Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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33397 Publications

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

Permalink: https://www.hzdr.de/publications/Publ-9228
Publ.-Id: 9228


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

Permalink: https://www.hzdr.de/publications/Publ-9227
Publ.-Id: 9227


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

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Permalink: https://www.hzdr.de/publications/Publ-9223
Publ.-Id: 9223


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

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Permalink: https://www.hzdr.de/publications/Publ-9222
Publ.-Id: 9222


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

Permalink: https://www.hzdr.de/publications/Publ-9221
Publ.-Id: 9221


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

Permalink: https://www.hzdr.de/publications/Publ-9220
Publ.-Id: 9220


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 Logo Journal of Physics: Conference Series 64(2007), 012011

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Permalink: https://www.hzdr.de/publications/Publ-9219
Publ.-Id: 9219


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

Permalink: https://www.hzdr.de/publications/Publ-9218
Publ.-Id: 9218


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

Permalink: https://www.hzdr.de/publications/Publ-9217
Publ.-Id: 9217


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

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Permalink: https://www.hzdr.de/publications/Publ-9216
Publ.-Id: 9216


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

Permalink: https://www.hzdr.de/publications/Publ-9215
Publ.-Id: 9215


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.

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Permalink: https://www.hzdr.de/publications/Publ-9214
Publ.-Id: 9214


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

Permalink: https://www.hzdr.de/publications/Publ-9213
Publ.-Id: 9213


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

Permalink: https://www.hzdr.de/publications/Publ-9211
Publ.-Id: 9211


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

Permalink: https://www.hzdr.de/publications/Publ-9210
Publ.-Id: 9210


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.

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Permalink: https://www.hzdr.de/publications/Publ-9209
Publ.-Id: 9209


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

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Permalink: https://www.hzdr.de/publications/Publ-9207
Publ.-Id: 9207


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

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Permalink: https://www.hzdr.de/publications/Publ-9205
Publ.-Id: 9205


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

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Permalink: https://www.hzdr.de/publications/Publ-9204
Publ.-Id: 9204


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

Permalink: https://www.hzdr.de/publications/Publ-9203
Publ.-Id: 9203


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

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Publ.-Id: 9202


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

Permalink: https://www.hzdr.de/publications/Publ-9201
Publ.-Id: 9201


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

Permalink: https://www.hzdr.de/publications/Publ-9200
Publ.-Id: 9200


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

Permalink: https://www.hzdr.de/publications/Publ-9199
Publ.-Id: 9199


Organische Supraleiter

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

Permalink: https://www.hzdr.de/publications/Publ-9198
Publ.-Id: 9198


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

Permalink: https://www.hzdr.de/publications/Publ-9197
Publ.-Id: 9197


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

Permalink: https://www.hzdr.de/publications/Publ-9195
Publ.-Id: 9195


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

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Publ.-Id: 9194


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

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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

Permalink: https://www.hzdr.de/publications/Publ-9192
Publ.-Id: 9192


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

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Publ.-Id: 9190


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

Permalink: https://www.hzdr.de/publications/Publ-9189
Publ.-Id: 9189


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

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Publ.-Id: 9188


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

Permalink: https://www.hzdr.de/publications/Publ-9187
Publ.-Id: 9187


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

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Publ.-Id: 9186


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

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Publ.-Id: 9185


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

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Publ.-Id: 9184


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.

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Publ.-Id: 9182


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.

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Publ.-Id: 9181


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.

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Publ.-Id: 9180


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.

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Publ.-Id: 9179


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

Permalink: https://www.hzdr.de/publications/Publ-9176
Publ.-Id: 9176


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

Permalink: https://www.hzdr.de/publications/Publ-9175
Publ.-Id: 9175


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

Permalink: https://www.hzdr.de/publications/Publ-9174
Publ.-Id: 9174


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

Permalink: https://www.hzdr.de/publications/Publ-9173
Publ.-Id: 9173


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

Permalink: https://www.hzdr.de/publications/Publ-9172
Publ.-Id: 9172


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

Permalink: https://www.hzdr.de/publications/Publ-9171
Publ.-Id: 9171


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

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Permalink: https://www.hzdr.de/publications/Publ-9170
Publ.-Id: 9170


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

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Permalink: https://www.hzdr.de/publications/Publ-9169
Publ.-Id: 9169


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

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Permalink: https://www.hzdr.de/publications/Publ-9166
Publ.-Id: 9166


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

Permalink: https://www.hzdr.de/publications/Publ-9165
Publ.-Id: 9165


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

Permalink: https://www.hzdr.de/publications/Publ-9164
Publ.-Id: 9164


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

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Permalink: https://www.hzdr.de/publications/Publ-9163
Publ.-Id: 9163


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

Permalink: https://www.hzdr.de/publications/Publ-9162
Publ.-Id: 9162


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 Logo Journal of Physics: Conference Series 51(2006), 39-42

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Permalink: https://www.hzdr.de/publications/Publ-9161
Publ.-Id: 9161


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 Logo Journal of Physics: Conference Series 51(2006), 619-622

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Permalink: https://www.hzdr.de/publications/Publ-9160
Publ.-Id: 9160


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 Logo Journal of Physics: Conference Series 51(2006), 411-414

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Permalink: https://www.hzdr.de/publications/Publ-9159
Publ.-Id: 9159


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 Logo Journal of Physics: Conference Series 51(2006), 67-70

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Permalink: https://www.hzdr.de/publications/Publ-9158
Publ.-Id: 9158


Electronic band structure of the borocarbide superconductor LuNi2B2C

Bianchi, A. D.; Bergk, B.; Ignatchik, O.; Wosnitza, J.; Perenboom, J.; Canfield, P. C.
We present de Haas–van Alphen (dHvA) measurements of the nonmagnetic rareearth borocarbide superconductor LuNi2B2C which have been performed by using a torque cantilever for temperatures down to 0.45K and in magnetic fields up to 32.5T. We mapped the dHvA oscillations of a high-quality single crystal by rotating between all three principal crystallographic axes [100], [001], and [110]. 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 resemble those observed in the isostructural compound YNi2B2C, which is another nonmagnetic member in the family of the borocarbide superconductors.
  • Open Access Logo Journal of Physics: Conference Series 51(2006), 263-266

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Permalink: https://www.hzdr.de/publications/Publ-9157
Publ.-Id: 9157


Incoherent interlayer electron hopping as a possible reason for enhanced magnetic quantum oscillations in the mixed state of a layered organic superconductor

Gvozdikov, V. M.; Wosnitza, J.
We present a theory which is able to explain enhanced magnetic quantum-oscillation amplitudes in the superconducting state of a layered organic metal with incoherent electronic transport across the layers. The incoherence acts through the deformation of the layer-stacking factor which becomes complex and decreases the total scattering rate in the mixed state. This novel mechanism restores the coherence by establishing a long-range order across the layers and can compensate the usual decrease of the Dingle factor below the upper critical magnetic field caused by the intralayer scattering.
  • Low Temperature Physics 32(2006), 152-157

