates that 1-g values calculated under the previous simplified model may not agree with the tallied values. Therefore, the original background cross section model was extended by implicitly accounting for the Dancoff and Bell factors. The method developed here reconstructs the correct value of σ0 by utilizing statistical data generated within the MC transport calculation by default. The proposed method was implemented in BGCore code system. The 1-g cross section values generated by BGCore were compared with those tallied directly from the MCNP code. Very good agreement (<0.05%) in the 1-g cross values was observed. The method does not carry any additional computational burden and it is universally applicable to the analysis of thermal as well as fast reactor systems.

  • Contribution to proceedings
    The 27th Conference of the Nuclear Societies in Israel, 11.-13.02.2014, Daniel Dead Sea Hotel, Israel
    Proceedings of the 27th Conference of the Nuclear Societies

Publ.-Id: 19697

Beyond the Liu limit: Extending the range of low-Pm magnetorotational instabilities

Kirillov, O. N.; Stefani, F.

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

Keywords: Magnetorotational instability; accretion disk; WKB approximation

  • Lecture (Conference)
    3rd workshop on Rotational fluid dynamics for planetary and stellar applications, 29.-30.05.2013, Exeter, United Kingdom

Publ.-Id: 19696

Ziegler-Bottema dissipation-induced instability and related topics

Kirillov, O. N.

Abstract: Exactly 60 years ago Ziegler [1] observed (I) that viscous dissipation can move pure imaginary eigenvalues of a Lyapunov stable time-reversible non-conservative mechanical system (Ziegler’s pendulum loaded by a follower force) to the right half of the complex plane and (II) that the threshold of asymptotic stability generically does not converge to the threshold of the Lyapunov stability of the non-damped system when dissipation coefficient tends to zero. In 1956 Bottema [2] related the structurally unstable situation (II) to the Whitney umbrella singularity [3] of the stability boundary. I will show the examples of Hamiltonian, reversible and PT -symmetric systems of physics and mechanics with the similar effects of dissipation-induced instabilities and non-commuting limits of vanishing dissipation. I will discuss the relation of these effects to the multiple non-derogatory eigenvalues occurring both on the stability boundary and inside the domain of asymptotic stability, show the connection to the spectral abscissa minimization [4] and in the Hamiltonian case will demonstrate that a suitable combination of damping and nonconservative positional forces can destabilize the eigenvalues with both positive and negative Krein (symplectic) signature of the unperturbed system [5-7].
1. H. Ziegler, Die Stabilit¨atskriterien der Elastomechanik, Ing.-Arch. 20, 49-56 (1952).
2. O. Bottema, The Routh-Hurwitz condition for the biquadratic equation, Indagationes Mathematicae, 18, 403-406 (1956).
3. W. F. Langford, Hopf Meets Hamilton Under Whitney’s Umbrella, in IUTAM Symposium on Nonlinear Stochastic Dynamics. Proceedings of the IUTAM Symposium, Monticello, IL, USA, Augsut 2630, 2002, Solid Mech. Appl. 110, edited by S.N. Namachchivaya et al. (Kluwer, Dordrecht, 2003), pp. 157-165.
4. J. V. Burke, A. S. Lewis and M. L. Overton, Optimal Stability and Eigenvalue Multiplicity, Foundations of Computational Mathematics 1, 205-225 (2001).
5. O. N. Kirillov, Gyroscopic stabilization in the presence of nonconservative forces, Dokl. Math. 76(2), 780-785 (2007).
6. O. N. Kirillov and F. Verhulst, Paradoxes of dissipation-induced destabilization or who opened Whitney’s umbrella? Z. Angew. Math. Mech., 90(6), 462-488 (2010).
7. O. N. Kirillov, Stabilizing and destabilizing perturbations of PT -symmetric indefinitely damped systems. Phil. Trans. R. Soc. A (2012).

Keywords: Dissipation-induced instabilities; nonconservative systems; flutter; modulational instability

  • Lecture (Conference)
    Third Conference on Particle-Based Methods (PARTICLES 2013), Invited Session “Instability Mechanisms, from Particles to Structures”, 18.-20.09.2013, Stuttgart, Germany

Publ.-Id: 19695

Inductionless Magnetorotational Instabilities: From Lab Tests To Accretion Disks

Kirillov, O. N.; Stefani, F.; Fukumoto, Y.

How stars and black holes are able to form from rotating matter is one of the big questions of astrophysics. What is known is that magnetic fields figure prominently into the picture via the mechanism of magnetorotational instability (MRI). However, the current understanding is that it only works if matter is electrically well conductive – but in rotating disks this is not always the case. In areas of low conductivity like the dead zones of protoplanetary disks or the far-off regions of accretion disks that surround supermassive black holes, the MRI’s effect is numerically difficult to comprehend and is thus a matter of dispute. Simulation of the MRI in a liquid metal experiment with an exclusively vertically oriented magnetic field requires that this field has to be rather strong. At the same time, since the rotational speed has to be very high, these types of experiments are extremely involved and thus far success has eluded them. By adding a circular magnetic field to a vertical one it became possible to observe the helical MRI at substantially smaller magnetic fields and rotational speeds. Very recently, the azimuthal MRI with m=1 has also been observed in the PROMISE facility in Dresden. However, one of the blemishes of these inductionless versions of MRI is the fact that they only act to destabilize rotational profiles that are relatively precipitous towards the periphery, which for now did not include rotation profiles obeying Kepler’s law. In this talk we present a study of the stability of rotational flows in the presence of a constant vertical magnetic field and an azimuthal magnetic field with a general radial dependence characterized by an appropriate magnetic Rossby number. Employing the short-wavelength approximation we develop a unified framework for the investigation of the standard, the helical, and the azimuthal version of the magnetorotational instability, as well as of current-driven kink-type instabilities. Considering the viscous and resistive case, our main focus is on the limit of small magnetic Prandtl numbers which applies, e.g., to liquid metal experiments but also to the colder parts of accretion disks. We rigorously demonstrate that the inductionless versions of MRI extend well to the Keplerian case if only the azimuthal field slightly deviates from its field-free profile.

