Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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31828 Publications
Energy Transfer from the Er3+ to Ge Nanocrystals During Electroluminescence in MOSLEDs.
Kanjilal, A.; Rebohle, L.; Voelskow, M.; Skorupa, W.; Helm, M.;
It is well established that Si nanocrystals (NCs) can act as sensitizers in Er-doped SiO2 during optical pumping [1-4]. In fact, following the recombination of excitons (electron-hole pairs) in optically excited Si NCs transfer their energy to the higher energy levels of the nearest Er3+ ions and subsequently decay to the ground state by intra-4f transitions. Among those, the 4I13/2 → 4I15/2 radiative transition has attracted substantial interest since the respective luminescence at ~ 1.53 m corresponds to the maximum transparency of silica-based optical fibers [2]. Ge is another group-IV element with similar electronic properties to that of Si. We have examined the impact of Ge NCs in Er-doped SiO2 layers by investigating electroluminescence (EL) of the metal-oxide semiconductor (MOS) structures, where the Er-doped Ge-rich SiO2 layers have been prepared by ion implantation technique combined with rapid thermal annealing (RTA). The samples have been prepared by two steps: (i) 130 keV Ge ions have been implanted with a dose of 2  1016 ions/cm2 in a 200 nm thick thermally grown SiO2 layers followed by RTA at 1050 oC for 180 s, and subsequently (ii) 250 keV Er ions have been implanted with a dose of 1  1015 ions/cm2 followed by RTA in the range of 850-1050 oC for 6-150 s in nitrogen ambience. Transmission electron microscopy experiments reveal formation of randomly oriented Ge NCs with average size ~4 nm. The MOS structures have been fabricated by depositing indium-tin-oxide (ITO) and aluminium in the front and rare sides of the samples, respectively, and patterning the ITO layer using photolithography. During EL measurements, in absence of the visible range band correlated to the quantum confinement in Ge NCs a band appears at ~400 nm in Ge-rich SiO2 layer as a consequence of hot electron mediated impact excitation in Ge-related oxygen-deficiency centres (GeODCs) during electrical pumping [5]. We find an increase of the 400 nm EL intensity with a concomitant reduction of the Er-related emission, and discuss the observed phenomenon on the ground of an inverse energy transfer process [4] from excited Er3+ to the GeODCs.

[1] A. Polman, J. Appl. Phys. 82, 1 (1997).
[2] O. Savchyn, F. R. Ruhge, P. G. Kik, R. M. Todi, K. R. Coffey, H. Nukala, and H. Heinrich, Phys. Rev. B 76, 195419 (2007).
[3] M. Fujii, K. Imakita, K. Watanabe, and S. Hayashi, J. Appl. Phys. 95, 272 (2004).
[4] I. Izeddin, A. S. Moskalenko, I. N. Yassievich, M. Fujii, and T. Gregorkiewicz, Phys. Rev. Lett. 97, 207401 (2006).
[5] L. Rebohle, J. von Borany, R. A. Yankov, W. Skorupa, I. E. Tyschenko, H. Fröb, and K. Leo, Appl. Phys. Lett. 71, 2809 (1997).
Keywords: nanocrystals, Er, energy transfer
  • Poster
    2008 MRS Fall Meeting, 01.-05.12.2008, Boston, MA, USA

Publ.-Id: 12055 - Permalink

Stabilization of extra dimensions in higher-dimensional cosmological models
Günther, U.;
We present an overview over research on higher-dimensional cosmological models carried out from 1997 till 2004. The basic starting point is the problem of stabilizing the sizes of the extra-dimensional factor spaces so that they are kept unobservable at low energies --- as indicated by current data from high-energy collider experiments and astrophysical observations. This problem is well known as the moduli stabilization problem in string theory and M-theory. Stabilizing the scale factors of the extra-dimensional factor spaces by some effective potentials (which are naturally induced via dimensional reduction of the higher-dimensional setups) fixes only the average sizes (moduli) but still allows for small (quantum) fluctuations around the minimum position (radion fluctuations). Once these fluctuations will depend on the coordinates of our external (uncompactified) space they will act as multicomponent scalar fields. Due to their Planck-scale-suppressed coupling to usual standard matter they may be considered as possible candidates for dark matter or UHECR (ultra-high energy cosmic rays).
In the talk, we comment on various dimensional reduction schemes, large extra dimensions (ADD-setups) as well as on orbifold compactification schemes of Randall-Sundrum type. We provide a brief summary about the obtained results published during the 8 years of active research in this field --- including discussions of effective static and dynamic perfect fluid scenarios, relations to reheating, transitions from radiation dominance to matter dominance, quintessence, UHECR, reaction channels with standard matter and possible creation of moduli excitations in ultra-strong background magnetic fields of magnetars. Finally, we give a brief overview about results on higher-dimensional f(R) theories as they are used in 4D as possible explanation for dynamically induced dark energy.
Keywords: string theory, M-theory, phenomenology, cosmology, extra dimensions, moduli stabilization, radion fluctuations, perfect fluids, UHECR, magnetars, f(R) gravity, dark matter, dark energy
  • Invited lecture (Conferences)
    Institutsseminar, 10.12.2008, Jena, Deutschland

Publ.-Id: 12054 - Permalink

Two models of Krein-space related physics: the MHD α2-dynamo and the PT-symmetric Bose-Hubbard model
Günther, U.; Kirillov, O.; Graefe, E.-M.; Korsch, H.-J.; Niederle, A.;
In the first part of the talk, the eigenvalue behavior λ(α,β) of the 2×2 matrix differential operator of the spherically symmetric α2-dynamo of magnetohydrodynamics is considered for constant α-profiles and boundary conditions which depend on a parameter β. Specifically, β∈[0,1] acts as parameter in the homotopic interpolation between idealized (Dirichlet) and physically realistic (Robin) boundary conditions (BCs). For the quasi-exactly solvable monopole setup (with spherical mode number l=0) the characteristic equation is derived explicitly. It is shown that the β-homotopy describes an interpolation between spectra of mesh type (idealized BCs) and a countably infinite set of parabolas (physically realistic Robin Bcs). Interestingly, the mesh nodes (semisimple twofold degenerate eigenvalues) are fixed points of the β-homotopy. An underlying ruled-surface structure of the spectrum is uncovered.

In the second part of the talk, we provide a brief summary of recent results on the spectral behavior of the PT-symmetric
Bose-Hubbard system as it is used for the description of quantum Bose-Einstein condensates with balanced gain-loss interactions. For an N-particle system the corresponding Fock-space Hamiltonian reduces to an N×N-matrix which is selfadjoint in an N-dimensional Pontryagin space. The unfolding of higher-order branch-points of the spectrum is considered under parameter perturbations. Numerical as well as analytical results are presented which demonstrate the relevance of the Hessenberg type of the Hamiltonian as defining matrix structure for the occurrence of specific Galois cycles in the eigenvalue rings of the unfolding branch points.
partially based on: J. Phys. A 41 (2008) 255206; arXiv:0802.3164 [math-ph].
Keywords: Krein space, operator theory, boundary values, homotopy, spectral mesh, ruled surface, Bose-Hubbard model, Bose-Einstein condensate, Hessenberg type, spectral degeneration, Jordan block structure
  • Lecture (Conference)
    8th Workshop "Operator Theory in Krein Spaces and Inverse Problems", 18.-21.12.2008, Berlin, Deutschland

Publ.-Id: 12053 - Permalink

J-self-adjoint operators with C-symmetries: extension theory approach
Kuzhel, S.; Günther, U.; Albeverio, S.;
A linear densely defined operator A acting in a Krein space with fundamental symmetry J and indefinite metric [.,.]J =(J.,.) is called J-selfadjoint if A*J = JA.  In contrast to self-adjoint operators in Hilbert spaces (which necessarily have a purely real spectrum), J-selfadjoint operators, in general, have a spectrum which is only symmetric with respect to the real axis. However, one can ensure the reality of the spectrum by imposing an extra condition of symmetry. In particular, a J-selfadjoint operator A has the property of C-symmetry if there exists a bounded linear operator C in H such that: (i) C2 =I; (ii) JC > 0; (iii) AC = CA. 
The properties of C are nearly identical to those of the charge conjugation operator in quantum field theory and the existence of C provides an inner product (.,.)C=[C.,.]J whose associated norm is positive definite and the dynamics generated by A is therefore governed by a unitary time evolution. However, the operator C depends on the choice of A and its finding is a nontrivial problem. 
The report deals with the construction of C-symmetries for J-selfadjoint extensions of a symmetric operator Asym with finite deficiency indices . We present a general method allowing us: (i) to describe the set of J-selfadjoint extensions A of Asym with C-symmetries; (ii) to construct the corresponding C-symmetries in a simple explicit form which is closely related to Clifford algebra operator structures; (iii) to establish a Krein-type resolvent formula for J-self adjoint extensions A with C-symmetries. 
The results are exemplified on 1D pseudo-Hermitian Schrödinger and Dirac Hamiltonians with complex point-interaction potentials. 
Keywords: J-selfadjoint operators, Krein space, extension theory, deficiency index, C-symmetry, Clifford algebra
  • Lecture (Conference)
    8th Workshop "Operator Theory in Krein Spaces and Inverse Problems", 18.-21.12.2008, Berlin, Deutschland

Publ.-Id: 12052 - Permalink

Determining role of Krein signature for 3D Arnold tongues of oscillatory dynamos
Kirillov, O.; Günther, U.; Stefani, F.;
Using a homotopic family of boundary eigenvalue problems for the meanfield α2-dynamo with helical turbulence parameter α(r)= α0 + γΔα(r) and homotopy parameter β∈[0,1], we show that the underlying network of diabolical points for Dirichlet (idealized, β=0) boundary conditions substantially determines the choreography of eigenvalues and thus the character of the dynamo instability for Robin (physically realistic, β = 1) boundary conditions. In the (α0,β,γ)-space the Arnold tongues of oscillatory solutions at β =1 end up at the diabolical points for β = 0. In the vicinity of the diabolical points the space orientation of the 3D tongues, which are cones in first-order approximation, is determined by the Krein signature of the modes involved in the diabolical crossings at the apexes of the cones. The Krein space induced geometry of the resonance zones explains the subtleties in finding α-profiles leading to spectral exceptional points, which are important ingredients in recent theories of polarity reversals of the geomagnetic field.
Keywords: MHD dynamos, oscillatory dynamos, Krein space, Krein signature, diabolical points, perturbation theory, homotopy, boundary conditions, Arnold tongues, resonance zones
  • Lecture (Conference)
    8th Workshop "Operator Theory in Krein Spaces and Inverse Problems", 18.-21.12.2008, Berlin, Deutschland

Publ.-Id: 12051 - Permalink

The Structure of Polynuclear Uranyl Sorption Complexes at the Gibbsite/Water Interface
Rossberg, A.; Tsushima, S.; Scheinost, A. C.;
Up to now only occasionally polynuclear sorption complexes of uranyl have been reported. This is undoubtedly surprising, since polynuclear hydrolysis species dominate aqueous uranyl speciation across a wide pH range and at solution concentrations typically used for sorption studies (10-6 - 10-4 M). Using U-LIII EXAFS spectroscopy at 15 K, we demonstrate here that polynuclear sorption complexes occur consistently at the gibbsite surface. They were observed across a pH range of 5.5 to 7.5 in equilibrium with atmospheric CO2, and at pH 8.5 in absence of CO2.
At these conditions, thermodynamic calculations predict the trimeric (UO2)3(OH)5+ complex to be the predominant hydrolysis species in the aqueous phase. This complex has been investigated recently by EXAFS spectroscopy and DFT calculations [1]. Both methods showed a stoichiometry of (UO2)3O(OH)3+ for this complex with a central oxo bridging, and provided a relatively short U-U distance of 3.8 Å. In contrast, coordination numbers and radial distances found for the sorption complex are 2xOaxial @ 1.8 Å, 6xOequatorial @ 2.4 Å and 1xU @ 4.2 Å. Both EXAFS shell fitting and a newly developed approach for the calculation of the radial pair distribution function achieved the same result. The U-U distance of 4.2 Å together with the coordination number of six for equatorial oxygen are in line with formation of uranyl dimers, where the two uranyl units are linked in edge-sharing configuration. This unusual structure is currently further investigated by DFT calculations.

1. S. Tsushima, A. Rossberg, A. Ikeda, K. Mueller, A. C. Scheinost, Inorganic Chemistry 46, 10819-10826 (2007).
  • Lecture (Conference)
    5th Workshop on Speciation, Techniques and Facilities for Radioactive Materials at Synchrotron Light Sources, Actinide-XAS-2008, 15.-17.07.2008, Saint-Aubin, France

Publ.-Id: 12050 - Permalink

Pair distribution function, Monte Carlo modelling and Factor Analysis: New approaches to EXAFS analysis.
Rossberg, A.; Funke, H.; Scheinost, A. C.;
X-ray absorption fine-structure (EXAFS) spectroscopy allows the study of a large number of elements and compounds in different physical and chemical states. The most prominent structural parameters derived from EXAFS are coordination numbers, interatomic distances, static and vibrational disorder expressed by the Debye-Waller factor. These parameters are used in the conventional shell fitting approach to approximate the true radial pair distribution function (PDF). This shell fitting approach has three critical limitations for which we present possible solutions.

a) Due to the approximation of the PDF with Gaussian peak shapes, the conventional shell fitting approaches fails for all systems which show anharmonic contributions to the vibrational or static displacement of atoms, caused for instance by temperature effects or week bonds in adsorbate-adsorbent interactions [1]. To overcome this limitation we present two techniques: (1) a Monte Carlo simulation technique for EXAFS spectra which takes not only the first order scattering, but also higher order scattering into account [2] and (2) a novel application designed for the direct calculation of the PDF from the EXAFS spectrum.

b) Due to the limited resolution in R, the shell fitting approach commonly fails, if the X-ray absorbing atom is present in different chemical environments at the same time, i.e. in case of chemical mixtures. For this case we present a way to isolate the pure spectral components by Iterative Factor Analysis [3] and/or by a mathematical combination of Factor Analysis and Monte Carlo simulation [2].

c) In order to find a unique structural solution, shell fitting tends to be a soft modelling approach, because many structural arrangements may lead to a similar description of the EXAFS signal and have to be tested. Especially for the investigation of the unknown structures of sorption complexes, a hard modelling approach, which can take the complete substrate structure into account, would be much better suited. We show that the Monte Carlo simulation technique can be used as a hard modelling approach to solve the structure of sorption complexes [4].

[1] Crozier, E. D. Impact of the Asymmetric Pair Distribution Function in the Analysis of Xafs. Physica B-Condensed Matter 209, 330-333 (1995).
[2] Rossberg, A. & Scheinost, A. C. Three-dimensional modeling of EXAFS spectral mixtures by combining Monte Carlo Simulations and Target Transformation Factor Analysis. Analytical and Bioanalytical Chemistry 383(1), 56-66 (2005).
[3] Rossberg, A., Reich, T. & Bernhard, G. Complexation of uranium(VI) with protocatechuic acid - application of iterative transformation factor analysis to EXAFS spectroscopy. Analytical and Bioanalytical Chemistry 376, 631-638 (2003).
[4] Ulrich, K.-U., Rossberg, A., Foerstendorf, H., Zänker, H. & Scheinost, A. C. Molecular characterization of uranium(VI) sorption complexes on iron(III)-rich acid mine water colloids. Geochimica Et Cosmochimica Acta 70, 5469-5487 (2006).
  • Invited lecture (Conferences)
    2008 SSRL/LCLS Users' Meeting and Workshops, 15.-18.10.2008, Stanford, USA

Publ.-Id: 12049 - Permalink

Neuartige kapazitive Sensoren für die Visualisierung von Mehrphasenströmungen
Da Silva, M. J.; Thiele, S.; Hampel, U.;
In diesem Beitrag werden zwei neuartige, bildgebende Sensoren zur Untersuchung von Mehrphasenströmungen beschrieben - der kapazitive Gittersensor und der kapazitive Flächensensor. Beide Sensoren basieren auf einer matrixförmigen Anordnung von Messelementen, mit denen die elektrische Kapazität eines umgebenden Fluides sehr schnell abgetastet wird. Dadurch sind diese Sensoren in der Lage, zeitlich und räumlich hoch aufgelöste Bilder der Phasenverteilung einer Mehrphasenströmung zu erzeugen. Die Sensoren und die zugehörige Messelektronik werden präsentiert. Darüber hinaus werden ausgewählte Ergebnisse von Strömungsvisualisierungen dargestellt und diskutiert.

