Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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31839 Publications
Deep level defects E1/E2 in n-type 6H silicon carbide induced by electron radiation and He implantation
Ling, C. C.; Chen, X. D.; Fung, S.; Beling, C. D.; Brauer, G.; Anwand, W.; Skorupa, W.; Gong, M.;
6H-SiC samples subjected to He-implantation and e–-irradiation (Ee=0.2MeV–1.7MeV) were investigated by deep level transient spectroscopy (DLTS). E1/E2 were identified in the He-implanted and the e–-irradiated samples with Ee0.3MeV. Considering the minimum e– energy required to displace the atoms in the lattice, the E1/E2 creation was related to the C-atom displacement. Similar to previous reports, the peak intensity and the capture cross sections of E1/E2 anomalously varies from samples to samples. It was shown that these anomalies were due to the presence of a DLTS peak overlapping with the E1/E2 signals.
  • Contribution to proceedings
    27th International Conference on the Physics of Semiconductors (ICPS-27), 26.-30.07.2004, Melville/NY, USA
    Physics of Semiconductors, AIP Conference Proceedings 772/1, 99-100

Publ.-Id: 8155 - Permalink

Stress relaxation by ion bombardment in cubic boron nitride thin films
Abendroth, B.; Möller, W.; Gago, R.; Kolitsch, A.;
Ion bombardment plays a special role in the deposition of cubic boron nitride (cBN) for hard coating applications. On one hand, low energy ion bombardment (100-500 eV) of the growing film surface is required to produce the hard cubic phase, on the other hand this implements extremely high compressive stresses (~10 Gpa) limiting film thickness and adhesion. Recently, high energy ion implantation (from keV to MeV range) has been successfully used to release the compressive stress in the films.
In this work the stress relaxation mechanism was investigated using the cantilever bending principle for in situ real time stress measurement during ion beam assisted deposition and Magnetron sputter deposition with simultaneous high energy ion bombardment. The amount of the relaxation is dependent on the product of the energy and the flux of the high energy ions. Using a variety of structural investigations, it can be shown that the relaxation takes place within the cBN grains, likely via the relaxation of interstitials. A relaxation due to the transformation of cBN to the more ductile hexagonal BN modification is less likely. This suggests a stress relaxation mechanism that is driven by a collisional relocation of strained film atoms due to high energy ion impact. A theoretical description of the stress relaxation based on TRIM simulation is presented and discussed. Assuming the stress in the layer to be proportional to the density of unrelaxed atoms, the calculation of the collisional relocation yield enables the calculation of a relative stress relaxation rate. The relocation yield is dependent on the incident ion energy and on the chosen relocation threshold energy. The experimental data are consistent with the model for different deposition parameters and processes for a relocation threshold energy of 5 eV.
Keywords: cubic boron nitride, stress relaxation, in situ stress measurement
  • Lecture (Conference)
    10th International Conference on Plasma Surface Engineering PSE 2006, 12.09.2006, Garmisch Partenkirchen, Deutschland

Publ.-Id: 8154 - Permalink

Effect of the annealing process on active properties of proton-exchanged optical waveguides in erbium-doped lithium niobate
Salavcova, L.; Spirkova, J.; Capek, P.; Novotna, M.; Vacik, J.; Mackova, A.; Kreissig, U.;
We report about our study of the annealing effect on the resultant chemical composition of the APE (Annealed Proton Exchange) layers and their optical properties, with emphasis on their potential active function. The samples were annealed at various conditions and characterised by a number of nuclear analytic methods (NDP; ERDA; HIERDA) to investigate concentration profiles of the exchanged ions. The content of OH groups, which are undesirable in the active waveguiding layers owing to their effect of erbium excited state lifetimes shortening, was studied by IR absorption spectrometry. The waveguiding properties (number of guided modes, refractive index vs. depth profile) were measured by mode spectroscopy at 632.8 nm. We found out that hydrogen introduced to the surface layers of LiNbO3 by PE (Proton Exchange) moves deeper into the substrate during A (Annealing), lowering thus total refractive index increment. Consequently, the crystallographic phase of the exchanged layers changes towards the a-phase. The lowest amounts of OH groups were found when highest annealing temperatures were used; however, a limitation exists there as temperatures above 400°C cause degradation of the waveguiding properties.
Keywords: Lithium niobate; Erbium; Annealed proton exchange (APE); Optical waveguides
  • Open Access LogoCeramics - Silikáty 49(2005), 86-90

Publ.-Id: 8153 - Permalink

Synthesis and characterization of boron-oxygen-hydrogen thin films at low temperatures
Music, D.; Kölpin, H.; Atiser, A.; Kreissig, U.; Bobek, T.; Hadam, B.; Mertens, R.; Schneider, J. M.;
We have studied the influence of synthesis temperature on chemical composition and mechanical properties of X-ray amorphous boron–oxygen–hydrogen (B–O–H) films. These B–O–H films have been synthesized by RF sputtering of a B-target in an Ar atmosphere. Upon increasing the synthesis temperature from room temperature to 550 °C, the O/B and H/B ratios decrease from 0.73 to 0.15 and 0.28 to 0.07, respectively, as determined by elastic recoil detection analysis. It is reasonable to assume that potential sources of O and H are residual gas and laboratory atmosphere. The elastic modulus, as measured by nanoindentation, increases from 93 to 214 GPa, as the O/B and H/B ratios decreases within the range probed. Hence, we have shown that the effect of impurity incorporation on the elastic properties is extensive and that the magnitude of the incorporation is a strong function of the substrate temperature.
Keywords: amorphous materials; sputtering; machanical properties
  • Materials Research Bulletin 40(2005)8, 1345-1352

Publ.-Id: 8152 - Permalink

Efficient light emission from Si pn diodes and metal-oxide-semiconductor structures
Sun, J. M.; Skorupa, W.; Dekorsy, T.; Schmidt, B.; Helm, M.;
Light emission from silicon has attracted considerable attention in the past few years due to the future potential in on-chip and inter-chip optical interconnects. This report reviews our current research work on efficient electroluminescence (EL) from silicon pn diodes and metal oxide semiconductor (MOS) devices. Efficient band edge EL with attractive power efficiencies up to 0.12 % has been observed in Si pn diodes prepared by boron implantation. We focus on the origin of the relatively high EL efficiency in Si pn diodes prepared by high-dose boron implantation, especially on the intriguing and anomalous increase of the EL for a temperature increase up to room temperature. EL from rare earth doped metal oxide semiconductor (MOS) devices was also studied using ion implantation of different rare earth luminescent centers (Gd3+, Tb3+, Eu3+, Ce3+, Tm3+, Er3+) into the silicon dioxide layers with a transparent top electrode made of indium-tin oxide. Strong EL was obtained from different rare earth centers in UV to infrared. The electroluminescence properties were studied with respect to the luminescence spectra, decay time, impact excitation, cross relaxation (Tb3+), and efficiency. Top external quantum efficiency above 15 % was obtained, which is comparable to the InGaN quantum well light emitting diodes
Keywords: electroluminescence, silicon, pn diode, rare earth, MOS structures
  • Invited lecture (Conferences)
    14th International Conference on Luminescence – ICL05, 2005, Beijing, July 25-29 China, WED_A_C02, 25.7.2005, Beijing, China

Publ.-Id: 8151 - Permalink

Modulation of the 1535 nm photoluminescence from Er-doped Si-rich silicon dioxide by field-induced quenching
Sun, J. M.; Skorupa, W.; Dekorsy, T.; Helm, M.; Rebohle, L.; Gebel, T.;
Field-induced quenching of the efficient photoluminescence at 1535 nm was observed from Si-rich SiO2:Er thin films prepared by Er and Si co-implantation. The quenching effect was strongly enhanced by increasing the density of silicon nanoclusters at an electric field above 5 MV/cm. A modulation ratio of 0.37 was obtained at an electric field of 9 MV/cm for a 200 nm Er-doped Si-rich layer containing 0.24 % of Er atoms and 10% excess Si nanoclusters. The mechanism of the field-induced quenching of the photoluminescence was studied by simultaneously measuring the light intensity from nanolusters and Er3+ ions, the injection current and the electric field. The quenching mechanism could be attributed to the field induced separation of the excitons created in silicon nanoclusters and tunneling of carriers between the Er ions and silicon nanoclusters. This strong field quenching effect will be useful for controlling the optical gain in a Si-rich SiO2:Er waveguide amplifiers, but also for the small size optical modulator in silicon photonics.
Keywords: Field induced quenching, Erbium, silicon nanoclusters, silicon dioxide
  • Lecture (others)
    E-MRS 2005 Spring Meeting May 31 – June 3, 2005 Symposium D Materials science and device issues for future Si-based technologies, 31.05.-3.6.2005, Strasbourg, France

Publ.-Id: 8150 - Permalink

Efficent electroluminescence from Tb-implanted silicon metal-oxide-semiconductor devices
Sun, J. M.; Skorupa, W.; Dekorsy, T.; Helm, M.; Rebohle, L.; Gebel, T.;
Strong green electroluminescence with brightness up to 2800 cd/m2 was obtained from indium-tin-oxide/SiO2:Tb/Si metal-oxide-semiconductor devices. The SiO2:Tb gate oxide was prepared by thermal oxidation followed by Tb+ implantation and annealing. Electroluminescence and photoluminescence properties were studied with variations of the Tb3+ ion concentration and annealing temperatures. The optimized device has a high external quantum efficiency of 16 % and a luminous efficiency of 2.1 lm/W. The excitation process of electroluminescence can be attributed to the impact excitation of the Tb3+ luminescent centers by hot electrons and the subsequent cross-relaxation from the 5D3 to 5D4 levels. Light emitting devices with micrometer size were demonstrated by the complementary metal-oxide-semiconductor technology.
Keywords: electrolumnescence, silicon dioxide, Terbium, MOS
  • Lecture (others)
    E-MRS 2005 Spring Meeting May 31 – June 3, 2005 SYMPOSIUM C Rare earth doped photonic materials, C-V.03, 31.05.-3.6.2005, Strasbourg, France

Publ.-Id: 8149 - Permalink

Forschungszentrum Rossendorf "Status report of FZR activities" / Status of Cathode System in FZR
Teichert, J.; Xiang, R.;
kein Abstract vorhanden
  • Lecture (Conference)
    CARE Collaboration Meeting, 23.-25.11.2005, CERN, Switzerland

Publ.-Id: 8148 - Permalink

The Superconducting photoinjector at Rossendorf - Present status of the Rossendorf Superconducting RF Photo injector development
Teichert, J.;
kein Abstract vorhanden
  • Invited lecture (Conferences)
    CARE Collaboration Meeting, 23.-25.11.2005, CERN, Switzerland


Publ.-Id: 8147 - Permalink

Effect of Ion Energy on Structure and Composition of Cathodic Arc Deposited Alumina Thin Films
Rosen, J.; Mraz, S.; Kreissig, U.; Music, D.; Schneider, J. M.;
The effect of energy supplied to the growing alumina film on the composition and structure has been investigated by varying substrate temperature and substrate bias potential. The constitution and composition were studied by X-ray diffraction and elastic recoil detection analysis, respectively. Increasing the substrate bias potential from −50 to −100 V caused the amorphous or weakly crystalline films to evolve into stoichiometric, crystalline films with a mixture of the α- and γ-phase above 700 oC, and γ-phase dominated films at temperatures as low as 200 oC. All films had a grain size of <10 nm. The combined constitution and grain size data is consistent with previous work stating that γ-alumina is thermodynamically stable at grain sizes <12 nm [McHale et al., Science 277, 788 (1997)]. In order to correlate phase formation with synthesis conditions, the plasma chemistry and ion energy distributions were measured at synthesis conditions. These results indicate that for a substrate bias potential of −50 V, ion energies in excess of 100 eV are attained, both from a high energy tail and the accelerated ions with charge >1. These results are of importance for an increased understanding of the evolution of film composition and microstructure, also providing a pathway to γ-alumina growth at temperatures as low as 200 o C.
Keywords: Alumina; ion energy; plasma chemistry; composition; microstructure
  • Plasma Chemistry and Plasma Processing 25(2005)4, 303-317