Keywords: Magnetorotational instability; accretion disks; WKB

  • Lecture (Conference)
    Workshop "Putting Accretion Theory to the Test", 04.-06.11.2013, Annapolis, Maryland, United States

Publ.-Id: 19694

Singular divergence instability thresholds of kinematically constrained circulatory systems

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

Static instability or divergence threshold of both potential and circulatory systems with kinematic constraints depends singularly on the constraintsʼ coefficients. Particularly, the critical buckling load of the kinematically constrained Zieglerʼs pendulum as a function of two coefficients of the constraint is given by the Plücker conoid of degree n=2. This simple mechanical model exhibits a structural instability similar to that responsible for the Velikhov–Chandrasekhar paradox in the theory of magnetorotational instability.

Keywords: Ziegler pendulum; Static instability; Kinematic constraints; Non-commuting limits; Magnetorotational instability; Material instabilities

Publ.-Id: 19693

Magnetization Reversal Mechanisms in Co-Antidot Arrays

Langer, M.; Bali, R.; Kowalska, E.; Neudert, A.; Lenz, K.; Potzger, K.; Kostylev, M.; Lindner, J.; Adeyeye, A.; Fassbender, J.

Co-antidots with holes arranged in the form of a square lattice, with lattice parameter of 415 nm and hole diameter d = 145 to 255 nm were fabricated using DUV photolithography. For arrays with film thickness of 50 nm, the angular dependence of the saturation field Hs shows presence of four-fold anisotropy with the hard axes along the <01> directions and easy axes was along the diagonal <11> directions. Spikes in the Hs were measured along the intermediate <12> directions. Kerr microscopy suggests that the reversal mechanism along the <01> is domain-wall (DW) depinning followed by propagation within the continuous channels along the <01>, whereas along the <11> the mechanism tends towards nucleation and growth. We postulate that the Hs-spikes occur because DW-propagation requires domino-like spin-reorientations through the continuous channels, whereas nucleation can only occur when a coherent region is formed with the spins oriented along the applied field. The frustration caused by the two possible spin-reorientation paths results in the larger Hs. We attempt to model these mechanisms using OOMMF and investigate the influence of varying d.

  • Poster
    DPG Frühjahrstagung, 10.-15.03.2013, Regensburg, Deutschland

Publ.-Id: 19692

Dependence of Ferromagnetic Resonance Behaviour on Chemical Disorder in Fe60Al40 Thin Films

Bali, R.; Schneider, T.; Gollwitzer, J.; Meutzner, F.; Boucher, R.; Potzger, K.; Bauch, J.; Fassbender, J.; Lenz, K.; Lindner, J.

We report on the influence of chemical disorder in Fe60Al40 thin films on their ferromagnetic resonance. Chemical disorder leads to increased nearest neighbour Fe-Fe magnetic interactions and plays a crucial role in inducing ferromagnetism. The saturation magnetization increases from 20 kA/m-1 for the chemically ordered film to 780 kA/m for disordered films. Disorder was induced by irradiation of Ne+ ions, and the depth-distribution of disorder was controlled by adjusting the ion-energy and -fluence. For moments aligned within the film plane, the resonant linewidth decreases with increasing ion-energy in the range from 2.5 to 30 keV, for a fixed ion-fluence. In-plane magnetic anisotropy is negligible in all cases. The linewidths for in-plane moment alignment are much larger than in materials that do not exhibit disorder induced ferromagnetism. These results may be explained by enhanced two-magnon scattering due to the presence of random defects, and help in preparing thin films with tailored spin-wave dynamic properties.

  • Poster
    DPG Frühjahrstagung 2014, 30.03.-04.04.2014, Dresden, Deutschland

Publ.-Id: 19691

Printing Nearly-Discrete Magnetic Patterns using Chemical Disorder Induced Ferromagnetism

Bali, R.; Wintz, S.; Meutzner, F.; Huebner, R.; Boucher, R.; Uenal, A. A.; Valencia, S.; Neudert, A.; Potzger, K.; Bauch, J.; Kronast, F.; Facsko, S.; Lindner, J.; Fassbender, J.