In this article, two novel imaging sensors for the investigation of multiphase flows are introduced – the capacitive wire-mesh sensor and the capacitive planar array sensor. Both sensor systems are based on a matrix-type arrangement of sensing elements by which the electrical capacitance of a surrounding fluid is very fast scanned. Thus these sensors are able to produce high temporal and spatial resolution images of the phase distribution in a multiphase flow. The sensors and associated measuring electronics are presented. Furthermore some selected flow visualization results are represented and discussed.
Keywords: flow visualization, multiphase flow, electrical capacitance, electric permittivity, wire-mesh sensor, interdigital sensor


Publ.-Id: 12048 - Permalink

Coupled neutronic thermo-hydraulic analysis of full PWR core with BGCore system
Kotlyar, D.; Fridman, E.; Shwageraus, E.;
BGCore reactor analysis system, recently developed at Ben-Gurion University for calculating in-core fuel composition and spent fuel emissions following discharge, couples the Monte Carlo neutronic code (MCNP4C) with an independently developed burnup and decay module SARAF. The BGCore utilizes multi-group approach for generation of one group cross-sections. According to this approach, only multi-group neutron spectrum is calculated by MCNP, while reaction rates are calculated in a separate subroutine using pre-generated multi-group cross-section set and the fine group neutron spectrum obtained from MCNP.
BGCore code system offers a number of advantages over similar MCNP-depletion codes. These include:
- Multi-group coupling approach significantly reduces the code execution time without compromising the accuracy of the results.
- Use of the most recent data based on JEFF-3.1 data files,
- Careful choice of about 1700 isotopes to cover all potentially significant aspects of fuel irradiation and decay. All nuclides are included in the calculation matrix with no asymptotic approximation,
- The fact that all of the isotopes, and not just the most neutronically important, are tracked in the BGCore throughout all depletion steps, allows calculations of post-irradiation fuel characteristics such as, activity, radiotoxicity, and decay heat with high degree of accuracy.
Substantial reduction in the BGCore code execution time allows consideration of problems with much higher degree of complexity, such as introduction of thermal hydraulic (T-H) feedback into the calculation scheme. Recently, a new T-H feedback module (THERMO) was developed and integrated into the BGCore system. At each computation point, the THERMO module receives as an input the power and the fuel burnup distributions in the core from the neutronic solver (MCNP) and calculates the temperatures distribution in core components and the coolant flow distribution in the core channels. The results of the THERMO calculations can be used for updating the relevant parameters in the MCNP input, such as fuel and moderator temperatures, and moderator density.
This study presents the results of coupled neutronic T-H analysis of full PWR core performed with BGCore system. The verification of BGCore system results against alternative state of the art computer code is also presented.
Keywords: Monte-Carlo burnup, coupled neutronic thermal-hydraulic analysis
  • Contribution to proceedings
    Jahrestagung Kerntechnik 2009, 12.-14.05.2009, Dresden, Deutschland
  • Lecture (Conference)
    Jahrestagung Kerntechnik 2009, 12.-14.05.2009, Dresden, Deutschland

Publ.-Id: 12047 - Permalink

Fracture mechanics characterisation of the WWER-440 reactor pressure vessel beltline welding seam of Greifswald unit 8
Viehrig, H.-W.; Schuhknecht, J.;
WWER-400 second generation (V-213) reactor pressure vessels (RPV) were produced by IZHORA in Russia by and SKODA the former Czechoslovakia. The surveillance Charpy-V and SE(B) specimens of both producers have different orientation. The main difference is the crack extension direction which is through the RPV thickness and circumferential for ISHORA and SKODA RPV, respectively. In particular for the investigation of weld metal from multilayer submerged welding seams is the crack extension direction of importance. Depending on the crack extension direction in the specimen there are different welding beads or a uniform structure along the crack front. This is especially important for the fracture toughness determined according to the Master Curve (MC) approach as standardised in the ASTM Standard Test Method E1921-05. This approach was applied on weld metal of the RPV beltline welding seam of Greifswald Unit 8 RPV. Charpy size SE(B) specimens from 13 locations equally spaced over the thickness of the welding seam were tested. The specimens are TL and TS orientation.
The fracture toughness values measured on the SE(B) specimens with both orientations follow the course of the MC. Nearly all values lie within the fracture toughness curves for 5% and 95% fracture probability. There is a strong variation of the reference temperature T0 though the thickness of the welding seam, which can be explained with structural differences. The scatter is more pronounced for the TS SE(B) specimens. It can be shown that specimens with TL and TS orientation in the welding seam have a differentiating and integrating behaviour, respectively. The statistical assumptions behind the MC approach are valid for both specimen orientation even if the structure is not uniform along the crack front.
Keywords: reactor pressure vessel, multilayer welding seam, specimen orientation, structure, fracture toughness, Master Curve approach, reference temperature, integrity assessment of base metal from the Greifswald Unit 8 RPV show large scatter
  • Lecture (Conference)
    Jahrestagung Kerntechnik 2009, 12.-14.05.2009, Dresden, Deutschland
  • Contribution to proceedings
    Jahrestagung Kerntechnik 2009, 12.-14.05.2008, Dresden, Deutschland
    Proceedings Jahrestagung Kerntechnik 2009: INFORUM GmbH

Publ.-Id: 12046 - Permalink

Intense white photoluminescence emission of V-implanted ZnO oxide thin films
Müller, S.; Lorenz, M.; Czekalla, C.; Benndorf, G.; Hochmuth, H.; Grundmann, M.; Schmidt, H.; Ronning, C.;
Pulsed laser deposited ZnO films were imlpanted with vanadium ions using ion energies between 30 and 250 keV with different fluences yielding vanadium concentrations in the range between 0.8 and 5 at. %. After annealing under oxygen ambient at 800°C, a broad luminescence band observed by photoluminescence covers nearly the total visible spectral region. This luminescence is a superposition of different bands triggered by the incoporated V and remaining implantation defects. The visual impression of the bright whitish emission of the implanted ZnO has been quantified using the color space map of the Commission internationale de l'Eclairage. Furthermore, the intensity of the white emission strongly increases with increasing V concentration, whereas Ar-implanted reference sample shows only weak white emission.
Keywords: ZnO, white luminescence

Publ.-Id: 12045 - Permalink

Hochdynamische Prozesse im Röntgenblick
Hampel, U.; Fischer, F.;
Ein ultraschneller Elektronenstrahl-Tomograph visualisiert strömende Stoffgemische berührungsfrei mit Bildraten von bis zu 7000 Bildern pro Sekunde und einer räumlichen Auflösung von einem Millimeter. Das Gerät kann so Prozesse in Blasensäulenreaktoren sichtbar machen.
Keywords: Elektronenstrahltomographie
  • Nachrichten aus der Chemie (2009)1, 47-49

Publ.-Id: 12044 - Permalink

Influence of air entrainment on the liquid flow field caused by a plunging jet
Krepper, E.; Alt, S.; Renger, S.;
During a jet gaseous bubbles are entrained. These bubbles influence the liquid flow field. The liquid flow field transports fibers in a sump geometry. Dependent on the flow situation different flow characteristics might occur. In the paper results of CFD calculations are presented and compared to experiments.
Keywords: plunging jet, two phase flow, gas entrainment, fiber transport
  • Contribution to proceedings
    Jahrestagung Kerntechnik 2009, 12.-14.05.2009, Dresden, Germany
    Proceedings of the Annual Meeting of Nuclear Technology (CD-ROM), paper No. 220
  • Lecture (Conference)
    Jahrestagung Kerntechnik 2009, 12.-14.05.2009, Dresden, Germany

Publ.-Id: 12043 - Permalink

Porovnani experimentalnich technik v oblasti dvoufazoveho proudeni (Comparison of experimental techniques in two-phase flow)
Otahal, J.; Hampel, U.; Schleicher, E.;
We performed wire-mesh and X-ray micro-tomography studies of the two-phase flow in the mixing chamber of an effervescent atomizer. Flow patterns in the mixing chamber can be revealed by the miniature wire mesh sensor with a temporal resolution of 10 kHz whereas microtomography provides accurate and high-resolution axial-radial gas fraction profiles. The paper describes both measurement techniques and first results of experimental investigation.
Keywords: effervescent atomizer, two-phase flow, wire mesh sensor
  • Contribution to proceedings
    27th International Conference of Fluid Dynamics and Thermodynamics Departments, 24.-27.06.2008, Plzen, Czech Republic
    Proceedings of 27th International Conference of Fluid Dynamics and Thermodynamics Departments, Paper No. SK06

Publ.-Id: 12042 - Permalink

Two-phase flow characteristics in the mixing chamber of the effervescent atomizer
Otahal, J.; Hampel, U.; Schleicher, E.; Jicha, M.;
The article deals with the description of two-phase flow in the mixing chamber of an effervescent atomizer. The first observation has been carried out with the use of high-speed records of the flow inside the mixing tube. The flow in the mixing chamber is very fast and inhomogeneous thus the need to use a high-sampling frequency device has arisen in order to describe changes in the flow. Therefore, an experimental technique has been found which is able to describe the liquid-air distributions in small channels. As a two-phase flow measurement instrument, a miniature wire-mesh conductivity sensor to deal with cross-sections of 8 mm in diameter was designed and built. The frame rate of this sensor is 10 000 images per second. In this study, a special model of a transparent nozzle spraying deionized water that makes use of air as the atomizing medium was used. The effervescent nozzle is of "inside-out gas injection" configuration with the internal diameter of the mixing channel 8 mm. During the experiment, the effervescent atomizer was operated at different air pressure levels ranging from 0.1 to 0.5 MPa and mass GLR (Gas-to-liquid- ratio) from 0.1 to 25%. Mass flow rates of water ranged from 5 up to 65 g·s-1. The results reveal the unstable behavior of two-phase flow in the mixing chamber.
Keywords: effervescent atomizer, two-phase flow, wire mesh sensor
  • Contribution to proceedings
    ILASS Europe 2008 - 22nd European Conference on Liquid Atomization and Spray Systems, 08.-10.09.2008, Como Lake, Italy

Publ.-Id: 12041 - Permalink

Empirical and numerical studies on gas entrainment by impinging jets
Schmidtke, M.; Danciu, D.;
This work concerns experiments as well as CFD simulations on the gas entrainment for the impinging jet configuration. Impinging jets may occur in different situations related to reactor safety analyses. Many experiments have been carried out on impinging jets. A comprehensive overview by Bin [1993] reveals that the results depend critically on the individual setup (e.g. the nozzle geometry) and it is difficult to draw general conclusions. For the qualification of Computational Fluid Dynamics (CFD) models for such flow situations data with high resolution in space and time are required. Therefore a new experiment with a very simple setup was designed and first CFD simulations were done for these experiments.
Keywords: impinging jet, bubble entrainment
  • Contribution to proceedings
    Jahrestagung Kerntechnik 2009, 12.-14.05.2009, Dresden, Deutschland
    Beitrag 215
  • Lecture (Conference)
    Jahrestagung Kerntechnik 2009, Beitrag 215, 12.-14.05.2009, Dresden, Deutschland

Publ.-Id: 12038 - Permalink

Huge performance increase of Tb-implanted MOS light emitting devices with SiOxNy layers moderating hot carrier effects
Rebohle, L.; Sun, J.; Prucnal, S.; Nazarov, A.; Tyagulskii, I.; Helm, M.; Skorupa, W.;
The electrical stability of Tb-implanted SiO2 light emitting devices was drastically improved by using a SiON dielectric buffer layer. For fabrication thermally grown oxide layers on Si were implanted with Tb followed by a thermal treatment and the deposition of a SiON protection layer by plasma-enhanced chemical vapor deposition. The structures were finally provided with an indium tin oxide front contact and an aluminum rear contact. The incorporation of the SiON layer increases the breakdown electric field from 7.5 to 10.5 MV/cm and enhances the operation time of the light emitters up to three orders of magnitude under constant injection currents. By varying the SiO2 and SiON layer thickness it was found that the largest stability enhancements can be achieved if the SiON layer thickness is more than twice the thickness of the SiO2 layer.
The beneficial role of the SiON layer is mainly explained by reducing the chance of destructive avalanche breakdowns in the oxide layer and by an efficient cooling process of hot electrons moving in the conduction band of SiO2. The latter effect is based on the lower electric fields in SiON as compared to SiO2 and the lower band offset of SiON relative to the gate electrode. In addition, the SiON layer acts as a diffusion barrier against moisture from the working ambient and broadens the operation range of the light emitters on the voltage scale.
Keywords: electroluminescence, Terbium implanted MOS device, Si based light emission, silicon oxynitride
  • Lecture (Conference)
    2008 MRS Fall Meeting, 01.-05.12.2008, Boston, USA

Publ.-Id: 12037 - Permalink

Electroluminescence, Charge Trapping and Clustering in Rare-Earth Implanted SiO2-Si Light-Emitting Diodes
Nazarov, A.; Tyagulskii, I.; Tyagulskiy, S.; Rebohle, L.; Prucnal, S.; Lehmann, J.; Biskupek, J.; Kaiser, U.; Skorupa, W.;
In this work a comparative study of charge trapping, electroluminescence intensity (ELI) and clustering in SiO2 implanted by different rare-earth (RE) impurities (Eu, Tb, Gd, Er, Tm) with following high-temperature annealing is performed to clarify the connection between the electrical properties, the structure of the luminescent centers, the ELI and the EL spectra. RE impurities were implanted into the bulk of thermally grown SiO2 on n-type Si. The implanted doses were chosen in such a way that the maximum concentration corresponded to 0.1, 0.5, 1.5 and 3.0 at %. To activate the RE implanted impurities a post implantation furnace anneal in the temperature range of 800-1100 °C for 30 min and flash lamp annealing (FLA) for 20 ms at 1000 °C in a nitrogen ambient have been carried out. The ITO layer was used as a transparent electrode. Charge trapping was studied by the shifting of the high-frequency CV characteristics and the changing of the applied voltage during constant current electron injection from Si into SiO2. The EL signal was recorded at the same injection regime at room temperature in the wavelength range of 300 to 750 nm. Some control structures were studies by transmission electron microscopy with high resolution (XTEM).
It was shown that RE impurities such as Tb, Gd, Er and Tm implanted into SiO2 cause mainly net positive charge trapping in the range of the injected charge from 1x1015 to 2x1017 e/cm2 and stable ELI of their main luminescence lines in green, UV, IR and blue spectral region of the EL spectra, respectively. Above 1x1018 e/cm2 of the injected charge an electron trapping in the bulk of the oxide and a hole trapping at the SiO2-Si interface is observed for all types of the RE impurities. The electron trapping correlates with the EL quenching of the main EL lines for all studied RE implanted structures with the exception of the Eu implanted one. The Eu implanted oxide demonstrates effective electron trapping up to 1x1020 e/cm2 without EL quenching of the main studied EL lines: in red spectral region with a maximum at 618 nm (5D0-7F2 transition for Eu3+ ions); in the blue-green spectral region around 460-470 nm and in blue-violet one at 410 nm (corresponding to a 4f6d-4f7 transition of the Eu2+ ion). The XTEM measurements discovered that the clustering in the Eu-implanted SiO2 is enhanced considerably in comparison with the Tb-implanted one. It is suggested that the enhanced electron trapping in the Eu implanted structures is associated with enhanced clustering, which is partly caused by low valency (2+) oxides existing for the Eu impurity such as EuO and Eu3O4. The use of FLA for the Eu implanted SiO2 results in a decrease of the nanocluster size and an increase of the ELI in the red region of the spectrum.
Keywords: electroluminescence, rare earth implanted MOS devices, charge trapping, clustering
  • Poster
    2008 MRS Fall Meeting, 01.-05.12.2008, Boston, USA

Publ.-Id: 12036 - Permalink

Correlation between electroluminescence and charge trapping in multi-color Eu-implanted Si-based light-emitting diodes
Nazarov, A. N.; Tyagulskii, I. P.; Tyagulskii, S. I.; Rebohle, L.; Skorupa, W.; Biskupek, J.; Kaiser, U.;
Electroluminescence (EL) spectra, charge trapping during operation of EL devices and clustering of rare earth oxides in SiO2 have been investigated in Eu-implanted SiO2-Si structures which demonstrate luminescence associated with the light-emitting transitions in Eu2+ and Eu3+. Strong electron trapping in all studied regions of the injected charge (from 1x10E14 to 1x10E18 e/cm2) during operation of the light-emitting devices has been found that considerably differed from the oxides implanted by other rare earth impurities (Ce, Tb, Gd, Er, Tm). It has been shown that the observed strong electron trapping and the low EL intensity in the Eu implanted structures were associated with enhanced clustering of the Eu oxides. The mechanisms of electron trapping in the SiO2 containing a large cluster concentration is discussed, and flash lamp annealing is proposed to decrease the nanocluster size and to enhance the EL intensity.
Keywords: MOSLEDs, rare earth implanted oxide, electroluminescence, charge trapping, clustering
  • Lecture (Conference)
    EMRS 2008 Spring Meeting, 26.-30.05.2008, Strasbourg, France
  • Physica E 41(2009), 902


Publ.-Id: 12035 - Permalink

Entwicklung neuer Chelatsysteme für nuklearmedizinische Anwendungen
Stephan, H.;
kein Abstract verfügbar
  • Invited lecture (Conferences)
    Gastvorlesung Fachhochschule Zittau/Görlitz, 11.12.2008, Zittau, Deutschland

Publ.-Id: 12034 - Permalink

Cis-Trans-Isomerie in Bispidinkomplexen
Kraus, W.; Emmerling, F.; Juran, S.; Matterna, M.; Walther, M.; Stephan, H.;
Radioaktive Kupferisotope nehmen sowohl für den Einsatz in der nuklearmedizinischen Diagnostik als auch in der Therapie einen besonderen Stellenwert ein. 64Cu und 67Cu sind dabei aufgrund günstiger kernphysikalischer Eigenschaften (Halbwertzeit, Art der Strahlung) von besonderem Interesse. Derivate des Bispidins (3,7-Diazabicyclo[3.3.1]nonan) bilden mit Übergangsmetall-kationen wie Cu2+, Co2+ oder Fe2+, Komplexe hoher Stabilität [1,2].
Für Bispidine ergeben sich drei unterschiedliche Konformationsisomere. Die abgeflachte Doppel-Sessel-Form repräsentiert die thermodynamisch stabilste Konformation. Darin sind die beiden Aminstickstoff-Donoratome N3 und N7 für die Koordination mit Metallionen optimal vororganisiert. Die Stellung von Substitutenten in den Positionen C2 und C4 bezüglich der Ringebene kann zur Bildung von Isomeren einer cis-trans-Konfigurationsisomerie führen. Sterisch anspruchsvolle Reste erzwingen die Bildung von trans-Isomeren. Das gilt in gleicher Weise für die Bindung voluminöser Donoreinheiten – wie Benzimidazolyl-Substituenten – in N3-Position des Bispidin-Gerüsts. Das entsprechende Piperidon (Fig.1) sowie das Bispidon (Fig. 2) zeigen die erwartete trans-Isomerie [3]. Dieser Befund wurde mit Hilfe der Kristallstrukturen nachgewiesen. Der Precursor (C27H25N5O5), a=8.1752(6) Å, b=11.1511(8) Å, c=15.8128(14) Å, V=1260.89(17) Å3, Z=2, R1=0.043 kristallisiert in der Raumgruppe P-1. In der Kristallstruktur des Kupferkomplexes [Cu(C35H33N7O5)(NO2)2] • H2O, P21/n, a=13.242(5) Å, b=17.971(7) Å, c=15.650(6) Å, V=3722.1(2) Å3, Z=4, R1=0.0451 2) ist das Kupferatom verzerrt quadratisch pyramidal koordiniert (dCu−N = 1.947(5) - 2.308(7) Å) und durch den Bispidin-Liganden nahezu vollständig von der Umgebung abgeschirmt.
Erste radiopharmakologische Untersuchungen zeigen, dass die Entwicklung kopplungsfähiger Liganden und deren Anknüpfung an ausgewählte Biomoleküle einen weiteren Schritt in Richtung einer besseren Bioverfügbarkeit von radioaktiv markierten Kupferverbindungen darstellt.
  • Poster
    17. Jahrestagung der Deutschen Gesellschaft für Kristallographie, 09.-12.03.2009, Hannover, Deutschland

Publ.-Id: 12033 - Permalink

Nanopatterning of semiconductor surfaces by sputtering from an inductively coupled plasma
Zhou, J.; Facsko, S.; Keller, A.; Möller, W.;
Self-organized dot patterns have been fabricated on GaSb and Si surfaces by sputtering from an inductively coupled plasma. The dependence of the patterns on the ion energy has been investigated. In agreement with previous studies using plasmas or Kaufman sources, the dot wavelength on GaSb increases with energy. On Si surfaces, however, the dot wavelength increases with energy only in the range E < 800 eV. For 800 eV < E < 1500 eV, the dot wavelength is constant.
  • Lecture (Conference)
    Workshop Complex Nanostructures, 06.-07.10.2008, Dresden, Germany

Publ.-Id: 12032 - Permalink

Digital positron lifetime spectroscopy at EPOS
Krille, A.; Krause-Rehberg, R.; Jungmann, M.; Becvar, F.; Brauer, G.;
As the digital equipment to measure positron lifetimes gets cheaper and more widely used, it is decided that EPOS, the ELBE positron source will sample the signals from the photomultipliers directly and evaluate it online or offline by digital means. Still using isotope sources, the EPOS lifetime spectrometer results in a timing resolution of around 170 ps (with Co-60), which compares good to analog equipment. A distinct improvement is expected when a coincidence setup will be used at ELBE. However, also the software needs further improvement: while one of the goals is of course to achieve the best time resolution, there is also the aspect of runtime and expandability. Results of evaluations will be presented and compared with results from other groups.

