Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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34122 Publications

QCD matter within a quasi-particle model and the critical end point

Kämpfer, B.; Bluhm, M.; Schulze, R.; Seipt, D.; Heinz, U.

We compare our quasi-particle model with recent lattice QCD results for the equation of state at finite temperature and baryo-chemical potential. The inclusion of the QCD critical end point into models is discussed. We propose a family of equations of state to be employed in hydrodynamical calculations of particle spectra at RHIC energies and compare with the differential azimuthal anisotropy of strange and charm hadrons

  • Nuclear Physics A 774(2006), 757-760

Publ.-Id: 7663

Beta decay of 103Sn

Kavatsyuk, O.; Kavatsyuk, M.; Batist, L.; Banu, A.; Becker, F.; Blazhev, A.; Brüchle, W.; Döring, J.; Faestermann, T.; Górska, M.; Grawe, H.; Janas, Z.; Jungclaus, A.; Karny, M.; Kirchner, R.; La Commara, M.; Mandal, S.; Mazzocchi, C.; Mukha, I.; Muralithar, S.; Plettner, C.; Płochocki, A.; Roeckl, E.; Romoli, M.; Schädel, M.; Schwengner, R.; Żylicz, J.

The β decay of 103Sn, a three-neutron-particle nucleus with respect to the 100Sn core, was investigated at the GSI on-line mass separator using an array of 17 germanium crystals and a total absorption spectrometer. A total of 31 β-delayed γ-rays (29 new) of the 103Sn →103 In decay were observed and, on the basis of β-γ-γ coincidences, the 103Sn decay scheme was established for the first time. By means of total absorption spectroscopy, β intensities, the Gamow-Teller strength distribution and the summed Gamow-Teller strength value of 3.5±0.5 were determined for this decay. Its half-life and QEC value were found to be 7.0±0.2 s and 7.64±0.7 MeV, respectively. The β-delayed proton branching ratio was measured to be 1.2±0.1%. The results are discussed in comparison with shell-model predictions based on realistic and empirical interactions.

  • European Physical Journal A 25(2005)2, 211-222

Publ.-Id: 7662

The local structure of U(VI)-Ferrihydrite sorption complexes revisited: EXAFS spectroscopy and Monte Carlo Simulations

Roßberg, A.; Ulrich, K. U.; Scheinost, A. C.

EXAFS analysis of actinyl sorption complexes is a complicated task due to the presence of overlapping shells, structural disorder and the presence of multiple scattering paths due to the specific actinyl structure. Hence often controversial interpretations arise from conventional shell fitting. A typical example is the proposed formation of ternary uranyl carbonato surface complexes on ferrihydrite, where a peak at ~2.4 Å in the Fourier transform is explained by backscattering carbon atoms at 2.86-2.94 Å. While such ternary carbonate complexes have been confirmed by complementary techniques like FTIR and electrophoretic mobility measurements, the EXAFS peak shows even up in those uranyl ferrihydrite systems, where great care has been taken to keep the system carbonate-free, rendering an EXAFS fit with carbon meaningless.
To overcome this common problem of EXAFS shell fitting, we developed a new analysis approach based on Monte-Carlo simulations coupled to theoretical EXAFS modeling using FEFF. Here, the position of the uranyl atom is first refined in relation to a given ferrihydrite surface structure. In a second step, the whole complex structure is refined to allow for e.g. surface relaxation effects. Using this approach, a match to the experimental EXAFS spectra of U(VI) ferrihydrite complexes without carbonate could be achieved. The local structure indicates a mononuclear bidentate (edge-sharing) surface complex, which was identified for the first time by EXAFS spectroscopy. Further fits were performed to elucidate the influence of carbonate and other anions on the structure of the surface complex. The results demonstrate the potential of the Monte-Carlo approach for determining the structure of actinyl surface complexes.

  • Lecture (Conference)
    Migration 2005, 10th International Conference on Chemistry and Migration Behaviour of Actinides and Fission Products in the Geosphere, 18.-23.09.2005, Avignon, France
  • Contribution to proceedings
    Migration 2005, 10th International Conference on Chemistry and Migration Behaviour of Actinides and Fission Products in the Geosphere, 18.-23.09.2005, Avignon, France

Publ.-Id: 7660

Electronic structure of LaSrMnO4: XPS and XES studies

Kuepper, K.; Klingeler, R.; Reutler, P.; Büchner, B.; Neumann, M.

We present a comprehensive investigation of the valence band of the single layered manganite LaSrMnO4. X-ray photoelectron spectroscopy (XPS) and x-ray emission emission spectroscopy (XES) were used to reveal a detailed picture of the total and partial densities of states in this compound. The results are discussed in the light of available theory.

Keywords: La1-xSr1+xMnO4; electronic structure; x-ray photoelectron spectroscopy; x-ray emission spectroscopy; valence band

  • Journal of Applied Physics 99(2006)8, 08Q308-1-08Q308-3
    DOI: 10.1063/1.2151792
  • Poster
    Magnetism and Magnetic Materials Conference, 30.10.-03.11.2005, San Jose, USA

Publ.-Id: 7659

Magnetic and electronic properties of the iron-containing polyoxotungstate [Fe4(H2O)10(β-SbW9O33)2]6-

Prinz, M.; Takács, A.; Schnack, J.; Balasz, I.; Burzo, E.; Kortz, U.; Kuepper, K.; Neumann, M.

The magnetic and X-ray photoelectron spectroscopy (XPS) studies on the transition metal substituted, dimeric polyoxotungstate [Fe4(H2O)10(β-SbW9O33)2]6- are reported. The magnetic data were analysed by using an isotropic Heisenberg Hamiltonian. The ground state of the frustrated molecule has a total spin of S = 2. The XPS Fe 2p spectra suggest a 2+ formal valence state. The deviation from the contained Fe3+ ions can be explained by charge-transfer e®ects.

Keywords: magnetic molecules; polyoxotungstates; Heisenberg model; magnetization measurements; x-ray photoelectron spectroscopy

  • Journal of Applied Physics 99(2006), 08J505-1-08J505-3
    DOI: 10.1063/1.2173613
  • Poster
    Magnetism and Magnetic Materials Conference, 30.10.-03.11.2005, San Jose, USA

Publ.-Id: 7658

Ion beam synthesis of Fe nanoparticles in MgO

Potzger, K.; Reuther, H.; Zhou, S.; Mücklich, A.; Eichhorn, F.; Grötzschel, R.; Fassbender, J.

MgO(001) single crystals were irradiated with 57Fe at an energy of 100 keV and an ion fluence of 6x1016cm-2 at implantation temperatures between 25°C(RT) and 1000°C.
Analysis was carried out by means of CEMS, XRD, RBS and TEM. We found that the implantation temperature plays the important role for the formation of Fe nanoparticles. The fraction of metallic Fe (CEMS Fe0 signal) increases from 28% for RT implantation to 60% for 800°C implantation, while the Fe profile remains unchanged (Rp ¡Ö 50 nm). The nanoparticles formed after 800°C implantation are about 5 nm in size and exhibit fcc-structure with an orientation relationship of Fe(111)/MgO(111) and Fe(220)/MgO(220). The nanoparticles exhibit paramagnetism at room temperature.
At an implantation temperature of 1000°C the Fe implantation profile smears out completely and 92% of the Fe atoms are found in the Fe3+
oxidation state.

Keywords: embedded nanoparticles; magnetism; ion beam synthesis

  • Contribution to HZDR-Annual report
    Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; FZR-427 Januar 2005, 52-52
    ISSN: 1437-322X

Publ.-Id: 7657

Electronic structure study by means of X-ray spectroscopy and theoretical calculations of the "ferric star" single molecule magnet

Takács, A.; Neumann, M.; Postnikov, A. V.; Kuepper, K.; Scheurer, A.; Sperner, S.; Prince, K. C.; Saalfrank, R. W.

The electronic structure of the single molecule magnet system {M[Fe(L1)2]3}*4CHCl3, (M = Fe, Cr; L1 = CH3N(CH2CH2O)2 2-) has been studied using X-ray photoelectron spectroscopy,X-ray absorption spectroscopy, soft X-ray emission spectroscopy, as well as theoretical density functional-based methods. There is good agreement between theoretical calculations and experimental data. The valence band mainly consists of three bands between 2 eV and 30 eV. Both theory and experiments show that the top of the valence band is dominated by the hybridization between Fe 3d and O 2p bands. From the shape of the Fe 2p spectra it is argued that Fe in the molecule is most likely in the 2+ charge state. Its neighboring atoms (O, N) exhibit a magnetic polarisation yielding effective spin S=5/2 per iron atom, giving a high spin state molecule with a total S=5 effective spin for the case of M = Fe.

Keywords: PACS numbers: 75.50.Xx; 31.15.Ar; 33.20.Rm; 33.60.Fy

Publ.-Id: 7656

Fe implanted ferromagnetic ZnO

Potzger, K.; Zhou, S. Q.; Reuther, H.; Mücklich, A.; Eichhorn, F.; Schell, N.; Skorupa, W.; Fassbender, J.; Helm, M.; Herrmannsdörfer, T.; Papageorgiou, T. P.

The origin of ferromagnetism in ZnO single crystals implant-doped with Fe is investigated using X-ray diffraction, transmission electron microscopy, superconducting quantum interference device magnetometry and Mössbauer spectroscopy. For an ion fluence of 4×1016 ions per cm2 and an implantation temperature of 620 K, Fe nanoparticles are responsible for room-temperature ferromagnetism of the ZnO single crystals. On the other hand Fe ions implanted with an ion fluence of 4×1015 ions per cm2 at a temperature of 253 K develop a ferromagnetic coupling within the host matrix. Consequently only high resolution methods allow to rule out secondary phases in doped magnetic semiconductors.

Keywords: diluted magnetic semiconductors; ZnO; implant doping

  • Applied Physics Letters 88(2006)5, 052508

Publ.-Id: 7655

Effects of implantation of magnetic ions into ZnO

Potzger, K.; Zhou, S.; Reuther, H.; Brauer, G.; Anwand, W.; Eichhorn, F.; Bischoff, L.; Herrmann, F.; Grambole, D.; Groetzschel, R.; Fassbender, J.

Recent achievements in the field of diluted magnetic semiconductors are summarized. Then, effects of the implantation of magnetic ions into ZnO single crystals are studied by various highly sensitive analysis methods. It is found that the implantation of Fe ions at elevated temperatures (620 K) yields the formation of small ferromagnetic Fe particles. Moreover, the host lattice exhibits open-volume type damage confined at the near surface region. Both effects strongly depend on the ion fluence. On the other hand, after 25 keV focused ion beam implantation of Co+ no magnetic domains could be detected on a ZnO single crystal surface. However, unscreened electric charges are locally introduced effectuating a contrast within a lift mode-operated atomic force microscope that can easily be confused with magnetic field gradients.

Keywords: ZnO; diluted magnetic semiconductors; ion implantation; magnetism

  • Lecture (Conference)
    HeT-SiC-05, 26.04.-01.05.2005, Krippen, Deutschland

Publ.-Id: 7652

Magnetic Materials and Ion Irradiation - New topics in Rossendorf

Potzger, K.

An introduction on new topics at the institute for ion beam physics and materials research concerning magnetic materials is given. Especially the field of ion beam synthesis of ferromagnetic nanoparticles in oxide host materials, magnetic patterning of exchange bias thin films and magnetic doping of ZnO is discussed.

Keywords: embedded ferrmoagnetic nanoparticles; diluted magnetic semiconductors; exchange bias; ion beam synthesis

  • Lecture (others)
    Abteilungsseminar, 28.01.2005, Leipzig, Deutschland
  • Lecture (others)
    Abteilungsseminar, Prof. W. Brewer, 10.02.2005, Berlin, Deutschland

Publ.-Id: 7651

Fabrication of Si nanocrystals for memory application by ion irradiation through SiO2/Si-interfaces

Schmidt, B.; Heinig, K.-H.; Roentzsch, L.; Mücklich, A.; Stegemann, K.-H.; Votintseva, E.; Klimenkov, M.

This contribution addresses self-assembling of Si-nanocrystals (NCs) in gate oxides, with special emphasis on size and position tailoring and their application as discrete charge storage centers in nanocrystal memories. The Si NCs for these multi-dot floating-gate memories have been produced by ion irradiation through SiO2/Si-interfaces. Si excess within SiO2 is formed by ion beam mixing of Si from the Si substrate and from the poly-Si capping layer into the gate oxide. Ion irradiation with 3x1015 -10x1015 Si+ cm-2 at 50-100 keV through 50 nm poly-Si and 15 nm SiO2 on (001)Si results in a considerable Si excess. At the upper and lower interfaces of the gate oxide, this ion irradiation forms a metastable SiOx composition. Si NCs are formed by phase separation into Si and SiO2 during post-irradiation thermal treatment. Adjacent to the recovering interfaces, narrow SiO2 zones becomes denuded of excess Si. More distant excess Si precipitates as Si NCs in the gate oxide. This approach was applied to nMOSFET-NC-memory fabrication in the standard CMOS line at ZMD. MOSFET characteristics in terms of write/erase voltage, duration of the programming time, endurance and retention have been evaluated.

Keywords: Si nanocrystals; ion iradiation; interface mixing; memory devices

  • Lecture (Conference)
    Frühjahrstagung der Deutschen Physikalischen Gesellschaft, Berlin, 04.03.-09.03.2005, 04.-09.03.2005, Berlin, Deutschland

Publ.-Id: 7650

Luminescent Defect dynamics in amorphous SiO2:H

Fitting, H.-J.; Ziems, T.; Salh, R.; Voncharnowski, A.; Schmidt, B.

The main luminescent centers in SiO2 are the red luminescence R(1.85eV) of the non-bridging oxygen hole center (NBOHC) and the oxygen deficient center (ODC) with a blue B(2.7eV) and a UV band (4.4eV). Implanted hydrogen diminishes the red luminescence but increases the blue and the UV bands. Thus hydrogen passivates the NBOHC and keeps the ODC's in active emission states. A preliminary model of luminescence center transformation is based on radiolytic dissociation and re-association of mobile oxygen and hydrogen at the centers as well as formation of interstitial H2, O2, and H2O molecules.

Keywords: Luminescence; SiO2; hydrogen ion implantation

  • Physica Status Solidi (C) 2(2005)1, 693-698

Publ.-Id: 7649

On the Determination of the Optical Constants of Very Thin (Lambda/50) Films

Gushterova, P.; Sharlandjiev, P.; Schmidt, B.; Pham, M.

The improvement of a recently developed spectrophotometric method for the determination
of the complex refractive index (ñ) and physical thickness (d) of very thin films (d = Lambda/50, Lambda is the wavelength in the visible and near infrared) is presented. The thin film transmittance (Tf), front side reflectance (Rf) and back side reflectance (Rf') are used for the estimation of (ñ, d). Utilizing the nanothickness of the films, we derive analytical expressions for Rf, Rf' and Tf, by development of the Abelès characteristic matrix elements up to the 4th order in ñd/Lambda. An optimization procedure is used to estimate (ñ, d). Thus, the problem related to multiple or lack of solutions is overcome. The method is applied to Au films, deposited on transparent glass substrates. For comparison of the resulting (ñ, d), Veriable Angle Spectroscopic Ellipsometry is used as an independent technique.

Keywords: Spectrophotometry; Ellipsometry; thin Au layers

  • Journal of Optoelectronics and Advanced Materials 7(2005)1, 305-308

Publ.-Id: 7648

Studies on the interaction of actinides with biomolecular and mineral surfaces and their contribution to long-term assessment

Raff, J.

An overview of our work concerning the interaction of actinides with the biosphere and the geosphere is given and possible contributions to long-term assessment were discussed.

  • Lecture (Conference)
    GBIZ, 12.-14.09.2005, Barcelona, Spain

Publ.-Id: 7647

Cathodoluminescence of wet, dry, and hydrogen-implanted silica films

Fitting, H.-J.; Ziems, T.; Salh, R.; Zamoryanskaya, M. V.; Kolesnikova, K. V.; Schmidt, B.; von Czarnowski, A.

