Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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Only approved publications

31839 Publications
Characterization of Ga-Bi Liquid Metal Alloy Ion Source
Akhmadaliev, C.; Pilz, W.; Bischoff, L.;
Liquid metal alloy ion sources (LMAIS) are now of increasing interest in mass-separated focused ion beam (FIB) systems where a variety of projectile ions can be used. Typically, these can be focused into diameters of the order of 10 nm, with current densities of several A/cm2 giving probe currents of 1 pA -30 nA.
A Gallium-Bismuth LMAIS with melting point temperature of 222°C has been studied. The ion source was based on a mechanical treated Ta emitter. The emission characteristics of the source were investigated. From a detailed analysis of the source mass spectra as a function of emission current, the mechanism of single and double-charged ions emission is established. Good agreement is obtained comparing these results with Swanson’s investigations of a pure Bi source.
GaBi LMAIS allows to provide FIB structuring of a silicon substrate using either shallow donor ions (Bi) or acceptors ions (Ga) without changing the ion source.
Keywords: Focused ion beam, liquid metal ion source, shallow donor
  • Lecture (Conference)
    The European Focused Ion Beam Users Group Meeting(EFUG), 02.10.07, Wuppertal, Deutschland

Publ.-Id: 9275 - Permalink


Low energy Ar ion accelerated diffusion of interstitial nitrogen
Abendroth, B.; Abrasonis, G.; Möller, W.; Ma, X. X.;
Interstitial N diffusion under low energy (700 eV) Ar+ bombardment at 673 K in ion beam nitrided austenitic stainless steel is investigated. Ar+ ion bombardment increases the N mobility in depths far beyond the ion penetration depth, resulting in an increased broadening of the N depth profile as a function of Ar+ flux. This effect cannot be explained by any established mechanism of radiation-enhanced diffusion. An explanation based on quasiparticle-enhanced mobility is proposed.
  • Lecture (Conference)
    13. Workshop "Oberflächentechnologie mit Plasma- und Ionenstrahlprozessen", 14.-16.03.2006, Mühlleithen, Deutschland

Publ.-Id: 9274 - Permalink


Simulations of FZR adiabatic air-water data with CFX-10
Krepper, E.; Lucas, D.; Shi, J.-M.; Prasser, H.-M.;
The CFD simulation of an adiabatic gas-liquid flow requires an adequate characterisation of the momentum exchange between the phases. This report describes the CFX simulation of adiabatic air/water bubbly flow in a vertical pipe and the comparison to experimental results for several test conditions that were obtained in FZ-Rossendorf. The measured cross sectional distribution of the gas volume fraction enables the validation of the applied models for the momentum exchange between the liquid and the gaseous phase. The drag bubble force determines the flow resistance in flow direction and influences the gas volume fraction for given superficial gas and liquid velocities. The non drag forces, namely the lift-, the wall- and the turbulent dispersion forces act perpendicularly to the flow direction and influence the cross sectional gas volume fraction distribution. Their correct simulation is important, since they have an essential influence on the flow regime.
In the report the model approaches for the drag and the non drag bubble forces are described. Several tests gained at MT-Loop that show low gas volume fractions are presented. These can be described by only one dispersed gaseous phase having a certain bubble size. These experiments are therefore suited for the validation of the non drag force models.
Increasing the gas injection rate, a bubble size distribution including bubble coalescence and fragmentation has to be considered. The paper describes the concept of the inhomogeneous MUSIG model, which is implemented in CFX-10. Several tests from MT-Loop and from TOPFLOW are presented to demonstrate the applicability of the model.
The simulations are intended for the comparison to other CFD models e.g. in the NURESIM-CFD platform.
Keywords: Two phase flow, CFD, drag forces, non drag forces, population balances, experiments, model validation
  • Article, self-published (no contribution to HZDR-Annual report)
    Forschungszentrum Rossendorf 2006
    NURESIM-SP2-TH-D2.2.3.1 (June 2006)
    22 Seiten

Publ.-Id: 9273 - Permalink


Progress report on the simulation of the plunging jet configuration. EU projetc NURESIM Deliverable D2.1.3.1 (June 2006)
Bodèle, E.; Lucas, D.;
This progress report presents the preliminary work done for the numerical prediction of the plunging jet configuration. It consists in the definition of the most appropriate numerical configuration which should permit to obtain the most realistic behaviour of the gas below the free liquid surface. Several numerical domain (mesh and boundary conditions), numerical assumptions (steady state or transient calculations) and numerical models (mainly the effects of the non drag forces acting on the gas phase) have been tested. This report presents the most realistic numerical results and concludes on the most appropriate numerical domain and assumptions for the following tasks.
Keywords: plunging jet, Pressurized Thermal Shock (PTS), non drag forces, numerical simulation, CFX
  • Article, self-published (no contribution to HZDR-Annual report)
    Forschungszentrum Rossendorf 2006
    0039 Seiten

Publ.-Id: 9272 - Permalink


Synthesis report on work package 2.1: Pressurized Thermal Shock (PTS)
Lucas, D.;
This report summarizes the results of the first 18 months period of the NURESIM project for the workpage 2.1 “Pressurized Thermal Shock (PTS)”. It mainly bases on the deliverables supplied by the partners involved in this workpage. In the Introduction chapter some more general information on the PTS issue is given, which should help to clarify the integration of the single activities. Since the PTS scenario involves different flow situations, for which also different modelling approaches are necessary, the contributions are sorted according to these flow situations. The relations of the work done to the general aim of the NURESIM project, which is to establish a new code platform, is indicated by assigning the activities to 6 different types. The present status PTS workpage is in agreement with the planning of the NURESIM project, the expected results were met by the deliverables. The work done leads to an improvement of the simulation capabilities regarding a PTS flow situation, but caused by the complexity of the issue it will still be a long way to enable reliable predictions for the whole process from such simulations.
Keywords: PTS
  • Article, self-published (no contribution to HZDR-Annual report)
    Forschungszentrum Rossendorf 2006
    FZR\FWS\2006\06
    19 Seiten

Publ.-Id: 9270 - Permalink


Mass separated FIB applications from alloy liquid metal ion sources
Bischoff, L.; Akhmadaliev, C.;
During the last decades, the focused ion beam (FIB) became a very useful and versatile tool in the microelectronics industry, as well as in the field of research and development. For special purposes like writing ion implantation or ion mixing in the µm- or sub-µm range ion species other than gallium are needed. Therefore alloy liquid metal ion sources (LMIS) were developed. The energy distribution of the ions from an alloy LMIS is one of the determining factors for the performance of an FIB column. Different source materials like Au73Ge27, Au82Si18, Au77Ge14Si9, Co36Nd64, Er69Ni31, and Er70Fe22Ni5Cr3 were investigated with respect to the energy spread of the different ion species as a function of emission current I, ion mass m and emitter temperature T. For singly charged ions a predicted dependence of the energy spread, DE µ I2/3 m1/3 T1/2 found for Ga could be reasonable confirmed. The alloy LMIS`s discussed above have been used in the Rossendorf FIB system IMSA-OrsayPhysics especially for writing implantation to fabricate sub-µm pattern without any lithographic steps. A Co-FIB obtained from a Co36Nd64 alloy LMIS was applied for the ion beam synthesis of CoSi2 micro-structures down to 60 nm. Additionally, the possibility of varying the current density of the FIB by changing the pixel dwell-time was used for investigations of radiation induced damage and its dynamic annealing in Ge, Si and SiC at elevated implantation temperatures. Furthermore, a broad spectrum of ions was employed to study the sputtering process depending on temperature, angle of incidence and ion mass on a couple of target materials using the volume loss method. Especially this direct patterning 3D technique was used for the fabrication of various kinds of micro-tools.
All these examples underline the importance of FIBs in modern research and the new possibilities opened up by a mass separated system applying a broad spectrum of ion species.
Keywords: FIB; alloy LMIS; micropatterning; tools; CoSi2
  • Invited lecture (Conferences)
    FIB User Meeting 2006, 18.-19.05.06, Fufeau, France

Publ.-Id: 9269 - Permalink


Sicherheit von Kernkraftwerken - Beiträge des Forschungszentrums Dresden-Rossendorf
Willschütz, H.-G.; Weiß, F.-P.;
Zur Zeit werden weltweit über 440 Kernkraftwerke im kommerziellen Leistungsbetrieb eingesetzt. Die überwiegende Mehrheit sind sogenannte Leichtwasserreaktoren (LWR). Das Risiko, dass es beim Betrieb von LWR der heutigen Generation zu einem schweren Unfall (engl. Severe Accident, SA) mit partiellem oder vollständigem Abschmelzen des Reaktorkerns kommt, ist gering. Es lässt sich aber trotz umfangreicher Sicherheitsvorkehrungen nicht vollständig ausschließen.
Bei der Entwicklung und Auslegung von Kernkraftwerken wurde von Beginn an ein erhöhtes Sicherheits- beziehungsweise Schutzkonzept verfolgt, weil bekannt war, dass das radioaktive Inventar, das aus den während des Betriebs entstehenden Spalt- und Aktivierungsprodukten besteht, nicht unkontrolliert freigesetzt werden darf. Es wurde daher von vornherein ein sogenanntes Mehrstufenkonzept („defence-in-depth“) eingeführt, um die in jeder technischen Anlage auftretenden Störungen innerhalb des Kraftwerks zu beherrschen und Unfälle auszuschließen.
Das Mehrstufenkonzept besteht heute aus 4 Ebenen. Die Ebenen 1 bis 3 – Normalbetrieb, Betriebsstörungen und Auslegungsstörfälle – wurden bereits bei der Reaktorauslegung berücksichtigt und dienen der Störfallverhinderung beziehungsweise der Störfallvermeidung. Zur Vermeidung und Begrenzung von schweren Unfällen ist mit dem sogenannten „anlageninternen Notfallschutz“ nachträglich die 4. Ebene eingeführt worden.
Die Wirksamkeit des Defence-in-Depth wird zum einen durch die technische Auslegung sichergestellt. Zum anderen durch die Umsetzung der sogenannten Sicherheitskultur. Die Sicherheitskultur stellt die Gesamtheit der Eigenschaften und Einstellungen von Personen und Organisationen dar, die dafür sorgt, dass dem sicheren Anlagenbetrieb die höchste Priorität zukommt.
Ein Pfeiler der Sicherheitskultur ist die Sicherheitsforschung. In diesem Vortrag werden zwei Beispiele der aktuellen Arbeiten im Forschungszentrum Rossendorf zu sicherheitsrelevanten Fragestellungen behandelt: die sogenannten Borverdünnungstransienten und die Kernschmelzerückhaltung im Reaktordruckbehälter.
Ein kurzer Überblick über die Historie der verschiedenen Kernkraftwerksgenerationen und die Erläuterung der wesentlichen Eigenschaften der aktuell in Bau befindlichen dritten Generation sowie der heute in der internationalen Forschung betrachteten zukünftigen Reaktortypen (Generation IV) schließen den Vortrag ab.
Keywords: Safety of Nuclear Power Plants, Defence in Depth, Saftey Research, Boron Dilution Transients, In Vessel Retention, Generation III, Generation IV
  • Invited lecture (Conferences)
    Vortragsreihe des VDI, Dresdner Bezirksverein - Arbeitskreis Energietechnik, 06.02.2007, Dresden, Deutschland

Publ.-Id: 9268 - Permalink


Application of a Mass Separated Focused Ion Beam
Bischoff, L.; Akhmadaliev, C.; Pilz, W.; Schmidt, B.;
During the last decades, the focused ion beam (FIB) became a very useful and versatile tool in the microelectronics industry, as well as in the field of research and development. For special purposes like writing ion implantation or ion mixing in the µm- or sub-µm range ion species other than gallium are needed. Therefore alloy liquid metal ion sources (LMIS) were developed. The energy distribution of the ions from an alloy LMIS is one of the determining factors for the performance of an FIB column. Different source materials like Au73Ge27, Au82Si18, Au77Ge14Si9, Co36Nd64, Er69Ni31, and Er70Fe22Ni5Cr3 were investigated with respect to the energy spread of the different ion species as a function of emission current I, ion mass m and emitter temperature T. For singly charged ions a predicted dependence of the energy spread, DE µ I2/3 m1/3 T1/2 found for Ga could be reasonable confirmed. The alloy LMIS`s discussed above have been used in the Rossendorf FIB system IMSA-OrsayPhysics especially for writing implantation to fabricate sub-µm pattern without any lithographic steps. A Co-FIB obtained from a Co36Nd64 alloy LMIS was applied for the ion beam synthesis of CoSi2 micro-structures down to 60 nm. Additionally, the possibility of varying the current density of the FIB by changing the pixel dwell-time was used for investigations of radiation induced damage and its dynamic annealing in Ge, Si and SiC at elevated implantation temperatures. Furthermore, a broad spectrum of ions was employed to study the sputtering process depending on temperature, angle of incidence and ion mass on a couple of target materials using the volume loss method. Especially this direct patterning 3D technique was used for the fabrication of various kinds of micro-tools.
All these examples underline the importance of FIBs in modern research and the new possibilities opened up by a mass separated system applying a broad spectrum of ion species.
Keywords: FIB; alloy LMIS; micro - and nanostructures
  • Poster
    1. FIB Workshop, Focused Ion Beams In Research, Science and Technology May 22 – 23, 2006, IFW Dresden, Germany, 22.-23.05.06, Dresden, Germany

Publ.-Id: 9267 - Permalink


Mn containing alloy LMIS for Spintronics
Akhmadaliev, C.; Pilz, W.; Bischoff, L.;
Magnetic ions such as Mn are of increasing interest for the structuring of diluted magnetic semiconductors, e. g. spin-based optoelectronics in III-V as well as II-VI materials. Only a few Mn alloy liquid metal ion sources (LMIS) for nano-patterning are reported, so an Au-Si-Mn or an Au-Ge-Mn sources were used in mass separated FIB applications. The Mn-Ge alloy LMIS (melting temperature of 720°C) showed a stable operation at emission current of 2 - 30 µA. The slope of the I-V characteristic curve was ~0.11 µA/V at a heating current of about 2.6 A.
Keywords: LMIS, focused ion beam
  • Poster
    The European Focused Ion Beam Users Group Meeting(EFUG), 02.10.06, Wuppertal, Deutschland

Publ.-Id: 9266 - Permalink


Formation of CoSi2 nanowires and nanochains in silicon by direct FIB writing
Akhmadaliev, C.; Bischoff, L.; Schmidt, B.; Mücklich, A.;
A Focused Ion Beam (FIB) equipped with a CoNd alloy liquid metal ion source was used for the formation of cobalt disilicide nanowires and nanochains by an ion beam synthesis process. Co ions at 60 keV were implanted into silicon (111) and (100) substrates at 400-450°C followed by a two-step annealing at 600°C and 1000°C. During the FIB patterning of the samples using a digital scanning system the dose, the pixel dwell time and the relaxation time between the irradiation cycles were varied. The FIB spot size was in the range of 40 nm. The formation of long, stable nanowires occurs along the favoured <110>-crystal direction. The misalignment of the FIB trace relative to this direction leads to a decay of the wire into shorter ones or to the formation of chains of single-crystalline nanoparticles. Nanowires of 20-80 nm diameter and lengths up to 50 microns were obtained. Imaging of nanostructures was done in-plane by SEM, AFM and TEM. Cross-sections through nanowires were prepared by conventional Ga FIB milling across the nanowire. Further efforts will be concentrated in a better control of the nanowires growth, in the characterization of the electrical properties and in the fabrication of nanodevices.
Keywords: Cobalt disilicide, nanowire, focused ion beam
  • Lecture (Conference)
    DPG-Tagung 2006, 27.-31.03.06, Dresden, Deutschland

Publ.-Id: 9265 - Permalink


Efficient oxidation protection of gamma-TiAl alloys by ion implantation of halogens
Yankov, R. A.; Richter, E.; Donchev, A.; Schütze, M.;
In this work, gamma-TiAl samples have been rendered highly oxidation-resistant by plasma immersion ion implantation using various Cl- or F-containing precursor gases. PI3 processing has been preceded by beamline ion implantation of either Cl or F because of the well-established nature of the process. Implanting F gives better results. Further work has involved the co-implantation of F and Si to study the combined effect of these elements on the alloy’s high temperature behavior.
Keywords: Titanium aluminides, ion implantation, oxidation resistance
  • Lecture (Conference)
    International Conference on Ion Beam Modification of Materials, Taormina, Sicily, Italy, 18 – 22 September 2006, 18.-22.09.2006, Catania, Sicily, Italy

Publ.-Id: 9264 - Permalink


FIB assisted silicide nanowires formation in silicon
Akhmadaliev, S.; Bischoff, L.; Schmidt, B.;
Focused Ion Beam (FIB) is one of the most suitable tools for sub-µm structure fabrication, modification and investigation. Combining FIB and self organization processes during ion beam synthesis a reduction of the FIB written structures can be provided. The Rossendorf FIB system allows the operation with a Ga liquid metal ion source (LMIS) as well as with a CoNd alloy LMIS. Formation of CoSi2 nanoparticles and nanowires in silicon was investigated using Co++ ions from the CoNd LMIS. Si(111) and Si(100) samples were implanted with a fine focused cobalt ion beam at elevated sample temperatures as well as at room temperature. Subsequent annealing steps lead to the formation crystalline CoSi2 long nanowires with diameter down to 10-20 nm in the crystalline substrate. These structures were analyzed using SEM and AFM. Two main mechanisms of the nanowires formation have been observed: via coalescence of the implanted Co nanoparticles with following Oswald ripening and via diffusion of Co atoms during annealing into “linear defects” induced by FIB irradiation. Further efforts are concentrated in increasing of reproducibility of nanowire growth and then the fabrication of nanodevices.
Keywords: Cobalt disilicide, nanowire, focused ion beam, ion beam synthesis
  • Lecture (Conference)
    E-MRS Spring Meeting 2006, 29.05.-02.06.06, Nice, France

