Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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33407 Publications

Ion-Beam-Assisted Nanocrystal Formation in Silicon Implanted with High Doses of Pb+ and Bi+ Ions

Kalitzova, M.; Zollo, G.; Yankov, R.; Angelov, C.; Simov, S.; Pizzuto, C.; Faure, J.; Kilian, L.; Bonhomme, P.; Manno, D.; Voelskow, M.; Vitali, G.
In this paper we discuss ion-beam-assisted nanocrystal nucleation in amorphized silicon (a-Si) layers produced by high-dose implantation of Pb+ and Bi+. (100)-oriented Si wafers were implanted at room temperature (RT) with 50 keV Pb+ and Bi+ ions at doses ranging from 5E13 to 1E18 cm−2 and a constant ion current density of 10μAcm−2. The resulting structures were studied by conventional transmission electron microscopy (CTEM), high resolution transmission electron microscopy (HRTEM) and Rutherford backscattering spectroscopy (RBS) in combination with computer simulations. The dynamics of the ion-beam-induced crystallization of new phases and precipitates evolution in the implanted layer were studied as a function of implant dose. It is established that the front of the new phase crystallization (cubic Pb and hexagonal Bi nanocrystals) starts approximately at the peaks of the implanted species profiles; the crystallography of the nucleated nanocrystal is examined as a function of the dose.
Keywords: ion implantation, precipitation, nanoclusters, silicon, electron microscopy
  • Japanese Journal of Applied Physics 40(2001)10, 5841-5849

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Permalink: https://www.hzdr.de/publications/Publ-13749
Publ.-Id: 13749


Transient enhanced diffusion and electrical activation of As in Si during rapid thermal annealing

Koegler, R.; Wieser, E.; Voelskow, M.; Otto, G.
(100) Si was implanted at 150 or 100 keV with fluences from 5 E 15 to 2 E16 cm-2. The samples were processed by rapid thermal annealing at temperatures between 1000 and 1200°C and dwell times at T(max) from 1 to 30 s. As depth distributions were measured by RBS and SIMS. By comparison of experimental profiles with computer simulations based on the diffusion model proposed by Tsai et al. and including a time independent enhancement factor or a transient enhancement according to Fair a transient enhanced diffusion has been found. The influence of As clustering or precipitation on the diffusion behaviour of high concentrations is discussed. The comparison of samples implanted through 30 nm SiO2 or in bare Si shows an enhanced As concentration at the SiO2 interface and a decreased diffusivity for the former case. These effects are explained by an interaction of As with oxygen recoil atoms.
Keywords: transient enhanced diffusion, RTA, implantation
  • Nuclear Instruments and Methods in Physics Research B 19-20(1987), 516-520

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Permalink: https://www.hzdr.de/publications/Publ-13748
Publ.-Id: 13748


Epitaxial lateral overgrowth of amorphous CVD silicon films induced by ion irradiation

Voelskow, M.; Skorupa, W.; Wollschlaeger, K.; Matthaei, J.; Knothe, P.; Heinig, K.-H.
Amorphous silicon layers deposited by chemical vapour deposition on monocrystalline silicon substrates partly covered with silicon dioxide to produce SOl structures were epitaxially recrystallised by ion beam induced epitaxial crystallisation at 400 C after preamorphisation of the transition region layer/substrate. The implantation with a dose of 5E17 cm-2 into the wafers with SOl structure resulted in a 1.5 um wide overgrown crystalline layer.
Keywords: CVD, epitaxy, ion irradiation
  • Applied Surface Science 43(1989)1-4, 196-199

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Permalink: https://www.hzdr.de/publications/Publ-13747
Publ.-Id: 13747


MeV carbon implantation into silicon: microstructure and electrical properties

Skorupa, W.; Kögler, R.; Voelskow, M.; Schmalz, K.; Morgenstern, G.; Gaworzewski, P.
Doping effects after carbon implantation at 0 .33 and 10 MeV were investigated at silicon wafers with different oxygen content. No distinct influence of the oxygen concentration on the carbon induced doping effect was found for rapid thermal annealing at 1250°C for 30 s whereas for furnace annealing at 1000°C the doping effect is higher for Czochralski-grown silicon wafers with their higher oxygen content. The gettering efficiency of a buried carbon implanted layer for additionally introduced iron atoms was investigated by deep level transient spectroscopy. Gettering sets in at a dose of 10E14 cm2 and is completed for a carbon dose of 1E16 cm2 for iron doses up to 1E13 cm2. The microstructure of such a buried layer is characterised by a narrow band of dark contrast containing mainly stacking faults of the extrinsic type .
Keywords: MeV ion implantation, DLTS
  • Nuclear Instruments and Methods in Physics Research B 68(1992)1-4, 408-412

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Permalink: https://www.hzdr.de/publications/Publ-13746
Publ.-Id: 13746


Model experiments on thermo-electromagnetic convection

Cramer, A.; Zhang, X.; Gerbeth, G.
Thermoelectromagnetic convection in electrically conducting cubic containers was studied experimentally. Two opposing side walls were cooled and heated, respectively, to produce a uniform temperature gradient. Inhomogeneous magnetic field distributions were achieved either with a small permanent magnet located above the melt layer, or with specifically shaped pole shoes of the magnetic system. Ultrasonic Doppler velocimetry measurements demonstrated that even a moderate temperature gradient may drive a distinct convection. Two different flow regimes were investigated with the permanent magnet. When it was positioned in the vicinity of an isothermal wall, with its direction of magnetisation parallel to the temperature gradient, a single vortex spreading the whole container developed while the flow might be assessed as relatively stable. Moving the magnet to the centre led to a modified distribution of the magnetic field which, in turn, altered the flow structure. The convective pattern changed to four vortices and the velocity fluctuations were intensified. A more generic case was realised with the pole shoes providing a gradient of the magnetic field only in one direction. Since the strength of the field could be raised significantly above that provided by the small permanent magnet and the area of impact onto the melt was larger, developed turbulent regimes were accomplished. Numerical results obtained for the Lorentz force and the rotor thereof support the experimental findings.
Keywords: Thermoelectricity, Model experiments, Magnetohydrodynamics, Liquid Metals, Thermocurrent, Electromagnetic stirring
  • Lecture (Conference)
    6th International Conference on Electromagnetic Processing of Materials EPM 2009, 19.-23.10.2009, Dresden, Deutschland
  • Contribution to proceedings
    6th International Conference on Electromagnetic Processing of Materials EPM 2009, 19.-23.10.2009, Dresden, Deutschland
    Proceedings of the EPM 2009, 978-3-936104-65-3, 94-97

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Permalink: https://www.hzdr.de/publications/Publ-13745
Publ.-Id: 13745


Ion beam synthesis by tungsten-implantation into 6H-silicon carbide

Weishart, H.; Steffen, H. J.; Matz, W.; Voelskow, M.; Skorupa, W.
Synthesis of a highly conductive surface layer on 6H-silicon carbide was achieved by high-dose, room temperature implantation of tungsten at 200 keV. Subsequently, the samples were annealed in two steps, namely at 500°C and 950°C. ‘I%e influence of both dose and annealing on the reaction of W with Sic was investigated. Rutherford Backscattering Spectrometry (RBS), X-Ray Diffraction (XRD) and Auger Electron Spectroscopy (AES) contributed to study the structure and composition of the layer as well as the chemical states of the elements. During implantation sputtering becomes significant for doses exceeding 1.0 X 10” cm- ‘. Formation of tungsten carbide and silicide is already observed in the as-implanted state. An annealing temperature of 950°C is necessary to crystallize tungsten carbide. However, tungsten silicide remains amorphous at this temperature. Therefore, a mixture of polycrystalline tungsten carbide and amorphous tungsten silicide develops under these conditions. The resistivity of such a layer implanted with 1.0 E17 W+ cm2 and annealed at 950°C is 565 uohmcm.
Keywords: Ion beam synthesis, 6H-SiC
  • Nuclear Instruments and Methods in Physics Research B 112(1996)1-4, 338-341

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Permalink: https://www.hzdr.de/publications/Publ-13744
Publ.-Id: 13744


A novel (SiC)1-x(AlN)x compound synthesized using ion beams

Pezoldt, J.; Yankov, R. A.; Mücklich, A.; Fukarek, W.; Voelskow, M.; Reuther, H.; Skorupa, W.
The formation of a novel (SiC)1-x(AlN)x compound (x=0.2) at low temperatures within the miscibility gap of the SiC/AlN phase diagram by hot, high-dose co-implantation of N+ and Al+ ions into 6H±SiC substrates is investigated. The compound layers have been studied by Rutherford backscattering spectrometry/ion channelling (RBS/C), Auger electron spectroscopy (AES), polarized infrared re¯ection spectroscopy (PIRR) and cross sectional electron microscopy (XTEM) and the temperature dependence of their fabrication has been examined. An optimum temperature window has been established within which the structure of the synthesized material retains good crystallinity during implantation.
Keywords: Ion beam synthesis, Silicon carbide; Aluminum nitride; Solid solutions; Polytypism
  • Nuclear Instruments and Methods in Physics Research B 147(1999)1-4, 273-278

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Permalink: https://www.hzdr.de/publications/Publ-13743
Publ.-Id: 13743


Characterisation of defects in ion implanted SiC by slow positron implantation spectroscopy and Rutherford backscattering

Anwand, W.; Brauer, G.; Coleman, P. G.; Voelskow, M.; Skorupa, W.
SiC(1-x)AlN(x) has been prepared by ion co-implantation of Nqand Alqinto a 6H-SiC n-type wafer. The substrate temperature during implantation was varied from 200°C to 800°C in order to reduce the damage created by ion implantation. The obtained structures have been investigated by Slow Positron Implantation Spectroscopy (SPIS). and Rutherford Backscattering and Ion Channeling (RBS). Both methods are sensitive to different kinds of defects and the results are complementary. The defect structures determined by SPIS and RBSrC are presented and the influence of the variation of the substrate temperature is discussed.
Keywords: Silicon carbide; Ion implantation; Vacancy-like defects; Defect profiles
  • Applied Surface Science 149(1999)1-4, 148-150

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Permalink: https://www.hzdr.de/publications/Publ-13742
Publ.-Id: 13742


Theoretical and experimental investigations of defect evolution in silicon carbide during N+ and Al+ ion implantation taking into account internal stress fields

Rybin, P. V.; Kulikov, D. V.; Trushin, Y. V.; Yankov, R. A.; Voelskow, M.; Scharmann, F.; Pezoldt, J.
A theoretical model is developed which allows to describe the defect evolution in silicon carbide implanted with high doses of nitrogen and aluminium ions and subsequently annealed to form a solid solution. The diffusion of defects, the formation of complexes of defect clusters and the influence of the internal elastic stress fields produced by the implanted ions and the complexes formed are taken into account. Results from the simulations have been correlated with data obtained by Rutherford backscattering spectrometry/ion channelling (RBS/C).
Keywords: Ion-beam synthesis; Computer simulation; Defect production; Kinetics of defects; Influence of stress
  • Nuclear Instruments and Methods in Physics Research B 178(2001)1-4, 269-274

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Permalink: https://www.hzdr.de/publications/Publ-13741
Publ.-Id: 13741


Vertrieb von Forschungsleistungen am Beispiel des FZD

Joehnk, P.
Vortrag im Rahmen der Reihe Dresdner Vertriebsfrühstück
  • Lecture (others)
    Vertriebsfrühstück, 29.01.2010, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-13740
Publ.-Id: 13740


Melt flow stabilisation in bulk crystal growth by means of external magnetic fields

Pätzold, O.; Lantzsch, R.; Greif, A.; Galindo, V.; Grants, I.; Gerbeth, G.; Stelter, M.
Several approaches to suppress a non-stationary melt flow and related fluctuations of the temperature and the dopant concentration in bulk crystal growth by means of external magnetic fields are presented. The paper includes results of model and growth experiments carried out in Bridgman- or Czochralski-like configurations under the influence of different fields (rotating, traveling, axial steady, cusp, combinations of which). It is shown that both time-dependent and steady fields can be used to stabilize a melt. The impact of a magnetic field on the melt flow, however, depends strongly on the configuration and thermal conditions of the growth. Therefore, type and parameters of the applied field have to be properly adjusted to the particular setup under consideration to achieve an optimal damping of fluctuations and to avoid unfavorable effects.
Keywords: bulk crystal growth, external magnetic fields
  • Contribution to proceedings
    6th International Conference on Electromagnetic Processing of Materials (EPM 2009), 19.-23.10.2009, Dresden, Germany, 978-3-936104-65-3, 849-862
  • Lecture (Conference)
    6th International Conference on Electromagnetic Processing of Materials (EPM 2009), 19.-23.10.2009, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-13738
Publ.-Id: 13738


Comparison of various contactless flow rate sensors

Buchenau, D.; Gerbeth, G.; Priede, J.
We consider three versions of recently developed contactless flowrate sensors: the well-known magnetic flywheel, a newly developed phase-sift sensor based on an applied alternating magnetic field, and a new force-free sensor based on a rotating single magnet. Comparative measurements were performed at a GaInSn-loop.
Keywords: Liquid metal, GaInSn-loop, Magnetic flywheel, Phase-shift sensor, Rotating magnet
  • Contribution to proceedings
    6th Int. Conf. on Electromagnetic Processing of Materials, 19.-23.10.2009, Dresden, BRD, pp. 383-386
  • Lecture (Conference)
    6th Int. Conf. on Electromagnetic Processing of Materials, 19.-23.10.2009, Dresden, BRD

Permalink: https://www.hzdr.de/publications/Publ-13737
Publ.-Id: 13737


Numerical Simulation of Two-phase Flow in a Slab Mold by MUSIG Model

Miao, X.; Galindo, V.; Lucas, D.; Gerbeth, G.; Ren, Z.
An Euler-Euler approach has been employed to investigate the effects of varying flow rate of argon gas and static magnetic field on the flow pattern in a slab mold. The mathematical model is based on the k − ǫ turbulence model and coupled with the MHD model in CFX. In this work, three dimensional localized DC magnetic fields were constructed and calculated by a finite element method and then imported into CFX. The results show that a static magnetic field does not always slow down the bulk flow, but occasionally gives rise to large eddies for increasing magnetic field strengths. In principle, the injection of Argon gas is able to suppress the fluctuation of the free surface and to reduce the penetration depth significantly. However, gas bubbles may produce a reversed flow surrounding the nozzle at the meniscus if large bubbles float up rapidly in the case the flow rate ratio of argon gas to molten steel reaches a certain value. The MUSIG (multiple size group) model considering coalescence and breakup of bubbles provides an effective tool to solve the multiphase flow and to get insight into the flow pattern in a continuous casting mold with argon gas injection.
Keywords: two-phase flow, continuous castig, musig model
  • Contribution to proceedings
    6th International Conference on Electromagnetic Processing of Materials (EPM 2009), 19.-23.10.2009, Dresden, Germany, 978-3-936104-65-3, 579-582
  • Lecture (Conference)
    6th International Conference on Electromagnetic Processing of Materials (EPM 2009), 19.-23.10.2009, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-13735
Publ.-Id: 13735


Numerical calculations for steam-water CCFL tests using the 1/3rd scale rectangular channel simulating a PWR hot leg

Kinoshita, I.; Murase, M.; Utanohara, Y.; Lucas, D.; Vallée, C.; Tomiyama, A.
In reflux cooling, steam generated in the reactor core and water condensed in a steam generator (SG) form a countercurrent flow in a hot leg, which consists of a horizontal pipe, an elbow and an inclined pipe. At Forschungszentrum Dresden-Rossendorf (FZD), both countercurrent air-water and steam-water tests were previously carried out using the 1/3rd scale rectangular channel simulating a PWR hot leg installed in the pressure chamber of the TOPFLOW facility. In this paper, in order to evaluate the effects of fluid properties, numerical calculations for the steam-water CCFL tests at FZD were conducted using the CFD code, FLUENT6.3.26. The numerical calculation region included the reactor vessel simulator, hot leg and SG inlet chamber, in order to avoid uncertainties of boundary conditions at both ends of the hot leg. The VOF (volume of fluid) model or two-fluid (2F) model was used. In the 2F model, we used the combination of three correlations on the interfacial friction coefficients as a function of void fractions, which had been validated for the 1/15th and 1/5th scale tests at Kobe University. The CCFL characteristics calculated by the 2F and VOF models agreed with the steam-water CCFL data at FZD and showed the same trends with the data for fluid properties.
Keywords: CCFL, stratified flow
  • Contribution to proceedings
    The 8th International Conference on Nuclear Thermal Hydraulics, Operations and Safety (NUTHOS-8), paper N8P0044, 10.-14.10.2010, Shanghai, China

Permalink: https://www.hzdr.de/publications/Publ-13733
Publ.-Id: 13733


Ultra large coercivity in barium ferrite thin films prepared by magnetron sputtering

Zhang, W.; Peng, B.; Zhang, W.; Zhou, S.; Schmidt, H.
Hexagonal barium ferrites were deposited onto sapphire substrates by radio frequency magnetron sputtering. The composition, microstructure, and magnetic properties of these isotropic thin films were investigated with Rutherford backscattering spectroscopy, X-ray diffraction, atomic force microscopy, magnetic force microscopy and SQUID magnetometry. The intrinsic coercivity of the films reaches about 11.5 kOe at room temperature. The mechanism of the coercivity is proposed to be nucleation in the decoupled single domain nanometer particles as shown by the characteristics of the magnetic domains and the virgin magnetization curves.
Keywords: Barium ferrite; Coercivity; Nucleation

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Permalink: https://www.hzdr.de/publications/Publ-13732
Publ.-Id: 13732


