Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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35836 Publications

Nanostructuring of semiconductors with ion beams

Skorupa, W.

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

(1) Superconducting germanium, Doping in SOI-chips, Superthin insulator in SOI
(2) Silicon nanowires, surface patterning for ripples, nanoclusters for silicon-based light emission, diluted magnetic semiconductors (DMS)
(3) Highly charged ions etc.: Can they flatten the path to a quantum computer…?

Keywords: ion beam processing; ion implantation; nanostructures; semiconductors

  • Invited lecture (Conferences)
    LENS 2009 Summer School, 11.-14.06.2009, Reykjavik, Iceland

Publ.-Id: 13692

Oxygen gettering in thin buried oxide layer fabrication

Ou, X.; Kögler, R.; Skorupa, W.; Möller, W.; Wang, X.

A cavity layer or nano-bubble layer introduced by He implantation before the oxygen implantation collects the implanted oxygen and increases the oxygen concentration. The average size and density of the oxygen precipitates formed in the initial stage of the Separation-by-implanted-oxygen (SIMOX) process is conform with the size and density of the cavities pre-formed by He implantation and annealing. The gettering ability of the cavity layer for oxygen is directly related to the area of the internal surface of the cavities. A nano-bubble layer accumulates oxygen in a very narrow range occurring between the damage maximum, DP, and the mean projected ion range, RP. Such a nano-bubble layer is most efficient in oxygen gettering due to their larger area of the internal surface and the small size of the oxide precipitates initially formed at the bubbles.

Keywords: SOI; ion implantation; buried oxide; gettering

  • Poster
    EUROSOI 2009, 19.-21.01.2009, Göteborg, Sweden

Publ.-Id: 13691

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

Krzyzanowska, H.; Kulik, M.; Zuk, J.; Rzodkiewicz, W.; Kobzev, A. P.; Skorupa, W.

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

Keywords: ion beam synthesis; ion implantation; germanium nanoclusters; Raman; RBS; ellipsometry; VASE

Publ.-Id: 13690

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

Zuk, J.; Romanek, J.; Skorupa, W.

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

Keywords: ion implantation; silicon carbide; Raman; 6H-SiC

Publ.-Id: 13689

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

Zhu, C.; Ling, C.; Brauer, G.; Anwand, W.; Skorupa, W.

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

Keywords: zinc oxide; doping; ion implantation; deep level

Publ.-Id: 13688

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

Keller, A.; Peverini, L.; Grenzer, J.; Mücklich, A.; Facsko, S.

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

Keywords: nanopatterning; thin film growth; ion sputtering; X-ray scattering

Publ.-Id: 13687

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

Heller, A.; Rönitz, O.; Barkleit, A.; Bernhard, G.; Ackermann, J.-U.

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

Keywords: europium; alanine; phenylalanine; threonine; TRLFS; heavy metal speciation

  • Applied Spectroscopy 64(2010)8, 930-935

Publ.-Id: 13686

P0702 - Ultraschallsensor zur Messung von lokalen Strömungsgeschwindigkeiten in flüssigen Schmelzen

Eckert, S.; Gerbeth, G.; Gundrum, T.

Die Erfindung betrifft einen dispersionsarmen Ultraschallsensor zur Messung von lokalen Strömungsgeschwindigkeiten in flüssigen Schmelzen bei hohen Temperaturen. Durch die Erfindung soll ein Ultraschallsensor zur Durchführung lokaler kontinuierlicher und zuverlässiger Geschwindigkeitsmessungen in heißen Schmelzen (T > 200°C) geschaffen werden. Erreicht wird das dadurch, dass der dispersionsarme Ultraschallsensor einen mit dem piezoelektrischen Wandler (1) verbundenen Ultraschallwellenleiter (2) aus einem Material enthält, das in einem für den Einsatzfall relevanten Temperaturbereich oberhalb von 200 °C eine geringe akustische Dämpfung aufweist sowie gegenüber der Schmelze chemisch resistent ist und dass die der Schmelze zugewandte Stirnfläche des Ultraschallwellenleiters (2) verschlossen und von der Schmelze benetzbar ist.

  • Patent
    DE 10 2007 027 391 B3 - 8.1.2009
  • Patent
    WO 2008/152031: Offenlegung-08.12.2008; Nationalisierung in EP, JP, KR, US

Publ.-Id: 13685

P0705 - Anordnung zur zweidimensionalen Messung der Temperaturverteilung in einem Messquerschnitt

Ritterath, M.; Hampel, U.; Da Silva, M. J.; Zimmermann, W.; Schleicher, E.

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

  • Patent
    DE 10 2007 019 925 A1 - 13.11.2008

Publ.-Id: 13684

P0704 - Si-basierter Lichtemitter

Skorupa, W.; Prucnal, S.; Rebohle, L.; Helm, M.

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

  • Patent
    DE 10 2007 019 209 A1 - 31. 10. 2008
  • Patent
    DE102007019209B4 - 05.01.2011

Publ.-Id: 13683

P0701 - Anordnung zur Röntgentomographie

Hampel, U.; Fischer, F.

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

  • Patent
    DE102007008349, Offenlegung - 21.08.2008, Erteilung - 15.10.2009; Nachanmeldung JP, US, WO, EP

Publ.-Id: 13682

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

Numazawa, S.; Heinig, K.-H.; Ranjan, M.; Facsko, S.

By grazing metal vapor deposition perpendicular to ripples of pre-patterned, oxidized Si surfaces, a chain-like formation of the metal nanoclusters along the ripples have been observed. The structures are located on the slopes which point towards the evaporation source. The self-ordering of metal nanostructure has been observed neither for normal deposition nor for low-angle deposition parallel to the ripple direction. The features of the metal nanostructure depend strongly on the evaporation angle.
In this work, we studied the process of silver deposition on pre-patterned, oxidized Si surfaces by means of 3D lattice kinetic Monte Carlo simulations. The experimentally observed Ag nanostructures could be reproduced. It was shown that the extremely low sticking probability of deposited Ag together with a slope-dependent deposition rate leads to a strongly selective Ag nanocluster nucleation on the surface because
the nucleation rate depends on the square of the adatom concentration.

Keywords: Kinetic Monte-Carlo; nanopatterninig

  • Poster
    Nanoscale Modification of Surfaces and Thin Films Rathen, 30.08.-03.09.2009, Rathen, Germany

Publ.-Id: 13681

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

Joseph, C.

Das Entsorgungskonzept für radioaktiven Abfall in Deutschland ist die Endlagerung in tiefen geologischen Formationen, um die Menschen und die Umwelt im Allgemeinen vor der Radioaktivität zu schützen. Mithilfe eines Multi-Barrier-Systems bestehend aus geologischen und technischen Barrieren soll der Abfall möglichst lange, isoliert von der Biosphäre, gelagert werden. In Deutschland stehen dazu drei mögliche Wirtsgesteine zur Verfügung (Salz, Granit, Ton). Für Salz gibt es bereits eine breite vorhandene Datenbasis. Derzeit werden die Untersuchungen am Ton intensiviert, um letztendlich zwischen drei Gesteinsformationen bezüglich ihrer Eignung als Endlager wählen zu können. Diese Untersuchungen werden am Beispiel Opalinuston (natürlicher Ton aus Mont Terri, Schweiz) und dem System U(VI) - Huminsäure - Opalinuston näher erläutert. Insbesondere der Einfluss des im Ton enthaltenen Calcits auf die U(VI)- und Huminsäurespeziation wird gezeigt. Dazu werden explizit Ergebnisse von Sorptions- und Diffusionsversuchen vorgestellt.

Keywords: opalinus clay; humic acid; uranium(VI); sorption; diffusion; host rock; nuclear waste repository; speciation; pore water; calcium; calcite

  • Lecture (others)
    Doktorandenseminar - Kompetenzzentrum Ost für Kerntechnik, 10.12.2009, Rossendorf, Deutschland

Publ.-Id: 13680

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

Liedke, B.; Heinig, K.-H.; Möller, W.

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

Keywords: ripple formation; nanopatterning; ion erosion; computer simulations; TRIM; kinetic Monte-Carlo; viscous flow

  • Lecture (Conference)
    FOR 845, Project Meeting Köln, 31.03.2009, Köln, Germany

Publ.-Id: 13679

Development of redox determination methods (WP 2)

Steinbrück, D.; Kumke, M.; Altmaier, R. M.; Neck, V.; Fellhauser, D.; Rumke, J.; Grambow, B.; Landesman, C.; Ribet, S.; Krawczyk-Bärsch, E.; Perdicakis, M.

The objective of WP2 is the development and testing of redox determination methods using different type of electrodes as well as optodes (optical sensors) in order to provide a broad and solid scientific-technical basis for the application of such. In combination with chemical analysis and associated thermodynamic modeling the redox state of systems (relevant for nuclear waste repositories) is assessed. The overall goals are (i) redox determination methods specifically designed for environmental applications, and (ii) a broader information base for interpretation of system conditions.

  • Contribution to proceedings
    1st Annual Workshop of the Recosy Project, 10.-12.02.2009, Barcelona, Spain
    Collaborative Project "Redox Phenomena Controlling Systems", Karlsruhe: Forschungszentrum Karlsruhe GmbH, KIT Report FZKA 7466 Dezember 2009, 9-22

Publ.-Id: 13678

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

Liedke, B.; Heinig, K.-H.; Facsko, S.; Möller, W.

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

Keywords: TRIM; kinetic Monte-Carlo; ion irradiation; ripples formation; scaling

  • Poster
    2009 MRS Fall Meeting, 30.11.-04.12.2009, Boston, USA

Publ.-Id: 13677

Analytische HPLC photokatalytischer Abbauprodukte von Wirkstoffen

Marquard, A.

Bakterielle Hüllproteine (S-Layer-Proteine) besitzen eine großen technische Anwendbarkeit. Eine ist die als Matrix für die Synthese von photokatalytisch aktiven Nanopartikeln wie ZnO und TiO2. Verwendung finden die mit ZnO oder TiO2 beschichteten Hüllproteine beim Abbau von Arzneimittelrückständen wie Diclofenac in Abwässern unter Anwendung von UV-Licht. Ein besonderes Augenmerk richtet sich auf die Analytik der Abbauprodukte bei der Aufspaltung von Diclofenac. Der folgende Vortrag soll einen Überblick über den Einsatz von HPLC zu Analyse des photokatalytischen Abbaus von Diclofenac geben.

Keywords: HPLC; photocatalytic degradation; ZnO; TiO2

  • Lecture (Conference)
    3. Workshop Möglichkeiten und Grenzen der HPLC in den Lebenswissenschaften, 29.01.2010, Dresden, Deutschland

Publ.-Id: 13676

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

Liedke, B.; Heinig, K.-H.; Möller, W.

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

Keywords: BCA; kinetic Monte-Carlo; collision cascade; ion irradiation; interface mixing; phase seperation; phase ordering; intermetallics

  • Lecture (others)
    Seminar at Department of Physics, University of Bialystok, 21.11.2009, Bialystok, Poland

Publ.-Id: 13675

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

Liedke, B.; Heinig, K.-H.; Facsko, S.; Möller, W.

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

Keywords: TRIM; kinetic Monte-Carlo; ion irradiation; ripples formation; scaling

  • Lecture (Conference)
    Nanoscale Modification of Surfaces and Thin Films Rathen, 30.08.-03.09.2009, Rathen, Germany

Publ.-Id: 13674

Prediction of surface pattern formation by surface defect generation and diffusion

Numazawa, S.; Heinig, K.-H.

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

Keywords: Kinetic Monte-Carlo simulation; ion erosion; surface pattern

  • Lecture (Conference)
    Symp. "Nanoscale Pattern Formation", MRS2009Fall Meeting, 30.11.-04.12.2009, Boston, USA

Publ.-Id: 13673

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

Liedke, B.; Heinig, K.-H.; Odor, G.

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

Keywords: Pattern formation; surface growth; computer simulation; Evolution equation; Scaling

  • Lecture (Conference)
    Symp. "Nanoscale Pattern Formation", MRS2009Fall Meeting, 30.11.-04.12.2009, Boston, USA

Publ.-Id: 13671

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

Heinig, K.-H.; Schmidt, B.; Vredenberg, A.; Polman, A.; Toulemonde, M.