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Publ.-Id: 9156


Magnetic properties of transition-metal nanoclusters on a biological substrate

Herrmannsdörfer, T.; Bianchi, A. D.; Papageorgiou, T. P.; Pobell, F.; Wosnitza, J.; Pollmann, K.; Merroun, M.; Raff, J.; Selenska-Pobell, S.
We have investigated the magnetic properties of transition-metal clusters with a single grain size of about 1 nm. These metallic nanoclusters have been deposed on a biological substrate. This substrate is a purified self-assembling paracrystalline surface layer (S-layer) of the Bacillus sphaericus strain JG-A12 which exhibits square symmetry and is composed of identical protein monomers. First data of the magnetic susceptibility, taken in a SQUID magnetometer at 0 < B < 7 T and 1.8 K < T < 400 K, reveal unusual magnetic properties. The Stoner enhancement factor of the d conduction-electron susceptibility in the Pd and Pt nanoclusters is dramatically reduced compared to the one of the corresponding bulk transition metals. The weakened magnetism of the 5d electrons is considered to play a crucial role for the occurrence of superconductivity in microgranular Pt by adjusting the balance between electron-phonon interaction and competing magnetic interactions.
Keywords: metallic nanoclusters, paracrystalline protein surface layer, magnetism of transition-metal nanoclusters
  • Journal of Magnetism and Magnetic Materials 310(2007), e821-e823
  • Lecture (Conference)
    International Conference on Magnetism (ICM 2006), IUPAP, 20.-25.08.2006, Kyoto, Japan

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Publ.-Id: 9155


[Cu(HF2)(pyz)2]BF4 (pyz = pyrazine): long-range magnetic ordering in a pseudo-cubic coordination polymer comprised of bridging HF2 and pyrazine ligands

Manson, J. L.; Conner, M. M.; Schlueter, J. A.; Lancaster, T.; Blundell, S. J.; Brooks, M. L.; Pratt, F. L.; Papageorgiou, T.; Bianchi, A. D.; Wosnitza, J.; Whangbo, M.-H.
[Cu(HF2)(pyz)2]BF4 consists of rare µ1,3 bridging HF2 anions and µ-pyrazine ligands leading to a 3D pseudo-cubic framework that antiferromagnetically orders below 1.54(1) K.

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Publ.-Id: 9154


Fermiology and superconductivity at high magnetic fields in a completely organic cation radical salt

Brooks, J. S.; Williams, V.; Choi, E.; Graf, D.; Tokumoto, M.; Uji, S.; Zuo, F.; Wosnitza, J.; Schlueter, J. A.; Davis, H.; Winter, R. W.; Gard, G. L.; Storr, K.
We report specialized interplane magnetoresistance (MR) measurements on the organic superconducting compound β´´-(BEDT-TTF)2SF5CH2 CF2SO3 (where BEDT-TTF is bis(ethylenedithio)tetrathiafulvalene) in both the superconducting (Tc ∼ 5K) and normal states versus magnetic field direction. In the normal state, detailed angular-dependent magnetoresistance oscillation (AMRO) studies reveal peculiar features of the Fermi surface topology of this compound, and very high magnetic field studies further support the unusual nature of the electronic structure. In the superconducting state we investigate, through detailedAMRO measurements, the anomalous MR peak that appears within the superconducting field-temperature phase diagram. Our results reveal a direct connection between the superconducting state determined from purely in-plane field, and the vortex lattice produced by the inter-plane magnetic field. We also describe several unique sample rotation instruments used in these high field experiments, including the use of dysprosium pole pieces in combination with a 45 T hybrid magnet to carry out measurements at the highest steady-state resistive magnetic field (47.8 T) yet achieved.
  • Open Access Logo New Journal of Physics 8(2006), 255

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Publ.-Id: 9153


Magnetic-field- and temperature-dependent Fermi surface of CeBiPt

Wosnitza, J.; Goll, G.; Bianchi, A. D.; Bergk, B.; Kozlova, N.; Opahle, I.; Elgazzar, S.; Richter, M.; Stockert, O.; von Löhneysen, H.; Yoshino, T.; Takabatake, T.
Abstract. The half-Heusler compounds CeBiPt and LaBiPt are semimetals with very low charge-carrier concentrations as evidenced by Shubnikov–de Haas (SdH) and Hall-effect measurements. Neutron-scattering results reveal a simple antiferromagnetic structure in CeBiPt below TN = 1.15K. The band structure of CeBiPt sensitively depends on temperature, magnetic field and stoichiometry. Above a certain, sample-dependent, threshold field (B > 25 T), the SdH signal disappears and the Hall coefficient reduces significantly. These effects are absent in the non-4f compound LaBiPt. Electronic-band-structure calculations can well explain the observed behaviour by a 4f-polarization-induced Fermi-surface modification.
  • Open Access Logo New Journal of Physics 8(2006), 174

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Publ.-Id: 9152


Spin-triplet excitons in the S = 1/2 gapped antiferromagnet BaCuSi2O6: Electron paramagnetic resonance studies

Zvyagin, S. A.; Wosnitza, J.; Krzystek, J.; Stern, R.; Jaime, M.; Sasago, Y.; Uchinokura, K.
BaCuSi2O6, a S = 1/2 quantum antiferromagnet with a double-layer structure of Cu2+ ions in a distorted planar-rectangular coordination and with a dimerized spin singlet ground state, has been studied by means of the electron paramagnetic resonance technique. It is argued that multiple absorptions observed at low temperatures are intimately related to a thermally activated spin-triplet exciton superstructure, which appears to be a characteristic feature of low-dimensional anisotropic spin- 1/2 systems with the dimerized spin-singlet ground state. We showed that analysis of the angular dependence of exciton modes could be used for accurate estimation of anisotropy parameters in BaCuSi2O6; the procedure can be applied for a large number of S = 1/2 quantum antiferromagnets. In addition, the temperature dependence of EPR intensity and linewidth in BaCuSi2O6 has been studied and discussed.

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Publ.-Id: 9150


Comparative resistivity studies under hydrostatic pressure on different variants of the organic superconductor κ - (ET)2Cu[N(CN)2]Br

Strack, C.; Akinci, C.; Wolf, B.; Lang, M.; Schlueter, J.; Wosnitza, J.; Schweitzer, D.
Resistivity measurements on four samples of κ - (ET)2Cu[N(CN)2]Br, synthesized by following two different preparation routes, yield strongly sample-dependent ρ(T) profiles. By comparing the interlayer resistivities and their response to hydrostatic pressure we infer: (i) a significant part of the inelastic-scattering contribution, causing the anomalous ρ(T) maximum around 90K, is extrinsic in nature, (ii) the abrupt change in the slope of ρ (T) around T* ≈ 40K is sample independent and most likely marks a second-order phase transition, (iii) the origin of the ρ(T) ∝ AT2 dependence at low temperatures, with a strongly sample dependent coefficient A and range of validity, is different from coherent Fermi-liquid excitations.
  • Poster
    Frühjahrstagung der Deutschen Physikalischen Gesellschaft, 03.-09.03.2005, Berlin, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-9149
Publ.-Id: 9149


Quantum Well Infrared Photodetector: High Absorption and High Speed Properties, and Two-Photon Response (Chapter 7)

Schneider, H.; Liu, H. C. Keywords: quantum well infrared photodetector, QWIP, GaAs/AlGaAs, two-photon transition
  • Contribution to external collection
    Paiella, R.: Intersubband Transitions in Quantum Structures, New York: Mc. Graw-Hill, 2006, 0071457925, 285-313

Permalink: https://www.hzdr.de/publications/Publ-9148
Publ.-Id: 9148


Surface Modification of Ti-6Al-4V Alloy with a Low-Energy, High-Current Electron Beam at Elevated Initial Temperatures