Publ.-Id: 9263 - Permalink


Improvement of the oxidation behavior of TiAl-alloys by treatment with halogens
Donchev, A.; Richter, E.; Schütze, M.; Yankov, R.;
The paper addresses the enhancement of the oxidation resistance of gamma-TiAl alloys with the aim of making them suitable for applications at temperatures in excess of 750 °C. Improvements in the oxidation resistance have been achieved by ion-implanting halogens, notably Cl and F, which favors the formation of an adherent protective alumina scale. Additional results are presented pertinent to the high-temperature creep behavior of the halogen-implanted alloys.
Keywords: Titanium aluminides, Ion implantation, Halogens, Oxidation, Creep
  • Intermetallics 14(2006)10-11, 1168-1174

Publ.-Id: 9262 - Permalink


Dampfgehaltsmessung in Brennelementbündeln mittels hochauflösender Gammatomographie
Bieberle, A.; Kronenberg, J.; Hampel, U.;
Für die Bestimmung des Dampfgehaltes in Brennelementbündeln wurde ein hochauflösendes Gammatomographie Messsystem am Forschungszentrum Dresden - Rossendorf entwickelt und erste Testmessungen an der Testanlage KATHY der Firma AREVA NP GmbH in Karlstein durchgeführt. Gegenstand des Vortrages ist die Vorstellung des Messsystems und erste Ergebnisse, die im Rahmen meiner Promotionsvorhabens entstanden sind.
Keywords: Gamma Tomographie
  • Lecture (others)
    Kompetenzzentrum Ost für Kerntechnik - Doktorandenseminar, 15.12.2006, Dresden, Germany

Publ.-Id: 9261 - Permalink


Gamma ray computed tomography for fast rotating objects
Bieberle, A.; Hampel, U.;
Recently, we have developed a high resolution gamma ray computed tomography system to analyze processes at hydro dynamic and multi phase flow facilities non-invasively. Typically, the measurement system consisting of a collimated isotopic source and a gamma ray detector is rotated around the object of investigation to record projections from different angle positions in one plane. In our case we use Cs137 with an activity of about 165 GBq. For fast rotating objects our developed measurement system is arranged in a fixed position and the stir of the object is used. By cyclically read-out of the measurement system’s electronic the number of projections per revolution can be determined. A trigger signal that is also included in the data transfer indicates a full revolution. That information is important for the later data processing if the object is rotating non-uniformly and thus the number of projections per revolution differs. After the recording the data of one projection can be resorted in a matrix – called sinogram - to the corresponding angle position column. Typical applications areas are the behaviour analysis of hydro dynamic couplings and the determination of gas fraction in a stirrer vessel reactor. Therefore we developed a new electronic that is compatible to the existing digital unit and realizes a periodical read-out of our 320 single detector arc every 40 µs. That means for an object that is rotating with 1500 rpm 1000 projections can be recorded per revolution.
Keywords: high speed gamma ray tomography
  • Contribution to proceedings
    5th World Congress on Industrial Process Tomography, 03.-06.09.07, Bergen, Norway, IPS01
  • Lecture (Conference)
    5th World Congress on Industrial Process Tomography, 03.-06.09.07, Bergen, Norway

Publ.-Id: 9260 - Permalink


PC driven etching system for emitter needle tips
Pilz, W.; Lange, H.; Akhmadaliev, C.; Zimmermann, L.; Bischoff, L.;
The reproducible forming of emitter needle tips is a serious demand for the fabrication of liquid metal ion sources. The movement of the needle into the etch solution, for tungsten 1n NaOH is used, a PC driven step motor with an increment of 2 µm is used. Due to the adjustment of the motion as a function of height and time the optimum shape of the tip can be repeatable etched. This process is controlled on a monitor optically using a long distance microscope and a video system. Characteristic needle tips with a radius of a few micron are presented.
Keywords: emitter needle; liquid metal ion source; etching; PC control
  • Invited lecture (Conferences)
    1st Workschop on Ion Beams from L.M.I.S. and Applications, 03.12.06, Lamia, Greece

Publ.-Id: 9259 - Permalink


The statistical properties of paleomagnetic reversals: measurements and models
Sorriso-Valvo, L.; Carbone, V.; Stefani, F.; Nigro, G.;
The spontaneous reversals of the geomagnetic field have recently been shown to own clustering properties. Poisson-like statistics (including non-stationary renewal processes) is indeed unable to describe some statistical properties observed in the data. Such statistical properties are thus used here to test some numerical models currently adopted to reproduce the geodynamo effect. Moreover, the model's parameters can be tuned in order to reproduce with the simulated reversals the same degree of deviation from Poisson statistics observed on the real data.
  • Open Access LogoAbstract in refereed journal
    Geophysical Research Abstracts 9(2007), 02863-02863

Publ.-Id: 9258 - Permalink


The application of alloy liquid metal ion sources in mass separated focused ion beams
Bischoff, L.; Akhmadaliev, C.; Pilz, W.;
For special purposes like writing ion implantation or ion mixing in the micrometer- or sub-micrometer range different ion species are needed. Therefore alloy liquid metal ion sources (LMISs) are used. The energy distribution of the ions from an alloy LMIS is one of the determining factors for the performance of a FIB column. Different source materials like Au73Ge27, Au82Si18, Au77Ge14Si9, Co36Nd64, Er69Ni31, Ga38Bi62, Mn43Ge57, In50Ga50, Sn86Pb14 and Er70Fe22Ni5Cr3 were investigated with respect to the energy spread of the different ion species as a function of emission current, ion mass, charge state and emitter temperature and the abundance of the species, emitted from the tip, in the mass spectra.
Most of the alloy LMISs discussed above have been used in the Rossendorf FIB system IMSA-Orsay Physics especially for writing implantation to fabricate sub-micrometer pattern without any lithographic steps. A Co-FIB was applied for the ion beam synthesis of CoSi2 micro-and nanostructures. Additionally, the possibility of varying the current density with the FIB by changing the pixel dwell time was used for radiation damage investigations in Si, Ge and SiC at elevated implantation temperatures. Furthermore, a broad spectrum of ions was employed to study the sputtering process depending on temperature, angle of incidence and ion mass on a couple of target materials using the volume-loss method as well as used for patterning of different surface structures, i.e. in nano-functional films. Especially this technique was used for the fabrication of various kinds of micro-tools.
Keywords: alloy liquid metal ion sources; focused ion beam; nano-structures; implantation
  • Invited lecture (Conferences)
    1st WORKSHOP ON ION BEAMS FROM L.M.I.S. AND APPLICATIONS, 03.12.06, Lamia, Greece

Publ.-Id: 9256 - Permalink


Magnetic and superconducting properties of RuSr2GdCu2O8
Papageorgiou, T. P.; Casini, E.; Braun, H. F.; Herrmannsdörfer, T.; Bianchi, A. D.; Skourski, Y.; Wosnitza, J.; Freudenberger, J.;
The high-temperature superconducor RuSr2GdCu2O8 (Ru1212) offers the rare opportunity to study how superconductivity develops in an already magnetically ordered state. In this compound the Ru moments order magnetically at TM 130 K and a G-type antiferromagnetic arrangement has been proposed from neutron-diffraction studies [1] with the spins aligned along the c axis. We have measured the magnetic-field dependence of the magnetization of Ru1212 at T < TM in fields up to B 50 T. At the lowest measuring temperature of 4.2 K no saturation of the magnetization was observed and at 50 T, assuming a Gd contribution of 7 μB/formula unit, the Ru contribution to the measured magnetic moment was estimated to be 2.1 μB/formula unit. This is consistent with a mixed-valence state of the Ru ions (Ru5+ and Ru4+) and in contrast to the neutron diffraction studies that estimate an ordered Ru moment of 1.18 μB. In the superconducting state of the sample (T < 50K) we show that the signature of a bulk Meissner state, diamagnetism, is absent. Nevertheless, we suggest that this could be the effect of the granular nature of the investigated samples. A discussion of the specific heat of Sr2GdRuO6, the precursor for the preparation of Ru1212, with respect to the reported specific heat of the latter compound strongly supports the claims that Ru1212 is a bulk superconductor.
  • Poster
    International Conference on Materials and Mechanisms of Superconductivity High Temperature Superconductors VIII (M2S-HTSC-VIII), 09.-13.07.2006, Dresden, Deutschland

Publ.-Id: 9255 - Permalink


Pressure dependence of the electronic properties of the quasi-two-dimensional organic superconductor β" - (BEDT-TTF)2SF5CH2CF2SO3
Ignatchik, O.; Hagel, J.; Wosnitza, J.; Pfleiderer, C.; Schlueter, J. A.; Mohtasham, J.; Gard, G. L.;
We report on the pressure-dependent superconducting and transport properties of the quasi-two-dimensional organic superconductor beta"-(BEDT-TTF)2SF5CH2CF2SO3, where BEDT-TTF stands for bisethylenedithio-tetrathiafulvalene (or ET for short). With increasing pressure the superconducting transition temperature, Tc, decreases monotonously. Superconducting traces can be observed up to 11.7 kbar; at higher pressures an insulating state appears. By use of Shubnikov-de Haas (SdH) and angular-dependent magnetoresistance oscillations the Fermi-surface topology as well as the effective masses were determined. Close to the insulating state a new SdH frequency can be resolved. The effective mass, mc, of the main orbit decreases approximately linear with pressure. By assuming a direct relationship between mc and the superconducting coupling parameter lambda, the pressure dependence of Tc can be well explained by the modi-fied McMillan equation. For all pressures in the metallic state the resistance can be described by R = R0 + AT2 at low temperatures. The coefficient A, however, is found to be not proportional to m2c as expected for a purely electronic origin of the T2 behavior.
  • Poster
    International Conference on Materials and Mechanisms of Superconductivity High Temperature Superconductors VIII (M2S-HTSC-VIII), 09.-14.07.2006, Dresden, Deutschland

Publ.-Id: 9254 - Permalink


Infrared pump-probe spectroscopy of carrier dynamics in semiconductor quantum structures
Helm, M.;
no abstract available
Keywords: intersubband relaxation, infrared, quantum well, carrier dynamics, femtosecond
  • Invited lecture (Conferences)
    International Conference on Engineering Physics and 9th Vietnamese-German Seminar, 09.-11.10.2006, Hanoi, Vietnam

Publ.-Id: 9253 - Permalink


Electronic band structure and superconducting gap of YNi2B2C and LuNi2B2C
Bergk, B.; Ignatchik, O.; Bianchi, A. D.; Jäckel, M.; Wosnitza, J.; Perenboom, J.; Jobiliong, E.; Souptel, D.; Behr, G.; Canfield, P. C.;
We present de Haas-van Alphen (dHvA) measurements of the nonmagnetic borocarbides YNi2B2C and LuNi2B2C. The measurements were carried out on high-quality crystals by the torque method in magnetic fields up to 33 T. The Fermi-surface topology has been measured in the normal state and compared with band-structure calculations. In the superconducting state below the upper critical field, Bc2, the dHvA-signal is strongly damped due to the opening of the superconducting gap, which allows to study the evolution of the superconducting gap. In order to investigate the symmetry of the order parameter we performed angle-dependent measurements
of this damping. We compare results from two differently grown kinds of crystals. The crystals produced by a zone-melting method show an abrupt vanishing of the dHvA signal at Bc2. In contrast, flux-grown crystals display a broader phase transition combined with a continuous decrease of the oscillation amplitude. The observed anisotrop of the dHvA-signal damping points to an anisotropic energygap in these materials.
  • Poster
    8th International Conference on Materials and Mechanisms of Superconductivity High Temperature Superconductors VIII (M2S-HTSC-VIII), 09.-14.07.2006, Dresden, Deutschland

Publ.-Id: 9252 - Permalink


The strongly correlated superconductor CeCoIn5: Evidence for the realization of a FFLO state
Bianchi, A. D.; Capan, C.; Movshovich, R.; Pagliuso, P. G.; Sarrao, J. L.;
I will be reporting on specific-heat and thermal-conductivity measurements at low temperatures on the strongly correlated superconductor CeCoIn5 in magnetic fields close to the upper critical field Hc2. This system is a prime example for illustrating how in a strongly correlated electron system superconductivity emerges near a so-called quantum critical point (QCP). Close to this point the system fluctuates between a paramagnetic heavy-fermion state and an uncorrelated antiferromagnetically ordered metal. What makes CeCoIn5 special is the fact that just before the magnetic order is established at the QCP, superconductivity supersedes it. Several aspects of the superconductivity in CeCoIn5 are unconventional: On the one hand, the temperature dependence of the specific heat and thermal conductivity well below the critical temperature suggests lines of zeroes in the energy gap of the superconducting state. On the other hand, we observed a second phase inside the superconducting part of the temperature-magnetic field phase diagram close to Hc2. The limiting upper critical field to superconductivity in CeCoIn5 is set by the Pauli criterion, suggesting that this second phase is a Fulde-Ferrell-Larkin-Ovchinnikov state (FFLO). In the FFLO state, the superconducting wave function acquires an additional modulation. The FFLO phase is also of great interest to the astrophysics community, as it could describe the dense quark matter inside neutron stars, or quasars.
  • Invited lecture (Conferences)
    8th International Conference on Materials and Mechanisms of Superconductivity High Temperature Superconductors VIII (M2S-HTSC-VIII), 09.-14.07.2006, Dresden, Deutschland

Publ.-Id: 9251 - Permalink


“Recent developments at the Dresden High Magnetic Field Laboratory”
Wosnitza, J.; Bianchi, A. D.; Herrmannsdörfer, T.; Zherlitsyn, S.; Zvyagin, S.;
A high magnetic field laboratory for pulsed non-destructive fields up to 100 T is under construction at the Forschungszentrum Rossendorf, situated at the outskirts of Dresden, Germany. Besides the ultimate goal of a pulsed magnet reaching 100 T for a timescale of 10 ms in a bore of 20 mm, further large-scale magnets (e.g. 60 T, 0.5 s, 40 mm) are planned. The necessary energy for the pulsed coils will be provided by a world-unique 50 MJ capacitor bank working at 24 kV that became operational this year (2006) within a newly built laboratory building. As an outstanding feature of the laboratory, the intense light of a next-door free-electron-laser facility will enable unique high-field infrared spectroscopy. Dedicated coil-winding facilities allow a fast realization of novel self-designed pulsed coils with diameters up to 750 mm. After a thorough test period of the coil design, user-type coils for up to 65 T, 10 ms, and bore of 20 mm, made out of soft copper wire with Zylon reinforcement, have been wound and tested successfully with high-field pulses repeatedly. The first large-scale coil for magnetic fields above 70 T with 100 ms pulse length and 24 mm bore has been realized. A two-coil system for the decisive goal of 100 T is scheduled. First tests of these high-energy coils will be performed in the near future. Cryotechniques and different sample probes for a broad range of experimental techniques custom-designed for the variety of pulsed magnets will be readily available for users and own in-house research. The new Hochfeld-Magnetlabor Dresden (HLD) is planned to open as user facility in 2007.
  • Invited lecture (Conferences)
    Megagauss 2006, 05.-10.11.2006, Santa Fe, USA

Publ.-Id: 9250 - Permalink


Gamma ray CT – system for multiphase flow imaging
Bieberle, A.; Schleicher, E.; Hampel, U.;
We present a recently developed gamma ray CT system that enables us to visualize rapidly rotating multi-phase distributions, such as in stirred chemical reactors and hydrodynamic machines. Transmission measurements with gamma rays or X-rays are often employed when the flow is confined in dense metal structures and the distribution of gas, liquid or solid suspensions have to be determined. For gamma ray tomography the object of investigation must be placed between an isotopic source and a detector that measures the attenuation of the radiation passing through the object. In the past our group developed a first gamma ray tomography device and supplied it successfully to rapidly rotating systems (Prasser 2003, Hampel 2005). The old system contains a detector made of 64 elements (BGO scintillation crystals and photo multipliers) and a pulse processing unit transferring projection data in 90 µs intervals. As isotopic source Cs137 was used with an activity of about 165 GBq. Our new high resolution gamma ray detector now comprises 320 single detector elements each with an active area of 2 mm by 8 mm. The detectors are made of avalanche photo diodes and lutetium yttrium orthosilicate (LYSO) scintillation crystals whose shape was optimized for a high gamma photon yield. All 320 elements produce weak negative voltage pulses that are shaped and amplified by a pulse processing unit which is built up fully parallel for all 320 channels. The signal processing unit contains also gain adjustable amplifiers, discrimination stages, and binary pulse counters. This allows energy discrimination of every detected gamma photon and thus dividing scattered from non-scattered photons. Data of one projection data set can now be transferred to a PC every 40 µs for 320 detectors periodically via USB2.0. This enables acquisition of 500 radiographic projections per revolution of objects rotating at 3000 rpm. To compound the sinogram a data matrix is initiated to zero. After each revolution the value of every detector element is added to the data matrix with respect to the current angle position in. The detailed procedure is described elsewhere (Prasser 2003, Hampel 2005). Figure 2 shows as an example the reconstructed image of a stirrer of 60 mm outer diameter rotating at 1500 rpm. The result was reconstructed using a standard filtered backprojection algorithm.
Keywords: phase flow imaging, gamma ray tomography
  • Contribution to proceedings
    International Conference on Multiphase Flow 2007, 09.-13.07.07, Leipzig, Germany
    Programme and Abstracts of the 6th International conference on Multiphase Flow, S7-Thu_C55
  • Lecture (Conference)
    International Conference on Multiphase Flow 2007, 09.-13.07.07, Leipzig, Germany

