Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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39317 Publications

Electronic band structure of the borocarbide superconductor LuNi2B2C

Bianchi, A. D.; Bergk, B.; Ignatchik, O.; Wosnitza, J.; Perenboom, J.; Souptel, D.; Behr, G.; Canfield, P. C.

We present de Haas-van Alphen (dHvA) measurements of the nonmagnetic rare-earth borocarbide superconductor LuNi2B2C which have been performed by using a torque cantilever for temperatures down to 0.03 K and in magnetic fields up to 33 T. We mapped the dHvA oscillations of a high-quality single crystal by rotating between all the three principal crystallographic axes [100], [001], and [110] in steps of 10 degrees. This set of data gives a complete overview of the electronic band structure of LuNi2B2C. A comparison with band structure calculations allowed us to assign the dHvA frequencies to individual bands. Overall positions and band dispersions look similar to that observed in the isostructural compound YNi2B2C, which is another non-magnetic member in the family of the borocarbide superconductors. Additionally, we also measured the temperature dependence of the amplitude of the dHvA oscillations for the three principal crystallographic directions which allows the determination of the effective mass of the different bands.

  • Poster
    Yamada Conference LX on Research in High Magnetic Fields (RHMF), 16.-19.08.2006, Sendai, Japan

Publ.-Id: 9189

Zwei-Skalen-Modellierung von Adsorptionsprozessen an strukturierten Oberflächen

Radke De Cuba, M.; Emmerich, H.; Gemming, S.

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

Keywords: hybrid scheme; phase-field; Monte-Carlo; surfaces; adsorption

  • Zeitschrift für Anorganische und Allgemeine Chemie 632(2006), 2144
    DOI: 10.1002/zaac.200670136
    ISSN: 0044-2313

Publ.-Id: 9188

The new High Magnetic Field Laboratory at Dresden/Rossendorf, HLD

Herrmannsdörfer, T.; Bianchi, A.; Krug, H.; Pobell, F.; Zherlitsyn, S.

  • Poster
    Megagauss X, 18.-23.07.2004, Berlin, Deutschland

Publ.-Id: 9187

Magnetoelastic and magnetothermal properties of low-dimensional quantum spin systems in high magnetic fields - a case study

Wolf, B.; Brühl, A.; Magerkurth, J.; Zherlitsyn, S.; Pashchenko, V.; Brendel, B.; Margraf, G.; Lerner, H.-W.; Wagner, M.; Lüthi, B.; Lang, M.

We report measurements of magnetic, magnetothermal and magnetoelastic properties of a new Cu(II)-coordination polymer Cu(II)-2,5-bis(pyrazol-1-yl)-1,4-dihydroxybenzene (CuCCP). According to our results which cover wide ranges of temperatures and magnetic fields B50 T, this material presents an almost ideal realization of an one-dimensional uniform Heisenberg antiferromagnet. Owing to the moderate exchange-coupling constant of , it was possible to study the system in its interesting high-field range, i.e., across the saturation field gμBBs=2|J|, which, at T=0, marks the endpoint of a quantum critical line. Using pulse-field techniques the high-field magnetization and elastic constant have been measured. A comparison with calculated magnetization curves reveals a distinct magnetocaloric effect at high fields for , which grows upon cooling. In addition, at temperatures T<|J|/kB, a pronounced acoustic anomaly has been found close to Bs and identified as a generic property of the uniform antiferromagnetic Heisenberg chain with a finite spin–lattice interaction

  • Journal of Magnetism and Magnetic Materials 290-291(2005), 411-415

Publ.-Id: 9186

The calculation of pulsed magnetic-field coils by means of the finite-element method

Herrmannsdörfer, T.; Zherlitsyn, S.; Wosnitza, J.

  • Physik Journal 5(2006)SPI, 34-36
    ISSN: 1617-9439

Publ.-Id: 9185

Thermal transport properties of U2Ru2Sn at low temperatures

Sanchez, A.; Paschen, S.; Wosnitza, J.; Mydosh, J. A.; Strydom, A. M.; Du Plessis, P. D. V.; Steglich, F.

U2Ru2Sn has been classified as the first tetragonal U-based Kondo insulator. Here, we present measurements of the thermal conductivity k and thermopower S of high-quality single-crystalline U2Ru2Sn along and perpendicular to the tetragonal c-axis, in the temperature range between 100mK and 1K, in zero field and in a magnetic field of 6T. Below 400 mK, the phonon contribution to kðTÞ shows a T2 behaviour for both directions that can be attributed to phonons scattered by electrons. SðTÞ presents a linear behaviour in the whole temperature range. S is positive along the c-axis and negative perpendicular to the c-axis. Using a one-band model the effective mass m is estimated to be 2m0 along and 16m0 perpendicular to the c-axis, where m0 is the free-electron mass. This indicates that U2Ru2Sn has a highly anisotropic residual density of states within the pseudogap.

  • Physica B 359-361(2005), 1015

Publ.-Id: 9184

Superconducting Properties of RuSr2RECu2O8 (RE = Eu, Gd)

Papageorgiou, T. P.; Casini, E.; Braun, H. F.; Herrmannsdörfer, T.; Bianchi, A. D.; Wosnitza, J.

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

Publ.-Id: 9182

Pulsed-magnet design at the Dresden High Magnetic Field Laboratory

Zherlitsyn, S.; Herrmannsdoerfer, T.; Skourski, Y.; Sytcheva, A.; Wosnitza, J.

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

Publ.-Id: 9181

Oscillation or rotation: a comparison of two simple reversal models

Stefani, F.; Xu, M.; Sorriso-Valvo, L.; Gerbeth, G.; Günther, U.

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

Publ.-Id: 9180

Experiments on the magnetorotational instability in helical magnetic fields

Stefani, F.; Gundrum, T.; Gerbeth, G.; Rüdiger, G.; Szklarski, J.; Hollerbach, R.

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

Publ.-Id: 9179

Spectroscopic ellipsometry of ZnO thin films: choice of optimum parameterization of dielectric function

Vinnichenko, M.; Ozerov, M.; Rogozin, A.; Shevchenko, N.; Kolitsch, A.

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

Keywords: ZnO thin films; dielectric function; spectroscopic ellipsometry

  • Lecture (Conference)
    Woollam-Ellipsometrie-Seminar, 25.10.2006, Darmstadt, Germany

Publ.-Id: 9176

Dresden pulsed magnetic field facility

Wosnitza, J.; Bianchi, A. D.; Herrmannsdörfer, T.; Zherlitsyn, S.; Zvyagin, S. A.

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

  • Poster
    International Conference on Magnetism 2006, 20.-25.08.2006, Kyoto, Japan

Publ.-Id: 9175

Fermi Surface of the Half Heusler Compounds Ce1−xLaxBiPt

Bianchi, A. D.; Wosnitza, J.; Kozlova, N.; Eckert, D.; Schultz, L.; Opahle, I.; Elgazzar, S.; Richter, M.; Hagel, J.; Doerr, M.; Goll, G.; von Löhneysen, H.; Zwicknagl, G.; Yoshino, T.; Takabatake, T.

We report on the Fermi surface in the correlated half-Heusler compound Ce1−xLaxBiPt. In CeBiPt we find a field-induced change of the electronic band structure as discovered by electrical-transport measurements in pulsed magnetic fields. For magnetic fields above 25 T, the charge-carrier concentration determined from Hall-effect measurements increases nearly 30%, whereas the Shubnikov–de Haas (SdH) signal disappears at the same field. In the non-4f compound LaBiPt the Fermi surface remains unaffected, suggesting that these features are intimately related to the Ce 4f electrons. Electronic band-structure calculations point to a 4f-polarization-induced change of the Fermi-surface topology. In order to test this hypothesis, we have measured the (SdH) signal in a Ce0.95La0.05BiPt sample with a low La concentration.

  • Poster
    Frühjahrstagung der DPG, 27.-31.03.2006, Dresden, Deutschland

Publ.-Id: 9174

Spin-zero anomaly in the magnetic quantum oscillations of a two-dimensional metal

Bergk, B.; Ignatchik, O.; Jäckel, M.; Wosnitza, J.; Gvozdikov, V. M.; Schlueter, J. A.; Mohtasham, J.; Winter, R. W.; Gard, G. L.

We present de Haas van Alphen (dHvA) and Shubnikov-de Haas (SdH) measurements on the quasi-two-dimensional organic superconductor 00- (BEDT-TTF)2SF5CH2CF2SO3. The measurements were carried out by the torque method and by four-point low-frequency ac-resistance measurements in magnetic fields up to 15 T. Unlike theoretical expectations for two-dimensional metals the dHvA signal shows an unconventional sawtooth wave-form, i. e., an ’inversed sawtooth’ wave form is observed. In order to investigate the behaviour in more detail we performed angledependent dHvA and SdH measurements. The SdH effect displays the behaviour predicted by the grand-canonical Lifshitz-Kosevich theorie. In contrast, the dHvA signal can be explained by a theory, which includes a slightly oscillating chemical potential. Even for simultaneous measurements of both effects the behaviour does not change. This means that the dHvA signal is not affected by an external charge carrier reservoir.

  • Poster
    Frühjahrstagung der DPG, 27.-31.03.2006, Dresden, Deutschland

Publ.-Id: 9173

Anisotropy and spin-triplet excitons in the S = 1/2 gapped antiferromagnet FaCuSi2O6

Zvyagin, S. A.; Wosnitza, J.; Krzystek, J.; Stern, R.; Jaime, M.; Sasago, Y.; Uchinokura, K.

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

  • Poster
    International Conference on Magnetism 2006, 20.-25.08.2006, Kyoto, Japan

Publ.-Id: 9172

The new High Magnetic Field Laboratory at Dresden: a Pulsed – Field Laboratory at an IR Free – Electron – Laser Facility

Pobell, F.; Bianchi, A. D.; Herrmannsdörfer, T.; Krug, H.; Zherlitsyn, S.; Zvyagin, S.; Wosnitza, J.

We report on the construction of a new high magnetic field user laboratory which will offer pulsed-field coils for the range (60 T, 500 ms, 40 mm) to (100 T, 10 ms, 20 mm) for maximum field, pulse time, and bore diameter of the coils. These coils will be energized by a modular 50 MJ/ 24 kV capacitor bank. Besides many other experimental techniques, as unique possibilities NMR in pulsed fields as well as infrared spectroscopy at 5 to 150 m will be available by connecting the pulsed field laboratory to a nearby free-electron-laser facility.

  • AIP Conference Proceedings 850(2006), 1649
  • Lecture (Conference)
    24th International Conference on Low Temperature Physics, 10.-17.07.2005, Orlando, USA

Publ.-Id: 9171

Polarized neutron scattering studies of chiral criticality, and new universality classes of phase transitions

Plakhty, V. P.; Wosnitza, J.; Kulda, J.; Brückel, T.; Schweika, W.; Visser, D.; Gavrilov, S. V.; Moskvin, E. V.; Kremer, R. K.; Banks, M. G.

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

  • Physica B 385-386(2006), 288-294

Publ.-Id: 9170

Magnetization, vortex state and specific heat in the superconducting state of RuSr2GdCu2O8

Papageorgiou, T. P.; Casini, E.; Braun, H. F.; Herrmannsdörfer, T.; Bianchi, A. D.; Wosnitza, J.