The main luminescent centers in SiO2 films are the red luminescence R (1.85 eV) of the non-bridging oxygen hole center (NBOHC), a blue B (2.7 eV) band of the oxygen deficient centers (ODC's), a UV (4.3 eV),band, and a yellow Y (2.2 eV) band appears especially in hydrogen-implanted silica after longer time of irradiation. By means of pulsed electron beam excitation and a new track-stop technique we have investigated the luminescence life time as well as the initial luminescence properties at the beginning of irradiation. Thus the dose dependence of the red (R) luminescence in wet and dry oxide differs, decreasing in wet oxide from an initial level and increasing in dry oxide from almost zero at room temperature. Additionally, implanted hydrogen diminishes the red luminescence in wet oxide but increases the blue and the UV bands. Thus hydrogen passivates the NBOHC and keeps the ODC's in active emission states. A preliminary, model of luminescence center transformation is based!
A model of luminescensecenter transformation is based on radiolytic dissociation and re-association of mobile oxygen and hydrogen at the centers as well as formation of interstitial H-2, O-2, and H2O molecules. A comparison with the CL of ice layers shows that the H2O molecules should be the origin of the yellow (Y) luminescence.

Keywords: Cathodoluminescence; SiO2; ion implantation

  • Journal of Non-Crystalline Solids 351(2005)27-29, 2251-2262

Publ.-Id: 7646

Iron nanoparticles in amorphous SiO2: X-ray emission and absorption spectra

Kurmaev, E. Z.; Zatsepin, D. A.; Cholakh, S. O.; Schmidt, B.; Harada, Y.; Tokushima, T.; Osawa, H.; Shin, S.; Takeuchi, T.

The local structure of the chemical bond of iron ions implanted into SiO2 glasses (implantation energy, 100 keV; fluence, 1 x 10(16) cm(-2)) is investigated using x-ray emission and absorption spectroscopy. The Fe L x-ray emission and absorption spectra are analyzed by comparing them with the corresponding spectra of reference samples. It is established that iron nanoparticles implanted into the SiO2 vitreous matrix are in an oxidized state. The assumption is made that the most probable mechanism of transformation of iron nanoparticles into an oxidized state during implantation involves the breaking of Si-O-Si bonds with the formation of Si-Si and Fe-O bonds.

Keywords: Nanoparticles; ion implantation; X-ray absorption and emission spectroscopy

  • Physics of The Solid State 47(2005)4, 754-757

Publ.-Id: 7645

Complex formation of U(VI) with the amino acid L-threonine and the corresponding phophate ester O-Phopho-L-threonine

Günther, A.; Geipel, G.; Bernhard, G.

The complex formation of uranium(VI) with L-threonine and O-Phospho-L-threonine was studied by time-resolved laser-induced fluorescence spectroscopy (TRLFS). An increase in fluorescence emission intensity and a corresponding red shift of the bands in the spectra compared to the free uranyl cation indicate a complex formation between UO22+ and the non- and phosphorylated amino acid threonine. The complex formation constants for a 1:1 and 1:2 complex in the case of L-threonine were determined to be logß111 = 10.33 ± 0.26 at ionic strength I = 0.1 M, logß111 = 10.25 ± 0.25 and logß122 = 19.94 ± 0.01 at ionic strength I = 0.5 M. The calculated constants of the different 1:1 uranyl complexes with O-Phospho-L-threonine are logß113 = 20.28 ± 0.11, logß112 = 18.94 ± 0.29 and logß111 = 15.02 ± 0.23 at I = 0.1 M.

Keywords: uranium; complexation; TRLFS; amino acid; phosphorylated amino acid; speciation

  • Radiochimica Acta 94(2006), 845-851

Publ.-Id: 7644

Identifizierung und Charakterisierung von U(VI)-Komplexen in höheren Pflanzen

Günther, A.

Zusammenfassende Darstellung der bisherigen Ergebnisse der Untersuchungen zur chmeischen Speziation von Uran in Pflanzen und Vorstellung der dafür notwendigen Modellkomplexierungen (ausgewählte Beispiele)

  • Lecture (others)
    FZR - FSU Jena Workshop, 27.-28.07.2005, Dresden, Germany

Publ.-Id: 7643

EXAFS-Untersuchungen von U(VI)-Komplexlösungen mit ausgewählten Aminosäuren und Peptiden

Günther, A.; Roßberg, A.; Merroun, M.; Raff, J.

Darstellung neuster EXAFS-Ergebnisse zur Aufklärung der Bindungsverhältnisse von U(VI) an verschiedenen Aminosäuren und Peptiden

  • Lecture (others)
    ROBL-Radiochemie Workshop, 13.12.2004, Dresden, Germany

Publ.-Id: 7642

Spektroskopische Charakterisierung von U-Spezies in Pflanzen

Günther, A.; Roßberg, A.

Darstellung von Resultaten verschiedener TRLFS - und EXAFS Messungen an uranhaltigen Pflanzenproben

  • Lecture (others)
    ROBL-Radiochemie-Workshop, 08.12.2003, Dresden (Rossendorf), Deutschland

Publ.-Id: 7641

Interaction of Desulfovibrio äspöensis with selected actinides

Moll, H.; Merroun, M.; Selenska-Pobell, S.; Bernhard, G.

Darstellung neuer Aspekte der Wechselwirkung von ausgewählten Aktiniden mit Desulfovibrio äspöensis.

Keywords: Actinides; Bacteria; Desulfovibrio äspöensis; Biosorption; Bioreduction; Bioaccumulation

  • Lecture (others)
    FZR - FSU Jena Workshop, 27.-28.07.2005, Dresden, Germany

Publ.-Id: 7640

The interaction of actinides with cells of Desulfovibrio äspöensis

Moll, H.; Merroun, M.; Stumpf, T.; Geipel, G.; Selenska-Pobell, S.; Rossberg, A.; Bernhard, G.

Darstellung der Wechselwirkungsprozesse zwischen ausgewählten Actiniden (U, Cm, Np, Pu) mit Bakterien des Typs Desulfovibrio äspöensis

Keywords: Actinides; Bacteria; Desulfovibrio äspöensis; Biosorption; Bioreduction; Bioreduction

  • Lecture (others)
    Project Meeting, 02.-04.05.2005, Göteborg, Sweden

Publ.-Id: 7639

Magnetic resonance of metallic nanoparticles in vitreous silicon dioxide implanted with iron ions

Guseva, V. B.; Zatsepin, A. F.; Vazhenin, V. A.; Schmidt, B.; Gavrilov, N. V.; Cholakh, S. O.

Silica glasses exposed to steady-state and pulsed irradiation with Fe+ ions are studied using magnetic resonance. The irradiation doses used in experiments are equal to 1 x 10(15), 1 x 10(16), and 1 x 10(17) cm(-2). It is found that, under both steady-state and pulsed irradiation conditions, glass samples exposed at a dose of 1 x 10(17) cm(-2) exhibit a broadband orientation-dependent signal. The shape of inclusions is evaluated under the assumption that the observed spectrum is caused by the ferromagnetic resonance induced in a new phase of metallic iron.

Keywords: Ion implantation; iron; glass; metal nanoparticles; magnetic resonance

  • Physics of The Solid State 47(2005)4, 674-677

Publ.-Id: 7638

The mobilization of actinides by microbial ligands taking into consideration the final storage of nuclear waste A new BMBF/BMWA proposal

Moll, H.; Bernhard, G.

Eine neue Projektidee zur Bestimmung des Einflusses von Bioliganden auf die Migration von Actiniden in der Umwelt wird vorgestellt.

Keywords: Bioligands; Actinides

  • Lecture (others)
    The Äspö - FZR Workshop, 17.-18.05.2004, Dresden, Germany

Publ.-Id: 7637

Multiplet luminescence of sulfur implanted silica - SiO2 : S

Salh, R.; Schmidt, B.; Fitting, H.-J.

Thermally wet oxidized SiO2 layers of 500 nm thickness have been implanted by sulfur ions of energy 150 keV and a dose 5 x 10(16) ions/cm(2) leading to an atomic dopant fraction of 4 at% at a mean depth of 190 nm. The cathodoluminescence spectra of these sulfur implanted SiO2 layers show besides a characteristic violet band at 405 nm a sharp and intensive multiplet structure beginning in the green region at 500 nm over the yellow-red region and extending to the near IR measured up to 820 nm. The energy step differences of the sublevels amount in average to 120 meV and indicate vibration associated electronic states, probably, of unsaturated sulfur radicals equivalent to Si-S center dot or equivalent to Si-O-S center dot substituting the former nonbridging oxygen hole center (NBOHC) equivalent to Si-O center dot as an intrinsic defect of the pure SiO2. After 1 min electron beam irradiation with a dose of 0.3 As/cm(2) the spectral multiplet structure is nearly lost but the NBO! HC red band R (660 nm) remains.

Keywords: SiO2; ion implantation; sulfur; cathodoluminesence

  • Physica Status Solidi (A) 202(2005)5, R53-R55

Publ.-Id: 7636

Interaction of actinides with Desulfovibrio äspöensis. What have we achieved after 3 years of research on this topic?

Merroun, M.; Geipel, G.; Stumpf, T.; Rossberg, A.; Selenska-Pobell, S.; Bernhard, G.

Die Wechselwirkungsprozesse zwischen U, Np und Cm mit Bakterien des Typs Desulfovibrio äspöensis werden dargestellt.

Keywords: Actinides; Bacteria; Desulfovibrio äspöensis; Biosorption; Bioreduction; Bioaccumulation

  • Lecture (others)
    The Äspö - FZR Workshop, 17.-18.05.2004, Dresden, Deutschland

Publ.-Id: 7635

Diagnostic Tools for Operation and Optimization of the ELBE-FEL

Michel, P.; Evtushenko, P.; Lehnert, U.; Schneider, C.; Schurig, R.; Teichert, J.; Seidel, W.; Wohlfarth, D.

A FEL in the mid infrared range is one of the applications of the ELBE cw-electron accelerator. The successful operation of the lasing process for the different wavelength is mainly determined by the alignment of the optical cavities, the bunch length and the energy spread of the electron beam so as the transversal adjustment of the beam through the FEL. The energy spread and the bunch length of the electron beam have their minima at different phase conditions of the accelerator. For various energy settings of the accelerator a special adjustment of both parameters has to be found for the lasing process. The presentation describes the diagnostic tools used at ELBE for the correct alignment of the optical cavity, the steering of the electron beam through the FEL and the adjustment of the electron beam parameters with respect to energy spread and bunch length.

  • Poster
    27th International Free Electron Laser Conference 2005, 21.-26.08.2005, Stanford, California, USA
  • Contribution to proceedings
    27th International Free Electron Laser Conference 2005, 21.-26.08.2005, Stanford, CA, USA
    Proceedings of the 27th International Free Electron Laser Conference,: JACoW / eConf C0508213, 102-104


Publ.-Id: 7633

Optical Beam Properties and Performance of the MID-IR FEL at ELBE

Lehnert, U.; Michel, P.; Teichert, J.; Seidel, W.; Stehr, D.; Wohlfarth, D.; Wünsch, R.

First lasing of the mid-infrared free-electron laser at ELBE was achieved on May 7, 2004. Since then stable lasing has been achieved in the IR range from 4 to 22~μm using electron beam energies from 15 to 35~MeV. At all wavelengths below 20~μm a cw optical power higher than 1~W can be produced with an electron beam of 50~pC bunch charge or less. The optical pulse width at its minimum (2.2~ps measured at 17~μm) resembles the typical electron bunch length of 2~ps without bunch compression but can be increased by detuning the optical cavity. The optical bandwidth was in all cases close to the fourier limit.

  • Poster
    27th International Free Electron Laser Conference 2005, 21.-26.08.2005, Stanford, California, USA
  • Contribution to proceedings
    27th International Free Electron Laser Conference, 21.-26.08.2005, Stanford, CA, USA
    Proceedings of the 27th International Free Electron Laser Conference: JACoW / eConf C0508213, 286-287

Publ.-Id: 7632

Progress of the Rossendorf SRF Gun Project

Teichert, J.; Arnhold, A.; Buettig, H.; Janssen, D.; Lehnert, P.; Michel, P.; Moeller, K.; Schneider, C.; Staufenbiel, F.; Xiang, R.; Kamps, T.; Lipka, D.; Marhauser, F.; Volkov, V.; Stephan, J.; Lehman, W.-D.; Will, I.

A superconducting rf photo electron injector (SRF gun) is under development at the Forschungszentrum Rossendorf. The project aims at several issues: improvement of the beam quality for the ELBE superconducting electron linac, demonstration of feasibility of this gun type, investigation of critical components, and parameter studies for future application (BESSY-FEL, 4GLS). In 2005, a substantial progress has been made. The two 3.5-cell niobium cavities for the gun have been delivered from the company ACCEL. The main parts for gun cryostat like vacuum vessel, cryogenic and magnetic shields are ready. Test benches for the cathode cooling system and the cavity tuner are being assembled. The photo cathode preparation lab has been arranged, and the diagnostic beam line has been designed (see T. Kamps et al., this conference). After delivering the gun cavities, their rf properties are being measured at room temperature and the warm tuning is being carried out. The set-up for this treatment and measurement as well as the results will be presented.

  • Poster
    27th International Free Electron Laser Conference 2005, 21.-26.08.2005, Stanford, California, USA
  • Contribution to proceedings
    27th International Free Electron Laser Conference 2005, 21.-26.08.2005, Stanford, CA, USA
    Proceedings of the 27th International Free Electron Laser Conference: JACoW / eConf C0508213, 534-537
  • Poster
    1 st Annual EUROFEL Workshop 2005, 07.-09.11.2005, Orsay, France

Publ.-Id: 7631

Transport Theories for Heavy-Ion Collisions in the 1 AGeV Regime

Kolomeitsev, E. E.; Hartnack, C.; Barz, H. W.; Bleicher, M.; Bratkovskaya, E.; Cassing, W.; Chen, L. W.; Danielewicz, P.; Fuchs, C.; Gaitanos, T.; Ko, C. M.; Larionov, A.; Reiter, M.; Wolf, G.; Aichelin, J.

We compare multiplicities as well as rapidity and transverse momentum distributions of protons, pions and kaons calculated within presently available transport approaches for heavy ion collisions around 1 AGeV. For this purpose, three reactions have been selected: Au+Au at 1 and 1.48 AGeV and Ni+Ni at 1.93 AGeV.

  • Journal of Physics G 31(2005), S741-S757

Publ.-Id: 7629

Small-angle neutron scattering and rate theory applied to neutron-irradiation-induced clustering of defects and copper atoms in iron

Bergner, F.; Gokhman, A. R.; Ulbricht, A.

Results of small-angle neutron scattering (SANS) experiments are presented for a low-Cu (0.015 wt%) and a high-Cu (0.42 wt%) iron-based model alloy as well as selected reactor pressure vessel (RPV) steels. In order to exclude a strong participation of nickel atoms in the cluster formation, the selection of RPV steels is restricted to either low Ni content or low Cu in connection with medium Ni content according to the present status of knowledge. These materials were irradiated at about the RPV service temperature up to two or more levels of neutron fluence each. A low-temperature irradiation (60°C) is also included. The results are analysed in terms of both measured cluster size distribution and ratio of magnetic and nuclear contributions to SANS intensities. The assumptions underlying the analysis (e. g. spherical vs. plane scatterers) are addressed.

Calculations are based on the direct solution of the master equation of rate theory for three special cases: (1) Long-term evolution of vacancy clusters (VCs) in the absence of copper atoms, (2) long-term evolution of copper clusters in the absence of vacancies but assuming irradiation-enhanced copper diffusion to occur, and (3) co-clustering of copper and vacancies. Assumptions and limitations are discussed and the results are compared with SANS results.

It turned out that pure VCs or pure copper clusters were never observed. The observations for the low-Cu model alloy and the high-Cu model alloy can be interpreted as being due to spherical vacancy-rich clusters and Cu-rich clusters, respectively. The mean radius is about 1 nm in both cases. The parameters of the rate theory models can be adjusted so as to correctly reflect some major observations. The remaining discrepancies are also discussed.

  • Lecture (Conference)
    Micromechanics and Microstructure Evolution: Modeling Simulation and Experiments, 12.-16.09.2005, Madrid, Spain

Publ.-Id: 7628

Skaleninvarianz und deren Bedeutung für die Modellierung der Ermüdungsrißausbreitung in Aluminiumlegierungen

Bergner, F.