Publ.-Id: 12031 - Permalink

Efforts to verify neutron fluence calculations at pressure vessels of decommissioned reactors by means of retrospective niobium dosimetry
Konheiser, J.; Noack, K.; Mittag, S.; Rindelhardt, U.; Borodkin, G.; Borodkin, P.; Gleisberg, B.;
For the first time, trepans from a decommissioned VVER-440 (Greifswald-1) reactor pressure vessel (RPV) have been examined. Activities of a trepan, taken at the RPV weld with the highest fast-neutron load, were measured and estimated on the basis of fluence calculations by the codes TRAMO and DORT. A maximum fluence of 4.05*1019 n/cm2 (E>0.5 MeV) was calculated. The average deviation between the two codes is 2.6 %. Activities resulting from the reaction 93Nb(n,n’)93mNb were measured, niobium being a trace element in the RPV steel. Unfortunately, 93mNb is also produced by neutron capture in the alloy component 92Mo, the built-up 93Mo decaying by electron capture. The ratios of calculated to measured (C/E) 93mNb gamma activities for several trepan samples are between 0.42 and 0.97. The fact that all C/E ratios are below unity suggests that the measured values may have been additionally heightened by activities from other nuclides.
  • Lecture (others)
    8.AAA Meeting Garching(München), 08.12.2008, München, Germany

Publ.-Id: 12030 - Permalink

A biogenic catalyst for hydrogenation, reduction and selective dehalogenation in non-aqueous solvents
Creamer, N. J.; Deplanche, K.; Snape, T. J.; Mikheenko, I. P.; Yong, P.; Samyahumbi, D.; Wood, J.; Pollmann, K.; Selenska-Pobell, S.; Macaskie, L. E.;
We report the activity of a new palladium catalyst supported on fundamentally different Gram negative (Desulfovibrio) and Gram positive (Bacillus) bacterial surfaces (bio-Pd). Under H-2 (electron donor), cells of both strains reduced Pd(II) to Pd(0) as discrete nanoparticles located in the periplasmic space of D. desulfuricans or between the peptidoglycan and the proteinaceous surface layer (S-layer) of B. sphaericus. The catalytic activity of the preparations was similar in their ability to reduce Cr(VI) to Cr(III) (aq), and in the hydrogenation of itaconic acid (aq.) Bio-Pd on D. desulfuricans was also an effective catalyst in a range of reactions in methanol, performing comparably to a commercially available catalyst (10% Pd/C) in the conversion of 4-azidoaniline to 1,4-phenytenediamine. In the hydrogenation of 3-nitrostyrene, the bio-Pd showed selectivity for the partly reduced (dehalogenated) product (1-ethyl-3-nitrobenzene -74%, 1-ethyl-3-aminobenzene -7%) whereas the ! commercial catalyst produced only the fully reduced product (1-ethyl-3-aminobenzene -73%). In the case of 1-bromo-2-nitrobenzene, again bio-Pd was selective for the dehalogenated product, nitrobenzene, whereas the commercial catalyst produced the salt aniline hydrobromide.

Publ.-Id: 12029 - Permalink

Activities towards p-type doping of ZnO
Brauer, G.;
  • Lecture (Conference)
    Seminar an der University of Hong Kong (Physics Department), 26.11.2008, Hong Kong, China

Publ.-Id: 12028 - Permalink

Potential of mirror-image oligonucleotides as molecular probes for pretargeting
Schlesinger, J.; Közle, I.; Bergmann, R.; Klussmann, S.; Vonhoff, S.; Pietzsch, H.-J.;
To explore the potential of complementary mirror-image oligonucleotides as recognition systems for pretargeting, the present work deals with radiopharmacological evaluation of an 86Y-labeled 17mer l-DNA and of a hybrid consisting of the radiolabeled l-DNA and a complementary l-RNA (Figure 1). The 17mer l-DNA was functionalized with DOTA-Nhydroxysuccinimide ester and radiolabeled with 86Y (t1/2 = 14.7 h) resulting in the HPLCpurified [86Y-DOTA]-17mer (31 MBq; 2.0 GBq/μmol). Biodistribution studies with [86Y-DOTA]-17mer in Wistar rats showed high renal excretion and moderate kidney uptake (SUV: 18 ± 2.4, 18 h p. i.). More than 87% of [86Y-DOTA]-17mer were found intact in rat urine 60 min after injection. In thermal denaturation studies, a high melting point of 68°C (32 mM [Na+]) was determined for the hybrid. In conclusion, the high metabolic stability of the l-DNA and the high thermal stability of the l-DNA/l-RNA hybrid suggest the potential of this class of compounds as molecular probes for pretargeting.
  • Poster
    XI Turku PET Symposium New Targets in Molecular Imaging, 24.-27.05.2008, Turku, Finland
  • Contribution to proceedings
    XI Turku PET Symposium New Targets in Molecular Imaging, 24.-27.05.2008, Turku, Finland
    Abstracts of the XI Turku PET Symposium, Kaarina, Finland: Painola, 978-951-29-3563-5, 38

Publ.-Id: 12027 - Permalink

The structure of monomeric and dimeric uranyl adsorption complexes on gibbsite: A combined DFT and EXAFS study
Hattori, T.; Saito, T.; Ishida, K.; Scheinost, A. C.; Tsuneda, T.; Nagasaki, S.; Tanaka, S.;
We investigated the structure of uranyl sorption complexes on gibbsite (pH 5.6 - 9.7) by two independent methods, density functional theory (DFT) calculations and extended X-ray absorption fine structure (EXAFS) spectroscopy at the U-LIII edge. To model the gibbsite surface with DFT, we tested two Al (hydr)oxide clusters, a dimer and a hexamer. Based on polarization, structure, and relaxation energies during geometry optimization, the hexamer cluster was found to be the more appropriate model. An additional advantage of the hexamer model is that it represents both edges and basal faces of gibbsite. The DFT calculations of (monomeric) uranyl sorption complexes show an energetic preference for the corner-sharing versus the edge-sharing configuration on gibbsite edges. The energy difference is so small, however, that possibly both surface species may coexist. In contrast to the edge sites, sorption to basal sites was energetically not favorable. EXAFS spectroscopy revealed in all investigated samples the same interatomic distances of the uranyl coordination environment (RU-Oax ≈ 1.80 Å, RU-Oeq ≈ 2.40 Å), and towards the gibbsite surface (RU-O ≈ 2.87 Å, RU-Al ≈ 3.38 Å). In addition, two U-U distances were observed, 3.92 Å at pH 9.7 and 4.30 Å at pH 5.6, both with coordination numbers of ~ 1. The short U-U distance is close to that of the aqueous uranyl hydroxo dimer, UO2(OH)2, reported as 3.875 Å in the literature, but significantly longer than that of aqueous trimers (3.81-3.82 Å), suggesting sorption of uranyl dimers at alkaline pH. The longer U-U distance (4.30 Å) at acidic pH, however, is not in line with known aqueous uranyl polymer complexes. Based on the EXAFS findings we further refined dimeric surface complexes with DFT. We propose two structural models: in the acidic region, the observed long U-U distance can be explained with a distortion of the uranyl dimer to form both a corner-sharing and an edge-sharing linkage to neighboring Al octahedra, leading to RU-U = 4.150 Å. In the alkaline region, a corner-sharing uranyl dimer complex is the most favorable. The U-O path at ~2.87 Å in the EXAFS spectra arises from the oxygen atom linking two Al cations in corner-sharing arrangement. The adsorption structures obtained by DFT calculations are in good agreement with the structural parameters from EXAFS analysis: U-Al (3.394 Å), U-U (3.949 Å), and U-O (2.823 Å) for the alkaline pH model, and U-Al (3.279 Å), U-U (4.150 Å), and U-O (2.743 Å) for the acidic pH model.
Keywords: EXAFS DFT uranyl sorption gibbsite dimer trimer
  • Geochimica et Cosmochimica Acta 73(2009)20, 5975-5988

Publ.-Id: 12025 - Permalink

Surface diffusion assisted phase separation during the growth of carbon : transition metal thin films
Abrasonis, G.;
Encapsulated nanostructures formed by surface diffusion assisted phase separation during thin film growth are promising candidates for the multifunctional devices, high density magnetic storage media, multifunctional coatings, as large scale templates for nanowire fabrication. In this talk our activities concerning the investigation of the growth mechanisms, structure of the metallic ‘inclusion’ and carbon ‘tissue’ phase as well as their interface structure of carbon: transition metal (TM=V,Co,Ni,Cu) thin films will be summarized. It will be demonstrated that a combined use of laboratory and element selective synchrotron radiation based analytical tools allows identification of the morphology, nearest neighbour coordination as well as the electronic structure of the metallic nanoparticles and the carbon matrix individually and tracking of their changes as a function of the growth temperature, metal type and metal content.
  • Lecture (others)
    Invited seminar, 28.11.2008, Melbourne, Victoria, Australia

Publ.-Id: 12024 - Permalink

A High Resolution Time-of-Flight Spectrometer for Fission fragments and Ion beams
Kosev, K. M.;
Thesis For the purpose of fission-fragment detection a double time-of-flight (TOF) spectrometer has been developed. The key component of the spectrometer is a TOF detector consisting of multichannel-plate (MCP) detectors with a position-sensitive readout, a foil for secondary electron production and an electrostatic mirror. The spectrometer performance is tested at tandem and superconducting linear accelerator.
  • Other report
    Dissertation: Technische Universität Dresden, 2009
    119 Seiten

Publ.-Id: 12023 - Permalink

An improved experiment for the investigation of the helical magnetorotational instability
Stefani, F.; Gerbeth, G.; Gundrum, T.; Szklarski, J.; Rüdiger, G.; Hollerbach, R.;
The magnetorotational instability (MRI) is widely believed to play an essential role in the formation of stars and black holes. Destabilizing hydrodynamically stable Keplerian flows, the MRI triggers turbulence and enables outward transport of angular momentum in accretion discs which is necessary to explain the mass accumulation rates of central objects. The Potsdam Rossendorf Magnetic InStability Experiment (PROMISE) is intended to study the helical version of MRI which works already at Reynolds numbers of the order of 1000 and Hartmann numbers of the order 10. We focus on the results of an improved experiment in which split end caps are used to minimize the effect of Ekman pumping.
  • Lecture (Conference)
    11th MHD days, 01.-03.12.2008, Ilmenau, Germany

Publ.-Id: 12022 - Permalink

Semiconductor-based spintronics
Schmidt, H.;
In the talk the advantages of semiconductor-based spintronics are presented.
  • Lecture (others)
    FZD Lecture, 05.05.2008, Dresden, Deutschland

Publ.-Id: 12021 - Permalink

Room temperature ferromagnetism in Nd- and Mn-codoped ZnO films
Xu, Q.; Schmidt, H.; Hochmuth, H.; Lorenz, M.; Setzer, A.; Meinecke, C.; Grundmann, M.;
Nd and Mn were codoped into ZnO films which have been grown on a-plane sapphire substrates by pulsed laser deposition with the thickness ranging between 46 and 971 nm. The room temperature resistivity of the codoped films is independent of the film thickness. Large positive magnetoresistance and clear anomalous Hall effect were observed at 5 K. Ferromagnetism with clear hysteresis up to 290 K was observed. Codoping is suggested to be an efficient method to introduce energy levels in the ZnO band gap to mediate electron spins of the magnetic doping ions.
Keywords: ZnO, ferromagnetism

Publ.-Id: 12020 - Permalink

Vacuum ultraviolet dielectric function and band structure of ZnO
Schmidt-Grund, R.; Rheinländer, B.; Kaidashev, E. M.; Lorenz, M.; Fritsch, D.; Schubert, M.; Schmidt, H.; Herzinger, C. M.;
For ZnO, the optical dielectric functions for polarizations parallel and perpendicular to the optical axis were determined in the photon energy range from 4.0 to 9.5 eV by using generalized spectroscopic ellipsometry and the band structure was calculated by means of the empirical pseudopotential method. From the band structure, a theoretical dielectric function was derived. The dielectric functions reveal features that were identified as band-to-band transitions. The energies of those transitions were assigned to band-to-band transition energies of critical points of the calculated band structure.
Keywords: ZnO, empirical pseudopotential, generalized spectroscopic ellipsometry, dielectric function
  • Journal of the Korean Physical Society 53(2008)1, 88-93

Publ.-Id: 12019 - Permalink

Intensity of optical absorption close to the band edge in strained ZnO films
Fritsch, D.; Schmidt, H.; Schmidt-Grund, R.; Grundmann, M.;
Besides other one of the remarkable properties making wurtzite ZnO such an interesting material is its large exciton binding energy of about 60 meV, leading to stable excitons at room-temperature. Also, the Curie temperature of this wide-gap material has been predicted to lie above room temperature, making ZnO alloyed with magnetic ions a possible material for spintronics applications. One big challenge in the fabrication of the ZnO-based heterostructure devices is the lattice mismatch between the ZnO films and the substrates and the different thermal expansion coefficient inducing biaxial strain. This work reports on the electronic band structure of biaxially strained ZnO for strains along the a- or c-axis ranging from -1% to 1 %, as calculated by means of the empirical pseudopotential method. Thereby, we also account for relativistic effects in the form of the spin-orbit interaction, as well as for the energy dependence of the crystal potential through the use of nonlocal model potentials. Moreover, the application of a variable plane wave basis set allows us to directly obtain the strain-induced variations of the electronic and the optical properties of wurtzite ZnO.
Keywords: ZnO, emipirical pseudopotential method, dielectric function
  • Journal of the Korean Physical Society 53(2008)1, 123-126

Publ.-Id: 12018 - Permalink

Homoepitaxial ZnO thin films by PLD: Structural properties
Lorenz, M.; Wagner, G.; Rahm, A.; Schmidt, H.; Hochmuth, H.; Schmid, H.; Mader, W.; Brandt, M.; von Wenckstern, H.; Grundmann, M.;
Homoepitaxial ZnO films deposited on annealed hydrothermal O-face ZnO single crystals show superior structural quality. This is demonstrated by narrow ZnO(00.2) rocking curves with FWHM of typically 23 to 35 arcsec, and nearly dislocation-free TEM cross sections. Nominally undoped ZnO films indicate a minor in-plane strain of about 250 ppm and no out-of-plane strain. Target doping by 0.01% P2O5 or 0.5% Li3N results in pseudomorphic film growth without in-plane strain. Increasing doping concentration of 0.1 and 1% P2O5 results in both in-plane and out-of-plane strain up to 0.9 % indicating relaxed films. The O-face polarity of the homoepitaxial ZnO films is confirmed by convergent beam electron diffraction.
Keywords: ZnO, pulsed laser deposition

Publ.-Id: 12017 - Permalink

THz sideband generation in multi quantum wells
Wagner, M.; Schneider, H.; Helm, M.; Schartner, S.; Andrews, A. M.; Roch, T.; Strasser, G.;
Ac THz electric fields which couple strongly with intraband excitations in semiconductors can lead to spectral sidebands when an interband excitation is present. In this nonlinear mixing process a near-infrared (NIR) laser beam is mixed with a THz beam to generate sidebands around the NIR frequency with a frequency spacing equal to the THz frequency or multiples of it. In the last years this effect has been investigated in various semiconductor systems (i.e. in bulk GaAs or in multi quantum wells).
We investigated the third-order nonlinear mixing process between a near-infrared laser and a free-electron laser in an undoped symmetric AlGaAs/GaAs multi quantum well. Differently from the literature where electronic intersubband transitions were used, we are using the transition between the heavy-hole and light-hole states. This transition around 73 µm is pumped close to normal incidence by FELBE, the free-electron laser (FEL) of the Forschungszentrum Dresden-Rossendorf. The picosecond NIR laser is transmitted through the sample where the GaAs substrate has been etched away. It is focused on the entrance slit of the spectrometer of a Streak-camera system. With the Streak-camera temporal and spectral measurements are possible.
The n=+2 sideband conversion efficiency is of the order of 0,005% with respect to the incoming NIR intensity. Among other things we present the power dependency on NIR and FEL intensity and the resonance behavior with respect to the NIR and FEL wavelengths.
Keywords: THz sidebands, free-electron laser, FEL
  • Poster
    GDRE-THz workshop 2008 Paris, 25.-26.09.08, Paris, Frankreich
  • Poster
    EOS Annual Meeting 2008, 29.09.-02.10.2008, Paris, Frankreich
  • Poster
    Nonna 2008 - Workshop on Nonequilibrium Nanostructures, 01.-06.12.2008, Dresden, Deutschland

Publ.-Id: 12016 - Permalink

High electron mobility of phosphorous-doped homoepitaxial ZnO thin films grown by pulsed-laser deposition
Brandt, M.; von Wenckstern, H.; Schmidt, H.; Rahm, A.; Biehne, G.; Benndorf, G.; Hochmuth, H.; Lorenz, M.; Meinecke, C.; Butz, T.; Grundmann, M.;
The transport properties of phosphorous-doped ZnO thin films, grown by pulsed-laser deposition on thermally pretreated hydrothermally grown ZnO single-crystal substrates, are reported. The ZnO:P thin films show very good morphological and structural properties as confirmed by atomic force microscopy (AFM), high resolution x-ray diffraction, and Rutherford backscattering (RBS) channeling. Steps of height c/2 are visible in AFM investigations for all samples. For an oxygen partial pressure of 0.1 mbar, two-dimensional growth was found. RBS channeling of a ZnO:P film shows a minimum yield of 0.034 which is comparable to that of an annealed substrate (0.033). Hall effect measurements revealed that all films are n-type for the present growth conditions. Peak mobilities of 800 cm^2/Vs have been observed around 70 K, in line with the high structural quality of the samples. Room-temperature mobility in ZnO:P is up to 170 cm^2/Vs.
Keywords: ZnO, phosphorous-doping

Publ.-Id: 12015 - Permalink

X-ray scattering and diffraction from Xe-induced ripples in crystalline (001) silicon
Biermanns, A.; Pietsch, U.; Grenzer, J.; Hanisch, A.; Facsko, S.; Carbone, G.; Metzger, H.;
The formation of surface-nanostructures with a characteristic size ranging from several nanometer up to microns has attracted significant interest in the last decades in the context of fabrication of novel opto-electronic and storage devices. One kind of those nanostructures are wave-like patterns (ripples) produced by an interplay between a roughening process caused by ion beam erosion (sputtering) of the surface and smoothening processes caused by surface diffusion. In this contribution we report on investigations of patterned Si (001) surfaces after irradiation with Xe-ions using ion-energies up to 70keV. During the sputtering, an amorphous surface-layer is formed followed by a rather sharp interface towards crystalline material, showing the same morphology as the surface. The structures of the amorphous layer and the amorphous-crystalline interface were studied by means of grazing incidence- small angle scattering (GISAXS) and diffraction (GID) using synchrotron-radiation. We found that the crystal structure at the interface is expanded along the ripples, caused by the creation of defects inside the surface region, whereas this expansion is strongly reduced across the ripples, which can be explained by an anisotropic defect distribution close to the amorphous-to-crystalline interface.
Keywords: nanostructures ion-beam patterning GISAXS GID
  • Poster
    16th International Conference on Ion Beam Modification of Materials - IBMM 08, 31.07.-05.09.2008, Dresden, Germany

Publ.-Id: 12014 - Permalink

Paramagnetism in Co-doped ZnO films
Xu, Q.; Zhou, S.; Markó, D.; Potzger, K.; Fassbender, J.ORC; Vinnichenko, M.; Helm, M.; Hochmuth, H.; Lorenz, M.; Grundmann, M.; Schmidt, H.
Co-doped ZnO films with various electron concentrations up to 4.61×1019 cm-3 at room temperature were prepared by pulsed laser deposition on a-plane sapphire substrates. Only paramagnetism was observed down to 2 K for all the samples, which was also confirmed by x-ray magnetic circular dichroism (XMCD) measurements at 30 K. The average magnetic moment per Co2+ ion is significantly smaller than the expected moment for Co2+ ions (L=1.07, S=3/2), mainly due to the antiferromagnetic exchange interaction between the neighbouring Co2+ ions in the ZnO matrix. Also clustering instead of a uniform distribution of Co2+ ions may play a role. The formation of Co clusters is hindered at higher substrate temperature during the thin film growth. Clear anomalous Hall effect was observed in the highly conducting Co-doped ZnO films at low temperatures up to 100 K.
Keywords: diluted magnetic semiconductor, paramagnetism, anomalous Hall effect

Publ.-Id: 12013 - Permalink

X-ray absorption and photoelectron spectroscopy investigation of selenite reduction by FeII-bearing minerals
Funke, H.; Scheinost, A.;
Wavelet transform (WT) has been proven as a valuable tool for EXAFS data analysis for structures, where two types of backscattering atoms are at the same distance from the central atom [1-3]. WT provides not only radial distance resolution of the spectra like the Fourier transform, but resolves also the wave vector space permitting to probe the discrimination of atoms by their elemental nature.
A short introduction to the continuous WT will be given. The variation of the parameters of the Morlet mother wavelet will be used to build an adapted wavelet for the analysis of specific EXAFS spectra. Thereby the analysis of the (Heisenberg) uncertainty boxes of the Morlet wavelet is a central point to understand the resolution limitations of the WT as well as the form of the wavelet ridges.
Two examples for the use of WT for EXAFS data analysis will be given.
First, the method is applied to a structural problem of Zn-Al layered double hydroxides, demonstrating the homogeneity of the metal cation distribution in the hydroxide layers. Depending on the specific problem, either the well-known Morlet wavelet was used, or a newly developed FEFF-Morlet wavelet, based on theoretical EXAFS back scattering functions.
Second, the reduction from soluble selenium species to elemental Se and iron selenides by Fe containing minerals is examined in detail [4]. Here, the wavelet analysis is used to answer the question: Is Se coordinated to Se atoms/elemental Se or to the Fe (and Se) atoms? This analysis is performed by comparison to well–known reference spectra.
In the outlook two open questions will be discussed: the k weighting and the destructive interference by phase shifts.