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

  • European Physical Journal B 52(2006), 383-388

Publ.-Id: 9169

Resistivity studies on different variants of κ-(BEDT-TTF)2Cu[N(CN)2]Br: evidence for disorder and/or defect-induced inelastic scattering contributions

Lang, M.; Strack, C.; Akinci, C.; Wolf, B.; Schlueter, J. A.; Wosnitza, J.; Schweitzer, D.; Schreuer, J.; Wiehl, L.

Comparative resistivity measurements have been performed on differently prepared κ-(ET)2Cu[N(CN)2]Br single crystals. While the Tc values and their shifts under hydrostatic pressure are found to be sample independent, the resistivity profiles, especially around the resistivity hump at 90 K and the low-temperature T2 behavior, show striking sample-to-sample variations. In the absence of significant differences in the crystals’ structural parameters and chemical compositions, as proved by high-resolution X-ray and electron-probe-microanalysis studies, these results indicate that real structure phenomena, i.e. disorder and/or defects, strongly affect the inelastic scattering in these molecular conductors.

  • Journal of Low Temperature Physics 142(2006), 191

Publ.-Id: 9166

New annealing methods of indium tin oxide films by electric current

Rogozin, A.; Shevchenko, N.; Vinnichenko, M.; Kolitsch, A.; Möller, W.

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

Keywords: ITO; electric current annealing; activation energy

  • Lecture (Conference)
    The International Conference on Coatings on Glass and Plastics, 18.-22.06.2006, Dresden, Germany

Publ.-Id: 9165

Solitons and spinons in the quantum sine-gordon spin chain

Zvyagin, S. A.; Wosnitza, J.; Kolezhuk, A. K.; Krzystek, J.; Feyerherm, R.

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

  • Poster
    International Conference on Magnetism 2006, 20.-25.08.2006, Kyoto, Japan

Publ.-Id: 9164

β′′-(ET)2SF5CH2CF2SO3 – a Layered 2D Metal with Vanishing Interlayer Coupling

Wosnitza, J.; Hagel, J.; Ignatchik, O.; Bergk, B.; Gvozdikov, V. M.; Schlueter, J. A.; Winter, R. W.; Gard, G. L.

We report on electrical transport and magnetization measurements of the quasi-two-dimensional layered superconductor β′′-(ET)2SF5CH2CF2SO3. The absence of a resistive peak when a strong magnetic field is aligned along the conducting planes reflects the fact that the material is one of the most anisotropic ET-based metals with possible incoherent interlayer transport. Consequences of this feature may be the enhanced amplitude of magnetic quantum oscillations in the superconducting state and an unusual angulardependent metal-insulator transition.

  • Journal of Low Temperature Physics 142(2006), 327-332

Publ.-Id: 9163

Optimization of reactive pulsed magnetron sputtering for epitaxial growth of undoped ZnO films

Rogozin, A.; Vinnichenko, M.; Shevchenko, N.; Kolitsch, A.; Moeller, W.

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

Keywords: ZnO; reactive magnetron sputtering; epitaxial growth

  • Lecture (Conference)
    10th International Conference on Plasma Surface Engineering, 10.-15.09.2006, Garmisch-Partenkirchen, Germany

Publ.-Id: 9162

Elementary excitations in S = 1/2 Heisenberg spin chains with alternating g-tensor and the Dzyaloshinskii-Moriya interaction

Zvyagin, S. A.; Wosnitza, J.; Kolezhuk, A. K.; Krzystek, J.; Feyerherm, R.

The magnetic-excitation spectrum of copper pyrimidine dinitrate, a material containing S = 1/2 antiferromagnetic chains with alternating g-tensor and the Dzyaloshinskii-Moriya interaction, and exhibiting a field-induced spin gap, is probed using tunable-frequency electron spin resonance spectroscopy in magnetic fields up to 25 T. The data are interpreted in frame of the sine-Gordon quantum-field theoretical concept proposed recently by Oshikawa and Affleck. The field-induced gap is measured directly; signatures of soliton and three breather branches are identified.

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

Publ.-Id: 9161

Status quo of the Dresden High Magnetic Field Laboratory

Wosnitza, J.; Bianchi, A. D.; Herrmannsdörfer, T.; Wünsch, R.; Zherlitsyn, S.; Zvyagin, S.

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

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

Publ.-Id: 9160

High magnetic field study of RuSr2GdCu2O8

Papageorgiou, T. P.; Casini, E.; Skourski, Y.; Herrmannsdörfer, T.; Freudenberger, J.; Braun, H. F.; Wosnitza, J.

Magnetization measurements in pulsed magnetic fields up to 47 T have been performed on the magnetic (TM,Ru ≈ 133 K) superconductor (TS ≈ 46 K) RuSr2GdCu2O8 in an attempt to determine the Ru valency in this compound. The Ru ions are most probably in a mixed valence state, but the ratio of Ru5+(S=3/2)/Ru4+(S = 1) ≈ 60%/40% suggested by NMR investigations is justified only if one considers the theoretical values of 3 μB/Ru5+ and 2 μB/Ru4+. Mixed valency could lead to a competition between ferromagnetic double exchange, evolving Ru4+ and Ru5+ ions, and antiferromagnetic superexchange, evolving Ru5+ ions, leading to magnetic phase separation. We conclude that the magnetic and superconducting properties of the rutheno-cuprates critically depend on the Ru5+/Ru4+ ratio which can be affected by the preparation conditions.

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

Publ.-Id: 9159

The magnetic properties of the multi-functional intermetallic compound Pr1-x-yLaxPbyTe in high magnetic fields

Herrmannsdörfer, T.; Bianchi, A. D.; Freudenberger, J.; Papageorgiou, T. P.; Skourski, Y.; Wosnitza, J.

The intermetallic compound Pr1-x-yLaxPbyTe shows a wide spectrum of physical
phenomena. Depending on the metallurgical composition as function of x and y, the compound
changes its behavior from van Vleck paramagnetism and hyperfine-enhanced nuclear-magnetic
order to super- or semiconductivity. In addition, there are remarkable interplay effects between
these ground states. In consequence, Pr1-x-yLaxPbyTe may serve as an interesting material for
nuclear-spin quantum-computing experiments. In this contribution, we focus on measurements
of the magnetic properties performed in high magnetic fields. We present first data of the
magnetization of Pr1-yPbyTe taken in pulsed magnetic fields up to 47 T for the compositions y =
0, 50, and 90 %.

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

Publ.-Id: 9158

Electronic band structure of the borocarbide superconductor LuNi2B2C

Bianchi, A. D.; Bergk, B.; Ignatchik, O.; Wosnitza, J.; Perenboom, J.; Canfield, P. C.

We present de Haas–van Alphen (dHvA) measurements of the nonmagnetic rareearth borocarbide superconductor LuNi2B2C which have been performed by using a torque cantilever for temperatures down to 0.45K and in magnetic fields up to 32.5T. We mapped the dHvA oscillations of a high-quality single crystal by rotating between all three principal crystallographic axes [100], [001], and [110]. This set of data gives a complete overview of the electronic band structure of LuNi2B2C. A comparison with band-structure calculations allowed us to assign the dHvA frequencies to individual bands. Overall positions and band dispersions resemble those observed in the isostructural compound YNi2B2C, which is another nonmagnetic member in the family of the borocarbide superconductors.

  • Open Access Logo Journal of Physics: Conference Series 51(2006), 263-266

Publ.-Id: 9157

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

Gvozdikov, V. M.; Wosnitza, J.

We present a theory which is able to explain enhanced magnetic quantum-oscillation amplitudes in the superconducting state of a layered organic metal with incoherent electronic transport across the layers. The incoherence acts through the deformation of the layer-stacking factor which becomes complex and decreases the total scattering rate in the mixed state. This novel mechanism restores the coherence by establishing a long-range order across the layers and can compensate the usual decrease of the Dingle factor below the upper critical magnetic field caused by the intralayer scattering.

  • Low Temperature Physics 32(2006), 152-157

Publ.-Id: 9156

Magnetic properties of transition-metal nanoclusters on a biological substrate

Herrmannsdörfer, T.; Bianchi, A. D.; Papageorgiou, T. P.; Pobell, F.; Wosnitza, J.; Pollmann, K.; Merroun, M.; Raff, J.; Selenska-Pobell, S.

We have investigated the magnetic properties of transition-metal clusters with a single grain size of about 1 nm. These metallic nanoclusters have been deposed on a biological substrate. This substrate is a purified self-assembling paracrystalline surface layer (S-layer) of the Bacillus sphaericus strain JG-A12 which exhibits square symmetry and is composed of identical protein monomers. First data of the magnetic susceptibility, taken in a SQUID magnetometer at 0 < B < 7 T and 1.8 K < T < 400 K, reveal unusual magnetic properties. The Stoner enhancement factor of the d conduction-electron susceptibility in the Pd and Pt nanoclusters is dramatically reduced compared to the one of the corresponding bulk transition metals. The weakened magnetism of the 5d electrons is considered to play a crucial role for the occurrence of superconductivity in microgranular Pt by adjusting the balance between electron-phonon interaction and competing magnetic interactions.
Keywords: metallic nanoclusters, paracrystalline protein surface layer, magnetism of transition-metal nanoclusters

  • Journal of Magnetism and Magnetic Materials 310(2007), e821-e823
  • Lecture (Conference)
    International Conference on Magnetism (ICM 2006), IUPAP, 20.-25.08.2006, Kyoto, Japan

Publ.-Id: 9155

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

Manson, J. L.; Conner, M. M.; Schlueter, J. A.; Lancaster, T.; Blundell, S. J.; Brooks, M. L.; Pratt, F. L.; Papageorgiou, T.; Bianchi, A. D.; Wosnitza, J.; Whangbo, M.-H.

[Cu(HF2)(pyz)2]BF4 consists of rare µ1,3 bridging HF2 anions and µ-pyrazine ligands leading to a 3D pseudo-cubic framework that antiferromagnetically orders below 1.54(1) K.

Publ.-Id: 9154

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

Brooks, J. S.; Williams, V.; Choi, E.; Graf, D.; Tokumoto, M.; Uji, S.; Zuo, F.; Wosnitza, J.; Schlueter, J. A.; Davis, H.; Winter, R. W.; Gard, G. L.; Storr, K.

We report specialized interplane magnetoresistance (MR) measurements on the organic superconducting compound β´´-(BEDT-TTF)2SF5CH2 CF2SO3 (where BEDT-TTF is bis(ethylenedithio)tetrathiafulvalene) in both the superconducting (Tc ∼ 5K) and normal states versus magnetic field direction. In the normal state, detailed angular-dependent magnetoresistance oscillation (AMRO) studies reveal peculiar features of the Fermi surface topology of this compound, and very high magnetic field studies further support the unusual nature of the electronic structure. In the superconducting state we investigate, through detailedAMRO measurements, the anomalous MR peak that appears within the superconducting field-temperature phase diagram. Our results reveal a direct connection between the superconducting state determined from purely in-plane field, and the vortex lattice produced by the inter-plane magnetic field. We also describe several unique sample rotation instruments used in these high field experiments, including the use of dysprosium pole pieces in combination with a 45 T hybrid magnet to carry out measurements at the highest steady-state resistive magnetic field (47.8 T) yet achieved.