Numerical calculations for air-water tests on CCFL in different-scale models of a PWR hot leg

M. Murase, M.; Kinoshita, I.; Utanohara, Y.; Lucas, D.; Vallée, C.; Tomiyama, A.
Air-water CCFL (countercurrent flow limitation) tests were previously carried out at Kobe University using the 1/5th scale rectangular channel and 1/15th scale circular tube simulating a PWR hot leg. Then numerical calculations for these tests and full-scale PWR conditions were made using the CFD code, FLUENT6.3.26. At Forschungszentrum Dresden-Rossendorf (FZD), similar tests were previously carried out for both air-water and steam-water flows using the 1/3rd scale rectangular channel simulating a PWR hot leg installed in the pressure chamber of the TOPFLOW facility.
In this paper, numerical simulations for the air-water CCFL tests of FZD using FLUENT6.3.26 are presented and compared with the experimental data obtained at Kobe University and FZD. In the calculations, the VOF (volume of fluid) model or two-fluid (2F) model was used. In the 2F model, we used the combination of three correlations on the interfacial friction coefficients as a function of void fractions, which had been validated for the 1/15th and 1/5th scale tests at Kobe University. Calculation parameters were the air flow rates and air inlet locations, which were at the top of the reactor vessel simulator simulating the FZD test facility (inlet 1) and the opposite side of the hot leg junction simulating the test loops at Kobe University (inlet 2). Conclusions were as follows : (1) the calculated CCFL characteristics using the 2F model for the FZD tests agreed well with the 1/15th scale circular tube data obtained at Kobe University and the calculated results for full-scale PWR conditions, which supported the validity of the 1/3rd scale rectangular channel to simulate CCFL in circular tubes; (2) there were no significant differences between the calculated CCFL characteristics with the air inlet 1 and inlet 2, which indicated that the air inlet location did not influence CCFL behavior in a hot leg; and (3) comparison with the FZD data showed that the calculations using the 2F and VOF models overestimated the water flow rates for deflooding.
Keywords: CCFL, air-water, stratified flow
  • Contribution to proceedings
    18th International Conference on Nuclear Engineering (ICONE18), paper ICONE18-29092, 17.-21.05.2010, Xi’an, China
    Proceedings of the 18th International Conference on Nuclear Engineering

Permalink: https://www.hzdr.de/publications/Publ-13731
Publ.-Id: 13731


Extension of the Inhomogeneous MUSIG model for bubble condensation

Lucas, D.; Frank, T.; Lifante, C.; Zwart, P.; Burns, A.
Bubble condensation plays an important role e.g. in sub-cooled boiling or steam injection into pools. Since the condensation rate is proportional to the interfacial area density, bubble size distributions have to be considered in an adequate modeling of the condensation process. The effect of bubble sizes was clearly shown in experimental investigations done previously at the TOPFLOW facility of FZD. Steam bubbles were injected into a sub-cooled upward pipe flow via orifices in the pipe wall located at different distances from measuring plane. 1 mm and 4 mm injection orifices were used to vary the initial bubble size distribution. Measurements were done using a wire-mesh sensor. Condensation is clearly faster in case of the injection via the smaller orifices, i.e. in case of smaller bubble sizes. Recently the Inhomogeneous MUSIG model was implemented into the CFD code CFX from ANSYS enabling the simulation of poly-dispersed flows including the effects of separation of small and large bubbles due to bubble size dependent lift force inversion. It allows to divide the dispersed phase into size classes regarding the mass as well as regarding the momentum balance. Up to now transfers between the classes in the mass balance can be considered only by bubble coalescence and breakup (population balance). Here an extension of the model is proposed to include the effects due to phase transfer. The paper focuses on the derivation of equations for the extension of the Inhomogeneous MUSIG model and presents some first results for verification and validation.
Keywords: two-phase flow, condensation, bubbly flow, poly-dispersion, CFD, MUSIG

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Permalink: https://www.hzdr.de/publications/Publ-13730
Publ.-Id: 13730


Recent results from HADES on electron pair production in relativistic heavy-ion collisions

Galatyuk, T.; Hades Collaboration
Systematic investigations of dilepton production are performed at the SIS accelerator of GSI with the HADES spectrometer. The goal of this program is a detailed understanding of di-electron emission from hadronic systems at moderate temperatures and densities. New results obtained in HADES experiments focussing on electron pair production in elementary collisions are reported here. They pave the way to a better understanding of the origin of the so-called excess pairs earlier on observed in heavy-ion collisions by the DLS collaboration and lately confirmed in two measurements of the HADES collaboration using C+C and Ar+KCl collisions. Results of these studies are discussed.
  • Contribution to proceedings
    5th International Workshop on Critical Point and Onset of Deconfinement - CPOD 2009, 08.-12.06.2009, New York, USA
    arXiv:0911.2411

Permalink: https://www.hzdr.de/publications/Publ-13729
Publ.-Id: 13729


Omega and Eta (Eta-prime) mesons from NN and ND collisions at intermediate energies

Kaptari, L. P.; Kämpfer, B.
The production of pseudo scalar, Eeta, Eta-prime, and vector, Omega, Rho, Phi, mesons in NN collisions at threshold-near energies is analyzed within a covariant effective meson-nucleon theory. It is shown that a good description of cross sections and angular distributions, for vector meson production, can be accomplished by considering meson and nucleon currents only, while for pseudo scalar production an inclusion of nucleon resonances is needed. The di-electron production from subsequent Dalitz decay of the produced mesons, eta' to gamma gamma^* to gamma e^+e^- and omega to pi gamma^* to pi e^+e^- is also considered and numerical results are presented for intermediate energies and kinematics of possible experiments with HADES, CLAS and KEK-PS.
We argue that the transition form factor omega to gamma^* pi as well as eta' to gamma^* gamma can be defined in a fairly model independent way and the feasibility of an experimental access to transition form factors is discussed.

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Permalink: https://www.hzdr.de/publications/Publ-13728
Publ.-Id: 13728


Ionen als Agenten und Detektive

Neelmeijer, C.
Dieser Vortrag für Schüler zeigt auf, wie Protonenstrahlanalytik an Atmosphäre erfolgt, welcher Informationsgehalt durch die Kombination von PIGE-PIXE-RBS gewonnen wird und welche typische Fragestellungen damit beantwortrt werden können.
Keywords: zerstörungsfreie Analyse, Kunstwerke, Unikate, mikroelektronische Strukture
  • Lecture (others)
    Schülervortrag, 01.02.2010, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-13727
Publ.-Id: 13727


Laser proton acceleration - First experiments

Zeil, K.; Kraft, S.; Metzkes, J.; Richter, T.; Bock, S.; Bussmann, M.; Kluge, T.; Schramm, U.; Cowan, T.; Sauerbrey, R.
In this talk first experiments of proton acceleration with the Draco laser are presented.
  • Lecture (Conference)
    American Physical Society: 51st Annual Meeting of the Division of Plasma Physics, 03.11.2009, Atlanta, United States of America

Permalink: https://www.hzdr.de/publications/Publ-13725
Publ.-Id: 13725


The Role of Transferrin in Actinide(IV) Uptake: Comparison with Iron(III)

Jeanson, A.; Ferrand, M.; Funke, H.; Hennig, C.; Moisy, P.; Solari, P. L.; Vidaud, C.; Den Auwer, C.
The impact of actinides on living organisms has been the subject of numerous studies since the 1950s. From a general point of view, these studies show that actinides are chemical poisons as well as radiological hazards. Actinides in plasma are assumed to be mainly complexed to transferrin, the iron carrier protein. This paper casts light on the uptake of actinides(IV) (thorium, neptunium, plutonium) by transferrin, focusing on the pH dependence of the interaction and on a molecular description of the cation binding site in the protein. Their behavior is compared with that of iron(III), the endogenous transferrin cation, from a structural point of view. Complementary spectroscopic techniques (UV/Vis spectrophotometry, microfiltration coupled with g spectrometry, and X-ray absorption fine structure) have been combined in order to propose a structural model for the actinide-binding site in transferrin. Comparison of our results with data available on holotransferrin suggests some similarities between the behavior of FeIII and NpIV/PuIV/ NpIV is not complexed at pH <7, whereas at pH ≈7.4 complexation can be regarded as quantitative. This pH effect is consistent with the in vivo transferrin “cycle”. PuIV also appears to be quantitatively bound by apotransferrin at around pH ~7.5, whereas ThIV was never complexed under our experimental conditions. EXAFS data at the actinide edge have allowed a structural model of the actinide binding site to be elaborated: at least one tyrosine residue could participate in the actinide coordination sphere (two for iron), forming a mixed hydroxo–transferrin complex in which actinides are bound with transferrin both through An–tyrosine and through An-OH bonds. A description of interatomic distances is provided.
Keywords: Actinides, Transferrin, EXAFS

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Permalink: https://www.hzdr.de/publications/Publ-13724
Publ.-Id: 13724


Influence of air entrainment on the liquid flow field caused by a plunging jet and consequences for fibre deposition

Krepper, E.; Weiß, F.-P.; Alt, S.; Kratzsch, A.; Renger, S.; Kästner, W.
Plunging jets play an important role in nuclear reactor safety research. In the present paper the case of the strainer clogging issue is considered. Entrained air caused by a plunging jet has an influence of the liquid flow field and on the fibre transport in the sump. In the paper the amount of entrained air is given as an inlet boundary condition according to correlations in the literature and confirmed by own experiments. The influence of entrained air on the fibre deposition pattern at the bottom of a tank and on the mixing procedure for the case of temperature differences between jet and tank water are investigated by Computational Fluid Dynamics (CFD) calculations and compared to experiments.
The presented work is part of a joint research project performed in cooperation between the University of Applied Science Zittau/Görlitz and Forschungszentrum Dresden-Rossendorf. The project deals with the experimental investigation of particle transport phenomena in coolant flow in Zittau and the development of CFD models for its simulation in Rossendorf Whereas an overview and a description of the main concepts of this project are described by Krepper et al. 2008, 2009, the focus of the actual paper is directed on the different aspects of a jet.
The entrained air has a remarkably influence on the generation of swirls und therefore on the transport and deposition of fibres. At least qualitative conclusions concerning main effects, critical regions of fibre deposition and design improvements avoiding undesired fibre deposition can be drawn. The CFD simulation of the sump flow conditions during a real accident scenario over several 1000 seconds however will fail caused by the large computational effort.
Keywords: fibres, experiments, cfd, multiphase flow

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Permalink: https://www.hzdr.de/publications/Publ-13723
Publ.-Id: 13723


Electron bunch length measurements from laser-accelerated electrons using single-shot THz time-domain interferometry

Debus, A. D.; Bussmann, M.; Schramm, U.; Sauerbrey, R.; Murphy, C. D.; Major, Z.; Hörlein, R.; Veisz, L.; Schmid, K.; Schreiber, J.; Witte, K.; Jamison, S. P.; Gallacher, J. G.; Jaroszynski, D. A.; Kaluza, M. C.; Hidding, B.; Kiselev, S.; Heathcote, R.; Foster, P. S.; Neely, D.; Divall, E. J.; Hooker, C. J.; Smith, J. M.; Ertel, K.; Langley, A. J.; Norreys, P.; Collier, J. L.; Karsch, S.
Laser-plasma wakefield based electron accelerators are expected to deliver ultrashort electron bunches with and unprecedented peak currents. However, their actual pulse duration has never been directly measured in a single-shot experiment.
We present measurements of the ultrashort duration of such electron bunches by means of THz time-domain interferometry. With data obtained using a 0.5J, 45fs, 800nm laser and a ZnTe-based electro-optical setup we demonstrate the duration of laser-accelerated, quasi-monoenergetic electron bunches (best fit of 32fs (FWHM) with a 90% upper confidence level of 38fs) to be shorter than the drive laser pulse, but similar to the plasma period.
Keywords: electron bunch length measurement coherent transition radiation laser plasma wakefield acceleration
  • Physical Review Letters 104(2010), 084802
    DOI: 10.1103/PhysRevLett.104.084802
  • Lecture (Conference)
    DPG Tagung 2010, 08.-12.03.2010, Hannover, Deutschland
  • Lecture (Conference)
    TR18-Treffen Bad Breisig, 04.03.-05.05.2010, Bad Breisig, Deutschland

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Permalink: https://www.hzdr.de/publications/Publ-13722
Publ.-Id: 13722


Absolute charge calibration of scintillating screens for relativistic electron detection

Buck, A.; Zeil, K.; Popp, A.; Schmid, K.; Jochmann, A.; Kraft, S.; Hidding, B.; Kudyakov, T.; Sears, C.; Veisz, L.; Karsch, S.; Pawelke, J.; Sauerbrey, R.; Cowan, T.; Krausz, F.; Schramm, U.
We report on new charge calibrations and linearity tests with high-dynamic range for eight different scintillating screens typically used for detection of relativistic electrons from laser-plasma based acceleration schemes. The absolute charge calibration was done with picosecond electron bunches at the ELBE linear accelerator in Dresden. The lower detection limit in our setup for the most sensitive scintillating screen (KODAK Biomax MS) was 10 fC / mm2. The screens showed a linear photon-to-charge dependency over several orders of magnitude. An onset of saturation effects starting around 10 - 100 pC / mm2 was found for some of the screens. Additionally, a constant light source was employed as a luminosity reference, to simplify the transfer of a one-time absolute calibration to different experimental setups.

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Permalink: https://www.hzdr.de/publications/Publ-13720
Publ.-Id: 13720


Absolute response of Fuji imaging plate detectors to picosecond-electron bunches

Zeil, K.; Kraft, S. D.; Jochmann, A.; Kroll, F.; Jahr, W.; Schramm, U.; Karsch, L.; Pawelke, J.; Hidding, B.; Pretzler, G.
The characterization of the absolute number of electrons generated by laser wakefield acceleration often relies on absolutely calibrated FUJI imaging plates (IP), although their validity in the regime of extreme peak currents is untested. Here, we present an extensive study on the dependence of the sensitivity of BAS-SR and BAS-MS IP to picosecond electron bunches of varying charge of up to 60 pC, performed at the electron accelerator ELBE, making use of about three orders of magnitude of higher peak intensity than in prior studies. We demonstrate that the response of the IPs shows no saturation effect and that the BAS-SR IP sensitivity of 0.0081 photostimulated luminescence per electron number confirms surprisingly well data from previous works. However, the use of the identical readout system and handling procedures turned out to be crucial and, if unnoticed, may be an important error source.
  • Review of Scientific Instruments 81(2010)1, 013307

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Permalink: https://www.hzdr.de/publications/Publ-13719
Publ.-Id: 13719


P0803 - Verfahren zur Herstellung für Kohlenstoffnanoröhrchen, durch das Verfahren hergestellte Kohlenstoffnanoröhrchen und deren Verwendung

Abrasonis, G.; Pollmann, K.; Raff, J.
Die Erfindung betrifft ein Verfahren, mit dessen Hilfe Kohlenstoffnanoröhrchen mit definiertem Durchmesser auf einem Substrat in gleichmäßiger Ausrichtung hergestellt werden können. Bei dem erfindungsgemäßen Verfahren wird die Eigenschaft von selbstorganisierenden Molekülen, geordnete Schichten auszubilden, ausgenutzt, um einheitliche Nanopartikel auf einem Trägersubstrat geordnet zu erzeugen und damit Nanokohlenstoffröhrchen mit definierter Anordnung auf diesem Trägersubstrat zu synthetisieren. Dazu bringt man zunächst eine Schicht aus selbstorganisierenden Molekülen auf ein Trägersubstrat auf und erzeugt auf der Schicht aus selbstorganisierenden Molekülen anorganische Nanopartikel. Anschließend wird die Schicht aus selbstorganisierenden Molekülen entfernt, wobei die anorganischen Nanopartikel auf dem Trägersubstrat zurückbleiben und an den Nanopartikeln Nanokohlenstoffröhrchen synthetisiert werden. Mit dem erfindungsgemäßen Verfahren können Kohlenstoffröhrchen mit definierter Größe in hoher Ausbeute und Einheitlichkeit hergestellt werden.
  • Patent
    DE 10 2008 023 229 A1 - 12.11.2009
  • Patent
    EP 2123602 A1 - 25.11.2009
  • Patent
    EP2123602B1: Erteilung-16.01.2013; Validierung in DE, FR, GB

Permalink: https://www.hzdr.de/publications/Publ-13717
Publ.-Id: 13717


2d-2c ultrasound Doppler array velocimeter for flow investigations in liquid metals

Franke, S.; Lieske, H.; Fischer, A.; Büttner, L.; Czarske, J.; Räbiger, D.; Eckert, S.
In magnetohydrodynamics ultrasound Doppler velocimetry (UDV) is applied for flow field investigations of liquid metal flows. Thereto, commercial UDV instruments are available. However, their application possibility for multi-dimensional, multi-componential flow mapping with high measurement rates is highly limited since these features cannot be applied simultaneously. Hence, we have developed an ultrasound Doppler velocimeter for measuring the two-dimensional two-componential (2d-2c) flow field of magnetically driven liquid metal. The velocimeter utilizes two identical linear ultrasound Doppler arrays arranged orthogonally to each other to facilitate the 2d-2c flow mapping in a plane of 70 x 70 mm². Each ultrasound array providing a centre frequency of 8 MHz comprises 25 transducer elements each with a piezo element size of 2.5 x 5 mm². In operation two adjacent elements are combined to a square transducer pair of 5 x 5 mm² allowing a small lateral scanning step width of 2.5 mm on the one hand and a low divergence of the ultrasound beam and accordingly a better lateral resolution up to 2 mm on the other hand. To achieve a high temporal resolution concurrently to the high spatial resolution, the measurement is parallelized as much as possible by simultaneous operation of four transducer pairs which are controlled by a special multiplex control unit. The operation principle, design considerations and the characterisation of the ultrasound Doppler array velocimeter will be reported. Flow mapping of a swirling flow in a cubic vessel with GaInSn generated by a rotating magnetic field were performed. Measurement results of a stationary as well as a periodically reversed flow will be presented.
Keywords: Ultrasound Doppler method, sensor array, liquid metal, rotating magnetic field
  • Lecture (Conference)
    6th Annual European Rheology Conference (AERC2010), ISUD7, 07.-09.04.2010, Göteborg, Schweden
  • Contribution to proceedings
    6th Annual European Rheology Conference (AERC2010), ISUD7, 07.-09.04.10, Göteborg, Schweden
    Proceedings of the 7th International Symposium on Ultrasonic Doppler Methods for Fluid Mechanics and Fluid Engineering, 89-92