[1] H. Funke, A. C. Scheinost, and M. Chukalina, Phys. Rev B, 71, 094110, 2005.
[2] H. Funke, M. Chukalina, and A. C. Scheinost, J. Synchrotron Rad. 14, 426-432, 2007.
[3] M. Muñoz, P. Argoul, and F. Farges, Am. Mineral. 88, 694, 2003.
[4] A. C. Scheinost, L. Charlet , Environ. Sci. Technol. 42, 1984, 2008.
  • Lecture (Conference)
    Workshop on X-ray absorption spectroscopy and advanced XAS techniques, 06.-10.10.2008, Villigen, Switzerland

Publ.-Id: 12012 - Permalink

S-Layer für neue Nanomaterialien
Pollmann, K.; Raff, J.;
Im Rahmen des Vortrags werden die Arbeiten zur Herstellung von Nanopartikeln und Nanomaterialien mit Hilfe von bakteriellen Hüllproteinen vorgestellt und Möglichkeiten einer zukünftigen Zusammerarbeit diskutiert.
  • Lecture (others)
    Koordinierungstreffen mit dem Leibniz-Institut für Katalyse e.V. der Universität Rostock, Außenstelle Berlin, 17.04.2008, Berlin, Deutschland

Publ.-Id: 12009 - Permalink

Tailoring the FePt orientation on amorphous substrates by magnetron sputtering, structural and magnetic investigations
Cantelli, V.; Grenzer, J.; von Borany, J.; Fassbender, J.ORC
Towards an increase of the magnetic recording density, materials with a high magnetic anisotropy are strongly recommended to overcome the physical limits due to superparamagnetism. For this reason, FePt alloys are widely studied because of the excellent magnetocrystalline anisotropy (KU ~ 5-8 x 10-7 erg/cm3) and large magnetic moments at 300K. [1] But, for perpendicular recording media, a (001) preferential orientation, perpendicular to the layer surface, is required.
10 and 15 nm Fe55Pt45 layers were deposited by dual magnetron sputtering on amorphous SiO2 / Si (001) substrate, varying the deposition methods, form co-deposition to monolayers sequence deposition, and working gas, from Ar to Xe, at 0.3 Pa.
The Ar plasma is more energetic than the Xe one: it is characterized by sputtered atoms with a mean energy of about 12 eV and Ar reflected neutrals, reaching a mean energy of about 100 eV when backscattered from the Pt target. This energy budget that enhance the surface adatom mobility during deposition (few eV are required), and create vacancies (E > 40 eV), that decrease the phase transition temperature to 450°C for thin layers. [2]
But, the impact of energetic atoms supports a vertical layers intermixing resulting in a randomly oriented FePt A1 structure at RT. Subsequent Rapid Thermal Annealing at 750°C is completely transforming the layer into the L10 phase, with a coercivity field HC = 1 T, but introducing a weak perpendicular magnetic anisotropy, not evidencing any difference between the deposition techniques.
The reduction of the plasma energy, by using Xe as working gas, is not decreasing the layer magnetic properties (HC = 1 T) after annealing, but strongly enhance the (001) preferential orientation, with a dispersion of the (001) direction around the surface normal of 6°, already in the co-deposition experiment.
The layer by layer technique, associated with Xe plasma, supports the (001) layer orientation after RTA at 750°C, underlining the importance to reduce the elements diffusion path to an atomistic scale. [3]

[1] H. Kanazawa, G. Lanhoff, T. Suzuki, J. Appl. Phys. 87 (2000) 6143
[2] V. Cantelli, J. von Borany, A. Mücklich, Shengqiang Zhou, J. Grenzer,
Nucl. Instr. and Meth. B, 257, 1-2 (2007) 406-410.
[3] M. L. Yan, N. Powers, D. J. Sellmyer, J. Appl. Phys. 93, 8292 (2003)
Keywords: FePt, sputtering gas, (001) orientation
  • Lecture (Conference)
    53th Conference on Magnetism and Magnetic Materials, 10.-14.11.2008, Austin Texas, USA
  • Lecture (Conference)
    DPG Frühjahrstagung der Sektion Kondensierte Materie (SKM) 2009, 22.-27.03.2009, Dresden, Germany

Publ.-Id: 12007 - Permalink

Experiments on nuclear astrophysics in Dresden
Bemmerer, D.;
Recent experimental work on nuclear astrophysics questions at Research Center Dresden-Rossendorf (FZD) is discussed. Several large scale experimental facilities hosted in the city of Dresden/Germany have been used. The ELBE accelerator provides a 40 MeV intensive electron beam driving secondary radiation sources, for example bremsstrahlung and neutron time-of-flight. At the FZD ion beam center, a study on hydrogen burning is underway. The Felsenkeller shallow-underground counting facility in Dresden is used for a study of the astrophysical p-process.
  • Invited lecture (Conferences)
    Seminar, INFN sezione di Padova, 27.11.2008, Padua, Italy
  • Invited lecture (Conferences)
    Nuclear Physics Seminar, 14.05.2009, Legnaro (PD), Italien

Publ.-Id: 12006 - Permalink

MRPC prototype developments for NeuLAND/R3B at FZ Dresden Rossendorf
Bemmerer, D.; Yakorev, D.; Stach, D.; Wagner, A.;
Multigap resistive plate chamber detector (MRPC) prototypes for the future NeuLAND detector at R3B/FAIR have been developed and built at Forschungszentrum Dresden-Rossendorf. The prototypes have been submitted to a variety of tests, including highly precise timing measurements at the ELBE electron beam in Dresden. Results and future perspectives of MRPC prototyping for NeuLAND by the Dresden group are discussed.
  • Lecture (Conference)
    Joint R3B/EXL/ELISE Collaboration Meeting, 11.-14.10.2008, Göteborg, Sweden

Publ.-Id: 12005 - Permalink

Präzise Kernphysik für die Sonne
Bemmerer, D.;
Neue astronomische Beobachtungen ermöglichen es, ein bisher unerreicht genaues Bild unserer Sonne zu zeichnen. Solch ein Bild ist erforderlich, um den langfristigen Einfluss der Sonne auf das Erdklima zu verstehen, und um aus der Sonne einen kalibrierten Referenzstern zu machen.

Allerdings gibt es beim Verständnis der für die Energieproduktion im Sonneninnern verantwortlichen Kernfusionsreaktionen noch Diskrepanzen. Um sie aufzuklären, sind präzise kernphysikalische Messungen vonnöten. In dem Vortrag werden in Dresden und am Gran Sasso (Italien) untersuchte und für die Sonne relevante Kernreaktionen diskutiert und gezeigt, wie die neu gewonnenen Daten bisher bestehende Genauigkeitslücken schließen.

Abschließend wird auch auf die Auswirkungen der neuen Daten auf das Verständnis der Urknall-Nukleosynthese und der Entstehung der chemischen Elemente in Sternen, die schwerer als die Sonne sind, eingegangen.
  • Invited lecture (Conferences)
    Physikalisches Kolloquium, 02.12.2008, Dresden, Deutschland

Publ.-Id: 12004 - Permalink

The 3He(alpha,gamma)7Be S-factor at solar energies: The prompt gamma experiment at LUNA
Costantini, H.; Bemmerer, D.; Confortola, F.; Formicola, A.; Gyürky, G.; Bezzon, P.; Bonetti, R.; Broggini, C.; Corvisiero, P.; Elekes, Z.; Fülöp, Z.; Gervino, G.; Guglielmetti, A.; Gustavino, C.; Imbriani, G.; Junker, M.; Laubenstein, M.; Lemut, A.; Limata, B.; Lozza, V.; Marta, M.; Menegazzo, R.; Prati, P.; Roca, V.; Rolfs, C.; Rossi Alvarez, C.; Somorjai, E.; Straniero, O.; Strieder, F.; Terrasi, F.; Trautvetter, H. P.;
The 3He(alpha,gamma)7Be process is a key reaction in both Big-Bang nucleosynthesis and p–p chain of Hydrogen Burning in Stars. A new measurement of the 3He(alpha,gamma)7Be cross section has been performed at the INFN Gran Sasso underground laboratory by both the activation and the prompt gamma detection methods. The present work reports full details of the prompt gamma detection experiment, focusing on the determination of the systematic uncertainty. The final data, including activation measurements at LUNA, are compared with the results of the last generation experiments, and two different theoretical models are used to obtain the S -factor at solar energies.

Publ.-Id: 12003 - Permalink

The effect of the sputtering gas (Ar, Xe) on FePt clusters formation. Structural and magnetic properties
Cantelli, V.; Grenzer, J.; von Borany, J.; Fassbender, J.ORC
In this study it will be reported about the effect of the sputtering gases, Ar and Xe, on FePt clusters formation using magnetron sputtering deposition at high working pressures. Two different deposition techniques were investigated, a sequential layer by layer deposition and a co-deposition of Fe and Pt. All layers with bulk equivalent thicknesses between 3 to 5 nm were realized at RT and subsequently rapid thermal annealed in order to induce the A1-L10 ordering transformation at 550°C.
The highest L10 fraction in the annealed samples was found using Xe as sputtering gas: Xe decreases the transformation activation energy and therefore, reduces the critical thickness necessary to obtain the strong ferromagnetic phase.
The Ar assisted depositions give FePt clusters with the L10 phase only if the layer-by-layer growth is used, whereas for Xe no differences in the deposition techniques were observed.
Keywords: FePt, Magnetron sputtering, sputtering gases, clusters
  • Lecture (Conference)
    53th Conference on Magnetism and Magnetic Materials, 10.-14.11.2008, Austin Texas, USA
  • Contribution to proceedings
    53th Conference on Magnetism and Magnetic Materials, 10.11.-14.12.2008, Austin Texas, USA
    Journal of Applied Physics 105(2009), 07B529-07B529-3
  • Poster
    DPG Frühjahrstagung der Sektion Kondensierte Materie (SKM) 2009, 22.-27.03.2009, Dresden, Germany


Publ.-Id: 12002 - Permalink

Cavity layer introduction in SIMOX technology
Ou, X.; Kögler, R.; Mücklich, A.; Skorupa, W.; Möller, W.; Wang, X.;
The oral conference contribution reports about latest results of the improvement of the SIMOX process for fabrication of silicon-on-insulator (SOI) materials by defect engineering.
Keywords: SOI, SIMOX, ion implantation, defect engineering
  • Lecture (Conference)
    72. Jahrestagung der DPG und DPG Frühjahrstagung des Arbeitskreises Festkörperphysik, 25.-29.02.2008, Berlin, Germany

Publ.-Id: 12001 - Permalink

Kelvin probe force microscopy imaging of cross-sections of Si multilayer structures
Baumgart, C.; Müller, A.-D.; Müller, F.; Helm, M.; Möller, A.; Schmidt, H.;
Kelvin probe force microscopy (KPFM) is a standard technique for the investigation of surface potentials. We present its applicability to cross-sectionally prepared p-p+ Si multilayer structures. The contact potential difference (CPD) image between tip and sample has been recorded by means of an Anfatec Level-AFM with a 2nd amplifier and NSC15 probes from MikroMash. Using an active mixer, the excitation amplitude of the NSC15 probes is almost independent on the working frequency. The probed CPD signal difference between the layers ranges between 60 meV and 850 meV and can be correlated to the variation of the diffusion potential in the Si multilayer structure. The p-type of majority charge carriers and the corresponding acceptor dopant profile have been pinpointed by scanning capacitance measurements. Starting from the known donor dopant concentration in the NSC15 probe, we simulated the CPD and determined the acceptor concentration in the whole p-p+ Si multilayer structure. From the frequency dependence of the CPD we can clearly distinguish between surface and bulk effects.
  • Lecture (Conference)
    DPG-Frühjahrstagung der Sektion Kondensierte Materie (SKM) 2009, 22.-27.03.2009, Dresden, Germany

Publ.-Id: 12000 - Permalink

Influence of the fluid properties on co-current two-phase flows in a horizontal channel connected to a riser
Vallee, C.; Seidel, T.; Lucas, D.; Beyer, M.; Prasser, H.-M.; Pietruske, H.; Schütz, P.; Carl, H.;
0In the event of a loss-of-coolant-accident (LOCA) in a pressurised water reactor (PWR), emergency strategies have to be mapped out in order to guarantee the reliable removal of the decay heat from the reactor core. During a hypothetical small break LOCA with failure of the high pressure emergency core cooling system, the decay heat has to be released to the secondary circuit over the steam generators. Therefore, the primary circuit is designed to forward a natural circulation if the main coolant pumps are not available. Furthermore, if steam is generated in the primary circuit due to its depressurisation, stratified two-phase flow regimes can occur in the main cooling lines, which could be relevant for the reactor safety. It is intended that a computational fluid dynamics (CFD) approach could increase the simulation accuracy of such transient accident scenarios compared to the state of the art system codes.

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 Forschungszentrum Dresden-Rossendorf (FZD). The hot leg is the line connecting the reactor pressure vessel (RPV) to the steam generator (SG) and is composed of a horizontal pipe, a 50° upward bend and an inclined riser (Figure 1). The hot leg model is operated in the pressure chamber of the TOPFLOW facility of FZD (Figure 1), which is used to perform high-pressure experiments under pressure equilibrium with the inside atmosphere of the chamber. Therefore, the test section does not have to support overpressures and can be designed with thin materials. Consequently, parts of the test section could be equipped with big size windows for the application of optical observation techniques, also at reactor typical boundary conditions. In order to provide optimal observation possibilities, a flat test-section design was chosen with a width of 50 mm.

Co-current flow experiments were performed in the hot leg model, simulating a two-phase natural circulation in the primary circuit of a PWR. The experiments were done with air and water at 3.0 bar and room temperature as well as with steam and water at pressures up to 50 bar and the corresponding saturation temperature (i.e. up to 264°C). Over this range of boundary conditions, the main fluid properties vary significantly. The frequency distribution of the water level measured in the RPV simulator was used to characterise the flow in the hot leg (Figure 2). It was found that the form of the distribution informs about the stationarity of the water flow to the steam generator: the flatter the distribution, the more discontinuous the transport of water over time. This tendency was confirmed by the high-speed video observations (Figure 3), which were also used to identify the flow regime. Furthermore, Figure 2 shows a comparison between the frequency distributions obtained from the air/water and the steam/water experiments. Generally, the distributions are flatter for the cold experiments than for the hot ones. This shows that, due to the lower surface tension and viscosity, the transport of water induced by the gas is more constant in time for the steam/water flow.
Keywords: two-phase flow, co-current flow, fluid properties, hot leg, pressurised water reactor, PWR
  • Contribution to proceedings
    ExHFT-7 - 7th World Conference on Experimental Heat Transfer, Fluid Mechanics and Thermodynamics, 28.06.-03.07.2009, Krakow, Poland, Krakow: AGH University of Science and Technology Press, 978-83-7464-235-4, 443-452
  • Lecture (Conference)
    ExHFT-7 - 7th World Conference on Experimental Heat Transfer, Fluid Mechanics and Thermodynamics, 28.06.-03.07.2009, Krakow, Poland

Publ.-Id: 11999 - Permalink

Comparison of air/water and steam/water flooding experiments in a model of the hot leg of a pressurised water reactor
Vallee, 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 (PWR) was built at Forschungszentrum Dresden-Rossendorf (FZD). Counter-current flow limitation (CCFL) experiments were performed with air and water at room temperature and pressures up to 3.0 bar as well as with steam and water at pressures up to 50 bar and the corresponding saturation temperature of 264°C.