Publ.-Id: 9248 - Permalink


A high-resolution gamma tomograph for void fraction distribution measurements in fuel element bundles
Bieberle, A.; Kronenberg, J.;
We would like to present our recently developed high-resolution gamma ray measurement system for analyzing dry-out effect and determine void fraction distributions in sub-channels of electrically heated fuel element bundles at the thermal hydraulic test loop KATHY in Karlstein (AREVA NP GmbH, Germany). The instrumentation setup enables a non-invasive measurement of cross-sectional void fraction profiles through the pressure vessel for fuel element bundles under typical nuclear reaction conditions. The gamma ray tomography system consists of a Cs137 isotopic source with an activity of about 165 GBq and a detector arc containing 320 single elements. The source radiation is restricted to a flat fan beam with a tungsten collimator. The average spatial resolution of the system is 3 mm in plane and 8 mm axial. With a special gantry vertical positioning and continuous rotation of the measurement setup is realised which is necessary for a complete tomography in different planes. Typically, transversal scans require an approximate recording time of 25 minutes. Gamma ray tomography is a relative measurement method. To determine void fraction calibration measurements are recorded at zero and one hundred percent void fraction respectively. It is a challenge to develop a tomography measurement system that is non-sensitive to temperature changes, high humidity and electrical fields to scale the void measurement to the calibration data. Cross-sectional images are reconstructed by standard filtered back projection algorithms.
Keywords: gamma ray tomography, void distribution
  • Contribution to proceedings
    15th International Conference on Nuclear Engineering (ICONE15), 22.-26.04.07, Nagoya, Japan
    Proceedings of the ICONE15, Paper No. ICONE15-10440
  • Lecture (Conference)
    15th International Conference on Nuclear Engineering (ICONE15), 22.-26.04.07, Nagoya, Japan

Publ.-Id: 9247 - Permalink


High Peak Current Design of a superconducting Cavity for a SRF Photoinjector
Janssen, D.; Marhauser, F.; Volkov, V.;
A 1.5-cell cavity for a superconducting RF gun has been designed and a magnetic RF mode for emittance compensation is applied. For a peak current of 125 A a transverse emittance of 1.8 mm mrad has been obtained.
  • Poster
    28 th Free Electron Laser Conference FEL 2006, 27.08.-01.09.2006, Berlin, Germany
  • Contribution to proceedings
    28 th Free Electron Laser Conference FEL 2006, 27.08.-01.09.2006, Berlin, Germany, 571-574

Publ.-Id: 9246 - Permalink


Kontrolle von Aluminium-Feinguss mittels Einsatz einer elektromagnetischen Induktionspumpe
Gerbeth, G.; Buchenau, D.; Eckert, S.; Galindo, V.; Willers, B.; Witke, W.;
Die numerischen und experimentellen Arbeiten zur Auslegung und dem Test einer elektromagnetischen Pumpe zur Kontrolle des Füllprozesses beim Aluminium-Feinguss werden zusammen gefasst. Weiterhin wird über die industriellen Ergebnisse des Einsatzes eines statischen Magnetfeldes auf die Gussteilqualität berichtet.
  • Article, self-published (no contribution to HZDR-Annual report)
    Forschungszentrum Rossendorf 2006
    Abschlussbericht zum BMBF-Projekt 01 RW 0304, Dezember 2006

Publ.-Id: 9245 - Permalink


Density functional investigation of the (113)[-110] twin grain boundary in TiO2 anatase and its influence on magnetism in diluted magnetic semiconductors
Gemming, S.; Janisch, R.; Schreiber, M.; Spaldin, N. A.;
Density-functional calculations were carried out for the (113)[-110] tilt grain boundary in the anatase modification of TiO2, with and without magnetic Co dopants. The boundary exhibits a low energy of 0.88 J/m^2 and no rigid translation of the grains. It is composed from four distinct structural units, and a deviation from the mirror-symmetric atom arrangement due to local relaxation is found. The analysis of the electronic structure indicates that the grain boundary is electronically inactive, because it introduces no boundary-specific states in the bulk band gap, and only minor differences between the valence band structures of the grain boundary and the pure bulk are obtained. The regular arrangement of the quite open structural units provides the possibility of doping the grain boundary with electronically or magnetically active elements, which is explored by doping the supercell with Co. In this diluted magnetic semiconductor the (113)[-110] grain boundary can enhance the ferromagnetic interaction by providing convenient bond angles for ferromagnetic superexchange.
Keywords: dilute magnetic semiconductor, oxide, grain boundary

Publ.-Id: 9244 - Permalink


Untersuchung von Spektraleigenschaften kugelsymmetrischer alpha2-dynamos mit Techniken der Funktionalanalysis und Operatortheorie
Günther, U.; Stefani, F.; Gerbeth, G.;
Zum besseren Verständnis natürlicher Dynamos und zur Datenauswertung und Auslegung von Dynamoexperimenten ist ein vertieftes Verständnis des Spektrums von Dynamooperatoren nötig. Dies gilt insbesondere für die Erklärung von Umpolungsprozessen des Erdmagnetfeldes, die sehr wahrscheinlich mit spektralen Phasenübergängen zwischen nicht-oszillierenden und oszillierenden Lösungen der Induktionsgleichung in engem Zusammenhang stehen. Der erste Schwerpunkt des Projektes lag auf spektraltheoretischen Grundlagenuntersuchungen einfacher Dynamomodelle mit kugelsymmetrischen helikalen Turbulenzparametern. Hier konnte gezeigt werden, dass der Differentialausdruck des entsprechenden Dynamo-Operators eine diskrete Symmetrie besitzt, welche es erlaubt, ihn für idealisierte Randbedingungen als selbstadjungierten Operator in einem Krein-Raum (einem Hilbert-Raum mit zusätzlicher indefiniter Metrik) zu behandeln. Dadurch besitzt er eine Vielzahl von Gemeinsamkeiten mit Hamilton-Operatoren der PT-symmetrisch erweiterten Quantenmechanik, welche sich ebenfalls als Operatortheorie in Krein-Räumen formulieren lässt. Viele dieser Parallelen wurden aufgezeigt, darunter das spektrale Verzweigungsverhalten zweiter und höherer Ordnung. Der zweite Schwerpunkt des Projektes lag auf der numerischen Behandlung des betrachteten einfachen Dynamomodells mit nichtlinearer Rückwirkung und Rauschen. Dabei konnte einerseits gezeigt werden, dass sich die typischen Eigenschaften von Umpolungen tatsächlich auf die Magnetfelddynamik in der Nähe spektraler Verzweigungspunkte zurückführen lassen. Andererseits wurde gezeigt, dass es eine starke Tendenz hochüberkritischer Dynamos gibt, sich in einen zu Umpolungen neigenden Zustand zu begeben, und dass sich die typischen Umpolungszeiten des Geodynamos ebenfalls auf die hohe Überkritikalität zurückführen lassen. Die bemerkenswerte Übereinstimmung der numerisch bestimmten Umpolungsmerkmale mit denjenigen des realen Geodynamos legen den Schluß nahe, dass der untersuchte Umpolungsmachanismus in der Nähe spektraler Verzweigungspunkte generischen Charakter hat und sich auch in komplizierteren Dynamomodellen identifizieren lassen sollte.
  • Article, self-published (no contribution to HZDR-Annual report)
    Forschungszentrum Rossendorf 2006
    Abschlussbericht zum DFG-Projekt Ge 682/12-2, Mai 2006

Publ.-Id: 9243 - Permalink


Fermi surfaces of the half heusler compounds Ce1-xLaxBiPt
Bianchi, A. D.; Wosnitza, J.; Kozlova, N.; Freudenberger, J.; Schultz, L.; Opahle, I.; Elgazzar, S.; Richter, M.; Goll, G.; von Löhneysen, H.; Yoshino, T.; Takabatake, T.;
We report on the Fermi surface in the correlated half-Heusler compounds Ce1-xLaxBiPt. In CeBiPt, as well as in Ce0.95La0.05BiPt, we find a temperature-dependent Fermi-surface topology. In addition, we observe a field-induced change of the electronic band structure as discovered by electrical-transport measurements in pulsed magnetic fields. For magnetic fields above about 25 T, the charge-carrier concentration determined from Hall-effect measurements increases nearly 30%, whereas the Shubnikovde Haas (SdH) signal disappears at the same field [1]. In the non-4f compound LaBiPt the Fermi surface remains unaffected, suggesting that these features are intimately related to the Ce 4f electrons. Electronic band-structure calculations point to a 4f-polarization-induced change of the Fermi-surface topology.
  • Poster
    International Conference on Magnetism (ICM), 20.-25.08.2006, Kyoto, Japan

Publ.-Id: 9242 - Permalink


Magnetic properties of transition-metal nanoclusters on biological substrates
Herrmannsdörfer, T.; Bianchi, A.; Papageorgiou, T.; Pobell, F.; Wosnitza, J.; Selenska-Pobell, S.; Pollmann, K.; Merroun, M.;
Compared to their bulk counterparts, micro- and nanogranular materials can reveal a diverse appearance of physical properties. In particular, their magnetic and superconducting behaviour can be drastically changed. Recently we have started to investigate transition metal clusters with a well defined grain size of 1 nm. These metal nanoclusters have been deposed on a regular square lattice of a biological template. In more detail, this template is a purified self-assembling paracrystalline surface layer (S-layer) of the bacillus sphaericus JG-A12 which exhibits square symmetry and is composed of identical protein monomers. The nucleation sites of the nanoclusters are most probably the pores of the S-layers. The S-layer proteins are capable of selective and reversible binding of high amounts of metals, making the S-layer also interesting for technological applications. The transition metal nanoclusters were investigated using EXAFS-spectroscopy and SQUID-magnetometry. First data of their magnetization at 0 < B < 7T and 1.8 K < T < 350 K reveal interesting magnetic properties. The Stoner enhancement factor of the d conduction-electron susceptibility in the Pd and Pt nano clusters is dramatically reduced compared to the one of bulk transition metals. In the case of granular Pt, the weakened magnetism of the 5d electrons is considered to play a crucial role for the occurrence of superconductivity by adjusting the balance between electron-phonon interaction and competing magnetic interactions observed for micron [1] and submicron [2] grain size powders. As the superconducting transition temperature has been observed to increase clearly with decreasing Pt grain size, we focus our interest also on the search of superconductivity in the transition metal nanoclusters.
  • Lecture (Conference)
    International Conference on Magnetism (ICM), 20.-25.08.2006, Kyoto, Japan

Publ.-Id: 9241 - Permalink


Development of a prototype superconducting cw cavity and cryomodule for energy recovery
Mcintosh, P. A. B.; Dykes, C. D.; Todd, D. M.; Belomestnykh, B.; Liepe, S.; Medjidzade, M.; Padamsee, V.; Sears, H.; Shemelin, J.; Proch, V. D.; Buechner, A.; Michel, P.; Teichert, J.; Kimura, T.; Smith, T. I.; Byrd, J.; Corlett, J. N.; Li, D.;
Energy Recovery LINAC (ERL) and LINAC-driven FEL proposals and developments are now widespread around the world. Superconducting RF (SRF) cavity advances made over the last 10 years for TESLA/TTF at 1.3 GHz, in reliably achieving accelerating gradients >20 MV/m, suggest their suitability for these ERL and FEL accelerators. Typically however, photon fluxes are maximised from the associated insertion devices when the electron bunch repetition rate is as high as possible, making CW-mode operation at high average current a fundamental requirement for these light sources. Challenges arise in controlling the substantial HOM power and in minimizing the power dissipated at cryogenic temperatures during acceleration and energy recovery, requiring novel techniques to be employed. This paper details a collaborative development for an advanced high-Q0 cavity and cryomodule system, based on a modified TESLA cavity, housed in a Stanford/Rossendorf cryomodule. The cavity incorporates a Cornell developed resistive-wall HOM damping scheme, capable of providing the improved level of HOM damping and reduced thermal load required.
  • Contribution to proceedings
    European Particle Accelerator Conference EPAC 2006, 26.-30.06.2006, Edinburgh, GB
    EPAC 2006 - Proceedings, 436

Publ.-Id: 9240 - Permalink


Crenarchaeota 1.1b and Firmicutes consortium recovered from a uranyl nitrate treated uranium waste sample and its possible role against the toxicity of uranium
Reitz, T.; Geissler, A.; Merroun, M.; Selenska-Pobell, S.;
Supplementations of a sample collected from a depleted uranium mining waste pile with uranyl nitrate induced significant changes in microbial community structure during the first four weeks of incubation. At the later stages of the treatment, however, the initial composition of the community, indigenous for the untreated samples and consisting mostly of uranium sensitive populations, started to set up. This indicates that the added uranium was no longer bio-available, possibly due to the interactions of the induced at the first stages of the treatment uranium resistant populations with the added radionuclide. Studies on archaeal diversity demonstrated a strong shifting from the subgroup 1.1a to the subgroup 1.1b of the mesophilic soil Crenarchaeota within the first four weeks of the incubations.
Our efforts to cultivate representatives of this crenarchaeal group on specific enrichment media from the sample treated with uranyl nitrate under anaerobic (corresponding to the natural) conditions, resulted in the recovery of a consortium consisting of the mentioned 1.1b Crenarchaeota mixed with populations of Firmicutes, mainly of Clostridium spp. Clostridia can effectively interact with uranium and they can also fermentatively reduce nitrate to ammonium. Because an ammonia oxidizing activity was deduced on the basis of meta-genomic analyses for the closest relative to the stimulated in our case 1.1b populations, we speculate that the clostridia possibly supply the crenarchaeal members of the recovered synergetic consortium with ammonia. In addition, a Paenibacillus sp. isolate was cultivated from this consortium and its interactions with uranium were studied by using TEM and EDX analyses.
  • Poster
    Annual Conference of the Association for General and Applied Microbiology (VAAM), 01.-04.04.2007, Osnabrück, Germany
  • Contribution to proceedings
    Annual Conference of the Association for General and Applied Microbiology (VAAM), 01.-04.04.2007, Osnabrück, Germany
    Biospektrum, Das Magazin für Biowissenschaften, Tagungsband: Elsevier, 0947-0867, 193

Publ.-Id: 9239 - Permalink


Interaction mechanisms of bacterial strains isolated from uranium mining waste piles with U and Pb
Merroun, M.; Geissler, G.; Raff, J.; Hennig, C.; Selenska-Pobell, S.;
Bacterial isolates belonging to two different groups of Gram-positive bacteria, namely to Arthrobacter sp. of Actinobacteria and to Bacillus sphaericus of Firmicutes were cultivated from a uranium mining waste pile near the town of Johanngeorgenstadt in Germany. We demonstrate that these two kinds of isolates possess different strategies to protect their populations from the toxicity of uranium. Transmission electron microscopy (TEM) analyses showed that the Arthrobacter sp. strains accumulated this radionuclide intracellularly, although a significant part of the uranium treated Arthrobacter sp. population remained radionuclide-free. X-ray absorption spectroscopy (XAS) studies demonstrated that uranium was mainly coordinated to bacterial organic phosphate groups in a monodentate binding mode.
In the case of the Bacillus sphaericus isolate JG-A12 uranium was bound on the cell surface by the bacterial surface layer (S-layer) protein. Extended x-ray absorption fine structure (EXAFS) spectroscopic analyses demonstrated that the radionuclide was complexed by carboxylic groups in a bidentate fashion and by phosphate groups in a monodentate fashion.
X-ray diffraction (XRD) analysis indicated that the growing cells of the arthrobacterial strains precipitated Pb as galena (PbS), whereas in non-growing conditions pyromorphite (Pb5(PO4)3Cl) phase was produced by the cells, alleviating probably the toxicity of Pb. TEM analyses showed that the pyromorphite precipitates were mainly located at the cell surface.
Because representatives of Arthrobacter and Bacillus were induced in uranium supplemented samples of the same uranium mining waste we suggest that these organisms play an important protective role for the natural bacterial community of the studied habitat.
  • Poster
    Annual Conference of the Association for General and Applied Microbiology (VAAM), 01.-04.04.2007, Osnabrück, Germany
  • Contribution to proceedings
    Annual Conference of the Association for General and Applied Microbiology (VAAM), 01.-04.04.2007, Osnabrück, Germany
    Biospektrum, Das Magazin für Biowissenschaften, Tagungsband: Elsevier, 0947-0867, 193