Publ.-Id: 8146 - Permalink

Enhancement of the simulation of scaled vessel failure experiments by a recursive coupling of the thermal and mechanical FEM-models
Willschuetz, H.-G.;
For the simulation of experiments investigating the behavior of the lower head of a nuclear power station in case of a core meltdown scenario like FOREVER (performed at the Royal Institute of Technology, Stockholm) it is necessary to model the melt pool convection and the temperature field within the vessel as well as creep and plasticity processes. Therefore a 2D Finite Element Model with 3 different physics environments is developed based on the code ANSYS® Multiphysics.
A thermal environment was build up including planar and contact elements for conductive heat transfer, additional surface elements to simulate convection and radiation from outer surface areas and a radiation matrix to account for internal radiative heat exchange. Normally a CFD-simulation would have been required for the natural convective heat transfer in the melt pool, but at very high internal Rayleigh numbers no turbulence model is capable for a correct simulation. Therefore an Effective Conductivity Convectivity Model (ECCM) was developed to simulate the heat transfer from the melt pool to its environment.
The resulting temperature field of the vessel wall is applied to the mechanical model. To describe the visco-plastic deformation a numerical creep data base (CDB) is developed where the creep strain rate is evaluated in dependence on the current total strain, temperature and equivalent stress. In this way the use of a single creep law, which employs constants derived from the data for a limited stress and temperature range, is avoided. For an evaluation of the failure times a damage model according to an approach of Lemaitre is applied.
The third physics environment is a kind of fictitious physics environment: it uses hyperelasticity and contact to move the melt pool along with the creeping vessel wall.
In this paper problems on the numerical side are explained and differences between the results of a simple coupled and a kinematically coupled FE-simulation are highlighted. The final comparison with the experiments shows that the kinematically coupled model is closer to reality than the single step model.
Keywords: Fully Coupled Physics Environments, Effective Conductivity Convectivity Model, Creep and Plasticity of Pressure Vessel Steel
  • Contribution to proceedings
    International Youth Nuclear Congress, 18.-23.06.2006, Stockholm and Olkiluoto, Sveden and Suomi
    Proceedings on CD-ROM, paper 275
  • Lecture (Conference)
    International Youth Nuclear Congress, 18.-23.06.2006, Stockholm and Olkiluoto, Sveden and Suomi

Publ.-Id: 8145 - Permalink

Core design and transient analyses for weapons plutonium burning in VVER-1000 type reactors
Rohde, U.; Grundmann, U.; Kozmenkov, Y.; Pivovarov, V.; Matveev, Y.;
The presented core calculations are aimed at the demonstration of the feasibility of weapon-grade plutonium burning in VVER-1000 type reactors with emphasis on safety aspects of the problem. Particular objectives of weapon-grade Pu burning are the net burning of fissile Pu isotopes in general, but also the conversion of the Pu vector of the fuel from weapon-grade to reactor plutonium. Three different fuel-loading options have been considered - full UO2 loading, mixed UO2 and MOX loading and full MOX loading. All considered cases meet the requirements on nuclear safety and design limits related to both normal operation and accident conditions. Two reactivity initiated accidents have been analyzed, caused by the ejection of the operational control rod group during 0.1 s and unauthorized withdrawal of the same control rod group with operational speed. The analyses have been performed for the beginning and the end of the fuel cycle. The maximum reactor power peak of 1.79 of the nominal reactor power was observed for the 2nd fuel-loading option (mixed loading). However, it does not cause an overheating of fuel rods.
The performed simulations demonstrated that the code DYN3D can be used for analyses of reactivity-initiated accidents in VVER type reactors with various fuel designs.
Feasibility of the VVER-1000 type reactor for burning weapon-grade Pu and changing its isotopic composition has been demonstrated.
Keywords: mixed oxide fuel, MOX, weapon-grade plutonium, core design, plutonium burning, plutonium vector, reactivity initiated accidents, nuclear safety, VVER-type reactors
  • Invited lecture (Conferences)
    Stand der Entwicklung für LWR Brennelemente und Auslegungsmethoden, 02.-03.03.2006, Dresden, Germany
  • Contribution to proceedings
    KTG-Fachtag "Stand der Entwicklung für LWR Brennelemente und Auslegungsmethoden", 02.-03.03.2006, Dresden, Germany
    CD-ROM Proceedings p. 265

Publ.-Id: 8144 - Permalink

Development of an optical wire-mesh tomograph for the study of multi-phase flows.
Schleicher, E.; Hampel, U.; Da Silva, M. J.; Zschau, J.; Futterschneider, H.; Zimmermann, W.;
We introduce a novel optical wire-mesh tomograph for the investigation of multiphase flows. The sensor consists of an optical fibre matrix that covers the cross-section of a vessel or pipeline with fibres arranged in two distinct axial planes. Optical measurement is performed at the cross-points of the fibres where the cladding material is partially removed to enable light crossing from a fibre of the emitter plane to fibres of the receiver plane. A rapid optoelectronic processing unit enables the acquisition of cross-sectional images with frame rates above 10 kHz. We demonstrate the operation of the sensor for an oil-gas two-phase flow.
Keywords: optical fibre, wire-mesh tomograph, multiphase flow, oil-gas two-phase flow
  • Contribution to proceedings
    OPTO 2006, 30.05.-01.06.2006, Nürnberg, Germany
    Sensor+Test 2006, Proceedings, Wunstorf: AMA Service GmbH, 3-9810993-0-3, 115-119
  • Lecture (Conference)
    OPTO 2006, 31.05.2006, Nürnberg, Germany

Publ.-Id: 8142 - Permalink

Thermomechanische Modellierung eines Reaktordruckbehälters in der Spätphase eines Kernschmelzunfalls
Willschütz, H.-G.;
Considering the late in-vessel phase of an unlikely core melt down scenario in a light water reactor (LWR) with the formation of a corium pool in the lower head of the re-actor pressure vessel (RPV) the possible failure modes of the RPV and the time to failure have to be investigated to assess the possible loadings on the containment. In this work, an integral model was developed to describe the processes in the lower plenum of the RPV. Two principal model domains have to be distinguished: The temperature field within the melt and RPV is calculated with a thermodynamic model, while a mechanical model is used for the structural analysis of the vessel wall.
In the introducing chapters a description is given of the considered accident scenario and the relevant analytical, experimental, and numerical investigations are discussed which were performed worldwide during the last three decades. Following, the occur-ring physical phenomena are analysed and the scaling differences are evaluated between the FOREVER-experiments and a prototypical scenario.
The thermodynamic and the mechanical model can be coupled recursively to take into account the mutual influence. This approach not only allows to consider the tem-perature dependence of the material parameters and the thermally induced stress in the mechanical model, it also takes into account the response of the temperature field itself upon the changing vessel geometry.
New approaches are applied in this work for the simulation of creep and damage. Using a creep data base, the application of single creep laws could be avoided which is especially advantageous if large temperature, stress, and strain ranges have to be covered. Based on experimental investigations, the creep data base has been de-veloped for an RPV-steel and has been validated against creep tests with different scalings and geometries.
It can be stated, that the coupled model is able to exactly describe and predict the vessel deformation in the scaled integral FOREVER-tests. There are uncertainties concerning the time to failure which are related to inexactly known material parame-ters and boundary conditions.
The main results of this work can be summarised as follows: Due to the thermody-namic behaviour of the large melt pool with internal heat sources, the upper third of the lower RPV head is exposed to the highest thermo-mechanical loads. This region is called hot focus. Contrary to that, the pole part of the lower head has a higher strength and therefore relocates almost vertically downwards under the combined thermal, weight and internal pressure load of the RPV.
On the one hand, it will be possible by external flooding to retain the corium within the RPV even at increased pressures and even in reactors with high power (as e.g. KONVOI). On the other hand, there is no chance for melt retention in the considered scenario if neither internal nor external flooding of the RPV can be achieved.
Two patents have been derived from the gained insights. Both are related to pas-sively working devices for accident mitigation: The first one is a support of the RPV lower head pole part. It reduces the maximum mechanical load in the highly stressed area of the hot focus. In this way, it can prevent failure or at least extend the time to failure of the vessel. The second device implements a passive accident mitigation measure by making use of the downward movement of the lower head. Through this, a valve or a flap can be opened to flood the reactor pit with water from a storage res-ervoir located at a higher position in the reactor building.
With regard to future plant designs it can be stated - differing from former presump-tions - that an In-Vessel-Retention (IVR) of a molten core is possible within the reac-tor pressure vessel even for reactors with higher power.
Keywords: Light Water Reactor, severe accident with core melt down, In-Vessel-Retention, recoursively coupled thermal and mechanical simulation, scaled experiments and prototypic scenario
  • Open Access LogoWissenschaftlich-Technische Berichte / Forschungszentrum Rossendorf; FZR-447 2006


Publ.-Id: 8141 - Permalink

Structural and magnetic modifications in Cr implanted Permalloy
Fassbender, J.ORC; von Borany, J.; Mücklich, A.; Potzger, K.; Möller, W.; McCord, J.; Schultz, L.; Mattheis, R.
The static and dynamic magnetic properties, especially the magnetic damping behavior, have been investigated as a function of saturation magnetization in thin Permalloy films. Ion implantation doping with Cr in the percentage regime has been used to effectively reduce the Curie temperature and thus the saturation magnetization at room temperature. In order to understand the magnetic modifications the changes in stoichiometry but also the ion induced structural changes have been addressed. As a function of fluence first an improvement of the (111) fiber texture, then a lattice expansion and finally a partial amorphization of the interface near region of the Permalloy layer is found. The region of amorphization can be understood quantitatively by the concentration profiles as a function of depth in combination with irradiation induced damage formation. The magnetic properties change correspondingly. For increasing Cr doping a drop in saturation magnetization and a decrease of the uniaxial magnetic anisotropy is observed. For a fluence of 0.8 x 10^16 Cr/cm^2 (4 at.%) the magnetic damping parameter  increases by a factor of 7. This strong increase is mainly caused by the reduction of the saturation magnetization and the altered sample morphology.
Keywords: magnetism, ion implantation, doping, Curie temperature, saturation magnetization, magnetic anisotropy, magnetic damping, amorphization, TRIDYN

Publ.-Id: 8140 - Permalink

Systematics of magnetic dipole strength in the stable even-mass Mo isotopes
Rusev, G.; Schwengner, R.; Dönau, F.; Erhard, M.; Frauendorf, S.; Grosse, E.; Junghans, A. R.; Käubler, L.; Kosev, K.; Kostov, L.; Mallion, S.; Schilling, K. D.; Wagner, A.; von Garrel, H.; Kneissl, U.; Kohstall, C.; Kreutz, M.; Pitz, H. H.; Scheck, M.; Stedile, F.; von Brentano, P.; Jolie, J.; Linnemann, A.; Pietralla, N.; Werner, V.;
The nuclides 92Mo, 98Mo and 100Mo have been studied in photon-scattering experiments by using bremsstrahlung. Dipole and quadrupole excitations in 92Mo were investigated in photon-scattering experiments at an electron energy of 6 MeV at the ELBE accelerator of the Forschungszentrum Rossendorf. Photon-scattering experiments on 98Mo and 100Mo were carried out at the Dynamitron accelerator of the Stuttgart University at electron energies from 3.2 to 3.8 MeV. Six dipole transitions in 98Mo and 19 in 100Mo were observed for the first time in the energy range from 2 to 4 MeV. Systematics of the magnetic dipole strength in the isotopic chain of the even-mass isotopes from 92Mo to 100Mo are discussed. The experimental results are compared with predictions of the shell model and with predictions of the quasiparticle-random-phase approximation in a deformed basis. The latter show significant contributions of isovector-orbital and isovector-spin vibrations.
Keywords: Photon scattering. Nuclear structure. Nuclear spectroscopy. Random phase approximation. Shell model.