Rotshtein, V. P.; Markov, A. B.; Proskurovsky, D. I.; Gunzel, R.; Pham, M.; Richter, E.; Shevchenko, N.; Shulov, V. A.; Rubshtein, A. P.
Surface topography, evolution of chemical and phase composition of the surface layers of Ti-6Al-4V alloy subjected to multiple pulsed electron-beam melting at the initial temperature of the target To ranging from 20 to 550 °С have been investigated using optical, laser microscopy, SEM/EDS, AES and XRD analyses. Pulsed melting was induced by a low-energy (~20 keV), high-current electron beam (3 µs, 2.5 J/cm2). At To<200 °С the cleaning of the near-surface layer from oxygen takes place. In contrast, at To<400 °С a 1 µm thick surface layer quenched from the melt is enriched with oxygen from the residual gases of vacuum chamber.
The influence of initial temperature on the microstructure and properties of the surface layers are discussed based on the results of temperature field predictions.
Keywords: Ti-6Al-4V alloy, high-current electron beam, surface modification, phase composition
  • Poster
    8th International Conference on Modification of Materials with Particle Beams and Plasma Flows, 10.-15.09.2006, Tomsk, Russia
  • Russian Physics Journal 49(2006)8, 337-342

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Publ.-Id: 9147


Surface alloying of Ti-6Al-4V with zirconium by pulsed electron-beam melting of film – substrate system

Rotshtein, V. P.; Markov, A. B.; Proskurovsky, D. I.; Kagadei, V. A.; Guenzel, R.; Shevchenko, N.; Reuther, H.; Shulov, V. A.
Evolution of chemical and phase composition of the surface layers of Ti-6Al-4V subjected to surface alloying with zirconium has been studied. Alloying was carried out by liquid-phase mixing of multilayer systems of type (Ti/Zr) film on (Ti-6Al-4V alloy) substrate by a low-energy, high-current electron beam with the following parameters: pulse duration 2.5 µs, beam energy density 2.5-3 J/cm2. The number of pulses and the overall thickness of coating was ranging from 1 to 5 and from 500 to 800 nm, respectively. It has been recognized using X-ray analysis, scanning electron microscopy and electron X-ray microanalyzer, that surface layer after one-pulsed melting has a two-phase microstructure consisting of matrix solid solution of titanium with ~ 23 at.% of zirconium and a relatively pure (~ 4.5 at.% Zr) titanium particles of micron dimensions. The formation of such a microstructure takes place owing to segregation of solid solution at high-rate cooling (~ 109 K/s) of melted Ti-Zr alloy. The following vacuum annealing (550 0С, 2 hours) courses a decrease in the size of particles and a reduction in zirconium concentration in precipitations of titanium to ~ 1 at.% whereas zirconium concentration in the matrix increases and reaches 26 at.%. Auger electron spectroscopy revealed that in the latter case a thickness of surface alloy is 1-2 µm and an average concentration of zirconium equals to 20 at.%. The concentration of aluminum and vanadium is 8 and 6 times less then that of untreated Ti-6Al-4V alloy, respectively. An increase in number of pulses results in a decrease in zirconium concentration near the surface due to its evaporation. Corrosion tests in 1% NaCl solution showed that surface alloying of Ti-6Al-4V with Zr leads to approximately one order of magnitude higher corrosion resistance than that for untreated specimen.
Keywords: Ti-6Al-4V, surface alloying, zirconium, electron beam
  • Lecture (Conference)
    8th International Conference on Modification of Materials with Particle Beams and Plasma Flows, 10.-15.09.2006, Tomsk, Russia
  • Russian Physics Journal 49(2006)8, 262-267

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Pulsed electron-beam irradiation followed by nitriding of Ti-6Al-4V titanium alloy

Markov, A. B.; Günzel, R.; Reuther, H.; Shevchenko, N.; Akhmadeev, Y. K.; Schanin, P. M.; Koval, N. N.; Rotshtein, V. P.; Proskurovsky, D. I.
Titanium alloys have some attractive properties enabling them to be used in many industries, while their poor tribological properties often are an obstacle in mechanical engineering applications. The latter properties can be improved by applying surface treatment, for instance, nitriding.
Aim of the research was to investigate the effect of pulsed electron-beam pre-irradiation on the process of titanium alloy (Ti–6Al—4V) low-temperature (783 K) nitriding.
AES revealed that the depth of penetration of nitrogen into the specimen bulk for the pre-irradiated specimen is noticeably larger than that for the non-irradiated one (110 and 170 nm, respectively). Moreover, the overall quantity of nitrogen absorbed by the pre-irradiated specimen during nitriding is two times as much as in the non-irradiated one. So, pre-irradiation of the titanium alloy stimulates its saturation with nitrogen.
XRD analysis revealed that irradiation of this titanium alloy leads to the formation of martensite phases referred to as alpha’ and alpha’’ in the thin surface layer of specimen. Appearance of these metastable phases results in high residual stress values in the irradiated target. In such a way the subsequent nitrogen diffusion in the irradiated specimens will take place in the field of intrinsic stresses. After nitriding the phase composition of titanium alloy was changed and the new TiN and Ti2N phases have appeared. It can be concluded from X-ray diffraction patterns that a fraction of these new phases is much larger for the pre-irradiated before nitriding specimen.
The microhardness measurements showed that the microhardness of surface layer of pre-irradiated with subsequent nitriding specimens is almost four times as much as the initial one (11.3 and 3 GPa, respectively). As for the specimens subjected to the nitriding without pre-irradiation their microhardness appeared to be 8.9 GPa, i.e. three times larger than that for the initial specimen.
Thus, the combined treatment, involving pulsed e-beam pre-irradiation, subsequent cleaning and nitriding is promising and leads to increase in the absorption of nitrogen, the fractions of TiN and Ti2N phases and the surface microhardness in processed titanium alloy.
Keywords: Titanium alloy, Ti–6Al—4V, pulsed electron-beam, nitriding
  • Lecture (Conference)
    8th International Conference on Modification of Materials with Particle Beams and Plasma Flows, 10.-15.09.2006, Tomsk, Russia
  • Russian Physics Journal 49(2006)8, 276-279

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Publ.-Id: 9145


Multigroup coupled neutron-gamma cross-section library for deterministic and Monte Carlo borehole logging analysis

Kodeli, I.; Aldama, D. L.; de Leege, P. F. A.; Legrady, D.; Hoogenboom, J. E.; Cowan, P.
A special purpose multigroup cross-section library optimized for nuclides and reactions arising in nuclear oil well logging was prepared for use in deterministic and Monte Carlo transport codes. The library is based on the recent ENDF/B-VI.8 evaluation, which includes among others improved oxygen and chlorine cross-sections. A 175 neutron and 45 gamma ray energy group structure was selected in a way to take into account the requirements of oil well logging applications. This library is expected to improve the prediction of the neutron and gamma spectra at the detector positions of the logging tool and its use for the interpretation of the Carbon/Oxygen (C/O) neutron logging measurements in boreholes was studied. For the Monte Carlo codes this library can be useful in particular in calculations requiring multigroup cross sections, like adjoint or MIDWAY methods. Furthermore, comparison of deterministic and Monte Carlo calculations using same or similar cross sections can reveal the uncertainty linked to the computational method and model. Preparation and testing of this library is described.
Keywords: Monte Carlo, Well Logging, Multigroup, Cross Section, Carbon/Oxygen Logging
  • Nuclear Science and Engineering 157(2007)2, 210-224