Spherical gold and germanium nanoclusters embedded in silicon dioxide can be shaped into rods and discs by high energy ion irradiation. The experimental work, modelling of the shaping mechanism and computer simulations will be presented.

Keywords: nanostructure; ion irradiation; theory; computer simulation

  • Invited lecture (Conferences)
    International workshop on nanostructures in silica, 06.-09.09.2009, Ivalo, Finland

Publ.-Id: 13670

Investigations on Dresden EBIS/T as charge breeders

Thorn, A.; Ritter, E.; Ullmann, F.; Zschornack, G.; Bischoff, L.; Pilz, W.

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

Keywords: charge breeders; Dresden EBIT

  • Lecture (Conference)
    5th SPARC Collaboration Symposium, 01.-04.09.2009, Lisboa, Portigal

Publ.-Id: 13669

3D nanostructures by combined FIB and electron beam processing

Bischoff, L.; Schmidt, B.; Lange, H.; Donzev, D.

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

Keywords: FIB; nanostructure; anisotropic etching

  • Lecture (Conference)
    35th Int. Conf. on Micro Nano Engineering, MNE 2009, 28.09.-01.10.2009, Ghent, Belgium

Publ.-Id: 13668

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

Kormoll, T.; Fiedler, F.; Wüstemann, J.; Enghardt, W.

no abstract available

Keywords: dose monitoring of proton irradiation; Compton imaging

  • Poster
    Oncoray Retreat, 27.-28.01.2010, Bautzen, Deutschland

Publ.-Id: 13667

Applicationof single gamma ray imaging the real time radiotherapy monitoring

Shakirin, G.; Fiedler, F.; Kormoll, T.; Schöne, S.; Enghardt, W.

no abstract available

Keywords: single gamma ray imaging; real time radiotherapy monitoring

  • Invited lecture (Conferences)
    Cerro, 19.-23.01.2010, Les Menuires, Frankreich

Publ.-Id: 13666

Ion-beam-assisted nanostructure formation – atomistic reaction pathways

Heinig, K.-H.; Liedke, B.; Numazawa, S.; Ranjan, M.; Möller, W.; Facsko, S.

This presentation highlights the role of ion beams for the formation of nanostructures. The focus is on the selforganization of regular surface pattern under low-energy ion irradiation and on the self-patterning of metal deposits on prepatterned silica surfaces. It will be shown that a deep understanding about the atomistic mechanisms involved can be gained from a combination of collision cascade simulations with 3D kinetic Monte-Carlo calculations.

Keywords: nanostructures; ion irradiation; self-organization; theory; modelling; kinetic Monte-Carlo simulation

  • Invited lecture (Conferences)
    Ion-Surface Interactions 2009, 21.-25.08.2009, Zvenigorod, Russia

Publ.-Id: 13665

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

Liedke, B.; Heinig, K.-H.

There are many cases of ion beam processing of materials where ion beam mixing with defect generation and thermally activated processes like defect annealing and phase separation occur at the same time. Examples are ion-irradiation-induced surface pattern selforganisation and nanocluster formation during ion irradiation through interfaces. Here, a new 3D program will be presented which combines the TRIM program for collision cascade simulation with a 3D kinetic Monte-Carlo program describing all kind of relaxation processes.

Keywords: theory; computer simulation; ion implantation; kinetic Monte-Carlo; TRIM

  • Lecture (Conference)
    Workshop Ionenstrahlphysik, 06.-07.04.2009, Jena, Deutschland

Publ.-Id: 13664

Swift Heavy Ions: a Tool for Nanotechnology?

Heinig, K.-H.; Schmidt, B.

Spherical gold and germanium nanoclusters embedded in silicon dioxide can be shaped into rods and discs by high energy ion irradiation. The experimental work, modelling of the shaping mechanism and computer simulations will be presentd.

Keywords: nanostructure; ion irradiation; theory; computer simulation

  • Lecture (Conference)
    Workshop Ionenstrahlphysik, 06.-07.04.2009, Jena, Detschland

Publ.-Id: 13663

Self-assembling biomolecules as a tool kit for new nanomaterials

Pollmann, K.

Biomolecules for new materials

  • Lecture (others)
    Zentrumskolloquium, 4.01.2010, Dresden, Deutschland

Publ.-Id: 13662

Proteinbasierte Oberflächenfunktionalisierung für die Umwelttechnolgie

Pollmann, K.; Raff, J.

Technologie-Plattform S-Layer für die Umwelttechnologie

  • Invited lecture (Conferences)
    Ideas to market, 15.01.2010, Dresden, Deutschland

Publ.-Id: 13661

Von der Mikrobiologie zur Nanotechnologie – Nachwuchsforschergruppe NanoBio am FZD

Pollmann, K.

Vorstellung der Arbeiten der Nachwuchsgruppe NanoBio

  • Lecture (others)
    Besuch von Herrn Gazlig, Pressesprecher der HGF, 20.01.2010, Dresden, Deutschland

Publ.-Id: 13660

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

Odor, G.; Liedke, B.; Heinig, K.-H.

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

Keywords: Kardar-Parisi-Zjang equation; lattice gas; computer simulation; scaling; surface growth

Publ.-Id: 13659

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

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

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

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

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

[1] Wahl, R. et al. (2001). Adv. Materials 13, 736-740
[2] Pollmann, K. et al. (2006). Biotechnol. Adv. 24, 58-68
[3] Raff, J. et al. (2003). Chem. Mater. 15, 240-244

  • Poster
    Chemical Nanotechnology Talks X, 26.-27.01.2010, Frankfurt, Deutschland
  • Lecture (Conference)
    Chemical Nanotechnology Talks X, 26.-27.01.2010, Dresden, Deutschland

Publ.-Id: 13658

Ion beam analysis with sub nanometer depth resolution

Kosmata, M.

no Abstract (keine Kurzbeschreibung erforderlich)

Keywords: Little John; QQDS; high resolution depth profiling; ERDA; RBS; magnetic spectrometer; ion beam analysis; concentration profile; thin layer

  • Lecture (others)
    4th Graduate Students Seminar, 16.-18.09.2009, Krögis, Germany

Publ.-Id: 13657

Surface pattern formation and scaling described by conserved lattice gases

Odor, G.; Liedke, B.; Heinig, K.-H.

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

Keywords: Surface pattern; Computer simulation; KPZ-equation; scaling; Mullins diffusion

  • Physical Review E 81(2010)5, 051114

Publ.-Id: 13656

Neon identifies two billion year old fluid component in Kaapvaal Craton

Lippmann-Pipke, J.; Sherwood Lollar, B.; Niedermann, S.; Stroncik, N.; Naumann, R.; van Heerden, E.; Onstott, T. C.

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

Keywords: noble gas; neon; methanogens; crustal fluid; metamorphic fluids; subsurface microbiology

Publ.-Id: 13654

Numerical Simulations of the von Karman Sodium dynamo

Giesecke, A.; Stefani, F.; Gerbeth, G.

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

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

Keywords: Dynamo; VKS; numerische Simulationen

  • Invited lecture (Conferences)
    Seminar Magnetofluiddynamik TU Dresden, 27.01.2010, Dresden, Deutschland

Publ.-Id: 13653

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

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

Self assembly is a widespread phenomenon in nature. We are working with bacterial surface layer proteins which represent the outermost cell envelope of many bacteria and almost all archaea. Our bacteria were isolated from a uranium mining waste pile and are therefore adapted to high contents of heavy metals. Most of them feature surface layer proteins possessing high metal binding capacities. Bacterial surface layer (S-layer) proteins exhibit self organizing properties combined with the ability to arrange at interfaces. In vitro they form a paracrystalline protein lattice with defined pores and cavi-ties as it can be naturally found on the bacterial surface. Our effort is to use the special properties of these proteins for the design of nano structured and functionalized com-posites. Current workings are focused on catalytic materi-als and sensory layers. We use the self assembling proper-ties for coating various substrates by recrystallizing pro-tein monomers direct on surfaces. The metal binding abil-ities of the lattice can be used for filtering or to form met-al nanoparticles of uniform size and distribution in the pores of the protein layer. The amino acid residues of the protein are suitable for linking further functional mole-cules to the lattice with high density

Keywords: S-layer; AFM; nanoparticles; biosensors; carbon nanotubes

  • Lecture (Conference)
    12th International and Interdisciplinary Symposium Biomaterials and Biomechanics: Fundamentals and Clinical Applications 2010, 17.-19.03.2010, Essen, Deutschland
  • Materialwissenschaft und Werkstofftechnik (2010)

Publ.-Id: 13652

Self-assembling proteins as basis for new nano materials.

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

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

Keywords: S-layer; nanoparticles; biosensors; AFM

  • Lecture (Conference)
    nanocoatings 2010, International Conference on Functional Nanocoatings, 28.-31.03.2010, Dresden, Deutschland

Publ.-Id: 13651

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

Doerr, M.; Raasch, S.; Rotter, M.; Frontzek, M.; Meyer, D. C.; Zschintzsch, M.; Svoboda, P.; Loewenhaupt, M.

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

  • Poster
    E-MRS Fall Meeting, 17.-21.09.2007, Warschau, Polen

Publ.-Id: 13650

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

Jeutter, N. M.; Zschintzsch, M.; von Borany, J.; Baehtz, C.

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

  • Lecture (Conference)
    DPG Frühjahrstagung der Sektion Kondensierte Materie (SKM) 2009, 22.-27.03.2009, Dresden, Deutschland

Publ.-Id: 13649

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

Zschintzsch, M.; Jeutter, N. M.; von Borany, J.; Muecklich, A.

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

  • Lecture (Conference)
    DPG Frühjahrstagung der Sektion Kondensierte Materie (SKM) 2009, 22.-27.03.2009, Dresden, Deutschland

Publ.-Id: 13648

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

Jeutter, N. M.; Zschintzsch, M.; von Borany, J.; Baehtz, C.

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

  • Lecture (Conference)
    E-MRS Spring Meeting, 08.-12.06.2009, Strasbourg, Frankreich
  • Lecture (Conference)
    DPG Frühjahrstagung der Sektion Kondensierte Materie (SKM) 2009, 22.-27.03.2009, Dresden, Deutschland

Publ.-Id: 13647

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

Doerr, M.; Raasch, S.; Rotter, M.; Frontzek, M.; Meyer, D. C.; Leisegang, T.; Zschintzsch, M.; Svoboda, P.; Loewenhaupt, M.

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

Publ.-Id: 13646

Two-phase CFD advances in the NURESIM and NURISP projects

Bestion, D.; Lucas, D.; Smith, B.; Boucker, M.; Scheuerer, M.; D’Auria, F.; Lakehal, D.; Macek, J.; Tilelj, I.; Hazi, G.; Tanskanen, V.; Ilvonen, M.; Seiler, N.; Boetcher, M.; Anglart, H.; Bartosiewicz, Y.

NURESIM and NURISP are two successive European Projects of the 6th and 7th Framework Program with the objective of building a multi-physics and multi-scale platform for numerical simulation of nuclear reactors. It includes core physics and thermalhydraulics with sensitivity and uncertainty methods and coupling of thermalhydraulics with fuel thermomechanics and neutron kinetics. The NURISP European Collaborative Project (FP7) includes 22 organizations from 14 European countries.
This paper summarizes some achievements and ongoing developments of the platform in Thermal-Hydraulics. Within the NURESIM project the development and validation of two-phase-CFD in open medium addressed mainly Departure from Nucleate Boiling, Dry-Out, Direct Contact Condensation and Pressurized Thermal Shock. Within NURISP, CFD use is now extended to some investigations related to LOCA such as flashing flow, and steam-droplet flow in a core during reflooding. The NEPTUNE-CFD code developed by EDF and CEA and sponsored by AREVA-NP and IRSN was first implemented in the NURESIM platform and The TRansaT code developed by ASCOMP is now also in the platform. New physical models have been developed, validation calculations were performed and NEPTUNE-CFD was benchmarked with commercial codes. DNS–ITM techniques (e.g. Lattice Boltzman Method or DNS of the TransAT code) were also used as numerical experiments to obtain information on smaller scale flow processes.
The paper summarizes the achievements, updates the state of the art in two-phase-CFD, and presents the future activities


  • Contribution to proceedings
    18th International Conference on Nuclear Engineering, ICONE18, paper ICONE 18-30205, 17.-21.05.2010, Xi’an, China

Publ.-Id: 13645

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

Doerr, M.; Rotter, M.; Devishvili, A.; Stunault, A.; Perenboom, J.; Tsutaoka, T.; Tanaka, A.; Narumi, Y.; Zschintzsch, M.; Loewenhaupt, M.