Publ.-Id: 8139 - Permalink

Effect of crystal orientation on self-assembled silicon nanostructures formed by electron beam annealing
Johnson, S.; Markwitz, A.; Rudolphi, M.; Baumann, H.; Kuo, P.-Y.; Blaikie, R.; Mücklich, A.;
This paper discusses the growth of silicon nanostructures on silicon (100), (110) and (111) substrates by electron beam annealing. The nanofabrication procedure involves annealing of the untreated Si substrates at 1100°C for 15 s using a raster scanned 20 keV electron beam. Nanostructuring occurs as a result of kinetic amplification of the surface disorder induced by thermal decomposition of the native oxide. Pyramidal and truncated pyramidal nanocrystals were observed on Si(100) surface. The nanostructures are randomly distributed over the entire surface and square-based, reflecting the two-fold symmetry of the substrate surface. Similar square-based pyramidal structures with four equivalent facets are observed following nanostructuring of Si(110). With Si(111), nanostructure growth occurs preferentially along step-edges formed on the vicinal surface. Significant differences in nanostructure shapes formed on step-edges and terraces are related to the different growth mechanisms on the unreconstructed and 7x7 reconstructed domains respectively.
  • Journal of Applied Physics 97(2005), 94301

Publ.-Id: 8138 - Permalink

Formation of SiC-surface nanocrystals by ion implantation and electron beam rapid thermal annealing
Markwitz, A.; Johnson, S.; Rudolphi, M.; Baumann, H.; Mücklich, A.;
SiC-surface nanostructures on silicon were produced by 10 keV carbon ion implantation into silicon followed by annealing to 1000°C for 15 s under high-vacuum conditions using a raster-scanned electron beam. Following implantation, an amorphous layer is produced which starts at the surface and extends 65 nm into the substrate. Following annealing, the implanted surface layer remains amorphous but becomes covered with semi-spherical crystalline features up to 300 nm in diameter. The nanocrystals have been confirmed to be SiC which, following nucleation, grow as a result of C and Si diffusion across the oxide free substrate surface during annealing.
  • Applied Physics Letters 86(2005), 013108-1

Publ.-Id: 8137 - Permalink

Defects in virgin and N+ ion-implanted ZnO single crystals studied by positron annihilation, Hall effect and deep level transient spectroscopy
Brauer, G.; Anwand, W.; Skorupa, W.; Kuriplach, J.; Melikhova, O.; Moisson, C.; von Wenckstern, H.; Schmidt, H.; Lorenz, M.; Grundmann, M.;
High quality single crystals of ZnO in the as-grown and N+ ion-implanted states have been investigated using a combination of three experimental techniques - namely, positron lifetime/slow positron implantation spectroscopy accompanied by theoretical calculations of the positron lifetime for selected defects, temperature-dependent Hall (TDH) measurements and deep level transient spectroscopy (DLTS). The positron lifetime in bulk ZnO is measured to be (151 + 2) ps and that for positrons trapped in defects (257 + 2) ps. On the basis of theoretical calculations the latter is attributed to Zn+O divacancies, existing in the sample in both neutral and single negative charge states, and not to the Zn vacancy proposed in previous experimental work. From TDH measurements the concentrations of negatively-charged and neutral Zn+O divacancies are estimated to lie between 4 × 1015 and 6.3 × 1016 cm-3. DLTS revealed the creation of the defect E1 and an increase in concentration of the defect E3 after N+ ion implantation. Furthermore, a p-conducting layer is formed at the surface after the implantation/annealing procedure that can be used to inject holes during a DLTS measurement. In this way, the acceptor traps A2 and A3 with thermal activation energies of about 150 and 280 meV, respectively, have been detected for the first time by DLTS.
Keywords: zinc oxide, point defects, positron annihilation, N+ implantation, electron traps, acceptor traps, hole injection, Hall effect, DLTS, p-conducting ZnO
  • Physical Review B 74(2006), 045208

Publ.-Id: 8136 - Permalink

Fluid-structure interaction during artificially induced water hammers in a tube with bend – experiments and analyses
Altstadt, E.; Carl, H.; Prasser, H. M.; Weiß, R.;
Experimental and numerical investigations of artificial water hammers in a pipe with a bend are presented. At FZR a cold water hammer test facility was used to measure the fluid pressures and the pipe wall stresses occurring during water hammers. The finite element code ANSYS® was used for the numerical analysis of the experiments. The focus was put on the local distributions of pressure and stress. It could be shown that the fluid pressure and pipe wall stress exhibit complex 3-dimensional structures, which is a consequence of the fluid-structure interaction. The highest stresses occur in the pipe bend. The pressure peak is lower than predicted by the extended Joukowsky formula.
Keywords: Fluid-structure interaction, water hammer, Finite element method

Publ.-Id: 8135 - Permalink

Wechselwirkung zwischen Corium und Reaktordruckbehälter - Experimente, Versagensmodus, Versagenszeitpunkt
Willschütz, H.-G.; Alstadt, E.; Weiß, F.-P.;
In-Vessel-Retention, betrachtetes Stadium, Debrisbett in der Bodenkalotte: Kühlbarkeit/Nichtkühlbarkeit (IKE-Arbeiten), mögliche Schmelzekonfigurationen, Fragestellungen.
Übersicht der Experimente: mechanisches Werkstoffverhalten, Wärmeübergang vom Schmelzepool, Materialwechselwirkung zwischen Corium und Stahlwand, integrale Experimente.
Versagensarten: thermisches Versagen, thermomechanisches Versagen, Versagensort und –form, Auswirkung auf Schmelzeaustrag.
Analysetools: bekannte Modelle, Vorgehensweise im FZR.
Versagenszeitpunkt / mögliche Gegenmaßnahmen
Ausblick: aktuelles Projekt BMWA Nr. 150 1279, weiterführende Fragestellungen.
Keywords: Nuclear Power Plant, Severe accident with core meltdown, Interaction between corium and reactor pressure vessel wall, investigation of failure modes
  • Invited lecture (Conferences)
    Workshop: Corium - Eigenschaften, Wechselwirkungen und Beherrschungskonzepte, 09.-10.02.2006, Köln, Germany
  • Contribution to proceedings
    Workshop: Corium - Eigenschaften, Wechselwirkungen und Beherrschungskonzepte, 09.-10.02.2006, Köln, Germany
    Proceedings on CD-ROM, Paper P03

Publ.-Id: 8134 - Permalink

Annealing of indium tin oxide films by electric current: properties and structure evolution
Rogozin, A.; Shevchenko, N.; Vinnichenko, M.; Seidel, M.; Kolitsch, A.; Möller, W.;
As a new method of indium tin oxide (ITO) annealing in vacuum, direct electric current flow through the film is proposed. ITO films of about 170 nm thickness were produced by reactive pulsed magnetron sputtering. During annealing at constant electric power, the film resistance, free electron density and structure evolution were monitored in situ. Compared to conventional isothermal annealing, the current annealing is more efficient with a noticeable reduction of the thermal budget and a decrease of the kinetic exponent of the crystallization. Electrical inhomogeneities of the film, which produce locally overheated regions, are discussed as potential reason for the acceleration of the crystallization process.
Keywords: indium tin oxide, annealing by electric current, reactive pulsed magnetron sputtering, in situ x-ray diffraction, in situ spectroscopic ellipsometry, activation energy, resistivity, optical properties
  • Applied Physics Letters 89(2006)6, 061908

Publ.-Id: 8133 - Permalink

Experimental study of interactions between suboxidized corium and reactor vessel steel
Bechta, S. V.; Khabensky, V. B.; Granovsky, V. S.; Krushinov, E. V.; Vitol, S. A.; Gusarov, V. V.; Almiashev, V. I.; Lopukh, D. B.; Tromm, W.; Bottomley, D.; Fischer, M.; Piluso, P.; Miassoedov, A.; Altstadt, E.; Willschütz, H.-G.; Fichot, F.;
One of the critical factors in the analysis of in-vessel melt retention is the vessel strength. It is, in particular, sensitive to the thickness of intact vessel wall, which, in its turn, depends on the thermal conditions and physicochemical interactions with corium.
Physicochemical interaction of prototypic UO2-ZrO2-Zr corium melt and VVER vessel steel was examined during the 2nd Phase of the ISTC METCOR Project. Rasplav-3 test facility was used for conducting four tests, in which the Zr oxidation degree and interaction front temperature were varied; in one of the tests, stainless steel was added to the melt.
Direct experimental measurements and posttest analyses were used for determining corrosion kinetics and maximum corrosion depth (i.e. the physicochemical impact of corium on the cooled vessel steel specimens), as well as the steel temperature conditions during the interaction, and finally the structure and composition of crystallized ingots, including the interaction zone. The minimum temperature on the interaction front boundary, which determined its final position and maximum corrosion depth was ~1090°С. An empirical correlation for calculation of corrosion kinetics has been derived.
Keywords: Corium-steel interaction, physicochemical properties, in vessel melt retention, reactor pressure vessel
  • Contribution to proceedings
    International Congress on Advances in Nuclear Power Plants (ICAPP) 2006, 04.-08.06.2006, Reno, United States
    Proceedings on CD-ROM, paper 6054, 1355-1362

Publ.-Id: 8132 - Permalink

Materialforschung für sichere Kernkraftwerke
Altstadt, E.;
Es wird ein Überblick zu den Aspekten der Materialsicherheit in der Kerntechnik gegeben. Im Mittekpunkt der Betrachtungen steht der Reaktordruckbehälter von Leichtwasserreaktoren. Im FRZ angwendete Methoden zur Mikrostrukturanalyse und zur Bruchmechanik werden erläutert.
Keywords: Reactor pressure vessel, Material Safety, Small Angle Neutron Scattering, Fracture Mechanics
  • Lecture (others)
    Ringvorlesung des Materialforschungsverbundes Dresden für das Studium generale der Technische Universität Dresden, 25.01.2006, Dresden, Germany

Publ.-Id: 8131 - Permalink

Aufbau eines Versuchsplatzes für die Positronen-Emissions-Tomographie
Würschig, T.;
Die Positronen-Emissions-Tomographie (PET) hat sich als bildgebendes Verfahren in der klinischen Routine sowie der medizinischen, biologischen und pharmazeutischen Forschung etabliert.
Daraus ergibt sich die Notwendigkeit, Mediziner sowie Physiker und Ingenieure mit der speziellen Ausrichtung auf multidisziplinäre Forschungsgebiete der Biologie und Medizin bzw. medizintechnischen Anwendungen im Rahmen ihrer Ausbildung möglichst praxisnah mit dieser Technik vertraut zu machen. Zu diesem Zweck soll ein Versuchsplatz für die PET aufgebaut werden, an welchem die allgemeinen Prinzipien der Computertomographie (CT), die Grundlagen der PET sowie die PET als kernphysikalisches Multiparameter-Messverfahren vermittelt werden. Für die Realisierung dieser Aufgabenstellung gibt es folgende Vorgaben:

- Der Tomograph besteht aus zwei kommerziellen, in Koinzidenz betriebenen, ortsempfindlichen Szintillationsdetektoren.
- Zum Gewinnen vollständiger Projektionsdatensätze wird ein Computer gesteuertes Bewegungssystem für die Translation und die Rotation verwendet.
- Die Signalverarbeitung basiert auf Standardmodulen der kernphysikalischen Messtechnik.
- Zur Gewährleistung einer flexiblen, den unterschiedlichen Anforderungen genügenden Auswertung erfolgt die Speicherung der Daten im Listen-Modus.
- Die tomographische Rekonstruktion mittels gefilterter Rückprojektion ist in die laufende Messung (Online-Betrieb) integriert. Daneben besteht
die Möglichkeit, die Daten auch nach der Messung in unterschiedlichen Konfigurationen zu rekonstruieren (Offline-Betrieb).

Diese Diplomarbeit soll zudem als Grundlage für das zu erstellende Lehrmaterial fungieren. Dabei wird zuerst auf die Anwendung und Entwicklung der PET eingegangen (Abschnitt 1.1). Im zweiten Kapitel werden die für die PET notwendigen Grundbegriffe erklärt sowie die physikalischen und mathematischen Prinzipien und Wirkungsweisen dargestellt. Daran anschließend wird im dritten Kapitel der Aufbau des PET-Versuchsplatzes beschrieben, wobei auch näher auf die einzelnen ausgewählten Komponenten eingegangen wird. Im vierten Kapitel werden systemspezifische Größen für den Versuchsplatz hergeleitet. Darauf folgend wird in Kapitel 5 die Software detaillierter vorgestellt. Die Ergebnisse der durchgeführten Messungen sind im sechsten Kapitel zu finden. Dabei handelt es sich sowohl um Messungen zur Charakterisierung des Messplatzes als auch um vollständige tomographische Rekonstruktionen von Punktquellen. Abschließend werden die Besonderheiten und Merkmale des aufgebauten Tomographen nochmals zusammengefasst sowie ein Ausblick gegeben (Kapitel 7).
  • Open Access LogoWissenschaftlich-Technische Berichte / Forschungszentrum Rossendorf; FZR-445 2006
  • Lecture (Conference)
    DPG Frühjahrstagung, 13.-15.03.2006, Heidelberg, Deutschland


Publ.-Id: 8130 - Permalink

Ion beam synthesis of Fe nanoparticles in MgO and YSZ
Potzger, K.; Reuther, H.; Zhou, S.; Mücklich, A.; Grötzschel, R.; Eichhorn, F.; Liedke, M.; Fassbender, J.ORC; Lichte, H.; Lenk, A.
In order to prepare epitaxially oriented Fe nanoparticles embedded below the surface of an oxide single crystalline host material the method of ion beam synthesis has been explored for MgO(001) and YSZ(001). At a fixed implantation energy and fluence the implantation temperature has been varied between *room temperature* and 1273 K. It was found, that for MgO substrates the fraction of metallic Fe increases up to a maximum of 60% (at 1073 K) as a function of implantation temperature, whilst the Fe depth profile remains the same. The Fe nanoparticles are nonmagnetic at room temperature exhibiting fcc structure. They show a mean diameter of 5 nm and an exclusive orientation relationship to the host. In YSZ the fraction of metallic Fe increases with increasing implantation temperature reaching 100% at 1273 K. However, the nanoparticles formed are of bcc structure with a mean diameter of 13 nm located mainly close to the sample surface. The ferromagnetic behavior is reflected by a magnetic hyperfine field of 330 kOe and a hysteretic magnetization reversal. Electron holography measurements have been carried out in order to visualize the stray field of the particles.
Keywords: MgO YSZ magnetic nanoparticles ion beam synthesis mossbauer spectroscopy
  • Lecture (Conference)
    Frühjahrstagung des Arbeitskreises Festkörperphysik zusammen mit der Condensed Matter Division der EPS (DPG-Tagung), 26.-31.03.06, Dresden, Deutschland