  • Open Access Logo New Journal of Physics 8(2006), 255

Publ.-Id: 9153

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

Wosnitza, J.; Goll, G.; Bianchi, A. D.; Bergk, B.; Kozlova, N.; Opahle, I.; Elgazzar, S.; Richter, M.; Stockert, O.; von Löhneysen, H.; Yoshino, T.; Takabatake, T.

Abstract. The half-Heusler compounds CeBiPt and LaBiPt are semimetals with very low charge-carrier concentrations as evidenced by Shubnikov–de Haas (SdH) and Hall-effect measurements. Neutron-scattering results reveal a simple antiferromagnetic structure in CeBiPt below TN = 1.15K. The band structure of CeBiPt sensitively depends on temperature, magnetic field and stoichiometry. Above a certain, sample-dependent, threshold field (B > 25 T), the SdH signal disappears and the Hall coefficient reduces significantly. These effects are absent in the non-4f compound LaBiPt. Electronic-band-structure calculations can well explain the observed behaviour by a 4f-polarization-induced Fermi-surface modification.

  • Open Access Logo New Journal of Physics 8(2006), 174

Publ.-Id: 9152

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

Zvyagin, S. A.; Wosnitza, J.; Krzystek, J.; Stern, R.; Jaime, M.; Sasago, Y.; Uchinokura, K.

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

Publ.-Id: 9150

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

Strack, C.; Akinci, C.; Wolf, B.; Lang, M.; Schlueter, J.; Wosnitza, J.; Schweitzer, D.

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

  • Poster
    Frühjahrstagung der Deutschen Physikalischen Gesellschaft, 03.-09.03.2005, Berlin, Deutschland

Publ.-Id: 9149

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

Schneider, H.; Liu, H. C.

Keywords: quantum well infrared photodetector; QWIP; GaAs/AlGaAs; two-photon transition

  • Contribution to external collection
    Paiella, R.: Intersubband Transitions in Quantum Structures, New York: Mc. Graw-Hill, 2006, 0071457925, 285-313

Publ.-Id: 9148

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

Rotshtein, V. P.; Markov, A. B.; Proskurovsky, D. I.; Gunzel, R.; Pham, M.; Richter, E.; Shevchenko, N.; Shulov, V. A.; Rubshtein, A. P.

Surface topography, evolution of chemical and phase composition of the surface layers of Ti-6Al-4V alloy subjected to multiple pulsed electron-beam melting at the initial temperature of the target To ranging from 20 to 550 °С have been investigated using optical, laser microscopy, SEM/EDS, AES and XRD analyses. Pulsed melting was induced by a low-energy (~20 keV), high-current electron beam (3 µs, 2.5 J/cm2). At To<200 °С the cleaning of the near-surface layer from oxygen takes place. In contrast, at To<400 °С a 1 µm thick surface layer quenched from the melt is enriched with oxygen from the residual gases of vacuum chamber.
The influence of initial temperature on the microstructure and properties of the surface layers are discussed based on the results of temperature field predictions.

Keywords: Ti-6Al-4V alloy; high-current electron beam; surface modification; phase composition

  • Poster
    8th International Conference on Modification of Materials with Particle Beams and Plasma Flows, 10.-15.09.2006, Tomsk, Russia
  • Russian Physics Journal 49(2006)8, 337-342

Publ.-Id: 9147

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

Rotshtein, V. P.; Markov, A. B.; Proskurovsky, D. I.; Kagadei, V. A.; Guenzel, R.; Shevchenko, N.; Reuther, H.; Shulov, V. A.

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

Keywords: Ti-6Al-4V; surface alloying; zirconium; electron beam

  • Lecture (Conference)
    8th International Conference on Modification of Materials with Particle Beams and Plasma Flows, 10.-15.09.2006, Tomsk, Russia
  • Russian Physics Journal 49(2006)8, 262-267

Publ.-Id: 9146

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

Markov, A. B.; Günzel, R.; Reuther, H.; Shevchenko, N.; Akhmadeev, Y. K.; Schanin, P. M.; Koval, N. N.; Rotshtein, V. P.; Proskurovsky, D. I.

Titanium alloys have some attractive properties enabling them to be used in many industries, while their poor tribological properties often are an obstacle in mechanical engineering applications. The latter properties can be improved by applying surface treatment, for instance, nitriding.
Aim of the research was to investigate the effect of pulsed electron-beam pre-irradiation on the process of titanium alloy (Ti–6Al—4V) low-temperature (783 K) nitriding.
AES revealed that the depth of penetration of nitrogen into the specimen bulk for the pre-irradiated specimen is noticeably larger than that for the non-irradiated one (110 and 170 nm, respectively). Moreover, the overall quantity of nitrogen absorbed by the pre-irradiated specimen during nitriding is two times as much as in the non-irradiated one. So, pre-irradiation of the titanium alloy stimulates its saturation with nitrogen.
XRD analysis revealed that irradiation of this titanium alloy leads to the formation of martensite phases referred to as alpha’ and alpha’’ in the thin surface layer of specimen. Appearance of these metastable phases results in high residual stress values in the irradiated target. In such a way the subsequent nitrogen diffusion in the irradiated specimens will take place in the field of intrinsic stresses. After nitriding the phase composition of titanium alloy was changed and the new TiN and Ti2N phases have appeared. It can be concluded from X-ray diffraction patterns that a fraction of these new phases is much larger for the pre-irradiated before nitriding specimen.
The microhardness measurements showed that the microhardness of surface layer of pre-irradiated with subsequent nitriding specimens is almost four times as much as the initial one (11.3 and 3 GPa, respectively). As for the specimens subjected to the nitriding without pre-irradiation their microhardness appeared to be 8.9 GPa, i.e. three times larger than that for the initial specimen.
Thus, the combined treatment, involving pulsed e-beam pre-irradiation, subsequent cleaning and nitriding is promising and leads to increase in the absorption of nitrogen, the fractions of TiN and Ti2N phases and the surface microhardness in processed titanium alloy.

Keywords: Titanium alloy; Ti–6Al—4V; pulsed electron-beam; nitriding

  • Lecture (Conference)
    8th International Conference on Modification of Materials with Particle Beams and Plasma Flows, 10.-15.09.2006, Tomsk, Russia
  • Russian Physics Journal 49(2006)8, 276-279

Publ.-Id: 9145

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

Kodeli, I.; Aldama, D. L.; de Leege, P. F. A.; Legrady, D.; Hoogenboom, J. E.; Cowan, P.

A special purpose multigroup cross-section library optimized for nuclides and reactions arising in nuclear oil well logging was prepared for use in deterministic and Monte Carlo transport codes. The library is based on the recent ENDF/B-VI.8 evaluation, which includes among others improved oxygen and chlorine cross-sections. A 175 neutron and 45 gamma ray energy group structure was selected in a way to take into account the requirements of oil well logging applications. This library is expected to improve the prediction of the neutron and gamma spectra at the detector positions of the logging tool and its use for the interpretation of the Carbon/Oxygen (C/O) neutron logging measurements in boreholes was studied. For the Monte Carlo codes this library can be useful in particular in calculations requiring multigroup cross sections, like adjoint or MIDWAY methods. Furthermore, comparison of deterministic and Monte Carlo calculations using same or similar cross sections can reveal the uncertainty linked to the computational method and model. Preparation and testing of this library is described.

Keywords: Monte Carlo; Well Logging; Multigroup; Cross Section; Carbon/Oxygen Logging

  • Nuclear Science and Engineering 157(2007)2, 210-224

Publ.-Id: 9144

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

Nievaart, V. A.; Legrady, D.; Moss, R. L.; Kloosterman, J. L.; van der Hagen, T. H. J. J.; van Dam, H.

Boron Neutron Capture Therapy is a well recognised cancer therapy applied usually for spread brain tumors. The alpha particles emitted at neutron capture in Boron will bring localised and excessive damage to surrounding cells while special medicaments are reponsible to achive higher Boron concentration in tumor than in healthy tissue. This article discusses a method to calculate treatment planning for BNCT using adjoint Monte Carlo. The proposed method aims at resolving a problematic issue of obtaining nonzero estimates for a monodirectional beam as sampled adjoint pseudoparticles would hardly coincide with a single preferred direction. The method descibed in this paper uses Legendre expansion to utilise adjoint scores at the beam exit not paralel with the beam tube to interpolate to the direction of paralel direction.

Keywords: adjoint; Monte Carlo; mono-directional; treatment planning

  • Medical Physics 34(2007)4, 1321-1335

Publ.-Id: 9143

Electrical Conductivity of Nitrogen Doped SiC Nanocrystals in Diamond

Weishart, H.; Heera, V.; Skorupa, W.

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

[i] H. Weishart, V. Heera, F. Eichhorn, B. Pécz, Á. Barna and
W. Skorupa, J. Appl. Phys. 94 (2003) 1195.

  • Poster
    5. Siliziumkarbid-Rundgespräch, 17.-18.07.2006, Kloster Banz, Staffelstein, Deutschland

Publ.-Id: 9142

Halbleiterspektroskopie mit ultrakurzen Laserpulsen

Schneider, H.

  • Lecture (others)
    Physikalisches Kolloquium, 05.07.2006, Freiberg, Deutschland

Publ.-Id: 9139

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

Beckert, C.; Grundmann, U.

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

Keywords: SP3; nodal methods; neutron transport; neutron diffusion; multigroup

  • Contribution to proceedings
    M&C+SNA 2007 - Joint International Topical Meeting on Mathematics & Computations and Supercomputing in Nuclear Applications, 15.-19.04.2007, Monterey, United States
  • Lecture (Conference)
    M&C+SNA 2007 - Joint International Topical Meeting on Mathematics & Computations and Supercomputing in Nuclear Applications, 15.-19.04.2007, Monterey, United States

Publ.-Id: 9138

Development and verification of a multigroup SP3 method for reactor calculations

Beckert, C.; Grundmann, U.

A nodal approach for the multigroup SP3 equations was developed and integrated in the DYN3D code. The method is verified by pinwise multigroup calculations for a steady state of the OECD/NEA and U.S. NRC PWR MOX/UO2 Core Transient Benchmark. The results of different approaches including diffusion theory are compared with the reference transport solutions of the code DeCART. Different approaches of the diffusion coefficient used in the SP3 equations are investigated. The SP3 results obtained with the transport cross section of multigroup diffusion theory show a good agreement with the DeCART transport solutions.

Keywords: SP3; DYN3D; nodal methods; multigroup; neutron transport; neutron diffusion

  • Contribution to proceedings
    Annual meeting on nuclear technology 2007, 22.-24.05.2007, Karlsruhe, Germany
  • Lecture (Conference)
    Annual meeting on nuclear technology 2007, 22.-24.05.2007, Karlsruhe, Germany

Publ.-Id: 9137

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

Vinnichenko, M.; Rogozin, A.; Shevchenko, N.; Kolitsch, A.; Moeller, W.

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

Keywords: ZnO thin film; in-plane ordering; reactive pulsed magnetron sputtering; optical properties

  • Poster
    E-MRS Spring Meeting, 29.05.-02.06.2006, Nice, France

Publ.-Id: 9136

Magnetic quantum oscillations in the normal and superconducting state of YNi2B2C

Ignatchik, O.; Wosnitza, J.; Jäckel, M.; Souptel, D.; Behr, G.; Canfield, P.