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

Publ.-Id: 13644

Multiple ferromagnetic secondary phases in Fe implanted yttria stabilized zirconia

Shalimov, A.; Zhou, S.; Roshchupkina, O.; Jeutter, N.; Baehtz, C.; Talut, G.; Reuther, H.; Potzger, K.

Fe ions have been implanted into YSZ(001) single crystals at elevated temperatures. Depending on the fluence not only an increase of α-Fe cluster formation but also the appearance of γ-Fe as well as Fe oxide based secondary phases was observed. The clusters are proposed to consist of a metallic core and an oxide shell. Ferromagnetic hyperfine splitting was detected by Mössbauer spectroscopy and mainly assigned to Fe3+ and α-Fe.

Keywords: yttria stabilizied zirconia; ion beam synthesis

Publ.-Id: 13643

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

Wiemann, R.; Kosmata, M.; Vieluf, M.; Hanf, D.; Liechtenstein, V. K.; Grötzschel, R.

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

[1] J.F. Ziegler, Nucl. Instr. and Meth. B 219-220 (2004) 1027. URL:
[2] W. Jiang et al, Phys. Rev. B 59 (1999) 226.
[3] A. Blažević et al, Phys. Rev. A 61 (2000) 032901.

  • Poster
    SNI 2010 - Deutsche Tagung für Forschung mit Synchrotronstrahlung, Neutronen und Ionenstrahlen an Großgeräten, 24.-26.02.2010, Berlin, Deutschland

Publ.-Id: 13642

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

Beckers, M.; Höglund, C.; Baehtz, C.; Martins, R. M. S.; Persson, P. O. Å.; Hultman, L.; Möller, W.

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

Keywords: in-situ magnetron sputtering; MAX phases

Publ.-Id: 13641

Next jump of energy efficiency of photovoltaics technology - not only a vision!

von Borany, J.

Present strategies of photovoltaic (PV) industry are strongly directed to lower the fabrication costs and/or to enhance the solar cell efficiency with the overall aim to achieve grid parity in near future. Bandgap engineered materials including semiconductor and metal nanoparticles can contribute to reduce energy conversion losses due to thermalization and missing infrared light absorption. Based on such materials, the European PV roadmap describes a clear route towards solar cells with significantly enhanced efficiencies.

Keywords: photovoltatics; 3rd generation solar cells; nanostructures

  • Invited lecture (Conferences)
    7th Innovationsforum for Automation, 21.-22.01.2010, Dresden, Deutschland

Publ.-Id: 13640

Charge order, enhanced orbital moment, and absence of magnetic frustration in layered multiferroic LuFe2O4

Kuepper, K.; Raekers, M.; Taubitz, C.; Prinz, M.; Derks, C.; Neumann, M.; Postnikov, A. V.; de Groot, F. M. F.; Piamonteze, C.; Prabhakaran, D.; Blundell, S. J.

Electronic and magnetic properties of the charge ordered phase of LuFe2O4 are investigated by means of x-ray spectroscopic and theoretical electronic structure approaches. LuFe2O4 is a compound showing fascinating magnetoelectric coupling via charge ordering. Here, we identify the spin ground state of LuFe2O4 in the charge ordered phase to be a 2:1 ferrimagnetic configuration, ruling out a frustrated magnetic state. An enhanced orbital moment may enhance the magnetoelectric coupling. Furthermore, we determine the densities of states and the corresponding correlation potentials by means of x-ray photoelectron and emission spectroscopies, as well as electronic structure calculations.

  • Physical Review B 80(2009)22, 220409

Publ.-Id: 13639

Microbial Links between Sulfate Reduction and Metal Retention in Uranium- and Heavy Metal-Contaminated Soil

Sitte, J.; Akob, D.; Kaufmann, C.; Finster, K.; Banerjee, D.; Burkhardt, E.-M.; Kostka, J.; Scheinost, A.; Büchel, G.; Küsel, K.

Sulfate-reducing prokaryotes (SRP) can affect metal mobility either directly by reductive transformation of metal ions, e.g., uranium and chromium, into their insoluble forms or indirectly by formation of metal sulfides. This study evaluated in situ and biostimulated activity of SRP in groundwater influenced soils from a creek bank contaminated with heavy metals and radionuclides within the former uranium-mining district, Ronneburg (Germany). In situ activity of SRP, measured by the 35S-SO4 2-radiotracer method, was restricted to reduced soil horizons with rates 142 ± 20 nmol cm-3 day-1. Although concentrations of heavy metals were enriched in the solid phase of the reduced horizons, porewater concentrations were low. XANES measurements demonstrated that ~80% of uranium was present as reduced uranium, but appeared to occur as a sorbed complex. Soil-based dsrAB clone libraries were dominated by sequences most closely affiliated to members of the Desulfobacterales, but also Desulfovibrionales, Syntrophobacteraceae and Clostridiales. 13C-acetate and 13C-lactate biostimulated soil microcosms were dominated by sulfate and Fe(III) reduction, which was associated with enrichment of similar SRP found using the dsrAB marker in soil and with sequences related to Geobacter. Concentrations of soluble nickel, cobalt, and occasionally zinc declined 100% during anoxic soil incubations. In contrast to other studies, soluble uranium increased in carbon-amended treatments reaching 1407 nM in solution. Our results suggest that (i) contaminated reduced soil with on-going sulfate reduction resulted in in situ metal attenuation and (ii) the fate of uranium mobility is not predictable and may lead to downstream contamination of adjacent ecosystems.

Keywords: heavy metals; Uranium; XANES; Sulfate-reducing bacteria

Publ.-Id: 13638

Macroscopic thermomagnetic convection: A more generic case and optimization

Cramer, A.; Zhang, X.; Gerbeth, G.

It was demonstrated in a previous paper that the interaction between a thermoelectric current j and an imposed static magnetic field B produced thermoelectromagnetic convection (TEMC). The prominent feature was utilisation of a wall material exhibiting a big difference in the thermoelectric power S in comparison to the fluid. Although high flow velocities were accomplished, the vigour was potentially mitigated by two design issues. Firstly, the side walls parallel to the temperature gradient Grad T were made from the same electrically high conducting material as the isothermal walls. This, in parts, shorts the thermoelectric current. Moreover, these walls might be seen as lowering the degree of the experiment of being generic. Secondly, the field created by a permanent magnet covered only a small fraction of the fluid volume. Again, albeit being mirror symmetric, the three-dimensional distribution of B lowers the degree of being generic.

The present paper reports on an experimental study on TEMC in a square box wherein the necessary Grad T is accomplished by heating and cooling of two opposing side walls, respectively, whereas the other two side walls are electrically non-conducting. An almost two-dimensional distribution of B is applied to a relatively large area of the interface between the fluid and the bottom of the container. The pole shoes of the magnet are specifically designed so as to have a high value of the curl of the Lorentz force, the non-vanishing of which is another pre-requisite for TEMC. Two containers with different bottom materials are build. The ferromagnetic nickel with negative S used in previous work is replaced by isotan in one variant, offering probably the highest absolute value of S among metals. To consider also the counterpart, nichrome with a high positive S is used in the construction of the second container. Ultrasonic Doppler velocimetry is employed to quantify the TEMC flow field. The results of all three configurations are compared and discussed. In addition, first results on more developed turbulent regimes are presented, which could not be reached in the previous setup because of a more limited Delta S x Delta T.

Keywords: Thermoelectricity; convection; liquid metal; electromagnetic stirring; static magnetic field

  • Magnetohydrodynamics 45(2009)4, 505-510

Publ.-Id: 13637

Ultraschnelle Röntgen-Computertomographie für die Untersuchung von Zweiphasenströmungen

Bieberle, M.; Fischer, F.; Hampel, U.

Die am Forschungszentrum Dresden-Rossendorf entwickelte ultraschnelle Röntgen-Computertomographie ist eine nichtinvasive Messmethode, die eine überlagerungsfreie Abbildung von Phasenverteilungen in transienten Zweiphasenströmungen mit bisher unerreichter zeitlicher und räumlicher Auflösung erlaubt. Damit können sicherheitsrelevante Aspekte in technischen Prozessen, beispielsweise aus der Chemie- und Bioverfahrenstechnik, der Mineralölförderung und der Kerntechnik, untersucht sowie CFD-Simulationscodes validiert werden.

Keywords: x-ray; computed tomography; ultrafast imaging; flow measurement

  • Poster
    Ideas to Market - Dresdner Materialinnovationen für die Praxis & Verleihung "Dresden Barkhausen Award 2009", 15.01.2010, Dresden, Deutschland

Publ.-Id: 13636

Anionic and cationic substitution in ZnO

von Wenckstern, H.; Schmidt, H.; Brandt, M.; Lajn, A.; Pickenhain, R.; Lorenz, M.; Grundmann, M.; Hofmann, D.; Polity, A.; Meyer, B. K.; Saal, H.; Binnewies, M.; Börger, A.; Becker, K.-D.; Tikhomirov, V. A.; Jug, K.

In this contribution we review the impact of anionic and cationic substitutions on the electronic properties of bulk ZnO crystals, thin films and ZnO powders. p-type doping is discussed with focus on the anionic substitution of oxygen by nitrogen or phosphorous. n-type doping is exemplarily reviewed for substitution of Zn by group III elements. The impact of isoelectronic substitution of zinc (with Cd or Mg) or of oxygen (with S, Se, Te) on the band gap are also discussed for the respective ternary alloy. The substitution of Zn by the transition metal Mn introduces several electronic levels in the band gap which significantly alter the absorption and emission properties. Further, devices based on substitutional effects in ZnO are reviewed: Schottky diodes (unipolar device) and pn-diodes (bipolar device).


Publ.-Id: 13635

Excited-state proton transfer of 3-hydroxybenzoic acid and 4-hydroxybenzoic acid

Vulpius, D.; Geipel, G.; Bernhard, G.

The excited-state proton transfer of 3-hydroxybenzoic acid and 4-hydroxybenzoic acid was studied by time-resolved laser-induced fluorescence spectroscopy with ultra-short laser pulses. The excited-state reactions were identified in aqueous media as a function of the pH value. Apart from the well-known inversion of the ordinary dissociation properties of these compounds, new species were found which exist only in the excited-state resulting from a temporal and reversible annihilation of the aromatic bond system. These species and their reaction mechanisms were detected by their absorption and fluorescence spectra.

Keywords: 3-Hydroxybenzoic acid; 4-Hydroxybenzoic acid; Excited-state proton transfer; Time-resolved laser-induced fluorescence; spectroscopy

Publ.-Id: 13634

Vergleich von Fluorierungstechniken zur industriellen Anwendung des Halogeneffekts mit kernphysikalischen Verfahren

Neve, S.; Masset, P. J.; Yankov, R. A.; Zschau, H.-E.; Kolitsch, A.; Dörner, R.; Schütze, M.