Publ.-Id: 8129 - Permalink

Fe doped ZnO – a diluted magnetic semiconductor?
Potzger, K.; Zhou, S.; Reuther, H.; Mücklich, A.; Eichhorn, F.; Talut, G.; Herrmannsdörfer, T.; Bianchi, A.; Fassbender, J.ORC
The fabrication of diluted magnetic semiconductors (DMS) by transition-metal (TM) doping of ZnO has attracted tremendous interest within the last 3 years. However, there are still vivid discussions if the ferromagnetic state stems from Zener-interaction between diluted TM ions or from magnetic secondary phases. In order to prove or exclude the possible formation of TM-secondary phases in ZnO we have investigated iron doping, since Fe-ZnO (n-type) DMS are theoretically predicted to exhibit ferromagnetism [1].
For these investigations Fe-ions have been implanted with an ion energy of 180 keV (projected range Rp=80 nm) at 250 K and 620 K into ZnO single crystals. Two fluences of either 0.4 or 4x1016 ions per cm2 were chosen which correspond to 0.5 and 5 at%, respectively. The samples were characterized by CEMS (conversion electron Mössbauer spectroscopy), XRD (X-ray diffraction) using synchrotron radiation, RBS (Rutherford back scattering), TEM (transmission electron microscopy) and SQUID (superconducting quantum interference device) magnetometry.
For the as implanted sample a high solubility of Fe was found. The ionic states are 2+ and 3+ but none of the ionic fractions could be clearly determined to occupy substitutional lattice sites. The sample implanted at high fluence and 620 K exhibits ferromagnetic behavior at room temperature as was observed by CEMS and SQUID. However, CEMS and XRD measurements confirm that the origin of the ferromagnetic behavior is due to Fe-nanocluster formation. These nanoclusters show the magnetic moment and hyperfine field of metallic bcc-Fe. For samples implanted at 250 K and a low fluence also a ferromagnetic behavior could be detected at room temperature. No secondary phase formation occurs suggesting the formation of a diluted magnetic semiconductor (DMS)

[1] K. Sato, H. Katayama-Yoshida, Jpn. J. Appl. Phys. 40, L334 (2001)
Keywords: Diluted magnetic semiconductors Ion beam doping ZnO
  • Lecture (Conference)
    364. Heraeus Workshop on Nanoscale Magnets - Top-Down meets Bottom-Up, 04.-06.01.2006, Bad Honnef, Deutschland

Publ.-Id: 8128 - Permalink

Control of magnetic damping by means of Ni implantation in thin Ni81Fe19 layers
Fassbender, J.ORC; McCord, J.
The static and dynamic magnetic properties of 20 nm thick Ni81Fe19 films have been investigated as a function of Ni ion fluence up to 1x10^16 Ni/cm^2 (5 atom-%). The implantation has been performed at 30 keV in order to implant the Ni ions in the center of the ferromagnetic layer and to achieve a rather homogeneous energy distribution throughout the film. With increasing ion fluence the saturation magnetization and the effective magnetic anisotropies (static and dynamic) are reduced by about 80%. However, the effective magnetic damping is drastically enhanced for higher ion fluences. Starting at a pure permalloy value of alpha= 0.008 a 7-fold increase to alpha= 0.058 is found for a fluence of 0.8x10^16 Ni/cm^2. This increase can be explained mainly by the drop in saturation magnetization in connection with structural changes. In addition ion implantation in an applied magnetic field allows the setting of the uniaxial anisotropy direction irrespective of the initial orientation for fluences as low as 5x10^13 Ni/cm^2.
Keywords: magnetism, ion implantation, magnetization dynamics, magnetic damping, permalloy, anisotropy
  • Poster
    Joint European Magnetics Symposium, 26.-30.06.2006, San Sebastian, Spanien

Publ.-Id: 8124 - Permalink

Exchange bias on rippled substrates
Liedke, M. O.; Rossbach, S.; Facsko, S.; Hillebrands, B.; Fassbender, J.ORC
The interface between ferromagnet (FM) and antiferromagnet (AFM) plays a crucial role for the exchange bias phenomenon. This is mainly because monoatomic steps, islands or point defects give rise to uncompensated spins at the interface which serve as the origin of exchange bias. The number of monoatomic steps and thus the magnitude of the induced uniaxial anisotropy can easily be varied by means of Ar+ ion erosion. Depending on the primary energy and the angle of incidence a rippled surface with a well defined periodicity (20 – 100 nm) and peak to valley height (2 – 5 nm) can be created. On top of this surface the exchange bias system 5 nm Ni81Fe19 coupled to 10 nm Fe50Mn50 has been prepared. The interface corrugation remained throughout the whole layer stack. By means of a field annealing cycle the exchange bias direction has been initialized either along or perpendicular to the ripple direction, which causes to align the uniaxial and unidirectional anisotropy contributions either parallel or perpendicular to each other. For both cases the magnetic easy- and hard-axes remain the same because the uniaxial anisotropy contribution is much larger than the unidirectional one. However, if the exchange bias is initialized along (perpendicular to) the ripple direction the easy-axis (hard-axis) magnetization reversal loop is shifted. In order to evaluate this behavior in more detail a complete angular dependency of the magnetization reversal behavior has been investigated in both cases and compared to simulations based on a Stoner-Wohlfarth coherent rotation model. A good agreement between experimental data and simulations is found.
M. O. L. acknowledges the financial support from the European Communities Human Potential Program NEXBIAS under Contract No. HPRN-CT2002-00296.
Keywords: magnetism, exchange bias, magnetic anisotropy, ion erosion, ripples
  • Poster
    3rd Joint European Magnetic Symposia, 26.-30.06.2006, San Sebastian, Spanien
  • Poster
    International Colloquium on Magnetic Films and Surfaces, 14.-18.08.2006, Sendai, Japan
  • Poster
    Workshop on Properties of ultrathin magnetic films, 06.-09.09.2006, Bialowieza, Polen

Publ.-Id: 8123 - Permalink

Exchange bias on rippled substrates – step induced uniaxial versus unidirectional anisotropy
Liedke, M. O.; Rossbach, S.; Facsko, S.; Hillebrands, B.; Fassbender, J.ORC
Ripples with a periodicity of 35 nm and a height of 2 nm were formed on a Si(001) substrate
by means of Ar+ ion erosion. The primary energy was 500 eV and the angle of incidence 70° with respect to the surface normal. One of the main characteristics of such a surface is the large step density which is usually only achieved for vicinal miscut substrates. After ripple preparation a 0.5 nm Pt buffer layer and a 5 nm Permalloy (Ni81Fe19) ferromagnetic layer were deposited by means of molecular beam epitaxy. In order to allow for an easy comparison between ferromagnetic layer and exchange biased system on half of the sample a 10 nm Fe50Mn50 antiferromagnetic layer was deposited. Then the whole sample was covered by a 2 nm Cr protection layer. Additional AFM images confirmed that the ripple structure remains throughout the whole layer system.

The magnetization reversal behavior of the ferromagnetic layer and the exchange bias system was then investigated by means of magneto-optic Kerr effect (MOKE). The Permalloy layer itself exhibits already a uniaxial anisotropy of Ku = 3.74×104 erg/cm3 which was determined from the saturation field HS of the hard-axis magnetization reversal curve. This value is already about 20 times larger than the uniaxial anisotropy observed in Permalloy films deposited on flat substrates. Since no field annealing has been performed only a strongly enhanced coercivity with respect to the Permalloy film is found. This is due to the coupling of the ferromagnetic layer to the antiferromagnetic layer. Two additional field annealing procedures have then been performed in order to set the exchange bias direction either along or perpendicular to the ripple direction. Since the uniaxial anisotropy contribution is much larger than the unidirectional one the easy- and hard-axes remain the same. However, if the exchange bias is set along the ripple direction a shift of the easy-axis loop is found. In contrast, if the exchange bias field is set perpendicular to the ripple direction the hard-axis loop is shifted. In order to evaluate this behavior in more detail a complete angular dependency of the magnetization reversal behavior has been investigated in both cases and compared to simulations based on a Stoner-Wohlfarth coherent rotation model. A good agreement between experimental data and simulations is found.
Keywords: magnetism, exchange bias, ripples, magnetic anisotropy, ripple formation, ion erosion
  • Lecture (Conference)
    International Magnetics Conference, Intermag 2006, 08.-12.05.2006, San Diego, USA

Publ.-Id: 8122 - Permalink

EXAFS investigation of U(VI) and U(IV) aquo chloro complexes with a newly developed spectro-electrochemical cell
Hennig, C.; Tutschku, J.; Rossberg, A.; Bernhard, G.; Scheinost, A.;
The coordination of the U(IV) and U(VI) ions as a function of the chloride concentration in aqueous solution has been studied by U LIII-edge extended X-ray absorption fine structure (EXAFS) spectroscopy. The oxidation state of uranium was changed in situ using a gas-tight spectro-electrochemical cell, specifically designed for the safe use with radioactive solutions. For U(VI) we observed the complexes UO2(H2O)52+, UO2(H2O)4Cl+, UO2(H2O)3Cl20 and UO2(H2O)2Cl3 with [Cl] increasing from 0 to 9 M, and for U(IV) the complexes U(H2O)94+, U(H2O)8Cl3+, U(H2O)6-7Cl22+ and U(H2O)5Cl3+. The distances in the U(VI) coordination sphere are U-Oax = 1.760.02 Å, Oeq = 2.410.02 Å and U-Cl = 2.710.02 Å, the distances in the U(IV) coordination sphere are U-O = 2.410.02 Å and U-Cl = 2.710.02 Å.
Keywords: EXAFS, aquo chloro complexes, uranium, U(VI), U(IV), spectro-electrochemistry
  • Poster
    ESRF Users' Meeting 2006, 07.-8.2.2006, Grenoble, France

Publ.-Id: 8121 - Permalink

Comparison of complexed species of Eu in Alumina-bound and free Polyacrylic Acid. A spectroscopic study.
Montavon, G.; Hennig, C.; Janvier, P.; Grambow, B.;
The speciation of Eu complexed with polyacrylic acid (PAA) and alumina-bound PAA
(PAAads) was studied at pH=5 in 0.1M NaClO4. Structural parameters were obtained from 7F0→5D0 excitation spectra measured by Laser Induced Fluoresence ectroscopy as well as from Eu LIII edge Extended X-ray Absorption Fine Structure (EXAFS) spectra. The mode of coordination was also investigated by Infra Red pectroscopy. To elucidate the nature of the complexed species, Eu-acetate complexes were used as references. The spectroscopic techniques show that two carboxylate groups with 2-3 (EuPAA) and 4-5 (EuPAAads) hydration water molecules are coordinated to Eu in the first coordination sphere. For EuPAAads, the coordination between carboxylate groups and Eu appears to be bidendate. A similar coordination is probable for EuPAA but the EXAFS data indicate a sligthly distorted coordination. The results show that the degree of freedom of carboxylate groups is not the same for free or adsorbed PAA. For PAA, the degree of freedom is constrained by the flexibility of the methylene chain. When PAA is adsorbed on alumina, the polymer chains cannot any more be treated as independent chains. One may rather assume formation of aggregates that form an organic layer at the mineral surface presenting a complex arrangement of carboxylate groups.
Keywords: polyacrylic acid; Eu; spectroscopic study; speciation; adsorption; ternary system
  • Journal of Colloid and Interface Science 300(2006), 482-490

Publ.-Id: 8120 - Permalink

Structure investigation of uranium in aqueous solution under reduced conditions
Hennig, C.;
The presentation refers to the application of a spectroelectrochemical cell for X-ray absorption spectroscopy to structure investigations under reduced conditions. The spectro-electrochemical cell will be used at the Rossendorf Beamline in Grenoble/France.
Keywords: Actinides, XAFS, Rossendorf beamline
  • Invited lecture (Conferences)
    Research Reactor Institute, Kyoto University, 19.01.2006, Kyoto, Japan

Publ.-Id: 8119 - Permalink

X-ray absorption spectroscopy as tool for speciation and structure analysis of actinides in solution
Hennig, C.;
The contribution comprises an introduction in X-ray absorption spectroscopy and several typical examples of speciation and structure analysis. XAFS sectroscopy is a appropriate method to study structure sequences of solution species.
Keywords: XAFS, actinides, ROBL beamline
  • Invited lecture (Conferences)
    Research Laboratory for Nuclear Reactors, Tokyo Institute of Technology, 17.01.2006, Tokyo, Japan