Die Arbeit ruht auf zwei Säulen: Die eine besteht in der Aufbereitung, Erprobung und konsequenten Anwendung von Methoden der Skaleninvarianzanalyse, die andere in einem breiten Fundus an experimentellen Daten für aushärtbare Aluminiumknetlegierungen in der Form dünner Bleche, die unter gleichartigen, streng kontrollierten Bedingungen gewonnen worden sind. Als methodische Weiterentwicklungen sind die Fundierung des Umgangs mit der algebraischen Korrelation zwischen Vorfaktor und Exponent einer beliebigen Potenzgleichung, die Übertragung des Ansatzes der finiten Skaleninvarianz auf die Ermüdungsrißausbreitung sowie die Kombination der Idee eines geschwindigkeitsbestimmenden Schrittes mit der Dimensionsanalyse der umgebungsabhängigen Ermüdungsrißausbreitung bis hin zur Kartierung der geschwindigkeitsbestimmenden Schritte zu nennen. Auf experimenteller Seite wurde eine Datensammlung mit gemessenen Streubändern für die Ermüdungsrißausbreitung und das Verfestigungsverhalten von 39 Orientierungen bzw. Auslagerungszuständen von Aluminiumlegierungen aufgebaut. Diese Sammlung wird durch ausgewählte Messungen der Ermüdungsrißausbreitung im schwellenwertnahen Bereich, Restfestigkeitsversuche, Rißschließmessungen, Rauheitsmessungen an Bruchflächen, frequenzabhängige Messungen zum Umgebungseinfluß sowie Untersuchungen an drei Stählen und einer Magnesiumlegierung sinnvoll ergänzt. Auf der Basis der Meßdaten und der Analysemethoden wurde der Werkstoffeinfluß auf die Ermüdungsrißausbreitung in dünnen Blechen aus Aluminiumknetlegierungen bei Belastung mit konstanter Amplitude im Gültigkeitsbereich der linear-elastischen Bruchmechanik untersucht. Dabei wurden folgende Größen als wesentliche Einflußfaktoren identifiziert: - für die Gruppenzugehörigkeit: der Kohärenz- und Ordnungsgrad der festigkeitsbestimmenden Ausscheidungen und die resultierende Gleitverteilung, - für den gemeinsamen Vorfaktor der Legierungen der Gruppe 1: die elastischen Eigenschaften und das Spannungsverhältnis (Translation der Paris-Geraden), - für die Exponenten der Legierungen der Gruppe 1: 0,2%-Dehngrenze, athermischer Verfestigungsparameter, Probendicke und Kc-Wert als dimensionsloses Potenzprodukt (Rotation der Paris-Geraden), - für die Legierungen der Gruppe 2: das Ausmaß der Rißablenkung und eine bleibende Mode-II-Komponente der Rißöffnungsverschiebung, - für den Umgebungseinfluß der Legierung 6013 T6: Frequenz und Schwingbreite des Spannungsintensitätsfaktors. Die Diskussion umfaßt den wertenden Vergleich der experimentellen Ergebnisse mit Befunden und Modellen aus der Literatur, Erklärungsansätze für die Ursachen der Einflußnahme der wesentlichen Parameter sowie einen Modellansatz für die Legierungen der Gruppe 1 auf der Basis einer Mischungsregel. Dabei hatte sich erwiesen, daß keines der aus der Literatur bekannten Modelle alle Befunde richtig wiedergibt. Einige der ausgearbeiteten Erklärungsansätze bedürfen der zukünftigen Vertiefung.

Keywords: aluminium alloys; damage tolerance; dimensional analysis; environmental effects; fatigue crack growth; scale invariance

Publ.-Id: 7627

Vector Meson Production in Collisions of Nucleons.

Brinkmann, K.; Abdel-Bary, M.; Abdel-Samad, S.; Clement, H.; Doroshkevich, E.; Dshemuchadse, S.; Dutz, H.; Ehrhardt, K.; Erhardt, A.; Eyrich, W.; Filippi, A.; Freiesleben, H.; Fritsch, M.; Georgi, J.; Gillitzer, A.; Gonser, P.; Jakel, R.; Karsch, L.; Kilian, K.; Koch, H.; Kress, J.; Kuhlmann, E.; Marcello, S.; Meyer, W.; Michel, P.; Morsch, H. P.; Moller, K.; Mortel, H.; Naumann, L.; Pinna, L.; Pizzolotto, C.; Roderburg, E.; Schamlott, A.; Schonmeier, P.; Schroeder, W.; Schulte-Wissermann, M.; Sefzick, T.; Steinke, M.; Stinzing, F.; Sun, G. Y.; Ucar, A.; Ullrich, W.; Wagner, G. J.; Wagner, M.; Wilms, A.; Wintz, P.; Wirth, S.; Wustner, P.; Zupranski, P.

The production of vector mesons in collisions between nucleons is studied in order to address a variety of issues concerning nucleon-nucleon interaction, reaction mechanism and properties of baryons. These studies are summarized with emphasis on the most recent experiments at the Time-of-Flight spectrometer TOF and results obtained at the COoler SYnchrotron COSY in Jülich. While currently the open questions regarding the so-called OZI violation, its relation to the meson exchange picture and the relative importance of contributions to the production mechanism from various channels within this formalism are still unresolved, the present-day experiments hold the potential to clarify the situation greatly. Possible extensions of the experimental program on vector mesons using 4π detection techniques for charged as well as neutral particles, in particular π0, are discussed.

Keywords: Nucleon-nucleon interaction; vector meson production; reaction mechanism and resonances

  • International Journal of Modern Physics A 20(2005)2-3, 427-435

Publ.-Id: 7626

Microstructure and non-basal plane growth of epitaxial MAX phase Ti2AlN thin films

Beckers, M.; Schell, N.; Martins, R. M. S.; Mücklich, A.; Möller, W.; Hultman, L.; (Editors)

Thin films of the MAX phase Ti2AlN were epitaxially grown onto single crystal MgO(111) and MgO(100) substrates by DC reactive magnetron co sputtering from Ti and Al targets in an Ar/N2 gas mixture at a temperature of 690 °C. To promote the nucleation of the MAX phase, an fcc (Ti0.63Al0.37)N seed layer was deposited before changing to Ti2AlN growth parameters. The nucleation processes have been studied by real time in situ specular x ray reflectivity. Independent of substrate orientation, the seed layer shows no roughening until its final thickness of approximately 100 Å indicating pseudomorphic layer by layer growth within the descriptive step-flow growth model of Kodambaka et al. [1]. The MAX phase shows heteroepitaxial layer by layer growth on MgO(111), with increased surface roughening up to approximately 200 Å, whereas on MgO(100) the growth mode changes to Volmer Weber type already after three monolayers. X ray scattering in Bragg Brentano geometry of the final, approximately 1000 Å thick, Ti2AlN film reveals lattice parameters of c = 13.463 Å and a = 2.976 Å on the MgO(111) substrate and c = 13.740 Å and a = 2.224 Å on the MgO(100) substrate. From ex situ pole figure measurements the epitaxial relationship between film and substrate lattice was determined to be MgO{111}<110> // Ti2AlN{101‾2}<1‾21‾0>, regardless of the substrate orientation. This tilted, non basal plane growth leads to a threefold grain orientation of Ti2AlN along the MgO<110> directions and a polycrystalline morphology, which is also confirmed by cross sectional transmission electron microscopy. The growth can be assumed to take place in a step-flow mode, i.e. emerging steps on the high surface free energy (0001) plane where adatoms come to rest after diffusion along A-facets, irrespective of epitaxial relationship.

Keywords: Nucleation and growth; Ti-Al-N MAX phase; sputter deposition; in situ x-ray diffraction

  • Journal of Applied Physics 99(2006), 34902


Publ.-Id: 7625

In-beam PET at high-energy photon beams: a feasibility study

H., M.; W., E.

For radiation therapy with carbon ion beams, either of the stable isotope {}^{12}C or of the radioactive one {}^{11}C, it has been demonstrated that the beta+-activity distribution created or deposited, respectively, within the irradiated volume can be visualised by means of positron emission tomography (PET). Those PET images provide valuable information for quality assurance and precision improvement of ion therapy. For this, dedicated PET scanners have been integrated into treatment sites at HIMAC (Japan) and GSI (Germany) to make feasible PET imaging during therapeutic irradiation (in-beam PET). A similar technique may be worthwhile for radiotherapy with hard bremsstrahlung. In addition to the dose delivery monitoring, in-beam PET has been primarily developed for, it may be expected that radiation response of tissue can be detected by means of in-beam PET. We investigate the applicability of PET for treatment control in case of using bremsstrahlung spectra produced by 15 - 50~MeV electrons. Target activation due to (gamma,n)~reactions at energies above 20~MeV yields moderate beta+-activity levels, which can be employed for imaging. The radiation from positrons produced by pair production turns out to be not usable at present because the detectors are overloaded due to the low duty cycle of medical electron linear accelerators, although the degradation of images caused by travelling of positrons between creation and annihilation seems to be tolerable.

  • Physics in Medicine and Biology 51(2006)7, 1779-1789

Publ.-Id: 7623

Steam bubble condensation in sub-cooled water in case of co-current vertical pipe flow

Lucas, D.; Prasser, H.-M.

The structure of a steam-water flow in a vertical pipe of 195.3 mm inner diameter was studied using novel wire-mesh sensors for high-pressure / high-temperature operation (max. 7 MPa / 286 °C). Tests were carried out at pressures of 1 and 2 MPa under nearly adiabatic conditions as well as with slightly sub-cooled water. Steam was injected into sub-cooled water and condensed during the upwards flow. The evolution of radial gas fraction profiles and bubble-size distributions along the pipe in a high-pressure steam-water flow was measured for the first time. The experimental data allow correlating the intensity of steam condensation in contact with sub-cooled water with the structure of the interfacial area and the bubble size distribution, which is very important for the model development. The data were used to test the complex interaction of local bubble distributions, bubble size distributions and local heat and mass transfer. The model considers a large number of bubble classes (50). This allows the investigation of the influence of the bubble size distribution. The results of the simulations show a good agreement with the experimental data. The condensation process is clearly slower, if the injection nozzle diameter is increased (from 1 to 4 mm orifices). Also bubble break-up has a strong influence on the condensation process because of the change of the interfacial area. Some modelling errors arises from the uncertainty of the interfacial area for large bubbles and the heat transfer coefficient.

Keywords: bubbly flow; phase transfer; condensation; bubble size distribution; population balance; vertical pipe

Publ.-Id: 7622

Influence of melt convection on microstructure evolution of Nd-Fe-B alloys using a forced crucible rotation technique

Biswas, K.; Hermann, R.; Filip, O.; Acker, J.; Gerbeth, G.; Priede, J.

The forced crucible rotation technique has been applied to the solidification of Nd-Fe-B alloys. Specially sealed samples were subjected to well-defined forced rotation during induction heating and solidification. The resulting microstructure of the Nd-Fe-B alloys in consideration of melt convection has been investigated using scanning electron probe microscopy. The determination of the a-Fe volume fraction by measuring the magnetic moment in a vibrating sample magnetometer (VSM) resulted in a distinct reduction of the a-Fe volume fraction in samples with high crucible rotation frequencies. Furthermore, a new category of experiment has been started where a tailored magnetic field was applied in order to study the microstructure evolution due to an enhancement or suppression of the melt convection by additional alternating magnetic fields.

  • Lecture (Conference)
    Magnetic and Superconducting Materials, 05.-09.09.2005, Agadir, Marocco
  • Physica Status Solidi (C) 3(2006), 3277-3280

Publ.-Id: 7621

Activities on applied MHD at Forschungszentrum Rossendorf

Gerbeth, G.

Magnetic fields provide an attractive contact-less influence on the motion of metallic or semiconductor melts and the related heat and mass transfer. An optimal design of the magnetic field is often difficult due to the lack of experimental access to the velocity field in such opaque melts. Several recently developed measuring techniques will be presented which allow an almost complete velocity resolution in metallic melts up to temperatures of about 400C. On this basis a combination of cold liquid metal model experiments with numerical simulations represents a powerful approach. Various examples will be presented ranging from crystal growth, aluminum investment casting to liquid metal two-phase flows. For the electromagnetic levitation process results will be given on sample instabilities and active means for stabilization as well as the flow field inside a molten sample.

  • Invited lecture (Conferences)
    Materials Science & Technology, Symposium “Electromagnetics in materials Processing”, 25.-28.09.2005, Pittsburgh, United States

Publ.-Id: 7620

HeT-SiC-05International Topical Workshop on Heteroepitaxy of 3C-SiC on Silicon and its Application to Sensor DevicesApril 26 to May 1, 2005,Hotel Erbgericht Krippen / Germany- Selected Contributions -

Brauer, G.; Skorupa, W.; (Editors)

This report collects selected outstanding scientific and technological results obtained within the frame of the European project “FLASiC” (Flash LAmp Supported Deposition of 3C-SiC) but also other work performed in adjacent fields. Goal of the project was the production of large-area epitaxial 3C-SiC layers grown on Si, where in an early stage of SiC deposition the SiC/Si interface is rigorously improved by energetic electromagnetic radiation from purpose-built flash lamp equipment developed at Forschungszentrum Rossendorf. Background of this work is the challenging task for areas like microelectronics, biotechnology, or biomedicine to meet the growing demands for high-quality electronic sensors to work at high temperatures and under extreme environmental conditions. First results in continuation of the project work – for example, the deposition of the topical semiconductor material zinc oxide (ZnO) on epitaxial 3C-SiC/Si layers – are reported too.

Keywords: beta-silicon carbide; biocompatibility; biosensor; doped metal oxide; epitaxy; flash lamp annealing; heterostructure; high-temperature device; hotplate; ion implantation; luminescence; magnetic ion; misfit defect; pulsed laser deposition; resonator; sensor; silicon carbide; simulation; stress; surface melting; zinc oxide

  • Open Access Logo Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; FZR-433 2005
    ISSN: 1437-322X


Publ.-Id: 7616

A possible mechanism for enhanced magnetic quantum oscillations in the mixed state of layered superconductors with incoherent electronic transport

Gvozdikov, V. M.; Wosnitza, J.

We present a new mechanism for the scattering rate in the mixed state of layered superconductors. This mechanism acts through the modification of the layer-stacking factor which suppresses magnetic quantum oscillations if the interlayer electron hopping is incoherent. In the superconducting state, the interlayer incoherence restores and gives a negative contribution to the interlayer quasiparticle scattering rate. The mechanism may explain recent findings of enhanced magnetic quantum-oscillation amplitudes in the superconducting state of a layered organic conductor which displays an incoherent electronic transport across the layers.

Keywords: Quantum magnetic oscillations; Superconductivity; Incoherence


Publ.-Id: 7615

Iron matrix effects on cluster evolution in neutron irradiated reactor steels

Gokhman, A. R.; Bergner, F.; Ulbricht, A.

The present model of vacancy cluster evolution in bcc iron under neutron irradiation, which is based on rate theory according to Odette, can be adjusted with respect to volume fraction and mean radius of vacancy clusters obtained by means of SANS measurements on a low-copper iron alloy. The values of the specific surface energy of clusters and the dislocation density taken to adjust the model are both reasonable. The expectation that the surface energies for the two dose rates considered should agree is best fulfilled, if the real solution model for vacancies in iron is taken into account.

Keywords: Reactor pressure vessel steels; Neutron irradiation; Rate theory; Small angle scattering

  • Contribution to external collection
    Schmelzer, J. W. P., Roepke, G., Priezzhev, V.B.: Nucleation Theory and Applications, Dubna, Russia: Joint Institute for Nuclear Research Publ., 2006, 408-419
  • Invited lecture (Conferences)
    9th Research Workshop Nucleation Theory and Applications, 25.06.-03.07.2005, Dubna, Russia

Publ.-Id: 7614

Magnetic quantum oscillations in the normal state of YNi2B2C

Ignatchik, O.; Coffey, T.; Hagel, J.; Jäckel, M.; Jobiliong, E.; Souptel, D.; Behr, G.; Wosnitza, J.

We present de Haas–van Alphen (dHvA) measurements of different YNi2B2C single crystals in magnetic fields up to 32 T. At high magnetic fields three different dHvA frequencies could be detected. The lowest frequency, Fα; could be well resolved down to lower fields just above the upper critical field. An unexpectedly sudden vanishing of the dHvA signal in the mixed state has been observed

Keywords: Rare earth–transition metal alloys; de Haas–van Alphen effect; Electronic structure; Superconductivity


Publ.-Id: 7611

Resistivity studies under hydrostatic pressure on a low-resistance variant of the quasi-2D organic superconductor κ-(BEDT-TTF)2Cu[N(CN)2]Br: quest for instrinsic scattering contributions

Strack, C.; Akinci, C.; Pashchenko, V.; Wolf, B.; Uhrig, E.; Assmus, W.; Lang, M.; Schreuer, J.; Wiehl, L.; Schlueter, J. A.; Wosnitza, J.; Schweitzer, D.; Müller, J.; Wykhoff, J.