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Publ.-Id: 9144


Application of adjoint monte carlo to accelerate simulations of mono-directional beams in radiotherapy treatment planning

Nievaart, V. A.; Legrady, D.; Moss, R. L.; Kloosterman, J. L.; van der Hagen, T. H. J. J.; van Dam, H.
Boron Neutron Capture Therapy is a well recognised cancer therapy applied usually for spread brain tumors. The alpha particles emitted at neutron capture in Boron will bring localised and excessive damage to surrounding cells while special medicaments are reponsible to achive higher Boron concentration in tumor than in healthy tissue. This article discusses a method to calculate treatment planning for BNCT using adjoint Monte Carlo. The proposed method aims at resolving a problematic issue of obtaining nonzero estimates for a monodirectional beam as sampled adjoint pseudoparticles would hardly coincide with a single preferred direction. The method descibed in this paper uses Legendre expansion to utilise adjoint scores at the beam exit not paralel with the beam tube to interpolate to the direction of paralel direction.
Keywords: adjoint, Monte Carlo, mono-directional, treatment planning
  • Medical Physics 34(2007)4, 1321-1335

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Publ.-Id: 9143


Electrical Conductivity of Nitrogen Doped SiC Nanocrystals in Diamond

Weishart, H.; Heera, V.; Skorupa, W.
Nanocrystals of silicon carbide were synthesized inside natural diamond using high dose silicon implantation. In order to retain the diamond structure implantation was done at 900 °C. The samples were subsequently annealed in an rf-heated furnace at 1500 °C for 10 min. A more detailed study on the formation of epitaxially aligned 3C-SiC nanocrystallites within the implanted diamond was published recently[i]. However, investigation of electrical properties was restricted to four-point measurements. Here we will present Hall measurements as function of temperature of the high-fluence Si-implanted diamonds. The results indicate a highly conductive, buried layer inside the diamond. The exceptional high electron concentration may originate in implantation-induced electrical active defects as well as n-type doping by unintentionally co-implanted 28(N2).

[i] H. Weishart, V. Heera, F. Eichhorn, B. Pécz, Á. Barna and
W. Skorupa, J. Appl. Phys. 94 (2003) 1195.
  • Poster
    5. Siliziumkarbid-Rundgespräch, 17.-18.07.2006, Kloster Banz, Staffelstein, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-9142
Publ.-Id: 9142


Halbleiterspektroskopie mit ultrakurzen Laserpulsen

Schneider, H.
  • Lecture (others)
    Physikalisches Kolloquium, 05.07.2006, Freiberg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-9139
Publ.-Id: 9139


A nodal expansion method for solving the multigroup SP3 equations in the reactor code DYN3D

Beckert, C.; Grundmann, U.
The core model DYN3D which has been developed for three-dimensional analyses of steady states and transients in thermal reactors with quadratic or hexagonal fuel assemblies is based on nodal methods for the solution of the two-group neutron diffusion equation. Loading cores with higher content of MOX fuel, the increase of the fuel cycle length and new types of reactors are challenging for these standard methods. A nodal expansion method for solving the equations of the simplified P3 approximation (SP3) of the multigroup transport equation was developed to improve the accuracy of the DYN3D code. In this paper, the method used in DYN3D-SP3 is described. It is applied for the pinwise calculation of a steady state of the OECD/NEA and U.S. NRC PWR MOX/UO2 Core Transient Benchmark. The eigenvalue keff, assembly powers and the pin powers are computed. The results calculated with different approaches including diffusion theory are compared with the reference solution obtained from a heterogeneous transport calculation with the code DeCART. Different approaches of the diffusion coefficient used in the SP3 equations are investigated. The SP3 results obtained with the transport cross section of multigroup diffusion theory show the smallest deviations from the reference solution. These deviations are in the same order as the results of the code DORT, whereas the DORT and DYN3D calculations were carried out with the same library of group constants for homogenized pin cells.
Keywords: SP3, nodal methods, neutron transport, neutron diffusion, multigroup
  • Contribution to proceedings
    M&C+SNA 2007 - Joint International Topical Meeting on Mathematics & Computations and Supercomputing in Nuclear Applications, 15.-19.04.2007, Monterey, United States
  • Lecture (Conference)
    M&C+SNA 2007 - Joint International Topical Meeting on Mathematics & Computations and Supercomputing in Nuclear Applications, 15.-19.04.2007, Monterey, United States

Permalink: https://www.hzdr.de/publications/Publ-9138
Publ.-Id: 9138


Development and verification of a multigroup SP3 method for reactor calculations

Beckert, C.; Grundmann, U.
A nodal approach for the multigroup SP3 equations was developed and integrated in the DYN3D code. The method is verified by pinwise multigroup calculations for a steady state of the OECD/NEA and U.S. NRC PWR MOX/UO2 Core Transient Benchmark. The results of different approaches including diffusion theory are compared with the reference transport solutions of the code DeCART. Different approaches of the diffusion coefficient used in the SP3 equations are investigated. The SP3 results obtained with the transport cross section of multigroup diffusion theory show a good agreement with the DeCART transport solutions.
Keywords: SP3, DYN3D, nodal methods, multigroup, neutron transport, neutron diffusion
  • Contribution to proceedings
    Annual meeting on nuclear technology 2007, 22.-24.05.2007, Karlsruhe, Germany
  • Lecture (Conference)
    Annual meeting on nuclear technology 2007, 22.-24.05.2007, Karlsruhe, Germany

Permalink: https://www.hzdr.de/publications/Publ-9137
Publ.-Id: 9137


Epitaxial thin films of undoped ZnO grown by reactive pulsed magnetron sputtering

Vinnichenko, M.; Rogozin, A.; Shevchenko, N.; Kolitsch, A.; Moeller, W.
The process of ZnO thin film growth by reactive pulsed magnetron sputtering is optimized to enable formation of epitaxial layers on Al2O3 (0001) substrates. The effects of the oxygen partial pressure, substrate temperature (Ts), base pressure, state of the target and substrate are investigated. X-ray diffraction (XRD) phi-scans suggest formation of the epitaxial ZnO layers with two types of domains in the case of chemically cleaned substrate (Ts=550°C, high oxygen, and base pressure of 5•10-7 mbar). One type of domains is 30° rotated relatively to the dominating orientation. Employing the target presputtering and additional substrate cleaning in oxygen plasma at the same other parameters, the formation of two-domain structure is suppressed and single-domain structure is obtained without additional buffer layers. The XRD rocking curve full width on half maximum is of 0.409°. According to spectroscopic ellipsometry analysis, the highly in-plane ordered ZnO films show no grading of optical constants and have significantly lower optical absorption. The Lorentz oscillator broadening obtained from the dielectric function is significantly smaller for the improved layer that also points to a higher ordering of the material. The oxygen plasma treatment of the sapphire substrate is shown to be crucial for preparation of epitaxial ZnO film with high in-plane alignment.
Keywords: ZnO thin film, in-plane ordering, reactive pulsed magnetron sputtering, optical properties
  • Poster
    E-MRS Spring Meeting, 29.05.-02.06.2006, Nice, France