Publ.-Id: 8118 - Permalink

Entwicklung eines 3D Neutronentransportcodes auf der Basis der Ray-Tracing-Methode und Untersuchungen zur Aufbereitung effektiver Gruppenquerschnitte für heterogene LWR-Zellen
Beckert, C.; Rohde, U.;
Standardmäßig erfolgt die Datenaufbereitung der Neutronenwirkungsquerschnitte für Reaktorkernrechnungen mit 2D-Zellcodes. Ziel dieser Arbeit war es, einen 3D-Zellcode zu entwickeln, mit diesem Code 3D-Effekte zu untersuchen und die Notwendigkeit einer 3D-Datenaufbereitung der Neutronenwirkungsquerschnitte zu bewerten. Zur Berechnung des Neutronentransports wurde die Methode der Erststoßwahrscheinlichkeiten, die mit der Ray-Tracing-Methode berechnet werden, gewählt. Die mathematischen Algorithmen wurden in den 2D/3D-Zellcode TransRay umgesetzt. Für den Geometrieteil des Programms wurde das Geometriemodul eines Monte-Carlo-Codes genutzt. Das Ray-Tracing wurde auf Grund der hohen Rechenzeiten parallelisiert. Das Programm TransRay wurde an 2D-Testaufgaben verifiziert.
Für einen Druckwasser-Referenzreaktor wurden folgende 3D-Probleme untersucht: Ein teilweise eingetauchter Regelstab und Void (bzw. Moderator mit geringerer Dichte) um einen Brennstab als Modell einer Dampfblase. Alle Probleme wurden zum Vergleich auch mit den Programmen HELIOS (2D) und MCNP (3D) nachgerechnet. Die Abhängigkeit des Multiplikationsfaktors und der gemittelten Zweigruppenquerschnitte von der Eintauchtiefe des Regelstabes bzw. von der Höhe der Dampfblase wurden untersucht. Die 3D berechneten Zweigruppenquerschnitte wurden mit drei üblichen Näherungen verglichen: linearer Interpolation, Interpolation mit Flusswichtung und Homogenisierung. Am 3D-Problem des Regelstabes zeigte sich, dass die Interpolation mit Flusswichtung eine gute Näherung ist. Demnach ist hier eine 3D-Datenaufbereitung nicht notwendig. Beim Testfall des einzelnen Brennstabs, der von Void (bzw. Moderator geringerer Dichte) umgeben ist, erwiesen sich die drei Näherungen für die Zweigruppenquerschnitte als unzureichend. Demnach ist eine 3D-Datenaufbereitung notwendig. Die einzelne Brennstabzelle mit Void kann als der Grenzfall eines Reaktors angesehen werden, in dem sich eine Phasengrenzfläche herausgebildet hat.
Keywords: Reactor physics, calculational methods, neutron transport, transport methods, Monte Carlo method, ray tracing, cross sections, cell calculation, absorber rod, void
  • Open Access LogoWissenschaftlich-Technische Berichte / Forschungszentrum Rossendorf; FZR-446 2006


Publ.-Id: 8117 - Permalink

Annealing of the indium tin oxide films with an electrical current
Rogozin, A.; Shevchenko, N.; Vinnichenko, M.; Seidel, M.; Kolitsch, A.; Möller, W.;
Indium tin oxide (ITO) films were grown by reactive middle frequency magnetron sputtering. Postdeposition annealing of transparent and conductive ITO films was performed with an electrical current in vacuum and air. The electrical power released by the current into the film during annealing was maintained at a constant level. The film structure and properties were characterized in situ by synchrotron produced X-ray diffraction, spectroscopic ellipsometry and resistance measurements.
The XRD data demonstrate transformation of the as-deposited amorphous film structure in to
crystalline during annealing. The films annealed in vacuum show two-stage decrease in the film resistance: first in amorphous state and second during crystallization. Increasing the electrical power of annealing hastens the onset of the second stage and reduces its total time. Resistance of the films annealed in air have three-stage behaviour: the resistance decreases at the beginning, then it starts to increase and finally, it decreases again. The experimental results are discussed in the terms of oxygen vacancy generation and tin donor activation.
Comparison of these results with data obtained during annealing of the indium oxide film without tin doping demonstrates significance of tin donor activation on the film resistance during crystallization process.
The mass analysis of the gas fractions escaping the ITO film during subsequent annealing in vacuum of the samples annealed already in air and vacuum was carried out. It is established that the samples annealed in air contain approximately one order of magnitude higher amount of water in comparison to the samples annealed in vacuum. This result shows that the water absorption deteriorates the improvement of the film resistance during annealing in air.
Keywords: ITO, annealing, electric current, film resistivity
  • Poster
    13th International Congress on Thin Films; 8th International Conference on Atomically Controlled Surfaces, Interfaces and Nanostructures, 19.-23.06.2005, Stockholm, Sweden

Publ.-Id: 8116 - Permalink

Mass dependence of nuclear isotopic temperature for binary and ternary fission.
Andronenko, M. N.; Andronenko, L. N.; Neubert, W.;
Method of Temperature Distributions based on isotope thermometers has been suggested and applied to determine nuclear temperatures related to spontaneous and neutron induced fission process. Binary and ternary fission modes show a pronounced difference for the mean temperature. Target mass dependence of nuclear temperatures is in agreement for both modes of fission process but in contradiction to one for high energy fragmentation.
Keywords: will be included
  • Other report
    Gatchina, Russia: Preprint St. Petersburg Nuclear Physics Institute, PN PI - 2643, 2005
    21 Seiten

Publ.-Id: 8115 - Permalink

Improved Monte Carlo Methods with Application to Borehole Logging Simulations
Legrady, D.;
Monte Carlo simulation is the most accurate method in general for nuclear particle transport calculations. The convergence properties are, however, often outstandingly poor. The efficiency can be enhanced by replacing the simulation by a statistically equivalent calculation by modifying the sampling algorithms by so-called variance reduction techniques. One way of achieving such aim is the adjoint Monte Carlo method, where particle interactions are simulated in reverse. The Midway Monte Carlo method combines a regular Monte Carlo forward simulation with an adjoint one on a virtual surface separating source and detector resulting in an enhanced convergence rate. The coupling of forward and ajoint calculations is a statistically evaluation of a bilinear surface integral of the radiation current and the adjoint function in every phase-space variable.
This doctorate thesis develops and applies the time dependent form of the Midway Monte Carlo method to a pulsed neutron-photon oil well logging tool. Full analysis is given on the accuracy and convergence properties of the coupling possibilities and of the efficiency increase for such an application. Additionally, the theoretical framework of the adjoint simulation of scintillation detectors (Pulse Height tallies) has been developed.
The thesis concludes that the Midway Monte Carlo method delivers a user-friendly general variance reduction tool with high efficiency improvement, moreover the application of conventional variance reduction techniques can further enhance the efficiency. On the downside the reliability of the delivered answer and confidence intervals are often poor for time dependent simulations. Also, the method requires high computer memory capacity for the current standards.
Keywords: Monte Carlo, Midway, Adjoint, Well logging, Borehole logging, pulse height, neutron, photon, time dependent
  • Book (Editorship)
    (Signatur: 518.2/4/1:1) Delft: Delft University Press, 2005
    140 Seiten
    ISBN: 90-407-2614-0

Publ.-Id: 8114 - Permalink

Potential energy retention of slow highly charged Ar-Ions into solid surfaces -a calorimetric measurement-
Kost, D.; Facsko, S.; Keller, A.; Grötzschel, R.; Möller, W.;
Highly charged ions (HCIs) carry a large amount of potential energy, which is defined as the sum of the binding energies of all electrons that are removed from the atom. In the case of low velocities of the ions this energy can exceed the kinetic energy of the ions. Retaining such a large energy in a very small surface area of typically about 1-10nm^2 and in a very short interaction time of typically 5-10 fs an enormous power flux of 10^13 W/cm^2 is given. Here the mechanisms of energy dissipation are not completely understood yet. A fraction of energy is released by emission of electrons and photons, the other part is retained in the surface. Micro-calorimetric techniques provide some advantages for the measurement of the energy retention. We used this technique to determine the fraction of the retained potential energy in collisions of argon ions of charge states from Ar+ to Ar9+ with atomically clean surfaces of Si. We measured values between 0.7 and 0.8 for the fraction of the retained energy. This values are compared with earlier measurements on a copper surface. The potential energy retention coefficient for silicon is about three times larger than in case of the copper surface.
  • Lecture (Conference)
    25th Brandt-Richie Workshop on Particle Penetration Phenomena and Excitations of Solids: Electronic Interactions at Surfaces, 10.-13.04.2005, Gainesville, USA

Publ.-Id: 8113 - Permalink

Magnetic domains and magnetization reversal of ion-induced magnetically patterned RKKY-coupled Ni81Fe19/Ru/Co90Fe10 films
Kuepper, K.; Fassbender, J.ORC; Bischoff, L.; Mattheis, R.; Fischer, P.
Pure magnetic patterning by means of ion beam irradiation of magnetic thin films and multilayers result often from a post deposition local modification of the interface structure with only minor effects on the film topography. In the study presented here a 60 keV fine focused Co ion beam was used to change the coupling in a Ni81Fe19/Ru/Co90Fe10 structure from antiferromagnetic to ferromagnetic on a micron scale. Thereby an artificial structure with locally varying interlayer exchange coupling and therefore magnetization alignment is produced. High-resolution fullfield x-ray microscopy is used to determine the magnetic domain configuration during the magnetization reversal process locally and layer resolved dueto the element specific contrast in circular x-ray dichroism. In the magnetically patterned structure there is in addition to the locally varying interlayer exchange coupling across the Ru layer also the direct exchange coupling within each ferromagnetic layer present. Therefore the magnetization reversal behaviour of the irradiated stripes is largely influenced by the surrounding magnetic film.
Keywords: magnetic patterning, ion irradiation, x-ray magnetic circular dichroism (XMCD), x-ray microscopy
  • Poster
    ALS Users' Meeting 2005, 20.-22.10.2005, Berkeley, USA
  • Poster
    364. WE-Heraeus-Seminar Nanoscale Magnets - Top down meets Bottom up, 04.-06.01.2006, Bad Honnef, Germany
  • Poster
    DPG - spring meeting of the Division Condensed Matter, 26.-31.03.2006, Dresden, Germany

Publ.-Id: 8110 - Permalink

Plasma-immersion ion-implanted nitinol surface with depressed nickel concentration for implants in blood
Maitz, M.; Shevchenko, N.;
Ion implantation into nitinol had been shown previously to decrease the surface nickel concentration of this alloy and produce a titanium oxide layer. Nothing is known yet about the blood compatibility of this surface and the suitability for implants in the blood vessels, like vascular stents. Nickel depletion of superelastic nitinol was obtained by oxygen or helium plasma-immersion ion implantation. The latter leads to the formation of a nickel-poor titanium-oxide surface with a nanoporous structure, which was used for comparison. Fibrinogen adsorption and conformation changes, blood platelet adhesion, and contact activation of the blood clotting cascade have been checked as in vitro parameters of blood compatibility; metabolic activity and release of cytokines IL-6 and IL-8 from cultured endothelial cells on these surfaces give information about the reaction of the blood vessel wall. The oxygen-ion-implanted nitinol surface adsorbed less fibrinogen on its surface and activated the contact system less than the untreated nitinol surface, but conformation changes of fibrinogen were higher on the oxygen-implanted nitinol. No difference between initial and oxygen-implanted nitinol was found for the platelet adherence, endothelial cell activity, or cytokine release. The nanoporous, helium-implanted nitinol behaved worse than the initial one in most aspects. Oxygen-ion implantation is seen as a useful method to decrease the nickel concentration in the surface of nitinol for cardiovascular applications.
Keywords: nitinol, ion implantation, nickel depletion, titanium oxide, blood compatibility
  • Journal of Biomedical Materials Research Part A 76A(2006)2, 356-365

Publ.-Id: 8109 - Permalink

Oxygen implanted NiTi surfaces for biomedical application
Shevchenko, N.; Richter, E.; Maitz, M. F.; Möller, W.;
no abstract delivered from author
Keywords: PIII, biomedical, NiTi, surface
  • Poster
    8th International Workshop on Plasma Based Ion Implantation and Deposition, 18.-22.09.2005, Chengdu, China