Publ.-Id: 9238 - Permalink


Bacterial response to sodium and uranyl nitrate treatments of uranium mining waste samples
Geissler, A.; Reitz, T.; Selenska-Pobell, S.;
The response of bacterial community of a depleted uranium mining waste pile to increased concentrations of uranyl or sodium nitrate was studied in microcosm experiments under conditions corresponding to the natural. For this, the 16S rRNA- and the narG-gene retrievals were applied. Both retrievals demonstrated that at the early stages of the treatments with sodium nitrate a strong activation of nitrate reducing and denitrifying populations, mainly of Firmicutes and Betaproteobacteria, occurred that had overgrown the originally predominating in the untreated samples populations of Acidobacteria, Alpha-, and Deltaproteobacteria. The parallel treatments with uranyl nitrate demonstrated that only particular populations of the above mentioned induced Firmicutes and betaproteobacterial nitrate-reducers are uranium resistant. More significant was the stimulation in these samples of the gammaproteobacterial denitrifyers, able also to effectively interact with and to immobilize the added uranium. After longer incubations both kinds of treatments resulted in an establishment of populations characteristic for the original non-treated sample. The latter indicates that particular members of the natural bacterial consortium of the studied uranium waste site possess a high potential to deal with increased and toxic concentrations of uranium and nitrate, which usually co-contaminate these environments. In this way the diversity of the whole community which includes also uranium sensitive populations is kept unaffected. These results explain our previous finding that the bacterial communities of a large variety of uranium mining waste samples collected from the same site but from different depths and polluted with uranium to a different extend, exhibit almost the same structure.
  • Contribution to proceedings
    VAAM-Jahrestagung 2007, 01.-04.04.2007, Osnabrück, Germany
    Biospektrum, Das Magazin für Biowissenschaften, Tagungsband:: Elsevier, 0947-0867
  • Poster
    VAAM-Jahrestagung 2007, 01.-04.04.2007, Osnabrück, Germany

Publ.-Id: 9237 - Permalink


Investigating the accuracy of the FLUKA code for transport of therapeutic ion beams in matter
Sommerer, F.; Parodi, K.; Ferrari, A.; Poljanc, K.; Enghardt, W.; Aiginger, H.;
In-beam positron emission tomography (PET) is currently used for monitoring the dose delivery at the heavy ion therapy facility at GSI Darmstadt. The method is based on the fact that carbon ions produce positron emitting isotopes in fragmentation reactions with the atomic nuclei of the tissue. The relation between dose and beta(+)-activity is not straightforward. Hence it is not possible to infer the delivered dose directly from the PET distribution. To overcome this problem and enable therapy monitoring, beta(+)-distributions are simulated on the basis of the treatment plan and compared with the measured ones. Following the positive clinical impact, it is planned to apply the method at future ion therapy facilities, where beams from protons up to oxygen nuclei will be available. A simulation code capable of handling all these ions and predicting the irradiation-induced beta(+)-activity distributions is desirable. An established and general purpose radiation transport code is preferred. FLUKA is a candidate for such a code. For application to in-beam PET therapy monitoring, the code has to model with high accuracy both the electromagnetic and nuclear interactions responsible for dose deposition and beta(+)-activity production, respectively. In this work, the electromagnetic interaction in FLUKA was adjusted to reproduce the same particle range as from the experimentally validated treatment planning software TRiP, used at GSI. Furthermore, projectile fragmentation spectra in water targets have been studied in comparison to available experimental data. Finally, cross sections for the production of the most abundant fragments have been calculated and compared to values found in the literature.
  • Physics in Medicine and Biology 51 (17)(2006)17, 4385-4398

Publ.-Id: 9236 - Permalink


Ursachenermittlung und Beseitigung der Folgen des Brandes am Heißstrangmodell der TOPFLOW-Anlage
Beyer, M.; Carl, H.;
Am 12.05.06 kam es gegen 13.00 Uhr bei einem Test von Wärmeisolationsmaterial in einem Druckbehälter der Versuchsanlage TOPFLOW zu einem Brand. Der vorliegende Bericht enthält eine Zusammenfassung dieses Ereignisses, basierend auf einer Vielzahl von Materialien, die in diesem Zusammenhang erarbeitet wurden. Nach einer kurzen Beschreibung des Ereignisablaufes werden die Gründe für die Entstehung des Brandes analysiert. Darauf aufbauend erläutern die Autoren die Maßnahmen zur Schadensbeseitigung sowie Änderungen in der Anlagentechnik, die einen erneuten Brand ausschließen. Zukünftig werden zur Isolation geeignetere Werkstoffe verwendet und die Behälteratmosphäre mit Stickstoff inertisiert.
Keywords: Polysiloxan, thermal insulation under pressure, insulation material
  • Article, self-published (no contribution to HZDR-Annual report)
    Forschungszentrum Rossendorf 2006
    FZR\FWS\2006\02
    8 Seiten

Downloads:

Publ.-Id: 9235 - Permalink


Berechnungen zur kritischen Leistung eines Siedewasserreaktors im kalten Zustand mit dem Programm DYN3D
Kliem, S.; Laczkó, G.; Mittag, S.;
Die in diesem Bericht dokumentierten Ergebnisse sind vertraulich.
  • Article, self-published (no contribution to HZDR-Annual report)
    Forschungszentrum Rossendorf 2006
    FZR\FWS\2006\04
    25 Seiten

Publ.-Id: 9234 - Permalink


Single Shot Intrared Ellipsometry with a Free Electron Laser and its Potential Applications
Gensch, M.; Lee, J. S.; Hinrichs, K.; Esser, N.; Seidel, W.; Röseler, A.; Schade, U.;
A novel division of amplitude polarimeter (DOAP) approach for single shot - infrared ellipsometry with a free electron laser source is presented. The set-up enables the simultaneous determination of the two independent ellipsometric parameters by measuring two ratios of intensities so that variations of the pulse power essentially do not affect the result. As proof-of-principle experiment we determined successfully the optical response of thin polymeric films on silicon. The high brilliance of the ELBE free electron laser combined with the DOAP principle gives unique opportunities for e.g. micro-focus, imaging or pump-probe ellipsometry.
  • Poster
    Joint 31st International Conference on Infrared and Millimeter Waves and 14th International Conference on Terahertz Electronics, 18.-22.09.2006, Shanghai, China
  • Contribution to proceedings
    Joint 31st International Conference on Infrared and Millimeter Waves and 14th International Conference on Terahertz Electronics, 18.-22.09.2006, Shanghai, China
    Conference digest of the 2006 IRMMW-THz 2006, 1-4244-0400-2, 416

Publ.-Id: 9233 - Permalink


First lasing at the U100-FEL
Seidel, W.;
First lasing of the far-infrared FEL at ELBE was achieved on August 21, 2006. This FIR-FEL bases on an undulator with 100 mm period and a cavity with a partial waveguide. The waveguide was installed to fit the optical resonator mode into the undulator gap.
  • Lecture (Conference)
    28th Int. Free Electron Laser Conference, 27.08.-01.09.2006, Berlin/Dresden, Deutschland

Publ.-Id: 9232 - Permalink


Remote Controlled IR-Diagnostic Station for the FEL at Rossendorf
Seidel, W.; Friebel, S.; Jainsch, R.; Justus, M.; Leege, K.-W.; Pröhl, D.; Stehr, D.; Weigelt, H.; Winnerl, S.; Wohlfarth, D.;
The remote controlled diagnostic station delivers a small amount of the IR radiation by means of a system of relocatable mirrors and beam splitters to the spectrometer and to various power detectors working in different power ranges. Furthermore, a long wavelength MCT detector is integrated in the diagnostic station for gain and loss measurement in the whole wavelength range of the U27-FEL. The average radiation power available for the users can be reduced by a remote controlled attenuator. To characterize the optical micropulse duration we have built a non-collinear background-free autocorrelator as a part of the diagnostic station. By using a CdTe single-crystal for second-harmonic generation a broad wavelength coverage is obtained. Certain experiments require high pulse energies but moderate or low average power. For such experiments the repetition rate of the Rossendorf FEL can be reduced from 13 MHz to 1 kHz, in the future also to 1 Hz, by a semiconductor plasma switch excited with a synchronized Nd:YAG amplifier. This system is under commissioning and we will report on first results.
  • Poster
    28th Int. Free Electron Laser Conference, 27.08.-01.09.2006, Berlin/Rossendorf, Deutschland
  • Contribution to proceedings
    28th Int. Free Electron Laser Conference, 27.08.-01.09.2006, Berlin/Dresden, Deutschland
    Remote Controlled IR-Diagnostic Station for the FEL at Rossendorf: JACoW, FEL06

Publ.-Id: 9229 - Permalink


The Radiation Source at Dresden-Rossendorf - a New FEL User Facility for the Infrared
Seidel, W.;
First lasing of the mid-infrared free-electron laser at ELBE was achieved on May 7, 2004. The Radiation Source ELBE at the Forschungszentrum Rossendorf in Dresden, Germany is currently under transition from commissioning to regular user operation. Presently the electron linac produces an up to 35 MeV, 1 mA (cw) electron beam which is allotted to generate various kinds of secondary radiation. After the successful commissioning of the bremsstrahlung and channeling-X-ray facilities during 2003 stable lasing has now been observed in the IR range. The oscillator FEL is equipped with two planar undulator units, both consisting of 34 hybrid permanent magnets with a period of 27.3 mm (Krms = 0.3 . . . 0.7). The distance between the two parts is variable and the gaps can be adjusted and tapered independently. This devise provides continuously tunable radiation in the spectral range of 450 - 2500 cm-1 (4 to 22 µm), at peak energies of several hundred nJ in a ps pulse train at 13 MHz repetition rate. To ensure the continuous variation of the wavelength up to 150 microns we want to complement the U27 undulator by a permanent magnet undulator with a period of 100 mm (U100) in 2006.
Starting 2005, the FEL operates as a user facility, being open to users worldwide, provided their scientific proposals have been favorably evaluated by the panel responsible for distribution of beam time. Under the name "FELBE" the facility is member of the EC funded "Integrating Activity on Synchrotron and Free Electron Laser Science (IA-SFS)", which comprises most synchrotron and FEL facilities in Europe and provides financial support to users from EC and associated states. Instructions for beam time applications is available on the FELBE website (www.fz-rossendof.de/FELBE) .
The relevant user facilities at FELBE comprise 6 laboratories. Some of these are also used by in-house groups, mainly in the areas of semiconductor physics, biophysics, and radiochemistry and experiments there will require a certain level of collaboration with the in-house researchers. In particular noteworthy is the fact that a number of other optical sources from the visible to the THz frequency range are available, e.g. for two-color pump-probe experiments. These sources (Ti:sapphire laser and amplifer, OPO, OPA, broad-band THz generator) are all based on Ti:sapphire oscillators which are synchronized with the FEL with an accuracy better than one ps. Two laboratories are intended to provide users with utmost flexibility for their own experiments, also in scientific areas not covered by in-house groups (e.g., surface physics, molecular physics).
For the ELBE team.
  • Poster
    WIRMS 2005, Int. Workshop on Infrared Microscopy and Spectroscopy with Accelerator-Based Sources, 26.-30.06.2005, Rathen, Deutschland

Publ.-Id: 9228 - Permalink


FEL-light induced changes in thin organic films observed by dynamic Brewster Angle Microscopy
Sczepan, M.; Furlinski, G.; Wohlfarth, D.; Seidel, W.; Fahmy, K.;
Brewster angle microscopy is a proven technique for the evaluation of thin organic films[1], especially for the observation of phase transitions in monolayers[2]. If a sample is observed under Brewster angle conditions, small changes in the refractive index of the surface can be observed and thus thin layers on the surface can be made visible. Coupling a Brewster angle microscope with a powerful light source like the FEL allows investigation of IR-induced changes in thin organic films. Using the temporal characteristics of the pump and sample illumination light, fast processes (down to 20 µs with camera shutter synchronization or even down to some nanoseconds with synchronized pulsed illumination) can be tracked.

[1] S. Hènon, J. Meunier; Rev. Sci. Instr. 62, 936 (1991)
[2] S. Rivière, S. Hènon et al.; J. Chem. Phys. 101(11), 10045 (1994)
  • Poster
    WIRMS 2005, Int. Workshop on Infrared Microscopy and Spectroscopy with Accelerator-Based Sources, 26.-30.06.2005, Rathen, Deutschland

Publ.-Id: 9227 - Permalink


Intranuclear cascade+percolation+evaporation model applied to the12C+197Au system at 1 GeV/nucleon
Seidel, W.; Volant, C.; Turzo, K.; Trautmann, W.; Auger, G.;
The nucleus-nucleus Lie`ge intranuclear-cascade+percolation+evaporation model has been applied to the12C+197Au data measured by the INDRA-ALADIN collaboration at GSI. After the intranuclear cascade stage, the data are better reproduced when using the Statistical Multiframentation Model as afterburner. Further checks of the model are done on data from the EOS and KAOS collaborations.
  • Nuclear Physics A 734(2004), 545-548

Publ.-Id: 9223 - Permalink


Hydrogen gettering at buried defect layers in ion-implanted silicon by plasma hydrogenation and annealing
Ulyashin, A.; Christensen, J. S.; Svensson, B. G.; Kögler, R.; Skorupa, W.;
In this study gettering of atomic hydrogen in-diffused from a plasma hydrogenated surface into self ion implanted and annealed Si is investigated. Cz Si p-type samples were implanted with 3.5 MeV Si+ ions to a fluence 5 × 1015 cm−2 and then annealed at 900 °C. The hydrogenation of the samples was performed by exposure to the direct RF hydrogen plasma in a plasma enhanced chemical vapour deposition (PECVD) reactor. A remote deuterium plasma treatment was used as well. Secondary ion mass spectrometry (SIMS) was employed for analysis of the hydrogen/deuterium distributions. It is demonstrated for the first time that accumulation of diffused hydrogen occurs both at the projected range of the silicon ions, Rp, and at Rp/2. It is shown that hydrogen accumulation by vacancy-type defects at Rp/2 is as efficient as for trapping by dislocations at Rp.
Keywords: Plasma, Defects, Defect trapping, Silicon, Hydrogen

Publ.-Id: 9222 - Permalink


Status quo of the Dresden High Magnetic Field Laboratory
Wosnitza, J.; Bianchi, A. D.; Herrmannsdörfer, T.; Zherlitsyn, S.; Zvyagin, S.;
At the outskirts of Dresden, Germany, a new high magnetic field laboratory for pulsed non-destructive magnetic fields up to 100 T is under construction. This user laboratory at the research center (Forschungszentrum) Rossendorf will offer access to different pulsed-field coils. Besides the ultimate goal of constructing a multi-pulse magnet reaching 100 T in a bore of 20 mm with a pulse width of about 10 ms, further self-designed high-energy coils will be provided. For thermodynamic experiments, e.g., a pulsed coil for 60 T in 40 mm and 0.5 s is planned. The necessary energy of up to 50 MJ for coil operation recently became available through a world-unique capacitor bank working at 24 kV. Coil design, coil winding, as well as coil testing have been established in house. First user-type magnets for fields up to 65 T for 10 ms in a bore of 20 mm have been tested successfully. As an outstanding feature of the newly built laboratory, the bright light of a next-door free-electron-laser facility will allow dedicated high-field infrared spectroscopy. A broad range of experimental techniques is being developed both for user and in-house research in static and pulsed magnetic fields. The new Hochfeld-Magnetlabor Dresden (HLD) is planned to open as user facility in 2007.
e-mail:j.wosnitza@fz-rossendorf.de
  • Poster
    Yamada Conference LX on Research in High Magnetic Fields (RHMF), 16.-19.08.2006, Sendai, Japan

Publ.-Id: 9221 - Permalink


Realistische Simulation von Reaktivitätsstörfällen mit gekoppelten neutronenkinetisch-thermohydraulischen Systemcodes
Kliem, S.;
Die in diesem Bericht dokumentierten Ergebnisse sind vertraulich.
  • Article, self-published (no contribution to HZDR-Annual report)
    Forschungszentrum Rossendorf 2006
    FZR\FWS\2006\01
    76 Seiten