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Publ.-Id: 9136


Magnetic quantum oscillations in the normal and superconducting state of YNi2B2C

Ignatchik, O.; Wosnitza, J.; Jäckel, M.; Souptel, D.; Behr, G.; Canfield, P.
The de Haas-van Alphen (dHvA) effect, or quantum oscillations of the magnetization, is the most direct method to study Fermi-surface properties in metals.It is remarkable, that these magnetic quantum oscillations persist deep into the vortex state of many type-II superconductors. The damping of the oscillation amplitude below the upper critical field can be related to the magnitude of the superconducting gap. For YNi2B2C, however, quite controversial results for the dHvA signal in the superconducting state have been reported. We will present dHvA measurements of YNi2B2C single crystals prepared by different methods. The flux-grown crystals exhibit dHvA oscillation in the superconducting state down to 3 T as reported in literature. However, we observed an unexpectedly sudden vanishing of the dHvA signal in the mixed state for crystals grown by a zone-melting method. The very quick disapppearance of the oscillating signal below B c2 suggests an unexpected fast opening of a large superconducting gap. At high magnetic fields six different dHvA frequencies could be detected.
  • Poster
    Frühjahrstagung Berlin, 03.-09.03.2005, Berlin, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-9135
Publ.-Id: 9135


Ion implantation of halogens: a promising technique for enhancing the high-temperature oxidation resistance of TiAl alloys

Yankov, R. A.; Donchev, A.; Schuetze, M.; Richter, E.
kein Abstrakt vorhanden
  • Poster
    21st General Conference (Meeting of the German Physical Society, Session MM: Metal- and Material Physics), 27.-31.03.2006, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-9134
Publ.-Id: 9134


Improving the Oxidation Resistance of TiAl-alloys with Fluorine

Donchev, A.; Richter, E.; Schuetze, M.; Yankow, R. A.
  • Poster
    12th International IUPAC-Conference on High Temperature Materials Chemistry HTMC, 17.-22.09.2006, Vienna, Austria

Permalink: https://www.hzdr.de/publications/Publ-9133
Publ.-Id: 9133


Improvement of the Oxidation behavior of TiAl-alldoys by treatment with halogens

Donchev, A.; Richter, E.; Schuetze, M.; Yankow, R. A.
Titanium aluminides are of great interest for several structural high temperature applications because of their low specific weight (about 4 g/cm3) and their excellent high temperature strength. They could replace the much heavier high temperature steels or Ni-based superalloys (up to 9 g/cm3) which are usually in service. The implementation of this new group of intermetallic alloys in e.g. the aerospace or automotive industry is therefore due to economic and ecologic reasons. The use of TiAl-based alloys is still limited to a temperature of about 750 °C because of their poor oxidation resistance despite of their good mechanical properties which would allow the use at higher temperatures. The oxidation resistance can be improved significantly by small amounts of halogens such as fluorine, chlorine, bromine and iodine (so called halogen effect). A defined dose of these halogens has to be provided at the metal/oxide interface of the component. The halogens promote the selective formation of gaseous Al-halides at temperatures above 700 °C which are oxidised to Al2O3 during their outward diffusion through the naturally grown oxide scale. So finally a protective alumina scale is formed which is stable for long times even under thermocyclic exposure and wet atmospheres. In this paper the results of isothermal and thermocyclic high temperature oxidation tests of technical TiAl-alloys with and without halogen treatment are shown. Additionally the results of high temperature creep tests of halogen treated TiAl-alloys are presented and compared with the untreated alloys.
  • Intermetallics 14(2006)10-11, 1168-1174

Permalink: https://www.hzdr.de/publications/Publ-9131
Publ.-Id: 9131


Wavelength-selective enhancement of the intensity of visible photoluminescence in hydrogen-ion-implanted silicon-on-insulator structures annealed under high pressure

Tyschenko, I. E.; Zhuravlev, K. S.; Cherkov, A. G.; Popov, V. P.; Misiuk, A.; Yankov, R. A.
Characteristic features of the visible photoluminescence (PL) spectra were studied in silicon-on-insulator (SOI) wafers following high-dose (3×1017 cm–2) ion implantation of hydrogen and annealing at high hydrostatic pressures. The PL behavior of the SOI material was compared with that of hydrogen-implanted bulk Si. Annealing at a pressure above 6 kbars produced a wavelength-selective increase (~37 times) in the intensity of the visible PL from the implanted SOI structures. The results are explained in terms of the effect of an optical resonant cavity formed between the air/SOI and the Si/SiO2 interfaces as a result of the high-pressure annealing.
  • Applied Physics Letters 89(2006), 013106 Jul 3 2006

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Publ.-Id: 9130


Materialaspekte bei der Untersuchung von Störfallszenarien in Kernkraftwerken

Altstadt, E.
Es wird ein Überblick zu den Aspekten der Materialsicherheit in der Kerntechnik gegeben. Im Mittekpunkt der Betrachtungen steht der Reaktordruckbehälter von Leichtwasserreaktoren bei hypothetischen Unfällen mit Kernschmelze. Es wird auf den Aufbau von Leichtwasserreaktoren und die Sicherheitsphilosophie bei deutschen KKW eingegangen. Die Im FZD angwendeten Methoden und Modelle zur Simulation von Schmelzerückhaltungsszenarien werden erläutert. (Vorlesung ca. 80 min.)
Keywords: Reactor pressure vessel, Material Safety, In-vessel melt retention, Corium
  • Lecture (others)
    Ringvorlesung des Materialforschungsverbundes Dresden für das Studium generale der Technische Universität Dresden, 29.11.2006, Dresden, Germany

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Publ.-Id: 9129


Modification of NiTi surface by plasma immersion ion implantation

Shevchenko, N.; Maitz, M. F.; Richter, E.
The NiTi alloy has a high nickel concentration of 50 at%, which may result in nickel ion release into the body environment, preventing from biomedical application. It was demonstrated that the nickel surface concentration may be reduced significantly using plasma immersion ion implantation (PIII). In the present work the surface processes during oxygen (or nitrogen) PIII and the microstructure and properties of the modified surface layers were studied. The samples were examined by X-ray diffraction analysis, Auger electron spectroscopy, atomic force microscopy, spectroscopic ellipsometry and corrosion and blood compatibility tests. Oxygen PIII at an ion energy of 40 keV and a substrate temperatures below 300°C results in the formation of a transparent rutile TiO2 surface layer with a Ni content down to below 1 at%. This layer prevents from corrosion and out-diffusion of Ni ions. Biocompatibility tests show a largely superior in vitro blood compatibility compared to the untreated samples.
Keywords: Shape memory alloy, biocompatibility, PIII
  • Lecture (Conference)
    International Conference on Shape Memory and Superelastic Technologies (SMST 2006), 07.-11.05.2006, Pacific Grove, California, USA

Permalink: https://www.hzdr.de/publications/Publ-9128
Publ.-Id: 9128


Electromagnetic control of a transitional boundary layer

Albrecht, T.; Grundmann, R.; Mutschke, G.; Gerbeth, G.
The stability of a transitional boundary layer controlled by a wall-parallel, streamwise oriented Lorentz force is investigated by means of direct numerical simulation. Damping of Tollmien-Schlichting waves is observed already at weak control amplitudes.
For a particular control amplitude, similar to homogeneous suction, the initial Blasius layer evolves towards an exponential velocity profile of strongly enhanced stability. Here, intermediate velocity profiles are found to have linear stability properties superior to that of the asymptotic exponential profile. Additional 3-D simulations support the 2-D results as Lorentz force control clearly damps the coherent structures of the transitional flow.
Furthermore, results to optimize the energy consumption of the control by evolutionary strategies are presented.
Keywords: MHD, Control, Boundary Layer, DNS, linear stability analysis
  • Lecture (Conference)
    Fifth international Conference on Computational Fluid Dynamics in the Process Industries, 13.-15.12.2006, Melbourne, Australia