Publ.-Id: 8108 - Permalink

Structure and properties of oxygen implanted NiTi surfaces
Shevchenko, N.; Richter, E.; Pham, M.-T.; Maitz, M. F.;
The memory shape and superelastic NiTi alloy for biomedical implants and devices has the drawback of the high nickel concentration of 50 at%. Plasma immersion ion implantation (PIII) for improved corrosion resistance and surface nickel depletion of NiTi has been suggested. In the recent work it could be shown that oxygen PII implantation (ion energy of 20 keV and fluence of 1e17 – 1e18 cm-2) can reduce the Ni concentration in 50-100 nm surface layers to concentration below 1 at%. This effect is combined with a Ni enriched layer below the Ni depleted surface layer, what suggests a reactive process as mechanism. Grazing incidence X-ray diffraction analysis revealed the formation of rutile TiO2 phase in the surface layer and perhaps Ni4Ti3 in the Ni enriched layer. The effect of ion fluence and implantation temperature on element profiles, phase composition, layers thickness has been systematically investigated.
The nickel depleted TiO2 layer prevents corrosion and out-diffusion of Ni ions. The oxygen ion implanted NiTi surface had a superior blood compatibility in vitro compared to untreated NiTi.
Keywords: Nitinol, PIII, oxide layer, surface properties
  • Poster
    13th International Congress on Thin Films /8th International Conference on Atomically Controlled Surfaces, Interfaces and Nanostructures, 19.-23.06.2005, Stockholm, Sweden

Publ.-Id: 8107 - Permalink

Real-time investigations of ITO film structure evolution during annealing
Shevchenko, N.; Rogozin, A.; Vinnichenko, M.; Cantelli, V.; Kolitsch, A.; Möller, W.;
The real-time in-situ evolution of the ITO film structure during annealing was continuously investigated by synchrotron X-ray diffraction at ROssendorf Beam Line (ROBL), which is located at the European Synchrotron Radiation Facility in Grenoble, France. The amorphous ITO films are produced by reactive pulsed middle frequency dual magnetron sputtering on the Si substrates covered with SiO2. The post-deposition annealing in vacuum of ITO samples was carried out with the ROBL UHV annealing chamber equipped with a hemispherical Be dome at two annealing modes: termal annealing (at constant temperature within the range of 200 - 240 °C) and annealing with an electrical current (at constant electrical power within the range of 1.25 – 2.0 W). In both experiments the resistivity behavior of the ITO film was monitored in situ by the four point probe technique or direct electrical measurement.
The evolution of XRD peaks of crystalline In2O3 phase with annealing time was shown. The time dependence of XRD peak integral intensity has the typical S-like shape. Using the Kolmogorov–Avrami–Johnson–Mehl equation for the dependence of the crystalline fraction on the annealing time, the kinetic parameters of crystallization process were determined. The value of kinetic exponent n is within the range of 2-3 for the thermal annealing and within the range of 1-2 for the annealing with an electrical current. The activation energy for the crystallisation at thermal annealing was found as 1.5 +/- 0.2 eV, whereas the activation energy at electrical current annealing was determined as 0.8 +/- 0.1 eV. It could be suggested that an electrical current stimulates the crystallization process.
Keywords: ITO, in-situ XRD, crystallization, activation energy
  • Lecture (Conference)
    13th International Congress on Thin Films /8th International Conference on Atomically Controlled Surfaces, Interfaces and Nanostructures, 19.-23.06.2005, Stockholm, Sweden

Publ.-Id: 8106 - Permalink

Optimized List-Mode Acquisition and Data Processing Procedures for ACS2 Based PET Systems
Langner, J.; Bühler, P.; Just, U.; Pötzsch, C.; Will, E.; van den Hoff, J.;
PET systems using the acquisition control system version 2 (ACS2), e.g. the ECAT Exact HR PET scanner series, offer a rather restricted list-mode functionality. For instance, typical transfers of acquisition data consume a considerable amount of time. This represents a severe obstacle to the utilization of potential advantages of listmode acquisition. In our study, we have developed hardware and software solutions which do not only allow for the integration of list-mode into routine procedures, but also improve the overall runtime stability of the system.
We show that our methods are able to speed up the transfer of the acquired data to the image reconstruction and processing workstations by a factor of up to 140. We discuss how this improvement allows for the integration of list-mode-based post-processing methods such as an event-driven movement correction into the data processing environment, and how list-mode is able to improve the
overall flexibility of PET investigations in general. Furthermore, we show that our methods are also attractive for conventional histogram-mode acquisition, due to the improved stability of the ACS2 system.
Keywords: Dynamic data acquisition, list mode, data processing, ACS2, ECAT Exact HR+, positron emission tomography
  • Zeitschrift für Medizinische Physik 16(2006)1, 75-82
    DOI: 10.1078/0939-3889-00294
  • Poster
    IEEE Medical Imaging Conference 2006, 29.10.-04.11.2006, San Diego, USA

Publ.-Id: 8105 - Permalink

Structural evolution on thermal cycling in Ti-rich NiTi SMA
Paula, A. S.; Canejo, J. P. H. G.; Schell, N.; Braz Fernandes, F. M.;
Shape-memory alloys (SMA) represent a class of metallic materials that has the capability of recovering a previously defined initial shape when subjected to an adequate thermomechanical treatment. Annealing of a Ti-rich Ni–Ti alloy has been followed by in situ high temperature diffraction in order to register the texture as well as the microstrain/microstress evolution. This type of study is relevant to the envisaged applications, because the type of preferential orientation and the corresponding anisotropic response of the material conditions contributes to the success of the SMA application. In the present study we have tested the feasibility of high temperature pole figures determination at ROBL (BM20) at the ESRF, and we have shown that there is a relation between the preferential orientation changing and the structural evolution taking place during annealing.
Keywords: Keywords: Shape-memory alloy; Texture; In situ high temperature X-ray diffraction
  • Nuclear Instruments and Methods in Physics Research B 238(2005)1-4, 111-114

Publ.-Id: 8104 - Permalink

Porous surface of NiTi alloy produced by plasma ion implantation
Shevchenko, N.; Muecklich, A.; Richter, E.; Maitz, M. F.;
For several applications a nanoporous surface layer of titanium oxide on titanium or NiTi is desired, e.g. for surface-increase for catalytical or electrochemical applications, or as carrier in a drug release system. This application requires interconnected pores with the size in the same order of magnitude as the drug molecule, few nanometers. A possibility to produce such a nanoporous structure is seen in the high dose ion implantation of a non reactive gas, which aggregates to nano-bubbles. To our knowledge this type of treatment has not yet been done with the superelastic or memory shape NiTi alloy.
Helium ion implantation of the NiTi and Ti samples was performed by means of plasma immersion ion implantation at following parameters: ion energy of 20 keV, ion fluence of ~1e18 cm -2, substrate temperature (100 – 400 °C). The implanted layers were examined by elastic recoil detection analysis, Auger electron spectroscopy, grazing incidence X-ray diffraction analysis, atomic force microscopy and transmission electron microscopy.
The He+-implanted region of NiTi samples contains a Ni depleted surface layer of TiOx, a Ni enriched zone with fine Ni4Ti3 crystallites and a nanoporous amorphous layer. Structure and morphology of these layers after etching in 1% HF acid were studied in order to characterize a deeper porous layer. An influence of implantation temperature on Ni transport from surface to the deeper layers and nanoporous layer formation are discussed.
Keywords: NiTi, nanoporous, surface, PIII
  • Poster
    European Materials Research Society Spring Meeting (E-MRS), 31.05.-03.06.2005, Strasbourg, France

Publ.-Id: 8103 - Permalink

Structural in situ studies of shape memory alloy (SMA) Ni–Ti thin films
Martins, R. M. S.; Schell, N.; Silva, R. J. C.; Braz Fernandes, F. M.;
Ni–Ti SMA thin films formed by sputtering have been attracting great interest as powerful actuators in microelectromechanical systems (MEMS) such as micro-valves, micro-fluidic pumps and micro-manipulators. Successful implementation of Ni–Ti micro-actuators requires a good understanding of the relationship among processing, microstructure and properties of Ni–Ti thin films. At the ROssendorf BeamLine (ROBL-CRG) at ESRF, we carried out a series of experiments that clearly illustrate the benefit of in situ studies, not only during annealing, but also during sputtering. The in situ sputtering experiments during film growth were performed using a magnetron sputter deposition chamber installed into the six-circle diffractometer of the materials research station. This facility allowed us to follow, almost in ‘‘real time’’, the structural evolution of the deposited thin films as a consequence of changing deposition parameters.
Keywords: Keywords: Structure and morphology; Deposition by sputtering; In situ X-ray diffraction
  • Nuclear Instruments and Methods in Physics Research B 238(2005)1-4, 319-322

Publ.-Id: 8102 - Permalink

Determination of absolute defect concentrations forsaturated positron trapping – deformed polycrystalline Ni as a case study
Krause-Rehberg, R.; Bondarenko, V.; Thiele, E.; Klemm, R.; Schell, N.;
Positrons may be used in many cases to determine defect densities of vacancies and dislocations. In case of saturated positron trapping, i.e. all positrons are getting trapped, only a lower-limit estimation can be given. However, a combination of positron back-diffusion measurements using a monoenergetic positron beam in combination with conventional lifetime spectroscopy can be used to overcome the problem of saturated positron trapping. As a case study, this combination was used for the determination of dislocation densities in polycrystalline nickel samples of highly varying dislocation density. Saturated positron trapping into dislocations and small voids was observed. The total positron trapping rate was calculated from the positron diffusion length obtained by back-diffusion experiments. The trapping rates of the two defects were finally obtained using the decomposition of lifetime spectra. The results were found in good agreement with those determined by the analysis of synchrotron Bragg-diffraction profiles, measured on the same set of samples. From the comparison of both techniques, the positron trapping coefficient was found to be ldisl = 3.9 ± 0.3 cm2/s for a high density of dislocations in Ni.
Keywords: Keywords: Positron annihilation; VEPAS; Dislocation density; Nickel; Specific trapping rate; Bragg-diffraction profiles
  • Nuclear Instruments and Methods in Physics Research B 240(2005)3, 719-725

Publ.-Id: 8101 - Permalink

Investigation of the formation and phase transitionof Ge and Co nanoparticles in a SiO2 matrix
Cantelli, V.; von Borany, J.; Mücklich, A.; Schell, N.;
The evolution of ion beam synthesized Co and Ge nanoclusters into a SiO2 matrix during annealing processes has been investigated by X-ray diffraction and transmission electron microscopy. Remarkable differences have been found between Ge and Co clusters behaviour. For Ge implanted SiO2 films, a clear influence of near-surface Ge oxidation and nanoclusters melting has been established. Annealing at temperatures around 1000 C leads to the formation of small (diameter 5 nm) nanocrystals. Classical Ostwald ripening mainly drives the clusters thermodynamical growth. On the contrary, for Co-implanted SiO2 films, a jump-like transition in nanoclusters evolution has been established at about 800 °C. A homogenous distribution of small (diameter 4 nm) amorphous clusters is transformed into a bimodal clusters profile, characterised by large (diameter between 20 and 40 nm) nanocrystals near the surface and a region of smaller clusters (diameter 7 nm) in depth. During Co nanoclusters formation the influence of nanoclusters melting can be neglected.
PACS: 81.07.Bc; 61.10.Eq; 68.37.Lp; 66.30.Pa
Keywords: Keywords: Nanoclusters; Ion-beam synthesis; Cobalt; Germanium; Silicon dioxide
  • Nuclear Instruments and Methods in Physics Research B 238(2005)1-4, 268-271

Publ.-Id: 8100 - Permalink

Novel and Efficient Preparation of Precursor [188Re(OH2)3(CO)3]+ for the Labeling of Biomolecules
Park, S. H.; Seifert, S.; Pietzsch, H.-J.;
A novel and efficient method for preparing 188Re(I) tricarbonyl precursor [188Re(OH2)3(CO)3]+ has been developed by reacting [188Re]perrhenate with Schibli’s kit in the presence of borohydride exchange resin (BER) as a reducing agent and an anion scavanger. The precursor was produced in more than 97% yield by reacting a solution of tetrahydroborate exchange resin (BER, 3 mg), borane-ammonia (BH3âNH3, 3 mg), and potassium boranocarbonate (K2[H3BCO2], 3 mg) in 0.9% saline with a solution of sodium perrhenate (Na188ReO4) with up to 50 MBq and concentrated phosphoric acid (85%, 7 íL) at 60 °C for 15 min. HPLC and TLC revealed 0% unreacted [188Re]-perrhenate ion and <3% of colloidal 188ReO2. Since the precursor is produced with high radiochemical purity and labeling efficiency under the milder conditions than those required for the conventional reducing agents, the latter can be replaced.
  • Bioconjugate Chemistry 17(2006), 223-225