Resistivity measurements have been performed on a low (LR)- and high (HR)-resistance variant of the κ-(BEDT-TTF)2Cu[N(CN)2]Br superconductor. While the HR sample was synthesized following the standard procedure, the LR crystal is a result of a somewhat modified synthesis route. Judging by their residual resistivities and residual resistivity ratios, the LR crystal is of distinctly superior quality. He-gas pressure was used to study the effect of hydrostatic pressure on the different transport regimes for both variants. The main results of these comparative investigations are (i) a significant part of the inelastic-scattering contribution, which causes the anomalous ρ(T) maximum in standard HR crystals around 90 K, is sample dependent, i.e., extrinsic in nature; (ii) the abrupt change in ρ(T) at T* ≈ 40 K from a strongly temperature-dependent behavior at T>T* to an only weakly T-dependent ρ(T) at T2 dependence at low temperatures, i.e., for Tc≤T≤T0, although with strongly sample-dependent coefficients A and upper bounds for the T2 behavior measured by T0. Provided that there are no differences in the Fermi surface between both variants—the present experiments give no indications for such differences—the latter result is inconsistent with the T2 dependence originating from coherent Fermi-liquid excitations.

Publ.-Id: 7610

Incoherence and 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 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 can compensate the usual decrease of the Dingle factor below the upper critical magnetic field caused by the intralayer scattering.

  • Open Access Logo HAIT Journal of Science and Engineering 1(2004)4, 771-781

Publ.-Id: 7609

First Structural Characterization of a Protactinium(V) Single Oxo Bond in Aqueous Media

Le Naour, C.; Trubert, D.; Di Giandomenico, V. M.; Fillaux, C.; Den Auwer, C.; Moisy, P.; Hennig, C.

We report here the first structural characterization of Pa(V) adducts in concentrated sulfuric and hydrofluoric solutions. In sulfuric medium, X ray Absorption Spectroscopic data show that unlike the other early actinide elements as uranium or neptunium, protactinium doesn’t form a transdioxo cation but a monooxo adduct. In contrast, concentrated hydrofluoric medium precludes the formation of any oxo bond.

Publ.-Id: 7608

A spectro-electrochemical cell for Actinide speciation

Hennig, C.

A new spectro-electrochemical cell for EXAFS spectroscopy was presented. The cell was specifically designed for the safe use of radioactive solutions. EXAFS spectra of the U(VI)/U(IV) couple in different ligand systems were discussed.

Keywords: spectro-electrochemical cell; EXAFS

  • Lecture (others)
    ACTINET Meeting, 25.08.2005, Manchester, Great Britain

Publ.-Id: 7607

Coolant mixing studies of natural circulation flows at the ROCOM test facility using CFX-10

Höhne, T.; Kliem, S.

Coolant mixing in the cold leg, downcomer and the lower plenum of pressurized water reactors is an important phenomenon mitigating the reactivity insertion into the core. Therefore, mixing of the de-borated slugs with the ambient coolant in the reactor pressure vessel was investigated at the four loop 1:5 scaled ROCOM mixing test facility. Thermal hydraulics analyses showed, that weakly borated condensate can accumulate in particular in the pump loop seal of those loops, which do not receive safety injection. After refilling of th primary circuit, natural circulation in the stagnant loops can re-establish simultaneously and the deborated slugs are shifted towards the reactor pressure vessel (RPV). In the ROCOM experiments, the length of the flow ramp and the initial density difference between the slugs and the ambient coolant was varied.

From the test matrix an experiment with 2% density difference between the de-borated slugs and the ambient coolant was used to validate the CFD software CFX-10. To model the effects of turbulence on the mean flow a Reynolds stress turbulence model was employed and a hybrid mesh consisting of 3.6 million nodes and 6.4 million elements was used.

The experiment and CFD calculation show a stratification in the downcomer. The less dense slugs flow around the core barrel at the top of the downcomer. At the opposite side the lower borated coolant is entrained by the colder safety injection water and transported to the core.The validation proves that CFX-10 is able to simulate appropriately the flow field and mixing effects of coolant with different densities.

Keywords: CFD; ROCOM; boron dilution; PWR

  • Lecture (Conference)
    23rd CADFEM Users’ Meeting 2005, 11.11.2005, Bonn, Germany
  • Contribution to proceedings
    23rd CADFEM Users’ Meeting 2005, 09.-11.11.2005, Bonn, Germany

Publ.-Id: 7606

Analyses of the V1000CT-1 benchmark with the DYN3D/ATHLET and DYN3D/RELAP coupled code systems including a coolant mixing model validated against CFD calculations

Kliem, S.; Kozmenkov, Y.; Höhne, T.; Rohde, U.

Plant-measured data provided within the specification of the OECD/NEA VVER-1000 coolant transient benchmark (V1000CT) were used to validate the DYN3D/RELAP5 and DYN3D/ATHLET coupled code systems. Phase 1 of the benchmark (V1000CT-1) refers to the MCP (main coolant pump) switching on experiment conducted in the frame of the plant-commissioning activities at the Kozloduy NPP Unit 6 in Bulgaria. The experiment was started at the beginning of cycle (BOC) with average core expose of 30.7 effective full power days (EFPD), when the reactor power was at 27.5% of the nominal level and 3 out of 4 MCPs were operating. The transient is characterized by a rapid increase in the primary coolant flow through the core and, as a consequence, a decrease of the space-dependent core inlet temperature. Both DYN3D/RELAP5 and DYN3D/ATHLET analyses were based on the same reactor model, including identical MCP characteristics, boundary conditions, benchmark-specified nuclear data library and nearly identical nodalization schemes. For an adequate modelling of the redistribution of the coolant flow in the reactor pressure vessel during the transient a simplified mixing model for the DYN3D/ATHLET code was developed and validated against a computational fluid dynamics calculation.

The results of both coupled code calculations are in good agreement with the available experimental data. The discrepancies between experimental data and the results of both coupled code calculations do not exceed the accuracy of the measurement data. This concerns the initial steady state data as well as the time histories during the transient. In addition to the validation of the coupled code systems against measured data, a code-to-code comparison between simulation results has been performed to evaluate relevant thermal hydraulic models of the system codes RELAP5 and ATHLET and to explain differences between the calculation results.

Keywords: Coupled code systems; 3D neutron kinetics; code validation; VVER-1000; coolant transient benchmark

Publ.-Id: 7605

Nanofabrication with a mass-separated FIB

Bischoff, L.

In the last two decades focused ion beams (FIB) have become a very useful tool for many tasks in micro- as well as in nano-technology. Probe sizes of less than 10 nm and current densities of more than 10 Acm-2 are now available and allow to use these beams for many applications. Integrated circuit repair and modification, failure analysis, TEM specimen preparation, lithographic mask repair or FIB lithography as well as the writing maskless implantation are the main application in microelectronic research and industry. Especially, in R&D the FIB is very advantageous because of its high spatial resolution and its flexibility varying dose, energy and pattern design on one chip, or even in one structure detail. Therefore also in the field of basic and applied research the FIB became more important, including plasmonics, photonics and nano-optics.
Most of the FIB systems employ a Ga liquid metal ion source (LMIS). Due of the broad spectrum of applications with Ga beams many cases suffer from the impurity incorporation. For special purposes like writing ion implantation or ion mixing in the µm- or nm range different ion species are needed. Therefore alloy liquid metal ion sources (LMIS) are used and the FIB column must be equipped with a mass separation, namely an ExB mass filter system.
The assembly of a modern FIB system is presented and the development and investigation of different alloy LMIS`s working with other materials than Ga as well as their corresponding application in FIB nano-fabrication will be dicussed.
The energy distribution of the ions from an alloy LMIS is one of the determining factors for the performance of an FIB column. Different source materials like Au73Ge27, Au82Si18, Au77Ge14Si9, Co36Nd64, Er69Ni31, and Er70Fe22Ni5Cr3 were investigated with respect to the energy spread of the different ion species as a function of emission current, ion mass and emitter temperature. The alloy LMIS`s discussed above have been used in the Rossendorf FIB system IMSA-100 and later in the improved IMSA-OrsayPhysics machine especially for writing implantation to fabricate nm pattern without any lithographic steps. A Co-FIB was applied for the ion beam synthesis of CoSi2 nano-structures. Also the Co-FIB was applied to modify thin magnetic multi-layers in the nm-scale. Additionally, the possibility of varying the current density of the FIB by changing the pixel dwell-time was used to investigate the radiation damage and the dynamic annealing in Si and SiC at elevated implantation temperatures. Furthermore, a broad spectrum of ions was employed to study the sputtering process depending on temperature, angle of incidence and ion mass on a couple of target materials using the volume loss method. Especially this technique was used for the fabrication of various kinds of micro-tools and other 3D devices. A nano-hole was made into an AFM tip acting as an aperture in a single ion implantation project.
The presented examples underline useful application possibilities to different tasks of nanotechnology (or nanofabrication) applying FIB tools equipped with a mass separation system to chose from a broad spectrum of ion species the desired one.

Keywords: focused ion beam; mass separation; liquid metal ion source; nanofabrication

  • Invited lecture (Conferences)
    FAHL Academica, 26.-27.09.2005, Wörlitz, Germany

Publ.-Id: 7604

Novel triazinium-imidothioate zwitterions: intermediates in the reaction of [1,3,4]thiadiazolo[2,3-d][1,2,4]triazolo[1,5-a][1,3,5]-triazinium cations with amines

Wermann, K.; Walther, M.; Günther, W.; Görls, H.; Anders, E.

Starting with bis([1,3,4]thiadiazolo)[1,3,5]triazinium halides 1, a novel class of heterocyclic compounds, the [1,3,4]thiadiazolo[2,3-d][1,2,4]triazolo[1,5-a][1,3,5]triazinium halides 5 were prepared. The reaction between 5 and primary or secondary amines 6 yielded highly substituted guanidines 8 and fused tricyclic bis([1,2,4]triazolo)[1,5-a:10,50-d][1,3,5]triazinium halides 9. The formation of the reactive triazinium-imidothioate zwitterions 7, which is controlled by the influence of negative hyperconjugation, was proven by NMR data and the X-ray structure of 7c. The subsequent ring-closure/ring-opening steps can be understood in terms of an SN(ANRORC) process accompanied by intramolecular proton-transfer reactions. The zwitterions 7 were reacted with EtI forming cationic derivatives 10 or hydrolyzed at pH 6–7 to give novel heterocyclic ethanethioamide 11.

  • Tetrahedron 61(2005)3, 673-685

Publ.-Id: 7603

Kortikobasale Degeneration. Asymmetrisch mit Dystonie, Myoklonus und Apraxie

Herting, B.; Beuthien-Baumann, B.; Reichmann, H.

Die kortikobasale Degeneration (CBD) ist eine in der 6. und 7. Lebensdekade sporadisch auftretende neurodegenerative Erkrankung, die klinisch durch ein asymmetrisches akinetisch-rigides Parkinson-Syndrom mit Dystonie, Myoklonus und kortikalen Funktionsstörungen (v.a. eine idiomotorische Apraxie) charakterisiert ist. In fortgeschrittenen Krankheitsstadien können Depression, Demenz und frontale Verhaltensveränderungen hinzutreten. Aktuellle molekulargenetische Befunde sprechen für eine einheitliche Ursache der CBD und der progressiven supranukleären Blickparese (PSP) im Sinne von Tauopathien. Diese Arbeit fasst klinisches Bild, aktuelle Diagnosekriterien, Differenzialdiagnosen, apparative Zusatzdiagnostik und Therapieoperationen zusammen.

  • Der Neurologe und Psychiater 1-2(2005), 41-44

Publ.-Id: 7602

Gene Expression Analysis of CD34+ Hematopoietic Stem Cultivated On Bioartifical Materials

Oswald, J.; Steudel, C.; Joergensen, B.; Salchert, K.; Ehninger, G.; Thiede, M.; Bornhäuser, M.; Werner, C.

Abstract wird nachgereicht.

  • Poster
    2nd Max Bergmann Symposium, 17.-18.02.2005, Dresden, Deutschland

Publ.-Id: 7601

β decay of 95Ag

Harissopulos, S.; Döring, J.; La Commara, M.; Schmidt, K.; Mazzocchi, C.; Borcea, R.; Galanopoulos, S.; Górska, M.; Grawe, H.; Hellström, M.; Janas, Z.; Kirchner, R.; Roeckl, E.; Johnstone, I. P.; Schwengner, R.; Skouras, L. D.

We studied the β-decay properties of the N=Z+1 nucleus 95Ag by measuring β-delayed γ-rays and β-γ-γ coincidences with a plastic scintillator as β-detector and a Ge-detector array. The 95Ag nuclei were produced by means of the 58Ni(40Ca,p2n) reaction and separated with the GSI online mass separator. The previously reported level scheme of the 95Pd daughter nucleus was extended considerably. The deduced level scheme is compared with different shell-model calculations with or without breaking the 100Sn core.

  • Physical Review C 72(2005)2, 4303

Publ.-Id: 7600

Module-assisted synthesis of the bifunctional labelling agent N-succinimidy 4-[18F]fluorobenzoate ([18F]SFB)

Mäding, P.; Füchtner, F.; Wüst, F.

The three-step radiosynthesis of N-succinimidyl 4-[18F]fluorobenzoate ([18F]SFB) was adapted to a remotely controlled synthesis module. After optimization of the reaction conditions, the final [18F]SFB was obtained in decay-corrected radiochemical yields of 34 - 38 % (related to [18]fluoride; n = 12) within a synthesis time of 68 min. The radiochemical purity was in the range of 93 -96 %.

Keywords: 18F-labelling; Positron emission tomography (PET); [18F]SFB; Automated module synthesis

  • Applied Radiation and Isotopes 63(2005), 329-332

Publ.-Id: 7598

Synthesis and copper(II) complexation of glycodendrimers having a cyclam-core

Röhrich, A.; Bernhard, G.; Geipel, G.; Stephan, H.

Derivatives of cyclam and its metal complexes are of considerable interest in bioinorganic chemistry, biology and medicine. In the latter nexus, cyclam compounds show anti-HIV activities, and metallated cyclams may be used in radiotherapy applying 64/67Cu or 186/188Re.1 Recently, we could show that the grafting of polyethylene glycol arms on the cyclam core leads to both a higher complex stability and an increasing shielding effect for copper(II).2 In this contribution the synthesis of two novel cyclams 1 and 2 (cf. Fig. 2) carrying sugar molecules as terminal groups will be presented. The complex formation of these glycodendrimers with copper(II) has been studied by UV-vis and time-resolved laser-induced fluorescence (TRLFS) measurements showing rapid formation of 1:1 complexes.

  • Poster
    XXX International Symposium on Macrocyclic Chemistry (ISMC), 17.-21.07.2005, Dresden, Deutschland

Publ.-Id: 7596

Material data measurements of molten Nd2Fe14B

Plevachuk, Y.; Sklyarchuk, V.; Hermann, R.; Gerbeth, G.

High performance Nd-Fe-B magnets are of enormous economic interest and play a key role in the development of electronics and motors. The excellent ferromagnetic properties of the Rare - Earth magnets are due to the hart magnetic Nd2Fe14B-phase (f-Phase) with high saturation polarization and magnetocrystalline anisotropy. Stoichiometric Nd-Fe-B alloys perform a peritectic reaction under near-equilibrium conditions, and the phase and microstructure selection plays a crucial role on the hard magnetic properties of this material. Besides additions and substitutes, the melt convection strongly influences the microstructure formation of Nd-Fe-B alloys, in particular the volume fraction and grain size of the properitectic g-Fe phase which deteriorates the hard magnetic properties of the material. Numerical simulations are essential in order to understand and design the various flow structures. Therefore, the investigation of electrophysical and structure sensitive properties of the system in the liquid state prior to solidification is very important.
We present new results for the electrical and thermal conductivity, thermoelectric power and viscosity carried out in a temperature range from the liquidus (1553 K) to 1620 K. The electrical conductivity and thermoelectric power were measured using a contact 4-probe method. The thermal conductivity was investigated by a steady-state concentric cylinder method. The shear viscosity measurements were performed using an oscillating-cup viscometer. Special attention was paid to the region close to the liquidus where heating and cooling rates were reduced and the measurement steps shortened to 1 K.