We show that sub-50 nm ion-induced lateral patterning of magnetic structures can be enabled by disorder induced ferromagnetism.[1] Disorder is induced through exposure of the chemically ordered alloy to energetic ions; collision cascades formed by the ions knock atoms from their ordered sites and the concomitant vacancies are filled randomly via thermal diffusion of atoms at room temperature. Here we consider the case of Fe60Al40 wherein the chemically ordered B2 structure is paramagnetic, and chemical disordering leads to the formation of the A2 structure which is ferromagnetic.[2] This ion-induced transition can be exploited to induce ferromagnetism in localized regions by ion-irradiation through lithographed shadow masks. We show that this technique may be useful for fabricating novel spin-transport devices.
First we demonstrate the disorder-induced increase in saturation magnetization, Ms, in continuous films. Fe60Al40 films of 40 nm thickness were deposited on SiO2(150 nm)/Si(001) substrates by magnetron sputtering. The films were annealed at 773 K in vacuum to form the chemically ordered B2 phase structure. Hysteresis loops were measured using a vibrating sample magnetometer (VSM). Figure 1a shows that the B2 film is weakly ferromagnetic with a saturation magnetization of Ms = 20 kA m-1.
The chemically ordered films were irradiated with 6 x 1014 ions cm-2 of Ne+-ions at 10 and 30 keV respectively. After irradiation, the Ms increases to 480 and 780 kA m-1, respectively for the 10 and 30 keV samples. The Ms of the 30 keV Ne+ sample is a factor of 40 larger than that of the annealed sample. Figure 1b shows X-ray Diffraction measurements around the 100 reflection for the sample after annealing, and after subsequent 10 keV Ne+-irradiation. The 100 reflection is allowed for the B2 superstructure but vanishes for the disordered A2 phase and this transition is clearly observed since the reflection initially present in the B2 film vanishes for the 10 keV sample.
Magnetic patterning was performed on a 10 μm wide and 400 μm long wire of chemically ordered Fe60Al40 (Figure 2a). The wire was covered with a 150 nm thick resist layer, and patterned using e-beam lithography. Simulations based on the binary collision approximation (TRIM) showed that the 150 nm thick resist layer is sufficient to block impinging 10 keV Ne+-ions.[3]
Lithography was used to carve out stripe like openings of 0.5 and 2 μm widths respectively. As shown in the micrograph in Figure 2b, the stripe-openings were separated by ~ 40 nm wide (and 150 nm high) resist walls, thereby stopping the impinging Ne+ ions reaching the areas directly underneath the resist. These areas can be expected to retain chemical order after exposure to Ne+, however, only if the lateral scattering of ions is restricted. The wire covered by the shadow-mask was exposed to 10 keV Ne+-ions at a fluence of 6 x 1014 ion cm-2. Figure 2c shows the magnetic contrast image, obtained using Kerr Microscopy on the sample prior to application of saturating magnetic fields. Striped magnetic regions are clearly observed possessing random magnetic orientations.
Magnetic contrast was captured whilst sweeping the field to obtain hysteresis loops shown in Figure 2d, on a set of 32 (0.5 μm/spacer/2 μm/spacer) stripe-pairs. Magnetization reversal occurs via a two-staged process; the first reversal step occurs at ≈ ±3 mT and the second step at ≈ ±7 mT. The magneto-optic intensity changes by 80% in the first reversal step, indicating that the 2 μm wide stripes reverse collectively at the smaller field. In the stripe geometry, the internal demagnetizing field increases with the stripe width. Reversal of the 2 μm wide stripes therefore occurs at smaller externally applied field as compared with the 0.5 μm stripes, resulting in selective reversal.
Magnetic contrast images were captured at remnant points of the above hysteresis loops and are shown in Figure 2e – h. Stripes with magnetization pointing towards the left or right appear as dark and bright contrast, respectively. Images captured after applying the saturating field of +/-18 mT followed by reduction to zero field show that the parallel magnetization configuration is preserved in remanence (Figure 2e and f). The antiparallel configuration is obtained after applying a reverse field of -/+5 mT to the saturated stripes and returning to zero field. Figure 2g and h show alternating light and dark contrast of the antiparallel state in remnant fields.
Spin-resolved Photo-Emission Electron Microscopy (SPEEM) measurements were performed to observe magnetic contrast with high spatial resolution of ~ 50 nm. The SPEEM micrographs are shown in Figure 2e and g as magnified equivalent regions of the Kerr-images. The color scale varies from red to blue for magnetic moments pointing left or right respectively. Straight, low-contrast regions are found to separate the 500 nm and 2 μm wide high-contrast regions that correspond to the magnetic stripes.
The straight low-contrast regions are unresponsive to the magnetic field and occur for both parallel and anti-parallel states. Since the straight low-contrast lines also exactly follow the pattern of the shadow mask, it can be concluded that these lines correspond to the 40 nm wide un-irradiated regions. Neighboring 500 nm and 2 μm magnetic stripes are therefore isolated by a continuous weakly magnetic spacer of 40 nm nominal width.
Thus, parallel and antiparallel magnetization configurations can be programmed using the magnetic field history and are non-volatile i.e., stable when the field is switched off. Selective reversal and the existence of binary magnetic states namely is a prerequisite for spin-valves and advantageous in devices for storing data bits. In particular with respect to spin-transport devices, it is also necessary to ensure that the magnetic regions are separated by narrow spacers of zero or low magnetization. Showing that discrete magnetic nanostructures can be prepared by ion-irradiation has important consequences not previously considered in literature, such as the possibility of laterally patterned spin-transport devices – our results are a step in this direction.

[1] R. Bali et al., Nano Letters 2013 (accepted). [2] J. Fassbender, et al., Phys. Rev. B 2008, 77, 174430. [3] J. F. Ziegler et al., Nucl. Instrum. Methods B 2010, 268, 11-12, 1818.

  • Lecture (Conference)
    Intermag 2014, 04.-08.05.2014, Dresden, Germany
  • Poster
    Joint European Magnetism Symposia, 25.-30.08.2013, Rhodos, Greece
  • Poster
    International Conference on Ion Beam Modification of Materials (IBMM 2014), 14.-19.09.2014, Leuven, Belgium
  • Lecture (Conference)
    59th Annual Magnetism and Magnetic Materials (MMM), 03.-07.11.2014, Honolulu, USA
  • Invited lecture (Conferences)
    Sixth Joint BER II and BESSY II User Meeting, 03.-05.12.2014, Berlin, Deutschland
  • Poster
    Joint European Magnetism Symposia 2012, 09.-14.09.2012, Parma, Italy

Publ.-Id: 19690

Draco The Dresden Laser Acceleration Source recent setups measurement techniques future perspectives

Bock, S.

The presentation depicts the recent setup and techniques we use to characterize the pulse properties of the lasersystem Draco. Also the upgrade of Draco is shown and its impact on the new diagnostics setup.

Keywords: Draco; diagnostic techniques

  • Lecture (Conference)
    Characterisation of ultra-short high energy laser pulses, 23.-24.09.2013, Abingdon, United Kingdom

Publ.-Id: 19689

The enduring secret of Meissen Porcelain

Neelmeijer, C.; Pietsch, U.; Ulbricht, H.

Prior to their restoration the porcelain bulks of 34 pieces from various 18th century authentic Meissen objects were studied by proton beam analysis. In either case attention was paid that the proton beam touches only the area of fracture. Thus, possible contributions from residues of surface glaze to the measured spectra were excluded. The chemical compositions obtained by light element (Na-Si) plus heavier element analysis represent quiet consistent mixtures of porcelain primary material. This finding reflects the consistent keeping of recipes and raw materials for Meissen porcelain production already at that time. The technology of surface glazing, by contrast, makes use of modified ingredients. It is shown that non-destructive analysis of intact glazed porcelain does not stand for the bulk material composition, hence may pretend wrong conclusions if bulk analysis is of interest.
The proton beam of 4 MeV-energy (Rossendorf 5 MV Tandem accelerator) leaves the vacuum beam line onto air and may hit unique objects without sampling. Extremely low beam intensities and short irradiation times ensure non-destructive analysis of the valuable objects. The chemical elements of the irradiated material respond emitting characteristic radiations. They are detected simultaneously in order to get non-destructive and complete composition analysis using the established ion beam techniques PIXE (Particle induced X-ray Emission), PIGE (Particle Induced Gamma-ray emission) and RBS (Rutherford Backscattering Spectrometry).