One selected 50 bar experiment is presented, analysed and high-speed camera images are shown. Furthermore, the flooding curves 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, both parameters fail to correlate properly the data: a discrepancy is observed between the air/water and steam/water series. Therefore, a modified Wallis parameter is proposed, which takes into account the effect of the fluid viscosities on the CCFL.
Keywords: two-phase flow, air water flow, steam water flow, flooding, counter-current flow limitation, CCFL, hot leg, pressurised water reactor, PWR, Wallis parameter, viscosity
  • Contribution to proceedings
    Jahrestagung Kerntechnik 2009, 12.-14.05.2009, Dresden, Germany, Berlin: INFORUM Verlags- und Verwaltungsgesellschaft mbH, Compact221
  • Lecture (Conference)
    Jahrestagung Kerntechnik 2009, 12.-14.05.2009, Dresden, Germany

Publ.-Id: 11998 - Permalink

Library Information Services - not only books in shelves
Reschke, E.;
The presentation shows the Library information services, focused on the elctronic services within the intranet and the internet. The main point was the link resolver for linking services.
Keywords: online catalogue, document deliver, Interlibrary loan, elctronic databases, virtual library, publishing, copyright, document managment systems, open access
  • Lecture (others)
    FZD Lecture, 01.12.2008, Dresden, Deutschland

Publ.-Id: 11997 - Permalink

On the influence of spatial discretization on cross-sction preparation during burnup calculations with HELIOS 1.9
Merk, B.;
Cell- and burnup calculations are the fundament for all deterministic static and transient 3D full core calculations for different operational states of the reactor. The spatial discretization used for the c burnup calculations influences the results for the used integral transport solutions significantly. The arising differences in the infinite multiplication factor and in the localized burnup ditribution in the fuel rod for identical averaged burnup are shown and analyzed. Special emphasis is given to the influence of different discretization strategies on the calculation of homogenized two group cross sections which are forwarded to the 3D full core calculations .
Keywords: Cell- and Lattice calculation, cross section preparation, HELIOS, Discretization, Burnup calculation, Depletion
  • Contribution to proceedings
    Jahrestagung Kerntechnik 2009, 12.-14.05.2009, Dresden, Deutschland
  • Lecture (Conference)
    Jahrestagung Kerntechnik 2009, 12.-14.05.2009, Dresden, Deutschland

Publ.-Id: 11995 - Permalink

Sicherheitsorientierte Regelungsstrategien für Batch- und Semibatch-Prozesse in der Feinchemie
Kryk, H.; Hessel, G.;
Insbesondere in der Feinchemie und der pharmazeutischen Industrie erfolgt die Produktion von Spezialchemikalien meist im Batch- oder Semibatch-Betrieb in sog. Mehrzweckanlagen. Als Reaktionsgefäße kommen Rührkesselreaktoren zum Einsatz. Das instationäre und nichtlineare Prozessverhalten ist dabei durch eine Reihe von Einflussfaktoren gekennzeichnet, welche sich sowohl auf die Prozesssicherheit als auch auf die Effizienz des Gesamtverfahrens auswirken können. Demgegenüber werden jedoch gerade in Mehrzweckanlagen meist konventionelle Prozessgrößen für die Steuerung komplexer chemischer Prozesse verwendet. Da PAT bei Mehrzweckanlagen nur in begrenztem Umfang einsetzbar ist, stehen Echtzeit-Informationen über Konzentrationsverläufe, die für den Prozesszustand und das Gefahrenpotenzial des Prozesses kennzeichnend sind, oftmals nicht zur Verfügung. Somit besteht für den Operator das Problem, tolerierbare von unerwünschten Prozessabweichungen zu unterscheiden und die Ursachen bestimmter Prozess-Trends zu identifizieren. Von besonderer Bedeutung ist die Entwicklung und Etablierung industriell anwendbarer Methoden für eine objektive Detektion des aktuellen Prozesszustandes in Echtzeit sowie für die frühzeitige Identifikation unerwünschter Betriebszustände. Aus diesen Gründen entwickelt das Institut für Sicherheitsforschung des FZD bereits seit Jahren Methoden zum Online-Monitoring sicherheitsrelevanter Batch- und Semibatch-Prozesse. Zur Vermeidung des Einsatzes von teuren und empfindlichen Online-Analysesystemen, wurden Methoden entwickelt, welche auf Echtzeit-Stoff- und Energiebilanzen basieren. Diese können den Anlagenfahrern als Hilfe zur Objektivierung der Prozessführung und, im Falle unerwünschter Prozesszustände, als Werkzeug zur Handlungsempfehlung für geeignete Gegenmaßnahmen dienen.
Die Idee ist nun, aufbauend auf die bisherigen Entwicklungen, derartige Verfahren als Komponente einer sicherheitsbasierten Regelungsstrategie zu nutzen. Die Echtzeit-Resultate des Monitoring-Systems könnten dann als Führungsgrößen für eine entsprechende Prozessregelung, bis hin zur inhärent sicheren, vollautomatischen Betriebsweise von Batch-Prozessen in Mehrzweckanlagen, genutzt werden.
  • Invited lecture (Conferences)
    ProcessNet-Arbeitsausschuss "Sicherheitsgerechtes Auslegen von Chemieanlagen", 19.-20.11.2008, Frankfurt a.M., Deutschland

Publ.-Id: 11994 - Permalink

The influence of different thermal hydraulic models on the results of a DYN3D boron dilution transient calculation
Kliem, S.; Mittag, S.; Rohde, U.; Weiß, F.-P.; Kozmenkov, Y.;
The availability of three different thermal hydraulic models for the neutron kinetic core model DYN3D gave the possibility to investigate their influence on the results of a boron dilution transient. Quantitative differences were found in the single solutions. So the different degree of numerical diffusion in the boron transport models affects the height and time of the first power peak. Differences were also found in the heat transfer and the drift flux models. Concerning assessed safety criteria like maximum fuel and cladding temperature as well the DNB ratio the same conclusions can be drawn from all calculations: Safety-relevant margins are not reached. A spreading of the calculated data is present but there are no qualitative differences in the consid-ered transient.
  • Contribution to proceedings
    Jahrestagung Kerntechnik 2009, 12.-14.05.2009, Dresden, Deutschland
    Tagungsband der Jahrestagung Kerntechnik 2009, paper 114, Berlin: INFORUM GmbH
  • Lecture (Conference)
    Jahrestagung Kerntechnik 2009, 12.-14.05.2009, Dresden, Deutschland

Publ.-Id: 11993 - Permalink

Complexation of uranium(IV) with fluoride and phosphate using TRLFS
Lehmann, S.;
A novel TRLFS system was set up for investigation of short-lived fluorescence emitting metal ions like uranium(IV) or americium(III). This laser system was applied to study the complexation of uranium(IV) with fluoride and phosphate and to determine their respective complex formation constants.
Keywords: uranium(IV) fluoride, uranium(IV) phosphate, time-resolved laser fluorescence spectroscopy
  • Lecture (others)
    Workshop of the Institute of Radiochemistry (IRC) and the Paul Scherrer Institute (PSI), Villigen , Switzerland, 03.-04.11.2008, Dresden, Germany

Publ.-Id: 11992 - Permalink

Computational Fluid Dynamics (CFD) for gas-liquid flows
Lucas, D.; Tiselj, I.; Hassan, Y.; Moretti, F.;
Computational Fluid Dynamics (CFD) codes are widely used in industrial applications for single phase flows, e.g., in the automotive or aircraft industries. On the other hand the application of CFD for multiphase systems is not yet mature. Safety analyses related to nuclear light water reactors require reliable simulations for different scenarios including two-phase flow situations. Prominent examples for Pressurized Water Reactor (PWR) analyses are the prevention from Departure from Nucleate Boiling (DNB) which is related to Critical Heat Flux (CHF) or the Pressurized Thermal Shock (PTS) problem which has to be considered in connection with some hypothetical Loss of Coolant Accident (LOCA) scenarios and may also lead to two-phase flow situations in the cold leg and in the downcomer. In case of Boiling Water Reactors (BWR) analyses e.g. the prevention from Dryout is an important issue. The special issue of the on Science and Technology of Nuclear Installations Journal on "Computational Fluid Dynamics (CFD) for Gas-Liquid Flows" discusses the state of the art and the progress regarding CFD simulations on such two-phase flows.
Keywords: CFD, two-phase

Publ.-Id: 11991 - Permalink

A novel time-resolved laser fluorescence spectroscopy system for research on complexation of uranium(IV)
Lehmann, S.; Geipel, G.; Grambole, G.; Bernhard, G.;
Research on the chemical speciation of complexes by determining the fluorescence properties of metal ions whose emitted fluorescence lifetime is in the range of only few nanoseconds, has been very limited to date due to a lack of the technical possibilities necessary to conduct respective measurements. We were able to overcome the technical problems and set up a new time-resolved laser fluorescence spectroscopy system that meets the requirements to carry out research on the fluorescence properties of metal ions with very short fluorescence lifetimes such as uranium(IV) and its compounds. We investigated the fluorescence of uranium(IV) in perchloric acid and determined the detection limit of uranium(IV) to be 1 ± 10-6M. Additionally, we found the fluorescence decay time of uranium(IV) to be 2.73 ns ± 0.40 ns. Further application of the novel laser system addressed the complexation of uranium(IV) with fluoride by studying the fluorescence properties during reaction. Evaluation of the data recorded resulted in the finding of a 1 : 1 complex (uranium(IV) : fluoride). We determined the corresponding complex formation constant of uranium(IV) fluoride (UF)3+ with logβº = 9.43 ± 1.94. The application of our novel time-resolved laser fluorescence spectroscopy system demonstrated that speciation measurements of metal ions and their compounds with very short-lived fluorescence lifetimes can be conducted successfully. Using this laser system, analytical investigation of such elements and compounds is possible in environmentally relevant concentration ranges.
Keywords: time-resolved laser fluorescence spectroscopy, uranium(IV) fluoride, detection limit, fluorescence lifetime, complex formation constant
  • Spectrochimica Acta Part A 73(2009)5, 902-908

Publ.-Id: 11990 - Permalink

Main results of the European project NURESIM on the CFD-modelling of two-phase Pressurized Thermal Shock (PTS)
Lucas, D.; Bestion, D.; Coste, P.; Pouvreau, J.; Morel, C.; Martin, A.; Boucker, M.; Bodele, E.; Schmidtke, M.; Scheuerer, M.; Smith, B.; Dhotre, M. T.; Niceno, B.; Lakehal, D.; Galassi, M. C.; Mazzini, D.; D’Auria, F.; Bartosiewicz, Y.; Seynhaeve, J.-M.; Tiselj, I.; ŠTrubelj, L.; Ilvonen, M.; Kyrki-Rajamäki, R.; Tanskanen, V.; Laine, M.; Puustinen, J.;
Pressurized Thermal Shock (PTS) and Direct Contact Condensation (DCC) were identified by the European project EUROFASTNET as two of the most important industrial needs related to nuclear reactor safety where CFD may bring a real benefit. One typical PTS scenario limiting the Reactor Pressure Vessel (RPV) lifetime is cold water Emergency Core Cooling (ECC) injection into the cold leg during a hypothetical SB-LOCA. The injected water mixes with the hot fluid present in the cold leg and the mixture flows towards the downcomer where further mixing with the ambient fluid takes place. Such a scenario may lead to high thermal gradients in the structural components and consequently to thermal stresses. Therefore, the loads upon the RPV must be reliably assessed. The NURESIM sub-project 2 (Thermohydraulics) Work Package 2.1 focuses on a two-phase flow configuration resulting from a partially or fully uncovered cold leg. In the case of a partially uncovered cold leg, a stratification of cold water on the bottom of the cold leg with counter-current flow of hot water and steam on top of this cold-water layer may occur. There is mixing between hot and cold water. Condensation takes place at the free surfaces between steam and water, e.g. at the cooling water jet. Mixing and condensation are strongly dependent on the turbulence in the fluids. Reliable numerical simulations are required. Two-phase PTS constitutes one of the most challenging exercises for a Computational Fluid Dynamics (CFD) simulation. Presently available CFD tools are not yet able to reproduce all the separate phenomena taking place in the cold leg and the downcomer during the ECC injection, let alone an accurate simulation of the whole process. Improvements of the two-phase modelling capabilities have to be undertaken to qualify the codes for the simulation of such flows. A really accurate simulation of all the phenomena that occur in the scenario will only be possible in the far future and a step-by-step improvement of the quality of the forecasts is necessary. However, a reasonable prediction of the most important phenomena may be reached in a short or medium term and the use of CFD in industrial studies related to PTS is already possible in the frame of some limitations.
Keywords: Pressurized Thermal Shock, CFD, two-phase flow
  • Kerntechnik 74(2009), 238-242

Publ.-Id: 11989 - Permalink

Experimental and numerical analysis of coolant mixing in VVER-1000 in the framework of TACIS project R2.02/02
Höhne, T.; Rohde, U.; Melideo, D.; Moretti, F.; D'Auria, F.; Shishov, A.; Lisenkov, E.;
A pump start-up experiment with the presence of a tracer slug, conducted on a Gidropress mixing facility in the framework of TACIS Project R2.02/02, was simulated with the CFD code ANSYS CFX. The numerical results were compared against the experimental data, which consist in tracer concentration measurements at several locations at the core inlet. The results showed an good agreement with the experiment from the qualitative point of view: in particular, the morphology of the tracer concentration distribution at the core inlet was correctly described. This qualitative agreement is quite an important achievement, since the addressed scenario is featured by a complex, highly three-dimensional, flow distribution in the downcomer. From a quantitative point of view, the results in terms of maximum perturbation (and related timing), core-averaged perturbation are also satisfactory. The perturbation peak is over-predicted by 5%, which is comparable with the experimental uncertainty. The predicted time history of the core-averaged perturbation shows a less smooth trend than the experiment, which seems to indicate a less effective mixing.
Keywords: CFD, pump start up, VVER-1000
  • Contribution to proceedings
    Jahrestagung Kerntechnik 2009, 12.-14.05.2009, Dresden, Deutschland
  • Lecture (Conference)
    Jahrestagung Kerntechnik 2009, 12.-14.05.2009, Dresden, Deutschland

Publ.-Id: 11986 - Permalink

Superconducting Ge:Ga layers produced by ion implantation and flash lamp annealing
Heera, V.; Herrmannsdörfer, T.; Ignatchik, O.; Mücklich, A.; Posselt, M.; Reuther, H.; Schmidt, B.; Skorupa, W.; Voelskow, M.; Wündisch, C.; Wosnitza, J.; Helm, M.;
Recently, superconductivity has been discovered in heavily boron-doped group IV semiconductors like diamond [1] and silicon [2]. Because theoretical studies predict only a weak tendency to superconductivity in heavy p-type doped Ge [3] investigations of the low-temperature transport behaviour in Ge are still lacking.
In order to obtain superconductivity in group IV semiconductors, heavy p-type doping above the metal-insulator-transition and low lattice damage is required. The combination of both conditions make it difficult to apply ion implantation as doping technique. The challenge is to reconstruct the damaged or even amorphized crystal lattice and to activate the acceptor atoms after implantation by annealing, avoiding at the same time long range diffusion and precipitation of the acceptors in the supersaturated semiconductor. So far only in-situ doping during growth (high-temperature-high-pressure synthesis [1] and chemical vapour deposition) for boron-doped diamond and ultra-short-time laser melting of the Si surface in BCl3 atmosphere (gas immersion laser doping [2]) have met these conditions.
Here an alternative process compatible with semiconductor technology is presented. Ga implantation and flash lamp annealing in the ms range enables the production of Ga supersaturated (up to 15 at%) crystalline Ge layers which become superconducting below 0.5 K.
The layer structure investigated by AES, XTEM, RBS/C and the electrical transport properties at low temperatures are reported.

[1] E. A. Ekimov, V. A. Sidorov, E. D. Bauer, et al. , Nature 428 (2004) 542
[2] E. Bustarret, C. Marcenat, P. Achatz, et al., Nature 444 (2006) 465
[3] L. Boeri, J. Kortus, O. K. Anderson, J. Phys. Chem. Solids 67 (2006) 552
Keywords: Germanium, Ga-Implantation, Flash lamp annealing, superconductivity
  • Poster
    IBMM 2008 - 16th International Conference on Ion Beam Modification of Materials, 31.08.-05.09.2008, Dresden, Deutschland

Publ.-Id: 11985 - Permalink

Structural identification of thioarsenates by EXAFS
Suess, E.; Scheinost, A. C.; Bostick, B. C.; Merkel, B. J.; Wallschlaeger, D.; Planer-Friedrich, B.;
short-range structure of thioarsenite and mono-, di-, tri-, and tetra-arsenate determined by XAS
Keywords: arsenic EXAFS XANES XAS thioarsenate thioarsenite
  • Poster
    Synchrotron Environmental Science IV, 11.-13.12.2008, San Francisco, USA
  • Poster
    AGU Fall Meeting 2008, 15.-19.12.2008, San Francisco, USA

Publ.-Id: 11984 - Permalink

NanoFoto - Neue Wege zur verwertungsorientierten Netzwerkbildung in der Nanobiotechnologie
Pollmann, K.; Raff, J.;
Ziel des Vortrags ist es, einen Überblick über die laufenden und geplanten Aktivitäten im Rahmen des NanoFoto-Projekts zu geben. Wissenschaftlich steht die Nutzung bakterieller Hüllproteine zur Entwicklung fotokatalytisch aktiver Schichten zur Eliminierung von Arzneimittelrückständen aus Wasser im Mittelpunkt. Ergänzt werden die wissenschaftlichen Arbeiten durch zahlreiche Maßnahmen zur Verwertung erhaltener Ergebnisse und zur verwertungsorientierten Netzwerkbildung.
  • Lecture (others)
    Kick-off Meeting / 1. Workshop „Entwicklung und Erprobung neuer Instrumente zur Bildung von Verwertungs- und Transfernetzen in der Leibniz-Gemeinschaft“, 11.03.2008, Berlin, Deutschland
  • Lecture (others)
    2. Projekt-Workshop zum Thema „Verwertungsorientierte Netzwerke“, 16.12.2008, Berlin, Deutschland

Publ.-Id: 11982 - Permalink

Granular magnetic ZnO: structure, magnetism and transport properties
Zhou, S.; Potzger, K.; Xu, Q.; Shalimov, A.; Schmidt, H.; Helm, M.; Fassbender, J.ORC
Transition metal (TM) doped ZnO has been extensively investigated due to its potential application as a diluted magnetic semiconductor with Curie temperature above room temperature (RT). After one decade effort, however the research community realized that (i) ZnO diluted with TM ions only shows paramagnetism [1], and (ii) the observed ferromagnetic signal mostly originates from secondary phases [2,3]. The aim of our research is now to investigate the application potential of granular structures which are created by TM ion implantation into ZnO single crystals. By varying implantation and post-annealing temperatures, we can control the chemical state of TM ions. ZnO with dispersed TM ions can be obtained by ion implantation at temperatures below RT or by using defective ZnO substrates. In this case, TM ions are in ionic states, and only show paramagnetism. Concerning the nature of phase separation, three regimes have been established. (I) ZnO embedded with TM nanocrystals can be obtained by ion implantation at elevated temperatures (e.g. 350oC) and by post-annealing at mild temperatures (below 350oC). In this regime, TM ions are mostly in metallic states (i.e. Fe, Co, Ni). Co and Ni nanocrystals have crystallographic orientation relationship with the ZnO matrix [2]. (II) ZnO embedded with nanocrystalline spinel ferrites AFe2O4 (A=Zn, Co, Ni) can be obtained by co-implantation pulsing post-annealing at 800 oC [4,5]. (III) ZnO embedded with disordered nanosized regions can be obtained by ion implantation with very large ion-fluences. The heavily disordered nanosized regions consists of large Co concentration [6]. Although ferromagnetism has been observed in all the three regimes, magneto-transport properties are drastically different. Only ordinary magneto-resistance (MR) has been observed in regimes I and II, while the samples in regime III reveal negative MR and anomalous Hall effect simultaneously. The anomalous Hall resistivity is saturated at low field giving hope for applicability in spintronics.