  • Poster
    European Congress on Advanced Materials and Processes (EUROMAT 2005), 05.-08.09.2005, Prague, Czech Republic

Publ.-Id: 7595

Anomalous ion accelerated bulk diffusion of interstitial nitrogen

Abrasonis, G.; Möller, W.; Ma, X. X.

Interstitial N diffusion under low energy (~700 eV) Ar+ bombardment at 673 K in ion beam nitrided austenitic stainless steel is investigated. Ar+ ion bombardment increases the N mobility in depths far beyond the ion penetration depth, resulting in an increased broadening of the N depth profile as a function of Ar+ flux. This effect cannot be explained by any established mechanism of radiation-enhanced diffusion. An explanation based on quasiparticle-enhanced mobility is proposed.

Keywords: Diffusion of impurities; Ion radiation effects; Anharmonic lattice modes

  • Physical Review Letters 96(2006), 065901

Publ.-Id: 7594

Experimental study on bubble motion in a rectangular bubble column using high-speed video observations

Zaruba, A.; Krepper, E.; Prasser, H.-M.; Reddy Vanga, B. N.

A two-phase flow in a rectangular bubble column of 100×20 mm cross-section and 1.5 mm height was studied using a high-speed video system. Series of images were taken at different elevations at a frequency of 500 Hz. The images were processed using a bubble recognition algorithm. In such a way, an individual bubble in the gas swarm could be tracked. The time-averaged velocity profiles and the turbulent diffusion coefficients were derived as a function of the superficial gas velocity. The lateral displacement of bubbles travelling over a certain vertical distance was transformed into a probability density distribution in order to measure the turbulent diffusion coefficient of the gaseous phase. The shape of the distributions obtained was found to fit well to the Gaussian standard distribution. The dispersion coefficients were observed to grow proportionally to the square root of the vertical distance. The diffusion coefficients were calculated from the proportionality factor and were compared with some correlations published in the literature. The experiments were performed for superficial gas velocities ranging from 1 to 6 mm/s. The bubbles were generated either by a porous sparger or a set of capillaries placed at the bottom of the column. The measurements were taken at different heights between 1 and 1.2 m where the bubble cloud was occupying the entire cross-section.

Keywords: Bubble flow; Rectangular channel; Image processing; Bubble dispersion; Turbulent diffusion

  • Flow Measurement and Instrumentation 16(2005)5, 277-287

Publ.-Id: 7593

TEM-Investigation of Si(001) Modified by Pr Implantation

Mücklich, A.; Kögler, R.; Eichhorn, F.

TEM-Investigation of Si(001) Modified by Pr Implantation

Keywords: high-K dielectrics; Pr oxide; Pr silicide; Pr silicate

  • Poster
    Microscopy Conference, 28.08.-02.09.2005, Davos, Schweiz
  • Contribution to proceedings
    Microscopy Conference 2005, 28.08.-02.09.2005, Davos, Switzerland

Publ.-Id: 7592

Complex formation of small organic ligands with uranium(VI) - comparison of stability constants with proton dissociation

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

During the past we have studied the complex formation behavior of uranium(VI) towards several aromatic carboxylic acids. These studies were continued, so that the formation constants of the monohydroxo- and dihydroxo- as well as some trihydroxobenzoic acids are available. A short review of these formation constants will be given.
Besides this we have compared the complex formation constants to the protonation constants of the carboxyl group. A linear relationship between these two properties was found. An decreasing protonation constant is connected to an increasing complex formation constant.
Nevertheless some exceptions of this rule were observed. These deviations can be explained by the different type of complex formation between uranium(VI) and the organic ligand. This concerns especially the number and position of the hydroxo groups in phenolic carboxylic acids. In the case of 2,3-dihydroxybenzoic the two OH-groups are involved in the complex formation already at relative low pH values. During the complex formation two protons are released from the organic ligand. The formed complex does not include the carboxylic group. The two phenolic hydroxo groups form a stable five atom ring with the uranylion. This result could be confirmed by EXAFS measurements.

  • Contribution to proceedings
    Migration 2005, 10th International Conference on Chemistry and Migration Behaviour of Actinides and Fission Products in the Geosphere, 18.-23.09.2005, Avignon, France
  • Poster
    Migration 2005, 10th International Conference on Chemistry and Migration Behaviour of Actinides and Fission Products in the Geosphere, 18.-23.09.2005, Avignon, France

Publ.-Id: 7591

Interaction mechanisms of bacterial strains isolated from extreme habitats with uranium

Merroun, M.; Nedelkova, M.; Rossberg, A.; Hennig, C.; Selenska-Pobell, S.

This paper summarizes the effect of pH on the speciation and cellular localization of uranium bound by bacterial strains isolated from the S15 deep-well montoring site, located at the Siberian radioactive subsurface depository Tomsk-7, Russia. Microbiological methods in combination with extended X-ray absorption fine structure (EXAFS) spectroscopy, transmission electron microscopy (TEM), and energy dispersive X-ray spectroscopy (EDX) were applied. EXAFS analysis showed that the cells of the two isolates, Microbacterium oxydans S15-M2 and Sphingomonas sp. S15-S1, precipitate U(VI) as m-autunite-like phase at pH 4.5, probably due to the release of inorganic phosphate from the cells as result of the microbial metabolism. However, at pH 2 uranium formed complexes with organically bound phosphates of the cell surface. The results of the EXAFS studies corroborate those found using TEM and EDX analysis. Different hypothesis explaining the different coordination chemistry of uranium to bacteria as a function of pH of uranium solution in terms of solubility of m-autunite and/or microbial activity will be discussed.

  • Radiochimica Acta 94(2006), 723-729
  • Contribution to proceedings
    Migration 2005, 10th International Conference on Chemistry and Migration Behaviour of Actinides and Fission Products in the Geosphere, 18.-23.09.2005, Avignon, France
  • Lecture (others)
    FZR - FSU Jena Workshop, 27.-28.07.2005, Dresden, Germany

Publ.-Id: 7590

Entwicklung neuer Chelatsysteme für nuklearmedizinische Anwendungen

Juran, S.; Schubert, R.; Stephan, H.; Kraus, W.

Ziel ist es radioaktive Kupfer(II)-Komplexe hoher Stabilität mit einstellbarer Bioverteilung auf der Basis von 3,7-Diazabicyclo[3.3.1]nonan (Bispidin) zu entwickeln. Voruntersuchungen haben gezeigt, dass insbesondere sechszähnige Liganden ein hohes inhärentes Anwendungspotential für die Radionuklidtherapie aufweisen. [1]
Es wird die Darstellung neuer sechszähniger Bispidinderivate mit Pyridin- und Imidazolgruppen präsentiert. Die Komplexbildungseigenschaften gegenüber Kupfer(II) sowie Möglichkeiten zur Kopplung von Biomolekülen werden diskutiert.
Die Synthese der Bispidinliganden (1) erfolgt durch zwei aufeinanderfolgende Mannich-Kondensationen, wobei Pyridin- und Imidazol-Edukte variieren.

Von ausgewählten Vertretern wurden kristalline Kupfer(II)-Komplexe isoliert und die Struktur mittels Röntgendiffraktometrie gelöst. Weiterhin erfolgten Untersuchungen zur Langzeitstabilität dieser Kupfer(II)-Komplexe in Anwesenheit der Konkurrenzliganden Glutathion und Histidin mittels UV/Vis-Spektroskopie.

  • Lecture (others)
    Wissenschaftstage Fachhochschule Lausitz, 23.-25.11.2005, Senftenberg, Germany

Publ.-Id: 7589

Synthese und Charakterisierung neuer sechszähniger 3,7-Diazabicyclo-[3.3.1]nonan-Derivate und ihrer Kupfer(II)-Komplexe

Juran, S.; Schubert, R.; Steinbach, J.; Stephan, H.; Kraus, W.

Es sollen radioaktive Kupfer(II)-Komplexe hoher Stabilität mit einstellbarer Bioverteilung auf der Basis von 3,7-Diazabicyclo[3.3.1]nonan (Bispidin) entwickelt werden. Voruntersuchungen haben gezeigt, dass hier sechszähnige Liganden am aussichtsreichsten sind [1]. Durch Modifizierung des Bispidingerüstes ergeben sich günstige Möglichkeiten zur Einführung von Biomolekülen und damit zur gezielten Beeinflussung der Bioverteilung.
Es wird die Darstellung sechszähniger Bispidinderivate mit Pyridin- und Imidazolgruppen vorgestellt. Die Komplexbildungseigenschaften gegenüber Kupfer(II) sowie Möglichkeiten zur Kopplung von Biomolekülen werden diskutiert.
Die Synthese der Bispidinliganden erfolgt durch zwei aufeinanderfolgende Mannich-Kondensationen, wobei Pyridin- und Imidazol-Edukte eingesetzt werden. Von ausgewählten Vertretern wurden kristalline Kupfer(II)-Komplexe isoliert und die Struktur mittels Röntgendiffraktometrie gelöst. Untersuchungen zur Stabilität dieser Kupfer(II)-Komplexe in Anwesenheit der Konkurrenzliganden Glutathion und Histidin sind mittels UV/Vis-Spektroskopie durchgeführt worden.
Die dargestellten sechszähnigen Bispidinliganden weisen eine schnelle Kinetik für die Komplexbildung mit Kupfer(II) in wässriger Lösung auf. Die kristallinen Kupfer(II)-Komplexe zeigen eine verzerrte oktaedrische Koordinationsgeometrie, wobei das Zentralatom nahezu vollständig von der Umgebung abgeschirmt ist. Die entsprechenden Kupfer(II)-Komplexe mit Bispidinliganden sind auch bei einem Überschuss von Konkurrenzliganden wie Glutathion und Histidin stabil.
Die dargestellten Kupfer(II)-Komplexe mit sechszähnigen Bispidinliganden weisen eine sehr hohe Stabilität auf und verfügen damit über ein hohes inhärentes Anwendungspotential für radiopharmazeutische Anwendungen in Diagnostik und Therapie. Dazu ist es notwendig, Biomoleküle an das Grundgerüst anzukoppeln, um eine selektive Anreicherung der radioaktiven Kupferkomplexe im Zielgewebe zu erzielen. Radiopharmakologische Untersuchungen zur Optimierung der radioaktiven Markierung der Bispidinderivate mit 64/67Cu sowie zur Biodistribution ausgewählter Radiotracer mittels micro-PET sollen sich anschließen.

  • Lecture (others)
    13. Arbeitstreffen AG Radiochemie/Radiopharmazie, 06.-08.10.2005, Seefeld, Austria

Publ.-Id: 7588

Synthese und Komplexbildungseigenschaften neuer sechszähniger Bispidinderivate mit Pyridin- und Imidazolgruppen

Juran, S.; Stephan, H.; Schubert, R.; Geipel, G.; Kraus, W.; Jakob, M.; Kerscher, M.; Comba, P.

Sechszähnige Derivate des Bispidins (3,7-Diazabicyclo[3.3.1]nonan) bilden mit einer Reihe von Übergangsmetallen Komplexe hoher Stabilität [1]. Insbesondere die Kupfer(II)-Komplexe weisen ein hohes inhärentes Anwendungspotential für die Radionuklidtherapie auf.
Zum Verbindungstyp 1 gelangt man durch zwei aufeinanderfolgende Mannich-Kondensationen, wobei durch Variation der Pyridin- und Imidazol-Edukte das Löslichkeits- und Komplexbildungsverhalten gezielt eingestellt werden kann.

Die zeitaufgelöste Laser-Fluoreszenz-Spektroskopie wurde eingesetzt, um Aussagen zur Stabilität von Kupfer(II)-Komplexen mit den Bispidinderivaten 1 zu erhalten. Die Struktur ausgewählter Komplexe konnte mittels Röntgendiffraktometrie aufgeklärt werden. Weiterhin wurden spektroskopische Untersuchungen (UV-Vis) zur Langzeitstabilität der Kupferkomplexe in Anwesenheit der Konkurrenzliganden Glutathion und Histidin durchgeführt.

  • Poster
    GDCh-Jahrestagung 2005, 11.-14.09.2005, Düsseldorf, Deutschland
  • Contribution to proceedings
    GDCh-Jahrestagung 2005: Chemie schafft neue Strukturen, 11.-14.09.2005, Düsseldorf, Deutschland
    Kurzreferate, 535

Publ.-Id: 7587

DYN3D version 3.2 - code for calculation of transients in light water reactors (LWR) with hexagonal or quadratic fuel elements - description of models and methods -

Grundmann, U.; Rohde, U.; Mittag, S.; Kliem, S.

DYN3D is an best estimate advanced code for the three-dimensional simulation of steady-states and transients in light water reactor cores with quadratic and hexagonal fuel assemblies. Burnup and poison-dynamic calculations can be performed. For the investigation of wide range transients, DYN3D is coupled with system codes as ATHLET and RELAP5.

The neutron kinetic model is based on the solution of the three-dimensional two-group neutron diffusion equation by nodal expansion methods. The thermal-hydraulics comprises a one- or two-phase coolant flow model on the basis of four differential balance equations for mass, energy and momentum of the two-phase mixture and the mass balance for the vapour phase. Various cross section libraries are linked with DYN3D.

Systematic code validation is performed by FZR and independent organizations.

Keywords: light water reactors; transients; computer code; core model; three-dimensional; two group neutron diffusion; nodal methods; two-phase flow; thermal hydraulics; fuel rod model; reactor safety; cross section libraries; burnup calculation; Xenon and Samarium dynamics; coupling; system codes

  • Open Access Logo Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; FZR-434 2005
    ISSN: 1437-322X


Publ.-Id: 7586

Nachrechnung des ROCOM Experiments T6655_Y1 mit dem CFD-Programm CFX-5

Burwell, M. J.; Höhne, T.; Scheuerer, M.

Im Rahmen des Vorhabens SR 2444 wurde eine Nachrechnung des ROCOM Experiments T6655_Y1 mit dem CFD-Programm CFX-5 durchgeführt. Die Anlage ROCOM dient zur Untersuchung der Vermischung hypotethischer Kühlmittelpfropfen mit verringerter Borkonzentration bei unterschiedlichen Schleifendurchsetzen des Primärkreislaufs. Für die Nachrechnung mit CFX wurde der Versuch T6655_Y1 ausgewählt. In diesem Versuch beträgt die Dichtedifferenz zwischen dem, in benachbarten Schleifen 1 und 2, vorgelegten Pfropfen und Umgebung 0,25 %. Das Ergebnis des Experiments besteht hauptsächlich in den mittleren und maximalen relativen Absenkungen der Borkonzentrationen (entspricht mittlerer und maximaler Tracerkonzentration in den Versuchen) am Kerneintritt. Die Ergebnisse der Rechnungen zeigen, dass das Rechenprogramm die Phenomena der Vermischung generell gut erfasst hat.

Keywords: Coolant Mixing; CFD; ROCOM

  • Other report
    München: GRS - A - 2871, 2005
    14 Seiten

Publ.-Id: 7585

A Far-Infrared FEL for the Radiation Source ELBE

Grosse, E.; Lehnert, U.; Michel, P.; Schlenk, R.; Seidel, W.; Wolf, A.; Willkommen, U.; Wohlfarth, D.; Wünsch, R.

After successfully commissioning the mid‐infrared FEL (U27) and adjoining a second accelerator unit (up to 35 MeV) at ELBE we have modified our plan how to produce radiation in the far infrared.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). The minimum gap of 24 mm and the hybrid construction consisting of Sm/Co magnets and soft iron poles ensures sufficient radiation resistance and allows rms undulator parameters up to 2.7. The large field variation allows us to cover the whole wavelength range by only two different electron energies (e.g. 20 and 35 MeV). To reduce the transverse beam size we use a partial waveguide which is 10 mm high and wide enough to allow free propagation inhorizontal direction. It spans from the last quadrupole in front of the undulator up to the downstream mirror and is somewhat longer than 8 m. To minimize the coupling losses between free propagation and the waveguide mode appropriate bifocal resonator mirrors will be sed. Detailed calculations and computer simulations predict an outcoupled laser power of roughly 35 W around 40 microns and 20 W at150 microns.