Keywords: Porcelain; chemical analysis; Ion beam Analysis; PIXE; PIGE

  • Lecture (Conference)
    38th International Symposium on Archaeometry, 10.-14.05.2010, Tampa, USA

Publ.-Id: 19688

Effect of the solidified shell thickness on the impact of an electromagnetic brake on the flow in the continuous casting mould

Miao, X.; Timmel, K.; Lucas, D.; Eckert, S.; Gerbeth, G.

This paper presents numerical investigations with respect to the fluid flow in the continuous casting process under the influence of a ruler-type EMBR. The impact of the DC magnetic field on the outlet flow from the Submerged Entry Nozzle has been studied up to Hartmann numbers of about 400. Numerical calculations were performed by means of the software package CFX with an implemented RANS-SST turbulence model. The non-isotropic nature of the MHD turbulence was taken into account by specific modifications of the turbulence model. The numerical results were validated by flow measurements carried out in the small-scale mockup mini-LIMMCAST using the eutectic alloy GaInSn. The electrical wall conductance ratio was identified as an important parameter, which has a serious influence on the mould flow just as it is exposed to an external magnetic field. In a real casting process the solidifying shell plays the role of a conducting wall. The wall conductance ratio increases with growing thickness of the shell. It turns out that the solidifying shell has a considerable impact on the magnetic damping of the flow. An increasing wall conductance ratio improves the efficiency of the magnetic damping effect.

Keywords: Continous casting; EMBR; RANS-SST; MHD turbulence model

  • Lecture (Conference)
    SteelSim 2013 conference, 10.-12.09.2013, Ostrava, Czech Republic

Publ.-Id: 19687

Comparative study of thermo-stimulated luminescence and electron emission of nitrogen nanoclusters and films

Boltnev, R. E.; Bykhalo, I. B.; Krushinskaya, I. N.; Pelmenev, A. A.; Khmelenko, V. V.; Lee, D. M.; Khyzhniy, I. V.; Uyutnov, S. A.; Savchenko, E. V.; Ponomaryov, A. N.; Gumenchuk, G. B.; Bondybey, V. E.

We have studied thermo-stimulated luminenscence and electron emission of nitrogen films and nanoclusters containing free radicals of atomic nitrogen. Thermo-stimulated electron emission from N2 nanoclusters was observed for the first time. Thermo-stimulated luminescence spectra obtained during the destruction of a N2–He sample are similar to those detected from N2 films pre-irradiated by an electron beam. This similarity reveals common mechanisms of energy transfer and relaxation. The correlation of luminescence intensity and electron current in both systems points to the important role of ionic species in relaxation cascades. Sublimation of solid helium shells isolating nitrogen nanoclusters is a trigger for the initiation of thermo-stimulated luminescence and electron emission in these nitrogen–helium condensates.

Publ.-Id: 19686

New evidence for the mixing length concept in a narrow bubble column operated in the transition regime

Nedeltchev, S.; Schubert, M.; Donath, T.; Rabha, S.; Hampel, U.

Different scales of liquid mixing exist in bubble columns and it is very important to determine the prevailing mixing scale in each flow regime. Two independent parameters were found to exhibit a monotonous decline in the transition flow regime, which could be attributed to the decrease of the mixing length values L. In this work, a new parameter called ‘maximum number of visits in a region’ Nvmax and the Kolmogorov entropy (KE) were extracted from the gas holdup time series (60 000 points). The latter were recorded at a high sampling frequency (2000 Hz) by a wire-mesh sensor. The measurements were performed in a narrow bubble column (0.15 m in ID, clear liquid height = 2 m) equipped with a perforated plate distributor (14 holes, Ø 4 × 10-3 m). Both parameters were capable of identifying concordantly the two main transition velocities at Utrans = 0.022 and 0.112 m/s, which delineate the boundaries of gas maldistribution, transition and churn-turbulent regimes, respectively.

Keywords: Narrow Bubble Column; Wire-Mesh Sensor; Gas Holdup Fluctuations; Mixing Length; Transition Flow Regime; Maximum Number of Visits; Kolmogorov Entropy

  • Open Access Logo Journal of Chemical Engineering of Japan 47(2014)9, 722-729

Publ.-Id: 19685

Anomalous low-temperature “post-desorption” from solid nitrogen

Savchenko, E. V.; Khyzhniy, I. V.; Uyutnov, S. A.; Ponomaryov, A. N.; Gumenchuk, G. B.; Bondybey, V. E.

Anomalous low-temperature post-desorption (ALTpD) from the surface of nominally pure solid nitrogen pre-liminary irradiated by an electron beam was detected for the first time. The study was performed using a combi-nation of activation spectroscopy methods — thermally stimulated exoelectron emission (TSEE) and spectrally resolved thermally stimulated luminescence (TSL) — with detection of the ALTpD yield. Charge recombination reactions are considered to be the stimulating factor for the desorption from pre-irradiated α-phase solid nitrogen.

Keywords: solid nitrogen; exoelectron emission; thermoluminescence; desorption

Publ.-Id: 19684

Lattice and orbital fluctuations in TiPO4

Wulferding, D.; Möller, A.; Choi, K.-Y.; Pashkevich, Y. G.; Babkin, R. Y.; Lamonova, K. V.; Lemmens, P.; Law, J. M.; Kremer, R. K.; Glaum, R.

In the s = 1/2 antiferromagnetic spin chain material TiPO4, the formation of a spin gap takes place in a two-step process with two characteristic temperatures, T = 111 K and TSP = 74 K. We observe an unusual lattice dynamics over a large temperature regime as well as evidence for an orbital instability preceding the spin-Peierls transition. We relate different intrachain exchange interactions of the high temperature compared to the spin-Peierls phase to a modification of the orbital ordering pattern. In particular, our observation of a high-energy excitation of mixed electronic and lattice origin suggests an exotic dimerization process different from other spin-Peierls materials.

Publ.-Id: 19683

Long waves from short bunches: Concepts and applications of super-radiant THz sources

Gensch, M.

  • Invited lecture (Conferences)
    Kolloquium der Fakultät für Physik, KIT, 31.01.2014, Karlsruhe, Deutschland

Publ.-Id: 19682

Investigations of the Magnetic Properties in the Pyrochlore Ho2Ti2O7

Schönemann, R.; Herrmannsdörfer, T.; Green, E. L.; Skrotzki, R.; Wang, Z.; Kaneko, H.; Suzuki, H.; Wosnitza, J.