[1] A. Ney, , et al., Phys. Rev. Lett. 100, 157201 (2008)
[2] S. Zhou, et al., Phys. Rev. B 77, 035209 (2008).
[3] K. Potzger, and S. Zhou, phys. stat. sol. (a), submitted (2008).
[4] S. Zhou, et al., J. Phy. D-Appl. Phys., 40, 964 (2007).
[5] S. Zhou, et al., Phys. Rev. B, submitted (2008).
[6] K. Potzger, et al., Appl. Phys. Lett., submitted (2008).
  • Poster
    Magnetism meets Semiconductors: Spin Phenomena in Heterostructures and Novel Materials, 05.-07.01.2009, Bad Honnef, Germany
  • Poster
    5th International School and Conference on Spintronics and Quantum Information Technology, 04.-11.07.2009, Krakow, Poland

Publ.-Id: 11981 - Permalink

Magneto-transport properties of nanocomposite cobalt/carbon systems
Zhou, S.; Berndt, M.; Bürger, D.; Abrasonis, G.; Heera, V.; Fassbender, J.ORC; Helm, M.; Schmidt, H.
In producing diluted magnetic semiconductors (DMS), it remains challenging to obtain a uniform distribution of magnetic ions. Composite ferromagnet/semiconductor systems are easily formed when the concentration of magnetic ions is larger than its solubility at given preparation conditions. This is usually considered as a failure for spintronics applications. However, as long as the embedded (nano)ferromagnets can polarize charge-carriers in the semiconducting matrix, the composite systems can also fullfill spintronics requirements. For example, nanocomposite systems with ferromagnetic MnAs nanocrystals being epitaxially embedded inside GaAs matrix reveal a giant magnetoresistance [1]. Recently, the phase separation in Mn doped Ge [2] and Si [3] has been indentified by high resolution characterization techniques. Therefore, the research interest in composite ferromagnet/semiconductor systems arises in parallel with that in DMS materials. Here we present the magnetic and magneto-transport properties of cobalt nanocrystals embedded inside carbon. Co(40%)/C nanocomposite films were prepared by ion beam co-sputtering method using silicon substrates with a 500 nm thick oxide layer. The phase separation was controlled by varing substrate temperatures from room temperature to 500 °C. We have measured their magnetic and magneto-transport properties. Two significant observations will be discussed: (i) a giant anomalous Hall effect (AHE) amounting to 2 μohm cm compared with pure Co metal [4], and (ii) a negative magnetoresistance. This encourages future applications in Hall sensors and spintronic-devices.
  • Poster
    Magnetism meets Semiconductors: Spin Phenomena in Heterostructures and Novel Materials, 05.-07.01.2009, Bad Honnef, Germany
  • Lecture (Conference)
    SPIE Europe Microtechnologies for the New Millennium, 04.-06.05.2009, Dresden, Germany
  • Poster
    International Conference on Magnetism, 26.-31.07.2009, Karlsruhe, Germany

Publ.-Id: 11980 - Permalink

ZnO-based magnetic tunnel junctions
Zhou, S.; Xu, Q.; Hartmann, L.; Mücklich, A.; Helm, M.; Biehne, G.; Hochmuth, H.; Lorenz, M.; Grundmann, M.; Schmidt, H.;
Spin-polarized tunnel magnetoresistance (TMR) effects occur when two ferromagnets are separated by a thin insulator. The resistance of the tunneling current changes with the relative magnetization orientation of the magnetic bottom and top electrode. The research in this field is fuelled by the demanding of magnetoresistive random access memory (MRAM) devices. Novel MRAM cells are based on magnetic tunnel junctions with current-induced switching. It has been shown that semiconductors need a current pulse for switching which is two orders of magnitude smaller in comparison to metals. Using wide-gap magnetic semiconductors, e.g. ZnO, the magnetic tunnel structure may be transparent and may possess a Curie temperature above room temperature. In this talk, we report the clearly observed tunneling magnetoresistance at 5 K in magnetic tunnel junctions with Co-doped ZnO as the bottom electrode and Co as the top electrode prepared by pulsed laser deposition and thermal evaporation [1], respectively. Spin-polarized electrons were injected from Co-doped ZnO to the crystallized Al2O3 separation layer and tunnelled through the amorphous part of the Al2O3 barrier. Our studies demonstrate the spin polarization in Co-doped ZnO and its possible application in future ZnO-based spintronics devices.
[1] Q. Xu et al., Phys. Rev. Lett. 101, 076601 (2008)
  • Lecture (Conference)
    DPG Frühjahrstagung der Sektion Kondensierte Materie (SKM) 2009, 22.-27.03.2009, Dresden, Germany

Publ.-Id: 11979 - Permalink

Semiconductor-based tunnel structures: preparation and application
Zhou, S.; Schmidt, H.;
Spin-polarized tunnel magnetoresistance (TMR) effects occur when two ferromagnets are separated by a thin insulator. The resistance of the tunneling current changes with the relative magnetization orientation of the magnetic bottom and top electrode [1,2]. The research in this field is fuelled by the demanding of magnetoresistive random access memory (MRAM) devices. In 2004, Parkin et al. were able to make Fe/MgO/Fe junctions with 200% TMR at room temperature [3]. However, the development of high-density metal-based MRAM scale devices is hampered by large switching fields and multidomain structures. Theoretically, diluted magnetic semiconductors (DMS) reveal a larger degree of spin polarization and therefore also bigger spin transport effects. Mn-doped GaAs is a successful DMS and magnetic tunnel junctions based on epitaxially grown GaMnAs/AlAs/GaMnAs have shown promising TMR values up to 75% at 8 K [5]. Novel MRAM cells are based on magnetic tunnel junctions with current-induced switching. It has been shown that semiconductors [6] need a current pulse for switching which is two orders of magnitude smaller in comparison to metals [7]. Using wide-gap magnetic semiconductors, e.g. ZnO, the magnetic tunnel structure may be transparent and may possess a Curie temperature above room temperature [9,10].

In this talk, we report the clearly observed tunneling magnetoresistance at 5 K in magnetic tunnel junctions with Co-doped ZnO as the bottom electrode and Co as the top electrode prepared by pulsed laser deposition and thermal evaporation [11], respectively. Spin-polarized electrons were injected from Co-doped ZnO to the crystallized Al2O3 separation layer and tunnelled through the amorphous part of the Al2O3 barrier. Our studies demonstrate the spin polarization in Co-doped ZnO and its possible application in future ZnO-based spintronics devices. Additionally, we will show preliminary results of Si:Mn based tunnelling structures. In this system, SiO2 is the barrier layer while ferromagnetic granular Si:Mn obtained by Mn ion implantation into Si and Co are the bottom and top electrode, respectively.

[1] J. S. Moodera et al., Phys. Rev. Lett. 74, 3273 (1995).
[2] T. Miyazaki et al., J. Magn. Magn. Mater. 139, L231 (1995).
[3] S. S. P. Parkin et al., Nat. Mat. 3, 862 (2004).
[4] S. D. Sarma et al., Solid State Commun. 119, 207 (2001).
[5] M.Tanaka et al., Phys.Rev. Lett. 87, 026602 (2001).
[6] M. Yamanouchi et al., Nature 428, 539 (2004).
[7] J.A. Katine et al., Phys. Rev. Lett. 84, 3149 (2000).
[8] T. Jungwirth et al., Phys. Rev. B 72, 165204 (2005).
[9] T. Dietl et al., Science 287, 1019 (2000).
[10] K. Sato et al., Jpn. J. Appl. Phys. 39, L555 (2000).
[11] Q. Xu et al., Phys. Rev. Lett. 101, 076601 (2008)
  • Invited lecture (Conferences)
    International Workshop on Advances in Spintronic Materials: Theory and Experiment, 26.-28.11.2008, Duisburg, Germany

Publ.-Id: 11978 - Permalink

n-type diamond produced by MeV lithium implantation in channeling direction
Chernyshev, V.; Meijer, J.; Grambole, D.; Herrmann, F.; Dagkaldiran, U.; Wieck, A.;
Natural diamond implanted with lithium ions at high energy (E = 2MeV) in axial channeling direction is investigated. Hall measurements show n-type conductivity caused by the lithium implantation. These measurements show two regions in the Arrhenius plot for both resistance and charge carrier concentration. The resistance measurement in the low and high temperature range revealed the activation energies of E-Rlow = 406meV and E-Rhigh = 105meV. The slope for the charge carrier concentration shows a more complex behaviour. After annealing, the n-type conductivity caused by implanted lithium disappears.
  • Diamond and Related Materials 17(2008)11, 1933-1935

Publ.-Id: 11977 - Permalink

Breakup and coalescence models for turbulent air-water mixtures in a vertical pipe
Liao, Y.; Lucas, D.;
The evolution of bubble size distribution and radial air volume fraction was studied by an efficient 1D test solver. New constitutive models for bubble coalescence and breakup due to different mechanisms, including coalescence due to turbulent fluctuation, velocity shear and wake entrainment, and breakup due to turbulent fluctuation, velocity shear and interfacial slip velocity, was proposed. Simulation results showed that at relatively low superficial gas velocities, the bubble size was small and had a narrow distribution, and coalescence was predominant; with an increase in the superficial gas velocity, large bubbles began to form due to the dominance of coalescence, resulting in a much wider bubble size distribution, and breakup became dominant. The simulation results were compared with the recent experimental data achieved on the TOPFLOW facility and good agreements were achieved.
Keywords: new models, bubble coalescence and breakup, bubble size distribution, radial gas volume fraction
  • Contribution to proceedings
    Jahrestagung Kerntechnik 2009, 12.-14.05.2009, Dresden, Germany
  • Lecture (Conference)
    Jahrestagung Kerntechnik 2009, 12.-14.05.2009, Dresden, Germany

Publ.-Id: 11976 - Permalink

A Silver Containing Liquid Alloy Ion Source
Mazarov, P.; Bischoff, L.; Pilz, W.; Wieck, A.;
A Silver-Germanium Liquid Alloy Ion Source (LAIS) was developed and is available. Good beam performance was obtained for application in any commercial focused ion beam (FIB) system. Emission current dependent measurements were carried out of the mass spectra and energy spreads of all ion components. The ratios of doubly- and singlecharged clusters to single-charged monomer ions were determined. The AgGe-LMAIS can be very helpful for controlled formation of silver quantum wires.
[1] Thibaut Capron Phys. Rev. B77, 033102 (2008).
Keywords: Silver-Germanium Liquid Alloy Ion Source; Focused Ion Beam; Quantum Wires
  • Poster
    DPG Frühjahrstagung der Sektion Kondensierte Materie (SKM) 2009, 22.-27.03.2009, Dresden, Deutschland

Publ.-Id: 11975 - Permalink

Alloy Liquid Metal Ion Sources for new FIB applications
Bischoff, L.; Pilz, W.; Mazarov, P.; Wieck, A.;
Recently, mass separated focused ion beams (FIB) become an increasing interest for local doping in nano-devices for optical, electrical or magnetic applications [1]. So on the basis of very stable metallic glass alloys, like AuSi or AuGe with a low melting point at 365°C different ion sources were developed and tested due to their performance in FIB systems. In detail, Au68Ge22B5Ni5, Au80Si12Sb8, Au68Ge28Mn10 alloys were analysed concerning the on-set and emission behaviour and the mass spectra. Among clusters, molecular ions, single and doubly charged species such important ions like boron for p-doping in silicon, antimony for n-doping in silicon or manganese for quantum dot fabrication in II-VI semiconductors (CdSe, CdS, ZnS) could be extracted.
[1] L. Bischoff, NIM B266 (2008) 1846.
Keywords: alloy liquid metal ion source; dopands; cluster
  • Poster
    DPG Frühjahrstagung der Sektion Kondensierte Materie (SKM) 2009, 22.-27.03.2009, Dresden, Deutschland

Publ.-Id: 11974 - Permalink

Focused ion beam activities at FZD
Bischoff, L.;
During the last decades, focused ion beams (FIB) became a very useful and versatile tool in microelectronics industry, as well as in the field of basic and applied research and derived an exceedingly importance within the nanotechnology. For special purposes like ion milling, ion beam writing for doping or patterning from the µm- to the nm-range without any lithographic steps using Gallium and also other ion species which are of increasing interest. An introduction in design and operation of mass separated FIB systems, equipped with alloy liquid metal ion sources and the development and characterization of suited ion sources is given.
Examples, like ion beam synthesis of CoSi2 nano-structures, sputtering investigations and applications, the formation of ripples under FIB irradiation or the fabrication of NEMS structures on SOI substrates should demonstrate the manifold utilization of the microbeam technology.
Finally an outlook to prospective work with FIB in FZD is presented.
Keywords: Focused Ion Beam; alloy Liquid Metal Ion Source; Nanotechnology
  • Lecture (others)
    Institutsseminar, 14.11.2008, Bochum, Deutschland

Publ.-Id: 11973 - Permalink

Ultra fast electron beam X-ray CT scanner for two-phase flow measurement
Fischer, F.; Hampel, U.;
Two-phase flows are of primary importance in the understanding of thermal hydraulic phenomena in nuclear light water reactors. The qualification of CFD codes for the simulation of stationary and even transient two-phase flows in complex three dimensional geometries requires extending our knowledge toward the details of the flow structure under various thermal hydraulic conditions. At Forschungszentrum Dresden-Rossendorf the thermal hydraulic test facility TOPFLOW is currently extensively used to conduct two-phase flow experiments which aim at the disclosure of fine flow structure details in generic and also more complex geometries. Consequently, we have extended our measurement technology for two-phase flow to highspeed X-ray tomography which offers non-intrusive flow measurement at high pressure and high temperatur at a speed comparable to the wire-mesh sensor [2], [3], [4], [5]. For that reason we have developed a scanned electron beam X-ray apparatus where a electron beam is swept around an object on a circular X-ray target. Thus a rapidly moving X-ray spot is generated. The apparatus can perform cross-sectional imaging at high frame rates and will in the future be extended to other measurement features, such as multi-plane tomography, phase velocity measurement, higher scanning diameters and high energy X-rays. This paper introduce the scanner design, discuss major performance parameters along with an application example and show how this scanner will be applied to air-water and steam-water two-phase flow measurement in a vertical test section of the TOPFLOW facility.
Keywords: electron beam X-ray CT, two-phase flow measurement
  • Contribution to proceedings
    Jahrestagung Kerntechnik 2009, 12.-14.05.2009, Dresden, Germany
  • Lecture (Conference)
    Jahrestagung Kerntechnik 2009, 12.-14.05.2009, Dresden, Germany

Publ.-Id: 11972 - Permalink

Inverse energy transfer process during electroluminescence in Er-doped SiO2 layers containing Ge nanocrystals
Kanjilal, A.; Rebohle, L.; Voelskow, M.; Skorupa, W.; Helm, M.;
For a comparative study of the energy transfer mechanism during room temperature electroluminescence (EL), two sets of samples have been prepared by implanting either Ge and Er ions (type-I) or Si and Er ions (type-II) into a 200 nm SiO2 layer combined with rapid-thermal-annealing. Three reference samples have been prepared by implanting only Er, Ge or Si ions in SiO2 followed by post-implantation annealing. The formation of Si and Ge nanocrystals (NCs) was confirmed by transmission electron microscopy. The metal-oxide-semiconductor dot structure was prepared by depositing indium-tin-oxide and Al films on the front and rear sides of the structure. Quantum-confinement mediated recombination of carriers in Si-nanocrystals (Si-NCs) as well as the triplet (T1) → singlet (S0) transition in the O3-Si-Si-O3 oxygen deficient centre (ODC) provides the 750 and 475 nm bands, respectively, in the only Si-implanted sample. Conversely, the 525, 550, 660 and 1532 nm emissions corresponding to the deexcitation of the 2H11/2, 4S3/2, 4F9/2 and 4I13/2 states to the ground state 4I15/2 of the Er3+, respectively, were recorded for the Er-doped SiO2 layer. A blue-violet light at ~400 nm, representing the T1→S0 transition in the O3-Si-Ge-O3 ODC, was observed in the Ge-NCs embedded SiO2 layer. Although the intensity of the Er-related visible/infrared EL signals in type-I sample was found disappearing/decreasing with a concomitant enhancement of the 400 nm band, a sharp rise in intensity of the 1532 nm Er EL at the expense of the Si-NC related 750 nm band was evidenced in type-II sample. While the later result confirms the energy transfer mechanism from Si-NCs to the nearest Er3+, the former finding can be explained in terms of the energy transfer from Er3+ to the Ge-related ODC.
Keywords: nanocrystals, Ge, electroluminescence
  • Lecture (Conference)
    IBMM2008 - 16th International Conference on Ion Beam Modification of Materials, 31.08.-05.09.2008, Dresden, Germany

Publ.-Id: 11971 - Permalink

Measurement of dynamic liquid distributions in a fixed bed using electrical capacitance tomography and capacitance wire mesh sensor
Matusiak, B.; Da Silva, M. J.; Romanowski, A.; Hampel, U.;
An intricate problem associated with fixed bed operation is liquid maldistribution, which denotes the fact that the liquid does not homogeneously flow through the bed. In a comparative study we evaluated two capacitance imaging methods - capacitance wire mesh sensor and electrical capacitance tomography (ECT) - with respect to their capability of measuring static and dynamic liquid holdup in a fixed bed. We performed experiments in a column of 100 mm diameter, packed with commercial porous Al2O3 catalyst particles. The column was operated at ambient pressure. Inlet flow of isopropanol from various point sources was applied at rates of 40 L/h and 60 L/h. The capacitance wire mesh sensor as an invasive instrument is able to disclose flow structures at higher spatial resolution and was therefore considered as the reference instrument for liquid holdup measurement. We found that both methods predict dynamic liquid holdup in the column in a similar way with only small systematic deviation. The results therefore prove that non-invasive electrical capacitance tomography can reliably measure cross-sectional dynamic liquid holdup in a fixed bed, even with a simple and fast linear back projection reconstruction algorithm.
Keywords: Wire-mesh sensor, ECT, Multiphase flow, Trickle bed, Liquid holdup, Liquid distribution
  • Industrial & Engineering Chemistry Research 49(2010)5, 2070-2077
    DOI: 10.1021/ie900988f

Publ.-Id: 11970 - Permalink

Research needed for improving heavy ion therapy
Kraft, G.; Kraft, S. D.;
The large interest in heavy ion therapy is stimulated from its excellent clinical results. The bases of this success are the radiobiological and physical advantages of heavy ion beams and the active beam delivery used for an Intensity Modulated Particle Radiotherapy (IMPT). Although heavy ion therapy has reached a high degree of perfection for the clinical use there is still large progress possible to improve this novel technique: In order to extend IMPT to more tumor entities and to tailor the planning more individually for each patient in an adaptive way, radiobiological work both experimentally and theoretically is required. It is also not clear whether the neighboring ions to carbon could have a clinical application as well. For this extension basic biological works as well as physics experiments have to be performed.

On the technical side many improvements of the used equipment seems to be possible. Two major topics are the extension of IMPT to moving organs and the transition to more compact and therefore cheaper particle accelerators.

In this paper these topics are treated to some extent in order to give an outline of the great future potential of ion beam therapy.