Keywords: undulator; free-electron laser; waveguide; radiation source ELBE

  • Poster
    27th Int. Free Electron Laser Conference, 21.-26.08.2005, Palo Alto, USA
  • Contribution to proceedings
    27th Free Electron Laser Conference, 21.-26.08.2005, Palo Alto, USA
    Proceedings of the 27th International Free Electron Laser Conference, 290-292


Publ.-Id: 7584

Spin correlations in the reaction pi(+/-)(D)over-right-arrow ->(Sigma)over-right-arrow(+/-)Theta(+) and the parity of Theta(+)

Kampfer, B.; Titov, A. I.

We analyze two types of spin observables in the reaction pi D->->Sigma(->)Theta(+) near the threshold. One concerns the spin-transfer coefficients K-x(x) and K-z(z). The second is the deuteron spin anisotropy. These observables are sensitive to the Theta(+) parity and can be used as a tool for the Theta(+) parity determination.

  • Physical Review C 71(2005), 062201(R)

Publ.-Id: 7583

Di-electron bremsstrahlung in intermediate-energy pn and Dp

Kämpfer, B.; Kaptari, K. L.

Invariant mass spectra of di-electrons stemming from bremsstrahlung processes are calculated in a covariant diagrammatical approach for the exclusive reaction Dp to pspnpe+e- with detection of a forward spectator proton, psp. We employ an effective nucleon-meson theory for parameterizing the sub-reaction np to pspnpe+e- and, within the Bethe-Salpeter formalism, derive a factorization of the cross section in the form dsigmaDp to pspnpe+e-/dM = dsigmanp to pspnpe+e-/dM x kinematical factor related solely to the deuteron (M is the e+e- invariant mass). The effective nucleon-meson interactions, including the exchange mesons pi, sigma, omega and rho as well as excitation and radiative decay of Delta(1232), have been adjusted to the process pp to pp e+e- at energies below the vector meson production threshold. At higher energies, contributions from omega and rho meson excitations are analyzed in both, NN and Dp collisions. A relation to two-step models is discussed. Subthreshold di-electron production in Dp collisions at low spectator momenta is investigated as well. Calculations have been performed for kinematical conditions envisaged for forthcoming experiments at HADES.

  • Nuclear Physics A 764(2006), 338-370

Publ.-Id: 7582

Algebraic approach to bare nucleon matrix elements of quark operators

Zschocke, S.; Kämpfer, B.; Plunien, G.

An algebraic method for evaluating bare nucleon matrix elements of quark operators is proposed. Thereby, bare nucleon matrix elements are traced back to vacuum matrix elements. The method is similar to the soft pion theorem. Matrix elements of two-quark, four-quark and six-quark operators inside the bare nucleon are considered.

  • Physical Review D 72(2005), 014005

Publ.-Id: 7581

In-depth distribution of silica nanoparticles in free-standing silica/vinyl polymer nanocomposite films

Gago, R.; Vazquez, L.; Grambole, D.; Herrmann, F.; Groetzschel, R.; Vela, M.; Amalvy, J. I.; Munoz-Martin, A.; Climent-Font, A.

Film-forming silica-based materials are potentially useful as tough, abrasion-resistant coatings and fire-retardants. However, these formulations are often solvent-based, and there is an actual tendency to replace them by more environmentally friendly, water-borne coatings. Herein we study surfactant-free and water-borne nanocomposite films consisting of silica nanoparticles (20 nm size) embedded in a vinyl polymer matrix. Highly transparent free-standing films were prepared by copolymerizing of 4-vinlypyridine (4VP) with low glass transition temperature comonomers such as n-butyl acrylate (n-BuA) or n-butyl methacrylate (n-BuMA) in the presence of an ultrafine aqueous silica sol. Films with different silica contents (ranging from 14% to 61%) were prepared with thickness around 100 um. The in-depth distribution of the nanoparticles has been studied by extracting the Si profile from Rutherford backscattering spectrometry (RBS) measurements. Standard RBS with 2 MeV He+ was performed to established the Si profile in the near surface region while a focused 3MeV Li+ ion beam (3-4 um) provided by a nuclear microprobe was used in cross-section specimens to determine the in-depth profile at larger depths.

  • Poster
    17th International Conference on Ion Beam Analysis, 26.06.-01.07.2005, Seville, Spain

Publ.-Id: 7577

Possible consideration of METCOR experimental results in FE models for IVR

Altstadt, E.; Willschuetz, H.-G.

At the Institute of Safety Research of the FZR a finite element model has been developed simulating the thermal processes and the viscoplastic behaviour of the vessel wall. An advanced model for creep and material damage has been established and has been validated using experimental data. The thermal hydraulic and the mechanical calculations are sequentially and recursively coupled. The model is capable of evaluating fracture time and fracture position of a vessel with an internally heated melt pool.
At the Alexandrov Research Institute of Technology in Sosnovy Bor (Russia), the thermo-chemical interaction between molten corium and RPV steel is experimentally investigated. The work is done in the frame of the ISTC project METCOR. The experiments show that the ablation of the steel occurs at interface temperatures below the steel melting temperature. The ablation rate significantly depends on the chemical compostion of the corium melt.
The presentation shows a concept for using the METCOR data within the finite element model of the FZR.

Keywords: In-vessel retention; finite element analysis; corium-steel interaction; METCOR; Nuclear rectors; Severe accident management

  • Lecture (others)
    6th METCOR Project Meeting, 12.07.2005, Sankt Petersburg, Russia

Publ.-Id: 7572

Potential of proton microbeam in the study of dental composites. 2. Compositional heterogeneity by micro-PIXE and complementary analysis by micro-PIGE and micro-PBS

Harangus, L.; Iordan, A.; Preoteasa, E. A.; Preoteasa, E.; Grambole, D.; Herrmann, F.; Groetzschel, R.

To investigate the structural and chemical heterogeneity of dental composites, we analyzed their composition both in whole maps and in selected points by μPIXE, μPIGE and μPBS (Proton Backscattering). Two qualitatively similar biomaterials labeled IV.a and V were studied. Thick disk-shaped, flat-surface samples were prepared by photopolymerization on a glass plate, and investigated at the Rossendorf nuclear microprobe with a 3.1 MeV proton beam focused to a ~3 μm spot. Areas of 250 x 250 μm² were mapped, and selected inclusions were analyzed in point mode using three detectors simultaneously. Five areas located ~0.5-2 mm apart of each other and five inclusions from a map for IV.a, as well as one area for V were analysed. Hydroxylapatite and pyrite were used as reference materials. Concentrations from μPIXE spectra were determined by GUPIX calculations. Up to 19 elements were detected, i.e. Ca, Zr, Ba, Yb (major), Fe, Sr, Hf (minor), Mn, Se, Ho (traces) by μPIXE; F, Na, Al, Si by μPIGE; and C, O, F, Al, Si, Ca (and possibly N, Na, Cl) by μPBS. As compared to IV.a, in composite V higher Ca, lower Zr and Ba, and similar Yb levels were found. The mixture in composite IV.a appeared as a heterogeneous map both on a ~1.0 and on a ~0.1 mm scale of the sample. Thus in all μPIXE maps the absolute concentrations of Ca, Zr, Ba and Yb showed rather high dispersion (relative standard deviations ~31-44 %), but the ratios Zr/Ca, Ba/Ca and Yb/Ca were largely constant. The inclusions analyzed in point mode were Zr-rich and although their relative concentrations were roughly constant the absolute ones showed very high dispersion (rel. SD ~120 %). Hence proton microprobe analysis methods are well suited to study the dental composites and to characterize in detail their heterogeneous structure.

  • Poster
    17th International Conference on Ion Beam Analysis, 26.06.-01.07.2005, Seville, Spain

Publ.-Id: 7571

Proton microprobe for analysis of normal and osteoporosis-affected compact bone. 2. Low-Z elements

Iordan, A.; Harangus, L.; Preoteasa, E. A.; Grambole, D.; Neelmeijer, C.; Herrmann, F.; Groetzschel, R.; Mihul, A.; Noveanu, D.; Batrina, D.

While μPIXE of normal and osteoporosis-affected bones was suitable for metals from Ca on (abstract 1 from our group, this volume), it fails to detect low-Z elements. Some of them may be involved in osteoporosis, e.g. F prevents demineralization and N occurs in bone proteins. Here we examined the potential of μPIGE, μPBS and μPIXE to study low-Z elements in the outer surface layer of rat and human bones with osteoporosis. The bone sections were as described (abstract 1), and the μPIGE, μPBS and μPIXE measurements were performed at the Rossendorf nuclear microprobe with 3.1 MeV protons focused to ~3 μm, using concomitantly three detectors.
μPIGE was useful to detect light elements like F, P, Na, S- the concentrations of these elements can be calculated by comparing the characteristic X- ray lines of suitable standards. CaF2, NaCl, pyrite and hydroxylapatite (HA) were used as reference materials. PBS provided information about C, N, O, F, Mg, P and Ca, mainly qualitative at this stage.
Further development would allow N and S analysis, which may help evaluate the bone collagen, supposedly altered in osteoporosis. Only P, S, Cl and Ca were monitored here by PIXE and the concentrations of these elements were calculated by GUPIX. In all bones, a P/Ca ratio of 0.32-0.39 was found, below the 0.46 value of HA, suggesting a fraction of Ca as carbonate in addition to HA. Both P and S concentrations showed variability from bone to bone. The μPIXE maps of P were positively corelated to the Ca maps, evidencing well- ressolved patterns.
Thus the information yielded by μPIGE and μPBS on the light elements from osteoporosis-affected bones was potentially quantitative, complementary to μPIXE, and pathologically relevant, and the three methods complement each other in understanding this bone disease.

  • Poster
    17th International Conference on Ion Beam Analysis, 26.06.-01.07.2005, Seville, Spain

Publ.-Id: 7570

Potential of proton microbeam in the study of dental composites. 1. Micro-PIXE mapping of Ca, Zr, Ba and Yb

Preoteasa, E. A.; Preoteasa, E.; Harangus, L.; Iordan, A.; Grambole, D.; Herrmann, F.; Neelmeijer, C.

In recent studies, PIXE and ERDA showed a high potential for dental composites [1, 2]. However, wide-beam IBA techniques can not explore the biomaterials' granular structure, which requires microbeam methods to be accounted for.
In this report we applied proton μPIXE for mapping the major elements in dental composites, with the aim of evaluating the method's potential. A flat sample with a smooth surface (~ 1 mm thick) of the composite previously labeled IV.a [1,2] was prepared by photopolymerization on a glass plate. Measurements were carried out at the Rossendorf nuclear microprobe with a 3.1 MeV proton beam focused to a spot of ~3 μm. Five areas ~250 x 250 μrn located ~0.5-2 mm apart of each other were mapped on the flat specimen at ~4 μm resolution. The μPIXE maps of Ca, Zr, Ba and Yb clearly evidenced the granular structure of the composite. The mineral particles revealed a polydisperse size distribution and different compositions. Thus while most mineral particles were Ca-rich and not larger than ~8 μm, a small number of much larger inclusions were seen, with size in the ~16-60 μm range and with high levels of Zr, Ba and Yb. Generally the maps of the elements were complementary, but some apparent deviations from this rule were seen in the different areas. This suggests that the mixture of mineral particles may show some degree of heterogeneity visible in the sample on a ~1 mm scale, which is comparable to the diameter of a dental filling. Therefore μPIXE mapping gives structural insight on the dental composites, potentially relevant for the study of their properties and behavior in the oral environment.
[1] E.A. Preoteasa et al., Nucl. Instr. and Meth. in Phys. Res. B 189 (2002) 426-430.
[2] E.A. Preoteasa et al., Anal. Bioanal. Chem. 379 (2004) 825-841.

  • Poster
    17th International Conference on Ion Beam Analysis, 26.06.-01.07.2005, Seville, Spain

Publ.-Id: 7569

Proton microprobe analysis of normal and osteoporosis-affected compact bone. 1. Calcium and other divalent metals

Harangus, L.; Iordan, A.; Preoteasa, E. A.; Grambole, D.; Herrmann, F.; Gomez, S.; Mihul, A.; Lonescu-Tirgoviste, C.; Gutu, D.

Normal and disease-affected bones have been studied by wide- and microbeam PIXE and other IBA methods, but the biologically-active outer surface layer of bone was not examined in detail. In osteoporosis, the altered metabolism of Ca and trace elements leading to low bone density is not fully understood. μPIXE, μPIGE and μPBS were applied to analyze Ca and other divalent cation-forming metals in the outer layer of femur and tibia from normal and experimental diabetes-affected rats, tibia from humans with osteoporosis-complicated diabetes, clinically sound human femoral neck and normal bovine metacarp. Measurements were carried out at the Rossendorf nuclear microprobe with a 3.1 MeV proton beam focused to a spot of ~3 μm, using concomitantly three detectors. Thick (~1 mm) transversal bone sections were scanned near the surface at ~4 μm effective resolution. Hydroxylapatite was used as a reference. Concentrations were determined from PIXE spectra by GUPIX calculations.
Most elements of the second main group were detected: Mg (at minor levels) by μPIGE and μPBS, and Ca (major) as well as Sr and Ba (traces) by μPIXE.
Other divalent ion-forming trace metals found by μPIXE included Cr, Mn, Fe, Ni, Cu and Zn from the transition groups, and Pb. Only normal bones contained Cr, Mn and Cu. Levels of Ca, Fe, Ni and Zn varied strongly even in the same bone, while Sr showed little change. Ca maps evidenced spatially well-defined patterns of bands, and diabetic rat bones presented Ca-poor regions at the surface. The spatial resolution was weaker in the Fe, Zn and Sr maps and improved in mean profiles normal to the surface.
Near the outer surface of bones the maps, profiles and area concentrations of most divalent metals determined by μPIXE evidenced complex features of element distributions and composition, which may be potentially relevant to the osteoporosis.

  • Poster
    17th International Conference on Ion Beam Analysis, 26.06.-01.07.2005, Seville, Spain

Publ.-Id: 7568

Micro-PIXE and histochemical studies of Zn and Ca distribution in normal bone

Gomez, S.; Preoteasa, E. A.; Harangus, L.; Iordan, A.; Grambole, D.; Herrmann, F.

To better understand the role of zinc in bone mineralization we studied the distribution of Ca and Zn by microbeam particle-induced X-ray emission (µ-PIXE) profiling and mapping, and of Zn by histochemical mapping and profiling in cortical bovine bone. For µ-PIXE, measurements were carried out at the Rossendorf nuclear microprobe with a 3.1 MeV proton beam focused to a spot of ca. 3 µm, at ca. 4-8 µm effective resolution. Maps, unique scans and side-to-side scan sequences were done for Ca and Zn. The noise in Zn profiles was filtered by Fast Fourier Transform (FFT). For histochemistry, Zn was stained in thick sections by the sulphide-silver reaction. Both µ-PIXE and histochemistry showed that Zn was localized mainly at the surfaces of various structures in bone tissue.

Keywords: Micro-PIXE; Bone; Calcium; Zinc; Histochemistry

  • Poster
    17th International Conference on Ion Beam Analysis, 26.06.-01.07.2005, Seville, Spain
  • Nuclear Instruments and Methods in Physics Research B 249(2006), 673-676

Publ.-Id: 7567

The effects of ion bombardment of ultra-high molecular weight polyethylene

Turos, A.; Abdul-Kader, A. M.; Grambole, D.; Jagielski, J.; Piątkowska, A.; Madi, N. K.; Al-Maadeed, M.

Ion bombardment is a suitable tool to improve tribological properties of polymers. In this study UHMWPE samples were bombarded with 130 keV He ions to the fluences ranging from 1 x 10(14) to 2 x 10(16) cm(-2). RBS and NRA techniques were applied to study compositional transformations induced by ion beam bombardment. Important hydrogen release was observed with increasing ion dose and was correlated with the linear energy transfer (LET). Another important effect observed was the rapid oxidation of samples, which apparently occurs after exposure of implanted samples to the air. Oxygen uptake continues during the prolonged storage of the samples in the air at RT. Up to 10 at.% of oxygen can be incorporated in the implanted layer. Changes of surface layer composition produced important increase in the layer hardness. Scratch tests revealed that the hardening of surface layers does not lead to their higher brittleness.