Pyrochlore compounds such as R2Ti2O7 (where R is Ho or Dy) have an highly degenerate ground state where the R3+ moments obey the "ice rules". This provides access to study extraordinary physical phenomena, like the formation of magnetic monopoles. Recent publications evidence monopoles which can be probed using high frequency (adiabatic) susceptibility measurements [1]. We performed ac susceptibility measurements on a single-crystal Ho2Ti2O7 sample at low temperatures down to 30 mK and magnetic fields up to 14 T. Based on isothermal frequency sweeps we were able to determine spin relaxation rates. Both the real and imaginary parts of the temperature-dependent magnetic susceptibility measurements show the spins freezing below 1 K and provide insight into the magnetic-monopole density.

  • Poster
    DPG Frühjahrstagung, 10.-15.03.2013, Regensburg, Deutschland

Publ.-Id: 19681

Multimodal imaging of a novel pheochromocytoma tumor model

Bergmann, R. K.; Ullrich, M.; Ziegler, C. G.; Kniess, T.; Ehrhart-Bornstein, M.; Schally, A. V.; Eisenhofer, G.; Bornstein, S.; Steinbach, J.; Pietzsch, J.

Objective. Pheochromocytoma (PHEO) is a rare but potentially lethal neuroendocrine tumor arising from catecholamine producing chromaffin cells. Available treatment strategies are limited and, if the tumor has metastasized, not very effective. The abundant expression of peptide hormone receptors on endocrine tumor cells allows specific targeting and imaging by radioactive and highly effective anti-tumor peptide analogs. The present study focuses on the preclinical imaging and evaluation of potential therapies in the treatment of pheochromocytoma targeting peptide hormone receptors. Design and method. Somatostatin receptor 2 (SSTR2), luteinizing hormone-releasing hormone receptor (LHRH-R) and growth hormone-releasing hormone receptors (GHRH-R) were characterized by both RT-PCR and immunohistological analysis in a mouse pheochromocytoma (MPC) cell line . Based on these data, we evaluated the effects of cytotoxic peptide hormone analogs on cell viability, apoptosis, and necrosis on MPC cells. For in vivo studies, we furthermore established a new MPC mCherry transfected cell line and produced a subcutaneous mouse model of PHEO. The tumors were evaluated by multimodal imaging using PET, MRI, CT and optical imaging. Results. Our data reveal significant anti-tumor effects mediated by the cytotoxic peptide hormone analogs AN-162 and AN-238 targeting SSTR2, by the antagonist Cetrorelix targeting LHRH-R and by the cytotoxic analog AN-152 targeting as well as by the antagonist MIA-602 targeting growth GHRH-R on MPCs. Furthermore, using our newly established mouse model, we were able to visualize the growth, perfusion, metabolism, and hypoxia of MPC cell-derived subcutaneous PHEO in vivo by multimodal molecular imaging including SSTR2 PET. Additionally, histological ex vivo tumor characterization demonstrated unaltered functional peptide hormone receptor expression during in vivo tumor growth in mice. Conclusion. Our current investigation provides strong evidence for a possible future treatment of malignant PHEO using targeted peptide hormone receptor therapy. Support. This work was supported by the Deutsche Forschungsgemeinschaft (Grants BE-2607/1 (R.B. & J.P.), and ZI-1362/2-1 (C.G.Z.&G.E.).

  • Poster
    World Molecular Imaging Congress, 18.-21.09.2013, Savannah, USA

Publ.-Id: 19680

Super-radiant THz sources: Perspectives

Gensch, M.

  • Invited lecture (Conferences)
    Workshop on "The Science and Technology of Accelerator-based THz Lightsources", 18.-19.11.2013, Upsala, Sweden

Publ.-Id: 19679

"Material Science „at Home“ and at the Synchrotron"

Grenzer, J.

  • Invited lecture (Conferences)
    Institutskolloquium, 21.01.2013, Freiberg, Germany

Publ.-Id: 19678

Numerical study of MHD instabilities in Liquid Metal Batteries

Weber, N.; Barry, L.; Galindo, V.; Grants, I.; Stefani, F.; Weier, T.

Nowadays, liquid metal batteries (LMBs) are considered as one promising device for storing electricity on the short and medium time scale. Built as a stable density stratification of two metals separated by a liquid salt electrolyte, liquid metal batteries offer comparatively very high current densities as well as a potentially superior live time, compared to solid batteries. Bearing in mind the low material price, LMBs may provide cheap power as well as energy, by simply upscaling the battery. This is where magnetohydrodynamics come into play. Currents in the order of kilo-amperes will induce fluid instabilities with the potential of short-circuiting the fully liquid battery. Beside of thermal convection and electro-vortex flows, surface instabilities, as known from aluminum smelters, and the kink-type Tayler instability (TI) are of particular significance.

We present a numerical model, based on the open source CFD library OpenFOAM which is able to simulate the Lorentz force induced fluid flow in LMBs. Starting with single phase simulations, the model shows good correspondence with a recent Tayler instability experiment. Further studies lead to a comprehensive characterization of the TI in liquid metal batteries and to a number of countermeasures for taming it. The influence of the current collectors and feeding cables of the battery is investigated, as well. Finally, first results of multiphase simulation are presented, particularly with regard to the deformation of the thin electrolyte layer.

Keywords: OpenFOAM Tayler instability simulation liquid metal battery

  • Lecture (Conference)
    9th PAMIR International Conference, 16.-20.06.2014, Riga, Lettland
  • Contribution to proceedings
    9th PAMIR International Conference, 16.-20.06.2014, Riga, Lettland

Publ.-Id: 19677

Nanoindentation on ion-irradiated Fe-Cr alloys

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

Ferritic/martensitic high-chromium steels are candidate structural materials for future nuclear applications such as fusion and generation IV fission reactors. Nevertheless these steels suffer hardening and embrittlement due to neutron irradiation. Ion irradiation is an efficient tool to simulate neutron irradiation effects without the drawbacks of producing radioactive material. In the present work ion-irradiation in combination with nanoindentation has been applied to study the irradiation-induced hardening of binary Fe-Cr alloys. The details of the approach are specified and the effects of Cr content and irradiation conditions including both single-beam and dual-beam irradiations are considered. Transmission electron microscopy is used to characterize irradiation-induced defects. Ion-irradiation-induced hardening is compared to hardening observed after neutron irradiation at similar conditions and dominant hardening mechanisms are identified.

