Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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33407 Publications

Morphology Induced Magnetic Anisotropy of Thin Films Deposited on Nanoscale Ripple Substrates

Körner, M.; Liedke, M. O.; Lenz, K.; Ranjan, M.; Fritzsche, M.; Facsko, S.; Fassbender, J.ORC; von Hörsten, U.; Krumme, B.; Wende, H.
Magnetic properties of thin films are influenced by the morphology of substrates with periodically modulated patterns on the nanometer scale [1]. These well ordered surface modulations (ripple) can be produced by low energy ion beam erosion and are tuneable over a wide range [2]. Thin magnetic films deposited on these ripple surfaces repeat the surface profiles of these patterns and thus an additional uniaxial magnetic anisotropy is induced. This is shown for thin films of Fe, Co as well as the quasi-Heusler compound Fe3Si. The magnetic anisotropy is determined by means of angular- as well as frequency-dependent ferromagnetic resonance measurements using a vector network analyzer. We find a strong uniaxial magnetic anisotropy induced by the ripple surface, which is superimposed on the cubic anisotropy in the case of single crystalline films.
This work is supported by DFG grant FA 314/6-1.
[1] M. Körner et al., Phys. Rev. B 80, 214401 (2009).
[2] J. Fassbender et al., New Journal of Physics 11, 125002 (2009).
  • Poster
    DPG Frühjahrstagung der Sektion AMOP (SAMOP) und der Sektion Kondensierte Materie (SKM) 2011, 13.-18.03.2011, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-14945
Publ.-Id: 14945


Novel biosensors by combining bacterial S-layers, fluorescent dyes and aptamers

Weinert, U.; Günther, T.; Pollmann, K.; Raff, J.
Bacterial surface layer (S-layer) represent the outermost cell envelope of various bacteria and feature a lot of functions such as protection, binding, filtration or framework. From the uranium mining waste pile “Haberland” near Johanngeorgenstadt in Saxony different Bacilli were isolated and their S-layer proteins were investigated. These S-layer proteins are able to self assemble in aqueous solution and form sheets or tubes with a hexagonal, square or oblique paracrystalline structure. By combining S-layers with polyelectrolytes, many technical surfaces, e.g. SiO2 wafers, can be covered with a closed and highly regular protein layer. The so modified materials are very promising for the construction of multifunctional materials, particularly new biosensors. Their high content of different and regularly arranged functional groups such as hydroxyl, amino and carboxyl groups provide a convenient platform for the sequential and defined coupling of sensor elements. So the idea is to construct a sensor system on the basis of S-layer proteins by combining fluorescence dyes with aptamers. Possible fluorescence dyes have an overlapping emission and excitation spectra and therefore the ability to induce a fluorescence resonance energy transfer (FRET). FRET describes a non radiation energy transfer between two chromophores. One chromophore (donor) in its excitated state will transfer energy to another chromophore (acceptor) and as a result the donor emission will decrease while the acceptor emission increases. The latter is detectable and can be used for the construction of the optical device of a sensor. One requirement therefore is the spatial proximity of both chromophores (<10nm), what can be easily achieved by using S-layers as nano-structured polymer with a high density of functional groups. Further components of the sensors are aptamers, working as specific receptors for analytes. Aptamers are short oligonucleotides with a high binding capacity towards a specific analyte, in present case specific pharmaceuticals and biocides. The combination of all three parts will lead to a selective, sensitive and adaptable sensory layer system useful for environmental technologies.
Keywords: S-layer, aptamers, fluorescence dyes, biosensor
  • Poster
    Nanocoatings-International Conference on Functional Nanocoatings, 28.-31.03.2010, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-14944
Publ.-Id: 14944


Entwicklung von sensorischen Schichten auf Basis bakterieller Hüllproteine

Weinert, U.; Günther, T.; Pollmann, K.; Raff, J.
Hüllproteine sind Strukturproteine, welche die äußerste Abgrenzung von zahlreichen Bakterien und fast allen Archaeen darstellen. Isoliert bilden diese Proteine in wässrigen Lösungen und an Grenzflächen regelmäßige parakristalline Gitterstrukturen aus, auf deren Oberfläche sich zahlreiche modifizierbare Carboxyl- und Aminogruppen befinden. Hüllproteine sind daher eine ideale Matrix zur Konstruktion von nanoskaligen sensorischen Schichten, bestehend aus Aptameren und Fluoreszenzfarbstoffen. Aptamere sind kurze Oligonukleotide, welche ähnlich wie Antikörper an Strukturmerkmale anderer Moleküle binden können, jedoch deutlich stabiler sind. Mittels dieser chemischen Antikörper lassen sich eine Vielzahl verschiedener Targetmoleküle spezifisch an die sensorische Schicht binden. Alle Komponenten des Detektionssystems befinden sich durch die regelmäßige Proteinmatrix in räumlicher Nähe, was einen Fluoreszenz Resonanz Energie Transfer zwischen den Fluoreszenzfarbstoffen ermöglicht. Dieser Energietransfer kann durch Binden eines Analyten an das Aptamer gestört werden (Quenching), was die Realisierung eines hochempfindlichen Sensors ermöglicht.
Keywords: S-layer, aptamers, fluorescence dyes, FRET, biosensor
  • Poster
    7. Max-Bergmann-Symposium, 16.11.2010, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-14943
Publ.-Id: 14943


Experimental characterisation of the interfacial structure during counter-current flow limitation in a model of the hot leg of a PWR

Vallée, C.; Nariai, T.; Futatsugi, T.; Tomiyama, A.; Lucas, D.; Murase, M.
In order to investigate the two-phase flow behaviour during counter-current flow limitation in the hot leg of a pressurised water reactor, dedicated experiments were performed in a scaled down model of Kobe University. The structure of the interface was observed from the side of the channel test section using a high-speed video camera. An algorithm was developed to recognise the stratified interface in the camera frames after background subtraction. The evolution of the water level along the hot leg is analysed in function of the liquid and gas flow rates.
Keywords: counter-current flow limitation, CCFL, hot leg, stratified two-phase flow, interfacial structure, image processing
  • Contribution to proceedings
    The 14th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-14), 25.-29.09.2011, Toronto, Canada
    Proceedings of the 14th International Topical Meeting on Nuclear Reactor Thermalhydraulics (NURETH-14), paper 175

Permalink: https://www.hzdr.de/publications/Publ-14942
Publ.-Id: 14942


1 J white-light continuum from 100 TW laser pulses

Petit, Y.; Henin, S.; Nakaema, W.; Béjot, P.; Jochmann, A.; Kraft, S.; Bock, S.; Schramm, U.; Stelmaszczyk, K.; Rohwetter, P.; Kasparian, J.; Sauerbrey, R.; Wöste, L.; Wolf, J.-P.
We experimentally measured the supercontinuum generation by 3 J, 30 fs laser pulses and measured white-light generation at the unprecedented level of 1 J. Such high energy is allowed by a strong contribution to the continuum by the photon bath, as compared to the self-guided filaments. This contribution due to the recently observed congestion of the filament number density in the beam profile at very high intensity, also results in a wider broadening for positively chirped pulses rather than for negatively chirped ones, similarly to broadening in hollow-core fibers.
Keywords: Beam trapping, self focusing and defocusing, self-phase modulation; Frequency conversion; harmonic generation, including higher-order harmonic generation

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Permalink: https://www.hzdr.de/publications/Publ-14941
Publ.-Id: 14941


Mn-doped Ge and Si: A Review of the Experimental Status

Zhou, S.; Schmidt, H.
Diluted ferromagnetic semiconductors (FMS) are in the focus of intense research due to their potential applications in spintronics and their striking new physical properties. So far Mn-doped III-V compound semiconductors such as GaMnAs are the most important and best understood ones, but they are ferromagnetic only at well below room temperature. An interesting alternative could be magnetic semiconductors based on elemental semiconductors, also owing to their compatibility with Si microelectronics. In the last decades, considerable amount of work has been devoted to fabricate Mn-doped Ge and Si FMS. In this article, the structural, magnetic and magneto-transport properties of Mn-doped Ge and Si will be reviewed.
Keywords: Diluted ferromagnetic semiconductor, Mn doped Si, Mn doped Ge

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Permalink: https://www.hzdr.de/publications/Publ-14940
Publ.-Id: 14940


XAS versus IC-ICP-MS for arsenic-sulfur speciation analysis

Planer-Friedrich, B.; Suess, E.; Scheinost, A. C.; Wallschläger, D.
Modern analytical methods have demonstrated that soluble arsenic-sulfur species constitute a major fraction of dissolved arsenic in sulfidic waters. However, an intense debate is going on about the exact chemical nature of these compounds, with X-ray absorption spectroscopy (XAS) data suggesting thioarsenites, ion chromatographic and mass spectroscopic (IC-ICP-MS) data suggesting thioarsenates. We show here by XAS that thioarsenites are the primary reaction products of arsenite and sulfide which convert rapidly to thioarsenates when exposed to atmospheric oxygen. The predominance of dithioarsenate determined by IC-ICP-MS in arsenite-sulfide solutions is thus an analytical artifact. When eliminating oxygen by conducting the chromatographic separation under anaerobic conditions, thioarsenites convert to arsenite as they are instable in the acidic and alkaline pH-range and undergo competitive dissociation at decreasing SH-:OH- ratios when diluting a sample. As thioarsenites were found to be necessary precursor species for thioarsenate formation, their analysis at environmentally relevant concentrations is a necessity for modern arsenic speciation analysis.
Keywords: arsenic sulfur XAS
  • Invited lecture (Conferences)
    11th International Conference on the Biogeochemistry of Trace Elements, 03.-07.07.2011, Florence, Italy

Permalink: https://www.hzdr.de/publications/Publ-14939
Publ.-Id: 14939


Experimentelle Untersuchung polydisperser Dampf/Wasser-Strömungen mit Phasenübergang in einer vertikalen DN200-Teststrecke

Beyer, M.; Lucas, D.; Szalinski, L.; Pietruske, H.; Schütz, P.; Lindner, K.
Zweiphasenströmungen spielen eine wichtige Rolle bei der Sicherheitsbewertung bzw. Optimierung verfahrenstechnischer Prozesse. Ein wichtiger Anwendungsbereich für Zweiphasenströmungen sind die konventionelle und die Kernkraftwerkstechnik, bei denen in Dampfkesseln, Dampferzeugern aber auch in Siedewasserreaktoren schon im Normalbetrieb unterschiedliche Dampfgehalte und damit verschiedene Strömungsformen auftreten. Für die nukleare Sicherheitsforschung ist die zuverlässige Vorhersage charakteristischer Parameter von Zweiphasenströmungen in Störfallanalysen wichtig. Bei hypothetischen Leck- bzw. Reaktivitätsstörfällen in Siedewasser- oder Druckwasserreaktoren können auf Grund der teilweisen Verdampfung des Kühlmittels komplexe Zweiphasenströmungen auftreten. Auch für solche Fälle muss die Abfuhr der im Kern generierten Nachzerfallswärme nachgewiesen werden.
Eine zweckmäßige Methode zur Modellierung von Mehrphasenströmungen ist die dreidimensionale rechnergestützte Simulation der Strömungsvorgänge mittels CFD (Computational Fluid Dynamics) Programmen. Während diese Programme gegenwärtig für einphasige Strömungen gute Ergebnisse liefern, besteht im Zweiphasenbereich noch Entwicklungsbedarf. Zur Modell-entwicklung und –validierung sind qualitativ hochwertige Daten von Experimenten in praxisrelevanten Geometrien bei hohen Drücken und Temperaturen erforderlich. Ein wesentlicher Teil dieser Datenbasis wird im Rahmen der TOPFLOW Projekte bereitgestellt.
Der Vortrag erläutert die Durchführung von Experimenten mit polydispersen nicht adiabaten Dampf/Wasser-Strömungen und beschreibt die speziell für den Hochtemperaturbereich entwickelte Messtechnik. Ein wesentlicher Bestandteil des Seminars ist die Diskussion von ausgewählten Ergebnissen der Kondensationsversuche, die die Entwicklung der Strömungsstruktur über die Höhe eines vertikalen Rohres sowie die dabei auftretenden Energie- und Stofftrans-portprozesse zwischen den Phasen veranschaulichen.
Keywords: Steam/Water-flow, non adiabatic flow, wire-mesh sensor, gas velocity profiles, bubble size distributions, vertical pipe
  • Lecture (others)
    Institutsseminar, 09.12.10, FZD, Germany

Permalink: https://www.hzdr.de/publications/Publ-14938
Publ.-Id: 14938


Atom probe characterization of solute atom clustering in decommissioned Greifswald unit 4 weld metal

Nishida, K.; Soneda, N.; Nomoto, A.; Dohi, K.; Bergner, F.; Viehrig, H.-W.
Characterization of irradiation-induced microstructural features in reactor pressure vessel (RPV) materials is essential for the understanding of the mechanisms of RPV embrittlement. Particularly, analyses of materials from decommissioned RPVs are very important because the simulated irradiations in material testing reactors can never be the same as that of actual commercial reactors. In this study, we performed microstructural characterization of the weld metals cut from the decommissioned Greifswald Unit 4 RPV. Atom probe tomography technique was used to characterize the microstructural features in terms of solute atom clustering and segregation. The following conclusions can be drawn: (1) Carbides containing large amount of vanadium with a small size of ~10nm in diameter were observed. (2) Clusters which consist of Cu, Ni, Mn, Si, Cr and P are formed at Layer 4 and 6. (3) At Layer 4, two kinds of solute atom clusters i.e. with and without Cu atoms are observed, whereas almost all clusters contain Cu at Layer 6. (4) Concentrations of Ni, Mn, Si and Cr in the clusters are independent of cluster size. Si concentration is different between Layer 4 and 6. (5) There is a large scatter in the concentrations of Cu and P. However, the sum of Cu and P concentrations in the clusters is almost constant.
Keywords: Reactor pressure vessel steel, Atom probe tomography
  • Lecture (Conference)
    MRS Fall Meeting, 29.11.-03.12.2010, Boston, USA

Permalink: https://www.hzdr.de/publications/Publ-14937
Publ.-Id: 14937


Exceptional points: Mathematical aspects and Krein space related physics (I + II)

Günther, U.
In the first one-hour lecture some basic mathematical facts are presented on an introductory level. Specifically, we discuss spectral singularities of various types, projective Hilbert space structures at exceptional points (EPs), Krein spaces and PT quantum mechanics (PTQM) as well as gauged PTQM and PTQM Jaynes-Cummings models.
The second one-hour lecture is devoted to Krein space related physics and some concrete applications. The topics of this lecture are higher-order EPs in PT-symmetric Bose-Hubbard models, the PTQM brachistochrone and entanglement dynamics. Additionally, we briefly comment on EPs in MHD dynamo setups.
Keywords: exceptional points, non-Hermitian operators, PT quantum mechanics, Krein space, projective Hilbert space, Bose-Hubbard model, Bose-Einstein condensate, gauged PT quantum mechanics, Jaynes-Cummings models, quantum brachistochrone, entangled states, MHD dynamos
  • Invited lecture (Conferences)
    The physics of exceptional points., 02.-05.11.2010, Stellenbosch, South Africa

Permalink: https://www.hzdr.de/publications/Publ-14936
Publ.-Id: 14936


Krein spaces and PT quantum mechanics

Günther, U.
In 1998, 1999 it was shown by Bender and collaborators that there are certain classes of Hamiltonians which at a first glance seem not selfadjoint in Hilbert spaces, but which nevertheless are having real spectra. Examples are Hamiltonians of the type H=p2+x2(ix)μ. For parameters μ ∈ [0,1] these Hamiltonians have positive real eigenvalues with square integrable eigenfunctions defined over the real line. It was found that the reality of the eigenvalues was connected with an underlying PT-symmetry of the Hamiltonians and their eigenfunctions, i.e. the systems are in a sector of unbroken PT-symmetry. There exist other sectors like μ ∈ (-1,0) where this PT-symmetry is spontaneously broken: although the Hamiltonian remains PT-symmetric, part of its eigenfunctions loose PT-symmetry and the corresponding eigenvalues are coming in complex conjugate pairs. A PT phase transition occurs at μ=-0.
It turns out that the PT-symmetry of the Hamiltonian H induces a natural indefinite metric structure in Hilbert space and that H, instead of being selfadjoint in a usual Hilbert space (with positive definite metric), is selfadjoint in a generalized Hilbert space with an indefinite metric --- a so called Krein space. Similar to time-like, space-like and light-like vectors in Minkowski space a Krein space has elements of positive and negative type as well as neutral (isotropic) elements. Moreover in analogy to passing via Wick-rotation from Minkowski space to Euclidian space, in the sector of exact PT-symmetry there exists an operator which allows to pass from a Krein space description of the system to a description in a Hilbert space with a highly nontrivial metric operator. At the PT phase transition point this operator becomes singular and the corresponding mapping breaks down.
In the talk, on an introductory level, some of the basic structures of PT-symmetric quantum mechanics and their relation to corresponding Krein-space setups are sketched. For gaining some rough intuition, the facts are illustrated by simple matrix models. The richness of the systems is demonstrated on the simple example of a PT-symmetric two-mode Bose-Hubbard model, PT-symmetric brachistochrone setups and gain-loss-balanced PT-symmetric optical waveguide systems.
Keywords: PT quantum mechanics, PT-symmetry, non-Hermitian operators, Krein space, indefinite metric, phase transition, quantum brachistochrone, Bose-Hubbard model, PT-symmetric optical waveguides, gain-loss balanced systems
  • Lecture (others)
    seminar of the Computational Physics Group, Institute of Theoretical Physics, TU Dresden, 26.11.2010, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-14935
Publ.-Id: 14935


Three models of Krein-space-related physics: PT-symmetric Quantum Mechanics, Squire equation and the MHD α²-dynamo

Günther, U.
PT-symmetric Quantum Mechanics, the Squire equation of hydrodynamics and the spherically symmetric α²-dynamo of magnetohydrodynamics (MHD) can be structurally linked and treated in a unified way as spectral problems in Krein spaces. We demonstrate their interrelation explicitly and provide examples for specific parameter dependencies of their spectra. Special emphasis is laid on the physical relevance of transitions between real and complex spectral branches in connection with phase transitions between sectors of exact PT-symmetry and spontaneously broken PT-symmetry in Quantum Mechanics as well as with possible polarity reversals of dynamo maintained magnetic fields of planets. We briefly comment on third order spectral branch points with geometric multiplicity one and algebraic multiplicity three as well as on a dynamo related resonant unfolding of diabolical points (spectral intersection points of geometric and algebraic multiplicity two). Finally, we sketch the general technique of versal deformations as specific unfolding of Jordan-block related singularities.
Keywords: operator theory, Krein space, PT-symmetric Quantum Mechanics, dynamo theory, Squire equation, spectral branch points, diabolical points, phase transition, perturbation theory, resonances, Puiseux expansions, versal deformations, Jordan block, unfolding of singularities
  • Lecture (others)
    weekly seminar of the Krein space group, 05.05.2010, Ilmenau, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-14934
Publ.-Id: 14934


PT-symmetry, Cartan decompositions, Lie triple systems and Krein space related Clifford algebras