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

  • Poster
    Frühjahrstagung Berlin, 03.-09.03.2005, Berlin, Deutschland

Publ.-Id: 9135

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

Yankov, R. A.; Donchev, A.; Schuetze, M.; Richter, E.

kein Abstrakt vorhanden

  • Poster
    21st General Conference (Meeting of the German Physical Society, Session MM: Metal- and Material Physics), 27.-31.03.2006, Dresden, Germany

Publ.-Id: 9134

Improving the Oxidation Resistance of TiAl-alloys with Fluorine

Donchev, A.; Richter, E.; Schuetze, M.; Yankow, R. A.

  • Poster
    12th International IUPAC-Conference on High Temperature Materials Chemistry HTMC, 17.-22.09.2006, Vienna, Austria

Publ.-Id: 9133

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

Donchev, A.; Richter, E.; Schuetze, M.; Yankow, R. A.

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

  • Intermetallics 14(2006)10-11, 1168-1174

Publ.-Id: 9131

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

Tyschenko, I. E.; Zhuravlev, K. S.; Cherkov, A. G.; Popov, V. P.; Misiuk, A.; Yankov, R. A.

Characteristic features of the visible photoluminescence (PL) spectra were studied in silicon-on-insulator (SOI) wafers following high-dose (3×1017 cm–2) ion implantation of hydrogen and annealing at high hydrostatic pressures. The PL behavior of the SOI material was compared with that of hydrogen-implanted bulk Si. Annealing at a pressure above 6 kbars produced a wavelength-selective increase (~37 times) in the intensity of the visible PL from the implanted SOI structures. The results are explained in terms of the effect of an optical resonant cavity formed between the air/SOI and the Si/SiO2 interfaces as a result of the high-pressure annealing.

  • Applied Physics Letters 89(2006), 013106 Jul 3 2006

Publ.-Id: 9130

Materialaspekte bei der Untersuchung von Störfallszenarien in Kernkraftwerken

Altstadt, E.

Es wird ein Überblick zu den Aspekten der Materialsicherheit in der Kerntechnik gegeben. Im Mittekpunkt der Betrachtungen steht der Reaktordruckbehälter von Leichtwasserreaktoren bei hypothetischen Unfällen mit Kernschmelze. Es wird auf den Aufbau von Leichtwasserreaktoren und die Sicherheitsphilosophie bei deutschen KKW eingegangen. Die Im FZD angwendeten Methoden und Modelle zur Simulation von Schmelzerückhaltungsszenarien werden erläutert. (Vorlesung ca. 80 min.)

Keywords: Reactor pressure vessel; Material Safety; In-vessel melt retention; Corium

  • Lecture (others)
    Ringvorlesung des Materialforschungsverbundes Dresden für das Studium generale der Technische Universität Dresden, 29.11.2006, Dresden, Germany

Publ.-Id: 9129

Modification of NiTi surface by plasma immersion ion implantation

Shevchenko, N.; Maitz, M. F.; Richter, E.

The NiTi alloy has a high nickel concentration of 50 at%, which may result in nickel ion release into the body environment, preventing from biomedical application. It was demonstrated that the nickel surface concentration may be reduced significantly using plasma immersion ion implantation (PIII). In the present work the surface processes during oxygen (or nitrogen) PIII and the microstructure and properties of the modified surface layers were studied. The samples were examined by X-ray diffraction analysis, Auger electron spectroscopy, atomic force microscopy, spectroscopic ellipsometry and corrosion and blood compatibility tests. Oxygen PIII at an ion energy of 40 keV and a substrate temperatures below 300°C results in the formation of a transparent rutile TiO2 surface layer with a Ni content down to below 1 at%. This layer prevents from corrosion and out-diffusion of Ni ions. Biocompatibility tests show a largely superior in vitro blood compatibility compared to the untreated samples.

Keywords: Shape memory alloy; biocompatibility; PIII

  • Lecture (Conference)
    International Conference on Shape Memory and Superelastic Technologies (SMST 2006), 07.-11.05.2006, Pacific Grove, California, USA

Publ.-Id: 9128

Electromagnetic control of a transitional boundary layer

Albrecht, T.; Grundmann, R.; Mutschke, G.; Gerbeth, G.

The stability of a transitional boundary layer controlled by a wall-parallel, streamwise oriented Lorentz force is investigated by means of direct numerical simulation. Damping of Tollmien-Schlichting waves is observed already at weak control amplitudes.
For a particular control amplitude, similar to homogeneous suction, the initial Blasius layer evolves towards an exponential velocity profile of strongly enhanced stability. Here, intermediate velocity profiles are found to have linear stability properties superior to that of the asymptotic exponential profile. Additional 3-D simulations support the 2-D results as Lorentz force control clearly damps the coherent structures of the transitional flow.
Furthermore, results to optimize the energy consumption of the control by evolutionary strategies are presented.

Keywords: MHD; Control; Boundary Layer; DNS; linear stability analysis

  • Lecture (Conference)
    Fifth international Conference on Computational Fluid Dynamics in the Process Industries, 13.-15.12.2006, Melbourne, Australia

Publ.-Id: 9127

Plasma immersion ion implantation for NiTi surface modification

Shevchenko, N.; Reuther, H.; Kreissig, U.; Richter, E.

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

Keywords: Plasma implantation; NiTi alloy; surface; phase composition

  • Lecture (Conference)
    International Conference on Ion Beam Modification of Materials (IBMM 2006), 18.-22.09.2006, Taormina, Italy

Publ.-Id: 9126

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

Sun, J. M.; Prucnal, S.; Skorupa, W.; Dekorsy, T.; Muecklich, A.; Helm, M.; Rebohle, L.; Gebel, T.

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

  • Journal of Applied Physics 99(2006), 103102

Publ.-Id: 9125

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

Ulbricht, A.; Bergner, F.; Cizek, J.; Melikhova, O.; Prochazka, I.; Kuriplach, J.

The aim of the present report is to contribute small-angle neutron scattering (SANS) data, positron annihilation (PAS) data and transmission electron microscopy (TEM) data to the experimental database. We draw conclusions from the combined application of these methods on the nature of the irradiation-induced features in RPV steels and model alloys.

Keywords: SANS; PAS; TEM; RPV steel; iron alloy; neutron irradiation; defect/solute atom clusters

  • Article, self-published (no contribution to HZDR-Annual report)
    Forschungszentrum Rossendorf 2006
    14 Seiten
    ISSN: 1437-322X

Publ.-Id: 9124

RPV-1 models sensitivity for VVER 1000 materials parameters

Bergner, F.; Ulbricht, A.

The multiscale prediction code RPV-1 was applied to VVER 1000 reactor pressure vessel steels. A sensitivity study was performed for VVER 1000 materials parameters.

  • Lecture (others)
    3rd Plenary Meeting of the Perfect Physics Subproject, 08.-10.11.2006, Mol, Belgium

Publ.-Id: 9123

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

Martins, R. M. S.; Schell, N.; Beckers, M.; Silva, R. J. C.; Braz Fernandes, F. M.

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

  • Lecture (Conference)
    ESRF Science Days 2006, 07.-08.06.2006, Autrans, France

Publ.-Id: 9122

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

Martins, R. M. S.; Schell, N.; Silva, R. J. C.; Mahesh, K. K.; Braz Fernandes, F. M.

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

  • Poster
    MICRODIFF'06 - Local Mechanical Stresses and Microdiffraction, 28.-29.09.2006, Grenoble, France

Publ.-Id: 9121

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

Martins, R. M. S.; Schell, N.; Beckers, M.; Silva, R. J. C.; Mahesh, K. K.; Braz Fernandes, F. M.

  • Poster
    ESRF Science Days 2006, 07.-08.06.2006, Autrans, France

Publ.-Id: 9120

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

Martins, R. M. S.; Schell, N.; Beckers, M.; Silva, R. J. C.; Mahesh, K. K.; Braz Fernandes, F. M.

  • Poster
    ESRF User's Meeting 2006, 07.-08.02.2006, Grenoble, France

Publ.-Id: 9119

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

Zhang, C.; Eckert, S.; Gerbeth, G.

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

Keywords: liquid metal; bubble plume; DC magnetic field; Ultrasound Doppler method; velocity measurements

  • Open Access Logo ISIJ International 47(2007)6, 795-801

Publ.-Id: 9118

Texture evolution during annealing of Ni-Ti Shape Memory Alloy

Braz Fernandes, F. M.; Paula, A. S.; Canejo, J.; Mahesh, K. K.; Silva, R. J. C.; Martins, R. M. S.; Cardoso, A. M. A.; Schell, N.

Anisotropy of the shape recovery associated with shape memory effect strongly depends on the type of preferential orientation, that is present, as well as the ‘strength’ of the texture. In the present paper, we report the results obtained by the in-situ study of texture evolution during the annealing process in Ti-rich Ni-Ti Shape Memory Alloys (SMAs) with different thermal and mechanical histories. For this purpose, a Be-dome furnace installed into a 6-circle goniometer at the BM20 beamline (ROBL-CRG) at the ESRF (Grenoble) has been used. It is shown that there is a significant change in the preferential orientation of B2 phase, with the change in microstrain/coherence domain size, as a function of annealing temperature. This effect is also observed in the B19’ phase after cooling. The alpha-fiber II (austenite texture - <110>||RD ({111}<110>-{110}<110>) was present in the as-received alloy, but only up to 400ºC. The evolution of {111}<110> austenite texture component is quite clear for annealing temperatures above 400ºC.

  • Lecture (Conference)
    Conference on Shape Memory and Superelastic Technology-Europe 2004, 03.-07.10.2004, Baden-Baden, Germany
  • Contribution to proceedings
    Conference on Shape Memory and Superelastic Technology-Europe 2004, 03.-07.10.2004, Baden-Baden, Germany
    Proceedings of Shape Memory and Superelastic Technology 2004, Baden-Baden: ASM International, 45-50

Publ.-Id: 9117

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

Martins, R. M. S.; Schell, N.; Beckers, M.; Mücklich, A.; Reuther, H.; Silva, R. J. C.; Mahesh, K. K.; Braz Fernandes, F. M.

The preferential orientation of Ni-Ti thin films is a crucial factor in determining the shape memory behavior. The texture has a strong influence on the extent of the strain recovery. The relationship between structure and deposition parameters is of extreme importance for future device applications. Our approach is in-situ x-ray diffraction during deposition carried out in a process chamber installed at a synchrotron radiation beamline. Near-equiatomic films were co-sputtered from Ni-Ti and Ti targets. Substrate type and bias voltage play an important role for the preferred orientation. On naturally oxidized Si(100) substrates the NiTi B2 phase starts by stacking onto (h00) planes and then changes to (110) fiber texture with increasing film thickness. For thermally oxidized Si(100) substrates, this cross-over is only observed when a bias voltage is applied. The experiments were supplemented by ex-situ transmission electron microscopy and Auger Electron Spectroscopy allowing an additional deeper insight into the film/substrate interface.

Keywords: Ni-Ti; Sputter deposition; In-situ x-ray diffraction; Texture development; Interface

  • Contribution to proceedings
    Conference on Shape Memory and Superelastic Technology 2006, 07.-11.05.2006, Asilomar, U.S.A.
    Proc. of SMST 2006, 363-372
  • Lecture (Conference)
    Conference on Shape Memory and Superelastic Technology 2006, 07.-11.05.2006, Asilomar, U.S.A.