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

  • Lecture (Conference)
    5th Workshop on Nuclear Fe Alloys: Modeling and Experiment, 28.-29.11.2013, Roma, Italia

Publ.-Id: 19676

In-situ X-ray Scattering & Diffraction: Studying the Formation of Nanostructures using ion beam techniques

Grenzer, J.; Facsko, S.; Holy, V.; Bähtz, C.; Roshchupkina, O.

  • Lecture (Conference)
    Workshop „Ionenstrahlen – Forschung und Anwendung“ 2013, 12.-14.06.2013, Leipzig, Germany

Publ.-Id: 19675

In-situ Ionen-Experimente @ ROBL-MRH

Grenzer, J.

  • Lecture (others)
    FWIZ Statusklausur 2013 am Institut für Ionenstrahlphysik und Materialforschung; Ionenstrahlzentrum, 10.-11.07.2013, HZDR, Germany

Publ.-Id: 19673

Structure dependent magnetic properties of Co implanted TiO2

Yildirim, O.; Cornelius, S.; Vinnichenko, M.; Butterling, M.; Wagner, A.; Smekhova, A.; Potzger, K.

Magnetic and structural properties of amorphous and anatase TiO2 thin films implanted with Co ions have been investigated. Implantation induced defects have been characterized using positron annihilation spectroscopy (PAS) while for magnetic chracterization we have used magnetometry. Up to a doping level of 2.5 at.%, only a paramagnetic contribution has been detected. The susceptibility strength , however, depends on the structure of the unimplanted film. Results on the formation of secondary phases at higher doping level will also be presented.

This work is supported by the Initiative and Networking Fund of the German Helmholtz Association, Helmholtz-Russia Joint Research Group HRJRG-314, and the Russian Foundation for Basic Research, RFBR #12-02-91321-SIG_а, Start: 01.02.2012

  • Lecture (Conference)
    DPG-Frühjahrstagung, 30.03.-04.04.2014, Dresden, Germany

Publ.-Id: 19672

Erzeugung funktionaler Schichten auf Basis von bakteriellen Hüllproteinen

Weinert, U.

Die hier vorliegende Arbeit beschäftigt sich mit Eignung bakterieller Hüllproteine als Bindungsmatrix für die Kopplung funktionaler Moleküle mit dem Ziel, sensorische Schichten zu erzeugen. Bakterielle Hüllproteine sind biologische SAMs, an deren Oberfläche sich modizierbare COOH-, NH2- und OH-Gruppen benden. Die Ausbildung polymerer Strukturen erfolgt dabei in wässrigen Systemen und auf Oberflächen. Im Zuge der boomenden Entwicklung von Biosensoren werden insbesondere Biotemplate gesucht, die zwischen biologischer Komponente und Sensoroberfläche vermitteln. Bakterielle Hüllproteine stellen eine solche Zwischenschicht dar. Als Anwendungsbeispiel wurden die Proteine daher mit einem FRET-Paar und Thrombin- und Kanamycin-Aptameren modiziert. Hierbei wurden das FRET-Paar H488 und H555 an die bakteriellen Hüllproteine der beiden Haldenisolate A12 und B53 mittels EDC mit einer Modifizierungsrate von 0,54 mol_Farbsto/mol_Protein kovalent gebunden. Bei der vorhandenen p4-Symmetrie bedeutet dies, dass ein FRET-Paar pro Einheitszelle vorhanden war. Der Nachweis eines Energietransfers zwischen den beiden am Protein gebundenen Fluoreszenzfarbstoffen H488 und H555 erfolgte mittels statischer und zeitaufgelöster Fluoreszenzmessung. Die Ergebnisse zeigten, dass ein Energietransfer nur möglich war, wenn die Proteine in polymerer Form vorlagen, unabhängig davon, ob sich die Proteine immobilisiert an einer Oberfläche oder in wässriger Lösung befanden. Mittels Variieren des Donor-Akzeptor-Verhältnisses konnte ein maximaler Energietransfer von 40 % generiert werden, wenn das Verhältnis der Fluoreszenzfarbstoffe von Donor und Akzeptor 4 betrug. Die Fluoreszenzintensität der Fluorophore wurde durch die Bindung an die Proteine nicht verringert oder gelöscht. Dies legt nahe, dass die Farbstoffe in den hydrophoben Poren immobilisiert wurden und die Poren die Fluoreszenzfarbstoffe schützen. Um weitere Aussagen über die Lage der gebundenen Fluoreszenzfarbstoffe zu erhalten, wurden die bakteriellen Hüllproteine der Stämme A12 und B53 enzymatisch verdaut und die Fragmente mittels SEC und SDS-PAGE untersucht. Dabei zeigten sich je nach Enzym und Protein unterschiedliche Bandenmuster bezüglich modifizierter und nativer Hüllproteine. Dies belegt, dass die Fluoreszenzfarbstoffe an NH2- und COOH-Gruppen der Proteine gebunden wurden und so teilweise den enzymatischen Verdau hinderten. Die SEC deutet an, dass die Fluoreszenzfarbstoffe an verschiedenen Stellen am Protein gebunden wurden. In einem zweiten Beispiel wurde das bakterielle Hüllprotein von A12 mit einem Aptamer modiziert. Aptamere sind kurze einzelsträngige Oligonukleotide, die u.a. mittels ihrer ausgebildeten 3D-Struktur spezifisch Zielstrukturen reversibel binden können. Die hier verwendeten Aptamere binden spezifisch Thrombin und Kanamycin. Die Aptamere wurden mit Hilfe einer der beiden Vernetzer PMPI oder Sulfo-SMCC an die bakteriellen Hüllproteine kovalent gebunden. Nach dem Modifizieren der Proteine wurden diese auf entsprechenden Sensorchips immobilisiert und die Aktivität des gekoppelten Aptamers mittels Affinitätsmessungen, SPR-Spektroskopie und QCM-D-Messungen analysiert. Die Funktion des gebundenen Thrombinaptamers konnte mittels Affinitätsmessungen und QCM-D nachgewiesen werden und entspricht in beiden Fällen einer Bindung von 2 nmol Thrombin pro Quadratzentimeter. Die Funktionalität des Kanamycinaptamers sollte mittels SPR bestimmt werden, jedoch konnte keine Funktionalität des gekoppelten Kanamycinaptamers nachgewiesen werden. Alle Messungen bestätigten jedoch, dass die Bindungsmatrix aus bakteriellen Hüllproteinen keinerlei oder nur ein sehr geringes Hintergrundsignal liefert. Werden nun beide Komponenten, FRET-Paar und Aptamere, an das Protein gebunden, ist es möglich, eine sensorische Schicht zu erzeugen. Die Zielstruktur, welche detektiert werden soll, wird an das Aptamer gebunden und so in räumliche Nähe zur Sensorfläche gebracht. Stellt die Zielstruktur einen Fluoreszenzlöscher dar, so wird der Energietransfer durch die räumliche Nähe des Fluoreszenzlöscher gestört. Die Detektion des Zielmoleküls erfolgt nun über die Änderung von Fluoreszenzintensitäten. Die hier vorgelegte Arbeit soll einen Grundstein legen für die Entwicklung eines solchen Sensors und insbesondere die Detektion eines Energietransfers optimieren und Schwachstellen in der Detektion nachweisen. Die systematische Untersuchung der Fluoreszenzfarbstoffe auf dem Protein ermöglichen es, in zukünftigen Arbeiten einen FRET zweifelsfrei zu detektieren. Die Modifizierung von bakteriellen Hüllproteinen von A12 mit Aptameren und die Detektion der Funktionalität der Aptamere mittels verschiedener Methoden zeigte auf, dass die bakteriellen Hüllproteine als universelle Bindungsmatrix für sensorische Moleküle dienen können, bei denen Affinitätsmessungen, SPR- oder QCM-D-Messungen genutzt werden. Besonders hervorzuheben ist, dass bakterielle Hüllproteine nahezu kein Hintergrundsignal liefern und aufgrund ihrer dünnen Monolage von etwa 6 - 9 nm die Sensitivität der Messungen nur gering beeinträchtigen.