Permalink: https://www.hzdr.de/publications/Publ-13716
Publ.-Id: 13716


Ultrasonic flow measurements in a low temperature liquid metal model of the continuous steel casting process

Timmel, K.; Eckert, S.; Gerbeth, G.
Fluid flow in the mould cavity of the continuous casting process can be controlled by the application of magnetic fields. Experiments have been performed at room temperature using a small-scale experimental set-up with the eutectic alloy GaInSn. The ultrasound Doppler method was applied for measuring the fluid velocity in the mould. An arrangement of 10 transducers was used to determine a two-dimensional distribution of the horizontal velocity component. According to the concept of the electromagnetic brake the impact of a DC magnetic field on the outlet flow from the submerged entry nozzle (SEN) has been studied. Our measurements deliver an authentic reproduction of the location and extension of the emergent jet and disclose the temporal behaviour of the flow inside the jet as well as in the recirculating zones. An important result of our study was the feature that a static magnetic field may give rise to non-steady, non-isotropic large-scale flow perturbations. Likewise, the flow measurements presented here did not confirm the expectation of a smooth reduction of the velocity fluctuations at the nozzle outlet due to the magnetic field. This problem requires further investigation, because the concept of an EMBR in the continuous casting process relies on a reliable damping effect of the applied magnetic field. The combination of liquid metal cold models and the ultrasound Doppler method as a powerful flow measuring technique in liquid metals appears as an important tool for an experimental investigation of such open questions and provides valuable experimental data for the validation of numerical flow simulations.
Keywords: continuous casting, liquid metal model experiment, flow measurements, Ultrasound Doppler Velocimetry
  • Lecture (Conference)
    6th Annual European Rheology Conference (AERC2010), ISUD7, 07.-09.04.2010, Göteborg, Schweden
  • Contribution to proceedings
    6th Annual European Rheology Conference (AERC2010), ISUD7, 07.-09.04.10, Göteborg, Schweden
    Proceedings of the 7th International Symposium on Ultrasonic Doppler Methods for Fluid Mechanics and Fluid Engineering, 93-96

Permalink: https://www.hzdr.de/publications/Publ-13715
Publ.-Id: 13715


Investigations of the bulk flow inside a cylindrical liquid metal column generated by diverse AC magnetic fields

Räbiger, D.; Zhang, C.; Grants, I.; Eckert, S.; Gerbeth, G.
This presentation considers various situations where the flow inside a liquid metal column is driven by different configurations of AC magnetic fields. The ultrasonic Doppler method has been used to determine profiles of the fluid velocity in the ternary alloy GaInSn. The azimuthal and vertical velocity components have been measured allowing for an analysis of both a swirling flow in the horizontal planes and the flow pattern in the radial-meridional plane. In the first part we consider the transient liquid metal flow which is generated inside a cylindrical container by the discontinuous application of a rotating magnetic field (RMF) and the alternating application of subsequent RMF and TMF pulses, respectively. Such new approaches have been recently suggested for melt stirring during solidification of metal alloys in order to control the heat and mass transfer at the solidification front. The second part is concerned with an RMF-driven flow which is influenced by an oxide layer at the free surface of the metallic melt. The oxide layer feels the effect of the viscous force arising from the moving liquid beneath and the friction force from the side walls. A complex interaction occurs if the both forces are in the same order of magnitude. In that case, our measurements demonstrate that the occurrence of the oxide layer may lead to an unexpected oscillating behaviour of the bulk flow. Finally, we study the combination of a travelling and a rotating magnetic field which may generate a specific flow phenomenon in form of a concentrated vortex with properties similar to a tornado. The travelling magnetic field (TMF) creates an intense converging flow at one end of the cylinder whereas the additionally superimposed rotating magnetic field (RMF) with a substantially different frequency sets the flow into rotation. The angular momentum conservation forces the rotation to intensify towards the centre of the converging flow. This phenomenon may be useful to stir floating particles into the melt.
Keywords: liquid metal, electromagnetic stirring, mixing, Ultrasound Doppler Velocimetry
  • Lecture (Conference)
    6th Annual European Rheology Conference (AERC2010), ISUD7, 07.-09.04.2010, Göteborg, Schweden
  • Contribution to proceedings
    6th Annual European Rheology Conference (AERC2010), ISUD7, 07.-09.04.10, Göteborg, Schweden
    Proceedings of the 7th International Symposium on Ultrasonic Doppler Methods for Fluid Mechanics and Fluid Engineering, 81-84

Permalink: https://www.hzdr.de/publications/Publ-13714
Publ.-Id: 13714


Experimental modeling of the continuous casting process of steel using low melting point metal alloys - the LIMMCAST program

Timmel, K.; Eckert, S.; Gerbeth, G.; Stefani, F.; Wondrak, T.
This paper presents the new experimental facility CONCAST which was designed for modeling fluid flow and transport processes in the continuous casting of steel. The facility operates at temperatures of 200°C - 400°C by using the low melting point alloy SnBi. The main parameters of the facility, including the dimensions of the test sections, will be given. The resultant possibilities with respect to flow investigations in the tundish, in the submerged entry nozzle, and in the mould will be discussed. Over the period of assembling and commissioning the CONCAST facility, the small-scale set-up Mini-CONCAST was employed which uses the alloy GaInSn that is liquid at room temperatures. At this precursory facility an experimental program was started which is focused on quantitative flow measurements in the mould and in the submerged entry nozzle (SEN). The Ultrasound Doppler Velocimetry (UDV) and the Contactless Inductive Flow Tomography (CIFT) were applied to determine the flow structure within the mould. First experimental results will be presented here for a single and a two-phase flow in which argon gas bubbles were injected at the inlet of the SEN. According to the concept of the electromagnetic brake the impact of a DC magnetic field on the emergent jet flow from the SEN has been studied.
Keywords: continuous casting, liquid metal model experiments, flow measurements, two-phase flow, electromagnetic brake

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Permalink: https://www.hzdr.de/publications/Publ-13713
Publ.-Id: 13713


P0710 - Verfahren zur Reduzierung von Temperaturfluktuationen in Schmelzen

Grants, I.; Gerbeth, G.
Die Erfindung betrifft ein Verfahren zur Reduzierung von Temperaturfluktuationen in Halbleiter- oder Metall-Schmelzen. Das Hauptinteresse gilt vor allem Schmelzen in Kristallzüchtungsprozessen wie Gallium-Arsenid (GaAs), Indium-Phosphid (InP) oder Silizium (Si).
Mit der Erfindung werden große Temperaturfluktuationen in der Schmelze unterdrückt, die den Prozess des Kristallwachstums stören bzw. teilsweise unmöglich machen.
Durch den Einsatz dieses Verfahrens können deutlich größere Schmelzvolumina als heute üblich verwendet werden.
  • Patent
    DE 10 2007 036 944 A1 - 05/02/09
  • Patent
    EP 2090679 A1 - 19/08/09

Permalink: https://www.hzdr.de/publications/Publ-13712
Publ.-Id: 13712


P0712 - Verfahren und Einrichtung zum elektromagnetischen Rühren von elektrisch leitenden Flüssigkeiten

Eckert, S.; Räbiger, D.; Willers, B.; Gerbeth, G.; Nikrityuk, P. A.; Eckert, K.; Grundmann, R.
Die Erfindung betrifft ein Verfahren und eine Einrichtung zum elektromagneti-schen Rühren elektrisch leitfähiger Flüssigkeiten (2) unter Verwendung eines in der horizontalen Ebene rotierenden Magnetfeldes RMF (34) und eines dazu in vertikaler Richtung wandernden Magnetfeldes WMF (47).

Die Aufgabe besteht darin, dass unsymmetrische Strömungsstrukturen in mit Schmelzen gefüllten Behältern, insbesondere zu Beginn und während des Ver-laufs der Erstarrung vermieden werden. Außerdem sollen eine effektive Durch-mischung der Flüssigkeit und/oder eine kontrollierte Erstarrung metallischer Le-gierungen unter Vermeidung der Ausbildung von Entmischungszonen im Erstar-rungsgefüge erreicht werden.

Die Lösung besteht darin, dass sowohl das rotierende Magnetfeld RMF (34) als auch das wandernde Magnetfeld WMF (47) diskontinuierlich in Form von zeitlich begrenzten und einstellbaren Periodendauern (TP,RMF,TP,WMF) und abwechselnd zeitlich nacheinander über zugehörige Induktionsspulen (31,32,33;41,42,43,44, 45,46) zugeschaltet werden.
  • Patent
    Patent DE 10 2007 038 281 B4 - 2009/06/18
  • Patent
    DE 10 2007 038 281 A1 - 19/02/2009
  • Patent
    WO 2009/018810 - 12/02/2009

Permalink: https://www.hzdr.de/publications/Publ-13711
Publ.-Id: 13711


P0711 - Verfahren und Einrichtung zum elektromagnetischen Rühren von elektrisch leitenden Flüssigkeiten

Eckert, S.; Räbiger, D.; Willers, B.; Gerbeth, G.; Nikrityuk, P. A.; Eckert, K.; Grundmann, R.
Die Erfindung betrifft ein Verfahren und eine Einrichtung zum elektromagnetischen Rühren von elektrisch leitenden Flüssigkeiten (2,21,22) im flüssigen Zustand und/oder im Zustand des Beginns der Erstarrung der Flüssigkeit (2,21,22) unter Verwendung eines in der horizontalen Ebene eine Lorentzkraft (FL) erzeugenden, rotierenden Magnetfeldes.
Die Aufgabe besteht darin, dass eine intensive dreidimensionale Strömung im In-nern der Flüssigkeit zum Durchmischen im flüssigen Zustand bis in die unmittelbare Umgebung von Erstarrungsfronten erreicht und gleichzeitig eine ungestörte, freie Oberfläche der Flüssigkeit gewährleistet werden. ...
  • Patent
    DE102007037340A1: Offenlegung-19.02.2009; Nachanmeldung WO (nationalisiert in US, EP, JP, US)
  • Patent
    Patent DE102007037340B4 2010/02/25

Permalink: https://www.hzdr.de/publications/Publ-13710
Publ.-Id: 13710


P0709 - Flüssigmetall-Ionenquelle zur Erzeugung von Lithium-Ionenequelle

Bischoff, L.; Akhmadaliev, S.
Die Erfindung betrifft eine Flüssigmetall-Ionenquelle (LMIS) zur Erzeugung von Lithiumionenstrahlen, insbesondere das den Emitter benetzende Quellenmaterial einer derartigen Ionenquelle.
Die Erfindung beinhaltet Flüssigmetall-Ionenquellen, deren Emitter mit einer definierten Legierung aus Lithium und einem oder mehreren der Elemente Gallium, Indium und Wismut als Quellenmaterial benetzt ist.
Mit derart ausgestatteten Flüssigmetall-Ionenquellen ist es möglich, langzeitig einen stabilen Ionenstrom, der im ausreichendem Maße aus Lithiumionen besteht, zu erhalten.
Die Bestandteile der Legierung im Zusammenspiel mit dem niedrigen Schmelzpunkt führen dazu, dass keine chemischen Reaktionen mit dem Emitter- und Heizermaterial auftreten sowie die Legierungsoberfläche relativ langsam an Luft korrodiert.
  • Patent
    DE 10 2007 027 097 A1

Permalink: https://www.hzdr.de/publications/Publ-13709
Publ.-Id: 13709


Combined Computational and Experimental Study of Uranyl(VI) 1:2-Complexation by Aromatic Acids

Wiebke, J.; Weigand, A.; Weißmann, D.; Glorius, M.; Moll, H.; Bernhard, G.; Dolg, M.
The bis(salicylhydroxamato), bis(benzohydroxamato), and bis(benzoato) complexes of UO22+ in aqueous solution have been investigated in a combined experimental and computational effort using extended X-ray absorption fine structure and UV−vis spectroscopy, and density functional theory (DFT) techniques, respectively. Experimental data indicates 5-fold UO22+ coordination with mean equatorial U−O distances of 2.42 and 2.40 Å for the salicyl- and benzohydroxamate systems, respectively. DFT calculations on microsolvated model systems [UO2L2OH2] indicate UO22+ eta-2-chelation via the hydroxamate and benzoate oxygen atoms in excellent agreement with experimental data; calculated complex stabilities support that UO22+ prefers hydroxamate over carboxylate coordination. The 414 nm absorption band of UO22+ in aqueous solution is blue-shifted to 390 and 386 nm upon complexation by salicyl- and benzohydroxamate, respectively. Calculated time-dependent DFT excitation energies of [UO2L2OH2], however, occasionally fail to reproduce accurately experimental UV−vis spectra, which are dominated by L− -to- UO22+ charge-transfer contributions. We additionally show that the UVI large-core pseudopotential approximation recently developed by some of the authors can routinely be applied for electronic structure calculations not involving uranium 5f occupations significantly different from UVI.
Keywords: Density-Functional Theory, Uranyl-Ion, Electronic-structures, Molecular-Structure, Hydroxamic acids, Benzoic acid

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Permalink: https://www.hzdr.de/publications/Publ-13708
Publ.-Id: 13708


Burning plutonium and minimizing radioactive waste in existing PWRs

Mittag, S.; Kliem, S.
Plutonium and other long-lived radioactive actinides are produced in light water reactors (LWR) using conventional fuel. "Innovative" fuel matrices may reduce the breeding of these nuclides. However, essential LWR safety features have to be preserved, which restricts the possibilities for new fuel-carrying matrices. Respective fuel-assembly and LWR-core safety studies indicate practicable new fuel options for the near future.

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Permalink: https://www.hzdr.de/publications/Publ-13706
Publ.-Id: 13706


Radiotracer studies on interaction processes related to humic-bound transport of radionuclides

Lippold, H.; Lippmann-Pipke, J.
Colloid-borne transport of actinides in aquifer systems is a topic of major interest in view of long-term risk assessments for underground radwaste repositories. In particular, complexation with aquatic humic substances can be decisive for the mobility of radiotoxic metals [1,2]. Depending on geochemical parameters, migration can be both enhanced and reduced. The respective conditions need to be identified, and models must be able to describe such complex systems by few parameters. According to the Linear Additive Model [3], total metal adsorption in the presence of humic matter can be calculated by linking parameters for the adsorption of both components and their interaction with each other. The basics of this approach are also implicit in advanced transport models [4].
In our study, the influence of humic acid on metal adsorption onto three clay materials (montmorillonite, illite, Opalinus clay) as a function of pH was investigated for Tb(III) as an analogue of trivalent actinides. 160Tb and 131I-labelled humic acid were used as radiotracers, allowing experiments at very low concentrations to mimic realistic conditions. For all clay materials under study, the presence of humic acid caused an increase in metal adsorption at neutral and acidic pH, i.e., metal desorption from clay barriers in consequence of acidification processes is generally counteracted in the presence of humic matter. Based on the pH-dependences of humic acid adsorption and Tb-humate complexation, this can be qualitatively explained by co-adsorption of humic-bound Tb. Quantitative estimates by means of the Linear Additive Model were, however, not successful.
In equilibrium models (Kd models), it is presumed that reaction rates for adsorption and desorption are both high enough to ensure a steady local equilibrium under flow conditions. Regarding the adsorption of humic substances onto geological materials, however, there is a lack of clarity concerning the dynamic character of this process. Recoveries in column experiments suggest a limited reversibility. In order to gain direct insight into the dynamics of the adsorption-desorption equilibrium, we conducted tracer exchange experiments with 14C-labelled humic acid. A negligible amount of the radiotracer was contacted with equilibrated systems of kaolinite and non-labelled humic acid for different periods of time. Tracer exchange at surface saturation provided evidence of a reversible process, but the time needed until the dynamic equilibrium was quantitatively represented by the tracer turned out to be much longer than the time needed to attain the overall adsorption equilibrium. This discrepancy between exchange kinetics and adsorption kinetics, which is indicative of a very slow desorption rate, has to be taken into consideration when the equilibrium condition is assigned to a maximum flow rate in transport systems.
  • Lecture (Conference)
    11th International Symposium on Environmental Radiochemical Analysis, 15.-17.09.10, Chester, United Kingdom

Permalink: https://www.hzdr.de/publications/Publ-13705
Publ.-Id: 13705


Counter-current flow limitation in a model of the hot leg of a PWR - comparison between air/water and steam/water experiments

Vallée, C.; Seidel, T.; Lucas, D.; Beyer, M.; Prasser, H.-M.; Pietruske, H.; Schütz, P.; Carl, H.
In order to investigate the two-phase flow behaviour in a complex reactor-typical geometry and to supply suitable data for CFD code validation, a model of the hot leg of a pressurised water reactor was built at Helmholtz-Zentrum Dresden Rossendorf (HZDR). The hot leg model is devoted to optical measurement techniques, therefore, a flat test section design was chosen and equipped with large windows. In order to enable the operation at high pressures, the test section is installed in the pressure chamber of the TOPFLOW test facility of HZDR, which is used to perform the experiments under pressure equilibrium with the inside atmosphere. Counter-current flow limitation (CCFL) experiments were performed, simulating the reflux-condenser cooling mode appearing in small break LOCA scenarios. The fluids used were air and water at room temperature and pressures of up to 3.0 bar, as well as steam and water at pressures of up to 50 bar and the corresponding saturation temperature of 264°C. One selected 50 bar experiment is presented in detail: the observed behaviour is analysed and illustrated by typical high-speed camera images of the flow.