Publ.-Id: 11969 - Permalink

Spectral-history modeling in DYN3D burnup calculations
Bilodid, Y.; Mittag, S.;
Burnup spectral-history effects are reflected in deviations in the actual nuclide concentrations within the fuel. The deviations of different nuclides are correlated. It is possible to treat the nuclide concentration change by tracing only one nuclide – Pu-239. Implementation of historical correction for 2-group cross sections method in DYN3D is described in this paper.
Keywords: DYN3D, spectral-history effects, burnup history effect, burnup, cross sections
  • Contribution to proceedings
    Jahrestagung Kerntechnik 2009, 12.-14.05.2009, Dresden, Germany
  • Lecture (Conference)
    Jahrestagung Kerntechnik 2009, 12.-14.05.2009, Dresden, Germany

Publ.-Id: 11968 - Permalink

Nitrogen diffusion in single crystalline austenitic stainless steel: ion energy and flux effects
Martinavičius, A.; Abrasonis, G.; Möller, W.; Chumlyakov, Y.;
Nitrogen diffusion in single crystalline austenitic stainless steel during ion beam nitriding is investigated. Single crystalline AISI 316L austenitic stainless steel (ASS) with orientation (001) has been ion beam nitrided at 400 °C using a Kaufman-type ion source. The acceleration voltage has been varied from 450 to 1200 eV, and the current density from 0.3 to 0.7 mA cm−2. XRD analysis shows the presence of the phase usually called “expanded” austenite or γN phase. The nitrogen depth profiles have been determined using nuclear reaction analysis (NRA). The profiles of nitrided samples can be depicted by an initial quasi-linear decrease followed by a sharp leading edge. The nitrogen penetration depth is significantly higher for higher implantation energies as well as for higher current densities. The result cannot be explained by the difference of the sputtering rate.
The “trapping-detrapping” model, which is able to reproduce the full shape of the nitrogen depth, has been used to fit nitrogen depth profiles and extract the diffusion coefficient values. The nitrogen profile fitting shows that the nitrogen diffusion coefficient strongly depends on irradiation flux and ion energy during ion beam nitriding, confirming the tendencies deduced directly from the nitrogen distribution profiles.
  • Lecture (Conference)
    22nd International Conference on Surface Modification Technologies - SMT22, 24.09.2008, Trollhättan, Sweden

Publ.-Id: 11967 - Permalink

Nitrogen diffusion in single crystalline austenitic stainless steel during ion beam nitriding and subsequent thermal annealing
Martinavičius, A.; Abrasonis, G.; Möller, W.; Templier, C.; Rivière, J. P.; Declémy, A.; Chumlyakov, Y.;
Nitrogen diffusion in single crystalline austenitic stainless steel during ion beam nitriding and subsequent annealing is investigated. Single crystalline [orientations (001), (110) and (111)] and polycrystalline AISI 316L austenitic stainless steel (ASS) has been ion beam nitrided at 400 °C for 60 min using a Kaufman-type ion source with an acceleration voltage of 1 keV and a current density of 0.5 mA cm−2. XRD analysis shows the presence of the phase usually called “expanded” austenite or γN phase. The samples have been subsequently vacuum annealed at 400°C for 30 min. The nitrogen distribution profiles have been determined using nuclear reaction analysis (NRA). The profiles of as-nitrided samples can be depicted by an initial quasi-linear decrease followed by a sharp leading edge. Despite identical nitriding conditions, the nitrogen penetration depth is significantly higher in the single crystal with the (001) orientation than in the samples with the orientations (011) or (111) which cannot be explained by the orientational dependence of the sputtering rate. The surface concentration for the single crystal with the (001) orientation was about 27 at.% with the depth of the quasi-linear part about 1.5 µm. For the orientations (011) and (111) the surface concentration was 25 at.% and the depth of the quasi-linear part about 1 µm and 0.7 µm respectively. Polycrystalline ASS presents an intermediate case. Subsequent annealing results in the decrease of near-surface nitrogen concentration, flattening of the quasi-linear part of the depth profile and nitrogen inward diffusion without any detectable nitrogen loss due to out-diffusion.
The “trapping-detrapping” model, which is able to reproduce the full shape of the nitrogen depth profile in as-nitrided as well as subsequently annealed single crystalline ASS, has been used to fit nitrogen depth profiles and extract the diffusion coefficient values. The nitrogen profile fitting shows that the nitrogen diffusion coefficient is strongly orientation dependent during ion beam nitriding confirming the tendencies deduced directly from the nitrogen distribution profiles. This anisotropy is not present during thermal annealing, while the diffusion coefficients extracted from the fitting exhibit significantly lower values than those obtained from as-nitrided samples.
  • Poster
    Eleventh International Conference on Plasma Surface Engineering, 16.09.2008, Garmisch-Partenkirchen, Germany

Publ.-Id: 11966 - Permalink

Fe nanoparticles embedded in MgO crystals
Shalimov, A.; Potzger, K.; Geiger, D.; Lichte, H.; Talut, G.; Misiuk, A.; Reuther, H.; Stromberg, F.; Zhou, S.; Baehtz, C.;
Iron nanoparticles embedded in MgO crystals were synthesized by Fe+ ion implantation at an energy of 100 keV and varying fluences from 3*10E16 to 3*10E17 cm-2. Investigations of structural and magnetic properties of Fe nanoparticles have been performed using magnetometry, x-ray diffraction, transmission electron microscopy and Mössbauer spectroscopy, as well as by theoretical Preisach modeling of bistable magnetic systems. It has been found that alpha- and gamma-Fe nanoparticles are formed for all fluences. The content of the alpha-Fe phase increases at higher fluences and after annealing. The influence of post implantation annealing at 800 C in vacuum and under enhanced up to 10 kbar hydrostatic pressure in argon atmosphere on the formation of nanoparticles has been analyzed. Investigations have been performed within DFG project PO1275/2-1 ”SEMAN”.
Keywords: magnetic nanoparticles, iron, Preisach modelling
  • Lecture (Conference)
    DPG Frühjahrstagung der Sektion Kondensierte Materie (SKM) 2009, 22.-27.03.2009, Dresden, Germany

Publ.-Id: 11965 - Permalink

’Invisible’ ferromagnetic secondary phases in Co doped ZnO
Potzger, K.; Zhou, S.; Muecklich, A.; Xu, Q.; Schmidt, H.; Helm, M.; Fassbender, J.ORC
The search for ferromagnetic transition-metal doped ZnO, i.e., diluted magnetic semiconductors (DMS), has turned into the search for unwanted secondary phases by high-resolution structural analysis [1]. Such phases even can lead to anomalous Hall effect arising from charge carrier spin polarization. In this talk we show that the general analysis technique for the identification, i.e. x-ray diffraction spectroscopy, fails to identify a recently observed kind of ferromagnetic inclusions with heavy crystalline disorder. We discuss the properties of those clusters using the popular Co:ZnO system.
[1] K. Potzger, S. Q. Zhou, H. Reuther, A. Mucklich, F. Eichhorn, N. Schell, W. Skorupa, M. Helm, J. Fassbender, T. Herrmannsdorfer, T. P. Papageorgiou, Appl. Phys. Lett. 88, 052508 (2006).
Keywords: zno, diluted magnetic semiconductors
  • Lecture (Conference)
    DPG Frühjahrstagung der Sektion Kondensierte Materie (SKM) 2009, 22.-27.03.2009, Dresden, Deutschland

Publ.-Id: 11964 - Permalink

Accelerator mass spectrometry (AMS) and ion beam analysis (IBA) with the new 6 MV accelerator at FZ Dresden-Rossendorf
Munnik, F.; Grambole, D.; Grötzschel, R.; Merchel, S.; Neelmeijer, C.;
Since more than 30 years IBA is performed at the Forschungszentrum Dresden-Rossendorf (FZD) for the determination of element distributions. Due to continuous upgrades of the different experimental set-ups, we are able to routinely perform:
• Rutherford Backscattering Spectrometry (RBS) & Channeling (C-RBS)
• Nuclear Reaction Analysis (NRA)
• Elastic Recoil Detection Analysis (ERDA)
• Particle-Induced X-Ray (PIXE) and Gamma-Emission (PIGE)
Most of our applications lie within material sciences. We are able to measure non-destructively “all natural” elements, i.e. H to U; most elements with lateral, some in 3-D resolution with the following typical parameters (matrix- and analyte-depending):
• depth resolution: 1-30 nm
• depth range: nm-µm
• lateral resolution: few µm
• usual mapping area: 2x2 mm2
• maximum sample size: 3x10 cm2 (vacuum) & “unlimited” (external beam)
• detection limits: ~10 µg/g (H); 500 µg/g – 1% (He-F); 10-100 µg/g (Na-U)
For some elements, e.g. H/D, isotope analysis is also possible.
In summer 2009, our 5 MV van-de-Graaff accelerator will be replaced by the latest 6 MV Tandetron model [1], which is even more sophisticated than the lately installed 5 MV one in Southern France [2]. The new accelerator will need less maintenance generally allowing more beam time. It might be also possible to expand from two to three 8-hour-shifts a day with the new fully automatic system. Scientifically, the main advantages are an increased depth range by a factor of 2 for ERDA and improved detection limits for NRA.
In addition, the machine will have special equipment for AMS [3]. There is a main advantage of using a high-energy accelerator for mass spectrometry: The background and interfering signals, resulting from molecular ions and ions with similar masses (e.g. isobars) are nearly completely eliminated. Thus, AMS provides much lower detection limits compared to conventional mass spectrometry (isotope ratios: 10-10-10-15).
In contrast to common low-energy AMS facilities, which have mainly specialized in radiocarbon analyses (14C), the FZD-AMS is the first modern-type facility in the EU that will run at a terminal voltage of 6 MV. Especially in environmental and geosciences, the determination of long-lived (t1/2 > 0.3 Ma) cosmogenic radionuclides like 10Be, 26Al, and 36Cl became more and more important within the last decades [4]. Using these nuclides dating of e.g. volcanic eruptions, rock avalanches, earth quakes, and glacier movements is possible.
References: [1] A. Gottdang et al., Nucl. Instr. and Meth. B 2002, 190, 177. [2] M.G. Klein et al., Nucl. Instr. and Meth. B 2008, 266, 1828. [3] [4] J.C. Gosse and F.M. Phillips, Quat. Sci. Rev. 2001, 20, 1475.
Keywords: accelerator mass spectrometry, ion beam analysis
  • Poster
    ANAKON 2009, 17.-20.03.2008, Berlin, Deutschland

Publ.-Id: 11963 - Permalink

The role of aspartyl-rich pentapeptides in comparative complexation of actinide(IV) and iron(III). Part 1
Jeanson, A.; Berthon, C.; Coantic, S.; Den Auwer, C.; Floquet, N.; Funke, H.; Guillaneux, D.; Hennig, C.; Martinez, J.; Moisy, P.; Petit, S.; Proux, O.; Quemeneur, P.; Solari, P. L.; Subra, G.;
Although there is a tremendous volume of data available on the interaction of actinides with living organisms as plants, nearly all the studies are limited to macroscopic or physiological 3 measurements with no specific information at the molecular level. Peptides allow the study of complex coordination chemistry, as that involving actinide(IV) and proteins, without the intricacy of tertiary structure properties. For that purpose, a linear pentapeptide, acetyldiaspartyl-prolyl-diaspartyl-amide (Ac-Asp-Asp-Pro-Asp-Asp-NH2, called PP1 in this report), was synthesized and investigated as a potential chelating ligand of thorium(IV), neptunium(IV), and/or plutonium(IV) cations. Comparison with biological relevant iron(III) cation is also provided. Noteworthy, PP1 was able to prevent Np(IV) from hydrolysis into an insoluble precipitate. Spectrophotometry, 13C NMR and EXAFS at the iron K edge and actinide L3 edges were used to probe the cation coordination sphere and better describe the cation-peptide interaction. The complexes were found to be polynuclear with oxo or hydroxo bridged cations, Fe(III) forming a binuclear complex, Th(IV), Np(IV) or Pu(IV) forming a polynuclear complex with higher nuclearities.
Keywords: Peptides, Actinides, EXAFS
  • New Journal of Chemistry 33(2009), 976-985

Publ.-Id: 11962 - Permalink

Ultrafast infrared and THz spectroscopy of semiconductor quantum structures
Schneider, H.;
This talk gives an overview on our activities in nonlinear laser spectroscopy using the free-electron laser at FZD and tabletop lasers. Our research concentrates on III-V semiconductor quantum wells and superlattices. In particular, I will discuss two-photon absorption and photocurrent autocorrelation involving intersubband transitions in quantum wells at mid-infrared wavelengths.
  • Lecture (others)
    Seminar, IIN-IFW Dresden, 12.12.2008, Dresden, Deutschland

Publ.-Id: 11961 - Permalink

Two-photon photocurrent studies of electron intersubband dynamics in multiple quantum wells
Schneider, H.;
Quantum wells comprising three equidistant subbands, two of which are bound in the well and the third one in the continuum, result in a resonantly enhanced coefficient for two-photon absorption, which is by six orders of magnitude stronger than in usual semiconductors. Exploiting this nonlinearity in two-photon detectors, quadratic autocorrelation of a free-electron laser has recently been demonstrated at room temperature [1]. Temporal resolution of such a two-photon autocorrelator is only limited by the sub-ps intrinsic time constants of the intersubband transition, namely the intersubband relaxation time and the phase relaxation time. Using sub-ps mid-infrared pulses, the approach allows us to determine systematically the dependence of these time constants on structural parameters, and to discriminate between different scattering processes [2].
[1] H. Schneider, H. C. Liu, S. Winnerl, O. Drachenko, M. Helm, J. Faist, Appl. Phys. Lett. 93, 101114 (2008).
[2] H. Schneider, T. Maier, M. Walther, H. C. Liu, Appl. Phys. Lett. 91, 191116 (2007).
Keywords: intersubband transition, two-photon absorption, quantum well infrared photodetector, phase relaxation, autocorrelation
  • Invited lecture (Conferences)
    International Workshop on Nonequilibrium Nanostructures (NONNA'08), 01.-06.12.2008, Dresden, Germany

Publ.-Id: 11960 - Permalink

Uporaba metode datiranja površinske izpostavljenosti na primeru podora Veliki vrh
Mrak, I.; Merchel, S.; Benedetti, L.; Braucher, R.; Bourlès, D.; Finkel, R. C.; Reitner, J. M.;
O podoru v Velikem vrhu (Košuta, Karavanke) ni zanesljivih zgodovinskih zapisov, vendar pa le ti obstajajo o podoru na Dobraču (25.1.1348), ki je od Velikega vrha oddaljen 46 km [1]. Podor je povzročil potres in naša hipoteza je bila, da je tudi podor v Velikem vrhu posledica istega dogodka. Tako smo s pomočjo metode datiranja površinske izpostavljenosti [2] analizirali vzorce matične kamnine v steni Velikega vrha ter vzorce s površine podornih blokov. Ugotavljali smo vsebnost 36Cl, ki se je začel tvoriti po podoru. Na podlagi poznavanja števila atomov 36Cl na gram Ca na leto izpostavljenosti, čas dogodka (podor) izračunamo iz koncentracij 36Cl izmerjenih s pomočjo pospeševalnika (AMS). Prvi rezultati kažejo, da sta se podora na Dobraču in Velikem vrhu zgodila istočasno, natančne analize podatkov pa še potekajo.

Zahvala: Del raziskave sofinancira program CRONUS-EU (Marie-Curie Action 6. okvirni program #511927).

Literatura: [1] C. Hammerl, Historical earthquake research – methods used as a basis for the hazard assessment applied to the earthquake of 1348 in Villach (Austria), Proceedings of the Third International Symposium on Historical Earthquakes in Europe (Prague 1991). [2] J. C. Gosse, F. M. Phillips, Terrestrial in situ cosmogenic nuclides: theory and application, Quaternary Science Reviews, 20 (2001) 1475.

The rockfall Veliki vrh is located in the valley Pod Košuto (Geben stream watershed Karavanke Mountains, Slovenia). The highest point of the researched area is Veliki vrh (2086 m); the lowest is the settlement Plaz (650 m). Among the geomorphologic processes nowadays the linear denudation and erosion prevails (the most common inclination of the surface is between 21-32° in 33-55°).
Between the settlement of Plaz and the Zajemen farm immense amounts of rockfall debris are present in different sizes, from big blocks (up to 10 x 10 m) to granule. The smaller grain sizes (fine sand, coarse silt…) are missing and the grain edges are sharp. The lithology of the material is the same as the one forming the Košuta ridge - Triassic Dachstein limestone and reefy limestone.
There are no reliable historical data about the rockfall event beside the oral heritage in form of a fairy tale describing the catastrophic falling of rocks over the settlement in the valley, killing many people and forcing the survivors to establish a new settlement further downstream. However, there are numerous written records about a historic rockfall taking place about 46 km away at Dobratsch, Carinthia on 25th January 1348 [1]. That rockfall was induced by an earthquake with the epicenter situated at Friuli (~74 km distance to Veliki vrh). There are no other records of natural hazards within historical times for the area, thus, it seems very likely that the same earthquake triggered both rockfalls. To test this hypothesis, we have applied the surface exposure dating method [2] on samples taken from the fresh bedrock and big boulders originating from the Veliki vrh rockfall.
As the long-lived radionuclide 36Cl is the product of nuclear reactions induced by the high-energy cosmic ray particles in a Ca-rich rock, its concentration can be used as a dating tool. The material has been previously shielded and production of 36Cl started as recently as the rockfall took place. Then, freshly produced surfaces – bedrock and boulders – have been exposed to cosmic rays launching the clock. As the so-called production-rate, i.e. how many atoms per gram Ca per year exposure, can be calculated for a certain environment, a precise time for the rockfall can be deduced from the 36Cl concentrations measured by accelerator mass spectrometry (AMS).
Preliminary results suggest a simultaneous timing of both rockfalls: Dobratsch and Veliki vrh. Detailed data analysis is in preparation.
Keywords: accelerator mass spectrometry; terrestrial cosmogenic nuclides (TCN); cosmogenic nuclide exposure dating
  • Poster
    1. Trienalni Posvet, Naravne Nesrece v Sloveniji (NNS '08 - 1st Symposium Natural Disasters in Slovenia), 11.12.2008, Ljubljani, Ljubeljana, Sloveniji , Slowenien

Publ.-Id: 11959 - Permalink

On the axissymmetric dominance of the magnetic field in the VKS dynamo experiment.
Giesecke, A.; Stefani, F.; Gerbeth, G.;
In order to understand the results of recent dynamo experiments, the behavior of kinematic dynamos in cylindrical geometries is analyzed. Simulations are performed applying a hybrid finite volume/boundary element method that allows a stringent treatment of insulating boundary conditions.

A suitable prescribed velocity field, either analytic or -- more realistic -- from measurement data of water experiments, leads to dynamo action if a critical value for the magnetic Reynolds number is exceeded.

In case of an axisymmetric velocity field the simulations always result in a non-axisymmetric eigenfield which is dominated by the azimuthal m=1-mode. However, in contradiction to this expected result, the experimental realisation exhibits an axissymmetric field configuration.

Until today, no satisfactory explanations for the dominating m=0-mode are established. A recently presented approach is based on an alpha-effect caused by helical fluid motions between the impeller blades that drive the flow. However, it turned out, that the necessary
amplitude which is required for m=0 dominated solutions is well above realistic values that might be realized in the experiment.