Publ.-Id: 8099 - Permalink

Synthesis of Azolyl Carboximidamides as Ligands for Zn(II) andCu(II): Application of the Zn(II) Complexes as Catalysts for theCopolymerization of Carbon Dioxide and Epoxides
Walther, M.; Wermann, K.; Lutsche, M.; Günther, W.; Görls, H.; Anders, E.;
A series of novel S,N-heterocyclic (thiazolyl) substituted carboximidamides 3 and 4 was synthesized in yields up to 82% from specific triazinium salts 1 and primary or secondary amines 2 which additionally bear pyridine or imidazole units. These carboximidamides are used as tailor-made ligands for the complexation of Cu(II) and Zn(II). The coordination behavior of 3 and 4 and the properties of the resulting metal complexes are affected a significant extent especially by the nature of these amine substituents. The most important structural feature of the novel complexes is that the ligation of the metal cations is achieved by a 1,3,5-triazapentadienyl anion system, compare the X-ray structure of the model complex Cu-4d. Analogous Zn(II) complexes 5, 6a, 6b, 6c, 7a, and 7b were obtained from carboximidamides 3, 4a, 4b, 4c, 4d, and 4e after reaction with diethylzinc. Interestingly, these Zn(II) complexes possess an intrinsic activity to catalyze the copolymerization of cyclohexene oxide and carbon dioxide to give polycarbonates 15 (TON up to 113; Turn Over Number: moles of substrate 14 consumed per moles of zinc. Molecular weights: up to 206â103 Da). Contaminations of 15 by polyethers are produced only in remarkably small amounts.
  • Journal of Organic Chemistry 71(2006)4, 1399-1406

Publ.-Id: 8098 - Permalink

Real time in situ diagnostics of PVD growth using synchrotron radiation
Andreasen, K. P.; Bøttiger, J.; Chevallier, J.; Schell, N.;
For specific applications of hard coatings, the microstructure (or nanostructure) has to be tailored for optimum performance. This requires information about the mechanisms of growth and the connection between the microstructure and the deposition parameters. In order to obtain this knowledge, in situ real time growth studies of magnetron-sputtered thin films were carried out. A growth chamber, equipped with two magnetrons and Kapton windows for X-ray diffraction and reflectivity, was mounted on a six-circle goniometer at a synchrotron beam line at ESRF in Grenoble. As an example, X-ray diffraction measurements were carried out in situ during growth of TiN to follow the development of the microstructure. Recrystallization was identified as the mechanism which controlled the development of texture. The driving force for these texture changes arose from minimalization of the sum of the surface energy and the strain energy of the individual grains. As another example, the heteroepitaxial growth of TiN on MgO(001) was studied. Bragg–Brentano as well as grazing-incidence in-plane wide angle scattering was used to establish the pseudomorphic growth of TiN to the underlying MgO(001). Using real-time specular X-ray reflectivity, layer-by-layer growth was observed, with the surface roughening decreasing with an increase in the deposition temperature. The growth of nanocrystalline Au was also investigated. Among the results we found that changes in the (111) fiber texture arose from grain rotations.
Keywords: Keywords: In situ diagnostics; X-ray diffraction; Magnetron; Gold; Titanium nitride; Nanostructure
  • Surface & Coatings Technology 200(2005), 1-6

Publ.-Id: 8096 - Permalink

A Low Energy Ion Beam Line for Highly Charged Ions
Zschornack, G.; Landgraf, S.; Großmann, F.; Kentsch, U.; Ovsyannikov, V. P.; Schmidt, M.; Ullmann, F.;
An ion beam line is presented, which is designed to study the interaction of highly charged ions with matter, especially solid surfaces. The highly charged ions are produced in a room temperature electron beam ion trap, the Dresden EBIT. This device delivers bare nuclei up to elements with an atomic number of about 28, and neon-like ions up to about Z=80. After leaving the trap the ion beam containing several neighbouring ion charge states passes through standard ion optics elements before entering an analysing magnet for separating a certain ion charge state. In a following deceleration unit, which will be integrated soon, the ions can be slowed down to a definite kinetic energy of a few eV. The characteristic of the HCI beam is presented, combined with ion extraction spectra of selected elements detected by a Faraday cup after passing through an analysing magnet.
Keywords: Highly Charged Ions, Electron Beam Ion Trap
  • Vacuum 78(2005)2-4, 319-323

Publ.-Id: 8095 - Permalink

Experimente zur CFD-Validierung für horizontale Zweiphasen-Strömungen
Vallee, C.;
Zur Weiterentwicklung und Validierung von CFD-Codes bei Zweiphasen-Strömungen wurden am Forschungszentrum Rossendorf zwei horizontale Luft/Wasser-Strömungskanäle aufgebaut. Die Teststrecken, mit unterschiedlichem rechteckigen Querschnitt, wurden für den Einsatz optischer Messverfahren aus Acrylglas konstruiert. Die Versuche fanden bei Umgebungsdruck und -temperatur statt.

Die erste Anlage wurde für Vorversuche genutzt: An dieser konnte die Instrumentierung getestet und weiterentwickelt werden. Es wurden optische Messungen mit einer Hochgeschwindigkeitskamera durchgeführt und mit dynamischen Druckmessungen synchronisiert. Aus den entstandenen Bildsequenzen wurde die Phasengrenzfläche durch eigenentwickelte Algorithmen ermittelt. Außerdem wurden Geschwindigkeitsfelder in einem Schwall mit PIV (Particle Image Velocimetry) gemessen.

Der zweite Testkanal profitierte von den Erfahrungen an der ersten Anlage: Seine Konstruktion wurde für die Validierung von CFD-Codes optimiert. Eine spezielle Einlaufkomponente sorgt für definierte und konstante Randbedingungen am Eintritt. Zudem kann die Kanallänge bis auf 14 m erweitert werden. Es werden erste qualitative Ergebnisse gezeigt, so zum Beispiel Visualisierungen verschiedener Strömungsformen.
Keywords: Horizontal two-phase flow, Slug flow, High-speed video observations, Image processing, PIV
  • Invited lecture (Conferences)
    Seminar des Lehrstuhl für Thermodynamik, 09.01.2006, Garching, München, Germany

Publ.-Id: 8094 - Permalink

Magic matching in semiconductor heterojunctions
Pecz, B.; Barna, Á.; Heera, V.; Skorupa, W.;
Matching of m crystal planes of a grown layer to n planes of the substrate is observed in many cases, when the difference in the lattice parameters is large. This kind of magic matching is explained by coincidence planes. Two examples are shown in this paper. SiC grains perfectly oriented to the substrate were prepared by high temperature ion implantation of Si into natural diamond. Considering the (111) lattice planes and the cases, when 5 planes of SiC match to 6 planes in diamond, or 4 planes of SiC match to 5 planes in diamond, the misfit is reduced to about 2% in both cases having opposite signs. High resolution images taken at the SiC/diamond interface were investigated and both of the above mentioned domains were found. When we consider the regular distribution of the above two domains, i.e. matching of 9 SiC lattice planes to 11 diamond planes a misfit value below 0.1% is obtained. This explains how the ion beam synthesised SiC can grow epitaxially despite the huge difference in lattice parameters. GaN synthesised in GaAs by ion implantation is presented as another example where magic matching of 5:4 reduces the misfit to 0.8%. That value is low enough to be compensated by elastic deformation of the lattice, therefore the insertion of another domain is not needed.
Keywords: ion beam synthesis, heteroeptitaxy, SiC-diamond, GaAs-GaN, lattice matching, XTEM
  • Lecture (Conference)
    14th International Conference on Microscopy of Semiconducting Materials- MSMXIV, 11.-14.04.2005, Oxford, U. K.
  • Contribution to proceedings
    Microscopy of Semiconducting Materials, 11.-14.04.2005, Oxford, UK
    Proceedings of the 14th Conference, Berlin, Heidelberg, New York: Springer, 3-540-31914-X, 159-162

Publ.-Id: 8093 - Permalink

Dependence of the linewidth of planar electron channeling radiation on the thickness of the diamond crystal
Azadegan, B.; Wagner, W.; Pawelke, J.;
Measurements of (110) planar channeling radiation have been performed at the radiation source ELBE at electron energies of 14.6, 17, 30 and 34 MeV using diamond crystals of thickness 42.5, 102, 168 and 500 micrometers. The influence of different line-broadening mechanisms on the spectral shape of radiation from the 1 - 0 transition has been investigated. The analysis bases on fitting a convolution of the intrinsic Lorentz-like line shape with a Gaussian-like multiple-scattering distribution to the measured spectra. The asymmetry parameter involved relates to the standard deviation of the multiple-scattering angle under channeling condition. Its dependence on the crystal thickness at channeling was found to be weaker than for nonchanneled particles. The deduced coherence lengths show no significant dependence on the electron energy.
Keywords: planar channeling radiation, linewidth, diamond, coherence length
  • Physical Review B 74(2006), 045209-1

Publ.-Id: 8092 - Permalink

Untersuchung der Verschiebung der bakteriellen Populationen in mit U(VI) inokulierten Bodenproben einer Uranabfallhalde mittels direkter molekularer Analysen
Tschikov, J.;
wird nachgereicht
  • Other report
    Hochschule Anhalt: Köthen, 2005
    45 Seiten

Publ.-Id: 8091 - Permalink

"Böttger Stoneware" - Authentic or Not?
Neelmeijer, C.; Mäder, M.; Pietsch, U.; Ulbricht, H.; Walcha, H.-M.;
The so-called "Böttger Stoneware", red porcelain invented by Böttger in the early 18th century, represents an independent development of high technological standard. In comparison to other ceramics Böttger stoneware is characterized by a high material density, consequently greater hardness and suitability for surface polishing. Hence museums show growing interest in obtaining objective criteria based on non-destructive methods of stoneware material analysis. In the present work the possibility of characteristic "fingerprints" for the different provenance of stoneware is tested by making use of ion beam analysis at the external proton beam, i.e. a proton beam on air.
Keywords: ceramics, Böttger, stoneware, material analysis, fingerprints, ion beam analysis, PIXE
  • Contribution to external collection
    Dagmar Hülsenberg: Ehrenfried Walther von Tschirnhaus Gesamtausgabe, Beiband, Leipzig: Sächsische Akademie der Wissenschaften zu Leipzig, 2003, 3-515-08464-9, 29-33

Publ.-Id: 8090 - Permalink

Schätze im Protonenlicht
Neelmeijer, C.; Mäder, M.;
Glas kann korrodieren wie Metall. Wenngleich die Prozesse andersartig sind, das Resultat ist identisch. Umgebungsbedingte chemische Reaktionen zerstören die Materialien. Schadstellen an wertvollen Gemälden lassen sich restauratorisch festigen und ergänzen, für Unikate aus Glas besteht diese Chance nicht. Der Erhaltungszustand von Glasoberflächen kann bestenfalls eingefroren werden. Voraussetzung dafür ist, dass man ihn kennt und dass es möglich ist, die potentielle Gefahr umweltbedingter Schädigung für das einzelne Glasobjekt objektiv einzuschätzen. Selbst unter dem Schutz von Klimaanlagen in den Museen altern die Schätze aus Glas. Einige hochkarätische Pretiosen befinden sich heute bereits in einem außerordentlich kritischen Zustand. Das Schadensbild reicht von Trübung über feine Haarrisse und großflächige Rissnetze bis zur Schuppenbildung, der Ablösung von Glasschichten und den Verlust von Farbfassungen. Viele Objekte erscheinen, visuell beurteilt, heute noch in recht gutem Erhaltungszustand. Genau hier setzt die Entwicklung unserer präventiven Untersuchungsmethode ein, in Analogie zur lebensrettenden Krebsfrüherkennung bei Patienten. Ohne Probenahme gelingt es mittels zerstörungsfreier Materialanalyse solche Gläser aufzufinden, deren Zusammensetzung für Glaskorrosion kritisch ist. Für diese empfehlen wir dem Museum vorsorgliche Erhaltungsmaßnahmen.
Keywords: Glass, museum, deterioration, non-destructive analysis, PIGE, PIXE, RBS
  • Contribution to HZDR-Annual report
    Wissenschaftlich-Technische Berichte / Forschungszentrum Rossendorf; FZR-398 März 2004, 62-71


Publ.-Id: 8089 - Permalink

Preventive ion beam inspection of glass treasures
Neelmeijer, C.; Mäder, M.;
Art objects made of glass may undergo deterioration when exposed to environmental stress. Even in air conditioned museums, susceptible glass surfaces may decompose. Thus, their transparency is reduced and initial tiny surface cracks may result in irreplaceable loss of glass. Degradation takes place via ion exchange reactions between the silicate network and the humidity of the ambient atmosphere. Endangered glass objects in important collections should be studied using non-destructive analytical methods. In this regard, the advantage of ion beam analysis by simultaneous Particle Induced Gamma-ray Emission (PIGE), Particle Induced X-ray Emission (PIXE) and Rutherford Backscattering Spectrometry (RBS) in a non-vacuum facility is demonstrated. This paper is concerned with both the current condition of the glass surface and the composition of the bulk of the glass. The result of such ion beam examination enables the scientist to recommend suitable storage conditions. In addition, the non-destructive study provides scientists studying art objects with means of objective material identification, enabling them to reach conclusions with respect to particular glass technologies or proveniences.
Keywords: Glass, museum, deterioration, non-destructive analysis, ion beam analysis, PIGE, PIXE, RBS
  • Contribution to external collection
    Annemie Adriaens, Christian Degrini, JoAnn Cassar: Benefits of non-destructive analytical techniques for conservation, Brussels: COST Office, 2005, 92-898-0010-0, 99-108