Furthermore, the flooding characteristics obtained from the different experimental runs are presented in terms of the Wallis parameter and Kutateladze number, which are commonly used in the literature. However, a discrepancy was first observed between the air/water and steam/water series. Further investigations show that the steam was probably wet due to heat losses and to liquid entrainment from the heater circuit. Consequently, a correction of the steam measurements was required. The amount of parasitic water was evaluated indirectly over the zero liquid penetration noticed in the CCFL diagram. Finally, the experimental results confirm that the Wallis similarity is appropriate to scale flooding in the hot leg of a pressurised water reactor over a wide range of pressure and temperature conditions.
Keywords: two-phase flow, counter-current flow limitation, flooding, hot leg, pressurised water reactor

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Permalink: https://www.hzdr.de/publications/Publ-13704
Publ.-Id: 13704


Gamma ray imaging with Compton camera

Schöne, S.; Shakirin, G.; Enghardt, W.
Feasibility of Compton camera for monitoring of ion beam therapy as well as for recognition of weak radioactive sources in a security interests application was investigated. First reconstruction results are presented.
Keywords: Compton camera monitoring ion beam therapy recognition of weak radioactive sources security interests application image reconstruction
  • Poster
    OncoRay Retreat Meeting 2010, 27.-28.01.2010, Bautzen, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-13703
Publ.-Id: 13703


Zur Gipsauflösung in Batch- und Säulenversuchen

Zorn, T.; Küchler, R.; Noack, K.; Dittmar, T.; Worch, E.
Die Auflösung von Gips, als ein Vertreter für Minerale mit einer hohen Auflösungsrate, wurde unter wassergesättigten und wasserungesättigten Bedingungen anhand von Batch- und Säulenexperimenten untersucht. Die erhaltenen experimentellen Daten wurden den numerischen Lösungen gegenübergestellt und mit ihnen verglichen. Die Säulenexperimente wurden mit einer Fließgeschwindigkeit des Wassers von υ = 0,015 cm/h durchgeführt. Es zeigte sich, dass unter wasserungesättigten Bedingungen nur ein sehr kleiner Teil der Oberfläche der Körner von 2,2 % als reaktiver Part fungiert. Weiterhin zeigten die Ergebnisse, dass die Auflösung von Gips in der Säule hauptsächlich durch die Darcy-Geschwindigkeit bestimmt wird.

The dissolution of gypsum under water-saturated and unsaturated conditions was studied using batch and column experiments. The experimental results were successfully verified with the use of model calculations. The column experiments were performed with a water flow velocity of 0.015 cm/h. Comparing the dissolution experiments, we conclude that under unsaturated conditions only 2.2 % of the grain surface is chemically reactive. Experiments and calculations show that gypsum dissolution in the columns is mainly determined by the Darcian velocity.
Keywords: unsaturated zone • batch and column experiments • modelling • dissolution
  • Grundwasser 14(2009)4, 287-295

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Permalink: https://www.hzdr.de/publications/Publ-13702
Publ.-Id: 13702


Entwicklung einer unterstützenden Auswerteroutine für in-beam PET bei der Ionentherapie

Santiago, A.; Fiedler, F.; Skowron, J.; Shakirin, G.; Enghardt, W.
no abstract available
Keywords: in-beam PET, monitoring of ion therapy, qualtiy assurance
  • Poster
    Oncoray Retreat, 28.-29.01.2010, Bautzen, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-13701
Publ.-Id: 13701


Electrical control of magnetoresistance in highly insulating Co-doped ZnO

Xu, Q.; Zhou, S.; Bürger, D.; Hochmuth, H.; Lorenz, M.; Grundmann, M.; Schmidt, H.
An insulating Zn0.96Co0.04O film on a highly conducting Zn0.99Al0.01O layer has been deposited on a-plane sapphire substrate by pulsed laser
deposition to study the magnetoresistance (MR) of depleted Co-doped ZnO with low electron concentration (about 1.5x1017 cm-3 at 21 K). Au ohmic contact and Pd Schottky contact were deposited on the Zn0.99Al0.01O and Zn0.96Co0.04O layer, respectively. Positive magnetoresistance (MR) of 30 % with current of 10-6 A was observed at 5 K. The positive MR decreases drastically at 5 K and changes to negative MR at 50 K with increasing current, which is considered to be due to the bias voltage control of the electron concentration in the Zn0.96Co0.04O layer. Our work demonstrates the electrically controllable magnetotransport behavior in insulating ZnO-based diluted magnetic semiconductors.
Keywords: diluted magnetic semiconductor, ZnO, magnetoresistance

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Permalink: https://www.hzdr.de/publications/Publ-13700
Publ.-Id: 13700


Improved Multimodality Imaging Using Alginate Molding in Xenograft Tumor Models

Strobel, K.; Bergmann, R.; Meister, S.; van den Hoff, J.; Pietzsch, J.
Purpose: To allow for reproducible rodent positioning using molding in multimodal tomographic imaging (positron emission tomography (PET), magnetic resonance imaging/spectroscopy (MRI/MRS)), minimization of magnetic field inhomogeneity during MRI investigations of peripheral structures, and reproducible positioning for subsequent histological sectioning of the separated tumor.
Materials and Methods: Chemical shift imaging (CSI) studies were carried out using phantoms and NMRI nu/nu mice bearing subcutaneous tumors. For embedding, three different materials were used: i) alginate, ii) gelatin, and iii) a mixture of wheat flour and salt. The animals were placed in an animal chamber including position markers visible by MRI and PET. The frozen embedded explanted tumors were sliced and examined autoradiographically as well as histologically.
Results: Alginate showed a substantial improvement of magnetic field homogeneity and histological sectioning was superior to the other methods. This embedding led to a significant reduction of the full width at half maximum (FWHM) of the water peak in the peripheral rim of the tumor in comparison to the same peak FWHM without embedding (41+-10 Hz vs. 80+-20 Hz).
Conclusions: Our research shows that animal positioning in an imaging chamber together with alginate embedding allows high quality multimodality investigations including coregistration of MRI/MRS, PET, and histological images.

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Permalink: https://www.hzdr.de/publications/Publ-13699
Publ.-Id: 13699


Photoluminescence from Si: Effect of ripple microstructures induced by argon ion irradiation

Chini, T. K.; Datta, D. P.; Lucchesi, U.; Mücklich, A.
We performed photoluminescence (PL) measurements on Si surface irradiated with 60 keV Ar+ at a fixed ion fluence of E18 ions/cm2 for two angles of ion incidence, namely 0° (with respect to surface normal of the sample) and 60°. Periodically modulated ripple morphology is observed for a 60° angle of ion incidence. The ripple microstructure consists of amorphous structure on the rear slope and a comparatively thicker amorphous layer with Ar bubbles on the front slope, whereas a uniformly thick amorphous layer with relatively large bubbles is created under normal bombardment. Room temperature PL of the rippled Si shows a visible band with a peak at ~700 nm and a strong infrared (IR) band having a peak at ~1000 nm. However, the visible PL was very weak and no IR emission was observed for normally irradiated Si.
Keywords: photoluminescence, ion irradiation, ripple

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Permalink: https://www.hzdr.de/publications/Publ-13698
Publ.-Id: 13698


Electrical properties, structure and phase composition of transparent conducting oxide thin films: effect of elevated temperatures

Vinnichenko, M.; Cornelius, S.; Rogozin, A.; Shevchenko, N.; Gago, R.; Kolitsch, A.; Möller, W.
Understanding of the mechanisms of donor impurity incorporation, its electrical activation and charge carrier transport in transparent conducting oxides (TCO) is required for further improvement of functionality of this class of materials. The present work focuses on investigation of indium oxide (IO), Sn-doped indium oxide (ITO), ZnO, and ZnO:Al (AZO) films grown by reactive pulsed magnetron sputtering (RPMS) with a precise control of the oxygen partial pressure at substrate temperatures, TS, ranging from RT to 550 °C. In order to explore potential advantages of RPMS, the relationship between the deposition parameters and structure, phase composition and physical properties of these TCOs was investigated. The films were characterized by spectroscopic ellipsometry, Hall effect measurements, X-ray diffraction (XRD) and, in case of ZnO and AZO films, by X-ray absorption near edge structures (XANES). The Sn concentration in ITO was determined by Auger analysis, while the Al concentration in ZnO matrix was estimated by elastic recoil detection analysis and Rutherford back scattering.
The comparison of the real-time behavior of the IO and ITO film structure and electrical properties during annealing provides a direct evidence of Sn donor activation (with an estimated efficiency of 40%) in ITO due to amorphous-to-crystalline transition. The ITO film crystallinity always improves with increasing substrate temperature or during isothermal annealing, with the electrical resistivity decreasing. In contrast, the electrical resistivity of AZO films shows a clear minimum at an optimum substrate temperature (200-400 °C), which depends on metal/oxygen flux ratio and correlates with a maximum in crystallinity (grain size). In this case, the highest mobility value of 46 cm2 V-1 s-1 is comparable to the best values achieved in AZO films grown by less cost-efficient techniques. This value is achieved at the free electron density of 6x1020 cm-3 which corresponds to maximum ~30% electrical activation of Al impurity. At higher temperatures, the AZO electrical properties and crystalline quality deteriorate abruptly according to the following mechanism. Increasing TS above its optimum value leads to a higher Al concentration in the AZO films, which exceeds the solubility limit and triggers the formation of an insulating metastable homologous (ZnO)3Al2O3 phase. This phase impedes crystal growth and causes a significant increase of free electron scattering both at grain boundaries and inclusions of this phase. In order to enable the growth of low-resistivity AZO films in a wider range of TS, lower metal/oxygen flux ratios should be used. The proposed approach to minimizing the influence of this undesirable phase may also be applied to other deposition methods of AZO involving high-energy particle bombardment.
Keywords: transparent conductive oxides, Sn-doped indium oxide, Al-doped ZnO, reactive pulsed magnetron sputtering, phase composition
  • Lecture (others)
    Invited lecture at Abt. Solare Brennstoffe, Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, 22.01.2010, Berlin, Germany

Permalink: https://www.hzdr.de/publications/Publ-13697
Publ.-Id: 13697


XAS on actinides – determining the coordination of solution species

Hennig, C.
This Presentation Gives An Overview On Recent Knowledge An Actinide Coordination, Speciation Complex Formation In Solutions
Keywords: EXAFS
  • Invited lecture (Conferences)
    X-ray absorption spectroscopy school - XASs2010, 14.-15.1.2010, Gent, Belgium

Permalink: https://www.hzdr.de/publications/Publ-13696
Publ.-Id: 13696


The use of EXAFS spectroscopy to determine metal coordination in solution

Hennig, C.
The availability of 3rd generation synchrotrons in Europe has strongly enhanced the use of Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy to determine the structure of systems that are not accessible with X-ray diffraction or NMR techniques alone. This presentation intends to demonstrate how the combination of EXAFS, UV-Vis and XRD provide insight in the coordination of solution species. The combination of EXAFS and UV-Vis is often successful, because both techniques are sensitive in the same concentration range. Statistical approaches like factor analysis allow the analysis of large series of titration data providing the coordination of the solution species as well as species distribution functions. At the other hand, XRD is nowadays a standard technique to reveal atomic structures of single crystals. However, there is often no link between structures in solution and its solid state structure. The capability of EXAFS to detect both, the near-order structure in solution and solid state, provides the unique opportunity to follow structural modifications during the crystallization process and to use the solid state structure or its modifications to reveal the coordination of metal complexes in solution.
Keywords: EXAFS
  • Invited lecture (Conferences)
    Institut de Chimie Moléculaire de l'Université de Bourgogne, 8.1.2010, Dijon, France

Permalink: https://www.hzdr.de/publications/Publ-13695
Publ.-Id: 13695


In-beam PET for moving targets

Laube, K.; Bert, C.; Chaudhri, N.; Fiedler, F.; Parodi, K.; Rietzel, E.; Saito, N.; Enghardt, W.
no abstract available
Keywords: in-beam PET, moving targets, ion beam therapy
  • Poster
    Oncoray Retreat, 27.-28.01.2010, Bautzen, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-13694
Publ.-Id: 13694


Advances in Si & Ge Millisecond Processing: From Silicon-on-Insulator to Superconducting Ge

Skorupa, W.
Recently we could demonstrate that advanced SOI material can be treated in advantageous manner regarding USJ formation [1]. Especially, strained Si and SiGe/Si heterostructures on insulator are promising channel materials for future nanoelectronics devices. Their successful integration into new device architectures depends on the ability of forming ultra shallow and ultra steep junctions. We present results for dopant activation in SOI, sSOI, HOI and sHOI [2]. FLA allows complete suppression of diffusion while obtaining sheet resistances lower than 500 Ω/□ in both, SOI and sSOI. Strained and unstrained SiGe heterostructures indicated significant diffusional broadening of Sb implant profiles and low electrical activation. In contrast, B shows higher activation but significant dopant loss in the near surface region. Moreover, we demonstrate that, after diamond and silicon, the third elemental group-IV semiconductor, germanium, exhibits superconductivity at ambient pressure [3]. For the first time, techniques of the state-of-the-art semiconductor processing as ion implantation and FLA were used to fabricate such material, i.e. a highly Ga-doped Ge (Ge:Ga) layer in near-intrinsic Ge. It is shown that superconductivity can be generated and tailored in the Ge host at temperatures as high as 0.5 K. Results of critical-field measurements demonstrate the quasi-two-dimensional character of superconductivity in the 60 nm thick Ge:Ga layer.

[1] F. Lanzerath, D. Buca, H. Trinkaus, M. Goryll, S. Mantl, J. Knoch, U. Breuer, W. Skorupa, B. Ghyselen, J. Appl. Phys. 104 (2008), 044908

[2] R. A. Minamisava, W. Heiermann, D. Buca, H. Trinkaus, J. Hartmann, W. Skorupa, U. Breuer, B. Ghyselen, S. Mantl, Proc. 215th ECS Meeting, Vol. 19, Issue 1, May 24-29, 2009

[3] T. Herrmannsdörfer, V. Heera, O. Ignatchik, M. Uhlarz, A. Mücklich, M. Posselt, H. Reuther, B. Schmidt, K.-H. Heinig, W, . Skorupa, M. Voelskow, C. Wündisch, R. Skrotzki, M. Helm, J. Wosnitza, Phys. Rev. Lett., 102 (2009) 217003
Keywords: millisecond processing, silicon, germanium, superconductivity, SOI
  • Invited lecture (Conferences)
    26. Deutsches Nutzertreffen "Heissprozesse und RTP", 12.11.2009, Bochum, Deutschland
  • Invited lecture (Conferences)
    17th IEEE International Conference on Advanced Thermal Processing of Semiconductors-RTP 2009, 29.09.-02.10.2009, Albany, NY, USA
  • Contribution to proceedings
    17th IEEE International Conference on Advanced Thermal Processing of Semiconductors RTP 2009, 29.07.-02.10.2009, Albany, NY, USA
    17th IEEE International Conference on Advanced Thermal Processing of Semiconductors RTP 2009, Piscataway, NJ, USA: IEEE Electron Devices Society, 978-1-4244-3816-7, 25-34

Permalink: https://www.hzdr.de/publications/Publ-13693
Publ.-Id: 13693


Nanostructuring of semiconductors with ion beams

Skorupa, W.
Surely in closed relation to the invention of the first bipolar transistor, W. Shockley filed also the first patent regarding the doping of semiconductors by ion implantation. Since that time ion beam engineering has been taken a tremendous development getting the dominant doping method of choice in chip technology. Automatically, ion beam engineering took also the move to nanotechnology with the Moore-law based miniaturisation of electronic devices.
In this lecture I will present after a short introduction into the basics of ion-solid interaction with a step-by-step philosophy the move to nanotechnology starting (1) with thinning of functional layers, then (2) moving to the world of nanowires and nanoclusters to reach finally (3) the treatment of materials with single ions. The latter item points already to dimensions of the subnano regime, to atom engineering (or, if you like, picotechnology)!
As well known, ion beam engineering is always closely connected to annealing treatments to remove the radiation-induced damage effects from the ion-treated material. With the transition to nanodimensions there developed, at least in silicon chiptechnology after the year of 2000, a need for shorter and shorter annealing times to keep the needed nanodimensions during the processing of the chips. In this context flash lamp annealing in the millisecond range will be included into the discussion of some of the topics.
The Rossendorf research center with one of the worldwide largest ion beam centers in its walls has developed a large variety of activities in the course of the last years to move its expertise in ion beam processing and short time annealing into the world of nanotechnology. Examples for the different above-mentioned approaches mostly based on Rossendorf activities, that will be touched in the lecture, are:

(1) Superconducting germanium, Doping in SOI-chips, Superthin insulator in SOI
(2) Silicon nanowires, surface patterning for ripples, nanoclusters for silicon-based light emission, diluted magnetic semiconductors (DMS)
(3) Highly charged ions etc.: Can they flatten the path to a quantum computer…?
Keywords: ion beam processing, ion implantation, nanostructures, semiconductors
  • Invited lecture (Conferences)
    LENS 2009 Summer School, 11.-14.06.2009, Reykjavik, Iceland

Permalink: https://www.hzdr.de/publications/Publ-13692
Publ.-Id: 13692


Oxygen gettering in thin buried oxide layer fabrication

Ou, X.; Kögler, R.; Skorupa, W.; Möller, W.; Wang, X.
A cavity layer or nano-bubble layer introduced by He implantation before the oxygen implantation collects the implanted oxygen and increases the oxygen concentration. The average size and density of the oxygen precipitates formed in the initial stage of the Separation-by-implanted-oxygen (SIMOX) process is conform with the size and density of the cavities pre-formed by He implantation and annealing. The gettering ability of the cavity layer for oxygen is directly related to the area of the internal surface of the cavities. A nano-bubble layer accumulates oxygen in a very narrow range occurring between the damage maximum, DP, and the mean projected ion range, RP. Such a nano-bubble layer is most efficient in oxygen gettering due to their larger area of the internal surface and the small size of the oxide precipitates initially formed at the bubbles.
Keywords: SOI, ion implantation, buried oxide, gettering
  • Poster
    EUROSOI 2009, 19.-21.01.2009, Göteborg, Sweden

Permalink: https://www.hzdr.de/publications/Publ-13691
Publ.-Id: 13691


Optical investigations of germanium nanoclusters - Rich SiO2 layers produced by ion beam synthesis

Krzyzanowska, H.; Kulik, M.; Zuk, J.; Rzodkiewicz, W.; Kobzev, A. P.; Skorupa, W.
In this work, refractive index and extinction coefficient spectra of germanium nanoclusters - rich SiO2 layers have been determined using variable angle spectroscopic ellipsometry (VASE) in the 2501000 nm range. The samples were produced by Ge+ ion implantation into SiO2 layers on Si substrates and subsequent annealing at temperatures from 700 to 1100 degrees C. It is known from previous investigations of similar samples that the Ge nanoclusterization process starts already at 800 degrees C and spherical Ge nanocrystallites 5-8 nm in diameter are observed in the SiO2 layers after annealing for I h at even higher temperatures of 1000-1100 degrees C. Rutherford backscattering spectrometry (RBS) was employed to measure the Ge atom concentration depth profiles in the studied samples. The RBS results helped us choose realistic models for the VASE analysis which were necessary for a proper interpretation of the VASE data. It has been found that the refraction index value for the SiO2/Si layer increases after Ge implantation. This effect can be explained by a defect-dependent compaction of ion-bombarded layers. A band's tail in the extinction coefficient spectra for all the samples is observed which originates from a strong ultraviolet absorption band at 6.8 eV due to a Germanium Oxygen-Deficiency Center (GeODC) and/or a Ge-E'center in SiO2. The annealing process results in the emergence of weaker extinction coefficient bands in the 400-600 nm region, associated with direct band-to-band transitions in Ge nanostructures. Transformation of these bands, including their blue-shift with the increasing annealing temperature could be explained via a quantum-confinement mechanism, by size and structural changes in Ge nanostructures.
Keywords: ion beam synthesis, ion implantation, germanium nanoclusters, Raman, RBS, ellipsometry, VASE

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Permalink: https://www.hzdr.de/publications/Publ-13690
Publ.-Id: 13690


Micro-Raman depth profile investigations of beveled Al+-ion implanted 6H-SiC samples

Zuk, J.; Romanek, J.; Skorupa, W.
6H-SiC single crystals were implanted with 450 keV Al+-ions to a fluence of 3.4 x 1015 cm-2, and in a separate experiment subjected to multiple Al+ implantations with the four energies: 450, 240, 115 and 50 keV and different fluences to obtain rectangular-like depth distributions of Al in SiC. The implantations were performed along [0 0 0 1] channeling and non-channeling ("random") directions. Subsequently, the samples were annealed for 10 min at 1650 degrees C in an argon atmosphere. The depth profiles of the implanted Al atoms were obtained by secondary ion mass spectrometry (SIMS). Following implantation and annealing, the samples were beveled by mechanical polishing. Confocal micro-Raman spectroscopic investigations were performed with a 532 nm wavelength laser beam of a 1 mu m focus diameter. The technique was used to determine precisely the depth profiles of TO and LO phonon lines intensity in the beveled samples to a depth of about 2000 nm. Micro-Raman spectroscopy was also found to be useful in monitoring very low levels of disorder remaining in the Al+ implanted and annealed 6H-SiC samples. The micro-Raman technique combined with sample beveling also made it possible the determination of optical absorption coefficient profiles in implanted subsurface layers.
Keywords: ion implantation, silicon carbide, Raman, 6H-SiC

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Permalink: https://www.hzdr.de/publications/Publ-13689
Publ.-Id: 13689


Deep-level defects study of arsenic-implanted ZnO single crystal

Zhu, C.; Ling, C.; Brauer, G.; Anwand, W.; Skorupa, W.
Unintentionally doped n-type zinc oxide (ZnC) single crystal was implanted by arsenic ions with fluence of 1014cm-2 at room temperature followed by post-implantation annealing up to 900 degrees C. Rectifying property was not observed in the As-implanted or the post-implantation annealed samples. Au Schottky contact was fabricated on the samples with the H2O2 pre-treatment. Deep-level transient spectroscopy measurements were performed on the Schottky contacts to study the deep-level defects and their thermal evolution. (C) 2008 Elsevier Ltd. All rights reserved.
Keywords: zinc oxide, doping, ion implantation, deep level

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Permalink: https://www.hzdr.de/publications/Publ-13688
Publ.-Id: 13688


Polycrystalline Ni thin films on nanopatterned Si substrates: from highly conformal isotropic to non-conformal anisotropic growth

Keller, A.; Peverini, L.; Grenzer, J.; Mücklich, A.; Facsko, S.
Nanostructured thin films are of growing relevance for numerous applications including magnetic recording media[1] and photovoltaics.[2] Control of the film and substrate morphology at the submicron scale enables the fabrication of functional thin films with tailored magnetic,[3,4,5] optical,[6,7] chemical[8,9] or biological properties.[10] Various methods have been utilized to fabricate those nanostructured thin films with well defined morphology. In the past, most of these methods have been based on lithographic techniques such as electron beam,[4] nanosphere,[6] or colloidal lithography,[8] as well as on spontaneous pattern formation during epitaxial growth[5,10] or thermal annealing.[7] However, these methods often suffer from various shortcomings, e.g. low throughput, the need of high temperatures, or a restriction to isotropic patterns. An alternative approach for creating topological nanopatterns on solid surfaces that overcomes these shortcomings uses the self-organized formation of periodic nanopatterns during broad beam ion sputtering.
Keywords: nanopatterning, thin film growth, ion sputtering, X-ray scattering

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Permalink: https://www.hzdr.de/publications/Publ-13687
Publ.-Id: 13687


Complexation of europium(III) with the zwitterionic form of amino acids studied with UV/vis and time-resolved laser-induced fluorescence spectroscopy

Heller, A.; Rönitz, O.; Barkleit, A.; Bernhard, G.; Ackermann, J.-U.
The complex formation of europium(III) with the zwitterionic form of amino acids (alanine, phenylalanine and threonine) has been studied in aqueous solution. Measurements were performed at I = 0.1 M (NaCl/NaClO4), room temperature and trace metal concentrations in the range of pH 2 to 8 using UV/vis and time-resolved laser-induced fluorescence spectroscopy. While complexation leads to a significant luminescence enhancement in the emission spectrum of the metal ion, absorption in the UV/vis spectrum of the amino acid (AA) decreases. As zwitterionic species (AAH) all three ligands form weak complexes with 1:1 stoichiometry and a general formulae of EuAAH3+ with the metal. The complex stability constants were determined to be log K ~ 1 for all complexes, indicating the negligible contribution of the amino acid side chain to the complex formation reaction.
Keywords: europium, alanine, phenylalanine, threonine, TRLFS, heavy metal speciation
  • Applied Spectroscopy 64(2010)8, 930-935

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Permalink: https://www.hzdr.de/publications/Publ-13686
Publ.-Id: 13686


P0702 - Ultraschallsensor zur Messung von lokalen Strömungsgeschwindigkeiten in flüssigen Schmelzen

Eckert, S.; Gerbeth, G.; Gundrum, T.
Die Erfindung betrifft einen dispersionsarmen Ultraschallsensor zur Messung von lokalen Strömungsgeschwindigkeiten in flüssigen Schmelzen bei hohen Temperaturen. Durch die Erfindung soll ein Ultraschallsensor zur Durchführung lokaler kontinuierlicher und zuverlässiger Geschwindigkeitsmessungen in heißen Schmelzen (T > 200°C) geschaffen werden. Erreicht wird das dadurch, dass der dispersionsarme Ultraschallsensor einen mit dem piezoelektrischen Wandler (1) verbundenen Ultraschallwellenleiter (2) aus einem Material enthält, das in einem für den Einsatzfall relevanten Temperaturbereich oberhalb von 200 °C eine geringe akustische Dämpfung aufweist sowie gegenüber der Schmelze chemisch resistent ist und dass die der Schmelze zugewandte Stirnfläche des Ultraschallwellenleiters (2) verschlossen und von der Schmelze benetzbar ist.
  • Patent
    DE 10 2007 027 391 B3 - 8.1.2009
  • Patent
    WO 2008/152031: Offenlegung-08.12.2008; Nationalisierung in EP, JP, KR, US

Permalink: https://www.hzdr.de/publications/Publ-13685
Publ.-Id: 13685


P0705 - Anordnung zur zweidimensionalen Messung der Temperaturverteilung in einem Messquerschnitt

Ritterath, M.; Hampel, U.; Da Silva, M. J.; Zimmermann, W.; Schleicher, E.
Aufgabe der vorliegenden Erfindung ist es, eine Anordnung zur Messung der Temperaturverteilung in einem Messquerschnitt anzugeben, mit der vor allem Flüssigkeits- oder Gasströmungen mit geringerem Aufwand vor allem an Verkabelung und Auswerteelektronik untersucht werden können.
Die Lösung beinhaltet im Wesentlichen, dass ein Gitter von draht- oder stabförmigen elektrischen Leitern, die innerhalb eines Sensorahmens (1) elektrisch gegeneinander und gegen das Erdpotential isoliert in zwei koplanaren Ebenen im Abstand von wenigen Millimetern aufgespannt sind, wobei die elektrischen Leiter der einen Ebene als Anregungselektroden (2) ausgeführt und parallel zueinander orientiert sind, die elektrischen Leiter der anderen Ebene als Empfängerelektroden (3) ausgebildet und ebenfalls parallel zueinander orientiert sind, sowie die Anregungselektroden (2) in einem Winkel größer 0° zu den Empfängerelektroden (3) orientiert sind und somit in der Draufsicht ein Gitter von Kreuzungspunkten bilden und die Anregungselektroden (2) und die Empfängerelektroden (3) in jedem Kreuzungspunkt des Gitters durch einen Festkörper mit temperaturabhänger elektrischer Impedanz elektrisch miteinander verbunden sind.
  • Patent
    DE 10 2007 019 925 A1 - 13.11.2008

Permalink: https://www.hzdr.de/publications/Publ-13684
Publ.-Id: 13684


P0704 - Si-basierter Lichtemitter

Skorupa, W.; Prucnal, S.; Rebohle, L.; Helm, M.
Der Erfindung liegt die Aufgabe zugrunde, einen mehrfarbig emittierenden Si-basierten Lichtemitter zu realisieren, der einfach aufgebaut und mit nur einer Seltenerde-Dotierung herstellbar ist.
Die Erfindung geht aus von einem Si-basierten Lichtemitter, der aus einem frontseitigen Metallkontakt, einer dielektrischen Schutzschicht, einem Si-Substrat und einer rückseitigen, leitfähigen Kontaktschicht besteht, und beinhaltet im Wesentlichen, dass sich zwischen Si-Substrat (1) und dielektrischer Schutzschicht (4) innerhalb einer dünnen SiO2-Schicht (3), die durch lokale thermische Oxidation innerhalb einer durch eine dickere SiO2-Schicht gebildeten Umgebung erzeugt wurde, Europium-Lumineszenzzentren (5) befinden und dass elektrische Anschlüsse an Metallkontakt (6) und rückseitiger Aluminiumschicht (8) vorgesehen sind, die mit einer Stromquelle zur Beaufschlagung mit einem veränderbaren, über eine wählbare Zeit konstanten Strom verbunden sind.
  • Patent
    DE 10 2007 019 209 A1 - 31. 10. 2008
  • Patent
    DE102007019209B4 - 05.01.2011

Permalink: https://www.hzdr.de/publications/Publ-13683
Publ.-Id: 13683


P0701 - Anordnung zur Röntgentomographie

Hampel, U.; Fischer, F.
Aufgabe der Erfindung ist es, eine Anordnung zur Röntgen-Computertomographie anzugeben, die ohne einen axialen Versatz zwischen Brennfleckbahn und Röntgendetektorbogen auskommt.
Die Erfindung beinhaltet, dass der Röntgendetektorbogen (2) und das Target (1) um den Untersuchungsquerschnitt innerhalb einer Bestrahlungsebene angeordnet sind, so dass die vom Elektronenstrahl (3) des Elektronenstrahlerzeugers (6) durch Strahlablenkung erzeugten Röntgenbrennflecke mit den aktiven Detektorelementen innerhalb einer axialen Ebene, der Durchstrahlungsebene (5), liegen, der Röntgendetektorbogen (2) in radialer Richtung hinter dem Target (1) angeordnet ist, so dass jeder von einer Brennfleckposition auf dem Target (1) zu einem Detektorelement des Röntgendetektorbogens (2) gedachter Röntgenstrahl im Bereich der winkelmäßigen Überlappung von Target (1) und Röntgendektorbogen (2) das in Strahlrichtung vor dem Auftreffpunkt auf dem Röntgendektorbogen (2) liegende Target (1) durchdringt, das Target (1) aus einem Targetkörper (7) besteht, der vorzugsweise durch ein Material geringer Kernladungszahl und hohem Wärmespeicher- bzw. Wärmeleitvermögen gebildet wird, auf der dem Elektronenstrahl zugewandten Seite des Targetkörpers (7) eine elektronenbremsende Materialschicht (8) vorzugsweise aus einem hochschmelzenden Material hoher Kernladungszahl aufgebracht ist.
  • Patent
    DE102007008349, Offenlegung - 21.08.2008, Erteilung - 15.10.2009; Nachanmeldung JP, US, WO, EP

Permalink: https://www.hzdr.de/publications/Publ-13682
Publ.-Id: 13682


Mechanisms of metal self-ordering at grazing PVD on ion-erosion-induced surface pattern

Numazawa, S.; Heinig, K.-H.; Ranjan, M.; Facsko, S.
By grazing metal vapor deposition perpendicular to ripples of pre-patterned, oxidized Si surfaces, a chain-like formation of the metal nanoclusters along the ripples have been observed. The structures are located on the slopes which point towards the evaporation source. The self-ordering of metal nanostructure has been observed neither for normal deposition nor for low-angle deposition parallel to the ripple direction. The features of the metal nanostructure depend strongly on the evaporation angle.
In this work, we studied the process of silver deposition on pre-patterned, oxidized Si surfaces by means of 3D lattice kinetic Monte Carlo simulations. The experimentally observed Ag nanostructures could be reproduced. It was shown that the extremely low sticking probability of deposited Ag together with a slope-dependent deposition rate leads to a strongly selective Ag nanocluster nucleation on the surface because
the nucleation rate depends on the square of the adatom concentration.
Keywords: Kinetic Monte-Carlo, nanopatterninig
  • Poster
    Nanoscale Modification of Surfaces and Thin Films Rathen, 30.08.-03.09.2009, Rathen, Germany

Permalink: https://www.hzdr.de/publications/Publ-13681
Publ.-Id: 13681


Opalinuston als potentielles Wirtsgestein für Endlager radioaktiver Abfälle – Einfluss von Huminsäure auf die U(VI)-Migration in Opalinuston

Joseph, C.
Das Entsorgungskonzept für radioaktiven Abfall in Deutschland ist die Endlagerung in tiefen geologischen Formationen, um die Menschen und die Umwelt im Allgemeinen vor der Radioaktivität zu schützen. Mithilfe eines Multi-Barrier-Systems bestehend aus geologischen und technischen Barrieren soll der Abfall möglichst lange, isoliert von der Biosphäre, gelagert werden. In Deutschland stehen dazu drei mögliche Wirtsgesteine zur Verfügung (Salz, Granit, Ton). Für Salz gibt es bereits eine breite vorhandene Datenbasis. Derzeit werden die Untersuchungen am Ton intensiviert, um letztendlich zwischen drei Gesteinsformationen bezüglich ihrer Eignung als Endlager wählen zu können. Diese Untersuchungen werden am Beispiel Opalinuston (natürlicher Ton aus Mont Terri, Schweiz) und dem System U(VI) - Huminsäure - Opalinuston näher erläutert. Insbesondere der Einfluss des im Ton enthaltenen Calcits auf die U(VI)- und Huminsäurespeziation wird gezeigt. Dazu werden explizit Ergebnisse von Sorptions- und Diffusionsversuchen vorgestellt.
Keywords: opalinus clay, humic acid, uranium(VI), sorption, diffusion, host rock, nuclear waste repository, speciation, pore water, calcium, calcite
  • Lecture (others)
    Doktorandenseminar - Kompetenzzentrum Ost für Kerntechnik, 10.12.2009, Rossendorf, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-13680
Publ.-Id: 13680