Further potential explanations involve non-axissymmetric contributions either caused by a drifting large scale vortex structure as observed in water experiments or introduced through the azimuthal varying high permeability region from the ferrous impeller blades, which should ideally give rise to a strong axisymmetric azimuthal field component within the impeller region.
Keywords: Dynamo
  • Lecture (Conference)
    11th MHD days, 01.-03.12.2008, Ilmenau, Germany

Publ.-Id: 11958 - Permalink

Equation of state for QCD matter in a quasiparticle model
Schulze, R.; Kämpfer, B.;
A phenomenological QCD quasiparticle model provides a means to map lattice QCD results to regions relevant for a variety of heavy-ion collision experiments at larger baryon density. We report on effects of collectives modes and damping on the equation of state.
Keywords: QCD quasipaticle model QPM heavy ion collective modes Landau damping equation of state EOS

Publ.-Id: 11957 - Permalink

Light emitting field effect transistor with two self-aligned Si nanocrystal layers
Beyer, V.; Schmidt, B.; Heinig, K.-H.; Stegemann, K.-H.;
Light emitting field-effect transistors based on narrow layers of silicon nanocrystals (NCs) in the gate oxide were fabricated. Direct quantum mechanical electron and hole tunneling into NCs was achieved by self-alignment of NCs-interface-distances to ~2 nm. The direct tunneling reduces oxide degradation, prolongs device lifetime and increases operation speed. Self-alignment occurs during thermal treatment of ion irradiated stacks of 50 nm polycrystalline silicon/15 nm SiO2 / (001)Si substrate. An alternating voltage (ac) was applied to the gate to inject charges into the NCs. Due to injection by direct tunneling, electroluminescence extends to higher ac frequencies than reported so far.
Keywords: Si nanocrystals, Si based light emission, electroluminescence, photoluminescence, ion irradiation, memory, MOSFET, Ostwald ripening
  • Applied Physics Letters 95(2009), 193501

Publ.-Id: 11956 - Permalink

Terawatt diode-pumped Yb:CaF2 laser
Siebold, M.; Hornung, M.; Boedefeld, R.; Podleska, S.; Klingebiel, S.; Wandt, C.; Krausz, F.; Karsch, S.; Uecker, R.; Jochmann, A.; Hein, J.; Kaluza, M. C.;
We present what we believe to be the first terawatt diode-pumped laser employing single-crystalline Yb:CaF2 as the amplifying medium. A maximum pulse energy of 420 mJ at a repetition rate of 1 Hz was achieved by seeding with a stretched femtosecond pulse 2 ns in duration, preamplified to 40 mJ. After recompression, a pulse energy of 197 mJ and a duration of 192 fs were obtained, corresponding to a peak power of 1 TW. Furthermore, nanosecond pulses containing an energy of up to 905 mJ were generated without optical damage.
Keywords: Diode pumped laser caf2
  • Optics Letters 33(2008)23, 2770-2772

Publ.-Id: 11955 - Permalink

Additional PET/CT in week 5-6 of radiotherapy for patients with stage III non-small cell lung cancer as a means of dose escalation planning?
Gillham, C.; Zips, D.; Poenisch, F.; Evers, C.; Enghardt, W.; Abolmaali, N.; Zoephel, K.; Appold, S.; Hoelscher, T.; Steinbach, J.; Kotzerke, J.; Herrmann, T.; Baumann, M.;
Background and purpose: Loco-regional failure after radiotherapy with total doses of 60-70 Gy for non-small cell lung cancer (NSCLC) remains a major clinical problem. Escalation of radiation dose is often limited because of exceeding normal tissue constraints. The present study was designed to test the hypothesis that a reduction in disease volume during radiotherapy detected by FDG PET/CT would facilitate radiation dose escalation, whilst remaining within normal tissue constraints.
Materials and methods: Ten patients with localised inoperable NSCLC were prospectively enrolled. Each received standard 3D-conformally planned radiotherapy to a dose of 66 Gy in 33 fractions over 6.5 weeks. FDG PET/CT imaging in the treatment position was performed prior to treatment and repeated following 50 or 60 Gy. CT and PET-delineated gross tumour volumes were generated and a composite created. A margin of 15 mm was added in all planes to form the planning target volume (PTV). Treatment planning was performed to compare two dose escalation strategies: 78 Gy delivered to the initial PTV with treatment in two phases (shrinking field), i.e., 66 Gy to the initial PTV with a 12 Gy-boost to the PTV after 50/60 Gy. As an alternative planning approach the maximal dose without exceeding normal tissue constraints was evaluated for each patient (individualized dose prescription).
Results: There was a median PTV reduction after 50/60 Gy of 20%. Delivering 78 Gy to the initial PTV could have been achieved in 4/10 patients. Of the remaining 6, delivering 78 Gy to the initial PTV would have exceeded normal tissue constraints and no benefit was seen when delivered in two phases. The results from the individualized dose prescription indicated a higher median maximal dose when treatment would be given in two phases compared to one phase resulting in a modest increase of calculated tumour control probability.
Conclusions: Our data suggest that despite tumour shrinkage determined by subsequent FDG PET/CT during treatment the tested adaptive targeting strategy would result only in a modest improvement in the context of dose escalation. Further studies on the optimal use of FDG PET/CT and other approaches for dose escalation in loco-regionally advanced NSCLC are warranted.
Keywords: Lung cancer, PET/CT, Dose escalation, Adaptive targeting, Radiotherapy

Publ.-Id: 11954 - Permalink

Experimental investigation of Lorentz-force controlled flat-plate boundary layer with a laser Doppler velocity profile sensor
Shirai, K.; Voigt, A.; Neumann, M.; Büttner, L.; Czarske, J.; Cierpka, C.; Weier, T.; Gerbeth, G.;
The application of Lorentz forces for flow control has been investigated in the field of magnetohydro-dynamics (MHD) research since it is capable of generating required mass force to control electrically conductive liquid flows. Separation control of a hydrofoil using Lorentz force has been intensively investigated in the MHD division in the Forschungszentrum Dresden-Rossendorf (FZD) in Germany.
Vortex structures around the hydrofoil have been investigated by Weier et al. (for example [1]). They investigated the vortex structure of the separated flow with particle image velocimetry (PIV) to seek optimum control of separation [2].
However, PIV has limitations particularly in the near-wall region which indeed is of great interest.
In general PIV has an accuracy of velocity measurement about a few percent at best optimized condition [3]. Hence, the application of PIV to the region of low turbulence has a difficulty to evaluate the real turbulence coming from the flow. Besides, the application of PIV to the near-wall region is problematic because of high velocity gradient and strong reflection at the wall. In addition, proper evaluation of velocity field near the wall is hindered when strong Lorentz force is applied. The electric current induced for generating the Lorentz force electrolyzes the liquid and generates bubbles at the wall. Unfortunately, the higher the induced current, the stronger the bubbles are generated.
Therefore, it is demanded to use a measurement technique capable of velocity measurement at low turbulence degree near the wall surface at bubbly conditions. Laser Doppler velocity profile sensor developed in the TU Dresden is attractive since it has high resolution (micrometer range) and accuracy (<0.1%) of velocity profile measurement demanded in the above application. The sensor has been successfully applied to the near-wall region of a turbulent channel flow [4].
The purpose of the present investigation is to study the fundamental mechanism of the flow control with Lorentz force. For that reason, the velocity profile near the wall is measured with the velocity profile sensor. As a first test, the preliminary experiment described in this abstract focused in the feasibility of measurement close to the wall under bubbly conditions and to observe the difference of the flow regime with and without Lorentz force applied.
Keywords: Lorentz force, laser Doppler Velocimetry
  • Lecture (Conference)
    6th International Symposium on Turbulence and Shear Flow Phenomena (TSFP6), 22.-24.05.2009, Seoul, Korea
  • Contribution to proceedings
    6th International Symposium on Turbulence and Shear Flow Phenomena (TSFP6), 22.-24.06.2009, Seoul, Südkorea
    Turbulence and Shear Flow Phenomena, Vol II, 755-760

Publ.-Id: 11951 - Permalink

Uranium coordination in liquids and amorphous solids determined by EXAFS spectroscopy
Hennig, C.;
The combination of UV-Vis and EXAFS to determine species distribution and structure will be discussed.
Keywords: EXAFS, UV-Vis, uranium
  • Lecture (others)
    University of Siegen, Inorganic Chemistry, 24.11.2008, Siegen, Germany

Publ.-Id: 11950 - Permalink

Influence of ionic strength, pH and silicate on colloidal UO2 formation
Hennig, C.;
The solubility of uranium in aqueous solutions under anaerobic conditions is low and the probability of solid UO2 formation increases with the U(IV) concentration. Only in solutions with low pH and high ionic strength the U(IV) hydrate itself is stable even at higher U(IV) concentrations. With increasing pH several U(IV) hydroxides becomes dominant. Below their solubility limits two solid phases can be observed, i.e. the microcrystalline UO2 and the amorphous UO2•xH2O/U(OH)4 which both can occur as colloids in solution. Also the presence of silicate influence the formation and structure of U(IV) nanoparticles. However, even in solutions with equimolar ratio of UO2 and SiO2 the precipitation do not result in the formation of a USiO4-like phase, which can be observed easily under hydrothermal conditions. Some structural aspects of the resulting solid phases have been investigated with x-ray diffraction, EXAFS and wide angle x-ray scattering techniques and will be briefly discussed.
Keywords: EXAFS, XRD, HEXS, UO2
  • Lecture (others)
    Ecole Polytechnique Federale Lausanne (EPFL) Environmental Microbiology Laboratory (EML), 20.11.2008, Lausanne, Switzerland

Publ.-Id: 11949 - Permalink

Influence of annealing on the Er luminescence in Si-rich SiO2 layers co-implanted with Er ions
Kanjilal, A.; Rebohle, L.; Voelskow, M.; Skorupa, W.; Helm, M.;
The impact of rapid thermal annealing (RTA) in producing samples by sequential implantation of Si and Er ions into a 200 nm SiO2 layer combined with different annealing cycles as well as the corresponding room-temperature visible and infrared photoluminescence (PL) have been studied. The Er-related PL intensity at 1533 nm for the samples prepared by implanting Si with subsequent annealing, followed by Er implantation and final annealing (type-I) was found to be stronger than the one produced similarly but without the first annealing step (type-II). In fact, the 1533 nm peak intensity in the optimized RTA processed sample is comparable to the PL yield of the furnace-annealed sample. Moreover, the excitation wavelength (405 nm) was found to be suitable for exciting the Si=O related point defects in the SiO2 layer, and can provide a PL band with a maximum at ~580 nm. While this band was further intensified in presence of Si nanocrystals (Si NCs), it became weaker by introducing additional Er3+ ions with a concomitant rise of the 1533 nm Er PL, confirming the visible range pumping of Er3+. The detailed spectral analyses suggest that the 580 nm band is the result of the excitation/deexcitation mechanism in molecule like states in Si=O or the Si=O state mediated recombination of carriers in Si NCs according to the model proposed by Wolkin et al. [Phys. Rev. Lett. 82, 197 (1999)]. The samples were further characterized by transmission electron microscopy and Fourier-transform infrared-spectroscopy. The time resolved PL measurements and a modelling by rate equations were also performed to determine and justify the energy migration mechanism from Si NC to the neighbouring Er3+.
Keywords: Nanocrystals, RTA, defects, photoluminescence
  • Journal of Applied Physics 104(2008)10, 103522-1-103522-9

Publ.-Id: 11948 - Permalink

Probing channeling radiation influenced by ultrasound
Wagner, W.; Azadegan, B.; Büttig, H.; Grigoryan, L. S.; Sobiella, M.; Pawelke, J.;
The effect of ultrasonic vibrations excited in quartz single crystals on channeling radiation (CR) emitted by relativistic electrons was probed experimentally at medium energy at the radiation source ELBE.

Essential preconditions for these investigations have been created by preceding series of measurements of planar CR on alpha-quartz as well as by extensive theoretical work concerning the treatment of the influence of ultrasound (US) on CR emission. First dedicated experiments became possible because the interaction phenomena and expected effects could certainly be predicted and simulated.

Compressional waves of suitable frequency were induced in x-cut quartz crystals by means of appropriately designed RF cavities applying the reverse piezoelectric effect. Although at the available electron energies the necessary resonance condition has been reached only for selected transitions of electrons channeled along specific crystallographic planes of the quartz single crystal, the occurrence of US stimulated CR should be evident.
Keywords: channeling radiation, quartz single crystal, ultrasound
  • Contribution to proceedings
    3rd International Conference on Charged and Neutral Particles Channeling Phenomena (Channeling 2008), 25.10.-01.11.2008, Erice, Sicily, Italy
    Probing channeling radiation influenced by ultrasound, Singapore, London: World Scientific, Science and Culture Series
  • Invited lecture (Conferences)
    3rd International Conference on Charged and Neutral Particles Channeling Phenomena (Channeling 2008), 25.10.-01.11.2008, Erice, Sicily, Italy

Publ.-Id: 11947 - Permalink

THEREDA - Ein Beitrag zur Langzeitsicherheit von Endlagern für nukleare und nichtnukleare Abfälle
Altmaier, M.; Brendler, V.; Hagemann, S.; Herbert, H.-J.; Marquardt, C.; Moog, H.; Neck, V.; Richter, A.; Voigt, W.; Wilhelm, S.;
Im Rahmen von Langzeitsicherheitsanalysen für deutsche Endlager radioaktiver bzw. Untertagedeponien chemotoxischer Abfälle sowie weiterer Einsatzfelder (Altlastensanierung) wird eine einheitliche und umfassende thermodynamische Referenzdatenbasis dringend benötigt. Der ehemalige „Arbeitskreis Thermodynamische Standarddatenbasis“ (ATS) hatte sich die Aufgabe gestellt, eine solche Datenbasis zu realisieren. Die Aktivitäten des ATS werden seit Juli 2006 im Projektverbund „THEREDA“ (Thermodynamische Referenzdatenbasis) von BMBF, BMWi und BfS zunächst für 3 Jahre gefördert. THEREDA setzt sich aktuell aus 5 Partnerinstitutionen zusammen, die im Wesentlichen die deutschen Forschungsinstitutionen auf dem Gebiet der Endlagersicherheitsforschung repräsentieren. THEREDA soll die Transparenz und Belastbarkeit der Sicherheitsanalysen in Deutschland entscheidend verbessern und stellt erstmalig konsistente thermodynamische Datensätze für die in Deutschland diskutierten Endlageroptionen bereit. Für jede thermodynamische Größe werden anhand eindeutig definierter Evaluierungskriterien Qualitätsstufen angegeben, mithilfe derer Anwender Daten, entsprechend der jeweiligen spezifischen Problemstellungen, gezielt einbeziehen oder ausschließen können. Für fehlende thermodynamische Daten werden im Rahmen von THEREDA begründete Schätzwerte ermittelt, sodass Modellrechnungen zur Sicherheitsanalyse in Zukunft auf einer deutlich breiteren Datenbasis durchgeführt werden können.
Die Datenbasis wird in einer Datenbank zentral verwaltet und Anwendern über das Internet frei und unentgeltlich verfügbar sein. Importformate, um THEREDA in die gängigsten Modellierungscodes (EQ3/6, PHREEQC, Geochemist’s Workbench, CHEMAPP, usw.) überführen zu können, werden ebenfalls unentgeltlich zur Verfügung gestellt.

Long-term safety analyses of German repositories of radioactive waste as well as underground repositories for chemical toxic waste and other uses (contaminated site remediation) urgently require a standardized, comprehensive thermodynamic reference database. The former "Thermodynamic Standard Database Working Party" was set up to establish such a database. The activities of that group have been supported within the integrated “THEREDA” (Thermodynamic Reference Database) project since July 2006 for an initial period of 3 years by the German Federal Ministries of Education and Research, of Economics, and by the Federal Office of Radiation Protection. THEREDA at present is composed of 5 partner institutions essentially representing the key German research institutions in the field of repository safety research.
THEREDA is to improve the transparency and validity of safety analyses in Germany and, for the first time, provides consistent thermodynamic datasets for the repository options discussed in Germany. Quality levels are indicated for each thermodynamic quantity on the basis of unambiguously defined evaluation criteria, which allow users to either include or exclude data in accordance with the specific problems at hand. Missing thermodynamic data are substituted in THEREDA by well-founded estimates, thus permitting future model calculations for safety analysis to be carried out on a clearly broader basis of data. The data are managed centrally in a database and will be available to users free of charge on the Internet. Import formats allowing THEREDA to be transferred into the most common modeling codes (EQ3/6, PHREEQC, Geochemist’s Workbench, CHEMAPP, etc.) are also made available free of charge.
Keywords: THEREDA, thermodynamic database, modelling, long term safety analyses
  • atw - International Journal for Nuclear Power 54(2008)4, 249-253

Publ.-Id: 11946 - Permalink

Complexation of Actinides with Organic and Inorganic Ligands
Geipel, G.; Bernhard, G.;
Two basic requirements are needed for speciation calculations – a database including stability constants of the formed species and a computerized program for the real calculation. For the input analytical data or theoretical concentrations of the basic species can be used.
Hydroxide and carbonate are two of the most important environmental ligands. Fuger /1/ resumes many available data.
Up to now several databases have been developed /2-6/. However, the most up-to-date and best-reviewed databases for the actinide elements uranium, neptunium, plutonium and americium are the NEA databases /4, 7/. For speciation calculations the listed data should be used including the desired estimations for correction of the ionic strength. Two estimates are widely used:
- Adapted SIT (Specific Ion Interaction Theory) method /4/.
- Davies equation, including extension for high ionic strength /5/.

On the basis of the database several program codes can be used for calculation of the species distribution as function of concentrations, pH, ionic strength. Which one will be selected depends on experience of the user. The most important input in such calculations is the use of a correct and validated database.

The most useful program code is EQ 3/6 /8/. The estimation of the stability constants at the ionic strength of the solution to be calculated is included in this program. Also reactions at the interphase gas/liquid can be included.
A newer code is SPECIES /9/. The input is comfortable; also a program code for the estimation of formation constants at different ionic strength is available. However, and this is mentioned by the authors, the attached database (SC Database) should be used only after checking of the original literature. The program is not able to include reactions with gas phases (CO2/CO2 (a.)).
Also available on the web is the program MEDUSA /10/. In the program a database is included and there is also the possibility to correct the used stability constants.
Keywords: Speciation, Trace elements, Distribution diagrams
  • Invited lecture (Conferences)
    School cum Workshop on Trace Element Speciation (SElS-08), 21.-29.11.2008, Kolkata, India

Publ.-Id: 11945 - Permalink

Spectroscopic Techniques in Actinide Speciation Studies
Geipel, G.; Bernhard, G.;
The determination of the behavior of actinides in the environment needs several spectroscopic techniques, adapted to spectroscopic properties and concentration ranges of these elements in the environment.

New techniques for the speciation of actinides have been developed during the past decades. Three main requirements are of importance:
- License for handling of radioactive elements, especially for α-emitting actinides.
- Availability of actinides, especially the higher actinides are available only in small amounts.
- Speciation methods covering the concentration range of actinides expected or found in nature.

Speciation analysis can be distinguished into two types: non-invasive and invasive methods. Among the first group are spectroscopic methods. They are not restricted to the form of the species (solid, liquid, gas). Non-invasive methods need usually no treatment of the sample and allow the direct speciation of an element in its environment. Invasive methods in general are applicable to solids and solutions. They need normally a pretreatment and a separation of the sample. Sequential extraction can be used for the determination of species in solid systems. Besides for the separation of actinides /1/ extraction techniques are important for the determination of oxidation states of the actinides in solution. For example the oxidation states of plutonium can be determined using α-thenoyltrifluoroacetone (TTA) at pH = 0. Tetravalent plutonium is extracted to the organic phase, whereas all other oxidation states and polymeric plutonium remain in the aqueous phase. The same extraction procedure after addition of chromate allows to separate plutonium(III) and plutonium(IV). Other common extraction agents are tributylphosphate (TPB) and bis(2-ethyl-hexyl)-hydrogen-phosphate (HDEHP).
Keywords: Spectiation, Trace elements, Spectroscopy
  • Invited lecture (Conferences)
    School cum Workshop on Trace Element Speciation (SElS-08), 21.-29.11.2008, Kolkata, India

Publ.-Id: 11944 - Permalink

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