Günther, U.; Kuzhel, S.
Gauged PT quantum mechanics (PTQM) and corresponding Krein space setups are studied. For models with constant non-Abelian gauge potentials and extended parity inversions compact and noncompact Lie group components are analyzed via Cartan decompositions. A Lie-triple structure is found and an interpretation as PT-symmetrically generalized Jaynes-Cummings model is possible with close relation to recently studied cavity QED setups with transmon states in multilevel artificial atoms. For models with Abelian gauge potentials a hidden Clifford algebra structure is found and used to obtain the fundamental symmetry of Krein space related J-selfadjoint extensions for PTQM setups with ultra-localized potentials.
Keywords: PT quantum mechanics, non-Hermitian Hamiltonians, gauge theory, Abelian gauge field, non-Abelian gauge field, Cartan decomposition, compact and noncompact components, Lie triple system, Clifford algebra, ultra-localized potential, Krein space, J-selfadjoint extension, Jaynes-Cummings system, multilevel artificial atoms, cavity QED, transmon states

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Permalink: https://www.hzdr.de/publications/Publ-14933
Publ.-Id: 14933


PT symmetry, Cartan decompositions, Lie triple systems and Krein space related Clifford algebras

Günther, U.; Kuzhel, S.
Gauged PT quantum mechanics (PTQM) and corresponding Krein space setups are studied. For models with constant non-Abelian gauge potentials and extended parity inversions compact and noncompact Lie group components are analyzed via Cartan decompositions. A Lie-triple structure is found and an interpretation as PT-symmetrically generalized Jaynes-Cummings model is possible with close relation to recently studied cavity QED setups with transmon states in multilevel artificial atoms. For models with Abelian gauge potentials a hidden Clifford algebra structure is found and used to obtain the fundamental symmetry of Krein space related J-selfadjoint extensions for PTQM setups with ultra-localized potentials.
The talk is based on arXiv:1006.1134[math-ph]
Keywords: PT quantum mechanics, non-Hermitian Hamiltonians, gauge theory, Abelian gauge field, non-Abelian gauge field, Cartan decomposition, compact and noncompact components, Lie triple system, Clifford algebra, ultra-localized potential, Krein space, J-selfadjoint extension, Jaynes-Cummings system, multilevel artificial atoms, cavity QED, transmon states
  • Lecture (Conference)
    21st International Workshop on Operator Theory and its Applications, 12.-16.07.2010, Berlin, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-14932
Publ.-Id: 14932


PTQM related involution structures

Günther, U.; Kuzhel, S.
Gauged PT quantum mechanics (PTQM) and corresponding Krein space setups are studied. For models with constant non-Abelian gauge potentials and extended parity inversions compact and noncompact Lie group components are analyzed via Cartan decompositions. A Lie-triple structure is found and an interpretation as PT-symmetrically generalized Jaynes-Cummings model is possible with close relation to recently studied cavity QED setups with transmon states in multilevel artificial atoms. For models with Abelian gauge potentials a hidden Clifford algebra structure is found and used to obtain the fundamental symmetry of Krein space related J-selfadjoint extensions for PTQM setups with ultra-localized potentials. Based on: arXiv:1006.1134[math-ph]
Keywords: PT quantum mechanics, non-Hermitian Hamiltonians, gauge theory, Abelian gauge field, non-Abelian gauge field, Cartan decomposition, compact and noncompact components, Lie triple system, Clifford algebra, ultra-localized potential, Krein space, J-selfadjoint extension, Jaynes-Cummings system, multilevel artificial atoms, cavity QED, transmon states
  • Invited lecture (Conferences)
    Pseudo-Hermitian Hamiltonians in Quantum Physics IX, 21.-24.06.2010, Hangzhou, China

Permalink: https://www.hzdr.de/publications/Publ-14931
Publ.-Id: 14931


PTQM related Cartan and Clifford structures

Günther, U.
Gauged PT quantum mechanics (PTQM) and corresponding Krein space setups are studied. For models with constant non-Abelian gauge potentials and extended parity inversions compact and noncompact Lie group components are analyzed via Cartan decompositions and an underlying Lie-triple structure is described. For models with Abelian gauge potentials a hidden Clifford algebra structure is found and used to obtain the fundamental symmetry of Krein space related J-selfadjoint extensions for PTQM setups with ultra-localized potentials.
Keywords: PT quantum mechanics, non-Hermitian Hamiltonians, gauge theory, Abelian gauge field, non-Abelian gauge field, Cartan decomposition, compact and noncompact components, Lie triple system, Clifford algebra, ultra-localized potential, Krein space, J-selfadjoint extension
  • Invited lecture (Conferences)
    Analytic and algebraic methods VI, 10.-11.05.2010, Prague, Czech Republic

Permalink: https://www.hzdr.de/publications/Publ-14930
Publ.-Id: 14930


Redox-dependent suphate coordination of neptunium in aqueous solutions

Hennig, C.; Ikeda-Ohno, A.; Tsushima, S.; Scheinost, A.
A direct determination of actinide coordination in aqueous solution under controlled redox conditions is an important issue to understand the specific chemical reactions and to predict the behavior in nuclear waste repositories. We developed several techniques to study actinide solutions under dedicated redox conditions at the ESRF. The methods to control the actinide redox state are based on potentiostatic or galvanostatic electrolyses. The solutions can be investigated either ex situ or in situ with a specific spectroelectrochemical cell where the electrochemical process is combined with EXAFS spectroscopy. As example we show the redox reaction of 0.05 M neptunium in presence of 2.0 M sulfate. The neptunium species occur preferred with one monodentate (Np5+) and two bidentate (Np6+) sulfate ligands. Np4+ forms very strong complexes with up to fife sulfate ligands. The EXAFS signal reveals a unique ligand rearrangement during the redox reaction. This provides the explanation why the cyclic voltammogram show irreversible reaction steps.
Keywords: Neptunium, EXAFS, elektrochemistry
  • Contribution to external collection
    G. Admans: ESRF Highlights 2009, Grenoble: Müllerdruck Mannheim, 2010, 84-85

Permalink: https://www.hzdr.de/publications/Publ-14929
Publ.-Id: 14929


Structure, energetics and thermodynamics of copper-vacancy clusters in bcc-Fe: An atomistic study

Al-Motasem, A. T.; Posselt, M.; Bergner, F.; Birkenheuer, U.
A combination of on-lattice simulated annealing based on Metropolis Monte Carlo simulations and off-lattice relaxation by Molecular Dynamics is applied in order to determine the structure and energetics of coherent copper-vacancy clusters in bcc-Fe. The most recent interatomic potential for Fe-Cu alloys is used. About 150 clusters consisting of up to 200 monomers (vacancies or copper atoms) are investigated. The atomic structure and the formation energy of the most stable configurations as well as their total and monomer binding energy are calculated. All clusters show facets which correspond to the main crystallographic planes. In the case of mixed clusters a core-shell structure is found where Cu atoms coat the outer surface of vacancy clusters. These findings are in agreement with previous theoretical results and with indications from measurements. For small clusters the total binding energy determined in this work shows a good agreement with literature data obtained by first-principle calculations. For further application in rate theory and object kinetic Monte Carlo simulations compact and physically-based fit formulae are derived from the atomistic data for the total and the monomer binding energy. The fit is based on the classical capillary model. An atomistic nucleation model is established, and for typical irradiation conditions the nucleation free energy of pure vacancy and pure copper as well as the critical size for cluster formation are estimated.
Keywords: Diluted iron alloy, Copper-vacancy clusters, Atomistic simulation.

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Permalink: https://www.hzdr.de/publications/Publ-14928
Publ.-Id: 14928


Das Arcanum von Meissner Porzellan: Beharrung oder Wandel?

Neelmeijer, C.; Pietsch, U.; Ulbricht, H.
Das Arcanum zur Herstellung von Hartporzellan in Europa geht auf ein Patent von Johann Friedrich Böttger im Jahre 1708 zurück. Seitdem ist die Porzellanmanufaktur Meißen Hersteller und Vertreiber des „Weißen Goldes“. Wie streng wird auf dem dort hinterlegten Geheimnis seiner Rezeptur beharrt? Gibt es durch Variationen in den Einsatzstoffen entscheidende Modifikationen in der chemischen Zusammensetzung?
Die zerstörungsfreie Materialanalyse mittels Protonenstrahl an Luft gestattet es, dieser Frage nachzugehen. Vor der Restaurierung war die nicht glasierte Porzellanmasse an Defekten von 34 gesicherten Originalen aus dem 18. Jahrhundert für den Rossendorfer Protonenstrahl (5 MV Tandembeschleuniger) und das Arrangement verschiedener, simultan arbeitender Nachweisgeräte zugänglich.
Über den Untersuchungszeitraum von knapp 100 Jahren erweist sich die Porzellanzusammensetzung als erstaunlich stabil. Unikate von höchstem Wert sind in die Untersuchungen eingebunden, auch deren Glasuren und Malfarben.
Keywords: Porcelain, chemical analysis, Ion beam Analysis, PIXE, PIGE
  • Invited lecture (Conferences)
    DGZfP Arbeitskreis – 09. Dezember 2010, 09.12.2010, Residenzschloss Dresden, Deutschland
  • Invited lecture (Conferences)
    Das Arcanum von Meissener Porzellan: Beharrung oder Wandel?, 09.12.2010, Residenzschloss Dresden, Deutschland
  • Communication & Media Relations
    DGZfP Dach-Zeitschrift 06.01.2011
    1 Seiten

Permalink: https://www.hzdr.de/publications/Publ-14927
Publ.-Id: 14927


Tuning the shape and damage in ion-beam induced ripples on silicon

Biermanns, A.; Hanisch, A.; Grenzer, J.; Metzger, T. H.; Pietsch, U.
We investigate the influence of ion beam parameters on the ripple formation on Si(001) surfaces after bombardment with Xe+ ions of 25 keV kinetic energy using a scanning ion beam system. By combining grazing incidence x-ray diffraction, small angle scattering and x-ray reflectivity, we show that during ion irradiation with 70◦ off-normal angle of incidence, changing the size of the irradiated area leads to an increased number of defects at the interface towards crystalline material. At 65◦ angle of incidence, the ripple amplitude grows.
Keywords: ion beam erosion, x-ray diffraction

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Permalink: https://www.hzdr.de/publications/Publ-14926
Publ.-Id: 14926


In-situ grazing incidence scattering investigations during magnetron sputtering deposition of FePt/Ag nanocomposite layers

Cantelli, V.; Grenzer, J.; Jeutter, N. M.; von Borany, J.
We report on an in-situ GISAXS study of the evolution of nanocomposite magnetic L10-FePt/Ag layers as a function of the Ag amount. Simultaneously, the formation of the hard ferromagnetic L10 phase has been detected by x-ray diffraction at grazing incidence. The methodology applied is a sequential magnetron sputtering deposition of FePt and Ag at 400°C on an a-SiO2 substrate: the deposition chamber is equipped with two Be windows to allow x-ray penetration and mounted on the six-circle goniometer of ROBL – BM 20 at the ESRF.

[1] V. Cantelli, J. von Borany, N.M. Jeutter, J. Grenzer, Adv. Eng. Mat. 11, 478 (2009).
Keywords: In-situ sputtering, X-ray scattering
  • Poster
    10th Biennial Conference on High Resolution X-Ray Diffraction and Imaging, 20.-23.09.2010, Warwick, England

Permalink: https://www.hzdr.de/publications/Publ-14925
Publ.-Id: 14925


X-ray scattering and diffraction from Xe-beam induced ripples in crystalline Si

Biermanns, A.; Hanisch, A.; Grenzer, J.; Facsko, S.; Metzger, T. H.; Pietsch, U.
In recent years, the creation of surface-nanostructures due to ion-beam sputtering has gained much interest due to the possibility to pattern large surface areas with tunable morphologies in a short time. 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 strengthening processes caused by surface diffusion [1]. 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 an interface towards crystalline material, showing the same morphology as the surface. The structure and morphology of the amorphous layer and the amorphous-crystalline (a/c) interface were studied using synchrotron-radiation. Whereas the combination of grazing-incidence small angle scattering (GISAXS) and X-ray reflectivity can be used to study the surface morphology with large statistical sampling (Fig. 1), grazing incidence diffraction (GID) gives access to the buried crystalline material and probes both the morphology and the crystal structure of the a/c interface.
We found that for non-optimal sputter conditions, defects are created at the a/c interface, leading to a net expansion of the crystal along the ripples [2]. This inclusion of defects can be reduced if optimal sputter conditions are chosen, leading to an increasing ripple amplitude rather than the formation of defects.
Referenzen
[1] M. A. Makeev et al., Nucl. Instrum. Methods Phys. Res., Sect. B 197, 185 (2002)
[2] A. Biermanns et al., J. Appl. Phys. 104, 044312 (2008)
Keywords: ion beam erosion, X-ray diffraction and scattering
  • Lecture (Conference)
    Deutsche Tagung für Forschung mit Synchrotronstrahlung, Neutronen und Ionenstrahlen an Großgeräten (SNI2010), 24.-26.02.2010, Berlin, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-14924
Publ.-Id: 14924


Growth of quantum dot crystals in amorphous matrix on rippled substrates

Buljan, M.; Grenzer, J.; Keller, A.; Radić, N.; Cornelius, T.; Metzger, T. H.; Holý, V.
The formation of quantum dot crystals by multilayer deposition has been reported and explained satisfactorily only in crystalline materials, so far. Here we demonstrate a method for the growth of quantum dot crystals in amorphous matrices. The ordering of the positions of quantum dots is induced by the deposition of a multilayer on a periodically rippled substrate at an elevated substrate temperature. During the deposition, the quantum dots self-arrange following the morphology of the substrate. The result is a formation of well ordered lattice of Ge quantum dots in amorphous silica matrix. We have investigated the ordering of the dots by grazing-incidence small-angle X-ray scattering and we found that the distance of the dots in the multilayer interfaces close to the rippled surface indeed equals the ripple period. However, in more distant interfaces the dot-dot distance approaches the value for non-rippled substrate and the dot ordering is slightly less pronounced. This finding confirms the beneficial influence of the rippled substrate on the ordering of quantum dots in an amorphous matrix.
Keywords: x-ray diffraction and scattering
  • Lecture (Conference)
    DPG Frühjahrstagung der Sektion Kondensierte Materie (SKM), 21.-26.03.2010, Regensburg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-14923
Publ.-Id: 14923


In-situ grazing incidence scattering investigations during magnetron sputtering deposition of FePt/Ag thin films

Grenzer, J.; Cantelli, V.; Jeutter, N. M.; von Borany, J.
We report on an in-situ study on the evolution of granular magnetic L10 -FePt/Ag layers deposited by magnetron sputtering on an amorphous SiO2 substrate. Using synchrotron radiation we investigated the nanostructure growth during deposition as function of the Ag thickness by the simultaneous detection of the cluster growth and of the formation of the hard ferromagnetic L10 -phase applying grazing incidence small-angle X-ray scattering (GISAXS) and X-ray diffraction, respectively. FePt/Ag nanoparticle were prepared using a dual magnetron deposition chamber, equipped with two Be windows to allow X-ray penetration, that was mounted on the six-circle goniometer of the Rossendorf beam line (ROBL BM20) at the ESRF (European Synchrotron Radiation Facility). The possibility to tune X-ray beam energy, to reduce air scattering and absorption, together with the high brilliance of the synchrotron source had made it possible to obtain a reliable GISAXS signal and to control the cluster morphology the initial stage [1].

[1] V. Cantelli, J. von Borany, N.M. Jeutter, J. Grenzer, Adv. Eng.Mat. 11, 478 (2009).
Keywords: in-situ x-ray diffraction
  • Lecture (Conference)
    DPG Frühjahrstagung der Sektion Kondensierte Materie (SKM), 21.-26.03.2010, Regensburg, Deutschland
  • Lecture (Conference)
    "Deutsche Tagung für Forschung mit Synchrotronstrahlung, Neutronen und Ionenstrahlen an Großgeräten“ (SNI2010), 24.-26.02.2010, Berlin, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-14922
Publ.-Id: 14922


In-situ X-ray Scattering: a Tool to Investigate the Formation of Nanostructures

Grenzer, J.
Nowadays, the development of new materials is often associated with specific properties of functionalized nanostructures. X-ray investigations are a very important tool to find the link between the functional (magnetism, luminescence) and the corresponding structural properties (size, orientation etc.) that are generating this function and to explain the underlying physical processes. This knowledge makes it possible to design new materials with specific properties. We report on (in-situ) X-ray studies that are focused to ion-beam sputtering (IBS) processes creating nanostructures either by ion beam erosion or by sputter deposition processes.
Keywords: in-situ x-ray diffraction; nano structures
  • Invited lecture (Conferences)
    SLS Seminar, 19.02.2010, Villigen, Schweiz

Permalink: https://www.hzdr.de/publications/Publ-14921
Publ.-Id: 14921


X-ray Investigations on CoSi2 nano wires manufactured by focused ion beam synthesis

Grenzer, J.; Biermanns, A.; Akhmadaliev, C.; Bischoff, L.
Nano wires and chains of nano particles are of emerging interest in nanoelectronics, nano-optics and plasmonics as well as for their monolithic integration into microelectronic devices; CoSi2 is a promising material due to its CMOS-compatibility that shows metallic behavior with low resistivity and high thermal stability. It is well known that cobalt disilicide films can be formed in silicon by implanting Co in stoichiometric concentration and a subsequent annealing procedure. It has been shown that ion beam synthesis allows the fabrication of epitaxial buried or surface CoSi2 layers on silicon. Submicron patterns can be directly produced by a writing focused ion beam (FIB) cobalt implantation. The formation of continuous nano wire structures follows always the <110> direction [1].
We have studied the strain of the Si host lattice in the surrounding area of a single nanostructures depending on their crystallographic orientation using high resolution X-ray diffraction in combination with a highly focused (~1µm) X-ray beam at the beam line ID01 at the ESRF. The crystalline nano wire is embedded into the Si matrix and shows a tensile strain of about 1.4%. This feature can be only found if the beam focused on the nano wire itself. We will show that it is possible to investigate a single nano wire of a size of below 50 nm. The CoSi2 peak intensity is strongly modulated if we move from one wire to an other. Moreover the diffuse scattered intensity around the Si bulk reflection is increased and is getting even more enhanced between the wires (see Figure 1). A possible mechanism, the formation of stable dislocation loops, lying behind the formation of CoSi2 wires will be discussed.