Atomistic Description of Ion-Induced Surface Patterning - Role of Surface / Bulk Defects and Viscous Flow

Liedke, B.; Heinig, K.-H.; Möller, W.
The role of viscous flow of amorphous Si, Ge, and SiO2 for surface pattern formation under ion irradiation is still a matter of discussions. Strong indications for viscous flow exist for ion energies >10keV. A theoretical treatment of ion-induced surface patterning including viscous flow is extremely difficult because mechanisms of surface patterning like curvature dependent ion erosion and diffusion cannot be separated. Therefore, a program package has been developed which allows a simultaneous treatment of the collision cascades, thermally activated processes and viscous flow. The 3D atom relocation by the collision cascades are calculated in the Binary Collision Approximation, the thermally activated relaxation of energetic atomic configurations as well as diffusive processes are simulated be a very efficient bit-coded kinetic 3D Monte Carlo algorithm, and the viscous flow is taken into account by a crude model allowing distant annihilation of interstitials at the surface. The simulations prove a significant contribution of viscous flow to surface patterning. A comparison of simulated pattern with experimental results will be presented.
Keywords: ripple formation, nanopatterning, ion erosion, computer simulations, TRIM, kinetic Monte-Carlo, viscous flow
  • Lecture (Conference)
    FOR 845, Project Meeting Köln, 31.03.2009, Köln, Germany

Permalink: https://www.hzdr.de/publications/Publ-13679
Publ.-Id: 13679


Development of redox determination methods (WP 2)

Steinbrück, D.; Kumke, M.; Altmaier, R. M.; Neck, V.; Fellhauser, D.; Rumke, J.; Grambow, B.; Landesman, C.; Ribet, S.; Krawczyk-Bärsch, E.; Perdicakis, M.
The objective of WP2 is the development and testing of redox determination methods using different type of electrodes as well as optodes (optical sensors) in order to provide a broad and solid scientific-technical basis for the application of such. In combination with chemical analysis and associated thermodynamic modeling the redox state of systems (relevant for nuclear waste repositories) is assessed. The overall goals are (i) redox determination methods specifically designed for environmental applications, and (ii) a broader information base for interpretation of system conditions.
  • Contribution to proceedings
    1st Annual Workshop of the Recosy Project, 10.-12.02.2009, Barcelona, Spain
    Collaborative Project "Redox Phenomena Controlling Systems", Karlsruhe: Forschungszentrum Karlsruhe GmbH, KIT Report FZKA 7466 Dezember 2009, 9-22

Permalink: https://www.hzdr.de/publications/Publ-13678
Publ.-Id: 13678


Classification of simulated surface morphologies induced by ion irradiation using combined TRIM and kinetic Monte-Carlo calculations

Liedke, B.; Heinig, K.-H.; Facsko, S.; Möller, W.
Atomistic understanding of surface morphology evolution induced by ion beam sputtering is still strongly limited. Available continuum models cannot explain microscopic processes during ion beam irradiation. Also atomistic simulation cannot describe pattern dynamics in the spatiotemporal scales of experiments.
Therefore, we develop a novel program package which unifies the collision cascade with kinetic Monte-Carlo simulations. The 3D atom relocations were calculated in the Binary Collision Approximation (BCA), whereas the thermally activated relaxation of energetic atomic configurations as well as diffusive processes were simulated by a very efficient bit-coded kinetic 3D Monte Carlo code.
Low energy (up to 5 keV) ion sputtering simulations have been performed on simulation cell of about 17 million atoms, where irradiation fluence goes up to few 1018 cm-2. The pattern topography has been study by means of various intensive parameters like incidence angle, ion beam energy, ion fluence, and migration energy of surface defects. Moreover, scaling behaviour of surface roughness and pattern periodicity has been analysed.
Finally, we compare our results with experiments as well as with continuum theory.
Keywords: TRIM, kinetic Monte-Carlo, ion irradiation, ripples formation, scaling
  • Poster
    2009 MRS Fall Meeting, 30.11.-04.12.2009, Boston, USA

Permalink: https://www.hzdr.de/publications/Publ-13677
Publ.-Id: 13677


Analytische HPLC photokatalytischer Abbauprodukte von Wirkstoffen

Marquard, A.
Bakterielle Hüllproteine (S-Layer-Proteine) besitzen eine großen technische Anwendbarkeit. Eine ist die als Matrix für die Synthese von photokatalytisch aktiven Nanopartikeln wie ZnO und TiO2. Verwendung finden die mit ZnO oder TiO2 beschichteten Hüllproteine beim Abbau von Arzneimittelrückständen wie Diclofenac in Abwässern unter Anwendung von UV-Licht. Ein besonderes Augenmerk richtet sich auf die Analytik der Abbauprodukte bei der Aufspaltung von Diclofenac. Der folgende Vortrag soll einen Überblick über den Einsatz von HPLC zu Analyse des photokatalytischen Abbaus von Diclofenac geben.
Keywords: HPLC, photocatalytic degradation, ZnO, TiO2
  • Lecture (Conference)
    3. Workshop Möglichkeiten und Grenzen der HPLC in den Lebenswissenschaften, 29.01.2010, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-13676
Publ.-Id: 13676


Modelling of ion beam mixing with phase separation - Simulation of damage formation and thermally activated relaxation

Liedke, B.; Heinig, K.-H.; Möller, W.
Until now, damage formation and thermally activated relaxation are calculated by different atomistic methods like Binary Collision Approximation (BCA) and kinetic Monte Carlo (kMC), respectively. However, frequently damage formation and relaxation happens simultaneously. Molecular Dynamics (MD), which treats both processes, can not describe them on experimental spatiotemporal scales due to insufficient computer power. Here, an unified BCA-kMC simulation method will be presented and applied to ion-induced mixing and phase separation of intermetallic compounds. In particular we will show the importance of employing these two approaches into one algorithm by studies of two contrary systems. We irradiate Al/Pb with He ions causing ballistic interface mixing. Additionally, creation of Al and Pb clusters can be observed due to the bulk thermal diffusion driving the system to the equilibrium. On the other hand, strongly enhanced intermixing in an ordering compound, like PtCo, after the He irradiation is observed. This effect cannot be understood by purely collisional results alone, and therefore the high miscibility of the system has to be taken into account.
Keywords: BCA, kinetic Monte-Carlo, collision cascade, ion irradiation, interface mixing, phase seperation, phase ordering, intermetallics
  • Lecture (others)
    Seminar at Department of Physics, University of Bialystok, 21.11.2009, Bialystok, Poland

Permalink: https://www.hzdr.de/publications/Publ-13675
Publ.-Id: 13675


Ion-induced surface pattern evolution in computer simulations with a new approach – unification of collision cascade and kinetic 3D Monte Carlo calculations

Liedke, B.; Heinig, K.-H.; Facsko, S.; Möller, W.
Aiming at a more complete but still efficient atomistic calculation of the action of low-energy ion impacts on surfaces, a novel program package has been developed which unifies the calculation of the collision cascade with kinetic 3D Monte Carlo simulations. The 3D atom relocations by the collision cascade were calculated in the Binary Collision Approximation (BCA), whereas the thermally activated relaxation of energetic atomic configurations as well as diffusive processes were simulated by a very efficient bit-coded kinetic 3D Monte Carlo code.
Here, we analyse the impact of bulk processes like vacancy and interstitial creation, defects annihilation and migration as well as ion erosion on surface morphology. In particular, we prove the importance of a complete description of the ion impacts. Collisional and thermally activated processes occurring simultaneously are important for the ripple formation and propagation. The novel program was applied to ripple formation on Si substrates under 1 keV Ar+ irradiation for fluences up to a few 1018 cm-2. Besides the angle of ion incidence, the crucial parameters deciding about ripple coarsening are migration energies of surface defects.
So far, simulation cell sizes of 100x100x50 nm3 with about 17 million atoms allow ripple formation up to 25 nm wavelength, thus direct comparison with experiment can be done.
Additionally, the scaling behaviour of the surface pattern wavelength and roughness has been studied.
Keywords: TRIM, kinetic Monte-Carlo, ion irradiation, ripples formation, scaling
  • Lecture (Conference)
    Nanoscale Modification of Surfaces and Thin Films Rathen, 30.08.-03.09.2009, Rathen, Germany

Permalink: https://www.hzdr.de/publications/Publ-13674
Publ.-Id: 13674


Prediction of surface pattern formation by surface defect generation and diffusion

Numazawa, S.; Heinig, K.-H.
The Bradley-Harper model assumes that under ion irradiation surface pattern develop by a competition between surface curvature dependent ion erosion and surface curvature driven diffusion. By our contribution it will be shown that the curvature dependence in Sigmund’s sputter theory is not the only possible origin for surface pattern formation. For instance, very low energy ion irradiation does not create collision cascades which justifies the Bradley-Harper model, but produces rather some defects at the surface.
Therefore, simple surface defect (adatoms, vacancies) production procedures are applied in combination with kinetic 3D Monte Carlo simulations of defect recombination and diffusion. Depending on the model parameters (ion incidence angle, temperature, defect creation,…) ripples perpendicular or parallel to the ion beam or even dots have been found.
Keywords: Kinetic Monte-Carlo simulation, ion erosion, surface pattern
  • Lecture (Conference)
    Symp. "Nanoscale Pattern Formation", MRS2009Fall Meeting, 30.11.-04.12.2009, Boston, USA

Permalink: https://www.hzdr.de/publications/Publ-13673
Publ.-Id: 13673


Efficient numerical studies of scaling properties and pattern formation during surface growth/erosion by surface mapping on a binary lattice gas model

Liedke, B.; Heinig, K.-H.; Odor, G.
We show how surfaces can be mapped onto two-dimensional lattice gases with binary site values, where surface growth/erosion is described by one-dimensional forward/backward migration of dimers, respectively. Using this mapping and a bit-coded numerical algorithm, very efficient simulations on large spatiotemporal scales have been performed. In addition, the bit-coding allows parallel simulations of 32 systems on a single 64-bit CPU core by the use of particular bit-pair (dimer) locations of the 64 bit words for each system. Using this novel mapping and the internal massive parallelization, we provide high-precision scaling results for the Kardar- Parisi-Zhang (KPZ) and Edwards-Wilkinson type of surface growth. The (smoothing/roughening) surface diffusion can be described by the correlated (attracting/repelling) motion of dimers and Mullins diffusion scaling can be simulated. The combination of competing KPZ and Mullins processes enables to generate various surface patterns (dots/ripples) analogously to the nonequilibrium states seen in driven Ising models. The relation of surface roughness and wavelength coarsening and the role of initial conditions (flat/tilted) will be analyzed.
Keywords: Pattern formation, surface growth, computer simulation, Evolution equation, Scaling
  • Lecture (Conference)
    Symp. "Nanoscale Pattern Formation", MRS2009Fall Meeting, 30.11.-04.12.2009, Boston, USA

Permalink: https://www.hzdr.de/publications/Publ-13671
Publ.-Id: 13671


Shaping of Au and Ge nanoparticles in SiO2 with swift heavy ions

Heinig, K.-H.; Schmidt, B.; Vredenberg, A.; Polman, A.; Toulemonde, M.
Spherical gold and germanium nanoclusters embedded in silicon dioxide can be shaped into rods and discs by high energy ion irradiation. The experimental work, modelling of the shaping mechanism and computer simulations will be presented.
Keywords: nanostructure, ion irradiation, theory, computer simulation
  • Invited lecture (Conferences)
    International workshop on nanostructures in silica, 06.-09.09.2009, Ivalo, Finland

Permalink: https://www.hzdr.de/publications/Publ-13670
Publ.-Id: 13670


Investigations on Dresden EBIS/T as charge breeders

Thorn, A.; Ritter, E.; Ullmann, F.; Zschornack, G.; Bischoff, L.; Pilz, W.
Highly charged ions (HCI) have become an important tool in a wide range of basic and applied research activities. At HITRAP, a project realized by SPARC and other collaborations at GSI, HCI up to bare uranium will be decelerated to low energies enabling, for example, the determination of the g-factor of bound electrons, laser spectroskopy investigations on the hyperfine structure, or high precision measurements of the mass of stable as well as radioactive nuclii. In 2007 the SPARC-EBIT, a room temperature electron beam ion trab (EBIT) of the Dresden EBIT type, was installed at GSI as an offline injector for tests of the beamline components at HITRAP and the chance to carry out experiments without the request of beam time at GSI’s Experimental Storage Ring (ESR). To further improve the viability of the EBIT at this or other research facilities we have carried out general source characterization as well as charge breeding measurements. The results revealed details for a better understanding of the ionization process inside the trap region as well as ways of increasing the number of elements of which HCI can be produced with the EBIT. Furtheron, tests with the more powerful Dresden EBIS-A have started which will lateron be used to evaluate its performance in comparison to the small but highly efficient Dresden EBIT.
Keywords: charge breeders, Dresden EBIT
  • Lecture (Conference)
    5th SPARC Collaboration Symposium, 01.-04.09.2009, Lisboa, Portigal

Permalink: https://www.hzdr.de/publications/Publ-13669
Publ.-Id: 13669


3D nanostructures by combined FIB and electron beam processing

Bischoff, L.; Schmidt, B.; Lange, H.; Donzev, D.
The further miniaturization of silicon sensor and actuator devices using highly developed semiconductor technology at the micro- and nanometer level will lead to a new generation of nano-electro-mechanical systems (NEMS). In the contribution a NEMS fabrication technique will be presented which combines high concentration p-type doping of silicon by high resolution writing focused ion beam (FIB) implantation and subsequent anisotropic and selective wet chemical etching. FIB-patterned and chemically etched 3D Si structures with nanoscale features have been fabricated using 30 keV Ga+ ion implantation (CANION 31Mplus) into silicon-on insulator (SOI) device layers followed by an anisotropic etching in KOH/H2O solution [1]. This technology is combined with classical microelectronic techniques, like lithography and broad beam implantation working on a 4 inch wafer to increase the fabrication efficiency especially for the contact areas. Fabrication considerations to achieve free-standing Si nanostructures, like nanowires nanobridges, see Fig. 1, nanocantilevers etc., are discussed and some typical nanostructures with potential NEMS applications, for example as nano-thermometer, gas sensors or solid-state vacuum nano-triodes, see Fig. 2, are shown. Because the selectively etched free-standing nanobeams are in a highly Ga-doped amorphous state their electrical resistance is quite large. For reduction of the beam resistance they were covered with a metal film using electron beam assisted deposition of a 30 nm Pt layer.
Finally, results of temperature-dependent resistance measurements on nanowires, of AC voltage excited nanobeam deflection measurements and of measurements on vacuum nano-triodes are presented, showing the potential for future device applications.
Keywords: FIB, nanostructure, anisotropic etching
  • Lecture (Conference)
    35th Int. Conf. on Micro Nano Engineering, MNE 2009, 28.09.-01.10.2009, Ghent, Belgium

Permalink: https://www.hzdr.de/publications/Publ-13668
Publ.-Id: 13668


Design Study for In-beam Dose Monitoring Based on Compton Imaging

Kormoll, T.; Fiedler, F.; Wüstemann, J.; Enghardt, W.
no abstract available
Keywords: dose monitoring of proton irradiation, Compton imaging
  • Poster
    Oncoray Retreat, 27.-28.01.2010, Bautzen, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-13667
Publ.-Id: 13667


Applicationof single gamma ray imaging the real time radiotherapy monitoring

Shakirin, G.; Fiedler, F.; Kormoll, T.; Schöne, S.; Enghardt, W.
no abstract available
Keywords: single gamma ray imaging, real time radiotherapy monitoring
  • Invited lecture (Conferences)
    Cerro, 19.-23.01.2010, Les Menuires, Frankreich

Permalink: https://www.hzdr.de/publications/Publ-13666
Publ.-Id: 13666


Ion-beam-assisted nanostructure formation – atomistic reaction pathways

Heinig, K.-H.; Liedke, B.; Numazawa, S.; Ranjan, M.; Möller, W.; Facsko, S.
This presentation highlights the role of ion beams for the formation of nanostructures. The focus is on the selforganization of regular surface pattern under low-energy ion irradiation and on the self-patterning of metal deposits on prepatterned silica surfaces. It will be shown that a deep understanding about the atomistic mechanisms involved can be gained from a combination of collision cascade simulations with 3D kinetic Monte-Carlo calculations.
Keywords: nanostructures, ion irradiation, self-organization, theory, modelling, kinetic Monte-Carlo simulation
  • Invited lecture (Conferences)
    Ion-Surface Interactions 2009, 21.-25.08.2009, Zvenigorod, Russia

Permalink: https://www.hzdr.de/publications/Publ-13665
Publ.-Id: 13665


Competition Ion Beam Mixing and Phase Separation: A novel program combining TRIM with kinetic Monte Carlo

Liedke, B.; Heinig, K.-H.
There are many cases of ion beam processing of materials where ion beam mixing with defect generation and thermally activated processes like defect annealing and phase separation occur at the same time. Examples are ion-irradiation-induced surface pattern selforganisation and nanocluster formation during ion irradiation through interfaces. Here, a new 3D program will be presented which combines the TRIM program for collision cascade simulation with a 3D kinetic Monte-Carlo program describing all kind of relaxation processes.
Keywords: theory, computer simulation, ion implantation, kinetic Monte-Carlo, TRIM
  • Lecture (Conference)
    Workshop Ionenstrahlphysik, 06.-07.04.2009, Jena, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-13664
Publ.-Id: 13664


Swift Heavy Ions: a Tool for Nanotechnology?