Permalink: https://www.hzdr.de/publications/Publ-9127
Publ.-Id: 9127


Plasma immersion ion implantation for NiTi surface modification

Shevchenko, N.; Reuther, H.; Kreissig, U.; Richter, E.
The shape-memory and superelastic nickel-titanium alloy (NiTi, nitinol) has a high nickel concentration of 50 at% which may result in nickel ion release in biological solutions, preventing from application in biomedical implants and devices. Recently, it was demonstrated that the nickel surface concentration may be reduced significantly using plasma immersion ion implantation (PIII) [1, 2]. Our previous biocompatibility tests show a superior in vitro blood compatibility of the oxygen ion implanted NiTi surfaces compared to the untreated ones [3]. Understanding of the mechanisms of surface modification and nickel depleted layer formation during PIII as well as its phase composition evolution is to date rather limited.
In present paper we consider the effect of both ion fluence and implantation temperature on the phase composition, surface morphology, and electrochemical properties of PIII processed NiTi. The samples were examined by grazing incidence X-ray diffraction analysis (GIXRD), Auger electron spectroscopy, elastic recoil detection analysis, atomic force microscopy, spectroscopic ellipsometry and corrosion test.
Oxygen PIII from an inductively coupled RF plasma at an ion energy of 20 keV, an ion fluence of E17-E18 cm-2, and a substrate temperature below 250°C results in the formation of a transparent rutile TiO2 surface layer with a thickness of 50-200 nm and a Ni content below 1 at%. In contrast, the underlying alloy is enriched with Ni. The GIXRD analysis indicates the presence of the Ni4Ti3 and Ni3Ti phases in addition to NiTi. The oxide layer thickness as well as the surface roughness are controlled by the balance of reactive ion-induced diffusion and ion sputtering. The nickel-depleted TiO2 layer prevents from corrosion and out-diffusion of Ni ions.
The results of this study show that PIII is a promising technique for the surface modification of NiTi alloy for biomedical applications.
Keywords: Plasma implantation, NiTi alloy, surface, phase composition
  • Lecture (Conference)
    International Conference on Ion Beam Modification of Materials (IBMM 2006), 18.-22.09.2006, Taormina, Italy

Permalink: https://www.hzdr.de/publications/Publ-9126
Publ.-Id: 9126


Electroluminescence properties of the GD3+ ultraviolet luminescent centers in SiO2 gate oxide layers

Sun, J. M.; Prucnal, S.; Skorupa, W.; Dekorsy, T.; Muecklich, A.; Helm, M.; Rebohle, L.; Gebel, T.
Electroluminescence (EL9) properties in the ultraviolet (UV) range were studied on Gd-implanted indium tin oxide/SiO2 :Gd/ Si metal-oxide-semiconductor light emitting devices. The efficient UV line at 316 nm from Gd3+ centers shows a maximum power density of 2 mW/cm2 and a quantum efficiency above 5%. The Gd3+ luminescent center has an excitation cross section above 7.4 x10−15 cm2 with an EL decay time around 1.6 ms at a Gd concentration of 3%. A decrease of the
EL efficiency is observed by a cross relaxation at a high Gd concentration and by clustering of Gd atoms at an annealing temperature of 1000 °C. A strong quenching of the UV EL due to electron trapping around optically active Gd3+ centers is observed during the injection of hot electrons.
  • Journal of Applied Physics 99(2006), 103102

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Publ.-Id: 9125


Complete characterization of selected model alloys and VVER1000 steels by SANS, TEM and PAS

Ulbricht, A.; Bergner, F.; Cizek, J.; Melikhova, O.; Prochazka, I.; Kuriplach, J.
The aim of the present report is to contribute small-angle neutron scattering (SANS) data, positron annihilation (PAS) data and transmission electron microscopy (TEM) data to the experimental database. We draw conclusions from the combined application of these methods on the nature of the irradiation-induced features in RPV steels and model alloys.
Keywords: SANS, PAS, TEM, RPV steel, iron alloy, neutron irradiation, defect/solute atom clusters
  • Article, self-published (no contribution to HZDR-Annual report)
    Forschungszentrum Rossendorf 2006
    FZR\FWS\2006\05
    14 Seiten

Permalink: https://www.hzdr.de/publications/Publ-9124
Publ.-Id: 9124


RPV-1 models sensitivity for VVER 1000 materials parameters

Bergner, F.; Ulbricht, A.
The multiscale prediction code RPV-1 was applied to VVER 1000 reactor pressure vessel steels. A sensitivity study was performed for VVER 1000 materials parameters.
  • Lecture (others)
    3rd Plenary Meeting of the Perfect Physics Subproject, 08.-10.11.2006, Mol, Belgium

Permalink: https://www.hzdr.de/publications/Publ-9123
Publ.-Id: 9123


Characterization of Ni-Ti SMA thin films: from annealing to in-situ sputtering

Martins, R. M. S.; Schell, N.; Beckers, M.; Silva, R. J. C.; Braz Fernandes, F. M.
Shape Memory Alloy (SMA) NiTi thin films have attracted much interest as functional and smart materials due to their unique properties. However, there are still important issues unresolved like formation of film texture and its control as well as substrate effects. For microelectromechanical systems (MEMS) integration, there is a need for an electrically and thermally insulating or sacrificial layer like poly-Si. In the present study, NiTi thin films have been prepared by d.c. magnetron sputtering on Si(100) and poly-Si/Si(100) substrates to elucidate the substrate influence on the crystallization of these films. Following the structural development of the films during crystallization (at a constant temperature of 430 ºC) by GIXD, is was observed that the crystallization process is significantly enhanced for low target/substrate distances of 4 cm instead of 7 cm for Si(100) substrates. The presence of an intermediate layer of poly-Si furthermore drastically enhances the crystallization process.
In-situ XRD during the growth of Ni-Ti thin films was chosen in order to investigate their texture development using a deposition chamber installed at ROBL. Near-equiatomic films were obtained by co-sputtering from Ni-Ti and Ti targets. The texture evolution during deposition is clearly affected by the substrate type and the ion bombardment of the growing film. On naturally oxidized Si(100) substrates the NiTi B2 phase starts by stacking onto (h00) planes, and as the thickness increases evolves into a (110) fiber texture. This pronounced cross-over is only observed when a substrate bias voltage (-45 V) is applied for the deposition on thermally oxidized Si(100) substrates. The oxide layer plays an important role on the development of the (100) orientation of the B2 phase during deposition on heated substrates (~ 470ºC).
The effect of a TiN layer deposited on top of the SiO2/Si(100) substrate prior to the deposition of the NiTi films was also analysed. These experiments have shown that TiN acts not only as a diffusion barrier, but also induces different crystallographic orientations. These are promising results concerning the manipulation of the crystallographic orientations of NiTi thin films, since the texture has a strong influence on the extent of the strain recovery.
  • Lecture (Conference)
    ESRF Science Days 2006, 07.-08.06.2006, Autrans, France