[1] Ch. Akhmadaliev, B. Schmidt and L. Bischoff, Appl. Phys. Lett. 89, 223129 (2006); Ch. Akhmadaliev, L. Bischoff and B. Schmidt; Mat. Sci. & Eng., C26, 818 (2006).
Keywords: Nanostrukturen, focused x-ray beams
  • Lecture (Conference)
    Science with X-ray Nano-beams, 09.-12.02.2010, Grenoble, Frankreich
  • Poster
    10th Biennial Conference on High Resolution X-Ray Diffraction and Imaging, 20.09.2010, Warwick, England

Permalink: https://www.hzdr.de/publications/Publ-14920
Publ.-Id: 14920


Structural characterization of buried superconducting Ga rich films in Si

Fiedler, J.; Heera, V.; Skrotzki, R.; Herrmannsdörfer, T.; Voelskow, M.; Mücklich, A.; Schmidt, B.; Skorupa, W.; Gobsch, G.; Helm, M.; Wosnitza, J.
Recently it has been shown that heavily p-doped group-IV semiconductors such as diamond, silicon and germanium can become superconducting at low temperatures. Here, we present a study of Ga-implanted Si that becomes superconducting due to precipitation after annealing. Ion implantation allows introducing a high Ga dose (4E16cm-2) in Si that leads to peak concentrations far beyond the solid solubility limit. Rapid thermal annealing (RTA) causes redistribution of the Ga and re-crystallization of the amorphous implanted Si layer. After annealing at temperatures up to 850°C the implanted layers are polycrystalline and contain Ga-rich precipitates. Structural investigations by means of RBS/C measurements and TEM demonstrate a high density of precipitates at the interface of a protective SiO2 layer and the silicon substrate. At optimized annealing conditions (600-700°C) such samples become superconducting with critical temperatures up to 7 K [1].
[1] Skrotzki R. et al. , Appl. Phys. Lett. 97 (2010) 192505
  • Lecture (Conference)
    DPG Frühjahrstagung der Sektion Kondensierte Materie (SKM) 2011, 13.-18.03.2011, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-14919
Publ.-Id: 14919


Acceptor deactivation in individual silicon nanowires: From thick to ultrathin

Ou, X.; Geyer, N.; Kögler, R.; Werner, P.; Skorupa, W.
An individual free standing spicular silicon nanowire (NW) fabricated by Ag assisted chemical etching was doped to 1018 dopants/cm-3 by boron ion implantation and annealed at 1000°C. The presented NW is around 900 nm in length and consists of two connected parts, a thicker basis with a diameter of about hundred nm and of a thin top part with an average diameter as thin as 16 nm. This NW was analyzed by scanning spreading resistance microscopy (SSRM). The paper demonstrates that SSRM is capable to spatially and electrically resolve such an ultrathin NW with the thinnest part down to 12 nm in diameter. Experimental results show the dependence of the acceptor deactivation on the diameter of the NW cross section. The doping efficiency of the NW dramatically decreases as the diameter is below 25 nm. Deactivation mechanisms are discussed.
Keywords: nanowire, SSRM, doping, implantation

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Permalink: https://www.hzdr.de/publications/Publ-14918
Publ.-Id: 14918


Three-dimensional carrier profiling of individual Si nanowires by scanning spreading resistance microscopy

Ou, X.; Das Kanungo, P.; Kögler, R.; Werner, P.; Gösele, U.; Skorupa, W.; Wang, X.
Individual silicon nanowires (Si NWs) grown by molecular beam epitaxy and in-situ doped with boron were investigated by scanning spreading resistance microscopy (SSRM), a technique based on the conductive atomic force microscopy. The carrier profiles of the NWs were derived from the measured spreading resistance values and calibrated with the known carrier concentration of the underlying epi-layer. The three-dimensional SSRM profile of a NW was obtained by measuring the NW cross sections at different depths along the radial direction. Scanning the same NW with a controlled force on the SSRM tip can abrade material from the cross-sectional surface and the tip moves deeper into the volume of the NW after each image scan. Repeated stripping of the material from the NW results in a "thinning" of the remaining NW segment and a corresponding increase of its resistance which can be addressed by an appropriate data correction. The achieved three-dimensional carrier profile reveals a multi-shell structure of the carrier distribution across the NW diameter which consists of a lower doped core region, a higher doped shell region and a carrier depleted sub-surface region.
Keywords: nanowire, doping, three-dimensional, carrier profile, SSRM

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Permalink: https://www.hzdr.de/publications/Publ-14917
Publ.-Id: 14917


Aqueous coordination chemistry and photochemistry of uranium(VI)

Tsushima, S.
We have been exploring aqueous coordination chemistry of uranium(VI) by combining different spectroscopic techniques and computational chemistry, i.e. EXAFS and FTIR spectroscopy and DFT calculations. In uranyl(VI) sulfate system we found sulfate may bound to uranium in both unidentate and bidentate modes.
Whether ligand bind to uranium in unidentate or bidentate might seem to be irrelevant. However the EXAFS and DFT study on uranyl(VI) oxalate system proved that this is entirely not the case and the mode of ligand coordination plays decisive role to the photoreactivity of uranyl(VI) oxalate. Only the uranyl(VI) oxalate having unidentate coordination was found to be photoreactive. The result is consistent with recent UV-Vis absorption spectroscopic study by Görller-Walrand and Servaes.
The validity of the use of DFT on uranium complexes is often disputed. Sophisticated theory such as CASPT2 is proved to be requisite for getting accurate excitation energies of uranyl(VI) complexes. However, DFT calculations were also proved to provide accurate geometries as long as the ground states and the lowest lying triplet states are concerned. Photoluminescence characters of uranium(VI) were also found to be well reproduced by cost-effective DFT calculations.
  • Invited lecture (Conferences)
    Seminar at Katholieke Universiteit Leuven, 14.01.2011, Leuven, Belgium

Permalink: https://www.hzdr.de/publications/Publ-14916
Publ.-Id: 14916


Improved vortex nucleation in truncated soft magnetic cones

Martin, N.; Mönch, I.; Schäfer, R.; Schultz, L.; McCord, J.
Magnetic vortex structures are promising for data storage applications due to the possibility to switch vortex chirality and core orientation independently. Subsequently two bits per element can be stored, which is favorable for high data storage densities. The magnetic vortex state of soft-magnetic nano-disks is stable over a large range of thickness and radii. Nevertheless the formation of a vortex state has to overcome an energy barrier in order to nucleate the vortex at the element’s edge. In the presented work the influence of a large edge tilt on the behavior of vortex nucleation is studied experimentally and by numerical simulations. Single elements and arrays of closely packed elements with a diameter of approx. 300 nm were fabricated by means of nanosphere lithography, by which an element edge tilt of 45° could be achieved. From the simulations it was found that with decreasing edge tilt from 90° (cylindrical dot) to 45° the probability to nucleate a vortex during magnetization reversal increases. For cylindrical elements at the onset of vortex nucleation the out of plane component of magnetization near the edge has opposite signs at the top and bottom of the element. For truncated cones, however, the magnetization points only in one direction and favors the nucleation of a magnetic vortex. Thus, the vortex formation in smaller elements is facilitated by engineering the shape of the dots. For narrowly packed structures it is shown that despite of strong dipolar interactions the magnetization reversal involves a vortex nucleation and annihilation process.
Keywords: magnetic vortex, nanosphere lithography, vortex nucleation
  • Lecture (Conference)
    55th Annual Conference on Magnetism & Magnetic Materials, 14.-18.11.2010, Atlanta, Georgia, USA

Permalink: https://www.hzdr.de/publications/Publ-14915
Publ.-Id: 14915


Competition of dipolar interactions and lateral exchange spring effect in NiFe elements

Martin, N.; Strache, T.; Mönch, I.; Schultz, L.; Fassbender, J.ORC; McCord, J.
Conventional exchange spring systems consist of directly exchange coupled hard and soft magnetic layers, which characteristic behaviour is related to an interlayer domain wall that is formed during reversal of magnetization. Recently, a similar exchange spring effect was achieved in lateral hard/soft magnetic stripe structures, which were fabricated by means of ion implantation of single layer films [1]. This technique offers the possibility to directly investigate the changes of magnetization in and between the hard/soft phases.

In the presented work, lateral exchange spring structures were prepared on patterned samples to investigate the interplay between structuring and additional dipolar fields. In contrast to extended films, the lateral exchange spring effect only occurs for a higher difference in saturation magnetization Ms between the two magnetic phases. The measured collective magnetization reversal of hard and soft phase is attributed to strong dipolar fields at the element edges that cause a hysteresis behaviour which is comparable to that of a magnetic homogeneous square element. The exchange spring behaviour, occurring with increasing difference in Ms between the two phases is related to an increase in effective shape anisotropy in the high Ms stripes. The magnetization reversal approaches an individual switching of the stripes, with the low Ms stripes switching first. This results in an antiparallel alignment of magnetization of the individual stripes with lateral domain walls in between, which configuration is stabilized by the inter-stripe flux closure. The resulting two-step reversal is modelled, taking the demagnetization and domain wall energy terms into account.
Keywords: ion implantation, thin films, Permalloy, magneto-optical imaging
  • Lecture (Conference)
    55th Annual Conference on Magnetism & Magnetic Materials, 14.-18.11.2010, Atlanta, Georgia, USA

Permalink: https://www.hzdr.de/publications/Publ-14914
Publ.-Id: 14914


Herstellung und Charakterisierung magnetisch heterogener, dünner Schichten

Martin, N.; Schäfer, R.; Fassbender, J.ORC; Schultz, L.; McCord, J.
In der Präsentation werden Methoden vorgestellt, die das Hystereseverhalten dünner magnetischer Schichten gezielt beeinflussen. Insbesondere geht es dabei um lokale Eigenschaftsveränderungen durch Strukturierung mittels lithografischer Techniken und anschließender Ionenimplantation. Der Einfluss der Strukturierung auf das Ummagnetisierungsverhalten der gesamten Schicht wird anhand von magneto-optisch gemessenen Hysteresekurven und Domänenaufnahmen dargestellt und mittels geeigneter Modelle erklärt.
Keywords: thin films, magnetic microstructure, magneto-optical imaging
  • Invited lecture (Conferences)
    VAC-Kolloqium, 09.-10.12.2010, Hanau, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-14913
Publ.-Id: 14913


Lipid Protein Interactions underlie an Evolutionary Conserved Proton Switch in a Transmembrane Peptide derived from Helix-3 of Class-1 GPCRs

Eichler, S.; Madathil, S.; Fahmy, K.
The visual photoreceptor rhodopsin is a proto¬typical class-I (rhodopsin-like) G protein-coupled receptor (GPCR). Photoisomerization of the covalently bound ligand 11-cis-retinal leads to restructuring of the cytosolic face of rhodopsin. The ensuing protonation of Glu-134 in the class-conserved D(E)RY motif at the C-terminal end of trans¬membrane helix-3 promotes the formation of the G-protein-activating state. Glu-134 acts as an autonomous proton switch also in synthetic transmembrane peptides, where lipid protein interactions couple protonation to helix extension and hydrophobic burial of the side chain resulting in an elevated side chain pKa. The implied change in "helical-end-solvation" by interfacial water has been investigated by pulsed hydration experiments. we observed within several seconds (i) lipid/peptide conformational changes by time-resolved Fourier transform infrared (FTIR) difference spectroscopy and (ii) water penetration into the lipidic phase using the simultaneous recording of the fluorescence of a tryptophan (trp) inserted 3 amino acids N-terminally from the ERY motif. Cross-correlation of both monitors reveals the linkage of lipid ester carbonyl hydration to helical end unwinding followed by water penetration into the bilayer one helical turn N-terminally of the conserved ERY motif. Trp-emission further shows that the indole ring is more water-exposed in the ionized than in the protonated state of the adjacent ERY motif evidencing a shift of the lipid/water phase boundary relative to the transmembrane peptide upon proton uptake. The proton-dependent reorganisation of the lipid/peptide/water microdomain N-terminally of the ERY motif is further supported by a pH-sensitive Förster-resonance-energy-transfer from the peptidic trp to 5-(dimethylamino)naphthalene-1-sulfonyl (DANSYL)-labelled lipids. In conclusion, the data reveal a conserved hydration site at the membrane water interface of GPCRs that attracts or repels water in response to protonation, thereby, linking proton uptake to protein conformation and rearrangement of the lipid/peptide/water phase boundary independently of helix-helix interactions.
Keywords: G protein infrared spectroscopy peptide rhodopsin
  • Contribution to proceedings
    Annual Meeting of the German Biophysical Society 2009, 03.-06.10.2009, Bochum, Deutschland
    Book of Abstracts

Permalink: https://www.hzdr.de/publications/Publ-14912
Publ.-Id: 14912


Zum Komplexbildungsverhalten ausgewählter Actiniden (U, Np, Cm) mit mikrobiellen Bioliganden

Glorius, M.
Diese Arbeit war ein eigenständiger Teil eines Projektes, welches sich mit der Aufklärung des Einflusses von Mikroorganismen auf die Ausbreitung von Actiniden bei einer Freisetzung dieser aus dem Endlager beschäftigt. Dabei wurde der Einfluss von mikrobiell produzierten Substanzen auf die Mobilisierung ausgewählter Actiniden untersucht. Die in diesem Projekt untersuchten mikrobiell produzierten Substanzen, sogenannte Bioliganden, wurden von Bakterien des Genus Pseudomonas unter speziellen Bedingungen produziert. Die von den Pseudomonaden freigesetzten Bioliganden, hier Siderophore vom Pyoverdin-Typ, haben ein hohes Potential, Metalle, insbesondere Eisen(III), zu komplexieren und so zu transportieren. Es wurde untersucht, in welcher Weise und unter welchen Bedingungen diese Bioliganden in der Lage sind, auch radioaktive Schadstoffe zu komplexieren und damit zu mobilisieren. Für die Untersuchungen wurden die α-strahlenden Actiniden Uran, Curium und Neptunium ausgewählt, weil diese auf Grund ihrer Langlebigkeit und Radiotoxizität von besonderem Interesse sind.
Diese Arbeit beschäftigte sich mit der Wechselwirkung der Actiniden U(VI), Np(V) und Cm(III) mit Modellliganden, die die Funktionalitäten der Pyoverdine simulieren. Für die Metallbindung der Pyoverdine sind die Katecholgruppe des Chromophors und die funktionellen Gruppen der Peptidkette (Hydroxamsäuregruppen und α-Hydroxysäurereste) verantwortlich. Für die Simulation der Hydroxamsäuregruppen kamen dabei die Monohydroxamate Salicylhydroxamsäure (SHA) und Benzohydroxamsäure (BHA) und das natürliche Trihydroxamat Desferrioxamin B (DFO) zum Einsatz und für die Katecholgruppe das 6-Hydroxychinolin (6HQ) und 2,3-Dihydroxynaphthalin (NAP). Als Vergleichsligand wurde außerdem Benzoesäure (BA) untersucht. Für die Bestimmung der Stabilitätskonstanten zur Einschätzung der Stärke der gebildeten Komplexe, die Aufklärung der Struktur der Actinid-Ligand-Verbindungen und die Verfolgung der Änderung der Speziation der Actiniden vor und nach der Wechselwirkung mit den Modellliganden kamen verschiedene spektroskopische Verfahren wie Absorptionsspektroskopie, Laserfluoreszenzspektroskopie,
Röntgenabsorptionsspektroskopie und Schwingungsspektroskopie zum Einsatz. Außerdem wurden erstmals theoretische Modellierungen zur Aufklärung der Struktur der Actinid-Modellligand-Komplexe durchgeführt.
Die Ziele dieser Arbeit waren also die spektroskopische Charakterisierung und Bestimmung der Speziation und Komplexbildungskonstanten sowohl der ausgewählten Modellliganden als auch der gebildeten Actinid-Modellligand-Komplexe, die Aufklärung möglicher Strukturen der Komplexe sowie ein Vergleich der Ergebnisse mit denen der Pyoverdine.
Der Vergleich der Stabilitätskonstanten der untersuchten Liganden mit den drei Actiniden U(VI), Cm(III) und Np(V) ergab im Wesentlichen folgende Reihenfolge der Komplexstärke:
PYO ≥ DFO > NAP > 6HQ > SHA ≥ BHA > BA.
Benzoesäure besitzt als einziger Ligand eine Carboxylfunktionalität und weist mit 103 die geringste Stabilitätskonstante auf. Die beiden Monohydroxamate SHA und BHA bilden mit allen drei Actiniden ähnlich starke 1:1-Komplexe. Bei den 1:2-Komplexen besitzt SHA mit Cm(III) und Np(V) etwas höhere Stabilitätskonstanten als BHA, wahrscheinlich verursacht durch einen stabilisierenden Einfluss der zusätzlichen phenolischen OH-Gruppe. Dieser Trend wurde auch in den theoretischen Modellierungen für die U(VI)-Komplexe beobachtet. Die natürlichen Siderophore DFO und PYO bilden die stärksten Komplexe mit den Actiniden (Stabilitätskonstanten von 1012 bis 1034). Dies liegt in der Struktur und der hohen Anzahl an funktionellen Gruppen begründet; DFO besitzt drei Hydroxamatgruppen, das Pyoverdinmolekül neben den Hydroxamatgruppen noch die Katecholgruppen der Chromophorfunktionalität. Die Modellliganden für die Chromophorfunktionalität, NAP und 6HQ, bilden stärkere Komplexe als die Monohydroxamate SHA und BHA, aber schwächere Komplexe als DFO und PYO. Daraus lässt sich schlussfolgern, dass die Chromophorfunktionalität eine wichtige Rolle bei der Anbindung der Actiniden an die Pyoverdine spielt.
Der Vergleich der Stabilitätskonstanten der Komplexe der Liganden SHA, BHA und 6HQ mit den drei untersuchten Actiniden U(VI), Cm(III) und Np(V) untereinander zeigte, dass die Stärke der Komplexe von U(VI) über Cm(III) zu Np(V) abnimmt. Der Grund dafür liegt in den unterschiedlichen Ladungsdichten der Actinidionen. Während das UO22+-Ion mit einer Koordinationszahl von 5 und einem Ionenradius von ~ 0.6 eine effektive Ladung von + 3.3 besitzt, hat das Cm3+-Ion eine effektive Ladung von + 2.6 und das NpO2+-Ion von + 2.3. Damit besitzt das NpO2+-Ion die geringste Ladungsdichte der untersuchten Actinidionen und bildet damit auch die schwächsten Komplexe mit den niedrigsten Stabilitätskonstanten. Die Stärke der Komplexe der Liganden NAP, DFO und PYO nimmt von Cm(III) über U(VI) zu Np(V) ab. Obwohl Cm(III) eine geringere effektive Ladung als U(VI) hat, bildet es stärkere Komplexe als U(VI). Eventuell sind dafür strukturelle Behinderungen der Koordination durch die lineare O=U=O Einheit verantwortlich.
In einer Kooperation mit dem Institut für Theoretische Chemie der Universität zu Köln wurden für die 1:1- und 1:2-Komplexe der wässrigen U(VI)-SHA-, U(VI)-BHA- und U(VI)-BA-Systeme erstmals theoretische Modellierungen durchgeführt. Dabei wurden die Strukturen der Komplexe sowohl in der Gasphase als auch unter Berücksichtigung der Solvatation optimiert und die relativen Stabilitäten und Anregungsspektren berechnet. Die mit DFT berechneten Bindungsenergien bestätigen die experimentell anhand der Stabilitätskonstanten log β ermittelte Reihenfolge der Komplexstabilitäten (SHA ≥ BHA > BA). Außerdem zeigen die höheren Bindungsenergien der 1:2-Komplexe, dass diese stabiler sind als die 1:1-Komplexe. Dies lässt sich auch anhand der experimentell ermittelten Stabilitätskonstanten nachweisen. Für den 1:1-Komplex des U(VI)-SHA-Systems konnte mit Hilfe der theoretischen Modellierung die strukturelle Anbindung des Uranylions an die Hydroxamsäuregruppe aufgeklärt werden. Der Vergleich der berechneten Strukturen, Bindungsenergien, Bindungslängen und Anregungsspektren der beiden möglichen Anbindungsmodi [O,O] und [N,O’] zeigte deutlich, dass das Uranylion bevorzugt über die beiden Sauerstoffatome der Hydroxamsäuregruppe, also den [O,O]-Modus, gebunden wird. Die Methode der DFT konnte also dazu beitragen, Defizite in der experimentellen Aufklärung der Komplexstruktur im Fall des U(VI)-SHA-Systems zu beheben.
Die Modellliganden und deren Komplexe mit U(VI), Cm(III) und Np(V) wurden zum größten Teil erstmals spektroskopisch charakterisiert sowie deren bisher weitgehend unbekannten Stabilitätskonstanten bestimmt. Außerdem konnte die Struktur der U(VI)-Hydroxamat-Komplexe mit Hilfe der ATR-FTIR-Spektroskopie und der theoretischen Modellierung aufgeklärt werden. Im Vergleich der Ergebnisse der Modellliganden mit denen der Pyoverdine konnte festgestellt werden, dass die Katecholfunktionalität der Pyoverdine eine große Rolle bei der Komplexierung mit den Actiniden spielen wird. Weiterhin ließen sich aus den Ergebnissen Schlussfolgerungen zur Stärke der gebildeten Actinid-Modellligand- und Actinid-Pyoverdin-Komplexe ziehen. Die Pyoverdine bildeten mit U(VI) Komplexe mit Stabilitätskonstanten bis 1030, mit Cm(III) bis 1032 und mit Np(V) bis 1020. Die wichtigsten, in höheren Konzentrationen vorkommenden anorganischen Komplexbildner in natürlichen Wässern sind das Hydroxidion OH- sowie das Carbonation CO32-. Diese besitzen eine hohe Komplexierungsfähigkeit und bilden mit den drei Actiniden U(VI), Cm(III) und Np(V) Komplexe mit Stabilitätskonstanten von 102 bis 1020. Der Vergleich der Konstanten von OH und CO32- mit denen der organischen, mikrobiellen Pyoverdin-Liganden zeigt, dass die Pyoverdine ähnlich starke bzw. teilweise stärkere Komplexe mit den Actiniden bilden als die anorganischen Komplexbildner. Daraus lässt sich ableiten, dass die Pyoverdine selbst in niedrigeren Konzentrationen ein hohes Potential besitzen, Actiniden in natürlichen Wässern zu binden und damit zu transportieren. Die untersuchten Bioliganden sind also in der Lage, bei Anwesenheit in der Natur in bestimmten Konzentrationen im Grundwasser Actiniden, z.B. durch Herauslösen aus Festphasen, zu mobilisieren. Damit können solche Bioliganden das Verhalten der Actiniden in der Umwelt entscheidend beeinflussen. Die Ergebnisse dieser Arbeit tragen dazu bei, den Einfluss der mikrobiellen Liganden auf die Mobilisierung und Ausbreitung der Actiniden besser einschätzen zu können. Damit können die Ergebnisse zur Quantifizierung des Mobilisierungseffekts der Actiniden durch freigesetzte Bioliganden im Nahfeld genutzt werden.
Keywords: Actiniden, Hydroxamsäure, Pyoverdin, Spektroskopie, Komplexierung, actinides, hydroxamic acids, pyoverdin, spectroscopy, complex formation
  • Article, self-published (no contribution to HZDR-Annual report)
    Forschungszentrum Rossendorf 2009
    Dissertation
    152 Seiten