Heinig, K.-H.; Schmidt, B.
Spherical gold and germanium nanoclusters embedded in silicon dioxide can be shaped into rods and discs by high energy ion irradiation. The experimental work, modelling of the shaping mechanism and computer simulations will be presentd.
Keywords: nanostructure, ion irradiation, theory, computer simulation
  • Lecture (Conference)
    Workshop Ionenstrahlphysik, 06.-07.04.2009, Jena, Detschland

Permalink: https://www.hzdr.de/publications/Publ-13663
Publ.-Id: 13663


Self-assembling biomolecules as a tool kit for new nanomaterials

Pollmann, K.
Biomolecules for new materials
  • Lecture (others)
    Zentrumskolloquium, 4.01.2010, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-13662
Publ.-Id: 13662


Proteinbasierte Oberflächenfunktionalisierung für die Umwelttechnolgie

Pollmann, K.; Raff, J.
Technologie-Plattform S-Layer für die Umwelttechnologie
  • Invited lecture (Conferences)
    Ideas to market, 15.01.2010, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-13661
Publ.-Id: 13661


Von der Mikrobiologie zur Nanotechnologie – Nachwuchsforschergruppe NanoBio am FZD

Pollmann, K.
Vorstellung der Arbeiten der Nachwuchsgruppe NanoBio
  • Lecture (others)
    Besuch von Herrn Gazlig, Pressesprecher der HGF, 20.01.2010, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-13660
Publ.-Id: 13660


Directed d-mer diffusion describing the Kardar-Parisi-Zhang surface growth

Odor, G.; Liedke, B.; Heinig, K.-H.
We show that d+1-dimensional surface growth models can be mapped onto driven lattice gases of d-mers. The Kardar-Parisi-Zhang growth corresponds to one dimensional drift of d-mers perpendicular to the (d − 1)-dimensional ”plane” spanned by the d-mers. This facilitates efficient, bit-coded algorithms with generalized Kawasaki dynamics of spins. Our simulations in d = 2, 3, 4, 5 dimensions provide scaling exponent estimates on much larger system sizes and simulations times published so far, where the effective growth exponent exhibits an increase. We provide evidence for the agreement of some field theoretical predictions and numerics. We show that the (2 + 1)-dimensional exponents conciliate with the values suggested by L¨assig within error margin. The increase of the effective growth exponents suggest a crossover to a different, anisotropic scaling behavior in d = 5 dimensions.
Keywords: Kardar-Parisi-Zjang equation, lattice gas, computer simulation, scaling, surface growth

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Permalink: https://www.hzdr.de/publications/Publ-13659
Publ.-Id: 13659


Bacteria as natural resources for novel materials: Bioinspired nanocomposites for environmental technology

Pollmann, K.; Günther, T.; Weinert, U.; Marquard, A.; Raff, J.
Nanoscaled materials comprised of organic and inorganic components are becoming more and more important in nanotechnology due to the diversity of applications. The use of self-assembling organic systems as part of such a hybrid material, serving as template for the fabrication of arrays of inorganic nanoparticles, is an attractive approach for the development of new materials. Especially the proteinaceous bacterial surface layers (S-layers) that envelop bacterial cells are attractive for fabricating and patterning of nanostructures. These proteins are composed of protein monomers with the ability to self-assemble into two-dimensional arrays on interfaces and surfaces. The regular distributed pores of these paracrystalline arrays work as binding sites for various metals and offer ideal structures for the formation of regular distributed metallic nanoclusters of a defined size [1]. Such arrays are very attractive for technical applications ranging from the development of novel catalysts to biomedical applications, the programmed assembly of nanometre scale electronic devices, and optical industry [2]. Another approach is the embedding of S-layer proteins into ceramics thus producing metal binding functionalized nanocomposites [3].

Aim of a current project is the development of novel biosensors. These biosensors are composed of three compounds:
1) Bacterial surface layer; these proteins are used for the nano-structuring of surfaces such as SiO2-wafers or glass; they provide a huge amount of orientated functional groups that can be used for coupling of molecules to the surface, thus introducing a high level of functionality in a small device
2) Aptamers, working as receptors; aptamers are oligonucleotides that specifically bind chemical compounds via their three-dimensional structure; the aptamers are coupled to S-layers
3) Fluorophores for detection, coupled to S-layers; two fluorophores are used as donor/acceptor pair; appropriate excitation/emission spectra and closest proximity permit FRET; FRET is interrupted when the analyte is binding to the aptamers.

Another project is focused on the development of novel photocatalysts for the degradation of organic pollutants in the environment. In this approach, S-layer proteins are used as matrix for synthesis as well as immobilization of phototcatalytic nanoparticles such as ZnO or TiO2. These materials, composed of S-layer coated carriers (e.g. alumina, mica, glass) and ZnO particles deposited on S-layer proteins, showed an enhanced catalytic activity in comparison to commercial ZnO nanopowder.

[1] Wahl, R. et al. (2001). Adv. Materials 13, 736-740
[2] Pollmann, K. et al. (2006). Biotechnol. Adv. 24, 58-68
[3] Raff, J. et al. (2003). Chem. Mater. 15, 240-244
  • Poster
    Chemical Nanotechnology Talks X, 26.-27.01.2010, Frankfurt, Deutschland
  • Lecture (Conference)
    Chemical Nanotechnology Talks X, 26.-27.01.2010, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-13658
Publ.-Id: 13658


Ion beam analysis with sub nanometer depth resolution

Kosmata, M.
no Abstract (keine Kurzbeschreibung erforderlich)
Keywords: Little John, QQDS, high resolution depth profiling, ERDA, RBS, magnetic spectrometer, ion beam analysis, concentration profile, thin layer
  • Lecture (others)
    4th Graduate Students Seminar, 16.-18.09.2009, Krögis, Germany

Permalink: https://www.hzdr.de/publications/Publ-13657
Publ.-Id: 13657


Surface pattern formation and scaling described by conserved lattice gases

Odor, G.; Liedke, B.; Heinig, K.-H.
We extend our 2 + 1 dimensional discrete growth model (PRE 79, 021125 (2009)) with a local exchange dynamics of octahedra, which describes surface diffusion. An inverse Mullins-Herring type of roughening process was realized by uphill diffusion of octahedra. By mapping the slopes on particles a two-dimensional, driven, nonequilibrium Ising model emerges in which the (smoothing/ roughening) surface diffusion can be described by the correlated (attracting/repelling) motion of dimers. We show that the pathological problem of freezing due to the short range jumps in a model, where the local height differences are restricted to ±1 can be overcome with the addition of a small external noise. In the limit of vanishing noise we provide numerical evidence for the Mullins-Herring class scaling by surface width scaling and roughness distribution studies. The competition of the inverse Mullins-Herring diffusion with a smoothing deposition which realizes a Kardar-Parisi-Zhang process one can generate different patterns: dots or ripples. We analyze numerically the scaling behavior and wavelength coarsening behavior in these models. In particular we confirm that the Kardar-Parisi-Zhang type of scaling is stable against surface diffusion, hence this is the asymptotic behavior of the Kuramoto-Sivashinsky equation as conjectured by field theory. In case of very strong, normal surface diffusion is added to KPZ we observe smooth surfaces with logarithmic growth, which can describe the mean-field KPZ behavior.
Keywords: Surface pattern, Computer simulation, KPZ-equation, scaling, Mullins diffusion
  • Physical Review E 81(2010)5, 051114

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Permalink: https://www.hzdr.de/publications/Publ-13656
Publ.-Id: 13656


Neon identifies two billion year old fluid component in Kaapvaal Craton

Lippmann-Pipke, J.; Sherwood Lollar, B.; Niedermann, S.; Stroncik, N.; Naumann, R.; van Heerden, E.; Onstott, T. C.
The deep gold mines of the Witwatersrand Basin, South Africa have gained recent attention not only because of investigations of the deep fracture water and associated CH4- and H2-rich gases found there, but because of recent reports of deep microbial communities persisting to depths of almost 3 kilometres - an exotic outpost of the Earth's deep biosphere. While shallower fluids in the basin (to approximately 1 km) were found to contain abundant populations of methanogens and sulphate-reducing bacteria, the deepest, oldest, most saline fracture waters in the basin hosted hitherto unrecognized low biomass and low biodiversity chemoautotrophic ecosystems independent from the photosphere. Shallow and deep fluids also show distinct differences in gas and fluid geochemistry. Paleometeoric waters are dominated by hydrocarbon gases with compositional and isotopic characteristics consistent with production by methanogens utilizing the CO2 reduction pathway. In contrast the deepest, most saline fracture waters contain gases that are dominated by high concentrations of H2 gas, and CH4 and higher hydrocarbon gases with isotopic signatures attributed to abiogenic processes of water-rock reaction. The high salinities (up to hundreds of g/L), highly altered delta -18O and delta2 H signatures, and both 36Cl and measurements of co-occurring nucleogenic noble gases for these fracture waters are consistent with extensive water-rock interaction over geologically long time scales in these high rock/water ratio environments. While the ultimate origin of these fluids has been attributed alternately to saline waters that penetrated the crystalline basement, formation water, or hydrothermal fluids in some cases, their delta 18O and delta 2 H isotopic signatures have typically been so profoundly overprinted by the effects of long-term water-rock interaction that, for the most saline end-members, little evidence of their primary composition remains. The key objective of the present study is to further investigate the origin of these fluids by integrating for the first time detailed neon isotope analyses on the dissolved gases. Helium isotopic analysis confirmed that there is no significant mantle-derived component associated with these fluids and gases. Neon isotope results show distinct differences in neon composition that correspond to the different fluid geochemical end-members previously identified. Typical crustal neon signatures (type A) are identified in the paleometeoric waters populated with abundant methanogens. In contrast, the deep more saline fracture waters contain an enriched nucleogenic neon signature unlike any previously reported in crustal fluids. These samples show the highest 21Ne/22Ne ratios (0.160 */- 0.003) ever reported in groundwater. Fluid inclusions in these rocks yield even higher 21Ne/22Ne ratios between 0.219 to 0.515, consistent with an extrapolated 21Ne/22Ne value of 3.3 +/- 0.2 at 20Ne/22Ne = 0. We show that this enriched nucleogenic neon end-member represents a fluid component that was produced in the fluorine-depleted Archaean formations and trapped in fluid inclusions > 2 Ga ago. The observation of enriched nucleogenic neon signatures in deep fracture water implies the release of this billion year old neon component from the fluid inclusions and its accumulation in exceptionally isolated fracture water systems. The observed association of this Archean neon signature with H2-hydrocarbon-rich geogases of proposed abiogenic origin dissolved in the same deep groundwater suggests that the fracture systems have also allowed for the accumulation of various products of water-rock reactions throughout geologic times. One of these fracture systems contained the deepest characterised microbial ecosystems on earth - chemolithotrophs eking out an existence at maintenance levels independent from sunlight. Consequently, the enriched nucleogenic neon isotope signature may indicate regions in the Archaean crust where investigations of the deep biosphere might be focused.
Keywords: noble gas, neon, methanogens, crustal fluid, metamorphic fluids, subsurface microbiology

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Permalink: https://www.hzdr.de/publications/Publ-13654
Publ.-Id: 13654


Numerical Simulations of the von Karman Sodium dynamo

Giesecke, A.; Stefani, F.; Gerbeth, G.
In the Cadarache von-Karman-Sodium (VKS) experiment a flow of liquid sodium is driven by two counterrotating impellers located at the top and the bottom of a cylindrical vessel. Dynamo action is obtained at a critical magnetic Reynolds number Rm_c=32. Striking property of the self-generated field is the high degree of axisymmetry. Furthermore, dynamo action is obtained only with impellers made of soft iron with a relative permeability of the order of mu_r ~ 100...1000. So far, no satisfying explanation is available that explains the failure of field generation when using steel impellers. Therefore, the role of the ferromagnetic material to obtain a dynamo, appears to be a critical issue and deserves further experimental and numerical investigations.

Numerical simulations of the kinematic induction equation have been carried out in a cylindrical domain that resembles the VKS setup. In case of a prescribed axisymmetric velocity distribution the resulting magnetic field is always determined by an azimuthal m=1 -- mode. Axisymmetric fields can be obtained applying a (localized) alpha-effect that might arise from the induction action of radially oriented helical outflow trapped between the impeller blades. However, it turns out, that the amplitude of alpha, which is necessary to generate an axisymmetric field, is far above realistic values. Therefore, a simple alpha-omega-model can be ruled out as the single explanation for the dynamo mechanism in the VKS experiment. Additional support of dynamo action stems from the presence of a high permeability domain within the cylindrical domain. In numerical simulations with a non-uniform permeability distribution that resembles the shape of the impeller disk (including the flow driving blades) the axisymmetric field mode is significantly enhanced, whereas the first non-axisymmetric mode remains nearly unaffected. To circumvent the restrictions of Cowling's theorem, still an alpha-effect is required for a growing axisymmetric field. However, the necessary magnitude of alpha is significantly reduced.
Keywords: Dynamo, VKS, numerische Simulationen
  • Invited lecture (Conferences)
    Seminar Magnetofluiddynamik TU Dresden, 27.01.2010, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-13653
Publ.-Id: 13653


Self assembling proteins as technology platform for the development of new bio-composite materials

Günther, T.; Weinert, U.; Raff, J.; Pollmann, K.
Self assembly is a widespread phenomenon in nature. We are working with bacterial surface layer proteins which represent the outermost cell envelope of many bacteria and almost all archaea. Our bacteria were isolated from a uranium mining waste pile and are therefore adapted to high contents of heavy metals. Most of them feature surface layer proteins possessing high metal binding capacities. Bacterial surface layer (S-layer) proteins exhibit self organizing properties combined with the ability to arrange at interfaces. In vitro they form a paracrystalline protein lattice with defined pores and cavi-ties as it can be naturally found on the bacterial surface. Our effort is to use the special properties of these proteins for the design of nano structured and functionalized com-posites. Current workings are focused on catalytic materi-als and sensory layers. We use the self assembling proper-ties for coating various substrates by recrystallizing pro-tein monomers direct on surfaces. The metal binding abil-ities of the lattice can be used for filtering or to form met-al nanoparticles of uniform size and distribution in the pores of the protein layer. The amino acid residues of the protein are suitable for linking further functional mole-cules to the lattice with high density
Keywords: S-layer, AFM, nanoparticles, biosensors, carbon nanotubes
  • Lecture (Conference)
    12th International and Interdisciplinary Symposium Biomaterials and Biomechanics: Fundamentals and Clinical Applications 2010, 17.-19.03.2010, Essen, Deutschland
  • Materialwissenschaft und Werkstofftechnik (2010)

Permalink: https://www.hzdr.de/publications/Publ-13652
Publ.-Id: 13652


Self-assembling proteins as basis for new nano materials.

Günther, T.; Weinert, U.; Raff, J.; Pollmann, K.
The investigation of the interactions of radionuclides with the biosphere revealed special adapted bacteria. Some of them were isolated from a uranium mining waste pile. These bacteria are covered with a protein envelope called S-layer as many other bacteria and most of archaea. In these cases, the S-layers bind toxic and radioactive heavy metal ions preventing an uptake and a damage of the cell. The proteins exhibit self assembling properties and form a two dimensional paracrystalline protein lattice. The S-layer can be isolated and dissolved into monomers under the influence of chaotropic agents. The purified proteins are able to recrystallize once the chaotrope is removed. Recrystallization occurs preferably at interfaces, but also in solution and is used in the present study to cover various surfaces with a single layer of highly ordered protein polymers. The protein layer features pores of uniform size and distribution. This lattice is useful for nanostructuring of surfaces. The protein lattice can be used as matrix to form nanoparticles. The different functional groups of the protein are potential binding sites for attaching further functional molecules like enzymes or fluorescence markers. The periodicity of the layer is suitable to immobilize molecules regularly and with high density.
One challenge is the complete coverage of the respective surface in an appropriate time. Another problem is the stability of the produced coating under harsh conditions. We have used AFM analysis on a variety of substrates in order to optimize the substrates pretreatment regarding S-layer coverage and time consumptions. While the recrystallization at cleaned silicon supports is too slow and incomplete, the pretreatment with polyelectrolytes enhances speed of the recrystallization process and allows a complete coverage of surfaces. The generated protein layer shows a thickness of about 9 nm which is in good agreement with data published in literature. These monolayers were used as matrix for the formation of Pt- and Pd-nanoparticles. The proteins are able to bind high amounts of Pt or Pd ions from solution. Subsequent reduction leads to the formation of nanoparticles. Afterwards most of the organic compounds can be removed by UV excitation without heating leaving the nanoparticles well arranged on the surface. Moreover the special properties of the S-layer proteins make them highly interesting to be used as a technology platform for the design of new nano-materials.
Keywords: S-layer, nanoparticles, biosensors, AFM
  • Lecture (Conference)
    nanocoatings 2010, International Conference on Functional Nanocoatings, 28.-31.03.2010, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-13651
Publ.-Id: 13651


Giant Magnetostrain Based on Strong Single Ion Anisotropy of Rare Earth Materials