Publ.-Id: 9220 - Permalink


Paradox of inductionless magnetorotational instability
Priede, J.; Grants, I.; Gerbeth, G.;
The magnetorotational instability (MRI) is sought to be responsible for the fast formation of stars and entire galaxies in accretion disks. The velocity distribution in accretion disks is apparently hydrodynamically stable by the Rayleigh criterion while the viscosity alone is not sufficient to account for the observable accretion rates. However, a hydrodynamically stable velocity profile in the cylindrical Taylor-Couette flow can become unstable in the presence of magnetic field (Velikhov, Sov. Phys. JETP 36, 995, 1959; Balbus and Hawley, Astrophys. J. 376, 214, 1991). In this case, an axial magnetic field provides an additional mechanism of energy exchange between the base flow and perturbations that, however, requires the magnetic Reynolds number to be at least Rm ~ 10. Note that for a liquid metal with the magnetic Prandtl number Pm ~ 10-5 this corresponds to a hydrodynamic Reynolds number Re = Rm/Pm ~ 106. Thus, this instability is hardly observable in the laboratory because any conceivable flow at such Reynolds number would be turbulent. However, it was shown recently (Hollerbach and Rüdiger, Phys. Rev. Lett. 95, 124501, 2005) that MRI can take place in the cylindrical Taylor-Couette flow at Re ~ 103 when the imposed magnetic field is helical. The most surprising fact is that this type of MRI works even in the inductionless limit of Pm = 0 where the critical Reynolds number of the conventional MRI with axial magnetic field diverges as ~ 1/Pm. The induced currents are so weak in this limit that their magnetic field is negligible with respect to the imposed field. Thus, on one hand, the imposed magnetic field does not affect the base flow, which is the only source of energy for the perturbation growth. But on the other hand, flow perturbations are subject to additional damping due to the Ohmic dissipation caused by the induced currents. We show rigorously that, in the limit of Pm=0, the imposed magnetic field increases the energy decay rate of any particular perturbation. On one hand, this means that the energy of any perturbation, which is growing in the presence of magnetic field, grows even faster without the field and vice versa. On the other hand, the flow which is found to be unstable in the presence of magnetic field is certainly known to be stable without the field. This apparent contradiction constitutes the paradox of the inductionless MRI which we address in this study. We consider MRI in the inductionless approximation at Pm=0 that allows us to eliminate the magnetic field and, thus, leads to a considerable simplification of the problem containing only hydrodynamic variables as in the classical Taylor-Couette problem. First, we use a Chebyshev collocation method to calculate the eigenvalue spectrum of the linearised problem. In this way, we confirm that MRI with helical magnetic field indeed works in the inductionless limit. Second, we integrate the linearised equations in time to study the transient behaviour of small amplitude perturbations.
In this way, we show that the energy arguments are correct as well - the energy of an unstable perturbation indeed starts to grow faster when the magnetic field is switched off. However, there is no real contradiction between both facts. The energy grows only for a limited time and then turns to decay in accordance to the linear stability predictions. It is important to stress that the linear stability theory predicts the asymptotic development of an arbitrary small-amplitude perturbation, while the energy stability theory yields the instant growth rate of any particular perturbation but it does not account for the evolution of this perturbation. Thus, although switching off the magnetic field instantly increases the energy growth rate of the most unstable as well as that of any other perturbation, in the same time the critical perturbation ceases to be an eigenmode without the magnetic field.
  • Lecture (Conference)
    2nd Int. Symposium "Instabilities and Bifurcations in Fluid Dynamics", 15.-18.08.2006, Copenhagen, Denmark
  • Open Access LogoJournal of Physics: Conference Series 64(2007), 012011

Publ.-Id: 9219 - Permalink


NURESIM-Thermohydraulic Subproject, Work Package Pressurized Thermal Shock (PTS)
Lucas, D.;
This presentaion summarizes the results of the first 18 months period of the NURESIM project for the workpage 2.1 “Pressurized Thermal Shock (PTS)”. It mainly bases on the deliverables supplied by the partners involved in this workpage. In the Introduction some more general information on the PTS issue is given, which should help to clarify the integration of the single activities. Since the PTS scenario involves different flow situations, for which also different modelling approaches are necessary, the contributions are sorted according to these flow situations. The relations of the work done to the general aim of the NURESIM project, which is to establish a new code platform, is indicated by assigning the activities to 6 different types. The present status PTS workpage is in agreement with the planning of the NURESIM project, the expected results were met by the deliverables. The work done leads to an improvement of the simulation capabilities regarding a PTS flow situation, but caused by the complexity of the issue it will still be a long way to enable reliable predictions for the whole process from such simulations.
Keywords: PTS, CFD
  • Invited lecture (Conferences)
    NURESIM Seminar, 07.-08.11.2006, Paris, France

Publ.-Id: 9218 - Permalink


Autocorrelation measurements of the FELBE free-electron laser and photocurrent saturation study in two-photon QWIPs
Schneider, H.; Drachenko, O.; Winnerl, S.; Helm, M.; Walther, M.;
The two-photon QWIP approach involves three equidistant subbands, two of which are bound in the quantum well, and the third state is located in the continuum. The intermediate subband induces a resonantly enhanced optical nonlinearity, which is about six orders of magnitude stronger than in usual semiconductors. Temporal resolution is only limited by the sub-ps intrinsic time constants of the quantum wells, namely the intersubband relaxation time and the dephasing time of the intersubband polarization. Both properties make this device very promising for pulse diagnostics of pulsed mid-infrared lasers. We have performed autocorrelation measurements of ps optical pulses from the free-electron laser (FEL) facility FELBE at the Forschungszentrum Dresden Rossendorf. Using a rapid-scan autocorrelation scheme at a scan frequency of 20 Hz, high-quality quadratic autocorrelation traces are obtained, yielding ratios close to the theoretically expected value of 8:1 between zero delay and large delay for interferometric autocorrelation, and 3:1 for intensity autocorrelation. Thus, two-photon QWIPs provide an excellent new technique for online pulse monitoring of the FEL. In addition, we have investigated the saturation mechanism of the photocurrent signal, which is due to internal space charges generated in the detector.
Keywords: quantum well infrared photodetector, QWIP, two-photon absorption, photocurrent saturation, GaAs/AlGaAs, free-electron laser
  • Invited lecture (Conferences)
    SPIE Photonics West, Conference on "Ultrafast Phenomena in Semiconductors and Nanostructure Materials XI", 20.-25.01.2007, San Jose, CA, USA
  • Contribution to proceedings
    SPIE Photonics West, Conference on "Ultrafast Phenomena in Semiconductors and Nanostructure Materials XI", 20.-25.01.2007, San Jose, CA, USA
    SPIE Vol. 6471, Ultrafast Phenomena in Semiconductors and Nanostructure Materials XI, Bellingham: SPIE, 9780819465849, 64710T

Publ.-Id: 9217 - Permalink


Channels of potential energy dissipation during multiply charged Argon ion bombardment of Copper
Kost, D.; Facsko, S.; Möller, W.; Hellhammer, R.; Stolterfoht, N.;
The dissipation of potential energy of multiply charged Ar ions incident on Cu has been studied by complementary electron spectroscopy and calorimetry at charge states between 2 and 10 and kinetic energies between 100 eV and 1 keV. The emitted and deposited fractions of potential energy increase at increasing charge state, showing a significant jump for charge states q > 8 due to the presence of L-shell vacancies in the ion. Both fractions balance the total potential energy, thus rendering former perceptions of a significant deficit of potential energy obsolete. The experimental data are reproduced by computer simulations based on the extended dynamic classical-over-the-barrier model.
Keywords: Multiply charged ions, ion-surface interaction, energy deposition, Auger electron emission, calorimetry, classical over-the-barrier model
  • Physical Review Letters 98(2007), 225503

Publ.-Id: 9216 - Permalink


Optical Stimulated Electron Emission from Amorphous Silicon Dioxide Implanted with Iron Ions
in Russian
Kortov, V. S.; Zatsepin, A. F.; Biryukov, D. Y.; Schmidt, B.;
The photoelectron emission from SiO2 glasses and films after implantation of Fe+ ions was studied. Emission–active oxygen–vacancy defects like E'centers were detected. A long–range effect, which consisted in formation of point defects on the back side of the samples, was revealed when the samples were exposed to pulsed ion irradiation. Effects of radiation charging of surface layers of the test materials were analyzed.
Keywords: ion implantation, glass, E'-centers, photoelectron emission
  • Poverchnost 7(2006)7, 84-87

Publ.-Id: 9215 - Permalink


Nature of defect clusters in neutron-irradiated iron-based alloys deduced from small-angle neutron scattering
Bergner, F.; Ulbricht, A.; Gokhman, A.; Erak, D.;
The nature of the defect-solute clusters and/or atmospheres responsible for the irradiation-induced degradation of the mechanical properties of reactor pressure vessel steels is still subject of debate. It is therefore helpful to study model alloys, where the diversity of those features is constricted due to composition and where dominant effects can be identified or even isolated. The present investigation is focussed on Fe-based model alloys with intentionally varied Cu levels. The aim is to interpret deviations of the measured ratio of magnetic and nuclear scattering cross sections from the ratios calculated for pure vacancy clusters and pure Cu clusters. For the case of the low-Cu alloy the SANS results suggest the average scatterer to be an Fe-Cu-vacancy cluster of about 1 nm radius the composition of which is constricted according to given inequalities. For the case of the Cu-enriched alloy the SANS results are consistent with Cu-rich clusters of about 1.5 nm radius containing 15% vacancies per bcc lattice site.

Publ.-Id: 9214 - Permalink


Monitoring von PV-Anlagen mittels terrestrischer Strahlungsdaten
Bodach, M.; Gasch, S.; Rindelhardt, U.; Hiller, W.; König, S.; Mehlich, H.;
Die Performance Ratio ist die am häufigsten verwendete Größe zur Charakterisierung der Qualität von Photovoltaik-Anlagen. Diese Größe widerspiegelt dabei die Wirkungs-grade der einzelnen Komponenten als auch die Qualität des Gesamtdesigns (Anpassung WR/Generator, Verschattung, Hinterlüftung etc.) der Anlage.
Dieser Wert lässt sich einfach aus dem Quotient der abgegebenen Energie (hier eingespeiste Energie) und der zugeführten Energie (hier Einstrahlung in Modulebene) über dem gleichen Zeitintervall darstellen. Die meisten Anlagenbetreiber kennen zwar die eingespeiste Energie aus dem Daten-ogging ihrer Wechselrichter, aber insbesondere bei kleineren PV-Anlagen stehen keine Strahlungssensoren zur Verfügung.
Im Beitrag soll eine einfache Möglichkeit vorgestellt werden, wie diese Anlagenbetreiber trotzdem zu einer verlässlichen Aussage über die Performance Ratio ihrer Anlage kommen, indem die Daten aus anderen, vorhandenen Globalstrahlungsmessungen in der näheren Umgebung genutzt werden. Diese stehen - oft unentgeltlich - im Internet (z.B. Agrar- Meteorolo-gisches Messnetz in Sachsen) zur Verfügung und erlauben eine brauchbare Abschätzung des Performance Ratio. Die Untersuchungen dazu werden exemplarisch für Sachsen präsentiert.
Die Untersuchungen ergaben, dass die gemessenen Globalstrahlungswerte in Sachsen nur relativ gering voneinander abweichen. Weiterhin wurde untersucht, welcher Einfluss zu erwarten ist, wenn der Abstand zwischen der Einstrahlungsmessstelle und der zu bewertenden PV-Anlage weiter voneinander entfernt ist als 50 km.
In Erweiterung bisheriger Ergebnisse werden hier Auswertungen über ein bzw. zwei Kalenderjahre vorgestellt.
Keywords: PV plant performance, performance ratio
  • Contribution to proceedings
    22. Symposium Photovoltaische Solarenergie, 07.-09.03.2007, Staffelstein, Germany
    Tagungsband, Beitrag 75, 978-3-934681-53-8
  • Poster
    22. Symposium Photovoltaische Solarenergie, 07.-09.03.2007, Staffelstein, Germany

Publ.-Id: 9213 - Permalink


Metallographic examination, depth-sensing microhardness and modulus of Eurofer'97
Heintze, C.;
Two halves of Charpy specimens of Eurofer’97 were examined by metallographic analysis, depth-sensing microhardness, Vickers hardness testing and ultrasonic pulse echo technique. The microstructure of the examined specimens of Eurofer’97 was found to be fine-grained and fully martensitic. Indentation hardness increases with decreasing load (indentation size effect). Eurofer’97 is elastically isotropic.
  • Article, self-published (no contribution to HZDR-Annual report)
    Forschungszentrum Rossendorf 2007
    FZD\FWS\2007\01
    10 Seiten

Publ.-Id: 9211 - Permalink


The Quantum-Functional Properties of Pr1-x-yLaxPbyTe
Herrmannsdörfer, T.; Bianchi, A.; Papageorgiou, T. P.; Wosnitza, J.;
The intermetallic compound Pr1-x-yLaxPbyTe shows a wide spectrum of physical phenomena. Depending on the metallurgical composition as function of x and y, the compound changes its behavior from nuclear magnetic order to super- or semiconductivity. In addition, there are interesting interplay effects between these ground states. In consequence, Pr1-x-yLaxPbyTe may serve as an interesting material for quantum-computing applications. In this contribution, we focus on our recent investigation of the magnetic properties of Pr1-yPbyTe. We present data of the magnetisation taken at 1.8 K < T < 350 K for various compositions y = 0, 90, 99, 99.9 %, i.e. turning the system from a van Vleck paramagnet, y = 0, into a doped semiconductor, y = 99.9 %.
  • Contribution to proceedings
    24th International Conference on Low Temperature Physics - LT24, 10.-17.08.2005, Orlando, United States
    AIP Conference Proceedings Vol. 850, 0-7354-0347-3, 1291-1292

Publ.-Id: 9210 - Permalink


Effect of nuclear deformation on the electric-dipole strength in the particle-emission threshold region
Dönau, F.; Rusev, G.; Schwengner, R.; Junghans, A.; Schilling, K. D.; Wagner, A.;
The role of the deformation for the photoabsorption cross section in the tail region of the electric Giant Dipole Resonance (GDR) is studied in terms of a deformed oscillator model and a Nilsson-plus-random-phase-approximation model. It is found within the framework of these approaches that extra electric dipole strength is generated at energies below the GDR maximum if the nuclear system is spacially deformed. This is important for the prediction of the stellar photodisintegration rates knowing that an extra strength can affect these rates even belo w the particle separation energies through the so-called gamma process. Because the nuclear deformation is governed by shell effects this extra strength does not directly correlate with varying neutron numbers.
Keywords: Oscillator Model, Nilsson-Model, Quasiparticle-Random-Phase-Approximation, nuclear deformation, Giant Dipole Resonance, photoabsorption cross section, E1 strength.

Publ.-Id: 9209 - Permalink


Monte Carlo study of backscatter in a flattening filter free clinical accelerator
Titt, U.; Vassiliev, O. N.; Pönisch, F.; Kry, S. F.; Mohan, R.;
In conventional linear accelerators, the flattening filter provides a uniform lateral dose profile. In intensity modulated radiation therapy applications, however, the flatness of the photon field and hence the presence of a flattening filter, is not necessary. Removing the filter may provide some advantages, such as faster treatments and smaller out-of-field doses to the patients. In clinical accelerators the backscattered radiation dose from the collimators must be taken into account when the dose to the target volume in the patient is being determined. In the case of a conventional machine, this backscatter is known to great precision. In a flattening filter free accelerator, however, the amount of backscatter may be different. In this study we determined the backscatter contribution to the monitor chamber signal in a flattening filter free clinical accelerator (Varian Clinac 21EX) with Monte Carlo simulations. We found that with the exception of very small fields in the 18-MV photon mode, the contribution of backscattered radiation to the monitor signal did not differ from that of conventional machines with a flattening filter. Hence, a flattening filter free clinical accelerator would not necessitate a different backscatter correction. (c) 2006 American Association of Physicists in Medicine.
  • Medical Physics 33(2006)9, 3270-3273

Publ.-Id: 9207 - Permalink


Bispidines as a new class of chelating agents for copper radionuclides
Juran, S.; Walther, M.; Stephan, H.; Steinbach, J.; Born, K.; Comba, P.; Kraus, W.; Emmerling, F.;
Introduction:
The synthesis, characterization and evaluation of novel hexadentate bispidine derivatives containing pyridine and/or imidazole units as donor groups are presented. Bispidine ligands (bispidine = 3,7-diazabicyclo[3.3.1]-nonane) show unique complexation behaviour towards transition metals [1,2]. The high thermodynamic stability of the complexes of these structurally reinforced ligands with Cu(II) offers the possibility to apply such complexes for diagnostic (64Cu) and therapeutic (67Cu) purposes [3]. Moreover the bispidine structure opens suitable chemical approaches to connect bio-molecules onto the skeleton, an important feature in view of the targeting of such complexes.

Experimental:
The ligands were prepared by two consecutive Mannich condensations according to the known procedure [1]. Cyclic voltammetry (CV) measurements were recorded on a BAS 100B instrument with a standard three-electrode cell (glassy carbon electrode, AgNO3/Ag reference electrode, Pt wire with auxiliary electrode) at 25 °C in degassed water in an Ar atmosphere. Bispidines were labelled with 67Cu using 67CuCl2. To 200 µl of the ligand solution (10-4 M ligand in 0.05 M MES/NaOH buffer, pH = 5.4) 250 kBq of 67CuCl2 were added. 67Cu-labelling yields were studied by TLC using RP18 TLC plates which were developed in acetonitrile /water (0.1%TFA) = 4/1.

Results and Discussion:
CV measurements were performed in order to estimate the stability of the copper(II) bispidine complexes. Strongly negative redox potentials were found for all compounds investigated indicating the high stability of the Cu(II) complexes [2]. Labelling experiments of the new bispidines with 67Cu and 64Cu indicate the rapid formation of radiocopper complexes under mild conditions in almost quantitatively yields.

Conclusion:
The radiocopper complexes were found to be stable in the presence of a high excess of competing ligands, and showed a high in vitro stability in rat plasma up to 24 h. Studies on the bioconjugation of the bispidine 64Cu complexes are now in progress.