Ein Hochtemperatur-Oxidationsschutz von Titanaluminiden kann durch Verwendung des Halogen-Effektes realisiert werden. Fluor erwies sich dabei als am besten geeignet, insbesondere bei termozyklischer Beanspruchung. Unter isothermen wie auch zyklischen Bedingungen ist die schützende Wirkung der sich bildenden Aluminiumoxidschicht für bis zu 4000 h bei 900° - 1050°C experimentell gezeigt werden. Als Technik zur Einbringung der Halogene unter die Metalloberfläche wurde die Beamline-Ionenimplantation intensiv untersucht. Die Größe des Strahlfleckes beträgt nur etwa 10 cm2 und bei der komplexen Geometrie der zu Behandelnden Bauteile kann ein einheitlicher Einschusswinkel nicht realisiert werden. Chemische Behandlungen, wie das Tauchen in verdünnter HF-Lösung, sind diffusionsgesteuert und damit weiterstehend unabhängig von der vorliegenden Bauteilgeometrie. Bei der kontrollierten Gasphasenfluorierung wurden die Fluorionen durch die thermische Zersetzung einer einer CFn-Verbindung erzeugt. Bei der am Forschungszentrum Dresden-Rossendorf durchgeführten Plasma-Immersions-Ionenimplantation (PIII) werden die Fluorinen von einem CH2F2/Ar-Plasma bereitgestellt. Die PIII Methode soll als Referenztechnik für die Behandlung komplexer Geometrien eingesetzt werden, da die Parameter genau kontrolliert werden können. Am IKF wurden dazu die Protonen induzierte Gamma-Emission (PIGE) und Rutherford Basckscattering (RBS) am 2.5 MV van de Graaf-Beschleuniger eingesetzt. Mit der PIGE können Fluorkonzentrationen mit einer Genauigkeit besser als 7% gemessen werden.

  • Contribution to external collection
    in: Jahresbericht 2009 des Instituts für Kernphysik der Goethe-Universität Frankfurt, Frankfurt am Main: Goethe-Universität Frankfurt, 2009

Publ.-Id: 13633

Surface modification of Ti and low Al-content Ti alloys for enhanced environmental stability at elevated temperatures

Yankov, R. A.; Kolitsch, A.; von Borany, J.; Munnik, F.; Donchev, A.; Schütze, M.

It is now well-established that TiAl alloys containing Al between about 40 and 55 at.% may be modified by introducing a halogen element, notably F, into their near-surface region (the so-called halogen effect) to protect them against high-temperature environmental degradation. Upon subsequent high-temperature oxidation, the TiAl alloys modified in this way acquire а highly protective alumina scale, and are suitable for advanced automobile, aerospace and power generation applications. Low-Al content (typically < 10 at.%) Ti alloys, however, contain insufficient amounts of Al for the halogen effect to be activated necessitating enrichment with Al of their near-surface region. In this work, both α-Ti and low-Al content Ti alloys have been processed to render them oxidation-resistant in air at temperatures of 600 to 1050°C by promoting the formation of a protective scale. Surface processing has generally involved two steps, namely Al enrichment and introduction of F. The Al enrichment has in turn involved deposition of a thin Al film by magnetron sputtering followed by either Ar ion bombardment or rapid thermal annealing. The introduction of F has been achieved by plasma immersion ion implantation. Analytical techniques such as ERDA, RBS, XRD, SEM and EDX have been used for sample characterization. Under optimized processing conditions the metal samples so modified have shown high-temperature environmental stability comparable to that of standard TiAl (40 < Al < 55 at.%) alloys.

  • Poster
    Surface modification of Ti and low Al-content Ti alloys for enhanced environmental stability at elevated temperatures, 08.-12.06.2009, Strasbourg, France

Publ.-Id: 13632

Comparison of fluorination treatments to improve the high temperature oxidation resistance of TiAl alloys in SO2-containing environments

Masset, P. J.; Yankov, R. A.; Kolitsch, A.; Schütze, M.

Surfaces of titanium aluminides were treated with fluorine either physically by plasma immersion ion implantation (PIII) or chemically using a F-based polymer. Under optimum conditions of fluorination, both treatments were shown to improve the oxidation resistance of the alloys even in aggressive environments containing sulfur dioxide (0.1 vol. %). No sulfur was detected in the oxide scale although thermodynamic calculations predict the formation of sulfides. The inward diffusion of oxygen and nitrogen was found to be reduced in the presence of SiO2.

  • Lecture (Conference)
    International Conference on PROCESSING & MANUFACTURING OF ADVANCED MATERIALS (THERMEC 2009), 25.-29.08.2009, Berlin, Germany

Publ.-Id: 13631

Oxidation resistance improvement of TiAl alloys by the halogen effect in industrial environments

Masset, P. J.; Neve, S.; Zschau, H.-E.; Yankov, R. A.; Kolitsch, A.; Schütze, M.

No abstract available.

  • Poster
    European Congress and Exhibition on Advanced Materials and Processes EUROMAT’09, 07.-10.09.2009, Glasgow, United Kingdom

Publ.-Id: 13630

Enhancing the resistance of Ti-alloys against environmental high temperature degradation by a combination of Al-enrichment and F-treatment

Donchev, A.; Kolitsch, A.; Schütze, M.; Yankov, R.

Titanium is a widely used structural material due to its low specific weight, mechanical properties and good corrosion resistance at low temperatures. The melting point (1677°C) is much higher than the maximum operating temperature of about 600°C. Because of increased oxidation rate and environmental embrittlement Ti-Alloys can not be used at higher temperatures. The surface treatment with F gives very good results for TiAl-alloys but has only little or no effect on the oxidation resistance of Ti-alloys. Enrichment of the near-surface zone of Ti-alloys with Al leads to an improvement in the oxidation resistance which, however, is insufficient. The combination of Al-enrichment in the surface zone so that a TiAl-layer is formed, and an additional F-treatment gives good results. The fluorine effect on TiAl-alloys leads to the formation of a protective alumina scale. Not only does the scale provide protection against environmental attack, but it also prevents oxygen inward diffusion which causes embrittlement. In this work results of high temperature oxidation tests several Ti-alloys (-Ti, Ti3Al, etc.) are presented without any treatment, single Al-treatment, pure F-treatment and the combination of both. Enrichment with Al has been done by either powder pack process or magnetron sputtering. Fluorine has been introduced using a liquid phase process as well as alternative techniques. Subsequent analyses by SEM and other methods reveal the formation of thinner oxide layer on the combined Al and F treated samples.

  • Lecture (Conference)
    European Congress and Exhibition on Advanced Materials and Processing EUROMAT’09, 07.-10.09.2009, Glasgow, United Kingdom

Publ.-Id: 13629

Combined Al- plus F-treatment of Ti-alloys for improved behaviour at elevated temperatures

Donchev, A.; Kolitsch, A.; Schütze, M.; Yankov, R.

Due to its low weight and good corrosion resistance at moderate temperatures, titanium is being currently used in a large number of applications. As a result of increased oxidation rate and environmental embrittlement the maximum operating temperature is only about 600°C while the melting point is much higher (1677°C). The oxidation behaviour can be improved by different methods e.g. Al-enrichment of the surface zone. This leads to an improvement which is, however, not sufficient. The combination of Al-enrichment in the surface zone so that a TiAl-layer is formed plus an additional F-treatment gives the best results because a protective alumina scale is formed. The fluorine effect is known for TiAl-alloys. An alumina scale is found on TiAl-alloys after F-treatment. This alumina scale prevents oxygen inward diffusion which causes embrittlement and protects the material against environ-mental attack. Now this effect is transferred to alloys with a very low Al-content or even no Al at all. These alloys can not form an alumina layer by themselves without any treatment. In this work results of oxidation tests of several Ti-alloys (-Ti, Ti3Al, etc.) are presented without any treatment and with Al-treatment, F-treatment and the combination of both. Aluminium was diffused into the samples by a powder pack process. Fluorine can be applied by several ways e.g. ion implantation or gas phase processes. The formation of a thinner oxide scale on treated samples is revealed by post experimental investigations like metallography. The results are discussed referring to the fluorine effect model for TiAl-alloys.

  • Poster
    European Federation of Corrosion Workshop, 30.09.-02.10.2009, Frankfurt am Main, Germany
  • Materials and Corrosion 62(2011)7, 695-698
    DOI: 10.1002/maco.201005870

Publ.-Id: 13628

Study of the role of sulfur functionalities in humic acids for uranium(VI) complexation

Sachs, S.; Reich, T.; Bernhard, G.

Sulfur containing humic acid model substances have been synthesized to study the role of sulfur functionalities for the complexation behavior of humic acids towards U(VI). Humic acids type M1-S with different sulfur contents (1.9, 3.9, 6.9 wt.-%) were synthesized and characterized. The identity of the sulfur species was determined by X-ray photoelectron spectroscopy (XPS). Reduced sulfur species, such as thiols, dialkylsulfides and/or disulfides, were determined as the dominating sulfur functionalities in the used humic acids. The U(VI) complexation of humic acids with different sulfur contents has been studied by time-resolved laser-induced fluorescence spectroscopy (TRLFS) and TRLFS with ultrashort femtosecond laser pulses (fs-TRLFS) in comparison to a sulfur-free humic acid type M1 (pH 3.80 ± 0.02; I = 0.1 M NaClO4; pCO2 = 10-3.5 atm). For all studied humic acids, similar complexation constants were determined. However, with increasing sulfur contents of the humic acids (>2 wt.-%) an increase of the number of humic acid binding sites for U(VI) was determined which is reflected in increasing U(VI) loading capacities and increasing total humic acid ligand concentrations for U(VI) measured by TRLFS and fs-TRLFS, respectively. This increase of the fraction of humic acid binding sites for U(VI) points to an involvement of reduced sulfur functionalities, such as thiol groups, in the complexation between U(VI) and humic acid. However, for environmentally relevant sulfur contents of humic acids (<2 wt.-%) it can be concluded that, compared to oxygen functionalities, especially carboxylic groups, reduced sulfur functionalities play only a subordinate role for the U(VI) complexation by humic acids in the acidic pH range.

Keywords: Humic acid; humic acid model substances; complexation; sulfur functionalities; uranium(VI); XPS; TRLFS; fs-TRLFS

Publ.-Id: 13627

Spin-dependent transport in C:Co and C:Ni nanocomposite thin films

Zhou, S.; Berndt, M.; Buerger, D.; Abrasonis, G.; Radnoczi, G.; Schmidt, H.; Kolitsch, A.; Helm, M.

Nanocomposites exhibiting spin-dependent transport properties show a potential for applications in spintronics. Carbon:transition metal nanocomposites are of particular interest due to their multifunctionality and easiness to control their morphology, and thus properties. In this contribution, we present the study of magneto-transport properties of C:Co and C:Ni nanocomposites. The films were grown by ion beam co-sputtering on thermally oxidized silicon substrates in the temperature range of 200-500°C. Two major effects have been found for C:Co films: (i) a large anomalous Hall effect amounting to 2 micro-Ohm-cm; (ii) a negative magnetoresistance. Both the field-dependent resistivity and Hall resistivity curves well correspond to the magnetization curve, which suggests a spin-dependent transport in the nanocomposite thin films. A similar effect is also reported for C:Ni nanocomposite films. A correlation is reported between the magneto-transport properties and the film microstructure.

  • Poster
    2009 MRS Fall Meeting, 30.11.-04.12.2009, Boston MA, USA

Publ.-Id: 13626

Analysis of non-protein amino acids as specific markers of protein oxidation: the use of N(O,S)-ethoxycarbonyl ethyl ester and N(O,S)-ethoxycarbonyl trifluoroethyl ester derivatives and GC-MS

Pietzsch, J.; Pietzsch, F.-J.; Kopprasch, S.

Oxidative modification of proteins is widely regarded as a crucial event in the pathogenesis of various inflammatory and metabolic diseases. In this line, a sensitive and specific GC-MS methodology using either N(O,S)-ethoxycarbonyl ethyl amino acid esters (ECEE) or N(O,S)-ethoxycarbonyl trifluoroethyl amino acid esters (ECEE-F3) for rapid and sensitive determination of modified amino acid side chain residues as specific oxidation markers in proteins has been developed.
Both ECEE and ECEE-F3 derivatives are formed by the unlabored reaction of amino acids with ethyl chloroformate plus ethanol or trifluoroethanol plus pyridine. The key steps of the methodology involve enzymatic hydrolysis of target proteins to prevent decomposition of oxidation products during hydrolysis and uniquely rapid derivatization of modified amino acids completing sample preparation for GC within a few minutes in aqueous solution at room temperature. The use of this methodology for assessing (glyc)oxidative damage in low density lipoprotein apolipoprotein B-100 (apoB-100) recovered from human plasma and various inflammatory compartments has been demonstrated. The observations provided quantitative chemical evidence for (glyc)oxidative processes in several inflammatory and metabolic diseases.