Publ.-Id: 9116

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

Martins, R. M. S.; Schell, N.; Beckers, M.; Silva, R. J. C.; Mahesh, K. K.; Braz Fernandes, F. M.

Ni-Ti thin films have been recognized as promising and high performance materials in the field of microelectromechanical system applications. However, important issues like formation of film texture and its control are still unresolved. Widening the scope of previous experiments concerning the influence of the deposition parameters on the Ni-Ti films structure, here we show how different crystallographic orientations can be obtained by changing the substrate type. The growth of near-equiatomic Ni-Ti films, deposited by magnetron co-sputtering from Ni-Ti and Ti targets on heated substrates ( 470C), has been studied in situ by x-ray diffraction at a synchrotron radiation beamline. As mentioned in other studies for depositions on Si(100), a (110) fiber texture is observed for the B2 phase. However, a preferential stacking of (100) planes of the B2 phase parallel to the film surface was observed when using a MgO(100) substrate. The preferential orientation of B2(100) // MgO(100) was very strong and was kept as such until the end of the deposition, which lasted for 2 hours (~ 900 nm). Ni-Ti films were also deposited on a TiN layer (~ 15 nm) previously deposited on top of a SiO2/Si(100) substrate. In this case, a crossover from (110) oriented grains dominating at small thicknesses, to (211) oriented grains taking over at larger thicknesses was observed. These are promising results concerning the manipulation of the crystallographic orientations of Ni-Ti thin films, since the texture has a strong influence on the extent of the strain recovery.

Keywords: structure and morphology; deposition by sputtering; in-situ x-ray diffraction

  • Poster
    ESOMAT 2006 - European Symposium on Martensitic Transformations and Shape Memory Alloys, 10.-15.09.2006, Bochum, Germany
  • Materials Science and Engineering A 4812-482(2008), 626-629

Publ.-Id: 9114

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

Martins, R. M. S.; Schell, N.; Silva, R. J. C.; Pereira, L.; Mahesh, K. K.; Fernandes, F. M. B.

Shape Memory Alloy (SMA) Ni-Ti thin films have attracted much interest as functional and smart materials due to their unique properties. However, there are still important issues unresolved like formation of film texture and its control as well as substrate effects. In this study, near-equiatomic films were obtained by co-sputtering from Ni-Ti and Ti targets in a process chamber installed at a synchrotron radiation beamline. In-situ x-ray diffraction during the growth of these films allowed establishing a relationship between structure and deposition parameters. The effect of a TiN layer deposited on top of the SiO2/Si(100) substrate prior to the deposition of the Ni-Ti films was analysed. These experiments show that TiN acts not only as a diffusion barrier, but also induces different crystallographic orientations. A TiN layer with ~ 215 nm thickness induces the preferential growth of (110) planes of the Ni-Ti B2 phase parallel to the substrate from the beginning of the deposition with a constant growth rate during the whole deposition. For a TiN thickness of ~ 15 nm, the diffraction peak B2(110) also appears from the beginning of the deposition but much less intense. In this latter case, the B2(211) peak was also detected having observed a crossover from <110> oriented grains dominating at small thicknesses, to <211> oriented grains taking over at larger thicknesses. The same orientations and similar intensities were observed for a Ni-Ti film deposited on a TiN layer with ~ 80 nm.

Keywords: Shape memory alloy; Ni-Ti; deposition by sputtering; in-situ x-ray diffraction; texture development

  • Poster
    E-MRS 2006 Spring Meeting, 29.05.-02.06.2006, Nice, France
  • Sensors and Actuators B 126(2007)1, 332-337

Publ.-Id: 9113

Structural in-situ studies of Ni-Ti thin films

Martins, R. M. S.; Braz Fernandes, F. M.; Silva, R. J. C.; Beckers, M.; Schell, N.

Ni-Ti thin films present great advantages for the fabrication of micro-actuators. The phase transformation and precipitation, which are responsible for the shape memory effect, have been widely studied in bulk material and thin films. However, in-situ studies have been limited to the ageing/annealing treatments after deposition. In this study we present a series of results that clearly illustrate the interest of in-situ studies, not only during annealing, but also during sputtering. The in-situ annealing experiments, using a Be-dome furnace installed into the six-circle diffractometer of the ROssendorf BeamLine (ROBL-CRG) at the ESRF, Grenoble, allowed us to determine the kinetics of the phenomena, to identify the sequence of precipitation and to correlate the build-up of the final structure with the processing conditions. The in-situ sputtering experiments were performed using a magnetron sputter deposition chamber also installed into the six-circle diffractometer of the ROBL-CRG beamline. This facility allowed us to follow the structural evolution of the films also during the deposition process.

Keywords: Ni-Ti; SMA; x-ray diffraction

  • Contribution to proceedings
    Shape Memory and Superelastic Technologies 2004, 03.-07/10/2004, Baden Baden, Germany
    Proceeding of SMST 2004, Baden Baden: ASM International, 421-426
  • Lecture (Conference)
    Conference on Shape Memory and Superelastic Technology-Europe 2004, 03.-07.10.2004, Baden-Baden, Germany

Publ.-Id: 9112

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

Schimmack, W.; Gerstmann, U.; Schultz, W.; Geipel, G.

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

Keywords: depleted Uranium; soil; corrosion; leaching; speciation

Publ.-Id: 9111

Structure, stability and electronic properties of composite Mo_(1-x)Nb_xS_2 nanotubes

Ivanovskaya, V. V.; Heine, T.; Gemming, S.; Seifert, G.

The effect of Mo -> Nb substitution on the electronic structure of MoS2 nanotubes has been investigated using the density functional tight binding method (DFTB). It has been found that composite Mo1-xNbxS2 nanotubes (with Nb contents of 5, 10 and 25 at%) are more stable than the corresponding pure tubes, especially for larger tube diameters. The defect-formation energy indicates that the most stable dopant arrangement is a NbS2 stripe along the tube direction. However, entropy effects may favor a random arrangement of Nb dopant atoms at high temperatures in the tubes with a larger diameter. All of the studied Mo1-xNbxS2 nanotubes have metallic properties, independent of their chirality, diameters and ordering type of substitutional atoms.


Publ.-Id: 9110

A study on the two-phase flow in a stirred tank reactor agitated by a gas inducing turbine

Hristov, H. V.; Boden, S.; Hampel, U.; Kryk, H.; Hessel, G.; Schmitt, W.

Experimental and numerical studies of a gas-liquid two-phase flow were applied to a non-baffled laboratory-scale stirred tank reactor, mechanically agitated by a gas-inducing turbine. The dispersion of air as gas phase into isopropanol as liquid phase at room temperature under different stirrer speeds was investigated. The X-ray cone beam computed tomography (CBCT) measurements were taken at five different stirrer speeds starting from 1000 rpm at which the gas inducement occurs for the given operating conditions. The considerable difficulties in acquiring the phase distribution due to beam hardening and radiation scattering effects were overcame by developing a suitable measurement setup as well as by calibration and software correction methods to achieve high accuracy. The computational fluid dynamics analyses of the stirred tank reactor were performed in 3D with CFX 10.0 numerical software.

Keywords: stirred tank reactor; gas-inducing impeller; mixing; X-Ray computed tomography; CFD

Publ.-Id: 9108

A Method for System Matrix Construction and Processing for Reconstruction of In-Beam PET Data

Shakirin, G.; Crespo, P.; Enghardt, W.

At the experimental heavy ion therapy facility (Gesellschaft für Schwerionenforschung Darmstadt, Germany) an in-beam PET scanner is operated for quality assurance monitoring simultaneously to the therapeutic irradiation. The fixed dual-head PET scanner, which is completely integrated into the treatment facility, registers the annihilation γ-rays following the decay of minor amounts of β+-radioactive nuclei produced via nuclear reactions between the ions of the therapeutic beam and the atomic nuclei of the irradiated tissue. From a comparison of the reconstructed activity distributions with those predicted from the treatment plan, deviations between the prescribed and the applied dose distributions can be detected. The quality assurance monitoring of the therapeutic irradiation could profit significantly of a very fast (ideally, real time) reconstruction algorithm and, therefore, an accurate knowledge of the system response function (system matrix) is required. These requirements lead to the development of a dedicated method of system matrix calculation which has to model the system response precisely and deliver system matrix values rapidly. By exploiting the system symmetries, in combination with an optimized interpolation and approximation strategies, the proposed method delivers the system response function in a continuous 3D image space with a high accuracy.

Keywords: Positron emission tomography; image reconstruction; biomedical applications of radiation; in-beam PET

  • Poster
    2006 Nuclear Science Symposium and Medical Imaging Conference, 31.10.-05.11.2006, San Diego, USA
  • Contribution to proceedings
    2006 Nuclear Science Symposium and Medical Imaging Conference, 31.10.-05.11.2006, San Diego, USA
    2006 IEEE Nuclear Science Symposium conference record: Institute of Electrical and Electronics Engineers, 1-4244-0561-0, 3351-3354
  • IEEE Transactions on Nuclear Science 54(2007), 1710-1716
    ISSN: 0018-9499

Publ.-Id: 9107

Experimental and numerical prediction of horizontal stratified flows

Höhne, T.; Vallee, C.; Prasser, H.-M.

Slug flow as a multiphase flow regime can occur in the cold legs of pressurized water reactors, for instance after a small break Loss of Coolant Accident (SB-LOCA). Slug flow is potentially hazardous to the structure of the system due to the strong oscillating pressure levels formed behind the liquid slugs. It is usually characterized by an acceleration of the gaseous phase and by the transition of fast liquid slugs, which carry out a significant amount of liquid with high kinetic energy. For the experimental investigation of air/water flows, a horizontal channel with rectangular cross-section was build at Forschungszentrum Dresden-Rossendorf (FZD). Experimental data were used to check the feasibility to predict the slugging phenomenon with the existing multiphase flow models build in ANSYS CFX. Further it is of interest to prove the understanding of the general fluid dynamic mechanism leading to slug flow and to identify the critical parameters affecting the main slug flow parameters (like e.g. slug length, frequency and propagation velocity; pressure drop).

Keywords: CFD; flow pattern; stratified flow; slug flow

  • Contribution to proceedings
    International Conference on Multiphase Flow ICMF 2007, 09.-13.07.2007, Leipzig, Germany
    CD-ROM, paper S5_Tue_C_23
  • Lecture (Conference)
    International Conference on Multiphase Flow ICMF 2007, 09.07.2007, Leipzig, Germany

Publ.-Id: 9106

CFD-simulation of thermal hydraulic benchmark V1000CT–2 using ANSYS CFX

Höhne, T.