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Publ.-Id: 14911


Fluence dependence of small-angle neutron scattering in neutron-irradiated Fe-Cr

Bergner, F.; Heintze, C.; Ulbricht, A.
Four Fe-Cr alloys with chromium concentrations ranging from 2.5 to 12.5 at% in three irradiation conditions (0.06, 0.6 and 1.5 displacements per atom) were investigated by means of small-angle neutron scattering. For Fe-12.5 at% Cr, alpha‘–phase particles were unambigiously identified. The size distribution of these particles was estimated and the kinetics of formation were compared with a rate theory model which allows to extrapolate the evolution of the nanostructure to still lower dpa-levels. For 2.5, 5 and 9 at% Cr, the results of the SANS investigation are more complex and the input from other methods, such as APT and TEM, is needed in order to explore the irradiation effects in detail.
Keywords: Fe-Cr alloy, neutron irradiation, SANS
  • Lecture (Conference)
    17th Workshop on Multiscale Modelling and Basic Experiments of Iron-Chromium Alloys for Nuclear Applications, 03.-04.11.2010, Stockholm, Schweden

Permalink: https://www.hzdr.de/publications/Publ-14910
Publ.-Id: 14910


Investigation of wear-out phenomena in Eu-implanted metal-oxide semiconductor light emitting devices

Lehmann, J.; Rebohle, L.; Kanjilal, A.; Voelskow, M.; Skorupa, W.; Helm, M.
The anomalous wear-out phenomenon of Eu-implanted MOS based light emitting devices (MOSLED’s) was investigated intensively by many different techniques, on samples exposed to different annealing temperatures and times. It will be shown, that in contrast to other rare earth elements the EL intensity of Eu-implanted SiO2 layers can rise under constant current injection before the known EL quenching will start. Under certain circumstances this rise may amount up to two orders of magnitude. The EL behaviour will be correlated with the microstructural and electrical properties of the devices. Transmission electron microscopy (TEM) and Rutherford backscattering spectroscopy (RBS) were used to trace the growth of Eu / Eu oxide clusters and the diffusion of Eu to the interfaces of the gate oxide layer, which are induced by the annealing process. Current-voltage (I(V)) characteristics, EL decay times (τ) and the evolution of the voltage under constant current injection (Vcc) as well as evolution of the EL spectrum with injected charge (EL(Qinj)) were studied with respect to charging and trapping phenomena in the oxide layer in order to reveal details of the EL excitation mechanism. A qualitative model for the anomalous wear-out phenomenon is proposed.
Keywords: Electroluminescence, rare earth, charge trapping, ion implantation, Europium, Si-based light emission, Electroluminescence wear-out, quenching
  • Poster
    Nanofair 2010 - 8th International Nanotechnology Symposium, 06.-07.07.2010, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-14909
Publ.-Id: 14909


Wear-out phenomena in Si-based light emitting devices with ion beam implanted europium

Lehmann, J.; Rebohle, L.; Kanjilal, A.; Voelskow, M.; Helm, M.; Skorupa, W.
Recently, it was shown that it is possible to obtain efficient electroluminescence (EL) from UV to IR by implanting lanthanides into the oxide layer of metal-oxide semiconductor (MOS) structures [1]. The best efficiencies could be achieved on a Tb-implanted light emitter with an external quantum efficiency of 16% and a corresponding power efficiency of 0.3%. With these electrically driven Si-based light emitting devices, also called MOSLEDs, it is possible to build an integrated biosensor for the detection of organic molecules like estrogene, e.g. see Ref. [2]. For this purpose, the intensity and stability of the emitted EL are the most critical properties of the light emitters. Usually, lanthanide implanted MOSLEDs show a quenching of the EL-signal with time, which can be attributed to charge trapping in the oxide layer. In contrast to this normal wear-out phenomenon, Eu-implanted MOSLEDs can show a rise in the EL-signal during the operation time of the device [3]. Due to this anomalous wear-out phenomenon, Eu-implanted MOSLEDs offer the possibility to build a device with an extremely stable EL if the occurring processes can be better understood. For this reason, an intensive investigation was performed on Eu-implanted MOSLEDs exposed to different annealing temperatures and times. Transmission electron microscopy (TEM) and Rutherford backscattering spectroscopy (RBS) were used to trace the growth of Eu / Eu oxide clusters and the diffusion of Eu to the interfaces of the gate oxide layer, respectively. Both of them were induced by the annealing process. Resonant nuclear reaction analysis (rNRA) was used to measure the hydrogen depth profile in the dielectric. Current-voltage (I-V) characteristics, the EL decay times (τ) and the evolution of the voltage under constant current injection (Vcc) as well as the evolution of the EL spectrum with injected charge (EL-Qinj) were studied with respect to charging and trapping phenomena in the oxide layer in order to reveal details in the occurring wear-out mechanism of the EL. It will be shown, that for certain annealing conditions the EL intensity of Eu-implanted SiO2 layers can increase during constant current injection which is followed by the known EL quenching. In extreme cases this rise may amount up to two orders of magnitude. The EL behaviour will be correlated with the microstructural and electrical properties of the devices. A qualitative model for the anomalous wear-out phenomenon is proposed.
Keywords: Electroluminescence, rare earth, charge trapping, ion implantation, Europium, Si-based light emission, Electroluminescence wear-out, quenching
  • Lecture (Conference)
    Ion Implantation and Other Applications of Ions and Electrons (ION 2010), 14.-17.06.2010, Kazimierz Dolny, Poland

Permalink: https://www.hzdr.de/publications/Publ-14908
Publ.-Id: 14908


Influence of Al concentration on structure and electrical properties of polycrystalline and epitaxial Al-doped ZnO films grown by reactive pulsed magnetron sputtering

Cornelius, S.; Vinnichenko, M.; Kolitsch, A.; Möller, W.
Al-doped ZnO (AZO) films which combine maximum carrier mobility (μe), moderate free electron densities (Ne) and high surface roughness are of special interest for application as transparent front electrode in thin film solar cells. They posses high transmission in the near infrared region, close to the bandgap energy of absorber materials like Si (Eg =1.11 eV), and enable a superior light trapping behaviour. A key to tailor AZO film properties is understanding the mechanisms and effects of the Al-dopant incorporation into the ZnO matrix. The present work focuses on investigation of the influence of Al concentration on the electrical properties of AZO and on establishing performance limits with respect to carrier mobility and resistivity (ρ). Polycrystalline and epitaxial AZO films are grown on fused silica and c-axis oriented sapphire substrates, respectively, by reactive pulsed magnetron sputtering using several sets of Zn/Al alloy targets with an Al concentration (cAl) between 0.7 and 8.7 at%. A systematic variation of process parameters such as substrate temperature (Ts) and oxygen partial pressure results in polycrystalline films with μe>45 cm2V-1s-1 and ρ<2.3x10-4 Ωcm at optimum conditions, whereas μe~55 cm2V-1s-1 could be obtained for epitaxial films. It is observed that cAl has a strong influence on the optimum value of Ts, the maximum μe and Ne values and also on film structure and surface roughness. Extensive XRD investigations reveal that Al incorporation in the ZnO matrix has a detrimental effect on in-plane orientation and texture of epitaxial films, even for the lowest cAl used. Furthermore RBS and ERDA confirm a considerable Al enrichment in the films which correlates with deterioration of μe, when Ts is increased above its optimum value. The observed dependence of carrier mobility on Ne in ZnO:Al is discussed in the framework of ionized impurity scattering and clustering as well as grain boundary limited transport which predicts a fundamental physical limit of μe.
Keywords: reactive sputtering, zinc oxide, AZO, mobility, density, resistivity, RBS, ERDA, transparent conductive oxides, ionized impurity scattering
  • Poster
    Twelfth International Conference on Plasma Surface Engineering (PSE 2010), 13.-17.09.2010, Garmisch Partenkirchen, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-14907
Publ.-Id: 14907


A Compton Imager for in-vivo Dosimetry of Proton Beams - A Design Study

Kormoll, T.; Fiedler, F.; Schöne, S.; Wüstemann, J.; Zuber, K.; Enghardt, W.
In-beam SPECT during therapeutic proton beam irradiation is a novel method for three dimensional in-vivo dose verification. For this purpose a Compton camera design is evaluated with respect to the special requirements and conditions that arise from this application. Different concepts are studied by means of simulation concerning the angular resolution and the efficiency. It was found that a cadmium zinc telluride system can perform sufficiently well. For further evaluation the construction of a semiconductor scintillator hybrid system is under way.
Keywords: in-beam SPECT, in vivo dosimetry, ion beam therapy, proton therapy

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Permalink: https://www.hzdr.de/publications/Publ-14906
Publ.-Id: 14906


Lateral straggling and its influence on lateral diffusion in implantation with a focused ion beam

Batabyal, R.; Roy, A.; Roy, S.; Bischoff, L.; Dev, B. N.
Ion implantation plays an important role in semiconductor industry. Different kinds of ions are introduced into semiconductors by implantation in order to form n-type and p-type semiconductors. Nanoscale doped structures are required to be fabricated, usually by a focused ion beam (FIB), for applications in nanoelectronics. However, how closely these structures could be fabricated for an effective device performance would be determined by the limitation imposed by the lateral diffusion of the implanted species. For ion implantation, lateral straggling of the ion beam also produces defects surrounding the implanted region. This would produce radiation enhanced lateral diffusion. It is important to understand the lateral diffusion in FIB-fabricated nanostructures. We present a method based on photoemission electron microscopy (PEEM) for the determination of lateral diffusion coefficient in nanostructures. As an example, we present the investigation of lateral diffusion of Ga in FIB-fabricated structures of Ga-implanted n-type Si. For a set of parallel Ga implanted stripes, the diffusion profiles at the end of the stripes along their length obey the standard diffusion equation and the diffusion coefficient is extracted. However, across the stripes the diffusion profile is more complex, due to the presence of defects due to lateral straggling in the neighbouring stripes.
Keywords: photoemission, focused ion beam, diffusion in nanostructures
  • Lecture (Conference)
    24th International Conference on ATOMIC COLLISIONS IN SOLIDS, ICACS-24, 18.-23.07.2010, Krakow, Poland

Permalink: https://www.hzdr.de/publications/Publ-14905
Publ.-Id: 14905


Spectroscopic studies of arsenic retention onto biotite

Chakraborty, S.; Bardelli, F.; Mullet, M.; Greneche, J.-M.; Varma, S.; Ehrhardt, J.-J.; Banerjee, D.; Charlet, L.
Biotite is a constituent Fe-bearing mineral of Delta subsoils in India and Bangladesh and has been hypothesized as a primary source of arsenic (As). The adsorption behavior of As onto structural Fe(II,III)-bearing biotite fractions (<50 µm) was investigated in the pH range 4-8 under a CO2-free, anoxic condition (O2 <1 ppmv) using X-ray Photoelectron Spectroscopy (XPS) and X-ray Absorption Spectroscopy (XAS). The batch experiments indicate that As adsorption is strongly pH dependent and As(V) adsorbs more efficiently than As(III). X-ray Absorption Near-Edge Structure (XANES) spectra show no oxidation or reduction of As by biotite after 3 days reaction with As(III) or As(V) solutions. Extended X-ray Absorption Fine Structure (EXAFS) spectroscopic results suggest that As(III) forms bidentate mononuclear edge-sharing (2E) and bidentate binuclear corner-sharing (2C) surface complexes at pH 7.7 as indicated by the average As-Fe bond distances at 3.00 ± 0.02 Å and 3.37 ± 0.03 Å respectively. The surface speciation retrieved by XPS does not provide any evidence of reduction of As(V) on biotite after 30 days further confirming the thermodynamic prediction and the XANES results. This study has therefore significant environmental implications for As contaminated areas, where biotite retards the release of As into reducing groundwater. The changes in soil redox condition and weathering of biotite may likely contribute to the occurrence of high As in groundwater.
Keywords: Arsenic, adsorption, biotite, surface complex, reduction
  • Chemical Geology 281(2011), 83-92

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Publ.-Id: 14904


On the "yl" bond weakening in uranyl(VI) coordination complexes

Tsushima, S.
The U–Oyl triple bonds in the UO22+ aquo ion are known to be weakened by replacing the first shell water with organic or inorganic ligands. Weakening of the U–Oyl bond may enhance the reactivity of “yl” oxygens and uranyl(VI) cation–cation interactions. Density functional theory calculations as well as previously published vibrational spectroscopic data have been used to study the origin of the U–Oyl bond weakening in uranyl(VI) coordination complexes. Natural population analyses (NPA) revealed that the electron localization on the Oyl 2p orbital is a direct measure of the U–Oyl bond weakening, indicating that the bond weakening is correlated to the weakening of the U–Oyl covalent bond and not that of the ionic bond. The Mulliken analysis gives poor results for uranium to ligand electron partitioning and is thus unreliable. Further analyses of molecular orbitals near the highest occupied molecular orbital (HOMO) show that both the sigma and pai donating abilities of the ligands may account for the U–Oyl bond weakening. The mechanism of the bond weakening varies with coordinating ligand so that each case needs to be examined independently.

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Permalink: https://www.hzdr.de/publications/Publ-14903
Publ.-Id: 14903


Influence of humic acids on the actinide migration in the environment: Suitable humic acid model substances and their application in studies with uranium – a review

Sachs, S.; Bernhard, G.
Humic acids (HA) can influence the speciation of metal ions, e.g., actinide ions, and thus their migration in the environment. Therefore, knowledge of the impact of HA on the actinide migration is required to assess their transport in natural systems. However, due to the complex and heterogeneous nature of HA, there are a lot of difficulties in the thermodynamic description of their geochemical interaction behavior. A more basic understanding of the interaction processes of HA can be obtained by investigations applying HA model substances with more defined and specific properties. This work gives a review of selected types of HA model substances (HA-alike melanoidins, synthetic HA with pronounced redox functionality, modified HA with blocked phenolic/acidic OH groups, synthetic humic substance-clay-associates), their synthesis, isotopic labeling, and characterization in comparison to isolated natural HA. Examples for their application in various geochemical studies, such as complexation, redox, sorption and migration studies with uranium as representative for actinides are presented.
Keywords: Humic acids, model substances, synthesis, characterization, labeling, modification, application, uranium, actinides

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Publ.-Id: 14902


On the use of different analytical solutions for recalculation of the YALINA-Booster experiment SC3A

Merk, B.; Glivici-Cotruţă, V.; Weiß, F.-P.
The SC3A experiment in the YALINA-Booster facility in Belarus is described and investigated. For this investigation the very special configuration of YALINA-Booster core, consisting of a fast and a thermal zone, decoupled with a neutron ‘valve’ is analyzed in detail based on a full HELIOS model for the calculations. The two region design causes unexpected results in the experiments The special problems for the analysis of the experiments are shown. For an improved representation, a recently developed two group analytical solution for the time dependent diffusion equation obtained by Green’s function method without separation of space and time is used. To model the streaming of neutrons from the thermal area into the fast area an analytical solution for the space-time dependent neutron flux with two sources has been developed from the available Green’s functions for two groups. The space-time dependent thermal and fast neutron flux distributions are discussed. The new analytical solution shows very good agreement in the comparison with the experimental results, even for the unexpected behavior at the outermost detector. Thus analytical solutions without separation of space and time are a very promising tool to develop a new method for the analysis of ADS experiments
Keywords: Yalina, experimental analysis, Green’s function, Two group diffusion equation

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Publ.-Id: 14901


Constraining the S factor of 15N(p,g)16O at Astrophysical Energies

Leblanc, P. J.; Imbriani, G.; Goerres, J.; Junker, M.; Azuma, R.; Beard, M.; Bemmerer, D.; Best, A.; Broggini, C.; Caciolli, A.; Corvisiero, P.; Costantini, H.; Couder, M.; Deboer, R.; Elekes, Z.; Falahat, S.; Formicola, A.; Fulop, Z.; Gervino, G.; Guglielmetti, A.; Gustavino, C.; Gyurky, G.; Kaeppeler, F.; Kontos, A.; Kuntz, R.; Leiste, H.; Lemut, A.; Li, Q.; Limata, B.; Marta, M.; Mazzocchi, C.; Menegazzo, R.; O'Brien, S.; Palumbo, A.; Prati, P.; Roca, V.; Rolfs, C.; Rossi Alvarez, C.; Somorjai, E.; Stech, E.; Straniero, O.; Strieder, F.; Tan, W.; Terrasi, F.; Trautvetter, H. P.; Uberseder, E.; Wiescher, M.
The 15N(p,g)16O reaction represents a break out reaction linking the first and second cycle of the CNO cycles redistributing the carbon and nitrogen abundances into the oxygen range. The reaction is dominated by two broad resonances at Ep = 338 keV and 1028 keV and a Direct Capture contribution to the ground state of 16O. Interference effects between these contributions in both the low energy region (Ep < 338 keV) and in between the two resonances (338
  • Physical Review C 82(2010), 055804
    DOI: 10.1103/PhysRevC.82.055804
  • Contribution to WWW
    ArXiV preprint server: http://arxiv.org/abs/1011.2518
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    Permalink: https://www.hzdr.de/publications/Publ-14900
    Publ.-Id: 14900