  • Trends in Chromatography 5(2009), 15-20

Publ.-Id: 13625

Mild glykatierte Lipoproteine > geringer Dichte (LDL) verstärken die Adipogenese von 3T3-L1-Zellen

Neuber, C.; Hoppmann, S.; Pietzsch, J.

Diabetes mellitus Typ 2 (T2D) und Adipositas sind zwei wichtige Facetten des Metabolischen Syndroms. Ein pathobiochemisches Bindeglied zwischen beiden Erkrankungen ist möglicherweise die Bildung glykatierter Lipoproteine geringer Dichte (glykLDL), einer frühen Form der advanced glycation endproducts (AGE). Ziel der Untersuchung war es, zu zeigen, ob und über welche Mechanismen glykLDL im Vergleich zu nativen LDL (nLDL) einen Einfluss auf die Adipogenese ausüben.
Durch Inkubation humaner LDL mit Glukose (200 mmol/L, 37°C, 144 h) konnten glykative Veränderungen am Apolipoprotein B-100 der LDL-Partikel erreicht werden, die vergleichbar zu den bei Patienten mit manifestem T2D in vivo auftretenden Veränderungen von LDL sind. Als Modell für die humane Adipogenese diente die hormoninduzierte Umwandlung muriner 3T3 L1-Präadipozyten zu Zellen, die morphologisch und physiologisch reifen Adipozyten ähneln. Mittels quantitativer RT PCR und Western Blotting wurde der Einfluss glykatierter LDL auf die mRNA Expression und Proteinbiosynthese verschiedener (Prä )Adipozytenmarker sowie potentieller glykLDL Rezeptoren untersucht. Darüber hinaus erfolgten Untersuchungen zur zellvermittelten Aufnahme von Fluor-18-markierten LDL.
Es konnte gezeigt werden, dass glykLDL die Lipideinlagerung, als Zeichen der Differenzierung von Präadipozyten zu Adipozyten, signifikant verstärkten, während es unter dem Einfluss der nLDL zu einer signifikant verminderten Adipogenese kam, die sich tendenziell auch in einer verminderten mRNA-Expression des Adipozytenmarkers PPAR2 zeigte. Als potenzielle Mediatoren der LDL-induzierten Effekte wurden sowohl der LDL-Rezeptor (LDLR), der Rezeptor für AGE (RAGE) als auch verschiedene Scavenger-Rezeptoren (SR) näher charakterisiert. Die Untersuchungen mit Fluor-18-markierten LDL zeigten, dass Präadipozyten etwa zehnmal mehr nLDL bzw. glykLDL internalisierten als Adipozyten, wobei die Bindung und Internalisierung von nLDL etwa um den Faktor zwei über der von glykLDL lag. Dies deutet auf eine verminderte Affinität der glykLDL beispielsweise zum LDLR hin. Obwohl glykLDL in vitro und in vivo Liganden für RAGE sind, spielte RAGE bei der Differenzierung von 3T3-L1-Zellen nur eine untergeordnete Rolle. Die Differenzierung von Präadipozyten zu Adipozyten ging mit einer unveränderten SR-B1- sowie mit einer verminderten LDLR-, RAGE-, CD36- und LOX-1-(lectin like oxidized LDL-1)-Rezeptor-Synthese einher. In Kombination mit den Ergebnissen der Zellaufnahmestudien wird deutlich, dass vorrangig der LDLR, der SR-B1 und möglicherweise auch LOX-1 für die Internalisierung der LDL von Bedeutung sind.
Als mögliche intrazelluläre Mechanismen für die glykLDL-induzierte Stimulation der Lipideinlagerung werden die Aktivierung des NF-κB oder des nukleären Leber-X-Rezeptors (LXR) diskutiert. Aus den Ergebnissen der vorliegenden Arbeit lässt sich schlussfolgern, dass bereits mild glykatierte LDL-Partikel die Adipogenese verstärken.

  • Poster
    25. Jahrestagung der Deutschen Adipositas-Gesellschaft und Herbsttagung der Deutschen Diabetes-Gesellschaft, 05.-07.11.2009, Berlin, D
  • Abstract in refereed journal
    AdipositasSpektrum 5(2009), 67

Publ.-Id: 13624

Long lifetimes of quantum-dot intersublevel transitions in the terahertz range

Zibik, E. A.; Grange, T.; Carpenter, B. A.; Porter, N. E.; Ferreira, R.; Bastard, G.; Stehr, D.; Winnerl, S.; Helm, M.; Liu, H. Y.; Skolnick, M. S.; Wilson, L. R.

Carrier relaxation is a key issue in determining the efficiency of semiconductor optoelectronic device operation. Devices incorporating semiconductor quantum dots have the potential to overcome many of the limitations of quantum-well-based devices because of the predicted long quantum-dot excited-state lifetimes. For example, the population inversion required for terahertz laser operation in quantum-well-based devices (quantum-cascade lasers1, 2) is fundamentally limited by efficient scattering between the laser levels, which form a continuum in the plane of the quantum well. In this context, semiconductor quantum dots are a highly attractive alternative for terahertz devices, because of their intrinsic discrete energy levels. Here, we present the first measurements, and theoretical description, of the intersublevel carrier relaxation in quantum dots for transition energies in the few terahertz range. 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), in very good agreement with our microscopic theory of the carrier relaxation process. Our studies pave the way for quantum-dot terahertz device development, providing the fundamental knowledge of carrier relaxation times required for optimum device design.

Keywords: THz; FEL; Quantum Dots

Publ.-Id: 13623

Experimental investigations on the condensation of steam bubbles injected into sub-cooled water at 1 MPa

Lucas, D.; Beyer, M.; Szalinski, L.

Bubble condensation plays an important role e.g. in sub-cooled boiling or steam injection into pools. Since the condensation rate is proportional to the interfacial area density, bubble size distributions have to be considered in an adequate modelling of the condensation process. To develop and validate closure models for CFD codes new experimental data are required. The effect of bubble sizes is clearly shown in experimental investigations done at the TOPFLOW facility of FZD. Steam bubbles are injected into a sub-cooled upward pipe flow via orifices in the pipe wall located at different distances from measuring plane. 1 mm and 4 mm injection orifices are used to vary the initial bubble size distribution. The variation of the distance between the location of the gas injection and the measuring plane allows investigating the evolution of the flow along the pipe. Measurements are done using wire-mesh sensors and thermocouples. Condensation is clearly faster in case of the injection via the smaller orifices, i.e. in case of smaller bubble sizes. Data on averaged void fraction, radial gas volume fraction profiles, profiles of the gas velocity and bubble size distributions in dependency of the L/D ratio are presented in the paper.

Keywords: bubble condensation; poly-dispersed flow; bubble size; pipe flow; experiment; CFD grade data

Publ.-Id: 13622

Electroluminescence induced by Ge nanocrystals obtained by hot ion implantation into SiO2

Bregolin, F.; Behar, M.; Sias, U.; Reboh, S.; Lehmann, J.; Rebohle, L.; Skorupa, W.

Commonly, electroluminescence (EL) from Ge nanocrystals (Ge NCs) has been obtained by room temperature (RT) Ge implantation into a SiO2 matrix followed by a high temperature anneal. In the present work, we have used a novel experimental approach: we have performed the Ge implantation at high temperature (T-i) and subsequently a high temperature anneal at 900 degrees C in order to grow the Ge NCs. By performing the implantation at T-i=350 degrees C, the electrical stability of the MOSLEDs were enhanced, as compared to the ones obtained from RT implantation. Moreover, by changing the implantation fluence from Phi=0.5 x 10(16) and 1.0 x 10(16) Ge/cm(2) we have observed a blueshift in the EL emission peak. The results show that the electrical stability of the hot implanted devices is higher than the ones obtained by RT implantation. (C) 2009 American Institute of Physics.

Keywords: Electroluminescence; Ge nanocluster; high temperature implantation

  • Journal of Applied Physics 106(2009)10, 106103

Publ.-Id: 13621

Free-space propagation of radially and azimuthally polarized terahertz Bessel-Gauss beams

Winnerl, S.; Zimmermann, B.; Hubrich, R.; Peter, F.; Schneider, H.; Helm, M.

Radially polarized Bessel-Gauss beams have interesting properties like smaller spot sizes in the focus as compared to linearly polarized beams, and longitudinal field components. These properties have been studied for
visible and near-infrared beams. In the THz range, radially polarized beams have been studied as plasmonically guided modes on metal wires, so called Sommerfeld modes. Recently a first experiment on free space
propagation of radially polarized beams, generated via velocity mismatched optical rectification in (100)-oriented ZnTe, was reported. Here we present microstructured emitters for radially and azimuthally polarized
beams, study for the first time the divergence of the beams behind the emitter and record transverse and longitudinal components of the beams in the focus.

Keywords: Terahertz; vector beams; Bessel-Gauss beams

  • Lecture (Conference)
    Conference on Lasers and Electro-Optics - European Quantum Electronics Conference, 14.-19.06.2009, München, Deutschland
  • Contribution to proceedings
    Conference on Lasers and Electro-Optics - European Quantum Electronics Conference, 14.-19.06.2009, München, Deutschland
    Conference Digest of the Conference on Lasers and Electro-Optics - European Quantum Electronics Conference

Publ.-Id: 13620

Nachweis von Östrogen- wirkenden Substanzen in wässrigen Lösungen

Cherkouk, C.; Rebohle, L.; Skorupa, W.; Helm, M.

In dieser Arbeit wird ein Sensorkonzept zum Nachweis von Östrogen-wirkenden Substanzen in wässrigen Lösungen vorgestellt. Das Kernstück des Sensors ist eine auf Chipebene integrierte Lichtquelle, die zur Fluoreszenzanalyse der Probe benutzt wird. Dieser Lösungsansatz ermöglicht eine deutliche Reduzierung der Geräteabmessungen, verbunden mit einer entsprechenden Ersparnis an Ressourcen, Energie und Herstellungskosten. Zur Realisierung des gesamten Konzepts wurde ein neues Verfahren entwickelt, das die Chipoberfläche einfach und effizient modifiziert.
Dies ermöglicht das Aufbringen einer an der Chipoberfläche kovalent gebundenen Bio-Schicht, die überwiegend aus APS (N,N´-Bis(3-aminopropyl)-2-butene-1,4-diamine)) Silanegruppen besteht. Der spätere Östrogenrezeptor hER(alpha) soll über funktionelle Aminogruppen adsorbiert werden.
Diese Oberflächenmodifizierung der Chips wurde mittels Infrarot-Spektroskopie (FTIR) charakterisiert. Dabei wurde die stabile Haftung der Silanegruppen durch die als Anker dienenden Methoxygruppen an der Chipoberfläche verifiziert. Weitere Untersuchungen sowohl zur chemischen Zusammensetzung als auch zur Rauhigkeit der Oberfläche wurden mit Hilfe von Röntgen-Photoemissionsspektroskopie (XPS) und der Rasterkraftmikroskopie (AFM) durchgeführt. Schließlich wurde mittels Elektrolumineszenzmessungen die Wechselwirkung zwischen der Si- basierten Lichtemission und dem an den Bio- Schicht adsorbierten Farbstoff getestet.

Keywords: Sensorkonzept; Östrogen-wirkenden; Fluoreszenzanalyse; Bio-Schicht; Silanegruppen; Östrogenrezeptor hER(alpha); Oberflächenmodifizierung

  • Poster
    6. Deutsches BioSensor Symposium in Freiburg (LOC-Lab-on-a-Chip und Point-of-Care Diagnostik), 30.03.-01.04.2009, Freiburg, Deutschland

Publ.-Id: 13619

Radiale Moden in THz-Feldern

Hubrich, R.