Permalink: https://www.hzdr.de/publications/Publ-9122
Publ.-Id: 9122


In-situ study of Ni-Ti film growth by synchrotron radiation scattering

Martins, R. M. S.; Schell, N.; Silva, R. J. C.; Mahesh, K. K.; Braz Fernandes, F. M.
Ni-Ti thin films are promising high performance materials in the field of micro-electro-mechanical system (MEMS) applications. Their preferential orientation is a crucial factor in determining the shape memory behavior since it has a strong influence on the extent of the strain recovery. The relationship between structure and deposition parameters is of extreme importance for future device applications. Our approach is in-situ x-ray diffraction during deposition carried out in a process chamber installed at a synchrotron radiation beamline. Near-equiatomic films (800nm) were co-sputtered from Ni-Ti and Ti targets on heated substrates (~470C) without applying a substrate bias voltage. The texture evolution during deposition is clearly affected by the substrate type. On naturally oxidized Si(100) substrates the Ni-Ti B2 phase starts by stacking onto (h00) planes, and, as the thickness increases, evolves to a (110) fiber texture. An initial significant change of the lattice parameter, as calculated from d(200) , is observed and its tendency for stabilization is coincident with the deposition time where the preferential stacking of B2 phase on (110) planes is starting. For the deposition on thermally oxidized Si(100) there is a strong preferential stacking on (h00) planes of B2 leading to a (100) fiber texture. The measured lattice constants do not exhibit such a strong initial variation as for the sample deposited on naturally oxidized Si(100) substrate, but a continuous slight decrease of this value is perceptible. Ni-Ti films were also deposited on top of a TiN buffer layer. There is a preferential growth of <110> oriented grains of the Ni-Ti B2 phase [ grains are defined as grains with a plane from the {hkl} family parallel to the film surface] from the beginning of the deposition, with a constant growth rate during the whole deposition for a Ni-Ti film deposited on TiN with a topmost layer formed mainly by <111> oriented grains. The Ni-Ti films deposited on top of a TiN layer where a dominating orientation could not be identified (primarily <001> and <111> oriented grains nucleate and grow) exhibit a different behavior. In this case <110> oriented grains of the Ni-Ti B2 phase dominate at small thicknesses while <211> oriented grains take over at larger thicknesses. The decrease of the lattice parameter suggests that the films experience compressive stress which is significantly relaxed with increasing film thickness.
  • Poster
    MICRODIFF'06 - Local Mechanical Stresses and Microdiffraction, 28.-29.09.2006, Grenoble, France

Permalink: https://www.hzdr.de/publications/Publ-9121
Publ.-Id: 9121


The role of a TiN buffer layer on the growth of Ni-Ti sputtered thin films

Martins, R. M. S.; Schell, N.; Beckers, M.; Silva, R. J. C.; Mahesh, K. K.; Braz Fernandes, F. M.
  • Poster
    ESRF Science Days 2006, 07.-08.06.2006, Autrans, France

Permalink: https://www.hzdr.de/publications/Publ-9120
Publ.-Id: 9120


In-situ XRD during sputtering deposition of Ni-Ti Shape Memory Alloys on TiN/SiO2/Si(100)

Martins, R. M. S.; Schell, N.; Beckers, M.; Silva, R. J. C.; Mahesh, K. K.; Braz Fernandes, F. M.
  • Poster
    ESRF User's Meeting 2006, 07.-08.02.2006, Grenoble, France

Permalink: https://www.hzdr.de/publications/Publ-9119
Publ.-Id: 9119


Modification of bubble-driven liquid metal flows under the influence of a DC magnetic field

Zhang, C.; Eckert, S.; Gerbeth, G.
The paper presents an experimental study devoted to a bubble-driven liquid metal flow under the influence of an external DC magnetic field. Experiments have been performed on laboratory scale at ambient temperature using the ternary alloy GaInSn. Measurements of the bubble-driven liquid metal flow have been carried out using the Ultrasound Doppler Velocimetry (UDV). The magnetic field has been imposed either in vertical direction parallel to the main bubble motion or in horizontal direction, respectively. Whereas a global damping of the flow field was generally observed in the case of the vertical aligned magnetic field, the application of a horizontal magnetic field can provoke a restructuring of the flow pattern with strong, non-steady vortical structures. This finding could attain relevance for metallurgical engineering, for instance the control of the mould flow during the continuous casting of steel by means of an electromagnetic brake.
Keywords: liquid metal, bubble plume, DC magnetic field, Ultrasound Doppler method, velocity measurements
  • Open Access Logo ISIJ International 47(2007)6, 795-801

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Permalink: https://www.hzdr.de/publications/Publ-9118
Publ.-Id: 9118


Texture evolution during annealing of Ni-Ti Shape Memory Alloy

Braz Fernandes, F. M.; Paula, A. S.; Canejo, J.; Mahesh, K. K.; Silva, R. J. C.; Martins, R. M. S.; Cardoso, A. M. A.; Schell, N.
Anisotropy of the shape recovery associated with shape memory effect strongly depends on the type of preferential orientation, that is present, as well as the ‘strength’ of the texture. In the present paper, we report the results obtained by the in-situ study of texture evolution during the annealing process in Ti-rich Ni-Ti Shape Memory Alloys (SMAs) with different thermal and mechanical histories. For this purpose, a Be-dome furnace installed into a 6-circle goniometer at the BM20 beamline (ROBL-CRG) at the ESRF (Grenoble) has been used. It is shown that there is a significant change in the preferential orientation of B2 phase, with the change in microstrain/coherence domain size, as a function of annealing temperature. This effect is also observed in the B19’ phase after cooling. The alpha-fiber II (austenite texture - <110>||RD ({111}<110>-{110}<110>) was present in the as-received alloy, but only up to 400ºC. The evolution of {111}<110> austenite texture component is quite clear for annealing temperatures above 400ºC.
  • Lecture (Conference)
    Conference on Shape Memory and Superelastic Technology-Europe 2004, 03.-07.10.2004, Baden-Baden, Germany
  • Contribution to proceedings
    Conference on Shape Memory and Superelastic Technology-Europe 2004, 03.-07.10.2004, Baden-Baden, Germany
    Proceedings of Shape Memory and Superelastic Technology 2004, Baden-Baden: ASM International, 45-50

Permalink: https://www.hzdr.de/publications/Publ-9117
Publ.-Id: 9117


In-situ study of the preferential orientation of magnetron sputtered Ni-Ti thin films as a function of bias and substrate type

Martins, R. M. S.; Schell, N.; Beckers, M.; Mücklich, A.; Reuther, H.; Silva, R. J. C.; Mahesh, K. K.; Braz Fernandes, F. M.
The preferential orientation of Ni-Ti thin films is a crucial factor in determining the shape memory behavior. The texture has a strong influence on the extent of the strain recovery. The relationship between structure and deposition parameters is of extreme importance for future device applications. Our approach is in-situ x-ray diffraction during deposition carried out in a process chamber installed at a synchrotron radiation beamline. Near-equiatomic films were co-sputtered from Ni-Ti and Ti targets. Substrate type and bias voltage play an important role for the preferred orientation. On naturally oxidized Si(100) substrates the NiTi B2 phase starts by stacking onto (h00) planes and then changes to (110) fiber texture with increasing film thickness. For thermally oxidized Si(100) substrates, this cross-over is only observed when a bias voltage is applied. The experiments were supplemented by ex-situ transmission electron microscopy and Auger Electron Spectroscopy allowing an additional deeper insight into the film/substrate interface.
Keywords: Ni-Ti; Sputter deposition; In-situ x-ray diffraction; Texture development; Interface
  • Contribution to proceedings
    Conference on Shape Memory and Superelastic Technology 2006, 07.-11.05.2006, Asilomar, U.S.A.
    Proc. of SMST 2006, 363-372
  • Lecture (Conference)
    Conference on Shape Memory and Superelastic Technology 2006, 07.-11.05.2006, Asilomar, U.S.A.