    Blitzlampentemperung für die Photovoltaik

    Skorupa, W.
    A review regarding the application of flash lamp annealing for photovoltaic purposes was presented.
    Keywords: Flash lamp annealing, doping, ion implantation, solar cells
    • Lecture (Conference)
      Topical meeting with members of the company Bosch, 10.02.2010, FZ Dresden-Rossendorf, Deutschland

    Permalink: https://www.hzdr.de/publications/Publ-14899
    Publ.-Id: 14899


    Advances in Si & Ge millisecond processing: From SOI to superconducting Ge

    Skorupa, W.; Wündisch, C.; Posselt, M.; Heera, V.; Herrmannsdörfer, T.; Buca, D.; Mantl, D.; Haeberlein, S.; Fendler, R.; Gebel, T.
    Recently we could demonstrate that advanced SOI material can be treated in advantageous manner regarding USJ formation [1]. Especially, strained Si and SiGe/Si heterostructures on insulator are promising channel materials for future nanoelectronics devices. Their successful integration into new device architectures depends on the ability of forming ultra shallow and ultra steep junctions. We present results for dopant activation in SOI, sSOI, HOI and sHOI [2]. FLA allows complete suppression of diffusion while obtaining sheet resistances lower than 500 Ω/□ in both, SOI and sSOI. Strained and unstrained SiGe heterostructures indicated significant diffusional broadening of Sb implant profiles and low electrical activation. In contrast, B shows higher activation but significant dopant loss in the near surface region. Moreover, we demonstrate that, after diamond and silicon, the third elemental group-IV semiconductor, germanium, exhibits superconductivity at ambient pressure [3]. For the first time, techniques of the state-of-the-art semiconductor processing as ion implantation and FLA were used to fabricate such material, i.e. a highly Ga-doped Ge (Ge:Ga) layer in near-intrinsic Ge. It is shown that superconductivity can be generated and tailored in the Ge host at temperatures as high as 0.5 K. Results of critical-field measurements demonstrate the quasi-two-dimensional character of superconductivity in the 60 nm thick Ge:Ga layer.
    [1] F. Lanzerath, D. Buca, H. Trinkaus, M. Goryll, S. Mantl, J. Knoch, U. Breuer, W. Skorupa, B. Ghyselen, J. Appl. Phys. 104 (2008), 044908
    [2] R. A. Minamisava, W. Heiermann, D. Buca, H. Trinkaus, J. Hartmann, W. Skorupa, U. Breuer, B. Ghyselen, S. Mantl, Proc. 215th ECS Meeting, Vol. 19, Issue 1, May 24-29, 2009
    [3] T. Herrmannsdörfer, V. Heera, O. Ignatchik, M. Uhlarz, A. Mücklich, M. Posselt, H. Reuther, B. Schmidt, K.-H. Heinig, W, . Skorupa, M. Voelskow, C. Wündisch, R. Skrotzki, M. Helm, J. Wosnitza,
    Phys. Rev. Lett., 102 (2009) 217003, Supercond. Sc. & Techn., 23 (2010) 034007
    Keywords: ion implantation, flash lamp annealing, SOI, superconduction, germanium, silicon
    • Invited lecture (Conferences)
      The VIII-th International Conference on Ion Implantation and other Applications of Ions and Electrons – ION 2010 will be held in Kazimierz Dolny, Poland, between 14-th and 17-th June 2010., 14.-17.06.2010, Kazimierz Dolny, Poland

    Permalink: https://www.hzdr.de/publications/Publ-14898
    Publ.-Id: 14898


    Doping of Vertical Si Nanowires by Ion Implantation

    Skorupa, W.
    A review of recent work published in:
    ADVANCED MATERIALS Volume: 22 Issue: 36 Pages: 4020-4024
    NANO LETTERS Volume: 10 Issue: 1 Pages: 171-175
    NANOSCALE RESEARCH LETTERS Volume: 5 Issue: 1 Pages: 243-246
    Keywords: ion implantation, silicon nanowires, doping, scanning spreading resistance microscopy
    • Invited lecture (Conferences)
      43.Deutsches Nutzertreffen Ionenimplantation, 06.05.2010, Erlangen, Deutschland

    Permalink: https://www.hzdr.de/publications/Publ-14897
    Publ.-Id: 14897


    Literaturübersicht Temperaturmessung in RTP Mit Augenmerk auf die Blitzlampenausheilung

    Reichel, D.; Skorupa, W.; Lerch, W.; Gelpey, J.
    No abstract available.
    • Lecture (Conference)
      25. Treffen der Nutzergruppe RTP, 07.05.2009, Erlangen, Deutschland

    Permalink: https://www.hzdr.de/publications/Publ-14896
    Publ.-Id: 14896


    Application of Large-Eddy Simulation to Pressurized Thermal Shock: assessment of the accuracy

    Loginov, M. S.; Komen, E.; Höhne, T.
    Pressurized Thermal Shock (PTS) is identied as one of the safety issues where Computational Fluid Dynamics (CFD) can bring real benefits. The turbulence modeling may impact overall accuracy of the calculated thermal loads on the vessel walls, therefore advanced methods for turbulent fows are required. The feasibility and mesh resolution of LES for single-phase PTS are assessed earlier in a companion paper. The current investigation deals with the accuracy of LES approach with respect to the experiment. Experimental data from the Rossendorf Coolant Mixing (ROCOM) facility is used as a basis for validation. Three test cases with dierent ow rates are considered. They correspond to a buoyancy-driven, a momentum-driven, and a transitional coolant mixing pattern in the downcomer. Time- and frequency-domain analysis are employed for comparison of the numerical and experimental data.
    Keywords: PTS, CFD, Coolant Mixing, ROCOM

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    Permalink: https://www.hzdr.de/publications/Publ-14895
    Publ.-Id: 14895


    Doping Issues of Si Nanowires

    Skorupa, W.
    A review of recent work published in:
    ADVANCED MATERIALS Volume: 22 Issue: 36 Pages: 4020-4024,
    NANO LETTERS Volume: 10 Issue: 1 Pages: 171-175,
    Keywords: Doping, ion implantation, scanning spreading resistance profiling, silicon nanowire
    • Invited lecture (Conferences)
      27.Deutsches Nutzertreffen RTP und Heissprozesse, 05.05.2010, Erlangen, Deutschland

    Permalink: https://www.hzdr.de/publications/Publ-14894
    Publ.-Id: 14894


    Biaxial optical anisotropy of self aligned silver nanoparticles and nanowires

    Ranjan, M.; Facsko, S.; Möller, W.
    In the present study ion beam sputtering has been used for prestructuring of a silicon substrate followed deposition of metal by ebeam evaporation. First a low energy ion beam (Ar+, 500 eV) is incident on the substrate surface at an angle of 67∘ to the surface normal to produce well ordered (20-50 nm) ripple patterns. Then physically vaporized Ag atoms are deposited at grazing angle of 70∘ to the surface normal and normal to the ripples direction. Varying deposition parameters, i.e. ripple periodicity, substrate temperature and atomic flux, we were able to produce well ordered nanoparticles and nanowires. Self-aligned Ag nanoparticles and nanowires deposited on pre-patterned ripple surfaces exhibit strong optical anisotropy. Generalised ellipsometry measurements show that off diagonal Jones matrix elements (Ψ_ps, Δ_ps, Ψ_sp, Δ_sp) are non zero and vary with Eulers angle \phi. This indicates that such a medium is biaxial in nature. A biaxial layer model approach is used to calculate dielectric functions for such a system. Tauc-Lorentz oscillators are used along x and y direction independently and Drude model along z-direction for nanoparticles. This approach provides a very good fitting with the measured Jones matrix element Ψ_pp, Δ_pp, Ψ_ps, Δ_ps, Ψ_sp, Δ_sp. Different cases for ordered nanoparticles and wires will be presented.
    • Lecture (Conference)
      DPG Frühjahrstagung der Sektion Kondensierte Materie (SKM) 2010, 21.-26.03.2010, Regensburg, Germany

    Permalink: https://www.hzdr.de/publications/Publ-14892
    Publ.-Id: 14892


    Self-Organisation of metal nanoparticles and nanowires grown on ripple templates

    Ranjan, M.; Oates, T. W. H.; Facsko, S.
    Nobel metal nanoparticles exhibit distinct optical properties due to their localized surface plas-mon resonance. Potential applications of these structures can be found in solar cells, nonlinear optical devices, or sensors. Especially for nanoscale optics aligned equidistant chains of metal nanoparticles are favored.
    Ion beam sputtered surfaces featuring self-organized ripple patterns have proven to be excellent templates for the alignment of these metal nanoparticles [1]. In the continuous sputtering proc-ess, induced by the bombardment with low-energy ions (100 – 2000 eV), periodic surface pat-terns appear in form of ripples or arrays of hexagonally ordered mounds, which show a very high degree of regularity [2]. The dimension of the pattern is related to the size of the typical collision cascade of a single ion event and lies in the range of ten to tens of nanometers. The periodicity and regularity of the pattern is established by the effective filtering of a narrow band of spatial frequencies on the surface, which results from the interplay between a surface instability caused by the sputtering and surface diffusion processes. Regular ripple morphologies have been pro-duced in this way on very different materials including semiconductors, isolators, and metals, demonstrating the universality of the mechanism [3].
    Depending on deposition angle, substrate temperature, beam flux, and deposition time, the metal nanostructures align parallel to the ripples, eventually coalesce forming nanowires [4]. Due to the alignment the nanoparticles exhibit strongly anisotropic optical properties. The difference in the interparticle distance along the parallel and perpendicular direction, respectively, leads to different plasmonic coupling in the respective directions. Therefore a red shift of the plasmon-polariton resonance is observed for light polarized parallel to the ripple direction. In addition, the resonance shifts with the aspect ratio of the nanoparticles. Energy shifts of the plasmon reso-nance of 0.2 eV to 0.7 eV have been determined for aspect ratios in the range of 2 to 5.
    This work is partly supported by DFG FOR 845.
    REFERENCES
    1. T.W.H. Oates, A. Keller, S. Facsko , A. Mücklich , Plasmonics 2, 47 (2007).
    2. A. Keller, S. Rossbach, S. Facsko, et al., Nanotechnology 19, 135303 (2008).
    3. A. Keller, S. Facsko, and A. Moller, Jour. Phys. Cond. Matt. 21, 495305 (2009).
    4. T.W. H.Oates, A.Keller, S.Noda, S.Facsko , Appl. Phys. Lett. 93, 063106 (2008
    • Poster
      Nanofair 2010, 06.07.-07.11.2010, Dresden, Germany

    Permalink: https://www.hzdr.de/publications/Publ-14891
    Publ.-Id: 14891


    Self-Organisation of metal nanoparticles on ion beam produced ripple templates

    Ranjan, M.; Facsko, S.; Möller, W.
    Ion beam sputtering has been used for pre-structuring of the substrate. Low energy ion beam (Ar+, 500 eV) incident on the substrate surface (Si in our case) at an angle of 67o to the surface normal to produce well ordered (20-50 nm) ripple patterns [1, 2]. The periodicity and regularity of the pattern is estab-lished by the effective filtering of a narrow band of spatial frequencies on the surface, which results from the interplay between a surface instability caused by the sputtering and surface diffusion processes. Regular ripple morphologies have been produced in this way on very different materials including semiconductors, iso-lators, and metals, demonstrating the universality of the mechanism [2].
    Depending on deposition angle, substrate temperature, beam flux, and deposition time, the metal nanostruc-tures align parallel to the ripples, eventually coalesce forming nanowires [3,4].A very high degree of align-ment not reported so far using the present technique has been achieved. Due to the alignment the nanoparti-cles exhibit strongly anisotropic optical properties. The difference in the interparticle distance along the paral-lel and perpendicular direction, respectively, leads to different plasmonic coupling in the respective direc-tions. Therefore a red shift of the plasmon-polariton resonance is observed for light polarized parallel to the ripple direction. In addition, the resonance shifts with the aspect ratio of the nanoparticles. Energy shifts of the plasmon resonance of 0.2 eV to 0.7 eV have been determined for aspect ratios in the range of 2 to 5.
    References:
    [1]. Keller.A, Rossbach.S, Facsko.S, Nanotechnology 19(2008) 135303
    [2]. Keller.A, Facsko.S,Möller.W, Jour. Phys. Cond. Matt. 21(2009) 495305
    [3]. Oates.T.W.H, Keller.A, Facsko.S, A. Mücklich, Plasmonics 2(2007) 47
    [4]. Oates.T.W.H, Keller.A, Noda.S, Facsko.S, Appl. Phys. Lett. 93(2008) 063106
    • Poster
      Workshop Ion Beam Physics, 29.-31.03.2010, Dresden, Germany

    Permalink: https://www.hzdr.de/publications/Publ-14890
    Publ.-Id: 14890


    Self-assembled Ag nanoparticles on plasma sputtered hexagonally ordered GaSb nanodots

    Ranjan, M.; Fritzsche, M.; Zhou, J.; Facsko, S.; Möller, W.
    Low energy ion-irradiation is capable to produce self-organized ripple and dot pattern on surfaces [1, 2].Ion bombardment normal to surface generate hexagonally correlated dot pattern on semiconductor surfaces [2]. Metal film grown on such pre-patterned substrate may lead to highly ordered self-assembled nanoparticles or nanowires [3]. Ordered metal nanoparticles show unique optical properties [4, 5]. In this work negatively biased (-1.2 kV) GaSb substrate was immersed in an inductively coupled RF plasma. Plasma sheath formation around the sample maintained the normal ion incidence. Ion fluence equivalent to 1x1018 cm-2 is sufficient to produce well pronounced hexagonally ordered dot structures. Later oblique incidence PVD growth of silver on such substrate, produce self-assemble nanoparticles fallowing the dots periodicity. Reflection measurement shows a plasmonic splitting and results in two pronounce resonance peak. Such a splitting is arises due to hexagonal arrangement of nanoparticles, not appeared for non-ordered particles. More details study of this work will be presented.

    References:
    [1] A. Keller, S. Facsko, W. Möller, New J. Phys. 10 (2008) 063004
    [2] S.Facsko, T.Dekorsy, C. Koerdt, H. Kurz, A. Vogt, H. Hartnagel, Science 285 (1999)1551
    [3] T.W. H.Oates, A.Keller, S.Noda, S.Facsko, Appl. Phy. Lett., 93(2008) 063106.
    [4] T.W. H.Oates, A.Keller, S.Facsko, A.Mücklich, Plasmonics 2(2007) 47.
    [5] A. Taleb, V. Russier, A. Courty, M. P. Pileni, Phys.Rev.B 59 (1999) 13350
    • Poster
      Plasma Surface Engineering (PSE), 13.-17.09.2010, Garmisch-Partenkirchen, Deutschland

    Permalink: https://www.hzdr.de/publications/Publ-14889
    Publ.-Id: 14889


    Radioökologische Forschung als Basis zur Entwicklung neuer Materialien

    Raff, J.
    wird nachgereicht
    • Lecture (others)
      Besuch ehemaliger IRC-Mitarbeiter, 19.11.2010, Dresden, Deutschland

    Permalink: https://www.hzdr.de/publications/Publ-14888
    Publ.-Id: 14888


    Vortex coupling in magnetic multilayer elements

    Wintz, S.; Puzic, A.; Strache, T.; Bunce, C.; Körner, M.; Schönherr, T.; Neubert, A.; McCord, J.; Moench, I.; Mattheis, R.; Raabe, J.; Quitmann, C.; Erbe, A.; Fassbender, J.ORC
    Spin vortices have attracted much attention due to their chiral nature and the variety of dynamic phenomena associated with them. In this contribution we present experimental findings on vortex coupling in trilayer elements, where two ferromagnetic layers are separated by a nonmagnetic spacer. For such systems the relative configurations of the in-plane flux senses (circulations) as well as the core orientations (polarities) of layered vortices are identified by means of scanning transmission x-ray microscopy (STXM). The dominant coupling mechanisms here are the magneto-dipolar interaction and interlayer exchange coupling (IEC). Remarkably, a modification of the IEC, which can be induced by noble gas ion irradiation, allows to specifically set the circulation configuration of a layered vortex pair to be either an- tiferromagnetic or ferromagnetic. In addition, time-resolved measurements of the response of interlayer coupled vortices to an excitation by sinusoidal magnetic fields will be shown.
    Keywords: magnetic vortex, coupling, STXM, interlayer exchange coupling
    • Poster
      DPG Frühjahrstagung der Sektion AMOP (SAMOP) und der Sektion Kondensierte Materie (SKM), 13.-18.03.2011, Dresden, Deutschland

    Permalink: https://www.hzdr.de/publications/Publ-14887
    Publ.-Id: 14887


    Iodine in alluvial platinum–palladium nuggets

    Cabral, A. R.; Radtke, M.; Munnik, F.; Lehmann, B.; Reinholz, U.; Riesemeier, H.; Tupinambá, M.; Kwitko-Ribeiro, R.
    Synchrotron radiation-induced X-ray fluorescence (SR-XRF) spectrometry was applied to determine iodine concentrations in alluvial Pt–Pd aggregates with delicate morphological features from Córrego Bom Sucesso, Minas Gerais, Brazil. The millimetre-sized botryoidal and rod-shaped grains of alluvial Pt–Pd–Hg intermetallic compounds have surprisingly high concentrations of iodine, in the range from 10 to ~120 µg/g. Because iodine is a strongly biophile element, known to be enriched in peatlands and plant remains in soils by microbial activity, its concentration in the Pt–Pd nuggets suggests biogenic precious-metal fixation in the aqueous alluvial milieu.
    Keywords: Iodine, Pt–Pd nuggets, Córrego Bom Sucesso, Minas Gerais, Brazil

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    Permalink: https://www.hzdr.de/publications/Publ-14886
    Publ.-Id: 14886


    Magnetically induced electric polarization in an organometallic magnet

    Zapf, V. S.; Kenzelmann, M.; Wolff-Fabris, F.; Balakirev, F.; Chen, Y.
    The coupling between magnetic order and ferroelectricity has been under intense investigation in a wide range of transition-metal oxides. The most direct coupling is obtained in so-called magnetically induced multiferroics where ferroelectricity arises directly from magnetic order that breaks spatial inversion symmetry. However, it has been difficult to find nonoxide-based materials in which these effects occur. Here we present a study of copper dimethyl sulfoxide dichloride (CDC), an organometallic quantum magnet containing S = 1/2 Cu spins, in which electric polarization arises from noncollinear magnetic order. We show that the electric polarization can be switched in a stunning hysteretic fashion. Because the magnetic order in CDC is mediated by large organic molecules, our study shows that magnetoelectric interactions can exist in this important class of materials, opening the road to designing magnetoelectrics and multiferroics using large molecules as building blocks. Further, we demonstrate that CDC undergoes a magnetoelectric quantum phase transition where both ferroelectric and magnetic order emerge simultaneously as a function of magnetic field at very low temperatures

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    Publ.-Id: 14885


    Breaking Translational Invariance by Population Imbalance: The Fulde-Ferrell-Larkin-Ovchinnikov States

    Zwicknagl, G.; Wosnitza, J.
    An overview is given of our present understanding of superconductivity with spontaneously broken translation symmetry in polarized Fermi systems. The existence of “crystalline” superconducting phases is considered in a wide range of systems, prominent examples being conduction electrons in metals, ultra-cold atoms in a trap, nuclear matter and dense quark systems. The underlying physics is delineated and theoretical approaches to the inhomogeneous phases and their properties are discussed. From the experimental side, it is argued that superconductivity with imbalance-induced order parameters is realized in layered organic compounds and potentially in heavy-fermion systems.