Keywords: S-layer Proteins; sensors; aptamers; FRET; Protein modification

  • Doctoral thesis
    TU Dresden, 2013
    180 Seiten

Publ.-Id: 19671

S-layers as multifunctional templates for nanotechnology

Weinert, U.; Günther, T.; Pollmann, K.; Raff, J.

Surface-layer (S-layer) proteins are biomolecules which can self-assemble in aqueous solutions and on surfaces. Those polymers form highly ordered two dimensional structures with unit cell sizes of few nanometers. On surface of such protein polymers one can find a high amount of modifiable groups like COOH-, NH2- and OH-groups. The latter and its nanostructuring make S-layers a perfect platform for nanotechnology.
Therefore S-layers can work as biotemplate to build biosensors consisting of fluorescence dyes and aptamers. Thereby fluorescence dyes will work as signal transducer system by performing a Foerster Resonance Energy Transfer (FRET) between each other. Aptamers serve as receptor for one specific analyte. Analyte binding by the aptamer leads to a detectable signal change because of a disturbed FRET. An idealized design of such a biosensor is shown in Fig. 1a. In a recent published work a FRET-pair was chemically linked to S-layers and showed an energy transfer efficiency of 40 % [1]. In further work aptamers will be chemically linked to the S-layer-FRET-system to reach proof of concept.
Another application for those S-layer proteins can be the development of catalytic materials based on highly ordered nanoparticles. Thereby nanoparticles of platinum or palladium are synthesized in the pores of S-layers. Fig. 1b shows an idealized scheme. After removal of the organic matrix nanoparticles are arranged on the surface having a defined size and order. These materials can now work as catalysts for e.g. organic synthesis or metallization of polymers.

Keywords: S-layer; nanotechnology; surface modification; sensors; aptamer; nanoparticles

  • Lecture (Conference)
    COST Action "Bio-inspired nanotechnologies: from concepts to applications", 08.-09.10.2013, Leipzig, Deutschland

Publ.-Id: 19670

Bakterielle Hüllproteine als Matrix für die Entwicklung funktionaler Schichten

Weinert, U.; Günther, T.; Pollmann, K.; Raff, J.

Sensoren für spezifische Substanzen, wie z.B. Medikamente und Umweltgifte, gewinnen mit dem wachsenden Umweltbewusstsein der Gesellschaft und der Industrie z.B. in Bereichen wie der Wasserüberwachung und -aufbereitung immer mehr an Bedeutung. Die vorliegende Arbeit beschäftigt sich daher mit der Konzipierung einer sensorischen Schicht, bestehend aus bakteriellen Hüllproteinen, Fluoreszenzfarbstoffen und Aptameren, die es ermöglichen soll, kleinste Mengen an Schadstoffen im Wasser zu detektieren. Bakterielle Hüllproteine sind selbstassemblierende Proteine, die in wässrigen Systemen und an Oberflächen ebenmäßige Gitterstrukturen ausbilden und an deren Oberfläche zahlreiche modifizierbare funktionelle Gruppen, wie z. B. COOH- und NH2-Gruppen, zu finden sind. Sie stellen damit eine nahezu perfekte Bindungsmatrix für die sequentielle Kopplung sensorischer Komponenten dar, die mit wenigen Nanometern Abstand zueinander auf eine Oberfläche fixiert werden sollen. Die vorliegende Arbeit nutzt ein FRET-Paar als optische Komponente und Aptamere als Rezeptor-Moleküle. Die räumliche Nähe aller Komponenten zueinander soll gewährleisten, dass nach der Bindung des zu detektierenden Analyten, der Energietransfer zwischen den beiden Fluoreszenzfarbstoffen unterbunden wird. Das veränderte optische Signal kann dann einfach mittels Fluorometer detektiert und ausgewertet werden. Die nachfolgende Abbildung soll schematisch und idealisiert einen möglichen Aufbau der sensorischen Schicht darstellen. Die derzeitigen Arbeiten beschäftigen sich mit der erfolgreichen Funktionalisierung von bakteriellen Hüllproteinen mit einem FRET-Paar und Aptameren.