Die im Forschungszentrum Dresden-Rossendorf entwickelten skalierbaren Emitter liegen nicht nur, wie aus der Literatur bekannten, in linearen Form vor, sondern werden auch mit anderen
Elektrodenstrukturen gefertigt. Durch einen radial-symmetrischen Emitter z.B. wird laut Theorie eine stärkere Fokussierung der THz-Strahlung möglich sein [2]. Ein Schwerpunkt bei
den Untersuchungen liegt in der Ermittlung der Moden bzw. der Strahlungsprofile der radialen Emitterstrukturen. Dabei werden mittels EOS sowohl die transversale, als auch die longitudinale
Komponente des THz-Feldes untersucht. Erstmals wurden dafür in unserer Forschungsgruppe THz-Linsen aus TPX verwendet, die das Strahlprofil weniger deformieren, als herkömmliche

Keywords: terahertz; emitters; vector beams

  • Lecture (Conference)
    Drittes THz-Frischlinge-Meeting 2009, 07.-10.06.2009, Berlin, Deutschland

Publ.-Id: 13618

Photoconductive Emitters and Detectors for Radially and Azimuthally Polarized Terahertz Beams

Winnerl, S.; Zimmermann, B.; Hubrich, R.; Peter, F.; Schneider, H.; Helm, M.

Photoconductive emitters and detectors are reviewed, advantages of scalable devices are discussed and new developements for radially and azimuthally polarized terahertz beams are presented.

Keywords: terahertz; emitters; detectors; vector beams

  • Lecture (Conference)
    GDR-E Workshop "Semiconductor sources and detectors of THz radiation", 16.-17.11.2009, Montpellier, France

Publ.-Id: 13617

On the difference of 3D and 4D in-beam PET for a periodically moving target

Laube, K.; Bert, C.; Chaudhri, N.; Fiedler, F.; Parodi, K.; Rietzel, E.; Saito, N.; Enghardt, W.

no abstract available

Keywords: in-beam PET; moving targets; ion beam therapy

  • Contribution to external collection
    Katrin Große: GSI Scientific Report 2009, Darmstadt: GSI Helmholtzzentrum für Schwerionenforschung, 2010, 503-503

Publ.-Id: 13616

The impact of FMISO hypoxic volume on local control after single dose irradiation in FADU HNSCC in nude mice

Schütze, C.; Bergmann, R.; Mosch, B.; Yaromina, A.; Hessel, F.; Krause, M.; Thames, H. D.; Zips, D.; Mäding, P.; Baumann, M.; Beuthien-Baumann, B.

kein Abstract verfügbar

  • Poster
    ICTR 2009 - Fourth International Conference on Translational Research in Radiation Oncology, 11.-13.03.2009, Genf, Schweiz

Publ.-Id: 13615

Characterization of ZnO nanostructures: A challenge to positron annihilation spectroscopy and other methods

Brauer, G.; Anwand, W.; Grambole, D.; Egger, W.; Sperr, P.; Beinik, I.; Wang, L.; Teichert, C.; Kuriplach, J.; Lang, J.; Zviagin, S.; Cizmar, E.; Ling, C. C.; Hsu, Y. F.; Xi, Y. Y.; Chen, X.; Djurisic, A. B.; Skorupa, W.

ZnO nanostructures are of special interest for device applications.
However, their structural characterization remains an ongoing challenge.
This paper reviews recent efforts and latest achievements in this direction. Results comprise PAS in the form of Slow Positron Implantation Spectroscopy (SPIS) and Pulsed Low Energy Positron Lifetime Spectroscopy (PLEPS), Nuclear Reaction Analysis (NRA), Atomic Force Microscopy (AFM), conductive AFM (C-AFM), Nuclear Magnetic Resonance (NMR), Electron Spin Resonance (ESR), Photoluminescence (PL) spectroscopy, and latest theoretical investigations of structure-related and positron properties of selected defects. The fundamental importance of a relationship between fabrication conditions, native defect formation, and resulting optical and electronic properties is demonstrated by getting either inferior (nanorods) or significantly improved (tetrapods) optical properties compared to single crystal samples, depending on the nanostructure fabrication method.

  • Physica Status Solidi (C) 6(2009)11, 2556-2560

Publ.-Id: 13614

Radiolabeled Cdk4/6 inhibitors for molecular imaging of tumors

Graf, F.; Köhler, L.; Mosch, B.; Pietzsch, J.

Overexpression of cell-cycle regulating cyclin-dependent kinases 4 and 6 (Cdk4/6) and deregulation of Cdk4/6-pRb-E2F pathway are common aspects in human tumors. The aim of our study was the evaluation of pyrido[2,3 d]pyrimidin-7-one derivatives (CKIA and CKIE) concerning their efficacy and suitability as small molecule Cdk4/6 inhibitors and, after iodine-124 ([124I]CKIA) or fluorine-18 ([18F]CKIE) radiolabeling, as radiotracers for Cdk4/6 imaging in tumors by positron emission tomography (PET).
CKIA and CKIE were analyzed concerning their biological properties (effects on cell growth, cell cycle distribution, Cdk4/6 mediated pRb-Ser780 phosphorylation, mRNA expression of pRb affected genes E2F-1 and PCNA) and radiopharmacological properties (cellular radiotracer uptake and PET studies) using human tumor cell lines HT-29, a colorectal adenocarcinoma cell line, FaDu, a head and neck squamous cell carcinoma cell line, and THP-1, an acute monocytic leukemia cell line, as well as phorbol ester TPA-activated THP-1 cells, as model of tumor-associated macrophages.
CKIA and CKIE were identified as potent inhibitors of Cdk4/6-pRb-E2F pathway due to decreased Cdk4/6 specific phosphorylation at pRb Ser780 and downregulation of E2F-1 and PCNA mRNA expression in HT-29, FaDu and THP-1 tumor cells. This resulted in arrest of these tumor cell lines in G1 phase of the cell cycle and growth inhibition. Otherwise, in non-proliferating TPA-activated THP-1 macrophages no change of cell-cycle distribution after treatment with CKIA and CKIE was observed. Furthermore, TPA-activated THP-1 macrophages showed lower Cdk4 mRNA and protein levels, than other tumor cell lines. In vitro radiotracer uptake studies using [124I]CKIA and [18F]CKIE demonstrated tumor cell uptake, which could be blocked with both nonradioactive CKIA and CKIE. However, THP-1 macrophages showed similar radiotracer uptake like other tumor cells. Preliminary small animal PET studies in mouse tumor xenograft models further analyzed the hypothesis that radiolabeled Cdk4/6 inhibitors are suitable tracers for molecular imaging of tumors

  • Open Access Logo Abstract in refereed journal
    Cancer Microenvironment 2(2009), S185
  • Poster
    5th International Conference On Tumor Microenvironment: Progression, Therapy & Prevention, 20.-24.10.2009, Versailles, France

Publ.-Id: 13613

Irradiation-induced changes in metabolism and metastatic properties of melanoma cells

Mosch, B.; Müller, K.; Steinbach, J.; Pietzsch, J.

As it is known that irradiation can influence cellular metabolism it is conceivable that it can induce metabolic changes which lead to a predisposition of certain cells to show enhanced survival, migratory activity and metastasis. The aim of this study was to investigate short term and long term irradiation effects on proliferation and metabolism of melanoma cells in vitro and their ability to form metastases in vivo.
B16-F10 melanoma cells were irradiated with different doses of X-ray irradiation in the range of 1 to 20 Gy. One, two, and three days (short term effects) and, furthermore, 7, 14 and 21 days (long term effects) after treatment cells were analyzed concerning cell growth, proliferation, viability, glucose and amino acid transport. Additionally, we performed in vivo studies in a syngeneic mouse model to analyze the capability of irradiated melanoma cells to form lung metastases.
The analysis of short term effects showed decreased cell growth, viability and arrest in the G2/M phase of the cell cycle while glucose transport is increased. Long term effects involve recovered proliferation, accompanied by increased glucose transport and decreased viability and amino acid transport. In vivo studies showed loss of metastasis immediately after irradiation and reduced metastasis if cells were allowed to recover proliferation before injection.
We conclude that melanoma cells as short term response to irradiation show cell cycle arrest and impairment in growth and viability. Three days after irradiation compensatory mechanisms start, leading to recovered growth within three weeks. Studies concerning metabolic properties indicate that a subpopulation of surviving melanoma cells compensate for the initial irradiation-induced damage possibly by metabolic modulations such as increase in glycolysis. As metastasis in vivo is impaired beyond recovered cell proliferation, the role of adjusted cell metabolism and additional extrinsic factors is strongly suggested.

  • Open Access Logo Abstract in refereed journal
    Cancer Microenvironment 2(2009), S150-S151
  • Poster
    5th International Conference on Tumor Microenvironment: Progression, Therapy & Prevention, 20.-24.10.2009, Versailles, France

Publ.-Id: 13612

Changes in metabolism and metastatic properties of melanoma cells after X-ray irradiation

Mosch, B.; Müller, K.; Steinbach, J.; Pietzsch, J.

Background: Malignant melanoma has the ability to form metastases at very early stages and in addition to surgical resection treatment involves immunotherapy, chemotherapy and also radiotherapy. As it is known that irradiation can influence cellular metabolism it is conceivable that it can induce metabolic changes which lead to a predisposition of certain cells to show enhanced survival, migratory activity and metastasis. The aim of this study was to investigate short term and long term irradiation effects on metabolism and proliferation of irradiated melanoma cells in vitro and their ability to form metastases in vivo.
Material and methods: B16-F10 melanoma cells were irradiated with different doses of X-ray irradiation in the range of 1 to 20 Gy. One, two, and three days (short term effects) and, furthermore, 7, 14 and 21 days (long term effects) after treatment cells were analyzed concerning cell growth, viability, proliferation, cell cycle distribution, glucose and amino acid transport. Additionally, we performed in vivo studies in a syngeneic mouse model to analyze the capability of irradiated melanoma cells to form lung metastases.
Results: The analysis of short term effects showed decreased cell growth, viability and arrest in the G2/M phase of the cell cycle. Long term effects involve increase in proliferation, cell growth and glucose uptake but still decreased viability and amino acid transport. Our in vivo studies showed no formation of lung metastases when cells were irradiated before injection. If irradiated cells were allowed to recover for 2 weeks before injection, mice again developed lung metastases although to a lesser extent than control mice.
Conclusions: We conclude that melanoma cells as short term response to irradiation show cell cycle arrest and decrease in cell viability, growth and metabolic properties. One to three weeks after irradiation, the re-start of proliferation and recurrence of metabolic properties such as glucose uptake indicate that a subpopulation of surviving melanoma cells compensate for the initial irradiation-dependent damage possibly by metabolic modulations such as increase in glycolysis. Furthermore, in vivo studies reveal that irradiated melanoma cells are able to resume their metastatic potential within two weeks. As lung metastasis is lower when using recovered cells versus untreated cells, the role of additional mechanisms is strongly suggested.

  • Abstract in refereed journal
    European Journal of Cancer 7(2009), 587
  • Poster
    ECCO 15 - 34th ESMO Multidisciplinary Congress, 20.-24.09.2009, Berlin, D

Publ.-Id: 13611

Influence of irradiation on the metabolism of melanoma cells and metastasis in mice.

Mosch, B.; Müller, K.; Steinbach, J.; Pietzsch, J.