Doerr, M.; Raasch, S.; Rotter, M.; Frontzek, M.; Meyer, D. C.; Zschintzsch, M.; Svoboda, P.; Loewenhaupt, M.
The volume, shape and microstructure of solids can be influenced by magnetic fields [1]. Much effort is focused on magnetic shape memory (MSM) materials. Recently, the MSM effect has been discovered to occur also in the paramagnetic state, e.g. in RCu2 compounds (R = rare earth) [2]. RMSM materials distinguish themselves from conventional MSM materials by the new origin of the magneto-crystalline anisotropy:
the strong rare-earth single ion anisotropy. Due to the pseudohexagonal symmetry of RCu2, three orientational variants exists, each of them rotated by about 60 deg with respect to the others. Switching these variants by an external field results in a change of the macroscopic shape. The strain is in the order of one percent (= Giant MagnetoStrain). The variant´s fraction stays unchanged still after ramping down the field. The virgin state can be recovered by heating or by a perpendicularly directed field. This irreversibility shows the potential to construct field controlled actuators or switches. We present temperature and field dependent measurements of magnetostrain and magentization at the model substance Tb0.5Dy0.5Cu2. The macroscopic characterization of the sample is complemented by a detailed microscopic analysis done by elastic neutron scattering. Although the GMS effect of RCu2 was worked out at single crystals, the principle of this magneto-mechanical coupling phenomenon is also useful for polycrystalline or microscaled applications. Futural preparation and characterization of thin or free-standing films are necessary to contsruct micro-mechanical actuators.
[1] M. Doerr et al.: Adv. Phys. 54 (2005) 1.
[2] S. Raasch et al.: Phys. Rev. B 73 (2005) 64402.
  • Poster
    E-MRS Fall Meeting, 17.-21.09.2007, Warschau, Polen

Permalink: https://www.hzdr.de/publications/Publ-13650
Publ.-Id: 13650


Formation of Ge NC’s out of (GeOx-SiO2) superlattice structures

Jeutter, N. M.; Zschintzsch, M.; von Borany, J.; Baehtz, C.
Semiconductor Nanocrystals (NC), consisting only of a few hundred of atoms, are of great interest for new generations of light emitters, nonvolatile memories or high efficiency solar cells [1]. However, it remains a remarkable challenge to achieve a high density (>1012cm-2) of equalsized, small (<5 nm) NC’s of Ge or Si embedded in dielectric films. In this study we present the fabrication of Ge-NC’s by decomposition of GeOx (1< x <2) out of a (GeOx -SiO2) superlattice structure (SL). The SL was grown by dual reactive DC magnetron sputtering from elemental targets. Different Ge/O ratios in the SL structures were realized by the variation of oxygen flow and deposition temperature. Using in-situ x-ray reflectivity and grazing incidence diffraction at the CRG Beamline ROBL at ESRF we studied the deposition of the SL and the Ge NC’s evolution during subsequent annealing. Depending on the GeOx stoichiometry closed nanocrystalline films or separated Ge NC’s with grain or particle sizes between 2-5 nm have been obtained with grazing incidence x-ray diffraction. The size of the NC’s can be tuned with thickness of the GeOx sublayer, its density exceeds 1012cm-2.
[1] A.Rogach (ED.), Semiconductor nanocrystal quantum dots, Springer, Wien 2008, ISBN 978-3211752357
  • Lecture (Conference)
    DPG Frühjahrstagung der Sektion Kondensierte Materie (SKM) 2009, 22.-27.03.2009, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-13649
Publ.-Id: 13649


Reactive Magnetron Sputtering of (GeOx-SiO2) Superlattices for Nanocrystal Synthesis

Zschintzsch, M.; Jeutter, N. M.; von Borany, J.; Muecklich, A.
The underlying motivation of this research is the tailored growth of Ge nanocrystals (NC) for photovoltaic applications [1,2]. Of special interest are the study of confinement effects to design bandgap engineered materials enabling light absorption within a wide range of the solar spectrum. In this contribution we enlighten the deposition process of (GeOx-SiO2) superlattice structures (SL) via reactive DC magnetron sputtering and the self-ordered Ge-nanocrystal formation during subsequent annealing. SL structure delivers a reliable method to control the NC size after phase separation. Main attention is directed to define proper deposition conditions for tuning the GeOx composition between elemental Ge (x=0) and GeO2 (x=2) by the variation of the deposition temperature and the oxygen partial pressure. A process window has been found which allows GeOx / SiO2 deposition without changing the oxygen flow during the deposition. The phase separation and Ge NCs formation after subsequent anneling was investigated with in − situ X-ray diffraction, Raman spectroscopy and electron microscopy, confirming the existence of 2-5 nm Ge NCs. As the used technique allows to produce SL stacks with very smooth interfaces (roughness <1 nm), the Ge NC layers could be separated by very thin SiO2 films (d >3 nm) which offers interesting possibilities for charge transport via tunneling.
  • Lecture (Conference)
    DPG Frühjahrstagung der Sektion Kondensierte Materie (SKM) 2009, 22.-27.03.2009, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-13648
Publ.-Id: 13648


In-situ x-ray studies of Germanium nanocrystals, formation out of (GeOx/SiO2) superlattices

Jeutter, N. M.; Zschintzsch, M.; von Borany, J.; Baehtz, C.
Semiconductor Nanocrystals (NC), consisting only of a few hundred of atoms, came recently even more into focus, because they might help to increase the efficiency of solar cells for the 3rd generation photovoltaics [1]. This could be mainly achieved by an engineered bandgap size of the material, which allows the light absorption of the complete sunlight spectrum. However, it remains a remarkable challenge to achieve a high density (>1012 cm-2) of equal-sized, small (< 5 nm) NC’s of Ge or Si embedded in dielectric films.
In this study we present the fabrication of Ge-NC's by decomposition of GeOx (1 < x < 2) out of a (GeOx -SiO2) superlattice structure (SL). The SL was grown by dual reactive DC magnetron sputtering from elemental targets. Different Ge/O ratios in the SL structures were realized by the variation of oxygen flow and deposition temperature. Using in-situ x-ray reflectivity (XRR) and grazing incidence diffraction (GIXRD) at the CRG Beamline ROBL at ESRF we studied the deposition of the SL and the Ge NC's evolution during subsequent annealing. The formation of Ge NC’s by the GeOx phase separation has been proofed with GIXRD. At 600°C a Ge (111) signal confirmed the existence of Ge NC’s in the size of 2-8 nm. Within the SL stability range, the NC size corresponds approximately to the GeOx sublayer thickness.
[1] Martin A. Green, Third generation photovoltaics, Springer, 2006, ISBN 1437-0379
  • Lecture (Conference)
    E-MRS Spring Meeting, 08.-12.06.2009, Strasbourg, Frankreich
  • Lecture (Conference)
    DPG Frühjahrstagung der Sektion Kondensierte Materie (SKM) 2009, 22.-27.03.2009, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-13647
Publ.-Id: 13647


Giant Magnetostrain Based on Strong Single Ion Anisotropy of Rare Earth Materials

Doerr, M.; Raasch, S.; Rotter, M.; Frontzek, M.; Meyer, D. C.; Leisegang, T.; Zschintzsch, M.; Svoboda, P.; Loewenhaupt, M.
The volume, shape and microstructure of solids can be influenced by magnetic fields. Much effort is focused on magnetic shape memory (MSM) materials. Recently, the MSM effect has been discovered to occur also in the paramagnetic state, e.g. in RCu2 compounds (R = rare earth). RMSM materials distinguish themselves from conventional MSM materials by the new origin of the magnetoic anisotropy: the strong rare-earth single ion anisotropy. Due to the pseudo-hexagonal symmetry of RCu2, three orientational variants exists, each of them rotated by about 60 deg with respect to the others. Switching these variants by an external field results in a change of the macroscopic shape. The strain is in the order of one percent (= GiantMagnetoStrain). The variants fraction remains unchanged when ramping down the field. The virgin state can be recovered by heating or by a perpendicularly directed field. We present temperature and field dependent measurements of magnetostrain and magentization at the model substance Tb0.5Dy0.5Cu2. The macroscopic characterization of the sample is complemented by a detailed microscopic analysis done by elastic neutron scattering. Although the GMS effect of RCu2 was worked out at single crystals, the principle of this magneto-mechanical coupling phenomenon is also useful for polycrystalline or microscaled applications. The existence of this structural irreversibility shows the potential to construct field controlled actuators or switches.

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Publ.-Id: 13646


Two-phase CFD advances in the NURESIM and NURISP projects

Bestion, D.; Lucas, D.; Smith, B.; Boucker, M.; Scheuerer, M.; D’Auria, F.; Lakehal, D.; Macek, J.; Tilelj, I.; Hazi, G.; Tanskanen, V.; Ilvonen, M.; Seiler, N.; Boetcher, M.; Anglart, H.; Bartosiewicz, Y.
NURESIM and NURISP are two successive European Projects of the 6th and 7th Framework Program with the objective of building a multi-physics and multi-scale platform for numerical simulation of nuclear reactors. It includes core physics and thermalhydraulics with sensitivity and uncertainty methods and coupling of thermalhydraulics with fuel thermomechanics and neutron kinetics. The NURISP European Collaborative Project (FP7) includes 22 organizations from 14 European countries.
This paper summarizes some achievements and ongoing developments of the platform in Thermal-Hydraulics. Within the NURESIM project the development and validation of two-phase-CFD in open medium addressed mainly Departure from Nucleate Boiling, Dry-Out, Direct Contact Condensation and Pressurized Thermal Shock. Within NURISP, CFD use is now extended to some investigations related to LOCA such as flashing flow, and steam-droplet flow in a core during reflooding. The NEPTUNE-CFD code developed by EDF and CEA and sponsored by AREVA-NP and IRSN was first implemented in the NURESIM platform and The TRansaT code developed by ASCOMP is now also in the platform. New physical models have been developed, validation calculations were performed and NEPTUNE-CFD was benchmarked with commercial codes. DNS–ITM techniques (e.g. Lattice Boltzman Method or DNS of the TransAT code) were also used as numerical experiments to obtain information on smaller scale flow processes.
The paper summarizes the achievements, updates the state of the art in two-phase-CFD, and presents the future activities
Keywords: CFD, PTS, CHF, NURESIM, NURISP
  • Contribution to proceedings
    18th International Conference on Nuclear Engineering, ICONE18, paper ICONE 18-30205, 17.-21.05.2010, Xi’an, China

Permalink: https://www.hzdr.de/publications/Publ-13645
Publ.-Id: 13645


Magnetostructural irreversibilities in R5Ge3 (R=Nd, Gd) intermetallics

Doerr, M.; Rotter, M.; Devishvili, A.; Stunault, A.; Perenboom, J.; Tsutaoka, T.; Tanaka, A.; Narumi, Y.; Zschintzsch, M.; Loewenhaupt, M.
Magnetoelastic phenomena of irreversible character were investigated on the rare earth germanides Nd5Ge3 and Gd5Ge3 which are prominent members of the hexagonal R5Ge3 series. Both compounds order antiferromagnetically at 52 K and 76 K, respectively. A strong magnetostructural irreversibility (i.e. a relative length change of about 10-3 which can be induced by a magnetic field and stays stable after ramping down the field) was detected for both samples by measurements of magnetostriction and thermal expansion using capacitive dilatometry. This transition can be reversed by heating the sample near the ordering temperature. Additional experiments by X-ray and neutron scattering at Gd5Ge3 in order to analyze the effect itself and the structural reversal on an atomistic scale indicate the polymorphic (or metastable) magnetic character (e.g. several propagation vectors (0 0 0.4) and (0.3 0.3 0) were found) which allow to induce strong lattice distortions by an external magnetic field via the magnetoelastic coupling.

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Publ.-Id: 13644


Multiple ferromagnetic secondary phases in Fe implanted yttria stabilized zirconia

Shalimov, A.; Zhou, S.; Roshchupkina, O.; Jeutter, N.; Baehtz, C.; Talut, G.; Reuther, H.; Potzger, K.
Fe ions have been implanted into YSZ(001) single crystals at elevated temperatures. Depending on the fluence not only an increase of α-Fe cluster formation but also the appearance of γ-Fe as well as Fe oxide based secondary phases was observed. The clusters are proposed to consist of a metallic core and an oxide shell. Ferromagnetic hyperfine splitting was detected by Mössbauer spectroscopy and mainly assigned to Fe3+ and α-Fe.
Keywords: yttria stabilizied zirconia, ion beam synthesis

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Publ.-Id: 13643


Ladungsabhängigkeit des Bremsvermögens und der Umladungsquerschitte von leichten MeV Schwerionen in ultradünnen DLC Kohlenstofffolien

Wiemann, R.; Kosmata, M.; Vieluf, M.; Hanf, D.; Liechtenstein, V. K.; Grötzschel, R.
Die Bremsung von Schwerionen mit MeV-Energien bei Bewegung in Materie hängt von deren Energie und Ladungszustand ab. Nach einer durchlaufenen Strecke von ca. 50 nm stellt sich eine energieabhängige Gleichgewichtsverteilung der Ladungszustände ein. Auf dieser Verteilung der Ladungszustände beruhen die tabellierten Werte für das mittlere Bremsvermögen [1], die bei den ionenstrahlanalytischen Verfahren der Rutherford-Rückstreu-Spektrometrie (Rutherford Backs-cattering Spectrometry - RBS) und der elastischen Rückstreuanalyse (Elastic Recoil Detection Analysis - ERDA) zur Berechnung der Streutiefe eingesetzt werden.
Die Verteilung der Ladungszustände der Ionen nach atomaren Stößen unterscheidet sich von der Gleichgewichtsverteilung. Beim Einsatz höchstauflösender magnetischer oder elektrostati-scher Spektrometer zur Charakterisierung ultradünner Schichten betragen die Weglängen der Ionen in der Probe nur wenige Nanometer. Es wird dabei kein Ladungsgleichgewicht erreicht und zur Auswertung der Messdaten müssen die unterschiedlichen Bremsvermögen und die Um-ladungsquerschnitte der einzelnen Ladungszustände berücksichtigt werden.
Experimentelle Daten für den für die Ionenstrahlanalyse interessanten Energiebereich von we-niger als 30 MeV liegen nach unserem Wissen nicht vor. Aus diesem Grunde wurden Brems-vermögen und Umladungsquerschnitte leichter Schwerionen (Bor, Kohlenstoff, Stickstoff, Sau-erstoff und Fluor) an ultradünnen DLC-Kohlenstofffolien (Diamond Like Carbon) im Energiebe-reich von 3-14 MeV für die unterschiedlichen Ladungszustände untersucht. Dazu wurde eine experimentelle Anordnung mit elektrostatischem Analysator, ähnlich der in [2] beschriebenen, verwendet, bei der zwei DLC-Folien hintereinander angeordnet sind. Die erste Folie mit einer Massenflächendichte von 2,0 bzw. 2,7 µg/cm² dient dabei als Stripperfolie. Die Ionen unter-schiedlicher Ladung haben nach dem Passieren dieser Folie eine identische Energieverteilung. In kurzem Abstand folgt eine ultradünne Targetfolie mit einer Massenflächendichte zwischen 0,5 und 0,9 µg/cm². Dies entspricht einer Dicke von ca. 2,5 bis 4,5 nm. Diese Folie ist ausreichend dünn, um Vielfachumladungen zu vermeiden. Zur Bestimmung der Umladungsquerschnitte wur-de, analog der von A. Blažević et al. beschriebenen Methode [3], das Potential der Stripperfolie um 30 kV gegenüber der Targetfolie angehoben.
Die hier gewonnen Ergebnisse fließen in die Verbesserung der Präzision und Richtigkeit der mit hochauflösender RBS und ERDA produzierten Daten ein.

Referenzen
[1] J.F. Ziegler, Nucl. Instr. and Meth. B 219-220 (2004) 1027. URL: http://www.SRIM.org.
[2] W. Jiang et al, Phys. Rev. B 59 (1999) 226.
[3] A. Blažević et al, Phys. Rev. A 61 (2000) 032901.
  • Poster
    SNI 2010 - Deutsche Tagung für Forschung mit Synchrotronstrahlung, Neutronen und Ionenstrahlen an Großgeräten, 24.-26.02.2010, Berlin, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-13642
Publ.-Id: 13642


The influence of substrate temperature and Al mobility on the microstructural evolution of magnetron sputtered ternary Ti–Al–N thin films

Beckers, M.; Höglund, C.; Baehtz, C.; Martins, R. M. S.; Persson, P. O. Å.; Hultman, L.; Möller, W.
Ternary Ti–Al–N films were deposited onto Al2O3 0001 substrates by reactive cosputtering from elemental Ti and Al targets and analyzed by in situ and ex situ x-ray scattering, Rutherford backscattering spectroscopy, transmission electron microscopy, and x-ray photoemission spectroscopy. The deposition parameters were set to values that yield Ti:Al:N ratios of 2:1:1 and 4:1:3 at room temperature. 2TiAlN depositions at 675 °C result in epitaxial Ti2AlN growth with basal planes parallel to the substrate surface. Nominal 4TiAl3N depositions at 675 °C and above, however, yield domain growth of TiN and Ti2AlN due to Al loss to the vacuum. Depositions at a lower temperature of 600 °C yield films with correct 4:1:3 stoichiometry, but Ti4AlN3 formation is prevented, supposedly by insufficient adatom mobility. Instead, an incoherent Tin+1AlNn structure with random twinned stacking sequences n is obtained that exhibits both basal plane orientations parallel and nearly perpendicular to the substrate interface. X-ray photoemission spectroscopy shows that in contrast to stoichiometric nitrides the Al is metallically bonded and hence acts as twinning plane within the Tin+1AlNn stackings. Domains with perpendicular basal plane orientation overgrow those with parallel orientation in a competitive growth mode. The resulting morphology is a combination of smooth-surface parallel-basal-plane-oriented domains interrupted by repeated facetted hillocklike features with perpendicular basal plane orientation.
Keywords: in-situ magnetron sputtering, MAX phases

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