Keywords: Ultra-high molecular weight polyethylene; Surface modification; Ion bombardment; Hydrogen release; Oxidation

  • Lecture (Conference)
    17th International Conference on Ion Beam Analysis, 26.06.-01.07.2005, Seville, Spain
  • Nuclear Instruments and Methods in Physics Research B 249(2006), 660-664

Publ.-Id: 7566

Traditional Hot-Electron MOS Devices for Novel Optoelectronic Applications

Dekorsy, T.; Sun, J. M.; Skorupa, W.; Helm, M.; Rebohle, L.; Gebel, T.

We report the realization of highly-efficient light emitting MOS devices which are based on hot-electron excitation of rare-earth ions implanted into SiO2. The implantation of Gd+ and Tb+ ions yields emission wavelengths of 316 nm and 541 nm with external quantum efficiencies up to 1% and 16%, respectively. The observed threshold electric fields for observing electroluminescence is in accordance with the injection of hot electrons via Fowler-Nordheim tunneling into SiO2 at field strengths in the range of 8-9 MV/cm. The presence of different electroluminescence bands of the Tb-implanted devices allows us to study details of the hot-electron excitation process.

Keywords: MOS devices; light emmtitting diode; rare earth

  • Poster
    14th Int. Conf. on Nonequilibrium Carriers in Semiconductors (HCIS-14), 24.-29.07.2005, Chiacgo, USA
  • Springer Proceedings in Physics 110(2006), 265


Publ.-Id: 7565

AdS and stabilized extra dimensions in multi-dimensional gravitational models with nonlinear scalar curvature terms R-1 and R4

Günther, U.; Zhuk, A.; Bezerra, V.; Romero, C.

We study multi-dimensional gravitational models with scalar curvature nonlinearities of types R-1 and R4. It is assumed that the corresponding higher dimensional spacetime manifolds undergo a spontaneous compactification to manifolds with a warped product structure. Special attention has been paid to the stability of the extra-dimensional factor spaces. It is shown that for certain parameter regions the systems allow for a freezing stabilization of these spaces. In particular, we find for the R-1 model that configurations with stabilized extra dimensions do not provide a late-time acceleration (they are AdS), whereas the solution branch which allows for accelerated expansion (the dS branch) is incompatible with stabilized factor spaces. In the case of the R4 model, we obtain that the stability region in parameter space depends on the total dimension D = dim(M) of the higher dimensional spacetime M. For D > 8 the stability region consists of a single (absolutely stable) sector which is shielded from a conformal singularity (and an antigravity sector beyond it) by a potential barrier of infinite height and width. This sector is smoothly connected with the stability region of a curvature-linear model. For D < 8 an additional (metastable) sector exists which is separated from the conformal singularity by a potential barrier of finite height and width so that systems in this sector are prone to collapse into the conformal singularity. This second sector is not smoothly connected with the first (absolutely stable) one. Several limiting cases and the possibility of inflation are discussed for the R4 model.

  • Classical and Quantum Gravity 22(2005), 3135-3167

Publ.-Id: 7564

Massive scalar fields in the early universe

Zhuk, A.; Günther, U.

We discuss the role of gravitational excitons/radions in different cosmological scenarios. Gravitational excitons are massive moduli fields which describe conformal excitations of the internal spaces and which, due to their Planck-scale suppressed coupling to matter fields, are WIMPs. It is demonstrated that, depending on the concrete scenario, observational cosmological data set strong restrictions on the allowed masses and initial oscillation amplitudes of these particles.

  • International Journal of Modern Physics D 13(2004)7, 1167-1175

Publ.-Id: 7563

Status of the 31/2 cell SRF gun project in Rossendorf

Xiang, R.; Büttig, H.; Evtushenko, P.; Janssen, D.; Lehnert, U.; Michel, P.; Schneider, C.; Schurig, R.; Teichert, J.; Möller, K.; Lehmann, W.-D.; Stephan, J.; Kamps, T.; Lipka, D.; Will, I.; Volkov, V.

In the paper, we report on the status and progress of the superconducting RF gun project in Rossendorf. The gun is designed for cw operation mode with 1 mA current and 9.5 MeV electron energy, and it will be installed at the ELBE superconducting electron linear accelerator. The gun will have a 3½ cell niobium cavity operating at 1.3 GHz. The cavity consists of three cells with TESLA geometry and a specially designed half-cell in which the photocathode will be placed. The production of two Nb cavities, with RRR 300 and 40 respectively, has be finished at the beginning of 2005. After delivery, the RF tests will be performed and the preparation of the cavities will be started. At the same time, the design of the cryostat and the fabrication of its components are already finished. Further activities are the design of the diagnostic beam line, the testing of the new photocathode preparation system, and the upgrade of the 262 nm driver laser system.

  • Poster
    Particle Accelerator Conference 2005, 16.-20.05.2005, Knoxville, TN, USA
  • Contribution to proceedings
    Particle Accelerator Conference 2005, 16.-20.05.2005, Knoxville, Tennessee, USA
    Proceedings of 2005 Particle Accelerator Conference, 1081-1083


Publ.-Id: 7560

Pygmy dipole strength close to particle-separation energies - the case of the Mo isotopes

Rusev, G.; Grosse, E.; Erhard, M.; Junghans, A. R.; Kosev, K.; Schilling, K. D.; Schwengner, R.; Wagner, A.

The distribution of electromagnetic dipole strength in {92, 98, 100}Mo has been investigated by photon scattering using bremsstrahlung from the new ELBE facility. The experimental data for well separated nuclear resonances indicate a transition from a regular to a chaotic behaviour above 4 MeV of excitation energy. As the strength distributions follow a Porter-Thomas distribution much of the dipole strength is found in weak and in unresolved resonances appearing as fluctuating cross section. An analysis of this quasi-continuum - here applied to nuclear resonance fluorescence in a novel way - delivers dipole strength functions, which are combining smoothly to those obtained from (gamma, n)-data. Enhancements at 6.5 MeV and at ca. 9 MeV are linked to the pygmy dipole resonances postulated to occur in heavy nuclei.

Publ.-Id: 7559

Coherent Theta+ and Lambda(1520) photoproduction off the deuteron

Titov, A. I.; Kämpfer, B.; Date, S.; Ohashi, Y.

We analyze an effect of the coherent Theta+Lambda(1520) photoproduction in gamma D interaction near the threshold. We demonstrate that the coherence effect becomes manifest in a comparison of the nK+ invariant mass distribution when the pK- invariant equals the Lambda(1520) mass. Our model calculations indicate a sizeable contribution of resonant and non-resonant background processes in the gamma D to np K+K- reaction which generally exceed the contribution of the coherent resonant channel. However, we find that the coherent Theta+Lambda(1520) photoproduction is enhanced relative to the background processes in the forward hemisphere of the pK- pair photoproduction. Moreover, the coherence effect does not depend on the Theta+ photoproduction amplitude and is defined by the probabilities of the Lambda(1520) photoproduction and the Theta+ to NK transition. Therefore, this coherence effect may be used as an independent method for studying the mechanism of Theta+ production and Theta+ properties.

  • Physical Review C 72(2005), 035206

Publ.-Id: 7558

A Novel High-Resolution Time-of-Flight Spectrometer with Tracking Capabilities for Photo-FissionFragments and Beams of Exotic Nuclei

Nankov, N.; Grosse, E.; Hartmann, A.; Junghans, A. R.; Kosev, K.; Schilling, K. D.; Sobiella, M.; Wagner, A.

Bremsstrahlung photons, produced at superconducting electron accelerator ELBE at the
FZ Rossendorf will be used for the production of neutron-rich nuclei by photo-induced fission. The properties of such exotic nuclei will be studied by decay spectroscopy. The mass and charge identification plays a key role in such experiments and is based on a double time-of-flight (TOF) method for both fission fragments. The reaction products are registered using secondary electrons emitted by thin foils and detected by position-sensitive MCP detectors. Currently a position resolution of 1.8(0.3) mm (FWHM) in both x and y directions and a time resolution of about 330 ps (FWHM) have been deduced using a source of alpha-particles.

Keywords: nuclear structure; nuclear astrophysics; bremsstahlung; photo-induced fission; time-of-flight spectrometry

  • Contribution to proceedings
    3rd International Workshop on Nuclear Fission and Fission-Product Spectroscopy, 11.-14.05.2005, Château de Cadarache, Saint Paul lez Durance, France
    AIP 798, 357

Publ.-Id: 7557

Photodissociation of p-process nuclei studied by bremsstrahlung induced activation

Erhard, M.; Junghans, A. R.; Beyer, R.; Grosse, E.; Klug, J.; Kosev, K.; Nair, C.; Nankov, N.; Rusev, G.; Schilling, K. D.; Schwengner, R.; Wagner, A.

A research program has been started to study experimentally the near-threshold photodissociation of nuclides in the chain of cosmic heavy element production with bremsstrahlung from the ELBE accelerator. An important prerequisite for such studies is good knowledge of the bremsstrahlung distribution which was determined by measuring the photodissociation of the deuteron and by comparison with model calculations. First data were obtained for the astrophysically important target nucleus 92-Mo by observing the radioactive decay of the nuclides produced by bremsstrahlung irradiation at end-point energies between 11.8 and 14.0 MeV. The results are compared to recent statistical model calculations.

Keywords: Photonuclear reactions; Photon absorption and scattering; Nucleosynthesis in novae; supernovae and other explosive environments

  • European Physical Journal A 27(2006)s01, 135-140
    DOI: DOI: 10.1140/epja/i2006-08-019-4
  • Lecture (Conference)
    Nuclear Physics in Astrophysics-II, 16.-20.05.2005, Debrecen, Hungary

Publ.-Id: 7556

The new bremsstrahlung facility at the superconducting electron accelerator ELBE

Wagner, A.; Beyer, R.; Erhard, M.; Dönau, F.; Grosse, E.; Hartmann, A.; Junghans, A. R.; Käubler, L.; Kosev, K.; Mallion, S.; Nair, C.; Nankov, N.; Rusev, G.; Schilling, K. D.; Schulze, W.; Schwengner, R.

A new facility for the production of polarised bremsstrahlung has been built at the superconducting electron accelerator ELBE of the Forschungszentrum Rossendorf. The bremsstrahlung facility and the detector setup are designed such that the background radiation due to scattering of photons and production of neutrons is minimised allowing for experiments close to and above particle separation energies in nuclei.
First results of photon-scattering and photo-dissociation experiments on {92,98,100}Mo are presented.
The results are compared to recent cross-section calculations for astrophysical networks.

Keywords: polarised bremsstrahlung superconducting electron accelerator ELBE photon-scattering and photo-dissociation Mo92 Mo98 Mo100 nuclear astrophysics

  • Journal of Physics G 31(2005), S1969

Publ.-Id: 7555

Experimente zur CFD-Validierung der Zweiphasen-Strömung im Heißstrang eines Druckwasser-Reaktors

Vallee, C.; Höhne, T.; Sühnel, T.

Zur Validierung von CFD-Codes bei reaktornahen Versuchsbedingungen wird derzeit das Heißstrang-Modell in der Druckkammer der TOPFLOW-Anlage in Betrieb genommen.
Vorversuche fanden bereits an einem horizontalen Luft/Wasser-Strömungskanal bei Atmosphärendruck statt. Es wurden optische Messungen mit einer Hochgeschwindigkeits-Kamera durchgeführt, die durch synchronisierte dynamische Druckmessungen ergänzt wurden. Außerdem wurden Geschwindigkeitsfelder in einem Schwall mit PIV (Particle Image Velocimetry) gemessen.
Zur Validierung des Codes CFX-5 wurden Nachrechnungen durchgeführt. Diese stimmten mit dem Experiment qualitativ gut überein. Zudem wurde eine Vorrausrechnung zum Heißstrang-Modell gezeigt.

Keywords: Horizontal two-phase flow; Slug flow; High-speed video observations; Image processing; PIV; CFD

  • Lecture (Conference)
    Annual Meeting on Nuclear Technology 2005, 10.-12.05.2005, Nürnberg, Germany

Publ.-Id: 7554

Experimental investigation and CFD simulation of an air/water flow in a horizontal channel (Part 1: Measurements)

Vallee, C.; Sühnel, T.

For the investigation of air/water stratified flow, a horizontal channel with rectangular cross-section was build at Forschungszentrum Rossendorf. The channel allows the investigation of air/water co- and counter-current flows under atmospheric pressure, especially the slug behaviour.
Optical measurements were performed with a high-speed video camera, and were complemented by simultaneous dynamic pressure measurements. An interface capture technique was developed, which allows to plot the time dependent water level in each cross-section. Further, Particle Image Velocimetry (PIV) measurements where presented, which shows the flow pattern inside of a slug.

Keywords: Horizontal two-phase flow; Slug flow; High-speed video observations; Image processing; PIV

  • Lecture (Conference)
    FZR & Ansys Multiphase flow workshop, 31.05.-03.06.2005, Dresden, Germany
  • Contribution to proceedings
    FZR & Ansys Multiphase flow workshop, 31.05.-03.06.2005, Dresden, Germany
    Workshop proceedings

Publ.-Id: 7553

High-Intensity THz Radiation from a Large-Aperture Photoconductive Emitter

Winnerl, S.; Dreyhaupt, A.; Peter, F.; Stehr, D.; Helm, M.; Dekorsy, T.

We report on the performance of photoconductive THz emitters based on an interdigitated metal-semiconductor-metal finger structure. In every second period of this structure optical excitation is inhibited. Thus carrier acceleration is unidirectional over the whole device area. Excitation with amplified laser pulses leads to THz amplitudes of 6 kV/cm. Saturation of the emission due to screening of the bias field was observed for excitation densities in the 1018 cm-3 range.

  • Lecture (Conference)
    14th International Conference on Nonequilibrium Carrier Dynamics in Semiconductors (HCIS-14), 24.-29.07.2005, Chicago, USA
  • Springer Proceedings in Physics 110(2006), 73-76


Publ.-Id: 7552

Evolution of sp2 networks with substrate temperature in amorphous carbon films: Experiment and theory

Gago, R.; Vinnichenko, M.; Jäger, H. U.; Belov, A. Y.; Jiménez, I.; Huang, N.; Sun, H.; Maitz, M. F.

The evolution of sp2 hybrids in amorphous carbon (a-C) films deposited at different substrate temperatures was studied experimentally and theoretically. The bonding structure of a-C films prepared by filtered cathodic vacuum arc was assessed by the combination of visible Raman spectroscopy, x-ray absorption, and spectroscopic ellipsometry, while a-C structures were generated by molecular-dynamics deposition simulations with the Brenner interatomic potential to determine theoretical sp2 site distributions. The experimental results show a transition from tetrahedral a-C (ta-C) to sp2-rich structures at ~500 K. The sp2 hybrids are mainly arranged in chains or pairs whereas graphitic structures are only promoted for sp2 fractions above 80%. The theoretical analysis confirms the preferred pairing of isolated sp2 sites in ta-C, the coalescence of sp2 clusters for medium sp2 fractions, and the pronounced formation of rings for sp2 fractions >80%. However, the dominance of sixfold rings is not reproduced theoretically, probably related to the functional form of the interatomic potential used.

Keywords: amorphous carbon; bonding structure; sp2 clustering; molecular dynamics

  • Physical Review B 72(2005)1, 014120-1-014120-9

Publ.-Id: 7551

Real time evidence of two-magnon scattering in exchange coupled bilayers

Weber, M. C.; Nembach, H.; Carey, M. J.; Hillebrands, B.; Fassbender, J.

Coherent spin waves in exchange biased bilayers have been excited by ultrafast photomodulation of the exchange bias anisotropy. Vector and time resolved Kerr effect was employed to trace the trajectory of the magnetization vector of the ferromagnetic layer in real time on the picosecond timescale. Photoinduced easy axis precession in CoFe/IrMn samples with different IrMn thicknesses, thus, different exchange bias fields, has been studied. The antiferromagnetic thickness dependence of the decay rate of the induced precession was investigated as a measure of the effective magnetic damping in the system.
The observed increase of the extracted effective damping parameter is proportional to the square of the exchange bias field. Two-magnon scattering of the coherent spin precession of the ferromagnetic layer at local interfacial fluctuations of the exchange bias field can account for an additional dissipation mechanism. The two-magnon damping field in exchange bias systems is proportional to the square of the exchange bias field. Hence, there is time-domain evidence of two-magnon damping involved in magnetic relaxation processes of photoexcited exchange coupled bilayers.