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    Publ.-Id: 14884


    On-chip superconductivity via gallium overdoping of silicon

    Skrotzki, R.; Fiedler, J.; Herrmannsdörfer, T.; Heera, V.; Voelskow, M.; Mücklich, A.; Schmidt, B.; Skorupa, W.; Gobsch, G.; Helm, M.; Wosnitza, J.
    We report on superconducting properties of gallium-enriched silicon layers in commercial (100) oriented silicon wafers. Ion implantation and subsequent rapid thermal annealing have been applied for realizing gallium precipitation beneath a silicon-dioxide cover layer. Depending on the preparation parameters, we observe a sharp drop to zero resistance at 7 K. The critical-field anisotropy proofs the thin-film character of superconductivity. In addition, out-of-plane critical fields of above 9 T and critical current densities exceeding 2 kA/cm2 promote these structures to be possible playgrounds for future microelectronic technology

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    Permalink: https://www.hzdr.de/publications/Publ-14883
    Publ.-Id: 14883


    Investigation of conducting nanostructures on ta-C films made by FIB lithography

    Philipp, P.; Bischoff, L.
    Tetrahedral amorphous carbon (ta-C) films with high sp3 content produced by mass filtered vacuum arc deposition were modified by Ga+ FIB irradiation. Surface swelling occurs as a function of fluence, caused by ion induced conversion of sp3 to sp2 hybridized carbon atoms. A model [1] for diamond swelling was applied to ta-C films to estimate the swelling for fluences up to 1 x 1016 cm-2. For higher fluences data from TRIDYN simulations were included due to sputtering in a good agreement with the experiments. Van der Pauw structures were produced by means of Ga+ FIB lithography. A decrease of the sheet resistance with increasing fluence due to the evolution of graphitic regions was observed. The lowest value of 290 Ohm/sq was achieved at 1.6 x 1017 cm-2. Additionally, conducting graphitic wires were produced (length: 10 µm, width: 300 nm to 5 µm). The wire resistivity was measured within 130 kOhm (5 µm width) and 3 GOhm (300 nm width). Ion induced graphitization of ta-C films by FIB offers prospective applications in nano technology to fabricate conductive nanostructures in an insulating thin film.
    [1] F. Bosia et al. Nucl. Instrum. Meth. B 268 (2010) 2991.
    Keywords: tetrahedral amorphous carbon, ta-C, FIB lithography, graphitization, nano structures
    • Poster
      75. Jahrestagung der DPG und DPG Frühjahrstagung, 13.-18.03.2011, Dresden, Deutschland

    Permalink: https://www.hzdr.de/publications/Publ-14882
    Publ.-Id: 14882


    Freestanding Si nanowires fabricated by Ga+ FIB implantation and subsequent anisotropic etching

    Böttger, R.; Bischoff, L.; Schmidt, B.; Krause, M.
    Localized Ga+ ion implantation in silicon-on-insulator substrates (top layer 2 µm) by focused ion beam and subsequent anisotropic and selective wet etching has been used to fabricate freely suspended nanowires with reproducible widths between 20 and 200 nm.
    The dependence of the resulting nanowire width on the implanted fluence has been investigated and is supported by a numerical model reproducing the experimental data and enabling an a priori estimation of the nanowire width as a function of the implanted fluence. Moreover, the temperature dependence of the nanowires’ resistivity and the activation energy for electrical current flow were investigated before and after direct current annealing in air and in vacuum ambient. Annealed nanowires showed a decrease of their resistivity up to two orders of magnitude, indicating a partial recrystallization of the nanowires through self-heating and a change in the conduction mechanism. The assumption of recrystallization is supported by scanning electron microscopy and Raman spectroscopy.
    The comprehension of the pinpointed fabrication of such Si nanostructures establishes a broad range of application in the field of nano-electro-mechanical systems.
    Keywords: silicon-on-insulator, Ga focused ion beam implantation, nanowire, anisotropic etching, width, resistivity, phase change, annealing, Raman spectroscopy
    • Poster
      DPG Frühjahrstagung der Sektion AMOP (SAMOP) und der Sektion Kondensierte Materie (SKM), 13.-18.03.2011, Dresden, Deutschland

    Permalink: https://www.hzdr.de/publications/Publ-14881
    Publ.-Id: 14881


    Complex formation of trivalent americium with salicylic acid at very low concentrations

    Müller, M.; Acker, M.; Taut, S.; Bernhard, G.
    For the first time, the complexation of americium(III) with salicylic acid was studied at trace metal concentrations using a 2.0 m Long Path Flow Cell for UV–vis spectroscopy. The detection limit of Am(III) in aqueous solution at pH 3.0 was found to be 5 9 10-9 M. Two Am(III)-salicylate complexes were formed at pH 5.0 in 0.1 M NaClO4, indicated by a clear red shift of the absorption maximum. The absorption spectra obtained from spectrophotometric titration were analyzed by means of factor analysis and complex stabilities were calculated to be log b110 = 2.56 ± 0.08 and log b120 = 3.93 ± 0.19.
    Keywords: Americium, Long path flow cell, UV–vis, Detection limit, Complexation, Salicylic acid

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    Permalink: https://www.hzdr.de/publications/Publ-14880
    Publ.-Id: 14880


    Development of a high resolution and high dispersion Thomson Parabola

    Jung, D.; Hoerlein, R.; Kiefer, D.; Letzring, S.; Gautier, D. C.; Schramm, U.; Huebsch, C.; Oehm, R.; Albright, B. J.; Fernandez, J. C.; Habs, D.; Hegelich, B. M.
    Here we report on the development of a novel high resolution and high dispersion Thomson Parabola for simultaneously resolving protons and low-Z ions of more than 100 MeV/nucleon necessary to explore novel laser-ion-acceleration schemes. High electric and magnetic ¯elds enable energy resolutions of ¢E=E < 5% at 100 MeV/nucleon and impede premature merging of di®erent ion species at low energies on the detector plane. First results from laser driven ion acceleration experiments performed at the Trident Laser facility demonstrate high resolution and superior species and charge state separation of this novel Thomson parabola for ion energies of more than 30 MeV/nucleon.
    Keywords: laser ion acceleration, ino spectrometer

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    Permalink: https://www.hzdr.de/publications/Publ-14879
    Publ.-Id: 14879


    Sicherheitstechnische Fragestellungen im Reaktorbetrieb am Beispiel eines DWR

    Schäfer, F.; Tusheva, P.; Weiss, F.-P.
    Der Vortrag erläutert grundlegende Prinzipien der nuklearen Sicherheit, gibt einen Überblick zu Betriebstransienten und hypothetischen Störfällen in einem DWR und diskutiert die verschiedenen Methoden, welche für Untersuchungen zur Reaktorsicherheit angewendet werden.
    Keywords: Nuclear Reactor, Reactor Safety
    • Invited lecture (Conferences)
      3. VDI-KTG Kolloquium "Perspektiven der Kernenergie", 26.10.2010, Dresden, Deutschland

    Permalink: https://www.hzdr.de/publications/Publ-14878
    Publ.-Id: 14878


    Spatial manipulation of magnetic damping in ferromagnetic-antiferromagnetic films by ion irradiation

    McCord, J.; Strache, T.; Mönch, I.; Mattheis, R.; Fassbender, J.ORC
    The effective magnetic damping parameter in ferromagnetic-antiferromagnetic-ferromagnetic NiFe/IrMn/NiFe try-layer structures is set over a wide range. Ultra-thin antiferromagnetic systems in combination with low fluence Ni-ion irradiation are used to control the magnetic damping parameter by two independent mechanisms. Changing the ferromagnetic-antiferromagnetic interface the initially strongly increased damping parameter is reduced. Applying the method locally, results in a magnetic layer with spatially distributed regions of different damping. The overall relaxation time of the mixed property film is found to be a direct superposition of the individual relaxation time contributions and thus determined by the ratio of phases with individual damping parameter.

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    Permalink: https://www.hzdr.de/publications/Publ-14877
    Publ.-Id: 14877


    Realization of radiobiological in vitro cell experiments at conventional X-ray tubes and unconventional radiation sources

    Beyreuther, E.
    More than hundred years after the discovery of X-rays different kinds of ionizing radiation are ubiquitous in medicine, applied to clinical diagnostics and cancer treatment as well. Irrespective of their nature, the widespread application of radiation implies its precise dosimetric characterization and detailed knowledge of the radiobiological effects induced in cancerous and normal tissue. Starting with in vitro cell irradiation experiments, which define basic parameters for the subsequent tissue and animal studies, the whole multi-stage process is completed by clinical trials that translate the results of fundamental research into clinical application. In this context, the present dissertation focuses on the establishment of radiobiological in vitro cell experiments at unconventional, but clinical relevant radiation qualities.
    In the first part of the present work the energy dependent biological effectiveness of photons was studied examining low-energy X-rays (≤ 50 keV), as used for mammography, and high-energy photons (≥ 20 MeV) as proposed for future radiotherapy. Cell irradiation experiments have been performed at conventional X-ray tubes providing low-energy photons and 200 kV reference radiation as well. In parallel, unconventional quasi-monochromatic channeling X-rays and high-energy bremsstrahlung available at the radiation source ELBE of the Forschungszentrum Dresden-Rossendorf were considered for radiobiological experimentation. For their precise dosimetric characterization dosimeters based on the thermally stimulated emission of exoelectrons and on radiochromic films were evaluated, whereas just the latter was found to be suitable for the determination of absolute doses and spatial dose distributions at cell position. Standard ionization chambers were deployed for the online control of cell irradiation experiments. Radiobiological effects were analyzed in human mammary epithelial cells on different subcellular levels revealing an increasing amount of damage for decreasing photon energy. For this reason, the assumed photon energy dependence was reconfirmed for a cell line other than human lymphocytes, an important finding that was discussed on the 2007 Retreat of the German Commission on Radiological Protection.
    After successful finalization of the photon experiments the focus of the present dissertation was directed to the realization of in vitro cell irradiation experiments with laser-accelerated electrons. This research was carried out in the frame of the project onCOOPtics that aims on the development of laser-based particle accelerators, which promise accelerators of potentially compact size and more cost-effectiveness suitable for a widespread medical application, especially for high precision hadron therapy. The unique properties, i.e., the ultrashort bunch length and resultant ultrahigh pulse dose rate, of these unconventional particle accelerators demand for extensive investigations with respect to potential effects on the dosimetric and radiobiological characterization. Based on the experiences gained at ELBE first experiments on the radiobiological characterization of laser-accelerated electrons have been performed at the Jena Titanium:Sapphire laser system. After beam optimization, a sophisticated dosimetry system was established that allow for the online control of the beam parameters and for the controlled delivery of dose to the cell sample. Finally, worldwide first systematic in vitro cell irradiation experiments were carried out resulting in a reduced biological effectiveness for laser-accelerated electrons relative to the 200 kV X-ray reference, irrespectively on the biological effect and cell lines examined. These successful results are the basis for future in vivo studies and experiments with laser-accelerated protons.
    Keywords: X-ray tubes, radiation sources
    • Open Access Logo Wissenschaftlich-Technische Berichte / Forschungszentrum Dresden-Rossendorf; FZD-540 2010

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    Permalink: https://www.hzdr.de/publications/Publ-14876
    Publ.-Id: 14876


    Time resolved spectroscopy on quantum dots and graphene at the FELBE free-electron laser

    Winnerl, S.; Stehr, D.; Wagner, M.; Schneider, H.; Helm, M.; Seidel, W.; Michel, P.; Zibik, E. A.; Carpenter, B. A.; Porter, N. E.; Skolnick, M. S.; Wilson, L. R.; Grange, T.; Ferreira, R.; Bastard, G.; Orlita, M.; Plochocka, P.; Kossacki, P.; Potemski, M.; Sprinkle, M.; Berger, C.; de Heer, W. A.
    The free-electron laser FELBE at the Forschungszentrum Dresden-Rossendorf enables experiments with spectral, temporal, and, by means of near-field microscopy, also high spatial resolution. FELBE delivers picosecond IR and THz pulses in a wavelength range from 5 µm to 280 µm. Operation in a continous pulsing regime and synchronization to various tabletop laser sources allows for two-color pump-probe experiments. Here we review the potential of the laser and focus on two highlight pump-probe experiments. In the first experiments, the relaxation dynamics in self assembled InGaAs quantum dots at energies below the Reststrahlen band is studied. Long intradot relaxation times (1.5 ns) are found for level separations of 14 meV (3.4 THz), decreasing very strongly to 2 ps at 30 meV (7 THz). The results are in very good agreement with our microscopic theory of the carrier relaxation process, taking into account polaron decay via acoustic phonons [1]. In the second experiment, the relaxation dynamics in graphene is investigated at photon energies E = 20 – 250 meV. For excitations below the phonon energy of the G-mode, long relaxation times (20 – 40 ps) are observed. While the pump-induced transmission is positive for E > 30 meV, pump-induced absorption occurred for E < 20 meV. The increased transmission for E > 30 meV is caused by bleaching of the interband transition. We attribute the induced absorption to heating of carriers by intraband free-carrier absorption for E < 2E_F (E_F: Fermi energy).

    [1] E. A. Zibik et al. Nature Materials 8, 803 - 807 (2009).
    Keywords: Quantum dots, graphene, relaxation dynamics, polarons, terahertz, infrared, pump-probe spectroscopy
    • Invited lecture (Conferences)
      SPIE Photonics West, 22.-27.01.2011, San Francisco, USA
    • Proceedings of SPIE 7937(2011), 793708
      DOI: 10.1117/12.873702

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    Publ.-Id: 14875


    Relaxation dynamics in epitaxial graphene probed at low excitation energies

    Winnerl, S.; Orlita, M.; Plochocka, P.; Schneider, H.; Helm, M.; Kossacki, P.; Potemski, M.; Sprinkle, M.; Berger, C.; de Heer, W. A.
    The relaxation dynamics of graphene has been investigated in various degenerate as well as two-color pump-probe studies at excitation energies E = 1.6 eV [1-5]. We report on degenerate pump-probe spectroscopy at much lower energies (E = 20 – 250 meV; radiation source: free-electron laser) on graphene multilayers grown by thermal decomposition. Relaxation times between 20 and 40 ps are found for photon energies E < 70 meV, where only acoustic phonons can contribute to the relaxation dynamics. At 245 meV a much faster relaxation with two time constants (tau_1 ≈ 1.2 ps, tau_2 = 4 – 8 ps) is observed and attributed to contributions of optical phonons. While the pump-induced transmission is positive for E > 30 meV, pump-induced absorption occurred for E < 20 meV (Fig. 1). The increased transmission for E > 30 meV is caused by bleaching of the interband transition. We attribute the induced absorption to heating of carriers by intraband free-carrier absorption for E < 2E_F (E_F: Fermi energy).
    [1] J.M. Dawlaty et al., Appl. Phys. Lett. 92, 042116 (2008).
    [2] D. Song et al., Phys. Rev. Lett. 101, 157402 (2008).
    [3] P.A. George et al., Nano Lett. 8 ,4248 (2008).
    [4] H. Wang et al., Appl. Phys. Lett., 96, 081917 (2010).
    [5] D. Sun et al., Phys. Rev. Lett. 104, 136802 (2010).
    Keywords: Relaxation dynamics, graphene, infrared, terahertz
    • Poster
      2nd International Symposium on the Science and Technology of Epitaxial Graphene, 14.-17.09.2010, Amelia Island, USA

    Permalink: https://www.hzdr.de/publications/Publ-14874
    Publ.-Id: 14874


    Compositional depth profiling of TaCN thin films

    Adelmann, C.; Conard, T.; Franquet, A.; Brijs, B.; Munnik, F.; Burgess, S.; Witters, T.; Meersschaut, J.; Kittl, J. A.; Vandervorst, W.
    The composition profiling of thin TaCN films was studied. For the composition profile determination using x-ray photoemission spectrometry (XPS) in combination with Ar sputtering, preferential sputtering effects of N with respect to Ta and C were found to lead to inaccurate elemental concentrations. Sputter yield calculations for the given experimental conditions allowed for the correction of a part of the error, leading to fair accuracy by reference-free measurements. Further improvement of the accuracy was demonstrated by the calibration of the XPS compositions against elastic recoil detection analysis (ERDA) results. For Auger electron spectrometry (AES) in combination with Ar sputtering, accurate results required the calibration against ERDA. Both XPS and AES allowed for a reliable and accurate determination of the compositional profiles of TaCN-based thin films after calibration. Time-of-flight secondary-ion mass spectrometry was also used to assess the composition of the TaCN films. However, the analysis was hampered by large matrix effects due to small unintentional oxygen contents in the films. Energy-dispersive x-ray spectrometry is also discussed, and it is shown that an accurate reference-free measurement of the average film concentration can be achieved.
    Keywords: TaC; TaN; TaCN; XPS; AES; ToF-SIMS; ERDA; EDX; composition profile

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    Publ.-Id: 14873


    Speciation of Uranium in Seepage and Pore Waters of Heavy Metal-Contaminated Soil

    Baumann, N.; Arnold, T.; Lonschinski, M.
    The uranium speciation in natural occurring seepage water samples, and in soil water samples, all samples from test site “Gessenwiese”, were analyzed by Time-resolved Laser-induced Fluorescence Spectroscopy (TRLFS). Test site Gessenwiese was installed as a part of a research program of the Friedrich Schiller University Jena for investigations within the area of a recultivated former uranium mining heap close to Ronneburg (Eastern Thuringia).
    Those investigations revealed that the uranium speciation in that seepage water is dominated by the uranium (VI) sulfate species UO2SO4(aq). The analyses were performed to compare presented results in a later stage with the uranium speciation in plants, which grow on the grassland test site Gessenwiese. It was showed that TRFLS is a useful tool for clearing up the speciation of uranium in water, which is affiliated by plants.
    • Book chapter
      Kothe, Erika; Varma, Ajit: Bio-Geo Interactions in Metal-Contaminated Soils, Berlin: Springer, 2012, 978-3-642-23326-5, 131-142

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    Permalink: https://www.hzdr.de/publications/Publ-14872
    Publ.-Id: 14872


    Reversals and the turbulent alpha-effect in kinematic simulations of natural and experimental dynamos

    Giesecke, A.; Stefani, F.; Gerbeth, G.
    From paleomagnetic observations, numerical simulations and -- meanwhile -- also experiments, it is evident that reversing dynamos are a quite common phenomenon. An easy access to the examination of reversing dynamos is provided by simplifying mean field simulations where the induction effects of helical small scale turbulence are parametrized by the so called α-effect.

    In a geodynamo-like α2-model reversing solutions are obtained only for a highly restricted class of radial α-profiles which are characterized by a proximity of oscillating and non-oscillating state. The required properties of the α-effect, indeed, have been found from local simulations of rotating magnetoconvection in a Cartesian box (Giesecke et al. 2005, PEPI 152, 90-102). Essential properties of the field reversals can be assigned to the behavior of so called exceptional points in the spectrum of the dynamo-operator where two different non-oscillatory field eigenmodes merge and continue as one oscillatory eigenmode (Stefani et al. 2005, PRL, 94, 184506). The connection between oscillating solutions and irregular occurring reversals arises from fluctuations of the α-effect, which causes a sporadic switching from steady to the oscillatory regime and vice versa. In this picture a reversal is an inevitable consequence of the behavior of the instantanous growthrate in conjuction with fluctuations of the driving source.