Irradiation is a powerful tool for the therapy of solid tumors. But often single cells elude this treatment and constitute a basis for recurrence of the primary tumor and formation of metastases. Until today it is unclear which properties enable some cells to this. One possible explanation could be predicted on irradiation-dependent metabolic changes which lead to a predisposition of certain cells to show enhanced survival and migratory activity. The aim of this study was to investigate metabolic properties and proliferation of irradiated melanoma cells in vitro and their ability to form metastases in vivo.
We applied different single-dose X-ray irradiation (200kV X-rays, 0.5mm Cu, ~ 1.2 Gy min-1; 1, 2, 5, 7, 10, and 20 Gy) to murine B16-F10 melanoma cells. At particular times we analyzed cell viability, growth properties and cell cycle distribution. Furthermore, we analyzed the cellular uptake of the radiotracers 2-[18F]fluoro-2-deoxy-D-glucose ([18F]FDG) and 3-O-methyl-[18F]fluoro-L-DOPA ([18F]OMFD), providing information about the glucose and amino acid metabolism before and after irradiation. Additionally, we performed in vivo studies in a syngeneic mouse model to analyze the capability of irradiated melanoma cells to form lung metastases after injection into the tail vein of NMRI mice.
In a dose-dependent manner we detected a decrease in cell viability and cell growth properties starting 3 days after irradiation. Decreased cell growth persists up to 1 week for 5 Gy irradiated cells and up to 2 weeks for 10 Gy irradiated cells. After this periods growth of irradiated cells is comparable to control cells. Cell cycle analyses showed an increase in G2/M phase cells up to 3 days after X-ray followed by an increase in S phase cells 6 days after X-ray. At this point of time uptake of radiotracers was altered inasmuch as [18F]FDG uptake decreased, whereas [18F]OMFD uptake increased. Our in vivo studies showed a loss of lung metastases when cells were irradiated (10 Gy) before injection. If irradiated cells were allowed to recover for 2 weeks before injection, mice again developed lung metastases although to a lesser extent than control mice.
We conclude that irradiation of melanoma cells leads to a dose-dependent decrease in cell viability, growth properties and glucose uptake. Cell cycle analyses suggest an arrest in the G2/M phase. One week after irradiation compensating mechanisms of these effects seems to start as indicated by the uptake of [18F]OMFD, the increase in S phase cells and recovered growth of low-dose (5 Gy) irradiated cells. Two weeks after irradiation cell growth is completely recovered in vitro. Accordingly, in vivo studies reveal that irradiated melanoma cells are able to resume their metastatic potential within two weeks, even though to a lesser extent than before irradiation. The questions why and how some cells modulate their metabolism and thus re-start proliferation and why metastasis is influenced in vivo although growth properties are recovered in vitro, need to be further investigated.

  • Poster
    2nd Workshop on Radiation and Multidrug Resistance via the Tumor Microenvironment, 09.-10.02.2009, Dresden, D

Publ.-Id: 13610

Detection and quantification of hypoxia in xenotransplanted human squamous cell carcinoma

Bergmann, R.; van den Hoff, J.; Pietzsch, J.; Strobel, K.; Mosch, B.; Schütze, C.; Brüchner, K.; Hofheinz, F.; Beuthien-Baumann, B.

kein Abstract verfügbar

  • Poster
    World Molecular Imaging Conference, 10.-13.09.2008, Nizza, Frankreich

Publ.-Id: 13609

Pre-treatment FMISO hypoxic volume is a significant prognostic factor for local control after irradiation of FaDu HNSCC xenografts

Schütze, C.; Bergmann, R.; Mosch, B.; Yaromira, A.; Hessel, F.; Krause, M.; Thames, H. D.; Zips, D.; Mäding, P.; Baumann, M.; Beuthien-Baumann, B.

Objective: To investigate whether pre-treatment FMISO hypoxic tumour volume (HV) adds significant information about radiotherapy outcome in FaDu human squamous cell carcinoma (hSCC) in nude mice.
Materials and Methods: The hSCC cell line FaDu was transplanted subcutaneously into the hind leg of NMRI nude mice. Seventy animals entered the study at tumour volumes ranging from 165-343 mm³. [18F]fluoromisonidazole ([18F]FMISO)-PET scanning was performed under anesthesia (9% desflurane in 40% oxygen/air) on a dedicated animal PET scanner (MicroPET® P4, CTI Molecular Imaging Inc, measured attenuation correction, 11 MBq 18FMISO i.v., list mode acquisition for 30 min after 210 min p.i). The regions of interest (ROI) include the FMISO positive hypoxic volume, the mean, the maximum concentration (ROVER software, ABX GmbH, Radeberg, Germany). After an initial FMISO-PET (day 0) the tumours were stratified according to the median hypoxic volume (HV) for single dose irradiation with either 25 Gy (tumour control probability, TCP20) or 35 Gy (TCP80) under normal blood flow conditions using 200 kV X-rays (0.5 mm Cu, ~ 1.2 Gy min-1). The endpoint was time to local failure. Five animals are currently still in follow up.
Results: Tumour local control rate after irradiation with 25 Gy was lower than after irradiation with 35 Gy (22% vs. 69%, log rank p<0.0001). HV ranged from 38-353 mm³. Median HV was 112 mm³ (95%CI: 92; 128 mm³). In tumours with HV less than the median, local control was 33% after 25 Gy vs. 82% after 35 Gy (p=0.001) and in tumours with HV above the median 15% after 25 Gy vs. 53% after 35 Gy (p=0.0005). Multivariate Cox analysis revealed a significant effect of hypoxic volume treated either as a continuous (p=0.009) or a dichotomic variable (stratification by median HV) (p=0.039) when corrected for dose and tumour volume effects. Dose had a significant impact on hazard of recurrence (p<0.0005), whereas total tumour volume showed no effect (p=0.5).
Conclusions: Hypoxic volume is a significant predictor of tumour control after irradiation with high single doses in a single tumour line. This supports the hypothesis that pre-treatment FMISO-PET may provide useful information for heterogeneous radiation dose prescription in sub volumes of individual tumours. Confirmatory investigations using other tumour models and fractionated radiotherapy are warranted.
This work was performed within the 6th framework EU-project BioCare, proposal# 505785.

  • Abstract in refereed journal
    Radiotherapy and Oncology 88(2008), S102
  • Poster
    27th conference of the European Society for Therapeutic Radiology and Oncology (ESTRO), 14.-18.09.2008, Göteborg, Schweden

Publ.-Id: 13608

Neuronal Aneuploidy in Health and Disease: A Cytomic Approach to Understand the Molecular Individuality of Neurons

Arendt, T.; Mosch, B.; Morawski, M.

Structural variation in the human genome is likely to be an important mechanism for neuronal diversity and brain disease. A combination of multiple different forms of aneuploid cells due to loss or gain of whole chromosomes giving rise to cellular diversity at the genomic level have been described in neurons of the normal and diseased adult human brain. Here, we describe recent advances in molecular neuropathology based on the combination of slide-based cytometry with molecular biological techniques that will contribute to the understanding of genetic neuronal heterogeneity in the CNS and its potential impact on Alzheimer´s disease and age-related disorders

Keywords: alu-repeats; Alzheimer´s disease; cell cycle; cell death; chromosomal mosaicism; in situ hybridisation; laser capture microdissection; neurodegeneration; slide-based cytometry

Publ.-Id: 13607

Grain growth in Ni-Mn-Ga alloys

Thoss, F.; Poetschke, M.; Gaitzsch, U.; Freudenberger, J.; Anwand, W.; Roth, S.; Rellinghaus, B.; Schultz, L.

The influence of annealing temperature and time on grain growth in polycrystalline Ni-Mn-Ga samples near the stoichiometric composition Ni2MnGa was investigated. Grain growth was only observed for compositions with a Ni content below 50 at.%. The existence of constitutional vacancies as a possible origin for the different grain growth behaviour was excluded by positron annihilation spectroscopy (PAS). In order to activate grain boundary motion and hence grain growth in Ni50Mn29Ga21 the samples were annealed and deformed in situ in compression up to various strain levels. A sharp threshold to initiate grain growth is observed between 8% and 10% of compression strain.

Keywords: Magnetically ordered materials; casting; grain boundaries

  • Journal of Alloys and Compounds 488(2009), 420-424

Publ.-Id: 13606

Isotopic Comparative Method (ICM) for the determination of variations of the useful ion yields in boron doped silicon as a function of oxygen concentration in the 0 - 10 at% range

Dupuy, J. C.; Dubois, C.; Prudon, G.; Gautier, B.; Kögler, R.; Akhmadaliev, S.; Perrat-Mabilon, A.; Peaucelle, C.

Specific samples containing O-18 and O-16 are used to measure the variations of the relative ion yields of boron, oxygen and silicon as a function of oxygen concentration. O-18 and O-16 are used to implement an Isotopic Comparative Method (ICM) which allows to correct the matrix effects involved by the presence of a high concentration of oxygen in the sample: the near-flat profile of O-18, measured in the 'dilute', linear regime (weak concentration) is used to calculate the real concentration of O-16. The ion yields of B+, O+, Si+, O- and Si- are measured as a function of the oxygen concentration. For B+ ion yield, the variation is important whereas they are weak for Si-+/- and O-+/- ion yields for the range [0-12 at.%]. This ICM applied to oxygen in silicon can be considered as an interesting complementary method of previous 'O-16 implantation method' and of 'O-18 single marker method'.

Keywords: Secondary ion mass spectrometry; SIMS; Isotopic comparative method; ICM; Oxygen; Silicon; Boron

  • Lecture (Conference)
    SIMS XVII Toronto, Canada, 13.-17.09.2009, Toronto, Canada
  • Surface and Interface Analysis 43(2010)1-2, 137-140
    DOI: 10.1002/sia.3657

Publ.-Id: 13605

Carrier profiling of individual Si nanowires by scanning spreading resistance microscopy

Ou, X.; Das Kanungo, P.; Kögler, R.; Werner, P.; Skorupa, W.; Gösele, U.; Wang, X.

Individual silicon nanowires (NWs) doped either by ion implantation or by in-situ dopant incorporation during NW growth were investigated by scanning spreading resistance microscopy (SSRM). The carrier profiles across the axial cross sections of the NWs are derived from the measured spreading resistance values and calibrated by the known carrier concentrations of the connected Si substrate or epi-layer. In case of the phosphorus ionimplanted and subsequently annealed NWs the SSRM profiles revealed a radial core-shell distribution of the activated dopants. The carrier concentration close to the surface of a phosphorus-doped NW is found to be by a factor of 6-7 higher than the value in the core and on average only 25% of the implanted phosphorus is electrically active. In contrast, for the insitu boron-doped NW, the activation rate of the boron atoms is significantly higher than for phosphorus atoms. Some specific features of SSRM experiments of Si NWs are discussed including the possibility of three-dimensional measurements.

Keywords: Nanowires; Silicon; Doping; Scanning Spreading Resistance Microscopy; SSRM

Publ.-Id: 13604

Physics and techniques at high pulsed magnetic fields

Herrmannsdörfer, T.

es hat kein Abstract vorgelegen

  • Invited lecture (Conferences)
    2nd Workshop of the Resonant Scattering and Diffraction Beamline (P09) at PETRA III, 04.11.2009, Hamburg, Deutschland

Publ.-Id: 13603

Superconductivity in p-doped elemental semiconductors

Herrmannsdoerfer, T.; Heera, V.; Ignatchik, O.; Uhlarz, M.; Muecklich, A.; Posselt, M.; Reuther, H.; Schmidt, B.; Heinig, K. H.; Skorupa, W.; Voelskow, M.; Wuendisch, C.; Skrotzki, R.; Helm, M.; Wosnitza, J.

We report the first observation of superconductivity in heavily p-type doped Germanium at ambient-pressure conditions. Using advanced doping and annealing techniques, we have fabricated a highly Ga-doped Ge (Ge:Ga) layer in near-intrinsic cubic Ge. Depending on the detailed annealing conditions, we demonstrate that superconductivity can be generated and tailored in the p-doped semiconducting Ge host at temperatures as high as 0.5 K. Critical-field measurements reveal the quasi-two-dimensional character of superconductivity in the ~ 60 nm thick Ge:Ga layer. We find critical magnetic in-plane fields up to about 1T, even slightly larger than the Pauli-Clogston limit. There might be interest in the technological potential of on-chip thin-film superconductivity in a semiconducting environment demonstrated here as our preparation method is compatible with state-of-the-art semiconductor processing used nowadays for the mass production of logic circuits. After its finding in Si [1] and diamond [2], our work adds another unexpected observation of superconductivity in doped elemental semiconductors and in one of the few remaining ‘islands of the periodic table of elements’ on which superconductivity has not been found so far.

  • Invited lecture (Conferences)
    The 9th European Conference on Applied Superconductivity, EUCAS 2009, 13.-17.09.2009, Dresden, Deutschland
  • Invited lecture (Conferences)
    Workshop: Noval approaches to pairing and condensation, 03.10.2009, Dresden, Deutschland
  • Invited lecture (Conferences)
    Workshop “Physics and Metrology at Very Low Temperatures", 10.12.2009, Berlin, Deutschland

Publ.-Id: 13602

Semiconductor quantum structures for quadratic detection at mid-infrared and THz frequencies

Schneider, H.

There is no abstract.