Keywords: magnetism; spin waves; exchange-bias; time-resolved measurements; pump-probe

  • Poster
    Magnetism and Magnetic Materials Conference, 30.10.-03.11.2005, San Jose, USA
  • Journal of Applied Physics 99(2006)8, 08J308
    DOI: 10.1063/1.2167634

Publ.-Id: 7550

Influence of He-ion-irradiation on thin NiMn/NiFe exchange bias films

Cantelli, V.; von Borany, J.; Grenzer, J.; Kaltofen, R.; Schumann, J.; Fassbender, J.

He ion irradiation has been demonstrated to be a versatile tool not only for interfacial mixing in the case of Co/Pt mulilayers [1] but also for low temperature L10-ordering of FePt alloys [2]. L10 ordered NiMn films are due to the high blocking temperature and if exchange coupled to a ferromagnetic material due to the large shift filed a promising candidate for magnetic sensor applications. However, for the creation of the L10 phase an annealing is required. The corresponding thermal budget should be as low as possible to impede the detrimental effect of fast Mn diffusion. In order to reduce the thermal budget for A1 - L10 phase transformation the potential of ion induced vacancy formation has been exploited.
Magnetron sputtered film stacks of 5nm Ta/50(15)nm NiMn/20nm Fe20Ni80 /5nm Ta deposited at Si/SiO2 substrates were subsequently irradiated with He+ ions (30 keV, 10^15-3*10^16cm-2, RT or 250°C). The transition from the paramagnetic NiMn phase (fcc) to the chemically ordered, antiferromagnetic tetragonal L10 phase during annealing (100-500°C, Vacuum) was studied by in-situ X-ray diffraction using synchrotron radiation. A small L10 fraction (< 15%) is already available after deposition. The transformation to a dominating L10 (LRO-parameter S > 0.5) ordered NiMn film takes place between 250-300°C irrespective of the irradiation. Annealing at elevated temperatures (T > 400°C) leads to a loss of L10 ordering due to a complete intermixing of the NiMn and the Permalloy films. A benefit of ion iradiation is the improvement of the crystallinity and the degree of <111> texture in the NiMn films already after low fluence (10^15 cm-2) implantation.

[1] C. Chappert, H. Bernas, J. Ferre, V. Kottler, J.-P. Jamet, Y. Chen, E. Cambril, T. Devolder, F. Rousseaux, V. Mathet, H. Launois, Science 280, 1919 (1998).
[2] H. Bernas, J.-P. Attane, K.-H. Heinig, D. Halley, D. Ravelosona, A. Marty, P. Auric, C. Chappert, Y. Samson, Phys. Rev. Lett. 91, 077203 (2003).

Keywords: magnetism; exchange-bias; NiMn; ion irradiation; interfacial mixing; phase transformation

  • Poster
    Magnetism and Magnetic Materials Conference, 30.10.-03.11.2005, San Jose, USA
  • Journal of Applied Physics 99(2006)8, 08C102
    DOI: 10.1063/1.2159227

Publ.-Id: 7549

L10 ordering of magnetron sputtered FePt films at temperatures below 400°C

Cantelli, V.; von Borany, J.; Beckers, M.; Fassbender, J.

Due to the high uniaxial anisotropy L10-ordered FePt is currently the most favoured candidate for future high density storage applications. However, in order to achieve the L10-phase either the deposition or post deposition annealing at temperatures above typically 500°C is required. Many attempts ranging from alternating monolayer deposition [1], different seed or cap layers [2] or doping with third elements [3] have been tried to reduce the ordering temperature with various degree of success.
Here we report on the L10-ordering of stoichiometric 30-125 nm thick FePt films which have been magnetron co-sputtered from elemental targets on SiO2/Si substrates with a deposition rate of (0.30-0.2) Å/s at various temperatures. Surprisingly, already for a deposition at 350°C the films are well chemically ordered in the tetragonal L10 structure with a long- range order parameter S=0.8-0.9 which has been determined by grazing incidence X-ray diffraction. The films exhibit a polycrystalline fiber texture with mean grain sizes of 12-18 nm and a random orientation distribution confirmed by pole figures measurements. In contrast, FePt films deposited at room temperature exhibit the fcc A1-phase with a mean grain size of (5.0 - 0.5) nm. In a sequence of annealing steps with successively increased temperatures, the A1 - L10 transition has been obtained between 300-400°C. After annealing at 400°C the films show nearly complete L10 ordering with S values equivalent to the films deposited at 350°C. During annealing the mean grain size grows to 10-12 nm. Using textured seed layers L10 ordered FePt films with preferred orientation can be realized. One of the key issues in observing the L10-ordering already at rather low temperatures is a combination of low deposition rate and low-energy ion irradiation during deposition.

[1] T. Shima, T. Moriguchi, S. Mitani, K. Takanashi, Appl. Phys. Lett. 80, 288 (2002).
[2] Z. L. Zhao, J. Ding, K. Inaba, J. S. Chen, J. P. Wang, Appl. Phys. Lett. 83, 2196 (2003).
[3] T. Maeda, T. Kai, A. Kiktsu, T. Nagase, J.-I. Akiyama, Appl. Phys. Lett. 80, 2147 (2002).

Keywords: magnetism; FePt; L10; ordering; phase transformation

  • Lecture (Conference)
    Magnetism and Magnetic Materials Conference, 30.10.-03.11.2005, San Jose, USA

Publ.-Id: 7548

Doping ZnO with Fe far from thermal equilibrium

Potzger, K.; Zhou, S.; Reuther, H.; Mücklich, F.; Talut, G.; Fassbender, J.; Herrmannsdörfer, T.; Bianchi, A.

The fabrication of diluted magnetic semiconductors (DMS) by transition-metal (TM) doping of ZnO has attracted tremendous interest within the last 3 years. However, there are still vivid discussions if the ferromagnetic state stems from Zener-interaction between diluted TM ions or from magnetic secondary phases. In order to prove or exclude the possible formation of TM-secondary phases in ZnO we have investigated iron doping, since Fe-ZnO (n-type) DMS are theoretically predicted to exhibit ferromagnetism [1].
For these investigations Fe-ions have been implanted with an ion energy of 180 keV (projected range Rp=80 nm) at 420 K into ZnO single crystals. Two fluences of either 0.4 or 4x1016 ions per cm2 were chosen which correspond to 0.5 and 5 at%, respectively. The samples were characterized by CEMS (conversion electron Mössbauer spectroscopy), XRD (X-ray diffraction) using synchrotron radiation, RBS (Rutherford back scattering), TEM (transmission electron microscopy) and SQUID (superconducting quantum interference device) magnetometry.
For the as implanted sample a high solubility of Fe was found, e.g. 100% for the low fluence and ~90% for the high fluence sample. The ionic states are 2+ and 3+ but none of the ionic fractions could be clearly determined to occupy substitutional lattice sites. The high fluence implanted sample exhibits ferromagnetic behavior at room temperature as was observed by CEMS and SQUID. However, CEMS and XRD measurements confirm that the origin of the ferromagnetic behavior is due to Fe-nanocluster formation. These nanoclusters show the magnetic moment and hyperfine field of metallic bcc-Fe. After annealing the samples at 800°C secondary phases (mainly zinc ferrite clusters) form and no ferromagnetic behavior could be detected. For the low fluence implanted sample neither as-implanted nor after annealing a ferromagnetic behavior could be detected although after annealing the Fe-ions develop a 2+ state suggesting an occupation of substitutional lattice sites.

[1] K. Sato, H. Katayama-Yoshida, Jpn. J. Appl. Phys. 40, L334 (2001)

Keywords: magnetism; doping; ZnO; magnetic semiconductors; nanoparticles

  • Lecture (Conference)
    Magnetism and Magnetic Materials Conference, 30.10.-03.11.2005, San Jose, USA

Publ.-Id: 7547

Ion beam synthesis of Fe nanoparticles in MgO and Y:ZrO2

Potzger, K.; Reuther, H.; Zhou, S.; Mücklich, A.; Grötzschel, R.; Eichhorn, F.; Liedke, M. O.; Fassbender, J.

In order to prepare epitaxially oriented Fe nanoparticles near the surface of a single crystalline host material the method of ion beam synthesis has been explored. Two different host matrices, i. e., MgO(001) and Y:ZrO2(001), were employed to study the influence of the lattice misfit, the solubility and the host oxidizing/reducing properties on the formation of the Fe nanoparticles. The Fe ions were implanted at a primary energy of 100 – 110 keV (mean projected range: 50 nm) with a constant fluence of 6x1016 cm-2 at implantation temperatures varying between 25 °C and 1000°C. Structural and magnetic characterization was performed by means of CEMS (conversion electron Mössbauer spectroscopy), XRD (X-ray diffraction), RBS (Rutherford back scattering), TEM (transmission electron microscopy) and MOKE (magneto-optical Kerr effect).
For MgO substrates the fraction of metallic Fe increases from 28% (25°C) to 60% (800°C) as a function of implantation temperature, whilst the Fe depth profile remains the same. For an implantation temperature of 800°C fcc Fe nanoparticles with a mean diameter of 5 nm and an exclusive orientation relationship of -Fe(111)//MgO(111) and -Fe[220]//MgO[220] have been found. However, for an implantation temperature of 1000°C, the amount of Fe incorporated in the calculated depth profile is strongly reduced due to an enhanced mobility and diffusion of the Fe ions in the matrix material. The remaining Fe is found to be in the 3+ oxidation state.
Also in Y:ZrO2 the fraction of metallic Fe increases with increasing implantation temperature reaching 96% at 1000 °C. However, the nanoparticles formed are mainly bcc with a mean diameter of 13 nm. The dominant epitaxial relation is Fe(110)//Y:ZrO2(001) and Fe[001]//Y:ZrO2[100]. The ferromagnetic behavior is reflected by a magnetic hyperfine field of 330 kOe and a hysteretic magnetization reversal. No in-plane anisotropy could be detected.

Keywords: magnetism; ion beam synthesis; nanoparticles

  • Poster
    Magnetism and Magnetic Materials Conference, 30.10.-03.11.2005, San Jose, USA
  • Journal of Applied Physics 99(2006)8, 08N701
    DOI: 10.1063/1.2159424

Publ.-Id: 7546

Domain structure during magnetization reversal of PtMn/CoFe exchange bias micro-patterned lines

Liedke, M. O.; Potzger, K.; Bischoff, L.; Bothmer, A. H.; Hillebrands, B.; Rickart, M.; Freitas, P. P.; Fassbender, J.

In order to investigate the relation between shape anisotropy and unidirectional anisotropy in exchange biased lines, the magnetic domain configuration during magnetization reversal was studied as a function of the ratio between both anisotropy contributions. For that purpose a number of glass / Ta 7nm / PtMn 20nm / CoFe 4nm / Ta 4nm samples were sputter deposited. By means of either optical lithography and physical etching or focus ion beam (FIB) milling several line pattern in the range between 0.5 and 2.5 µm width and 20 µm length have been prepared. In order to modify the ratio between both anisotropy contributions the exchange bias field strength was reduced by means of 5 keV He+ ion irradiation. The domain structure during magnetization reversal was then investigated by means of magnetic force microscopy. For the as-prepared samples a mono-domain magnetization state with the magnetization direction aligned along the exchange bias field direction was found regardless of its shape. After irradiation, i. e., reduction of the unidirectional anisotropy, the situation has changed completely. The homogeneous magnetization state broke up into small domains with 360° domain walls in between. The appearance of these domain walls was only observed for the descending branch of the magnetization reversal. In addition it was found that the number of domain walls created depends strongly on the stripe width and orientation.

Keywords: magnetism; ion irradiation; FIB; exchange-bias; magnetic domains; MFM

  • Poster
    Magnetism and Magnetic Materials Conference, 30.10.-03.11.2005, San Jose, USA

Publ.-Id: 7545

Magnetic domains and magnetization reversal of ion-induced magnetically patterned RKKY-coupled Ni81Fe19/Ru/Co90Fe10 films

Fassbender, J.; Bischoff, L.; Mattheis, R.; Fischer, P.

Pure magnetic patterning by means of ion beam irradiation of magnetic thin films and multilayers result from a post deposition local modification of the interface structure with only minor effects on the film topography. In the study presented here a 50 keV fine focused Co ion beam was used to change the coupling in a Ni81Fe19/Ru/Co90Fe10 structure from antiferromagnetic to ferromagnetic on a micron scale. Thereby an artificial structure with locally varying interlayer coupling and therefore magnetization alignment is produced. High-resolution full-field x-ray microscopy is used to determine the magnetic domain configuration during the magnetization reversal process locally and layer resolved due to the element specific contrast in circular x-ray dichroism. In the magnetically patterned structure there is in addition to the locally varying interlayer exchange coupling across the Ru layer also the direct exchange coupling within each ferromagnetic layer present. Therefore the magnetization reversal behaviour of the irradiated stripes is largely influenced by the surrounding magnetic film. We found that at the boundaries between irradiated and non-irradiated areas magnetic domain walls form during magnetization reversal with a magnetization component perpendicular to the film plane. This can be explained by the stray field generated by this domain wall which is partially compensated by a corresponding domain wall in the second ferromagnetic layer with opposite direction. It is expected that a pure magnetic patterning, as demonstrated here, can provide an additional degree of freedom in tailoring the overall magnetic properties of thin multilayer structures.

Keywords: ion irradiation; magnetic patterning; magnetism; RKKY coupling; magnetic domains; x-ray microscopy; XMCD

  • Poster
    Magnetism and Magnetic Materials Conference, 30.10.-03.11.2005, San Jose, USA
  • Journal of Applied Physics 99(2006)8, 08G301
    DOI: 10.1063/1.2158967

Publ.-Id: 7544

Neue Konzepte für die kombinierte Leitfähigkeits- und Impedanzmessung in hochtransienten Mehrphasenströmungen

Da Silva, M. J.; Hampel, U.; Schleicher, E.

Messungen mit leitfähigkeitsbasierter Nadelsondensysteme sind gängige Messverfahren für hochtransiente Zweiphasenströmungen. Leitfähigkeits-Nadelsonden eignen sich jedoch nicht zur Untersuchung nichtleitender Fluide bzw. Mehrphasenströmungen. Um dieses Problem zu behandeln, kann die kombinierte Leitfähigkeits- und Permittivitäts- bzw. Kompleximpedanzmessung eingesetzt werden. Dafür wird in diesem Beitrag eine Impedanznadelsonde und eine dazugehörige Messelektronik vorgestellt. Erste vielversprechende Ergebnisse von Messungen an ausgewählten organischen Fluiden werden dargestellt und diskutiert.

Keywords: needle probe; impedance measurement; complex permittivity; multiphase flow

  • Contribution to proceedings
    7. Dresdner Sensor-Symposium - Neue Herausforderungen und Anwendung in der Sensortechnik, 12.-14.12.2005, Dresden, Deutschland
    Proceedings: TUDpress, 139-142

Publ.-Id: 7543

Electron-phonon interaction in quantum cascade structures probed by Landau level spectroscopy

Drachenko, O.; Leotin, J.; Galibert, J.; Sirtori, C.; Page, H.; Semtsiv, M. P.; Ziegler, M.; Dreßler, S.; Müller, U.; Masselink, T.

In this work we present a method to study the energy of the phonon modes responsible for nonradiative energy relaxation of electrons in the active zone of quantum cascade lasers (QCLs). The method is based on the analysis of the oscillations pattern of QCLs emission intensity as a function of magnetic field applied along the growth direction. We studied first GaAs/AlGaAs QCLs with different Al concentration in the barriers (33% and 45%). We demonstrated that in the case of high Al concentration the relaxation via AlAs- like LO phonon can be significant. We have also shown that in case of In0.73Ga0.27As/AlAs short-wavelength QCL in spite of the high Al concentration in the barriers and the low GaAs contents in the wells, the nonradiative energy relaxation happens principally via GaAs-like or InAs-like (or mixed modes) phonon emission, while a clear signature of AlAs-like phonons was not observed.

Keywords: Quantum Cascade Lasers; Phonon spectroscopy; High magnetic fields; magneto-phonon resonance

  • Contribution to proceedings
    12th International Conference on Narrow Gap Semiconductors, 03.-7.07.2005, Toulouse, France
    Proceedings of the 12th International Conference on Narrow Gap Semiconductors, Part VII, 530-535

Publ.-Id: 7542

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