    Recent results of the French von-Kármán-Sodium (VKS) dynamo offer a possibility for detailed investigations of reversing magnetic fields. In the VKS experiment a turbulent flow of liquid sodium is driven by two counter rotating soft iron impellers located close to the endplates of a cylindrical vessel. The geometric structure of the observed magnetic field is dominated by an axisymmetric dipole that exhibits regular and irregular reversals if the impellers rotate with different frequencies. Recent simulations show that the induction process is essentially determined by the material properties of the flow driving impellers (high permeability) because of internal boundary conditions for the magnetic field on the interface between fluid and impeller (Giesecke et al. 2010, PRL 104, 044503). However, only the combined interaction of soft iron disks and a comparatively small α-effect allows to explain the dominating axisymmetric field. Contributions of dipole and quadrupole type fields deduced from the equatorial symmetry show nearly the same growth rate supporting the reversal model presented by Pétrélis & Fauve (2009, PRL 102, 144503) that is based on the coupling between these two modes.
    Keywords: Dynamo Geodynamo alpha-effect Simulations
    • Poster
      AGU Fall Meeting 2010, 13.-17.12.2010, San Francisco, USA
    • Contribution to proceedings
      AGU Fall Meeting 2010, 13.-17.12.2010, San Francisco, USA
      Reversals and the turbulent α-effect in simulations of natural and experimental dynamos

    Permalink: https://www.hzdr.de/publications/Publ-14871
    Publ.-Id: 14871


    High permeability material and dynamo action

    Giesecke, A.; Stefani, F.; Gerbeth, G.
    A prescribed flow of liquid sodium provides an energy source for self-generation of a magnetic field. The influences of non-uniform material properties on the dynamo process are examined by means of kinematic simulations of the electromagnetic induction equation.

    High permeability material even if localized in a small volume like the flow driving impellers in the French VKS dynamo experiment, essentially determines the field generation process (decrease of the effective critical magnetic Reynolds number and enforcement of internal boundary conditions on material interfaces). Permeability caused facilitation of dynamo action might be important as well for the helical flow in cooling circuits of fast breeders. Preliminary simulations for a model flow in and around soft-iron sub-assemblies (that comprise the nuclear fuel pins) show a reduction of the critical magnetic Reynolds number for the onset of dynamo action by a factor of 2.
    Keywords: Dynamo Permeability
    • Poster
      MHDDAYS 2010, 22.-23.11.2010, Dresden, Germany

    Permalink: https://www.hzdr.de/publications/Publ-14870
    Publ.-Id: 14870


    Multiple active mirror concept for high energy short-pulse lasers

    Loeser, M.; Kroll, F.; Röser, F.; Siebold, M.; Schramm, U.; Sauerbrey, R.
    Ytterbium-doped gain media are preferably utilized in high-energy, diode-pumped lasers due to their comparably long fluorescence lifetime, absence of excited state absorption, and quenching effects. Despite exhibiting a low quantum defect, thermal lensing and stress birefringence within the amplifying medium limits the maximum repetition rate of large aperture lasers. Furthermore, the quasi-three-level scheme of Yb3+ leads to re-absorption losses at room temperature especially when operating at low fluences. Here, we present a novel approach combining longitudinal cooling of a disk-laser design with the energy storage capability of a rod amplifier. Therefore, a multiple active mirror amplifier is presented for improved optical-to-optical conversion efficiency and reduced thermally induced aberrations at high repetition rates. Multi-passing both pump and extraction beams through the gain medium, which is well known from thin-disk lasers, also reduces the re-absorption losses. However, energy scaling of a single thin-disk design is limited by parasitic lasing due to a high aspect ratio between longitudinal and transverse gain. We also introduce simulation results on a multiple active mirror short-pulse amplifier employing various Ytterbium-doped gain media such as Yb:YAG, Yb:CaF2, Yb:glass, and Yb:silica. Furthermore, time resolved measurements of thermally induced aberrations at pulse-pumped operation are illustrated.
    Keywords: Diode-pumped lasers, Ytterbium-doped solid state lasers
    • Lecture (Conference)
      DPG Frühjahrstagung der Sektion AMOP 2010, 08.-12.03.2010, Hannover, Deutschland

    Permalink: https://www.hzdr.de/publications/Publ-14869
    Publ.-Id: 14869


    Ion-beam induced hydrogen redistribution in a-Si:H-based triple layer structures

    Pantchev, B.; Danesh, P.; Schmidt, B.; Grambole, D.; Bischoff, L.
    Ion-beam induced hydrogen migration has been studied in triple layer structures, a-Si/a-Si:H/a-Si and SiO2/a-Si:H/SiO2. Nuclear reaction analysis has been used for simultaneous irradiation with MeV ions and measurement of hydrogen distribution in the structures. It has been established that there is no hydrogen loss from SiO2/a-Si:H/SiO2 structures, but an asymmetric redistribution due to hydrogen penetration into the bottom SiO2 layer. Hydrogen loss has been observed from the a-Si/a-Si:H/a-Si structures. The inspection of the surface of these samples by means of atomic force microscope has shown that it proceeds by bubble formation and blistering at the inner interface. The observed ion-beam induced selective penetration of hydrogen into the underlying material can be used as a tool for preparation of microcavity and microchannel arrays.
    Keywords: a-Si:H, ion implantation, hydrogen migration
    • Lecture (Conference)
      16 th International School on Condensed Matter Physics “Progress in Solid State and Molecular Electronics, Ionics and Photonics”, 29.08.-03.09.2010, Varna, Bulgaria
    • Open Access Logo Journal of Physics: Conference Series 253(2010), 012055
      DOI: 10.1088/1742-6596/253/1/012055

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    Permalink: https://www.hzdr.de/publications/Publ-14868
    Publ.-Id: 14868


    Nanoindentation-induced pile-up in hydrogenated amorphous silicon

    Pantchev, B.; Danesh, P.; Wiezorek, J.; Schmidt, B.
    Nanoindentation-induced material extrusion around the nanoindent (pile-up) leads to an overestimation of elastic modulus, E, and nanohardness, H, when the test results are evaluated using the Oliver and Pharr method. Factors affecting the pile-up during testing are residual stresses in film and ratio of film and substrate mechanical properties. Nanoindentation of hydrogenated amorphous silicon (a-Si:H) films has been carried out with the aim to study the effect of residual compressive stress on the pile-up in this material. To distinguish the contribution of compressive stress to the appearance of pile-up ion implantation has been used as a tool, which reduces the compressive stress in a-Si:H. Scanning probe microscope has been used for the imaging of the indent and evaluation of the pile-up. The values of E and H have been obtained from the experimental load-displacement curves using depth profiling with Berkovich tip, which has created negligible pile-up. A sharper cube corner tip has been used to study the pile-up. It has been established that pile-up is determined by the material plasticity, when the compressive stress is below 200 MPa. The contribution of mechanical stress to the pile-up is essential for the stress as high, as about 500 MPa.
    Keywords: Nanoindentation, silicon hardness, ion implantation
    • Lecture (Conference)
      16 th International School on Condensed Matter Physics “Progress in Solid State and Molecular Electronics, Ionics and Photonics”, 29.08.-03.09.2010, Varna, Bulgaria
    • Open Access Logo Journal of Physics: Conference Series 253(2010), 012054
      DOI: 10.1088/1742-6596/253/1/012054

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    Permalink: https://www.hzdr.de/publications/Publ-14867
    Publ.-Id: 14867


    Effect of hydrogen on hardness of amorphous silicon

    Danesh, P.; Pantchev, B.; Wiezorek, J.; Schmidt, B.; Grambole, D.
    A comparative study of hardness of thin films of hydrogenated amorphous silicon (a-Si:H) and hydrogen-free amorphous silicon (a-Si) was carried out to reveal the role of hydrogen in the plastic properties of amorphous silicon. In addition, the effect of hydrogen on hardness was established by changing hydrogen concentration in the material using post-deposition processing of the samples. The hydrogen concentration in a-Si:H was decreased by thermal annealing. In a-Si hydrogen was introduced by plasma hydrogenation. The values of hardness of the as-prepared a-Si and a-Si:H films were determined by nanoindentation using depth profiling. Low-depth indentation was applied to evaluate the effect of post-hydrogenation. The results obtained show that the presence of hydrogen in the amorphous silicon network leads to the increase in hardness. The conducted experiments demonstrate that plasma hydrogenation can be used as an effective tool to increase the hardness of amorphous silicon. Hardness of a-Si:H of about 12.3–12.7 GPa is as high as of crystalline silicon, suggesting a-Si:H can be a substitute for crystalline silicon in some MEMS.
    Keywords: Hydrogenated amorphous silicon, Ion implantation, Elastic modulus, Hardness

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    Permalink: https://www.hzdr.de/publications/Publ-14866
    Publ.-Id: 14866


    Effect of keV ion irradiation on mechanical properties of hydrogenated amorphous silicon

    Danesh, P.; Pantchev, B.; Wiezorek, J.; Schmidt, B.
    The susceptibility of mechanical properties of hydrogenated amorphous silicon (a-Si:H) to the implantation-enhanced disorder has been studied with the aim to extend the application field of this material in the technology of micro-electromechanical systems. Effect of keV ion irradiation on the elastic modulus, E, of hardness, H, and of root-mean-squared roughness to silicon ion implantation has been determined. The mechanical properties were evaluated by nanoindentation testing. E of 119 GPa and H of 12.3 GPa were determined for the as-prepared a-Si:H film. The implantation of silicon ions leads to a decrease in E and H, evaluated for a series of the implantation fluences in the range of 1.0x1013–5.0x1016 cm-2. Surface smoothing has been observed at high fluences and low ion energy of 18 keV, suggesting that ion beam may be used as a tool to reduce the roughness of the a-Si:H surface, while keeping intact the mechanical properties inside the film. The conducted experiments show that it is possible to prepare a-Si:H films with hardness and smoothness comparable to crystalline silicon.
    Keywords: Hydrogenated amorphous silicon, Ion implantation, Elastic modulus, Hardness

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    Permalink: https://www.hzdr.de/publications/Publ-14865
    Publ.-Id: 14865


    Magnetic hybrid films - magnetic property patterning by ion irradiation

    McCord, J.; Hamann, C.; Strache, T.; Martin, N.; Mönch, I.; Mattheis, R.; Kaltofen, R.; Quandt, E.; Fassbender, J.ORC
    Ion irradiation and implantation allows for a focussed materials modification in the range of a few nanometer. Effects of periodic patterning of the physical properties circumventing topographic patterning in the conventional sense are exploited. Magnetic materials with mixed hybrid magnetic properties are created. An overview over ongoing activities at the FZD will be given.
    • Invited lecture (Conferences)
      „Struktur und Eigenschaften kondensierter Materie“ Seminar der TU Chemnitz, 23.11.2010, TU Chemnitz, Germany

    Permalink: https://www.hzdr.de/publications/Publ-14864
    Publ.-Id: 14864


    Electrical characterization of oxygen vacancies in oxides by means of space charge spectroscopy

    Schmidt, H.
    The development of new materials for cool devices, e.g. memristive and spintronics devices, needs non-destructive techniques to characterize defects in new materials. The knowledge on defects is strongly desired and will help to prevent device degredation. The non-destructive characterization of certain defects is possible by means of positron annihilation spectroscopy (PAS) if open volume-defects are large and electrically neutral/negatively charged, if segregations are attractive for positrons and change the annihilation rate, and/or if the electron density and with that annihilation rate changes during phase transitions. The complementary, destructive characterization of defects in semiconductors prepared as diodes by means of space charge spectroscopy is possible if the defects are charged/decharged in response to electrical pulses applied to the diode.
    Keywords: defects, space charge spectroscopy, positron annihilation spectroscopy
    • Lecture (Conference)
      Workshop on Positron Annihilation Spectroscopy, 19.10.2010, FZD, Germany

    Permalink: https://www.hzdr.de/publications/Publ-14862
    Publ.-Id: 14862


    Electrical characterization of semiconductors on the mm-nm length scale

    Schmidt, H.
    The electrical conductivity of semiconductors is controlled by the activated dopant level and the intrinsic carrier concentration. Semiconductor devices are prepared with either holes or electrons as the majority charge carriers. Hall effect measurements yield carrier concentration and mobility and estimates of scattering mechanisms. The use of Hall effect measurements and of capacitance-voltage and deep level transient spectroscopy measurements for profiling depth dependent free carrier concentrations and for identifying deep traps within the forbidden gap of semiconductors, respectively, yields a potent suite of characterization techniques on the mm-mum length scale. Insight into the electrical properties of doped semiconductor nanostructures may be obtained from scanning spreading resistance microscopy and Kelvin probe force microscopy measurement. Dielectric semiconductor conductivities on the nm scale may be obtained from scanning probe microscopy measuremens. Examples of current investigations by means of the presented electrical characterization techniques are given.
    Keywords: space charge spectroscopy, electrical nanometrology
    • Invited lecture (Conferences)
      IZFP-Kolloquium, 25.10.2010, Saarbrücken, Germany

    Permalink: https://www.hzdr.de/publications/Publ-14861
    Publ.-Id: 14861


    Temperature Measurement in Rapid Thermal Annealing

    Reichel, D.; Skorupa, W.; Lerch, W.; Gelpey, J.
    Microelectronics Industry and consequently semiconductor research have developed into pillars of modern technology. Industrial demands for short process times at low cost are steadily increasing. Considerable attention is thereby drawn to ultra-short annealing cycles on the order of just a few milliseconds.
    One major application for thermal annealers is to anneal damage caused by ion implantation. For this purpose temperatures above 600 °C are preferred, although a high diffusion rate of the dopants ought to be avoided. Therefore, short heating periods with steep ramp rates are desired.
    This is where Flash Lamp Annealing comes into play. It allows for directed thermal treatment of surfaces within just a few milliseconds without or with drastically reduced thermal stress of the bulk material. Due to the selected wavelength range in the visible and near infrared region the lightpulse is absorbed by the near-surface layers and diffusion into the bulk is limited by the ultra-short time span. Thereby temperatures up to 2000°C are achieved dependent on the energy of the lightpulse and the optical properties of the sample. Cooling takes place by heat conduction into the bulk.
    The applications are numerous, especially in thermal treatment of semiconductor surfaces where doping concentrations far beyond the solubility limit are desired, e.g. for ultra shallow implantation profiles. Similarily, highly doped layers are required when studying small scale effects like superconductivity brought about by the implanted dopant.
    Due to the high energy density on the sample even high melting points can be achieved for defect annealing during recrystallization of the melt.
    The response of various materials to subsecond thermal treatment, however, is not well understood for most cases, especially the temperature dependence of many material parameters is unknown to a large extent. Clearly, for deeper investigation into the subject a real-time temperature measurement with a high temperature resolution (ΔT << 5K), is crucial and is regarded as a key component in order to achieve rapid and reliable processing.
    For this purpose traditional means of temperature measurement, e.g. thermocouples, must be excluded. Not only do they lead to wafer contamination but their long response time contradicts the ultra-fast annealing time of the Flash Lamp Device.
    In the framework of the presentation previous non-contact approaches to rapid temperature measurement will be discussed with special regard to temperature resolution and industrial mass production.
    Keywords: Temperature Measurement, Rapid Thermal Annealing, Flash Lamp Annealing
    • Lecture (Conference)
      9th International Workshop on Subsecond Thermophysics, 22.-24.09.2010, Graz, Österreich

    Permalink: https://www.hzdr.de/publications/Publ-14860
    Publ.-Id: 14860


    Rückbau des Zyklotrons U-120 am Forschungszentrum Dresden-Rossendorf

    Naumann, B.; Friedrich, M.; Matz, W.
    Der Beitrag gibt einen Überblick über den Stand des Rückbaus des Zyklotrons U-120, das von 1958 bis 1999 eines der größten experimentellen Anlagen im Forschungszentrum Rossendorf war. Der Rückbau der Beschleunigeranlage begann im Jahr 2001. Bis zum November 2010 sind alle Anlagenteile und Experimentaufbauten radiologisch bewertet und größtenteils entsorgt worden. Der Beitrag beschreibt u. a. die Verfahren zur Bewertung der Aktivierung großer Bauteile des Zyklotrons.
    • Invited lecture (Conferences)
      4. Symposium Stilllegung und Rückbau kerntechnischer Anlagen, 02.-03.11.2010, Hannover, Deutschland

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    Permalink: https://www.hzdr.de/publications/Publ-14859
    Publ.-Id: 14859


    A trigonal nodal solution approach to the multi-group simplified P3 equations in the reactor code DYN3D

    Duerigen, S.; Grundmann, U.; Mittag, S.; Merk, B.; Fridman, E.; Kliem, S.
    The neutronics model of the nodal reactor dynamics codeDYN3D developed for 3-D analyses of steady states and transients in light-water reactors has been extended by a simplified P3 (SP3) neutron transport option to overcome the limitations of the diffusion approach. To provide a method being applicable to reactors with hexagonal fuel assemblies and furthermore allowing flexible mesh refinement, the nodal SP3 method has been developed on the basis of a flux expansion in trigonal-z geometry. In this paper, the derivation of the trigonal SP_3 method is presented and preliminary assessment of the methodology is performed.
    Keywords: simplified P3, SP3, nodal method, trigonal, triangular, hexagonal
    • Contribution to proceedings
      International Conference on Mathematics and Computational Methods Applied to Nuclear Science and Engineering (M&C 2011), 08.-12.05.2011, Rio de Janeiro, Brazil, 978-85-63688-00-2
    • Lecture (Conference)
      International Conference on Mathematics and Computational Methods Applied to Nuclear Science and Engineering (M&C 2011), 08.-12.05.2011, Rio de Janeiro, Brazil

    Permalink: https://www.hzdr.de/publications/Publ-14858
    Publ.-Id: 14858


    Preparation of laser-accelerated proton beams for radiobiological applications

    Metzkes, J.; Cowan, T. E.; Karsch, L.; Kraft, S. D.; Pawelke, J.; Richter, C.; Richter, T.; Zeil, K.; Schramm, U.
    This paper presents the concept of transport and filtering of laser-accelerated proton pulses used for the first cell irradiation experiments performed with the Dresden 150 TW laser DRACO. Based on a simple non-focusing magnetic dipole equipped with two apertures the concept makes use of an energy dependent angular asymmetry of the proton spectra. For micron thin target foils protons of interest with energies above 7 MeV are observed to be significantly oset from target normal where low energy emission is dominantly centered. As the eect can be controlled via the target rotation with respect to the incoming light, it can be used to optimize the transport efficiency for high energy protons while simultaneously suppressing background radiation.
    Keywords: laser acceleration of ions, target normal sheath acceleration, magnetic energy filter, radiobiological studies

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    Permalink: https://www.hzdr.de/publications/Publ-14857
    Publ.-Id: 14857


    Bispidine-derivatives for radiopharmaceutical applications

    Fähnemann, S.
    kein Abstract verfügbar
    • Lecture (others)
      Seminarvortrag School of Chemistry, Monash University, 07.10.2010, Melbourne, Australia

    Permalink: https://www.hzdr.de/publications/Publ-14856
    Publ.-Id: 14856


    Correlation between the microstructure and the degradation of rare earth implanted Si-based light emitters

    Rebohle, L.; Nazarov, A.; Tyagulskii, S.; Tyagulskii, I.; Lehmann, J.; Skorupa, W.
    The degradation of rare earth (RE)-implanted light emitters based on a Si-SiO2-SiON-ITO structure was investigated using the example of Tb and Eu as a function of their microstructural, electrical and electroluminescence (EL) properties. As shown by transmission electron microscopy and Rutherford backscattering spectroscopy the different implantation and annealing conditions lead to two different types of microstructures: devices with small RE oxide clusters and devices with large RE oxide clusters and strong RE agglomerations at the SiO2 interfaces. The electrical and EL properties of the devices were characterized by constant current injection measurements, in which the EL and the applied voltage is monitored with time, and IV, CV and EL spectrum measurements. As a result of these investigations it is shown that devices with small RE oxide clusters normally exhibit a high EL intensity and degrade in a two-step process characterized by a negative and a positive net charge trapping. In contrast to this, devices with large RE oxide clusters have a lower EL intensity, but the first step of degradation is suppressed resulting in lower quenching cross sections and thus a longer operation life time. The degradation is explained by a defect shell model in which the RE oxide clusters are surrounded by defect regions of different extensions leading to the different behavior of devices with small and large RE oxide clusters.
    Keywords: Electroluminescence, rare earth, MOS capacity, charge trapping, ion implantation
    • Lecture (Conference)
      3rd Int. Meeting on Recent Developments in the study of Radiation Effects in Matter, 24.-28.10.2010, Gramado, Brazil

    Permalink: https://www.hzdr.de/publications/Publ-14855
    Publ.-Id: 14855


    Comparison of the stability of Y-90-, Lu-177- and Ga-68- labeled human serum albumin microspheres (DOTA-HSAM)

    Wunderlich, G.; Schiller, E.; Bergmann, R.; Pietzsch, H.-J.
    Introduction:
    Microparticles derived from denatured human serum albumin (DOTA-derivatized human serum albumin microspheres, or DOTA-HSAM) are attractive carriers of radionuclides for both therapeutic and diagnostic purposes. In this article, we describe a labeling procedure for diagnostic (Ga-68) and therapeutic (Y-90, Lu-177) radionuclides and report on the results of stability studies of these products.