Acknowledgement:
Roger Schibli (Paul Scherrer Institute, Villigen, Switzerland) is gratefully acknowledged for providing copper-67.

[1] P. Comba, W. Schiek, Coord. Chem. Rev. 2003, 238-239, 21-29.
[2] C. Bleiholder et al. Inorg. Chem. 2005, 44, 8145-8155.
[3] M. J. Welch, C. S. Redvanly, Eds., Handbook of Radiopharmaceuticals: Radiochemistry and Applications, J. Wiley & Sons, Chichester, 2003
  • Poster
    17th International Symposium on Radiopharmaceutical Sciences, 30.04.-04.05.2007, Aachen, Deutschland
  • Abstract in refereed journal
    Journal of Labelled Compounds and Radiopharmaceuticals 50(2007)Suppl. 1, S234

Publ.-Id: 9205 - Permalink


A Monte Carlo model for calculating out-of-field dose from a Varian 6 MV beam
Kry, S. F.; Titt, U.; Pönisch, F.; Followill, D.; Vassiliev, O. N.; White, R. A.; Mohan, R.; Salehpour, M.;
Dose to the patient outside of the treatment field is important when evaluating the outcome of radiotherapy treatments. However, determining out-of-field doses for any particular treatment plan currently requires either time-consuming measurements or calculated estimations that may be highly uncertain. A Monte Carlo model may allow these doses to be determined quickly, accurately, and with a great degree of flexibility. MCNPX was used to create a Monte Carlo model of a Varian Clinac 2100 accelerator head operated at 6 MV. Simulations of the dose out-of-field were made and measurements were taken with thermoluminescent dosimeters in an acrylic phantom and with an ion chamber in a water tank to validate the Monte Carlo model. Although local differences between the out-of-field doses calculated by the model and those measured did exceed 50% at some points far from the treatment field, the average local difference was only 16%. This included a range of doses as low as 0.01% of the central axis dose, and at distances in excess of 50 cm from the central axis of the treatment field. The out-of-field dose was found to vary with field size and distance from the central axis, but was almost independent of the depth in the phantom except where the dose increased substantially at depths less than d(max). The relationship between dose and kerma was also investigated, and kerma was found to be a good estimate of dose (within 3% on average) except near the surface and in the field penumbra. Our Monte Carlo model was found to well represent typical Varian 2100 accelerators operated at 6 MV. (c) 2006 American Association of Physicists in Medicine.
  • Medical Physics 33(2006)11, 4405-4413

Publ.-Id: 9204 - Permalink


Supramolekulare Netzwerke auf der Basis von Kupfer(II)-Bispidinkomplexen
Juran, S.; Matterna, M.; Stephan, H.; Kraus, W.; Emmerling, F.;
Mehrzähnige Derivate des Bispidins (3,7-Diazabicyclo[3.3.1]nonan) bilden mit ¨Ubergangsmetallen Komplexe hoher Stabilität [1]. In Abhängigkeit von der Art und Position der gewählten Donorgruppen liegen Kupfer(II)-Bispidinkomplexe zumeist in einer verzerrt quadratisch-pyramidalen bzw. oktaedrischen Koordinations-
geometrie vor [2]. Im Hinblick auf eine Ausbildung sehr stabiler Kupferkomplexe scheinen Imidazoleinheiten als Donorgruppen geeignet zu sein. Es wurden zwei neue Liganden mit Imidazolgruppen isoliert und die entsprechenden Kupfer(II)-Komplexe strukturell charakterisiert. In den Kristallstrukturen der beiden neuen Verbindungen ([Cu(C32H34N7O5)(NO2)2], P21/c, a=13.830(8) °A, b=11.464(7) °A, c=24.639(13) °A,
beta=98.33(1)o, V=3865.3(8) °A3, Z=4, R1=0.1047 1 und
[Cu(C35H33N7O5)(NO2)2] · H2O, P21/n, a=13.242(5) °A, b=17.971(7) °A, c=15.650(6) °A, beta=91.97(1)o, V=3722.1(2) °A3, Z=4, R1=0.0451 2) sind die Kupferatome verzerrt quadratisch pyramidal koordiniert (dCu−N=1.940(7)-2.212(7) °A 1; 1.947(5)-2.308(7) °A 2) und durch den Bispidin-Liganden nahezu vollständig von der Umgebung abgeschirmt. Die Koordinations- sphäre des Kupfers wird im Falle von 2 durch einen deutlich größere Kontakt zu einem NO3 Gegenanionen ergänzt (dCu−O=2.764(9)°A). In ihren Kristallstrukturen ergeben sich auf aufgrund von Wasserstoffbrückenbindungen dreidimensionale Netzwerke. In beiden Strukturen sind die Komplexe untereinander über nicht-klassische Wasserstoffbrücken kettenförmig parallel zur b-Achse verknüpft, die dann über zusätzliche Wasserstoffbrückenbindungen zu den NO3 Anionen untereinander verbunden werden [3].

[1] P. Comba, W. Schiek, Coord. Chem. Rev. 238-239, 21-29 (2003).
[2] H. Stephan, S. Juran, M. Walther, J. Steinbach, K. Born, P. Comba, in ”Technetium, Rhenium and other Metals in Chemistry and Nuclear Medicine“, U. Mazzi (Ed.), SGE Editoriali, Padova, Italy, 7, 219-222 (2006).
[3] S. Juran, M. Matterna, H. Stephan, P. Comba,W. Kraus, F. Emmerling, Eur. J Inorg. Chem., in Vorbereitung
  • Poster
    15. Jahrestagung der Deutschen Gesellschaft für Kristallographie 2007, 05.-09.03.2007, Bremen, Deutschland

Publ.-Id: 9203 - Permalink


Application of the virtual test reactor RPV-1 to VVER-1000 RPV steels
Bergner, F.; Ulbricht, A.;
In the presentation a reference data set is defined, a short overview on RPV-1 is given, results of calculations are presented and conclusion are drawn. It turns out that the size distribution obtained by SANS complemented with other techniques is well suited to validate models of long-term microstructure evolution, that tensile test and hardness results are well suited to validate models of irradiation-hardening and that the order of magnitude of the yield stress increase and some trends are correctly reproduced by RPV-1 for a low-Cu VVER-1000 RPV steel. The subject should be reconsidered in future after completion of RPV-2 in order to take into account the effect of solutes more adequately.
  • Lecture (others)
    The 5th Perfect Users Group Meeting, 22.-23.11.2006, Bergen, Niederlande

Publ.-Id: 9202 - Permalink


Magnetic Excitations in S = 1/2 Spin Chains with Alternating g-tensor and the Dzyaloshinskii-Moriya Interaction
Zvyagin, S. A.; Wosnitza, J.; Kolezhuk, A. K.; Krzystek, J.; Feyerherm, R.;
The magnetic excitation spectrum in copper pyrimidine dinitrate, a spin-1/2 antiferromagnetic (AFM) chain system with an alternating g-tensor and the Dzyaloshinskii-Moriya interaction, has been studied using electron-spin resonance (ESR) spectroscopy in magnetic fields up to 25 T. Ten modes were resolved in the spectrum. The data were analyzed in terms of the sine-Gordon quantum field theory [Phys. Rev. Lett. 79, 2883 (1997)]; signatures of three breather branches and a soliton were identified. The field-induced gap was measured directly. In addition, a new theoretical concept proposed recently by Oshikawa and Affleck [Phys. Rev. Lett. 82, 5136 (1999)] has been tested. Their theory, based on bosonization and the self-energy formalism, can be applied for the precise calculation of ESR parameters of spin-1/2 AFM chains in the perturbative spinon regime. Excellent quantitative agreement between the theoretical predictions and experiment is obtained.
e-mail: s.zvyagin@fz-rossendorf.de
  • Lecture (Conference)
    Yamada Conference LX on Research in High Magnetic Fields (RHMF), 16.-19.08.2006, Sendai, Japan

Publ.-Id: 9201 - Permalink


The capacitive 49MJ pulsed power supply system for the High Magnetic Field Laboratory at FZ-Rossendorf
Weise, T. H. G. G.; Hofmann, J.; Anderson, R.; Jörling, J.; Kerschke, R.; Herrmannsdörfer, T.; Krug, H.;
  • Contribution to proceedings
    2nd European Pulsed Power Symposium 2004, 20.-23.09.2004, Hamburg, Deutschland
    The capacitive 49MJ pulsed power supply system for the High Magnetic Field Laboratory at FZ-Rossendo

Publ.-Id: 9200 - Permalink


AMRO measurements on the organic conductor (BEDT-TTF)4[Ni(dto)2]
Schmidt, W.; Hagel, J.; Balthes, E.; Wosnitza, J.; Schweitzer, D.;
The charge-transfer salt [ (BEDT-TTF) 4] 2+[ Ni(dto) 2] 2- is a quasi two-dimensional organic metal [1]. This is confirmed by the resistivity ratio ρc(a,b) = 100 at 300K, where (a,b) represents the high conducting plane. The material shows strong quantum oscillations (QOs) above about 1.2T (at 20mK) with two QO frequencies F T and F =4245T. We report on AMRO (angular dependent magneto-resistance oscillation) measurements on this material, which were performed by rotating single crystals around different axes within the (a,b) plane at different fixed fields (up to 13T). The results confirm the size and also approximately the shape of the slightly warped lens-shaped orbit obtained by the band structure calculations as well as Shubnikov-de Haas (SdH) and de Haas-van Alphen (dHvA) measurements. In addition a strong sharp magneto-resistance peak was found at 90° (i.e., B//(a,b) plane), which hints to coherent interlayer carrier transport [3]. In the vicinity of this peak further anomalies were observed, which may be oscillations reported by Danner et al. caused by a warped one dimensional band [4].
  • Journal de Physique IV 114(2004), 373

Publ.-Id: 9199 - Permalink


Organische Supraleiter
Wosnitza, J.;
  • Contribution to external collection
    in: Organische Supraleiter, Heidelberg: Elsevier GmbH, Spektrum Akademischer Verlag, 2004, 301-312

Publ.-Id: 9198 - Permalink


Unconventional Superconductivity in Novel Materials
Maple, M. B.; Bauer, E. D.; Zapf, V.; Wosnitza, J.;
  • Contribution to external collection
    Bennemann, K.H.; Ketterson, J.B.: The Physics of Superconductors - Vol. 2, Berlin: Springer, 2004, 555-730
  • Contribution to external collection
    in: Superconductivity - Conventional and Unconventional Superconductors, Berlin: Springer, 2008, 639-762

Publ.-Id: 9197 - Permalink


High magnetic field study of RuSr2GdCu2O8
Papageorgiou, T.; Casini, E.; Herrmannsdörfer, T.; Skourski, Y.; Freudenberger, J.; Braun, H. F.; Wosnitza, J.;
.The ruthenate-cuprate RuSr2GdCu2O8 (Ru1212) is a high-Tc superconductor whose crystal structure can be derived from the very well-known structure of YBa2Cu3O7-δ (YBCO) with the substitution Y → Gd, BaO layer → SrO layer, CuO chains → RuO2 planes. Apart from superconductivity at Tc ≈ 50 K, Ru1212 shows also magnetic ordering of the Ru moments at TRu ≈ 130 K and the Gd moments at TGd ≈ 2.5 K. We present magnetization measurements of Ru1212 in pulsed magnetic fields with B ≤ 50 T and investigate the possibility of mixed valency of the Ru ions [60 % Ru5+ (S =3/2) and 40 % Ru4+ (S = 1)]. Within this model, the magnetic ordering of the Ru moments could be realized as the result of a double-exchange interaction between Ru5+ and Ru4+ ions. Superconductivity occurs in the CuO2 layers, but transport of charge carriers, not in a superconducting state, also takes place in the RuO2 planes. Different Ru5+/ Ru4+ ratios can explain many of the contradicting results on Ru1212.
e-mail:T.Papageorgiou@fz-rossendorf.de
  • Poster
    Yamada Conference LX on Research in High Magnetic Fields (RHMF), 16.-19.08.2006, Sendai, Japan

Publ.-Id: 9195 - Permalink


Production of K+ and of K− Mesons in Heavy-Ion Collisions from 0.6 to 2.0 A GeV Incident Energy
Förster, A.; Uhlig, F.; Böttcher, I.; Brill, D.; Debowski, M.; Dohrmann, F.; Grosse, E.; Koczon, P.; Kohlmeyer, B.; Lang, S.; Laue, F.; Mang, M.; Menzel, M.; Müntz, C.; Naumann, L.; Oeschler, H.; Ploskon, M.; Scheinast, W.; Schmah, A.; Schuck, T. J.; Schwab, E.; Senger, P.; Shin, Y.; Speer, J.; Ströbele, H.; Sturm, C.; Surowka, G.; Wagner, A.; Walus, W.;
This paper summarizes the yields and the emission patterns of K+ and of K− mesons measured in inclusive C+C, Ni+Ni and Au+Au collisions at incident energies from 0.6 A GeV to 2.0 A GeV using the Kaon Spectrometer KaoS at GSI. For Ni+Ni collisions at 1.5 and at 1.93 A GeV as well as for Au+Au at 1.5 A GeV detailed results of the multiplicities, of the inverse slope parameters of the energy distributions and of the anisotropies in the angular emission patterns as a function of the collision centrality are presented. When comparing transport-model calculations to the measured K+ production yields an agreement is only obtained for a soft nuclear equation of state (compression modulus KN ~ 200 MeV). The production of K− mesons at energies around 1 to 2 A GeV is dominated by the strangeness-exchange reaction K−N <->pi Y (Y = Lambda, Sigma) which leads to a coupling between the K− and the K+ yields. However, both particle species show distinct differences in their emission patterns suggesting different freeze-out conditions for K+ and for K− mesons.
Keywords: PACS numbers: 25.75.Dw
  • Physical Review C 75(2007)2, 024906

Publ.-Id: 9194 - Permalink


Broadening of the superconducting transition by fluctuations in three-dimensional metals at high magnetic fields
Maniv, T.; Zhuravlev, V.; Wosnitza, J.; Ignatchik, O.; Bergk, B.; Canfield, P. C.;
The Bragg-chain model of the two-dimensional (2D) vortex state at high magnetic field [V. N. Zhuravlev and T. Maniv, Phys. Rev. B 60, 4277 (1999)] is extended to an array of coupled superconducting (SC) layers. Application to MgB2 and YNi2B2C yields good quantitative agreement with high-field magnetization measurements, indicating that the smeared transitions observed in these materials are, at least in great part, due to SC fluctuations. Similar to the situation in a 2D system, the melting of the vortex lattice in strongly coupled SC layers is predicted to occur well below the mean field H-c2.
  • Physical Review B 73(2006), 134521

Publ.-Id: 9193 - Permalink


The Magnetic Properties of the Multi-Functional Intermetallic Compound Pr1-x-yLaxPbyTe in Highest Magnetic Fields
Herrmannsdörfer, T.; Bianchi, A. D.; Freudenberger, J.; Papageorgiou, T.; Skourski, Y.; Wosnitza, J.;
The intermetallic compound Pr1-x-yLaxPbyTe shows a wide spectrum of physical phenomena. Depending on the metallurgical composition as function of x and y, the compound changes its behavior from van Vleck paramagnetism and hyperfine enhanced nuclear magnetic order to super- or semiconductivity. In addition, there are interesting interplay effects between these ground states. In consequence, Pr1-x-yLaxPbyTe may serve as an interesting material for nuclear spin quantum-computing experiments. In this contribution, we focus on measurements of the magnetic, thermodynamic, and transport properties performed in high magnetic fields up to 50 T as well as in a wide temperature range. In particular, we present data of the magnetization of Pr1-yPbyTe taken in pulsed magnetic fields up to 50 T for various compositions y = 0, 90, 99, 99.9, 99.99 %, i.e. turning the system from a van Vleck paramagnet, y = 0, into a doped semiconductor, y > 99.9 %.
e-mail: T.Herrmannsdoerfer@fz-rossendorf.de
  • Poster
    Yamada Conference LX on Research in High Magnetic Fields (RHMF), 16.-19.08.2006, Sendai, Japan

Publ.-Id: 9192 - Permalink


Electronic structure of four-coordinate C-3v nickel(II) scorpionate complexes: Investigation by high-frequency and -field electron paramagnetic resonance and electronic absorption spectroscopies
Desrochers, P. J.; Telser, J.; Zvyagin, S. A.; Ozarowski, A.; Krzystek, J.; Vicic, D. A.;
A series of complexes of formula Tp*NiX, where Tp*(-)) hydrotris( 3,5-dimethylpyrazole) borate and X) Cl, Br, I, has been characterized by electronic absorption spectroscopy in the visible and near-infrared ( NIR) region and by high-frequency and -field electron paramagnetic resonance ( HFEPR) spectroscopy. The crystal structure of Tp*NiCl has been previously reported; that for Tp*NiBr is given here: space group) Pmc2(1), a) 13.209( 2) angstrom, b) 8.082( 2) angstrom, c) 17.639( 4) angstrom, alpha = beta = gamma = 90 degrees, Z = 4. Tp*NiX contains a four- coordinate nickel( II) ion ( 3d(8)) with approximate C-3v point group symmetry about the metal and a resulting S= 1 high-spin ground state. As a consequence of sizable zero-field splitting ( zfs), Tp*NiX complexes are "EPR silent" with use of conventional EPR; however, HFEPR allows observation of multiple transitions. Analysis of the resonance field versus the frequency dependence of these transitions allows extraction of ! the full set of spin Hamiltonian parameters. The axial zfs parameter for Tp*NiX displays pronounced halogen contributions down the series: D) +3.93( 2), -11.43( 3), -22.81( 1) cm(-1), for X = Cl, Br, I, respectively. The magnitude and change in sign of D observed for Tp*NiX reflects the increasing bromine and iodine spin - orbit contributions facilitated by strong covalent interactions with nickel( II). These spin Hamiltonian parameters are combined with estimates of 3d energy levels based on the visible-NIR spectra to yield ligand-field parameters for these complexes following the angular overlap model ( AOM). This description of electronic structure and bonding in a pseudotetrahedral nickel( II) complex can enhance the understanding of similar sites in metalloproteins, both native nickel enzymes and nickel-substituted zinc enzymes.
  • Inorganic Chemistry 45(2006), 8930-8941