Keywords: intersubband transition; two-photon detection; terahertz

  • Invited lecture (Conferences)
    Novel Quantum Structure Detectors for Opto-electronic Conversion 2010, 04.-06.01.2010, Sanya, China

Publ.-Id: 13601

Ultrafast infrared and Terahertz spectroscopy of semiconductor quantum structures

Schneider, H.

This seminar gives an overview on our recent experimental studies involving ps and fs lasers, including the free-electron laser at FZD. In particular, I briefly discuss nonlinear sideband spectroscopy and time-resolved photoluminescence. Then I will focus on quadratic photocurrent autocorrelation involving intersubband transitions in semiconductor quantum wells at mid-infrared wavelengths, and present our concept for scalable photoconductive Terahertz emitters.

Keywords: intersubband transition; two-photon detection; terahertz

  • Lecture (others)
    Physics Colloquium, Shanghai Jiao Tong University, 30.12.2009, Shanghai, China

Publ.-Id: 13600

Fulde-Ferrell-Larkin-Ovchinnikov State in the Organic Superconductor κ-(BEDT-TTF)2Cu(NCS)2

Lortz, R.; Wang, Y.; Demuer, A.; Sheikin, I.; Bergk, B.; Wosnitza, J.; Nakazawa, Y.

extraordinary high and the Pauli limit becomes of importance instead. For this case the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state was theoretically predicted. It is now 55 years that this state is being looked for experimentally. The most promising candidates are layered superconductors such as the organic compound κ-(BEDT-TTF)2Cu(NCS)2. When the field is applied parallel to the layers, the orbital limit exceeds the Pauli limit at 22 T. I will present specific heat and magnetic torque experiments up to 30 T and down to 50 mK. The upper critical field transition changes from second to first-order nature above 21 T, the transition line shows a characteristic upturn and a novel transition line separates an unconventional high-field SC phase from the conventional low-field phase. Additional transitions are observed in slightly tilted angles, suggesting a rich physics with a competition between orbital and Pauli limits. These results provide strong evidence for the FFLO state in κ-(BEDT-TTF)2Cu(NCS)2.

  • Invited lecture (Conferences)
    9th Conference on Materials and Mechanisms of Superconductivity (M2S), 07.-12.09.2009, Tokyo, Japan

Publ.-Id: 13599

Fermi-Surface Topology of the Iron-Pnictide Compound LaFe2P2

Ignatchik, O.; Bartkowiak, M.; Wosnitza, J.; Blackburn, S.; Pesant, S.; Côté, M.; Seyfarth, G.; Bianchi, A. D.; Capan, C.; Fisk, Z.; Goodrich, R. G.

A thorough knowledge on the electronic band structure of metals is a prerequisite for gaining insight in their electronic properties. This becomes especially true for a better understanding of the occurrence of superconductivity. Here, we present results of a comprehensive de Haas-van Alphen (dHvA) study of LaFe2P2, a non-superconducting parent compound of the recently discovered family of iron-pnictide superconductors. By use of the cantilever torque magnetometry we were able to observe dHvA oscillations in high-quality LaFe2P2 single crystals starting at about 10 T at dilution-refrigerator temperatures. From the angular dependence of the oscillations we find a strongly anisotropic, but three-dimensional Fermi-surface topology. The effective masses of two different bands observed for magnetic fields aligned along the c axis are 1.4 and 1.7 me, where me is the free-electron mass. The dHvA frequencies and the effective masses in-crease considerably when rotating away from the c axis. We compare our results to state-of-the-art band-structure calculations.

  • Poster
    9th Conference on Materials and Mechanisms of Superconductivity, 07.-12.09.2009, Tokyo, Japan

Publ.-Id: 13598

Thin-film Superconductivity in Ga-doped Germanium

Herrmannsdörfer, T.; Skrotzki, R.; Heera, V.; Ignatchik, O.; Uhlarz, M.; Mücklich, A.; Posselt, M.; Reuther, H.; Schmidt, B.; Heinig, K.-H.; Skorupa, W.; Voelskow, M.; Wündisch, C.; Helm, M.; Wosnitza, J.

We report the first observation of superconductivity in heavily p-type doped germanium at ambient pressure conditions. Using Ga as dopant, we have produced Ge:Ga samples by ion-beam implantation and subsequent short-term (msec) flash-lamp annealing. The combination of these techniques allows for Ga-doping levels up to 6%, not accessible to any other preparation method so far. The superconducting critical parameters strongly depend on the annealing conditions. Transport measurements reveal Tc up to 0.5 K and anisotropic Bc(T) with a linear temperature dependence reflecting the two-dimensional character of the superconducting state in the ~ 60 nm thin Ge:Ga layer. We find critical magnetic in-plane fields even larger than the Pauli-Clogston limit. After its finding in Si [1] and diamond [2], this work reports another unexpected observation of superconductivity in doped elemental semiconductors. Our fabrication techniques are compatible to industrial semiconductor processing and allow for on-chip superconductivity in integrated circuits.

  • Poster
    9th International Conference on Materials and Mechanisms of Superconductivity (M2S), 07.-12.09.2009, Tokyo, Japan

Publ.-Id: 13597

Phase-sensitive terahertz spectroscopy with backward-wave oscillators in reflection mode

Pronin, A. V.; Goncharov, Y. G.; Fischer, T.; Wosnitza, J.

In this article we describe a method which allows accurate measurements of the complex reflection coefficient rˆ=|rˆ| ·exp(iφR) of a solid at frequencies of 1–50 cm−1 (30 GHz–1.5 THz). Backward-wave oscillators are used as sources for monochromatic coherent radiation tunable in frequency. The amplitude of the complex reflection (the reflectivity) is measured in a standard way, while the phase shift, introduced by the reflection from the sample surface, is measured using a Michelson interferometer. This method is particular useful for nontransparent samples, where phase-sensitive transmission measurements are not possible. The method requires no Kramers–Kronig transformation in order to extract the sample’s electrodynamic properties (such as the complex dielectric function or complex conductivity). Another area of application of this method is the study of magnetic materials with complex dynamic permeabilities different from unity at the measurement frequencies (for example, colossal-magnetoresistance materials and metamaterials). Measuring both the phase-sensitive transmission and the phase-sensitive reflection allows for a straightforward model-independent determination of the dielectric permittivity and magnetic permeability of such materials.

  • Review of Scientific Instruments 80(2009), 123904

Publ.-Id: 13596

Short-range correlations in quantum frustrated spin system

Sytcheva, A.; Chiatti, O.; Wosnitza, J.; Zherlitsyn, S.; Zvyagin, A. A.; Coldea, R.; Tylczynski, Z.

We report on results of sound-velocity and sound-attenuation measurements in the low-dimensional spin-1/2 antiferromagnet Cs2CuCl4 (TN = 0.6 K), in external magnetic fields up to 15 T, applied along the b axis, and at temperatures down to 300 mK. The experimental data are analyzed with a theory based on exchange-striction coupling resulting in a qualitative agreement between theoretical results and experimental data.

  • Physical Review B 80(2009), 224414

Publ.-Id: 13595

Spatiotemporal observation of transport in fractured rocks

Kulenkampff, J.; Enzmann, F.; Gründig, M.; Mittmann, H.; Wolf, M.

We apply positron emission tomography (PET) with a high-resolution "small-animal" PET-scanner (ClearPET by Raytest, Straubenhardt) for process observation in rocks. Without affecting its physico-chemical properties, the fluid is labelled with the PET-tracer, a positron-emitting isotope. The annihilation radiation from individual decaying tracer atoms is detected with high sensitivity, and tomographic reconstruction of the recorded events yields a quantitative 3D-image of the tracer concentration. Sequential tomograms during tracer injection are used for the spatiotemporal observation of transport.
The raw data have to be corrected, prevalently with respect to background radiation (randoms) and Compton scattering, which is more significant than in common biomedical applications. Although these effects can be considered exactly in principle, we had to develop and apply simplified correction methods for performance reasons. Deficiencies of these correction algorithms generate some artefacts, that cause a lower limit of the tracer concentration in the order of 1 kBq/µl or about 107 atoms/µl, outranging other methods (e.g. nmr or resistivity tomography) by many orders.
A number of injection experiments in different rocks have been conducted with PET-process-tomography. New 3D-visualizations of the process-tomograms in fractured rocks showed strongly localized and complex flow paths and some unexpected deviations from the fractures that are deducible from µCT-images.
At least, the results demonstrate the large discrepancy between the µCT-derived volume and specific surface area and the hydraulic effective parameters, which also can be analyzed quantitatively with this method. Possibly, these discrepancies and the complexity of the process show the limits of parameter determination methods with model simulations based on structural pore-space models - as long as the simulations are not verified by experimental data.

  • Lecture (Conference)
    European Geosciences Union General Assembly 2010, 02.-07.05.2010, Wien, Österreich

Publ.-Id: 13594

Nuclear Engineering Handbook - Chapter 1.4: VVER-type reactors of Russian design

Gado, J.; Rohde, U.; (Editors)

The Russian designed VVER-type reactors represent a special kind of pressurised light water reactors. The most important features of the VVER-440 and VVER-1000 reactor series are presented here by the representatives of the Russian design company OKB “GIDROPRESS”, Podolsk, Russian Federation.
Design and basic safety properties are described in details, mentioning the differences between various reactors. VVER-440 and VVER-1000 reactors are presented separately. The successful operational experience of the two series is summarised together with data on decommissioned reactors.

Keywords: VVER-type reactors; pressurized water reactors; basic design; safety features; operation experience; decommissioning

  • Contribution to external collection
    D. G. Cacuci, J. Gado, U. Rohde: Handbook of Nuclear Engineering; Vol.IV - Reactors of Generation III and IV, Chapter 20: VVER-Type Reacctors of Russian Design, Heidelberg: Springer, 2010, 978-0-387-98130-7

Publ.-Id: 13593

Prediction of positron emitter distributions produced during 7Li irradiation

Priegnitz, M.; Fiedler, F.; Kunath, D.; Laube, K.; Parodi, K.; Enghardt, W.

No abstract available

  • Contribution to external collection
    in: GSI Scientific Report 2009, Darmstadt: GSI Helmholtzzentrum für Schwerionenforschung GmbH, 2010, 497

Publ.-Id: 13592

Electromagnetic inspection of a two-phase GaInSn/Argon flow

Terzija, N.; Yin, W.; Gerbeth, G.; Stefani, F.; Timmel, K.; Wondrak, T.; Peyton, A.

Adequate control of steel flow through the submerged entry nozzle during continuous casting is essential for maintaining steel cleanliness and ensuring good surface quality in downstream processing. Monitoring the flow in the nozzle presents a challenge for the instrumentation system because of the high temperature environment and the limited access to the nozzle in between the tundish and the mould. We study the distribution of two-phase liquid metal/gas flows by using a laboratory model of an industrial steel caster and an inductive sensor array. The experiments were performed with GaInSn as an analogue for liquid steel, which has similar conductive properties as molten steel and allows the measurements at the room temperature. A scaled (approx. 10:1) experimental rig consisting of a tundish, stopper rod, nozzle and mould was used. Argon gas was injected through the centre of the stopper rod and the behavior of two phase GaInSn/Argon flows was studied. The electromagnetic system used in our experiments to monitor the behavior of two phase GaInSn/Argon flows consisted of an array of 8 equally spaced inductive coils arranged around the object, a data acquisition system and a host computer. The present system operates at 10 kHz and has a capture rate of 10 frames per second. The results showed clearly that the injection of the Argon gas was distinguishable from the continuous flow by observing the appearance of oscillation patterns in the raw signals. These oscillations become more dominant with the increase of the Argon flow. In some cases two main oscillation patterns were present in the raw signals and our results suggested that those patterns are highly correlated with the level height in the mould and with the pressure in the nozzle.

  • Contribution to proceedings
    6th International Conference on Electromagnetic Processing of Materials (EPM), 19.-23.10.2009, Dresden, Germany, 19.-23.10.2009, Dresden, Germany
    6th International Conference on Electromagnetic Processing of Materials EPM 2009, Dresden: FZD, 978-3-936104-65-3, 391-394
  • Lecture (Conference)
    6th International Conference on Electromagnetic Processing of Materials (EPM), 19.-23.10.2009, Dresden, Germany

Publ.-Id: 13591

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