Keywords: FRET; aptamer; sensor; surface-layer Proteins; modification

  • Poster
    8. Deutsches BioSensor Symposium, 10.-13.03.2013, Wildau, Deutschland

Publ.-Id: 19669

X-ray diffraction and grazing-incidence diffraction

Grenzer, J.

  • Invited lecture (Conferences)
    9th Autumn School on X-ray Scattering from Surfaces and Thin Layers, 25.-28.09.2013, Smolenice Castle, Slovakia

Publ.-Id: 19668

Material Science at „Home“ and at the Synchrotron: Investigations of nanocrystalline films

Grenzer, J.

"Material Science at „Home“ and at the Synchrotron: Investigations of nanocrystalline films"

  • Invited lecture (Conferences)
    Firma PANalytical B.V., 12.09.2013, ALMELO, The Netherlands

Publ.-Id: 19667

Inter-sublevel dephasing in quantum dots

Teich, M.; Schneider, H.; Bhattacharyya, J.; Winnerl, S.; Wilson, L.; Helm, M.

We use the Dresden Free-Electron-Laser (FELBE) to investigate intersublevel coherence times in semiconductor quantum dots (QDs) by degenerate four-wave mixing (DFWM) spectroscopy. We know from pump-probe measurements1 on a series of quantum dot samples with varying intersublevel energy that intersublevel relaxation times of the s-p intersublevel transition can become very long (up to 1.5 ns). Due to the discrete nature of these sublevels, intersublevel coherence times should exhibit similar time constants at low temperatures where “pure dephasing” is suppressed.

Keywords: semiconductor quantum dot; inter-sublevel transition; terahertz free-electron laser; degenerate four-wave mixing; homogeneous and inhomogeneous broadening

  • Contribution to proceedings
    38th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz 2013), 01.-06.09.2013, Mainz, Deutschland: IEEE Xplore Digital Library
    DOI: 10.1109/IRMMW-THz.2013.6665455
  • Poster
    38th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz 2013), 01.-06.09.2013, Mainz, Deutschland

Publ.-Id: 19666

Extra-long hole spin relaxation time in InGaAs/GaAs quantum wells probed by cyclotron resonance spectroscopy

Drachenko, O.; Kozlov, D.; Ikonnikov, A.; Spirin, K.; Gavrilenko, V.; Schneider, H.; Helm, M.; Wosnitza, J.

We report a long, ms range, spin relaxation time of holes in InGaAs/GaAs quantum wells probed by cyclotronresonance spectroscopy in pulsed magnetic fields up to 60 Tesla. We found a strong hysteresis in the spectral weights of the cyclotron resonance absorption when a rapidly changing magnetic field is used for the experiment, while the hysteresis vanishes when a much slower changing magnetic field is used. We attribute this behavior to a long, comparable to the magnetic-field rise time, energy relaxation time between the two lowest spin-split hole Landau levels, i.e., a long hole spin relaxation time.

Keywords: cyclotron resonance spectroscopy; hole spin relaxation; pulsed magnetic fields; InGaAs/GaAs quantum well

  • Lecture (Conference)
    2013 38th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz 2013), 01.-06.09.2013, Mainz, Deutschland
  • Contribution to proceedings
    2013 38th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz 2013), 01.-06.09.2013, Mainz, Deutschland: IEEE Xplore Digital Library
    DOI: 10.1109/IRMMW-THz.2013.6665921

Publ.-Id: 19665

Plasmonic focusing on metal and semiconductor disks under radially polarized terahertz illumination

Kaltenecker, K. J.; Wallauer, J.; Waselikowski, S.; Hodapp, J.; Fischer, C.; Winnerl, S.; Schneider, H.; Fischer, B. M.; Walther, M.

Optimal focusing of surface plasmon polaritons in the center of a metal disc illuminated by radially polarized terahertz pulses is demonstrated. Due to the cylinder symmetrical structure surface plasmons can be excited along the entire circumference, which interfere constructively in the center of the disk forming a sharp frequency-depended focal spot. We map the field distribution on the disk by THz near-field microscopy and compare our result to numerical simulations. For comparison, behavior under linearly polarized THz illumination is characterized. Furthermore, first results of semiconducting plasmonic lenses are presented.

Keywords: Terhertz radiation; plasmon polaritons; radial polarization

  • Lecture (Conference)
    2013 38th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz 2013), 01.-06.09.2013, Mainz, Deutschland
  • Contribution to proceedings
    2013 38th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz 2013), 01.-06.09.2013, Mainz, Deutschland: IEEE Xplore Digital Library
    DOI: 10.1109/IRMMW-THz.2013.6665612

Publ.-Id: 19664

Krein space related physics: from mathematical structures towards experiments

Günther, U.

A compact overview is given about physical systems with antilinear symmetries as they have been intensively studied during the past 15 years and as they are currently still under intensive investigation worldwide. Starting from a few comments on the historical background, the underlying basic mathematical structures are sketched. This especially concerns the properties of the corresponding effective Hamiltonians, their non-selfadjointness in usual Hilbert spaces with positive definite (Euclidean type) inner products and their selfadjointness in Hilbert spaces with indefinite inner products, so called Krein spaces. Specific properties of these Hamiltonians like non-diagonalizability at spectral branch-points, hidden Jordan block structures, perturbation theory in terms of Puisseux series expansions instead of Taylor expansions as well as related group structures will be briefly discussed. Realizations of the antilinear symmetries are demonstrated for physical systems with simultaneous time-reversal and parity-inversion symmetries (PT symmetries). Specific physical effects like PT phase transitions and exciting new features of these systems are illustrated on simulations for various optical waveguide systems, Bose-Einstein condensates (BECs), microwave cavities, systems of coupled oscillators etc. Finally, a brief overview is given about recent experimental implementations as well as about a couple of promising new directions of research with interconnections to other areas of active research in theoretical and experimental physics.

Keywords: PT physics; PT phase transitions; operator theory; Krein spaces; branch points; Jordan blocks; Puisseux series expansions; Bose-Einstein condensates; optical waveguide systems; microwave cavities

  • Lecture (others)
    Lecture presented at the Physics Department, College of Sciences, Koc University, Istanbul, 16.12.2013, Istanbul, Turkey

Publ.-Id: 19663

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