The OECD/NEA and AER coupled code benchmarks for light water reactors markedly contribute to the testing of best estimate coupled codes in reactivity transients. At the same time, these benchmarks and flow mixing studies indicate that further improvement of the mixing computation tools in the integrated codes is necessary.
Plant measured data from VVER-1000 coolant mixing experiments were used to test and validate CFD codes. The task is to compare the various calculations with measured data, using specified boundary conditions and core power distributions.
The experiments, which are provided for CFD validation, include single loop cooling down or heating-up by disturbing the heat transfer in the steam generator (SG) through the steam valves at low reactor power in the range of 5-14% and with all main coolant pumps (MCP) in operation. They were conducted during the plant commissioning phase at Kozloduy-6, Bulgaria and Kalinin-1, 2, Russia.
CFD calculations have been performed for the thermal hydraulic benchmark V1000CT-2 using ANSYS CFX. The numerical grid model was generated with the grid generator ICEM-CFD and contains 4.7 Mio. tetrahedral elements. The Best Practice Guidelines (BPG) in using CFD in Nuclear Reactor Safety Applications have been used. Different advanced turbulence models were used in the numerical simulation. The best agreement with the Kozloduy heating-up experiment at the core inlet shows the Detached Eddy Simulation (DES). Strong fluctuations occur in the downcomer of the RPV. The results show a clear sector formation of the affected loop at the downcomer, lower plenum and core inlet. The maximum local values of the relative temperature rise in the experiment amount 97.7% and in the calculation 97.3%. Uncertainties are still the estimation and interpolation of experimental values at the core outlet to the core inlet.

Keywords: WWER-1000; CFD; Benchmark; Coolant Mixing

  • Contribution to proceedings
    15th International Conference on Nuclear Engineering (ICONE15), 22.-26.04.2007, Nagoya, Japan
    CD-Rom, ICONE15-10259
  • Lecture (Conference)
    15th International Conference on Nuclear Engineering (ICONE15), 22.04.2007, Nagoya, Japan

Publ.-Id: 9105

Erzeugung von Nano-Strukturen mit Ionenstrahlen

Schmidt, B.

  • Lecture (others)
    Seminar bei AMD, 27.03.2006, Dresden, Germany

Publ.-Id: 9103

Materials Science issues for the fabrication of nanocrystal memory devices by ultra low energy ion implantation

Claverie, A.; Bonafos, C.; Ben Assayag, G.; Schamm, S.; Cherkashin, N.; Paillard, V.; Dimitrakis, P.; Kapetenakis, E.; Tsoukalas, D.; Muller, T.; Schmidt, B.; Heinig, K.-H.; Perego, M.; Fanciulli, M.; Mathiot, D.; Carrada, M.; Normand, P.

Nanocrystal memories are attractive candidate for the development of non volatile memory devices for deep submicron technologies. In a nanocrystal memory device, a 2D network of isolated nanocrystals is buried in the gate dielectric of a MOS and replaces the classical polysilicon layer used in floating gate (flash) memories. Recently, we have demonstrated a route to fabricate these devices at low cost by using ultra low energy ion implantation. Obviously, all the electrical characteristics of the device depend on the characteristics of the nanocrystal population (sizes and densities) but also on their exact location with respect to the gate and channel of the MOS transistor. It is the goal of this paper to report on the main materials science aspects of the fabrication of 2D arrays of Si nanocrystals in thin SiO2 layers and at tunable distances from their SiO2/interfaces.

Keywords: Silicon nanocrystals; non volatile memories; Ion implantation; diffusion in SiO2; TEM; Raman spectroscopy; photoluminescence; single electron phenomena

  • Lecture (Conference)
    2nd International Conference on Diffusion in Solids and Liquids, 26.-28.07.2006, Aveiro, Portugal

Publ.-Id: 9102

FIB induced cobalt disilicide nanowire growth in silicon

Schmidt, B.; Akhmadaliev, C.; Bischoff, L.

In the present work FIB ion implantation of Co+ ions and subsequent anneaeling was applied to ion beam synthesis of CoSi2 nanowires with feature dimensions of about 20-50 nm in diameter and wire lengths of some µm. Using the CANION 31Mplus FIB column (Orsay Physics) a focusing of the Co++ ion beam down to a spot diameter of 30-50 nm was achieved. The ion energy was chosen to be 60 keV corresponding to a mean ion penetration depth of Rp = 33 nm. For the study of the conventional ion beam synthesis of CoSi2 nanowires (phase separation through precipitation and wire ripening during thermal treatment) and their decay into chains of nanoparticles due to nanowire instabilities the samples were implanted with high doses (1x1016-2x1017 cm-2) and at 420 °C sample temperature. Additionally, the scan direction of the FIB relative to the crystal directions was varied (normal FIB scan-direction was parallel to the [110]-direction on the Si surface). Small misalignment of the FIB trace relative to the [110] orientations leads to the decay of the CoSi2 nanowires into chains of more or less prolonged CoSi2 nanoparticles. Samples implanted at lower ion doses (1014-1016 cm-2) and at room temperature were used to investigate the influence of locally FIB induced irradiation defects on the CoSi2 nanowire growth. In this case, nanowires were again formed during thermal treatment by reacting of cobalt from a thin evaporated layer on the sample back side with defects induced by Co+ ion implantation with the FIB. The nanowires here are self-aligned along the in-plane [110] silicon crystal directions in (001)- and (111)-Si. In contrast to conventional ion beam synthesis of CoSi2 nanowires by high dose FIB implantation along a narrow trace defect-induced and self-aligned nanowire growth seems to be more stable.

Keywords: FIB; ion beam synthesis; CoSi2 nanowires

  • Lecture (Conference)
    15th International Conference on Ion Beam Modification of Materials, 18.-22.09.2006, Taormina, Italy

Publ.-Id: 9100

Vorstellung des Instituts für Radiochemie und Erläuterungen zum Ablauf des Kernbrennstoffkreislaufes

Steudtner, R.

Erläuterungen zum Kernbrennstoffkreislauf, zur Herstellung von Brennelementen sowie zur Funktionsweise von Reaktoren

  • Lecture (others)
    Vortrag anlässlich des Besuches einer Schülergruppe, 13.06.2006, Dresden, Germany

Publ.-Id: 9099

Bacteria from extreme environments and their interaction with uranium(VI)

Raff, J.

After a long lasting period of uranium mining and production in Saxony and Thuringia, Eastern Germany, mines have fallen into disuse.
Soil, subsoil and waste waters of former mines and production sites contain still high concentrations of heavy metals and radionuclides, such as uranium. Besides chemical and physical factors influencing the mobility of uranium, also microbial metabolism plays a decisive role in enhancing or retarding migration effects. For instance bacteria are able to bind uranium on the cell surface, to accumulate uranium inside the cell, to reduce or oxidize uranium or to form insoluble uranium precipitates. Intensive studies on the uranium-microbe interaction allow on the one hand to obtain a more detailed understanding of the macroscopic behaviour of uranium in nature and on the other hand the development of new innovative bioremediation strategies for cleaning uranium contaminated water and soil. Starting from several examples of microbes interacting with uranium, the lecture will give an overview about bacterial detoxification strategies, the underlying molecular mechanisms and their application potential for bioremediation.

  • Invited lecture (Conferences)
    Institut für Gewässerschutz/Wassertechnologie, Forschungszentrum für Limnologie (EAWAG), 25.-27.06.2006, Kastanienbaum, Swizerland

Publ.-Id: 9097

Solution processable organic field-effect transistors utilizing an alpha,alpha '-dihexylpentathiophene-based swivel cruciform

Zen, A.; Bilge, A.; Galbrecht, F.; Alle, R.; Meerholz, K.; Grenzer, J.; Neher, D.; Scherf, U.; Farrell, T.

A pentathiophene-based swivel cruciform, which allows rotation between the cruciform arms, was synthesized. Homogeneous microcrystalline films were processed from solution, and field-effect transistors utilizing this dimer gave hole mobilities up to 0.012 cm2/V·s.

Keywords: organic field-effect transistors (OFETs); pentathiophene-based swivel cruciform; hole mobilities

  • Journal of the American Chemical Society 128(2006)12, 3914-3915

Publ.-Id: 9096

Investigation of Environmental Colloids/Nanoparticles at the FZD

Zänker, H.

  • wird nachgereicht
  • Lecture (others)
    1st meeting of the working group "Aquatic Nanoscience and Nanotechnology", 11.-12.12.2006, Vienna, Austria

Publ.-Id: 9095

Joint Project: Migration of Actinides in the System Clay, Humic Substance, Aquifer - Migration Behavior of Actinides (Uranium, Neptunium) in Clays: Characterization and Quantification of the Influence of Humic Substances (Final Report BMWi Project No.: 02 E 9673)

Sachs, S.; Krepelova, A.; Schmeide, K.; Koban, A.; Günther, A.; Mibus, J.; Brendler, V.; Geipel, G.; Bernhard, G.

Objective of this project was the study of interaction processes between humic substances, U(VI), Np(V) and kaolinite KGa-1b. It contributed to the attainment of a better process understanding, the improvement of the knowledge on the interaction of humic substances and metal ions and the enhancement of the thermodynamic database.
With a synthetic humic acid (HA), N-containing functional groups of HA were characterized by 15N-NMR spectroscopy. Based on these results, model studies of the influence of amino groups on the complexation behavior of HA were performed. Spectroscopic studies with amino acids show that the amino group do not contribute to the U(VI) complexation at pH 4.
The impact of kaolinite on the formation of HA and humic substance-kaolinite-sorbates was studied in model syntheses. The results exhibit that the presence of kaolinite during the syntheses mainly influences the yields on HA and their elemental compositions. Synthetic humic substance-kaolinite-sorbates were isolated.
Under exclusion of CO2, the U(VI) complexation by HA was investigated at pH 7 by means of the conventional time-resolved laser-induced fluorescence spectroscopy (TRLFS) and TRLFS with ultrafast pulses. Complexation parameters for the ternary complex UO2(OH)HA(I) were determined.
Studies of the Np(V) reduction in presence of HA with different functionalities under anaerobic conditions have shown that Np(V) is reduced to Np(IV) by HA. The redox capacity depends on the HA functionality. Applying a modified HA it was verified that phenolic/acidic OH groups play a dominating role in the Np(V) reduction.
The influence of HA on the U(VI) and Np(V) sorption onto kaolinite was investigated in batch experiments. In dependence on the experimental conditions, HA effects the sorption and consequently the mobility of U(VI) and Np(V). From studies of the U(VI) sorption onto synthetic humic substance-kaolinite-sorbates it was concluded that the structure and functionality of sorbed/associated humic substances considerably influence the sorption behavior of U(VI). The structure of U(VI)-kaolinite-surface complexes in presence of HA was studied by means of X-ray absorption spectroscopy and TRLFS and compared to those of U(VI)-kaolinite-complexes.
Investigations of the migration of HA and U(VI) in the laboratory system kaolinite-water were carried out in diffusion experiments. The migration of HA in compacted clay is governed by diffusion and influenced by its colloidal properties. Humic substances exert an immobilizing effect on the U(VI) transport in compacted kaolinite.

Keywords: Actinides; Uranium; Neptunium; Humic substances; Humic acids; Model substances; Clay; Kaolinite; Complexation; Reduction; Sorption; Migration; Diffusion; Repository

  • Other report
    Dresden: Forschungszentrum Dresden-Rossendorf, 2006
    116 Seiten
  • Open Access Logo Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; FZD-460 2007
    ISSN: 1437-322X
  • Contribution to external collection
    C.M. Marquardt: Migration of Actinides in the System Clay, Humic Substances Aquifer. Forschungszentrum Karslruhe, Wissenschaftliche Berichte FZKA 7407, Karlsruhe: Forschungszentrum Karlsruhe, 2008, 23-140


Publ.-Id: 9094

EXAFS spectra analysis: the mother wavelet choice

Schabelnikova, S.; Funke, H.; Chukalina, M.