    Methods:
    DOTA-HSAM was labeled in 0.5 M ammonium acetate buffer, pH 5.0, containing 0.02 mg/ml detergent. After adding the radionuclide, the mixture was shaken for 15 min at 90°C. Labeling yields and in vitro stability were determined by thin-layer
    chromatography. For determination of the in vivo stability of Ga-68 and Y-90 DOTA-HSAM, the particles were injected intravenously in Wistar rats.

    Results:
    Labeling yields up to 95% in the case of Ga-68 and Lu-177 were achieved. Ga-68-labeled DOTA-HSAM showed high in vitro and in vivo stability. The amount of particle-bound radioactivity of Lu-177 DOTA-HSAM declines slowly in a linear manner to approximately 72% after 13 days. For Y-90, the labeling yield decreased with increasing radioactivity level. We presume radiolysis as the reason for these findings.

    Conclusion:
    The labeling of DOTA-HSAM with different radionuclides is easy to perform. The radiation-induced cleavage of the labeled chelator together with the rather short half-life of radioactivity fixation in vivo (3.7 days) is, in our opinion, opposed to therapeutic applications of DOTA-HSAM. On the other hand, the high stability of Ga-68 DOTA-HSAM makes them an attractive candidate for the measurement of regional perfusion by PET.
    Keywords: Human serum albumin microspheres; Stability; Radiolabeled particles; Radiolysis; Thiourea bond

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    Permalink: https://www.hzdr.de/publications/Publ-14854
    Publ.-Id: 14854


    Production of Lambda and Sigma(0) hyperons in proton-proton collisions

    Abdel-Bary, M.; Abdel-Samad, S.; Brinkmann, K.-T.; Clement, H.; Dietrich, J.; Doroshkevich, E.; Dshemuchadse, S.; Ehrhardt, K.; Erhardt, A.; Eyrich, W.; Filges, D.; Filippi, A.; Freiesleben, H.; Fritsch, M.; Gast, W.; Georgi, J.; Gillitzer, A.; Gottwald, J.; Hesselbarth, D.; Jaeger, H.; Jakob, B.; Jaekel, R.; Karsch, L.; Kilian, K.; Koch, H.; Krapp, M.; Kress, J.; Kuhlmann, E.; Lehmann, A.; Marcello, S.; Marwinski, S.; Mauro, S.; Meyer, W.; Michel, P.; Moeller, K.; Morsch, H. P.; Moertel, H.; Naumann, L.; Paul, N.; Pinna, L.; Pizzolotto, C.; Plettner, C.; Reimann, S.; Richter, M.; Ritman, J.; Roderburg, E.; Schamlott, A.; Schoenmeier, P.; Schroeder, W.; Schulte-Wissermann, M.; Sefzick, T.; Stinzig, F.; Steinke, M.; Sun, G. Y.; Teufel, A.; Ullrich, W.; Wagner, G. J.; Wagner, M.; Wenzel, R.; Wilms, A.; Wintz, P.; Wirth, S.; Wuestner, P.; Zupranski, P.
    This paper reports results on simultaneous measurements of the reaction channels pp → pK+Λ and pp → pK+Σ0 at excess energies of 204, 239, and 284MeV (Λ) and 127, 162, and 207MeV (Σ0). Total and differential cross-sections are given for both reactions. It is concluded from the measured total cross-sections that the high-energy limit of the cross-section ratio is almost reached at an excess energy of only about 200MeV. From the differential distributions observed in the overall CMS as well as in the Jackson and helicity frames, a significant contribution of interfering nucleon resonances to the Λ production mechanism is concluded while resonant Σ0 production seems to be of lesser importance and takes place only through specific partial waves of the entrance channel. The data also indicate that kaon exchange plays a minor role in the case of Λ but an important role for Σ0 production. Thus the peculiar energy dependence of the Λ/Σ0 cross-section ratio appears in a new light as its explanation requires more than mere differences between the pΛ and the pΣ0 final-state interaction. The data provide a benchmark for theoretical models already available or yet to come.

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    Permalink: https://www.hzdr.de/publications/Publ-14853
    Publ.-Id: 14853


    Characterization of microstructural defects in melt grown ZnO single crystals

    Anwand, W.; Brauer, G.; Grynszpan, R. I.; Cowan, T. E.; Schulz, D.; Klimm, D.; Čížek, J.; Kuriplach, J.; Procházka, I.; Ling, C. C.; Djurišić, A. B.; Klemm, V.; Schreiber, G.; Rafaja, D.
    Various nominally undoped, hydrothermally or melt grown (MG) ZnO single crystals have been investigated by standard positron lifetime measurements. Furthermore, optical transmission measurements and structural characterizations have been performed; the content of hydrogen in the bound state was determined by nuclear reaction analysis.
    A positron lifetime of 165-167 ps, measured for a brownish MG ZnO sample containing (0.30 +/- 0.03) at.-% of bound hydrogen, matches perfectly the value found for colorless MG ZnO crystals. The edge shift, observed in the "blue light domain" of the optical absorption for the former sample with respect to the latter samples, is estimated to be 0.70 eV, and found equal to a value reported previously. The possible role of zinc interstitials as well as nitrogen-related defects is considered and discussed. Microstructure analysis by X-ray diffraction and transmission electron microscopy revealed the presence of stacking faults in MG crystals in a high concentration, which suggests these defects to be responsible for the observed positron lifetime.
    Keywords: zinc oxide, microstructure defects, positron annihilation, optical transmission, X-ray diffraction, transmission electron microscopy

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    Permalink: https://www.hzdr.de/publications/Publ-14852
    Publ.-Id: 14852


    Bakterielle Wechselwirkungen ausgewählter Actinide vor dem Hintergrund der Endlagerung von radioaktivem Abfall

    Moll, H.
    Bakterien, ubiquitär vorkommende Mikroorganismen, können signifikant die Speziation und damit das Verhalten von Schwermetallen in der Umwelt beeinflussen. Detaillierte Kenntnisse der Wechselwirkungsprozesse von Bakterien mit Actiniden sind z.B. für Langzeitsicherheitsanalysen für zukünftige Endlager hochradioaktiver Abfälle sowie zur Sanierung kontaminierter Flächen und Einrichtungen erforderlich. Das Interesse an mikrobiellen Prozessen der Actinide ist in den letzten Jahren stetig gestiegen. Dennoch sind die Kenntnisse zur mikrobiellen Diversität an möglichen Endlagerstandorten von nuklearem Abfall relativ begrenzt.
    Im Vortrag werden am Beispiel ausgewählter Actinide detaillierte Untersuchungen zur Aufklärung von deren Speziation mit speziellen Bakterien vorgestellt. Ein kurzer Überblick zur Bestimmung der mikrobiellen Diversität in Umweltproben wird gegeben. Der Hauptschwerpunkt liegt auf direkten und indirekten Wechselwirkungsprozessen der Actinide mit Bakterien.
    Keywords: bacteria, actinides, nuclear waste disposal
    • Invited lecture (Conferences)
      Seminar für Kern- und Radiochemie am Institut für Kernchemie der Johannes Gutenberg-Universität Mainz, 29.11.2010, Mainz, Deutschland

    Permalink: https://www.hzdr.de/publications/Publ-14851
    Publ.-Id: 14851


    Surface Modification on KBr (001) with Slow Highly Charged Ions

    Wilhelm, R. A.; Heller, R.; El-Said, A. S.; Facsko, S.
    Highly Charged Ions (HCI) carry an enormous amount of potential energy (up to 100 keV for Xe50+) which is defined as the sum of the binding energies of all missing electrons. This unique parameter offers new ways of surface modifications without a significant bulk damage.
    During neutralization and de-excitation processes of the HCI the potential energy is released into electronic excitations within the solid (creation of electron hole pairs). These electron hole pairs get rapidly self-trapped due to strong electron-phonon coupling in the ionic lattice and decay into color centers (mainly H, F and F*-centers).
    Finally these color centers lead to a desorption of K and Br neutralized atoms at the surface site, which after a agglomeration of many of these color centers forms a pit-like nanostructure on atomically flat KBr(001) surfaces.
    The influence of kinetic and potential energy effects will be discussed.
    Keywords: HCI, DIET, KBr, electron-hole pair, pit, nanostructures, color center
    • Lecture (Conference)
      International Symposium on Electron Beam Ion Sources and Traps, EBIST2010, 07.-10.04.2010, Stockholm, Sverige
    • Poster
      International Symposium on Electron Beam Ion Sources and Traps, EBIST2010, 07.-10.04.2010, Stockholm, Sverige

    Permalink: https://www.hzdr.de/publications/Publ-14850
    Publ.-Id: 14850


    The traceless Staudinger ligation with fluorine-18: a novel and versatile labeling technique for the synthesis of PET-radiotracers

    Pretze, M.; Wuest, F.; Peppel, T.; Köckerling, M.; Mamat, C.
    The development of rapid radiolabeling techniques under mild reaction conditions involving the short-lived positron emitter fluorine-18 remains a special challenge in organic PET chemistry. This work describes a novel and facile application of the traceless Staudinger ligation as a mild and versatile labeling method for preparation of various radiotracers labeled with fluorine-18.
    Keywords: Radiolabeling; Traceless Staudinger ligation; Bioorthogonal; Fluorine-18

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    Permalink: https://www.hzdr.de/publications/Publ-14849
    Publ.-Id: 14849


    The speciation of U(VI) in aqueous solution and sorbed onto TiO2 studied by in situ vibrational spectroscopy

    Müller, K.; Meusel, T.; Brendler, V.; Foerstendorf, H.; Bernhard, G.
    The migration behavior of uranium in the environment is controlled by prominent molecular phenomena such as hydrolysis and complexation reactions in aqueous solutions as well as the diffusion and sorption onto minerals present along groundwater flow paths. These reactions significantly influence the mobility and bioavailability of the metal ions in the environment, in particular at water-mineral interfaces. Hence, for the assessment of migration processes the knowledge of the mechanisms occurring at interfaces is crucial. The required structural information can be obtained using various spectroscopic techniques.
    In the present study, the speciation of uranium(VI) at the TiO2-water interface has been investigated by the application of attenuated total reflection Fouriertransform infrared (ATR FT-IR) spectroscopy. Moreover, the distribution of the hydrolysis products in micromolar aqueous solutions of U(VI) at ambient atmosphere has been characterized for the first time, by a combination of ATR FT-IR spectroscopy, near infrared (NIR) absorption spectroscopy, and speciation modeling applying updated thermodynamic databases.
    • Lecture (others)
      Seminar at the Department of Nuclear Engineering, Kyoto University, 29.06.2010, Kyoto, Japan

    Permalink: https://www.hzdr.de/publications/Publ-14848
    Publ.-Id: 14848


    Speciation of actinyl ions in aqueous solution and at water-mineral interfaces. A vibrational spectroscopic approach

    Müller, K.
    The migration behavior of actinides in the environment is controlled by prominent molecular phenomena such as hydrolysis and complexation reactions in aqueous solutions as well as the diffusion and sorption onto minerals present along groundwater flow paths. These reactions significantly influence the mobility and bioavailability of the metal ions in the environment, in particular at water-mineral interfaces. Hence, for the assessment of migration processes the knowledge of the mechanisms occurring at interfaces is crucial. The required structural information can be obtained using various spectroscopic techniques.
    In the present study, the speciation of uranium(VI) and neptunium(V) at environmentally relevant mineral-water interfaces of oxides of titania, alumina, silica, iron, zinc, and alumosilicates has been investigated by the application of attenuated total reflection Fouriertransform infrared (ATR FT-IR) spectroscopy.
    Moreover, the distribution of the hydrolysis products in micromolar aqueous solutions of U(VI) and Np(V/VI) at ambient atmosphere has been characterized for the first time, by a combination of ATR FT-IR spectroscopy, near infrared (NIR) absorption spectroscopy, and speciation modeling applying updated thermodynamic databases.
    • Lecture (others)
      Jahresseminar des Graduiertenkollegs 826/3, 08.11.2010, Burg Schönburg in Oberwesel, Deutschland

    Permalink: https://www.hzdr.de/publications/Publ-14847
    Publ.-Id: 14847


    Uranium sorption on various forms of titanium dioxide – influence of surface area, surface charge and impurities

    Comarmond, M. J.; Payne, T. E.; Harrison, J. J.; Thiruvoth, S.; Wong, H. K.; Aughterson, R. D.; Lumpkin, G. R.; Müller, K.; Foerstendorf, H.
    Titanium dioxide (TiO(2)) has often served as a model substrate for experimental sorption studies of environmental contaminants. However, various forms of Ti-oxide have been used, and the different sorption properties of these materials have not been thoroughly studied. We investigated uranium sorption on some thoroughly characterized TiO(2) surfaces with particular attention to the influence of surface area, surface charge, and impurities. The sorption of U(VI) differed significantly between samples. Aggressive pretreatment of one material to remove impurities significantly altered the isoelectric point, determined by an electroacoustic method, but did not significantly impact U sorption. Differences in sorption properties between the various TiO(2) materials were related to the crystallographic form, morphology, surface area, and grain size, rather than to surface impurities or surface charge. In-situ attenuated total reflection Fourier-transform infrared (ATR FT-IR) spectroscopic studies showed that the spectra of the surface species of the TiO(2) samples are not significantly different, suggesting the formation of similar surface complexes. The data provide insights into the effect of different source materials and surface properties on radionuclide sorption.

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    Permalink: https://www.hzdr.de/publications/Publ-14846
    Publ.-Id: 14846


    Preparation, 99mTc-labeling and biodistribution studies of a PNA oligomer containing a new ligand derivative of 2,2′-dipicolylamine

    Gasser, G.; Jäger, K.; Zenker, M.; Bergmann, R.; Steinbach, J.; Stephan, H.; Metzler-Nolte, N.
    A new azido derivative of 2,2′-dipicolylamine (Dpa), 2-azido-N,N-bis((pyridin-2-yl)methyl)ethanamine, (Dpa-N3) was readily prepared from the known 2-(bis(pyridin-2-ylmethyl)amino)ethanol (Dpa-OH). It was demonstrated that Dpa-N3 could be efficiently labeled with both [Re(CO)3(H2O)3]Br and [99mTc(H2O)3(CO)3]+ to give [Re(CO)3(Dpa-N3)]Br and [99mTc(CO)3(Dpa-N3)]+, respectively. Furthermore, Dpa-N3 was successfully coupled, on the solid phase, to a Peptide Nucleic Acid (PNA) oligomer (H-4-pentynoic acid-spacer-spacer-tgca-tgca-tgca-Lys-NH2; spacer = –NH–(CH2)2–O–(CH2)2–O–CH2–CO–) using the Cu(I)-catalyzed [2 + 3] azide/alkyne cycloaddition (Cu-AAC, often referred to as the prototypical “click” reaction) to give the Dpa-PNA oligomer. Subsequent labeling of Dpa-PNA with [99mTc(H2O)3(CO)3]+ afforded [99mTc(CO)3(Dpa-PNA)] in radiochemical yields > 90%. Partitioning experiments in a 1-octanol/water system were carried out to get more insight on the lipophilicity of [99mTc(CO)3(Dpa-N3)]+ and [99mTc(CO)3(Dpa-PNA)]. Both compounds were found rather hydrophilic (log Do/w values at pH = 7.4 are −0.50: [99mTc(CO)3(Dpa-N3)]+ and −0.85: [99mTc(CO)3(Dpa-PNA)]. Biodistribution studies of [99mTc(CO)3(Dpa-PNA)] in Wistar rats showed a very fast blood clearance (0.26 ± 0.1 SUV, 1 h p.i.) and modest accumulation in the kidneys (5.45 ± 0.45 SUV, 1 h p.i.). There was no significant activity in the thyroid and the stomach, demonstrating a high in vivo stability of the 99mTc-labeled Dpa-PNA conjugate.
    Keywords: Bio-organometallic chemistry; Click chemistry; Nuclear medicine; Peptide nucleic acid (PNA); Rhenium compounds; Technetium compounds

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    Permalink: https://www.hzdr.de/publications/Publ-14845
    Publ.-Id: 14845


    Characterization of Si nanowires fabricated by Ga+ FIB implantation and subsequent selective wet etching

    Böttger, R.; Bischoff, L.; Schmidt, B.; Krause, M.
    Local gallium (Ga) ion implantation in silicon (Si) by focused ion beam (FIB) and subsequent anisotropic and selective wet etching has been used to fabricate freely suspended nanowires (NWs) with reproducible widths between 20 and 200 nm. The dependence of the resulting NW width on the implanted fluence has been investigated and is supported by a numerical model reproducing the experimental data and enabling an a priori estimation of the NW width as a function of the implanted fluence. Furthermore, the resistance of the NWs, its temperature response and the activation energy for electrical current flow were investigated before and after direct current (DC) annealing in air and in vacuum. Annealed NWs showed a decrease of their resistivity up to two orders of magnitude, indicating a partial re-crystallization of the NWs through self-heating and a change in the conduction. The assumption of recrystallization is supported by scanning electron microscopy (SEM) and Raman spectroscopy.
    Keywords: silicon-on-insulator, Ga focused ion beam implantation, nanowire, anisotropic etching, width, resistivity, phase change, annealing, Raman spectroscopy

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    Permalink: https://www.hzdr.de/publications/Publ-14844
    Publ.-Id: 14844


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