Permalink: https://www.hzdr.de/publications/Publ-9116
Publ.-Id: 9116


Role of the substrate on the growth of Ni-Ti sputtered thin films

Martins, R. M. S.; Schell, N.; Beckers, M.; Silva, R. J. C.; Mahesh, K. K.; Braz Fernandes, F. M.
Ni-Ti thin films have been recognized as promising and high performance materials in the field of microelectromechanical system applications. However, important issues like formation of film texture and its control are still unresolved. Widening the scope of previous experiments concerning the influence of the deposition parameters on the Ni-Ti films structure, here we show how different crystallographic orientations can be obtained by changing the substrate type. The growth of near-equiatomic Ni-Ti films, deposited by magnetron co-sputtering from Ni-Ti and Ti targets on heated substrates ( 470C), has been studied in situ by x-ray diffraction at a synchrotron radiation beamline. As mentioned in other studies for depositions on Si(100), a (110) fiber texture is observed for the B2 phase. However, a preferential stacking of (100) planes of the B2 phase parallel to the film surface was observed when using a MgO(100) substrate. The preferential orientation of B2(100) // MgO(100) was very strong and was kept as such until the end of the deposition, which lasted for 2 hours (~ 900 nm). Ni-Ti films were also deposited on a TiN layer (~ 15 nm) previously deposited on top of a SiO2/Si(100) substrate. In this case, a crossover from (110) oriented grains dominating at small thicknesses, to (211) oriented grains taking over at larger thicknesses was observed. These are promising results concerning the manipulation of the crystallographic orientations of Ni-Ti thin films, since the texture has a strong influence on the extent of the strain recovery.
Keywords: structure and morphology, deposition by sputtering, in-situ x-ray diffraction
  • Poster
    ESOMAT 2006 - European Symposium on Martensitic Transformations and Shape Memory Alloys, 10.-15.09.2006, Bochum, Germany
  • Materials Science and Engineering A 4812-482(2008), 626-629

Permalink: https://www.hzdr.de/publications/Publ-9114
Publ.-Id: 9114


In-situ study of Ni-Ti thin film growth on a TiN intermediate layer by x-ray diffraction

Martins, R. M. S.; Schell, N.; Silva, R. J. C.; Pereira, L.; Mahesh, K. K.; Fernandes, F. M. B.
Shape Memory Alloy (SMA) Ni-Ti thin films have attracted much interest as functional and smart materials due to their unique properties. However, there are still important issues unresolved like formation of film texture and its control as well as substrate effects. In this study, near-equiatomic films were obtained by co-sputtering from Ni-Ti and Ti targets in a process chamber installed at a synchrotron radiation beamline. In-situ x-ray diffraction during the growth of these films allowed establishing a relationship between structure and deposition parameters. The effect of a TiN layer deposited on top of the SiO2/Si(100) substrate prior to the deposition of the Ni-Ti films was analysed. These experiments show that TiN acts not only as a diffusion barrier, but also induces different crystallographic orientations. A TiN layer with ~ 215 nm thickness induces the preferential growth of (110) planes of the Ni-Ti B2 phase parallel to the substrate from the beginning of the deposition with a constant growth rate during the whole deposition. For a TiN thickness of ~ 15 nm, the diffraction peak B2(110) also appears from the beginning of the deposition but much less intense. In this latter case, the B2(211) peak was also detected having observed a crossover from <110> oriented grains dominating at small thicknesses, to <211> oriented grains taking over at larger thicknesses. The same orientations and similar intensities were observed for a Ni-Ti film deposited on a TiN layer with ~ 80 nm.
Keywords: Shape memory alloy; Ni-Ti; deposition by sputtering; in-situ x-ray diffraction; texture development
  • Poster
    E-MRS 2006 Spring Meeting, 29.05.-02.06.2006, Nice, France
  • Sensors and Actuators B 126(2007)1, 332-337

Permalink: https://www.hzdr.de/publications/Publ-9113
Publ.-Id: 9113


Structural in-situ studies of Ni-Ti thin films

Martins, R. M. S.; Braz Fernandes, F. M.; Silva, R. J. C.; Beckers, M.; Schell, N.
Ni-Ti thin films present great advantages for the fabrication of micro-actuators. The phase transformation and precipitation, which are responsible for the shape memory effect, have been widely studied in bulk material and thin films. However, in-situ studies have been limited to the ageing/annealing treatments after deposition. In this study we present a series of results that clearly illustrate the interest of in-situ studies, not only during annealing, but also during sputtering. The in-situ annealing experiments, using a Be-dome furnace installed into the six-circle diffractometer of the ROssendorf BeamLine (ROBL-CRG) at the ESRF, Grenoble, allowed us to determine the kinetics of the phenomena, to identify the sequence of precipitation and to correlate the build-up of the final structure with the processing conditions. The in-situ sputtering experiments were performed using a magnetron sputter deposition chamber also installed into the six-circle diffractometer of the ROBL-CRG beamline. This facility allowed us to follow the structural evolution of the films also during the deposition process.
Keywords: Ni-Ti, SMA, x-ray diffraction
  • Contribution to proceedings
    Shape Memory and Superelastic Technologies 2004, 03.-07/10/2004, Baden Baden, Germany
    Proceeding of SMST 2004, Baden Baden: ASM International, 421-426
  • Lecture (Conference)
    Conference on Shape Memory and Superelastic Technology-Europe 2004, 03.-07.10.2004, Baden-Baden, Germany

Permalink: https://www.hzdr.de/publications/Publ-9112
Publ.-Id: 9112


Long-term corrosion and leaching of depleted uranium (DU) in the soil

Schimmack, W.; Gerstmann, U.; Schultz, W.; Geipel, G.
The corrosion and leaching of depleted uranium (DU) was investigated for three years using six DU munitions (145 – 264 g DU) each buried in a column with a soil core of ca. 3.3 kg dry soil mass. The columns were installed in an air-conditioned la-boratory. Each week they were irrigated and 238U was determined in the effluents by Inductively Coupled Plasma Mass Spectrometry. In addition, 235U was measured oc-casionally in order to assure that the origin of 238U was predominantly the DU muniti-on. On average, 14.5 g corresponding to 7.9 % of the initial DU mass was corroded after three years indicating an acceleration of the corrosion as compared to the first year (see Schimmack et al., Radiat Environ Biophysics 44: 183-191 (2005)). The leaching rates increased much stronger than the corrosion by factors of more than 100 resulting in a mean total amount of leached 238U of 13 mg as compared to 0.03 mg after the first year. The uranium species identified by time-resolved laser-induced fluorescence spectroscopy were mainly hydroxo and carbonate compounds in the seepage water and phosphate compounds in the corroded material. It is concluded that the dramatic increase of the leaching and its large temporal and spatial variability do not allow any extrapolation into the future. However, the high level of the 238U concentrations in the seepage water demands further investigations on the transport of 238U through the soil in order to estimate the concentration of 238U from DU muniti-ons in the groundwater for areas affected by DU weapons.
Keywords: depleted Uranium, soil, corrosion, leaching, speciation

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Permalink: https://www.hzdr.de/publications/Publ-9111
Publ.-Id: 9111


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