  • wird nachgereicht
  • Contribution to proceedings
    International science-technical Conference "Fundamental problems of the radioelectronic instrument-making industry", 24.-28.10.2006, Moscow, Russia
    Book of Proceedings, MIREA, 143-146
  • Poster
    International science-technical Conference "Fundamental problems of the radioelectronic instrument-making industry", 24.-28.10.2006, Moscow, Russia

Publ.-Id: 9093

Wavelet analysis of the EXAFS spectra: new wavelet function as a linear combination of two Morlet wavelets

Schabelnikova, S.; Funke, H.; Chukalina, M.

  • wird nachgereicht
  • Contribution to proceedings
    Digest Reports of the XVI International Synchrotron RadiationConference., 10.-14.07.2006, Novosibirsk, Russia
    Book of Abstracts, 76
  • Poster
    Digest Reports of the XVI International Synchrotron RadiationConference. Book of Abstracts, 11.-14.07.2006, Novosibirsk, Russia

Publ.-Id: 9092

Wavelet transform usage to analyse the signals and images collected by the X-ray techniques

Chukalina, M.; Funke, H.

  • wird nachgereicht
  • Contribution to proceedings
    International scientific Workshop "Modern techniques for the X-ray diffraction data analysis", 22.-25.05.2006, Velikii Novgorod, Russia, 278-281
  • Lecture (Conference)
    Wavelet transform usage to analyse the signals and images collected by the X-ray techniques, 22.-25.05.2006, Velikii Novgorod, Russia

Publ.-Id: 9091

The local structure of soddyite: EXAFS shell fitting and wavelet analysis

Funke, H.; Hennig, C.; Rossberg, A.; Scheinost, A.

  • wird nachgereicht
  • Poster
    Actinides XAS 2006, 18.-20.09.2006, Karlsruhe, Deutschland

Publ.-Id: 9090

XAFS studies of cobalt(II) binding by solid peat and soil-derived humic acids and plant-derived humic acid-like substances

Ghabbour, E.; Scheinost, A.; Davies, G.

This work has examined cobalt(II) binding by a variety of solid humic acids (HAs) isolated from peat, plant and soil sources at temperatures down to 60 K. The results confirm that X-ray absorption near-edge spectroscopy (XANES) measurements cannot distinguish between aquo and carboxylato ligands in the inner coordination sphere of Co(II). However, between I and 2 inner-sphere carboxylato ligands can be detected in all the peat, plant and soil-derived HA samples by extended X-ray absorption fine structure (EXAFS) measurements, indicating inner-sphere coordination of HA-bound Co(II). The precision of C(carboxylate) detection is limited by the extent and quality of the data and the contribution from inner-sphere O to the Fourier transformed peaks used to detect carbon. Putative chelate ring formation is consistent with a relatively negative entropy change in step A, the stronger Co(II) binding step by HA functional groups, and could relate to 'non-exchangeable' metal binding by HSs.

  • Chemosphere 67(2007)2, 285-291
    ISSN: 0045-6535

Publ.-Id: 9089

Investigation of a TSEE dosimetry system for determination of dose in a cell monolayer

Lehnert, A.; Beyreuther, E.; Lessmann, E.; Pawelke, J.

A prototype system for radiobiological studies has been investigated. It is based on thermally stimulated exoelectron emission (TSEE) detectors and can be used for precise determination of the absorbed dose in a live cell monolayer of several µm thickness. In the present study, five types of BeO detectors, different in structure and method of production, were tested in combination with a Geiger-Müller counter. The dose response and dose range, reproducibility and long-time stability of response, as well as the applicability in a simulated cell culture environment have been studied. The dose response was found to be linear over two orders of magnitude and limited by the counter resolution. However, by a variation of detector sensitivity, the whole dose range of interest for radiobiological experiments can be covered. The irradiation in a simulated cell environment was successful only for one detector type. The system performance was found to be limited by the variation in the system response for time periods longer than several hours, therefore, it is suitable for absolute dose measurement with calibrated detectors if reproducible laboratory conditions are provided.

Keywords: TSEE; exoelectron emission; BeO; Geiger-Müller counter; dosimetry; cell monolayer

Publ.-Id: 9088

Plutonium incorporation in phosphate and titanate ceramics for minor actinide containment

Deschanels, X.; Picot, V.; Glorieux, B.; Jorion, F.; Peuget, S.; Roudil, D.; Jegou, C.; Broudic, V.; Cachia, J. N.; Advocat, T.; Den Auwer, C.; Fillet, C.; Coutures, J. P.; Hennig, C.; Scheinost, A.

Two ceramics, zirconolite and a monazite-brabantite solid solution (MBss) were studied for the immobilization of minor actinides (Np, Am, Cm) produced by reprocessing spent fuel. Monoclinic zirconolite (CaZrTi2O7) is a fluorite derivative structure and is the primary actinide host phase in Synroc (a titanate composite). Monazite (LnPO(4), where Ln = La, Ce, Nd, Gd, etc.) is a monoclinic orthophosphate containing trivalent cations, and brabantite (Ca(0.5)An(0.5)PO(4)) is ail isostructural monazite compound containing tetravalent cations (An = Th and U). The nominal composition of the ceramics studied in this work is (Ca0.87Pu0.13)Zr(Al0.26Ti1.74)O-7 for zirconolite and (Ca0.09Pu0.09La0.73Th0.09)PO4 for the monazite-brabantite solid solution. These formulas correspond to 10 wt% PuO2 loading ill each material. XANES spectroscopy showed that the plutonium is tetravalent in zirconolite and trivalent in MBss. Thorium, another tetravalent cation, call be incorporated at 10 wt% ThO2 in MBss. Aluminum and calcium balance the excess cationic charge resulting from the incorporation of Pu(IV) in zirconolite and Th(IV) in brabantite, respectively. The relative density of the pellets exceeded 90% of theoretical density. The samples exhibited a homogeneous microstructure even if some minor phases. representing less than 2% of the surface area, were detected. The two ceramics are compared in terms of actinide loading, and preliminary results on their long-term behavior are discussed. (c) 2006 Elsevier B.V. All rights reserved.

  • Journal of Nuclear Materials 352(2006)1-3, 233-240
    ISSN: 0022-3115

Publ.-Id: 9087

Enhancing cerium and plutonium solubility by reduction in borosilicate glass

Cachia, J. N.; Deschanels, X.; Den Auwer, C.; Pinet, O.; Phalippou, J.; Hennig, C.; Scheinost, A.

High-level radioactive wastes produced by spent fuel reprocessing containing fission and activation products as well as actinides are incorporated in a borosilicate glass. To ensure optimum radionuclide containment, the resulting glass must be as homogeneous as possible. Microscopic heterogeneity can arise from various processes including the excess loading of an element above its solubility limit. The current actinide loading limit is 0.4 wt%. Work is in progress to assess the actinide solubility in these glasses, especially for plutonium. Initially the actinides were simulated by lanthanides and hafnium. The results show that trivalent elements (La, Gd) exhibit greater solubility than tetravalent elements (Pu, Hf). Cerium is an interesting element because its oxidation state varies from IV to III depending on the process conditions, such as the temperature and redox potential of the melt. In order to quantify the solubility increase, cerium-doped glass samples were melted under reducing conditions by adding a reducing agent. The solubility observed at 1473 K increased significantly from 0.95 to 13.00 wt%. Several reducing compounds have been tested. This paper deals with this study and the application to reduce Pu(IV) to Pu(III). The reduction state was characterized by X-ray absorption spectroscopy (XANES) for plutonium and by chemical analysis for cerium. The material homogeneity was verified by optical and scanning electron microscopy. Preliminary findings concerning the reduction of Pu-doped glasses fabricated in hot cells are also discussed. (c) 2006 Elsevier B.V. All rights reserved.

  • Journal of Nuclear Materials 352(2006)1-3, 182-189
    ISSN: 0022-3115

Publ.-Id: 9086

The molecular topology of uranium(VI) bonding to iron and aluminium oxyhydroxide nanoclusters revisited by EXAFS spectroscopy

Rossberg, A.; Ulrich, K.-U.; Scheinost, A. C.

Applying a novel approach to the spectral analysis of Extended X-ray Absorption Fine Structure (EXAFS) we were able to derive an advanced 3-D structural model of the uranyl sorption complex on hydrated carbonate-free surfaces of aluminum(III) and iron(III) oxyhydroxide nanoclusters. The calculated molecular model fits the EXAFS data consistently up to a radial sphere of 4.5 Å around the uranium absorber. Being unaware of the physicochemical reasons for the specific complex topology characterized by a slightly tilted and distorted geometry, alternative ideas of EXAFS interpretation are discussed.

Keywords: uranium; sorption; iron oxides; monte carlo simulation; x-ray absorption spectroscopy

  • Poster
    Actinides XAS 2006, 18.-20.09.06, Karlsruhe, Germany
  • Contribution to proceedings
    Actinides XAS 2006, 18.-20.09.2006, Karlsruhe, Germany
    Speciation Techniques and Facilities for Radioactive Materials at Synchrotron Light Sources: OECD, 978-92-64-99006-7, 281

Publ.-Id: 9085

Spectroscopic Studies on Colloid-borne Uranium(VI)

Rossberg, A.; Ulrich, K.-U.; Scheinost, A. C.

wird nachgereicht

Keywords: uranium; mining; sorption; iron oxide; x-ray absorption spectroscopy

  • Poster
    16th Users Meeting, ESRF, 08.-11.02.2006, Grenoble, France, 06.-10.02.2006, Grenoble, France

Publ.-Id: 9084

Production of 86Y and 56Co at the Rossendorf CYCLONE 18/9

Preusche, S.; Wüst, F.; Seifert, S.; Schilling, K.-D.; Wenzel, R.; Dohn, N.; Steinbach, J.

The Rossendorf version of the CYCLONE 18/9 is equipped with a 2 m long external beam transport line (BTL) to have the possibility of producing non-standard PET radionuclides. For this purpose a solid target system was developed and mounted to the BTL. This system increases the flexibility of the CYCLONE 18/9 and enables the production of e.g. 86Y and 56Co for applications in radiochemistry, nuclear medicine and nuclear physics. The solid target system is introduced shortly and the parameters, data and results of the production of 86Y and 56Co are given.

  • Lecture (Conference)
    11th International Workshop on Targetry and Target Chemistry, 28.-31.08.2006, Cambridge, Great Britain
  • Contribution to proceedings
    11th International Workshop on Targetry and Target Chemistry, 28.-31.08.2006, Cambridge, UK
    11th International Workshop on Targetry and Target Chemistry, 86

Publ.-Id: 9083

Experimental investigation and CFD validation of horizontal air/water slug flow

Vallee, C.; Höhne, T.

In different scenarios of small break Loss of Coolant Accident (SB-LOCA), stratified two-phase flow regimes can occur in the main cooling lines of pressurized water reactors. Because these flow patterns cannot be predicted with the required accuracy and spatial resolution by the one-dimensional system codes, the stratified flows are increasingly modelled with computational fluid dynamics (CFD) codes. In CFD, closure models are required that must be validated, especially if they are to be applied to nuclear reactor safety. Because the structure of the interface is strongly connected with the momentum transfer between the phases, the water surface characteristics can be used for validation purposes. Experimental data suitable for CFD validation must satisfy special quality criteria, in particular the boundary conditions and the measurement resolution.