Publ.-Id: 9190 - Permalink


Electronic band structure of the borocarbide superconductor LuNi2B2C
Bianchi, A. D.; Bergk, B.; Ignatchik, O.; Wosnitza, J.; Perenboom, J.; Souptel, D.; Behr, G.; Canfield, P. C.;
We present de Haas-van Alphen (dHvA) measurements of the nonmagnetic rare-earth borocarbide superconductor LuNi2B2C which have been performed by using a torque cantilever for temperatures down to 0.03 K and in magnetic fields up to 33 T. We mapped the dHvA oscillations of a high-quality single crystal by rotating between all the three principal crystallographic axes [100], [001], and [110] in steps of 10 degrees. This set of data gives a complete overview of the electronic band structure of LuNi2B2C. A comparison with band structure calculations allowed us to assign the dHvA frequencies to individual bands. Overall positions and band dispersions look similar to that observed in the isostructural compound YNi2B2C, which is another non-magnetic member in the family of the borocarbide superconductors. Additionally, we also measured the temperature dependence of the amplitude of the dHvA oscillations for the three principal crystallographic directions which allows the determination of the effective mass of the different bands.
  • Poster
    Yamada Conference LX on Research in High Magnetic Fields (RHMF), 16.-19.08.2006, Sendai, Japan

Publ.-Id: 9189 - Permalink


Zwei-Skalen-Modellierung von Adsorptionsprozessen an strukturierten Oberflächen
Radke De Cuba, M.; Emmerich, H.; Gemming, S.;
Eine Kombination aus einem kontinuumstheoretischen Phasenfeld-Ansatz fuer das Burton-Cabrera-Frank-Modell und einem teilchenbasierten Metropolis-Monte-Carlo-Verfahren erlaubt es, die Bedeckung strukturierter Oberflaechen mit Teilchen (Molekuelen) und die zeitliche Evolution der Bedeckung bzw. der Oberflaechenkonzentration in Abhaengigkeit von der Temperatur zu studieren. Phasenfeldschritte zur zeitlichen Entwicklung der Oberflaechenstruktur und Monte-Carlo-Schritte zur Ausbildung und zum Reifen von Clustern werden abwechselnd ausgefuehrt. Die Grundgroessen der BCF-Theorie (Teilchen-Fluss, Desorption, Diffusion) werden als Randbedingungen in die Monte-Carlo-Schritte uebernommen. Da die Wechselwirkung der Monte-Carlo-Teilchen untereinander, mit der Oberflaeche und speziell mit Stufenkanten (Schwoebel-Barriere) kurzreichweitig ist, koennen auch umgekehrt die lokalen Konzentrationen und Phasenfeld-Werte aus der MC-Teilchen-Verteilung berechnet werden. Eine systematische Variation der Wechselwirkungsparameter ermoeglichte es, neben den Kontinuums- und Teilchen-dominierten Regimes auch Strukturbildungen zu simulieren, die erst durch das Zusammenwirken beider Ansaetze moeglich sind.
Keywords: hybrid scheme, phase-field, Monte-Carlo, surfaces, adsorption

Publ.-Id: 9188 - Permalink


The new High Magnetic Field Laboratory at Dresden/Rossendorf, HLD
Herrmannsdörfer, T.; Bianchi, A.; Krug, H.; Pobell, F.; Zherlitsyn, S.;
  • Poster
    Megagauss X, 18.-23.07.2004, Berlin, Deutschland

Publ.-Id: 9187 - Permalink


Magnetoelastic and magnetothermal properties of low-dimensional quantum spin systems in high magnetic fields - a case study
Wolf, B.; Brühl, A.; Magerkurth, J.; Zherlitsyn, S.; Pashchenko, V.; Brendel, B.; Margraf, G.; Lerner, H.-W.; Wagner, M.; Lüthi, B.; Lang, M.;
We report measurements of magnetic, magnetothermal and magnetoelastic properties of a new Cu(II)-coordination polymer Cu(II)-2,5-bis(pyrazol-1-yl)-1,4-dihydroxybenzene (CuCCP). According to our results which cover wide ranges of temperatures and magnetic fields B50 T, this material presents an almost ideal realization of an one-dimensional uniform Heisenberg antiferromagnet. Owing to the moderate exchange-coupling constant of , it was possible to study the system in its interesting high-field range, i.e., across the saturation field gμBBs=2|J|, which, at T=0, marks the endpoint of a quantum critical line. Using pulse-field techniques the high-field magnetization and elastic constant have been measured. A comparison with calculated magnetization curves reveals a distinct magnetocaloric effect at high fields for , which grows upon cooling. In addition, at temperatures T<|J|/kB, a pronounced acoustic anomaly has been found close to Bs and identified as a generic property of the uniform antiferromagnetic Heisenberg chain with a finite spin–lattice interaction
  • Journal of Magnetism and Magnetic Materials 290-291(2005), 411-415

Publ.-Id: 9186 - Permalink


The calculation of pulsed magnetic-field coils by means of the finite-element method
Herrmannsdörfer, T.; Zherlitsyn, S.; Wosnitza, J.;
  • Physik Journal 5(2006)SPI, 34-36

Publ.-Id: 9185 - Permalink


Thermal transport properties of U2Ru2Sn at low temperatures
Sanchez, A.; Paschen, S.; Wosnitza, J.; Mydosh, J. A.; Strydom, A. M.; Du Plessis, P. D. V.; Steglich, F.;
U2Ru2Sn has been classified as the first tetragonal U-based Kondo insulator. Here, we present measurements of the thermal conductivity k and thermopower S of high-quality single-crystalline U2Ru2Sn along and perpendicular to the tetragonal c-axis, in the temperature range between 100mK and 1K, in zero field and in a magnetic field of 6T. Below 400 mK, the phonon contribution to kðTÞ shows a T2 behaviour for both directions that can be attributed to phonons scattered by electrons. SðTÞ presents a linear behaviour in the whole temperature range. S is positive along the c-axis and negative perpendicular to the c-axis. Using a one-band model the effective mass m is estimated to be 2m0 along and 16m0 perpendicular to the c-axis, where m0 is the free-electron mass. This indicates that U2Ru2Sn has a highly anisotropic residual density of states within the pseudogap.
  • Physica B 359-361(2005), 1015

Publ.-Id: 9184 - Permalink


Superconducting Properties of RuSr2RECu2O8 (RE = Eu, Gd)
Papageorgiou, T. P.; Casini, E.; Braun, H. F.; Herrmannsdörfer, T.; Bianchi, A. D.; Wosnitza, J.;
The superconducting properties of the magnetic (TM = 130 K) superconductors RuSr2RECu2O8 (RE = Eu, Gd) (Tc;Eu = 27.5 K, Tc;Gd = 46 K) were investigated using resistance and ac-susceptibility measurements. Tc;Eu showed a magnetic-¯eld dependence up to 14 T which can be described by the empirical relation Tc(B) = Tc(0)[1-B/Bc(0)]1/2, contrary to previous reports pointing out the possibility of phase separation in the ruthenocuprates. A plausible explanation of this discrepancy is based on the signi¯cance of the Ru5+/Ru4+ ratio in the ruthenocuprates a®ecting the competition between antiferromagnetic superexchange and ferromagnetic double exchange in these compounds.

Publ.-Id: 9182 - Permalink


Pulsed-magnet design at the Dresden High Magnetic Field Laboratory
Zherlitsyn, S.; Herrmannsdoerfer, T.; Skourski, Y.; Sytcheva, A.; Wosnitza, J.;
The current status of the pulsed-magnet program of the Dresden High Magnetic Field Laboratory (HLD) is reported. The non-destructive pulsed magnets for the HLD include a wide spectrum of coils designed for energies between 1 and 46MJ, magnetic fields of 60 - 100T, and pulse durations of 10 - 1000 ms. Various experimental techniques at pulsed magnetic fields will be available for external users soon. Some user magnets for first scientific experiments have been installed and tested. A 8.5MJ / 70 T mono-coil magnet has been built and first test results for this magnet are presented. The design of a two-coil 46 MJ magnet for magnetic fields above 85T has been completed. This magnet is under construction now. Important issues of the coil design are numerical simulations of the pulsed-magnet performance. Both analytical approaches and finite-element analysis are used for these simulations at the HLD.

Publ.-Id: 9181 - Permalink


Oscillation or rotation: a comparison of two simple reversal models
Stefani, F.; Xu, M.; Sorriso-Valvo, L.; Gerbeth, G.; Günther, U.;
The asymmetric shape of reversals of the Earth's magnetic field indicates a possible connection with relaxation oscillations as they were early discussed by van der Pol. A simple mean-field dynamo model with a spherically symmetric alpha coefficient is analysed with view on this similarity, and a comparison of the time series and the phase space trajectories with those of paleomagnetic measurements is carried out. For highly supercritical dynamos a very good agreement with the data is achieved. Deviations of numerical reversal sequences from Poisson statistics are analysed and compared with paleomagnetic data. The role of the inner core is discussed in a spectral theoretical context and arguments and numerical evidence is compiled that the growth of the inner core might be important for the long term changes of the reversal rate and the occurrence of superchrons.

Publ.-Id: 9180 - Permalink


Experiments on the magnetorotational instability in helical magnetic fields
Stefani, F.; Gundrum, T.; Gerbeth, G.; Rüdiger, G.; Szklarski, J.; Hollerbach, R.;
The magnetorotational instability (MRI) plays a key role in the formation of stars and black holes, by enabling outward angular momentum transport in accretion disks. The use of combined axial and azimuthal magnetic fields allows the investigation of this effect in liquid metal flows at moderate Reynolds and Hartmann numbers. A variety of experimental results is presented showing evidence for the occurrence of the MRI in a Taylor-Couette flow using the liquid metal alloy GaInSn.

Publ.-Id: 9179 - Permalink


Spectroscopic ellipsometry of ZnO thin films: choice of optimum parameterization of dielectric function
Vinnichenko, M.; Ozerov, M.; Rogozin, A.; Shevchenko, N.; Kolitsch, A.;
The aim of the study is to test various parameterizations of ZnO dielectric function. Epitaxial thin films grown by reactive magnetron sputtering at different oxygen partial pressures were chosen for analysis by spectroscopic ellipsometry. Three different model dielectric functions (MDF) were applied: Lorent oscillator, critical point parabolic band (CPPB) and parametric semiconductor (PSEMI) model. All three approaches provide reasonable fit of the model to the experimental data below 3 eV. However, Lorentz oscillator provides bad agreement with experimental data at the energies of photons higher than 3 eV. The CPPB model provides unphysically high values of dielectric function imaginary part in the transparency region. The PSEMI model is more adequate compared to Lorentz oscillator and CPPB. PSEMI model yields the energy gap of the film EG=3.30±0.01 eV which does not depend on the O2 partial pressure during growth. The broadening of the film MDF increases with oxygen pressure while the film strain decreases. The variation of the defect structure inside ZnO grains with oxygen pressure can be discussed as a reason.
Keywords: ZnO thin films, dielectric function, spectroscopic ellipsometry
  • Lecture (Conference)
    Woollam-Ellipsometrie-Seminar, 25.10.2006, Darmstadt, Germany

Publ.-Id: 9176 - Permalink


Dresden pulsed magnetic field facility
Wosnitza, J.; Bianchi, A. D.; Herrmannsdörfer, T.; Zherlitsyn, S.; Zvyagin, S. A.;
The Dresden High Magnetic Field Laboratory (HLD) is under construction at the Forschungszentrum Rossendorf in Dresden, Germany [1, 2]. Along with in-house research, this laboratory is planned to provide external users with the possibility to carry out a variety of experiments in pulsed magnetic fields as high as 100 T. Typical pulse duration will be from 10 ms for a 100 T two-coil magnet up to 1000 ms for a 60 T long pulse magnet. Magnet bores will be in the range from 20 to 40 mm, providing adequate space for the experiments. The magnets will be energized by a world-wide unique modular 50 MJ capacitor bank operating at 24 kV. The design, development, and manufacture of pulsed magnets are established at the HLD. First coils using copper wire have repeatedly reached 64 T for 15 ms in a 24 mm bore. Currently these kinds of magnets are routinely used to provide 60 T. A multi-coil 100 T magnet is under design. Additionally, the HLD is being equipped with a number of superconducting magnets up to 20 T. A wide temperature range from mK to above room temperature will be available for research in high magnetic fields. A number of experimental techniques will be provided for users. This includes magneto-resistance, magnetization, specific-heat, ultrasound, and magnetic-resonance methods. The HLD is located nearby a free-electron-laser facility which is planned to deliver a high-brilliance infrared radiation (from 5 to 150 m wavelength) for infrared spectroscopy in pulsed magnetic field [3]. Besides, the HLD offers various equipment for sample preparation and characterization, such as SQUID systems and physical property measurement systems.
  • Poster
    International Conference on Magnetism 2006, 20.-25.08.2006, Kyoto, Japan

Publ.-Id: 9175 - Permalink


Fermi Surface of the Half Heusler Compounds Ce1−xLaxBiPt
Bianchi, A. D.; Wosnitza, J.; Kozlova, N.; Eckert, D.; Schultz, L.; Opahle, I.; Elgazzar, S.; Richter, M.; Hagel, J.; Doerr, M.; Goll, G.; von Löhneysen, H.; Zwicknagl, G.; Yoshino, T.; Takabatake, T.;
We report on the Fermi surface in the correlated half-Heusler compound Ce1−xLaxBiPt. In CeBiPt we find a field-induced change of the electronic band structure as discovered by electrical-transport measurements in pulsed magnetic fields. For magnetic fields above 25 T, the charge-carrier concentration determined from Hall-effect measurements increases nearly 30%, whereas the Shubnikov–de Haas (SdH) signal disappears at the same field. In the non-4f compound LaBiPt the Fermi surface remains unaffected, suggesting that these features are intimately related to the Ce 4f electrons. Electronic band-structure calculations point to a 4f-polarization-induced change of the Fermi-surface topology. In order to test this hypothesis, we have measured the (SdH) signal in a Ce0.95La0.05BiPt sample with a low La concentration.
  • Poster
    Frühjahrstagung der DPG, 27.-31.03.2006, Dresden, Deutschland

Publ.-Id: 9174 - Permalink


Spin-zero anomaly in the magnetic quantum oscillations of a two-dimensional metal
Bergk, B.; Ignatchik, O.; Jäckel, M.; Wosnitza, J.; Gvozdikov, V. M.; Schlueter, J. A.; Mohtasham, J.; Winter, R. W.; Gard, G. L.;
We present de Haas van Alphen (dHvA) and Shubnikov-de Haas (SdH) measurements on the quasi-two-dimensional organic superconductor 00- (BEDT-TTF)2SF5CH2CF2SO3. The measurements were carried out by the torque method and by four-point low-frequency ac-resistance measurements in magnetic fields up to 15 T. Unlike theoretical expectations for two-dimensional metals the dHvA signal shows an unconventional sawtooth wave-form, i. e., an ’inversed sawtooth’ wave form is observed. In order to investigate the behaviour in more detail we performed angledependent dHvA and SdH measurements. The SdH effect displays the behaviour predicted by the grand-canonical Lifshitz-Kosevich theorie. In contrast, the dHvA signal can be explained by a theory, which includes a slightly oscillating chemical potential. Even for simultaneous measurements of both effects the behaviour does not change. This means that the dHvA signal is not affected by an external charge carrier reservoir.
  • Poster
    Frühjahrstagung der DPG, 27.-31.03.2006, Dresden, Deutschland