For the investigation of co-current two-phase flows at atmospheric pressure and room temperature, the Horizontal Air/Water Channel (HAWAC) was built at Forschungszentrum Dresden-Rossendorf. At the channel inlet, a special device was designed for a separate injection of water and air into the test-section. A blade separating the phases can be moved up and down to control the free inlet cross-section for each phase. This provides adjustable and well-defined inlet boundary conditions and therefore very good CFD validation possibilities.

The HAWAC facility is designed for the application of optical measurement techniques, which deliver the high resolution required for CDF validation. Therefore, the 8 m long acrylic glass test-section with rectangular cross-section provides good observation possibilities. High-speed video observation and particle image velocimetry (PIV) were applied during slug flow. The camera images show the generation of slug flow from the inlet of the test-section. An algorithm was developed to recognise the interface and the extraction of quantitative values, like water level and slug propagation velocity. The PIV measurements reveal the inner flow rotation inside a slug.

Parallel to the experiments, CFD calculations were carried out. The aim of the numerical simulations is to validate the prediction of slug flow with the existing multiphase flow models built in the commercial code ANSYS CFX. The Euler-Euler two-fluid model with the free surface option was applied to a grid of 600,000 control volumes. The turbulence was modelled separately for each phase using the k-ω based shear stress transport (SST) turbulence model. The results compare well in terms of slug formation, velocity, and breaking. The qualitative agreement between calculation and experiment is encouraging, while quantitative comparison show that further model improvement is needed.

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

  • Contribution to proceedings
    15th International Conference on Nuclear Engineering (ICONE15), 22.-26.04.2007, Nagoya, Japan
    Paper ICONE15-10469
  • Lecture (Conference)
    15th International Conference on Nuclear Engineering (ICONE15), 22.-26.04.2007, Nagoya, Japan

Publ.-Id: 9082

Impact of optical in-plane anisotropy on near-field phonon polariton spectroscopy

Schneider, S.; Seidel, J.; Grafström, S.; Eng, L. M.; Winnerl, S.; Stehr, D.; Helm, M.

To examine the influence of optical anisotropy on the near-field signal measured in a scattering-type scanning near-field optical microscope, we excite optically uniaxial LiNbO3 close to a phonon resonance at a wavelength of 13 µm in the infrared regime using a tunable free-electron laser. This allows us to excite a phonon polariton resonance in the coupled tip-sample system. We find that the resonance shows a clear dependence on the orientation of the optical axis of the birefringent crystal.

  • Applied Physics Letters 90(2007), 143101

Publ.-Id: 9081

High-resolution rapid-scan THz spectrometer using a large-area photoconductive emitter in combination with asynchronous optical sampling

Dreyhaupt, A.; Winnerl, S.; Schneider, H.; Helm, M.; Bartels, A.; Thoma, A.; Janke, C.; Dekorsy, T.

We present an approach for photoconductive THz generation providing a broad bandwidth and exceptionally high electric-field amplitude. A large-area interdigitated two-electrode structure on a GaAs substrate offers high electric fields at moderate bias voltages. In order to avoid destructive interference of the THz waves in the far field, every second electrode gap is masked by an additional metallization [1]. Thus all semiconductor regions exposed to incident radiation exhibit parallel electric fields and photocarriers excited by a mode locked Ti:Sapphire laser with MHz or GHz repetition rates are accelerated in the same direction. Areas with anti-parallel fields do not contribute to the THz radiation, thus the resulting constructive interference gives rise to an intense THz output. Using electro-optic sampling, we detect a THz field amplitude of 1.7 kV/cm, which is almost one order of magnitude higher as compared to previous photoconductive emitters excited with pulses from an unamplified oscillator. This field value corresponds to an average THz power of 145 µW and yields a NIR-to-THz power-conversion efficiency as high as 2 × 10-4. We have employed this emitter concept in a compact THz spectrometer based on asynchronous optical sampling (ASOPS) [2]. ASOPS allows us to scan the THz electric field over a nanosecond time delay at a kilohertz scan rate without using a mechanical delay stage. To this end, two mode-locked femtosecond lasers with approximately 1 GHz repetition rate are combined at a fixed, stabilized kHz difference frequency ∆f. One laser delivers the THz excitation pulse, the other provides the probe pulses for electro-optic detection. In this way, the relative time delay between the THz pulses and the probe pulses is linearly ramped, thus enabling high-speed scanning over a 1 ns time delay with the scan rate ∆f. At a scan rate of 9 kHz a time resolution of 230 fs is accomplished. High-resolution spectra from 50 GHz up to 3 THz are obtained and water absorption lines with a width of 11 GHz are observed. A dynamic range larger than 3 orders of magnitude is achieved in a few 10 seconds averaging time.
[1] A. Dreyhaupt, S. Winnerl, T. Dekorsy, M. Helm, Appl. Phys. Lett. 86, 121114 (2005).
[2] A. Bartels, A. Thoma, C. Janke, T. Dekorsy, A. Dreyhaupt, S. Winnerl, M. Helm, Opt. Express 14, 430-437 (2006).

  • Poster
    2nd Workshop on Terahertz Technology, 01.-02.03.2006, Kaiserslautern, Deutschland

Publ.-Id: 9080

Radiation damage in zirconia investigated by positively charged particles

Grynszpan, R. I.; Anwand, W.; Brauer, G.

nicht vorhanden

  • Lecture (Conference)
    19th International Conference on the Application of Accelerators in Research and Industry (CAARI2006), 20.-25.08.2006, Ft. Worth/Texas, USA

Publ.-Id: 9079

Characterization of semi-conducting nanorods by AFM and conducting AFM

Andreev, A.; Hou, Y.; Teichert, C.; Brauer, G.; Djurisic, A.

nicht vorhanden

  • Lecture (Conference)
    56. Jahrestagung der Österreichischen Physikalischen Gesellschaft (ÖPG), 18.-21.09.2006, Graz, Österreich

Publ.-Id: 9078

Electrical characterization of deep acceptor states in ZnO

von Wenckstern, H.; Schmidt, H.; Pickenhain, R.; Biehne, G.; Brandt, M.; Brauer, G.; Lorenz, M.; Dadgar, A.; Krost, A.; Grundmann, M.

nicht vorhanden

  • Lecture (Conference)
    MRS Fall Meeting 2006, 27.11.-01.12.2006, Boston/MA, USA

Publ.-Id: 9077

Synthesis of Nanowire Structures using Focused Ion Beams

Röntzsch, L.; Heinig, K.-H.; Akhmadaliev, C.; Bischoff, L.; Schmidt, B.

Nanowires (NWs) play an important role as basic components of electronic and photonic devices. Here, theoretical studies using atomistic computer simulations and experi¬mental results are presented on the CMOS-compatible fabrication of metal silicide and semiconductor NWs by focused ion beam (FIB) implantation and subsequent thermal annealing. The FIB implantation along a straight trace leads to a local and surface-near supersaturation in the substrate. Post-implantation annealing causes NW formation by self-organization. It is demonstrated that the evolution of the FIB implantation profile proceeds in three well-separated stages: (1) Phase separation by nucleation and growth, (2) NW formation by coalescence of nanoclusters, (3) NW surface smoothening. Likewise, components for functional devices involving several NWs, like T- or X-junctions, can be obtained by crossing different FIB traces. During long-term thermal annealing, NWs disintegrate into regular chains of nanoparticles (Rayleigh instability) that can be used as surface-plasmon-polariton waveguides. Crosses, corners or ends of NWs are subject to a preferential disintegration. Thus, structures suitable for single-electron-transistors and for multi-gate NW field effect transistors may be fabricated by crossing FIB traces.

Keywords: Nanowire; computer modeling; kinetic Monte Carlo; TRIM; ion beam synthesis; phase separation

  • Invited lecture (Conferences)
    17th Symposium of the MRS-J, 08.-10.12.2006, Tokyo, Japan

Publ.-Id: 9076

Pages: [1.] [2.] [3.] [4.] [5.] [6.] [7.] [8.] [9.] [10.] [11.] [12.] [13.] [14.] [15.] [16.] [17.] [18.] [19.] [20.] [21.] [22.] [23.] [24.] [25.] [26.] [27.] [28.] [29.] [30.] [31.] [32.] [33.] [34.] [35.] [36.] [37.] [38.] [39.] [40.] [41.] [42.] [43.] [44.] [45.] [46.] [47.] [48.] [49.] [50.] [51.] [52.] [53.] [54.] [55.] [56.] [57.] [58.] [59.] [60.] [61.] [62.] [63.] [64.] [65.] [66.] [67.] [68.] [69.] [70.] [71.] [72.] [73.] [74.] [75.] [76.] [77.] [78.] [79.] [80.] [81.] [82.] [83.] [84.] [85.] [86.] [87.] [88.] [89.] [90.] [91.] [92.] [93.] [94.] [95.] [96.] [97.] [98.] [99.] [100.] [101.] [102.] [103.] [104.] [105.] [106.] [107.] [108.] [109.] [110.] [111.] [112.] [113.] [114.] [115.] [116.] [117.] [118.] [119.] [120.] [121.] [122.] [123.] [124.] [125.] [126.] [127.] [128.] [129.] [130.] [131.] [132.] [133.] [134.] [135.] [136.] [137.] [138.] [139.] [140.] [141.] [142.] [143.] [144.] [145.] [146.] [147.] [148.] [149.] [150.] [151.] [152.] [153.] [154.] [155.] [156.] [157.] [158.] [159.] [160.] [161.] [162.] [163.] [164.] [165.] [166.] [167.] [168.] [169.] [170.] [171.] [172.] [173.] [174.] [175.] [176.] [177.] [178.] [179.] [180.] [181.] [182.] [183.] [184.] [185.] [186.] [187.] [188.] [189.] [190.] [191.] [192.] [193.] [194.] [195.] [196.] [197.] [198.] [199.] [200.] [201.] [202.] [203.] [204.] [205.] [206.] [207.] [208.] [209.] [210.] [211.] [212.] [213.] [214.] [215.] [216.] [217.] [218.] [219.] [220.] [221.] [222.] [223.] [224.] [225.] [226.] [227.] [228.] [229.] [230.] [231.] [232.] [233.] [234.] [235.] [236.] [237.] [238.] [239.] [240.] [241.] [242.] [243.] [244.] [245.] [246.] [247.] [248.] [249.] [250.] [251.] [252.] [253.] [254.] [255.] [256.] [257.] [258.] [259.] [260.] [261.] [262.] [263.] [264.] [265.] [266.] [267.] [268.] [269.] [270.] [271.] [272.] [273.] [274.] [275.] [276.] [277.] [278.] [279.] [280.] [281.] [282.] [283.] [284.] [285.] [286.] [287.] [288.] [289.] [290.] [291.] [292.] [293.] [294.] [295.] [296.] [297.] [298.] [299.] [300.] [301.] [302.] [303.] [304.] [305.] [306.] [307.] [308.] [309.] [310.] [311.] [312.] [313.] [314.] [315.] [316.] [317.] [318.] [319.] [320.] [321.] [322.] [323.] [324.] [325.] [326.] [327.] [328.] [329.] [330.]