Publ.-Id: 9173 - Permalink


Anisotropy and spin-triplet excitons in the S = 1/2 gapped antiferromagnet FaCuSi2O6
Zvyagin, S. A.; Wosnitza, J.; Krzystek, J.; Stern, R.; Jaime, M.; Sasago, Y.; Uchinokura, K.;
BaCuSi2O6 (also known as Han Purple Pigment) can be regarded as an almost ideal realization of the S = 1/2 system of weakly-interacting spin dimers with the spin-singlet ground state and gapped excitation spectrum [1]. By application of an external magnetic field the gap can be closed, creating a gas of interacting bosonic spin-triplet excitations (triplons). In BaCuSi2O6 this phenomenon can be effectively described in terms of the field-induced Bose-Einstein condensation of triplons [2]. Here, we focus on another interesting phenomenon associated with interacting excited triplets but in the low-field quantum-disordered state. We argue that a fine structure observed in low-temperature EPR spectra of BaCuSi2O6 is a fingerprint of triplet excitations (excitons), which are mobile at low temperatures and getting localized when temperature is increased. Analyzing the angular dependence of exciton modes in BaCuSi2O6 allows us to precisely calculate zero-field splitting with the triplet state and, correspondingly, the anisotropy parameter, D = 0:07 cm¡1. The proposed procedure can be applied for a large number of S = 1/2 gapped quantum antiferromagnets with dimerized or alternating
spin structure and might be of particular importance for studying anisotropy effects in S = 1/2 quantum chains (see for instance [3]). In addition, the temperature dependence of the EPR intensity and linewidth has been measured and discussed. The magnitude of the energy spin gap determined by analyzing the temperature dependence of the integrated signal intensity (¢ = 53 K) is in excellent
agreement with data obtained from the neutron scattering measurements [1].
  • Poster
    International Conference on Magnetism 2006, 20.-25.08.2006, Kyoto, Japan

Publ.-Id: 9172 - Permalink


The new High Magnetic Field Laboratory at Dresden: a Pulsed – Field Laboratory at an IR Free – Electron – Laser Facility
Pobell, F.; Bianchi, A. D.; Herrmannsdörfer, T.; Krug, H.; Zherlitsyn, S.; Zvyagin, S.; Wosnitza, J.;
We report on the construction of a new high magnetic field user laboratory which will offer pulsed-field coils for the range (60 T, 500 ms, 40 mm) to (100 T, 10 ms, 20 mm) for maximum field, pulse time, and bore diameter of the coils. These coils will be energized by a modular 50 MJ/ 24 kV capacitor bank. Besides many other experimental techniques, as unique possibilities NMR in pulsed fields as well as infrared spectroscopy at 5 to 150 m will be available by connecting the pulsed field laboratory to a nearby free-electron-laser facility.
  • AIP Conference Proceedings 850(2006), 1649
  • Lecture (Conference)
    24th International Conference on Low Temperature Physics, 10.-17.07.2005, Orlando, USA

Publ.-Id: 9171 - Permalink


Polarized neutron scattering studies of chiral criticality, and new universality classes of phase transitions
Plakhty, V. P.; Wosnitza, J.; Kulda, J.; Brückel, T.; Schweika, W.; Visser, D.; Gavrilov, S. V.; Moskvin, E. V.; Kremer, R. K.; Banks, M. G.;
Using a novel polarised neutron scattering technique, the critical exponents for the spin chirality and chiral susceptibility are determined for the triangular lattice antiferromagnet (TLA) CsMnBr3 in the ranges of reduced temperature τ>10-3 and τ>7x10-3 respectively. Their values, βc= 0.44(2) and γc= 0.85(3), together with the scaling relation α+2βcc=2.13(9), including the critical exponent where a for the specific heat, prove that the spin-ordering transition belongs to the XY chiral universality class. In the case of helimagnet Ho, it is found that βc - 2β = 0.14(4), where β is the staggered magnetisation exponent. The scaling relation α+2β+γ=2 could be fulfilled with a reasonable α= 0.23(4), although for the chiral critical exponents βc= 0.90(2) and γc=0.69(5) one needs α=-0.49(5) in contradiction with any experimental data. As the scaling relation always holds, we assume that the spin-ordering transition in Ho is of the first order. In the quantum antiferromagnet CsCuCl3, a triangular spin order coexists with a long-period Dzyaloshinskii helix. The Dzyaloshinskii axial vector should remove the helix chiral degeneracy, which has not been observed in reality. The critical exponent β= 0.22(2) is found to be in agreement with the XY chiral scenario for a TLA. Chiral scattering above TN is very weak, probably being masked by zero-point quantum fluctuations. A modulation of the crystal structure with the periodicity of the helix is observed, indicating strong coupling of the Dzyaloshinskii–Moriya interaction with the lattice.
  • Physica B 385-386(2006), 288-294

Publ.-Id: 9170 - Permalink


Magnetization, vortex state and specific heat in the superconducting state of RuSr2GdCu2O8
Papageorgiou, T. P.; Casini, E.; Braun, H. F.; Herrmannsdörfer, T.; Bianchi, A. D.; Wosnitza, J.;
Based on field-cooled dc-magnetization measurements in a SQUID magnetometer with carefully controlled magnetic-field profiles, we present evidence that diamagnetism is missing in the superconducting state (T < 50 K) of the (weakly) ferromagnetic (TM ≈ 130 K) superconductor RuSr2GdCu2O8 (Ru1212). Nevertheless, taking into account the granular nature of the samples investigated so far, this cannot be taken as evidence for the lack of a Meissner state or bulk superconductivity. It is shown that for low applied magnetic fields a vortex state most probably involves the intergrain area (area between the grains) rather than the individual grains (bulk Ru1212). Furthermore, the wide superconducting transition of Ru1212 (Tc,onset = Tc ≈ 48 K, Ts(R = 0) = Ts = 32 K) realized in resistance measurements in zero applied magnetic field can be readily understood as the effect of resistive grain contacts and is not necessarily related to the movement of spontaneously induced vortices in bulk Ru1212, as it has been suggested previously. A comparison of the low-temperature specific heat of Sr2GdRuO6 (Sr2116), the precursor for the preparation of Ru1212 and thus a possible impurity phase, with previously reported data for Ru1212 shows that it is unlikely that Sr2116 is responsible for the specific-heat features attributed to the superconductivity of Ru1212 and supports the existence of a bulk superconducting state in the latter compound.
  • European Physical Journal B 52(2006), 383-388

Publ.-Id: 9169 - Permalink


Resistivity studies on different variants of κ-(BEDT-TTF)2Cu[N(CN)2]Br: evidence for disorder and/or defect-induced inelastic scattering contributions
Lang, M.; Strack, C.; Akinci, C.; Wolf, B.; Schlueter, J. A.; Wosnitza, J.; Schweitzer, D.; Schreuer, J.; Wiehl, L.;
Comparative resistivity measurements have been performed on differently prepared κ-(ET)2Cu[N(CN)2]Br single crystals. While the Tc values and their shifts under hydrostatic pressure are found to be sample independent, the resistivity profiles, especially around the resistivity hump at 90 K and the low-temperature T2 behavior, show striking sample-to-sample variations. In the absence of significant differences in the crystals’ structural parameters and chemical compositions, as proved by high-resolution X-ray and electron-probe-microanalysis studies, these results indicate that real structure phenomena, i.e. disorder and/or defects, strongly affect the inelastic scattering in these molecular conductors.
  • Journal of Low Temperature Physics 142(2006), 191

Publ.-Id: 9166 - Permalink


New annealing methods of indium tin oxide films by electric current
Rogozin, A.; Shevchenko, N.; Vinnichenko, M.; Kolitsch, A.; Möller, W.;
Novel methods of indium tin oxide (ITO) annealing in vacuum by electric current flowing through the film are proposed. These methods exhibit a number of technical advantages: (i) no external heater is required, and (ii) the Joule heat is released only in the ITO films reducing the heat load to thermally sensitive substrates. Transparent and conductive films with thickness of 170 nm were deposited by reactive pulsed magnetron sputtering. In the first set of experiments Si plates covered by 500 nm SiO2 were used as substrates. Annealing was performed in direct current (DC) mode at a constant power released in the film. During annealing the film resistance, free electron density and structure evolution were monitored in situ. Similar to thermal annealing, a two-stage decrease of the resistivity was observed, however the crystallization proceeds faster at significant lower temperatures. The activation energy of crystallization for the isothermally annealed films is about 1.44 ± 0.18 eV. In the case of annealing by electric current the activation energy is reduced by nearly a factor of 2 to 0.81 ± 0.09 eV.
In a second set of experiments the ITO films deposited on fused silica substrates were annealed in vacuum by microwave radiation. In contrast to the DC mode, the annealing current was induced in the ITO film by microwaves without electrical contacts. It is shown that such treatment causes a fast film transformation from amorphous to crystalline state with a significant decrease of resistivity up to approximately one order of magnitude.
Keywords: ITO, electric current annealing, activation energy
  • Lecture (Conference)
    The International Conference on Coatings on Glass and Plastics, 18.-22.06.2006, Dresden, Germany

Publ.-Id: 9165 - Permalink


Solitons and spinons in the quantum sine-gordon spin chain
Zvyagin, S. A.; Wosnitza, J.; Kolezhuk, A. K.; Krzystek, J.; Feyerherm, R.;
An isotropic S = 1/2 Heisenberg antiferromagnetic (AFM) chain with uniform nearest-neighbor exchange coupling represents one of the paradigm models of quantum magnetism. Its ground state is a spin singlet, and the dynamics are determined by a gapless two-particle continuum of spin- 1/2 excitations, commonly referred to as spinons. Since the S = 1/2 AFM chain is critical, even small perturbations can considerably change fundamental properties of the system. One of the most prominent examples is the S = 1/2 AFM chain perturbed by an alternating g-tensor and the Dzyaloshinskii-Moriya interaction; this situation is realized experimentally in the copper pyrimidine dinitrate, Cu-PM. In the presence of such interactions, application of a uniform external field H induces an effective transverse staggered field h / H, which leads to the opening of an energy gap ¢ / H2=3. Here we report on the excitation spectrum in Cu-PM measured using submillimeter wave electron spin resonance (ESR) spectroscopy in fields up to 25 T [1]. Ten excitation modes are resolved in the low-temperature spectrum. The field-induced gap is measured directly. Signatures of three breather branches and a soliton, as well as those of several multi-particle excitation modes are identified. The experimental data are sufficiently detailed to make a very accurate comparison with predictions based on the quantum sine-Gordon field theory [2]. In addition, a new theoretical concept proposed recently by Oshikawa and Affleck [3] has been tested. Their theory, based on bosonization and the self-energy formalism, can be applied for precise calculation of ESR parameters of S = 1/2 AFM chains in the perturbative spinon regime. Excellent quantitative agreement between the theoretical predictions and experiment is obtained [4].
  • Poster
    International Conference on Magnetism 2006, 20.-25.08.2006, Kyoto, Japan

Publ.-Id: 9164 - Permalink


β′′-(ET)2SF5CH2CF2SO3 – a Layered 2D Metal with Vanishing Interlayer Coupling
Wosnitza, J.; Hagel, J.; Ignatchik, O.; Bergk, B.; Gvozdikov, V. M.; Schlueter, J. A.; Winter, R. W.; Gard, G. L.;
We report on electrical transport and magnetization measurements of the quasi-two-dimensional layered superconductor β′′-(ET)2SF5CH2CF2SO3. The absence of a resistive peak when a strong magnetic field is aligned along the conducting planes reflects the fact that the material is one of the most anisotropic ET-based metals with possible incoherent interlayer transport. Consequences of this feature may be the enhanced amplitude of magnetic quantum oscillations in the superconducting state and an unusual angulardependent metal-insulator transition.
  • Journal of Low Temperature Physics 142(2006), 327-332

Publ.-Id: 9163 - Permalink


Optimization of reactive pulsed magnetron sputtering for epitaxial growth of undoped ZnO films
Rogozin, A.; Vinnichenko, M.; Shevchenko, N.; Kolitsch, A.; Moeller, W.;
The process of ZnO thin films deposition by reactive pulsed magnetron sputtering is optimized for epitaxial growth on Al2O3 (0001) substrates at the temperature of 550 °C. The influence of base pressure, target presputtering, chemical substrate cleaning and additional O2 RF plasma cleaning of the substrate on the film structure and properties is investigated. The films are characterized by X-ray diffraction (XRD) phi-scans and spectroscopic ellipsometry (SE). Chemical cleaning results in the formation of epitaxial ZnO layers in a wide range of deposition parameters, with two types of domains, one of them being rotated by 30° relative to the dominating orientation. The additional oxygen plasma cleaning of the substrate allows to form single-domain epitaxial films. Under optimized conditions, these films remain epitaxial for a wide range of the oxygen partial pressures (1.4•10-4 - 3.4•10-3 mbar). The largest grain size of approximately 100 nm and the best (0001)-type texture of ZnO are formed at the oxygen partial pressure of 1•10-3 mbar with a minimum FWHM of the XRD rocking curve of 0.366°. SE indicates the absence of grading of the optical constants across the film, and a significantly lower optical absorption compared to films grown without oxygen plasma pretreatment. The broadening of the Lorentz oscillator used for parameterization of the optical constants is significantly smaller, which confirms the higher degree of ordering.
Keywords: ZnO, reactive magnetron sputtering, epitaxial growth
  • Lecture (Conference)
    10th International Conference on Plasma Surface Engineering, 10.-15.09.2006, Garmisch-Partenkirchen, Germany

Publ.-Id: 9162 - Permalink


Elementary excitations in S = 1/2 Heisenberg spin chains with alternating g-tensor and the Dzyaloshinskii-Moriya interaction
Zvyagin, S. A.; Wosnitza, J.; Kolezhuk, A. K.; Krzystek, J.; Feyerherm, R.;
The magnetic-excitation spectrum of copper pyrimidine dinitrate, a material containing S = 1/2 antiferromagnetic chains with alternating g-tensor and the Dzyaloshinskii-Moriya interaction, and exhibiting a field-induced spin gap, is probed using tunable-frequency electron spin resonance spectroscopy in magnetic fields up to 25 T. The data are interpreted in frame of the sine-Gordon quantum-field theoretical concept proposed recently by Oshikawa and Affleck. The field-induced gap is measured directly; signatures of soliton and three breather branches are identified.
  • Open Access LogoJournal of Physics: Conference Series 51(2006), 39-42

Publ.-Id: 9161 - Permalink


Status quo of the Dresden High Magnetic Field Laboratory
Wosnitza, J.; Bianchi, A. D.; Herrmannsdörfer, T.; Wünsch, R.; Zherlitsyn, S.; Zvyagin, S.;
We report on the recent progress made at the Dresden High Magnetic Field Laboratory (Hochfeld-Magnetlabor Dresden = HLD). This facility, under construction at the research center (Forschungszentrum) Rossendorf, is planned to open as user facility in 2007 offering access to various pulsed-field magnets. Besides the ultimate goal of constructing a multi-pulse magnet reaching 100T in a bore of 20mm with a peak-pulse duration of about 10 ms, further self-designed high-energy coils will be provided. For thermodynamic experiments, e.g., a pulsed coil for 60T in 40mm and 1 s is planned. The necessary energy of up to 50MJ for coil operation recently became available through a world-unique capacitor bank working at 24 kV. First user-type magnets for fields up to 71T for 100ms in a bore of 24mm have been tested successfully. As an outstanding feature of the laboratory, the bright light of a next-door free-electron-laser facility will allow dedicated high-field infrared spectroscopy. A broad range of experimental techniques is being developed both for user and in-house research in static and pulsed magnetic fields.
  • Open Access LogoJournal of Physics: Conference Series 51(2006), 619-622

Publ.-Id: 9160 - Permalink


High magnetic field study of RuSr2GdCu2O8
Papageorgiou, T. P.; Casini, E.; Skourski, Y.; Herrmannsdörfer, T.; Freudenberger, J.; Braun, H. F.; Wosnitza, J.;
Magnetization measurements in pulsed magnetic fields up to 47 T have been performed on the magnetic (TM,Ru ≈ 133 K) superconductor (TS ≈ 46 K) RuSr2GdCu2O8 in an attempt to determine the Ru valency in this compound. The Ru ions are most probably in a mixed valence state, but the ratio of Ru5+(S=3/2)/Ru4+(S = 1) ≈ 60%/40% suggested by NMR investigations is justified only if one considers the theoretical values of 3 μB/Ru5+ and 2 μB/Ru4+. Mixed valency could lead to a competition between ferromagnetic double exchange, evolving Ru4+ and Ru5+ ions, and antiferromagnetic superexchange, evolving Ru5+ ions, leading to magnetic phase separation. We conclude that the magnetic and superconducting properties of the rutheno-cuprates critically depend on the Ru5+/Ru4+ ratio which can be affected by the preparation conditions.
  • Open Access LogoJournal of Physics: Conference Series 51(2006), 411-414

Publ.-Id: 9159 - Permalink


The magnetic properties of the multi-functional intermetallic compound Pr1-x-yLaxPbyTe in high magnetic fields
Herrmannsdörfer, T.; Bianchi, A. D.; Freudenberger, J.; Papageorgiou, T. P.; Skourski, Y.; Wosnitza, J.;
The intermetallic compound Pr1-x-yLaxPbyTe shows a wide spectrum of physical
phenomena. Depending on the metallurgical composition as function of x and y, the compound
changes its behavior from van Vleck paramagnetism and hyperfine-enhanced nuclear-magnetic
order to super- or semiconductivity. In addition, there are remarkable interplay effects between
these ground states. In consequence, Pr1-x-yLaxPbyTe may serve as an interesting material for
nuclear-spin quantum-computing experiments. In this contribution, we focus on measurements
of the magnetic properties performed in high magnetic fields. We present first data of the
magnetization of Pr1-yPbyTe taken in pulsed magnetic fields up to 47 T for the compositions y =
0, 50, and 90 %.
  • Open Access LogoJournal of Physics: Conference Series 51(2006), 67-70

Publ.-Id: 9158 - Permalink


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