Publ.-Id: 8088 - Permalink

IBA of iridescent Art Nouveau glass - comparative studies
Mäder, M.; Jembrih-Simbürger, D.; Neelmeijer, C.; Schreiner, M.;
Simultaneous PIXE, PIGE, and RBS in air were employed to characterise the surface structure of iridescent Art Nouveau glass artefacts produced around 1900 by Tiffany, USA and Loetz, Austria. Using PIXE and PIGE, the chemical composition of the bulk glass and the overlays was determined in a non-destructive manner. Furthermore, the combination of PIXE and RBS enabled the layer structure of the analysed glasses (bulk, overlays, and iridescent layers) and the thicknesses of the thin layers in the near-surface domain to be determined. The measurement and evaluation procedure is demonstrated on blue iridescent glass fragments of Tiffany and Loetz by way of example. The initial results showing similarities but also differences in the layered glass structure of Tiffany and Loetz objects are presented.
Keywords: Ion beam analysis (IBA); Proton induced X-ray emission (PIXE); Proton induced γ-ray emission (PIGE); Rutherford backscattering spectrometry (RBS); Iridescent Art Nouveau glass; Tiffany; Loetz
  • Nuclear Instruments and Methods in Physics Research B 239(2005), 107-113

Publ.-Id: 8087 - Permalink

Three-dimensional modeling of EXAFS spectral mixtures by combining Monte-Carlo Simulations and Target Transformation Factor Analysis
Rossberg, A.; Scheinost, A.;
wird nachgereicht
  • Poster
    15th Users Meeting, 08.-11.02.2005, Grenoble, France

Publ.-Id: 8086 - Permalink

Wavelet analysis of EXAFS Data
Funke, H.; Chukalina, M.; Hennig, C.; Rossberg, A.; Scheinost, A.;
wird nachgereicht
  • Poster
    15th Users Meeting, 08.-11.02.2005, Grenoble, France

Publ.-Id: 8085 - Permalink

The Rossendorf Beamline for Actinide Research
Scheinost, A.;
wird nachgereicht
  • Lecture (others)
    CEA, 11.05.2005, Valduc, France

Publ.-Id: 8084 - Permalink

Coolant mixing studies of natural circulation flows at the ROCOM test facility using ANSYS CFX
Höhne, T.; Kliem, S.;
Coolant mixing in the cold leg, downcomer and the lower plenum of pressurized water reactors is an important phenomenon mitigating the reactivity insertion into the core. Therefore, mixing of the de-borated slugs with the ambient coolant in the reactor pressure vessel was investigated at the ROCOM mixing test facility. The Rossendorf Coolant Mixing Model (ROCOM) was constructed for the investigation of coolant mixing in PWR. The ROCOM facility has four loops each with an individually con¬trol¬led pump. This allows to per¬form tests in a wide range of PWR flow conditions from natural con¬vec¬tion flow up to forced con¬vec¬tion flow at nominal flow rates including flow ramps. ROCOM is operated with wa¬ter at ambient tem¬pe¬ra¬tures because the re¬ac¬tor pressure ves¬sel (RPV) mock-up and its internals are made of perspex. The model has a linear scale 1:5 to the prototype, the water inventory in the loops is kept in scale 1:125 and the traveling time of the coolant is identical to the original reactor.

Thermal hydraulics analyses showed, that weakly borated condensate can accumulate in particular in the pump loop seal of those loops, which do not receive safety injection. After refilling of the primary circuit, natural circulation in the stagnant loops can re-establish simultaneously and the de-borated slugs are shifted towards the reactor pressure vessel (RPV). In the ROCOM experiments, the length of the flow ramp and the initial density difference between the slugs and the ambient coolant was varied. During inherent dilution the slug could have a higher temperature and a lower density. Additionally the boron content influences the fluid density. In ROCOM this density difference is adjusted by the addition of ethyl alcohol. The acquisition of the concentration fields is performed with high spatial and temporal resolution mea¬sure¬ments of the tracer con¬¬¬centration.

Experiments with 0 up to 2% density differences between the de-borated slugs and the ambient coolant were used to validate the CFD software ANSYS CFX. A Reynolds stress turbulence model was employed and a hybrid mesh consisting of 3.6 million nodes and 6.4 million elements was used. The Best Practice Guidelines were applied to ensure the quality of the calculations. In the calculations, the High-Resolution discretisation scheme of ANSYS CFX was used to discretize the convective terms in the model equations. A second-order implicit scheme was utilized to approximate the transient terms. The time step size was set to 0.1 s. The ethyl alcohol water, which had a lower density, was applied as a tracer. It was modelled with the multi-component model of ANSYS CFX. The ethyl alcohol water was modelled as a component with different density and viscosity compared to water.

Depending on the degree of density differences the experiments and CFD calculations show a more or less intense stratification in the cold leg and downcomer. The ANSYS CFX calculations show a good qualitative agreement with the data. At some local positions differences in the predicted and measured concentration fields occur. The obtained experimental and numerical results can be used for further studies of the core behaviour using coupled thermo-hydraulic and neutron-kinetic code systems.
Keywords: CFD, ROCOM, boron dilution, PWR
  • Contribution to proceedings
    OECD/NEA International Workshop on The Benchmarking of CFD Codes for Application to Nuclear Reactor Safety (CFD4NRS), 05.-09.09.2006, Garching, Germany
  • Lecture (Conference)
    OECD/NEA International Workshop on The Benchmarking of CFD Codes for Application to Nuclear Reactor Safety (CFD4NRS), 05.-09.09.2006, Garching, Germany

Publ.-Id: 8083 - Permalink

Neural correlates of anosognosia for cognitive impairment in Alzheimer's disease.
Salmon, E.; Perani, D.; Herholz, K.; Marique, P.; Kalbe, E.; Holthoff, V.; Delbeuck, X.; Beuthien-Baumann, B.; Pelati, O.; Lespagnard, S.; Collette, F.; Garraux, G.;
We explored the neural substrate of anosognosia for cognitive impairment in Alzheimer's disease (AD). Two hundred nine patients with mild to moderate dementia and their caregivers assessed patients' cognitive impairment by answering a structured questionnaire. Subjects rated 13 cognitive domains as not impaired or associated with mild, moderate, severe, or very severe difficulties, and a sum score was calculated. Two measures of anosognosia were derived. A patient's self assessment, unconfounded by objective measurements of cognitive deficits such as dementia severity and episodic memory impairment, provided an estimate of impaired self-evaluative judgment about cognition in AD. Impaired self-evaluation was related to a decrease in brain metabolism measured with 18F-2-fluoro-2-deoxy-D-glucose positron emission tomography (FDG-PET) in orbital prefrontal cortex and in medial temporal structures. In a cognitive model of anosognosia, medial temporal dysfunction might impair a comparison mechanism between current information on cognition and personal knowledge. Hypoactivity in orbitofrontal cortex may not allow AD patients to update the qualitative judgment associated with their impaired cognitive abilities. Caregivers perceived greater cognitive impairments than patients did. The discrepancy score between caregiver's and patient's evaluations, an other measure of anosognosia, was negatively related to metabolic activity located in the temporoparietal junction, consistent with an impairment of self-referential processes and perspective taking in AD.
Keywords: dementia • neuroimaging • cognition • awareness • evaluation • self • perspective taking • beliefs • confabulation

Publ.-Id: 8082 - Permalink

Surface Passivation of Silicon Solar Cells by Amorphous Silicon/Silicon Nitride Dual Layers
Bentzen, A.; Ulyashin, A.; Suphellen, A.; Sauar, E.; Grambole, D.; Wright, D. N.; Marstein, E. S.; Svensson, B. G.; Holt, A.;
We have investigated surface passivation of silicon by a dual structure consisting of a hydrogenated amorphous silicon thin film capped by a silicon nitride anti-reflection layer, both layers deposited by plasma enhanced chemical vapor deposition. The results show that a synergetic effect on the surface passivation properties is obtained from such a dual structure. Moreover, we find that the surface passivation can be significantly enhanced after a short anneal for temperatures up to about 500 °C, whereas anneals at higher temperatures result in degradation of the passivation properties. From nuclear reaction analyses of the as-deposited and annealed structures, the enhanced surface passivation experienced after annealing is indicated to be due to hydrogen release from the structure towards the silicon substrate, possibly followed by a redistribution of hydrogen and subsequent passivation of silicon dangling bonds in the sub-interface region.
Keywords: Surface Passivation, Amorphous Silicon, Silicon Solar Cells
  • Contribution to proceedings
    15th International Photovoltaic Science and Engineering Conference (PVSEC-15), 10.-15.10.2005, Shanghai, China, 316-317

Publ.-Id: 8081 - Permalink

Experimental investigation and CFD simulation of horizontal stratified two-phase flow phenomena
Vallee, C.; Höhne, T.; Prasser, H.-M.; Sühnel, T.;
For the investigation of stratified two-phase flow, two horizontal channels with rectangular cross-section were built at Forschungszentrum Rossendorf. The channels allow the investigation of air/water co-current flows, especially the slug behaviour, at atmospheric pressure and room temperature. The test-sections are made of acrylic glass, so that optical techniques, like high-speed video observation or particle image velocimetry (PIV), can be applied for measurements. The rectangular cross-section was chosen to provide better observation possibilities. Moreover, dynamic pressure measurements were performed and synchronised with the high-speed camera system.

CFD post test simulations of stratified flows were performed using the code ANSYS-CFX. The Euler-Euler two fluid model with the free surface option was applied on grids of minimum 400'000 control volumes. The turbulence was modelled separately for each phase using the k-ω based shear stress transport (SST) turbulence model. The results compare very well in terms of slug formation, velocity, and breaking. The qualitative agreement between calculation and experiment is encouraging and shows that CFD can be a useful tool in studying horizontal two-phase flow.
Keywords: Horizontal two-phase flow, Slug flow, High-speed video observations, Image processing, PIV, CFD
  • Contribution to proceedings
    CFD4NRS - Benchmarking of CFD Codes for Application to Nuclear Reactor Safety, 05.-07.09.2006, Garching, München, Germany
    Paper A6-31
  • Lecture (Conference)
    CFD4NRS - Benchmarking of CFD Codes for Application to Nuclear Reactor Safety, 05.-07.09.2006, Garching, München, Germany
  • Nuclear Engineering and Design 238(2008), 637-646
    DOI: 10.1016/j.nucengdes.2007.02.051

Publ.-Id: 8080 - Permalink

Heterogeneity of brain glucose metabolism in mild cognitive impairment and clinical progression to Alzheimer disease
Anchisi, D.; Borroni, B.; Franceschi, M.; Kerrouche, N.; Kalbe, E.; Beuthien-Baumann, B.; Cappa, S.; Lenz, O.; Ludecke, S.; Marconi, A.; Mielke, R.; Ortelli, P.; Padovani, A.; Pelati, O.; Pupi, A.; Scarpini, E.; Weisenback, S.; Herholz, K.; Salmon, E.; Holthoff, V.; Sorbi, S.; Fazio, F.; Perani, D.;
BACKGROUND: Subjects with amnesic mild cognitive impairment (aMCI) may include patients at high risk for progression to Alzheimer disease (AD) and a population with different underlying pathologic conditions. OBJECTIVE: To evaluate the potential roles of positron emission tomography with fluorodeoxyglucose F 18 (18FDG-PET) and memory scores in identifying subjects with aMCI and in predicting progression to dementia.
DESIGN, SETTING, AND PATIENTS: Sixty-seven patients at European centers for neurologic and AD care who were diagnosed as having aMCI each underwent an extensive clinical and neuropsychological examination and an 18FDG-PET study. Forty-eight subjects were followed up periodically for at least 1 year, and progression to dementia was evaluated.

MAIN OUTCOME MEASURES: Brain glucose metabolism and memory scores. RESULTS: Fourteen subjects with aMCI who converted to AD within 1 year showed bilateral hypometabolism in the inferior parietal, posterior cingulate, and medial temporal cortex. Subjects with "stable" aMCI presented with hypometabolism in the dorsolateral frontal cortex. The severity of memory impairment, as evaluated by the California Verbal Learning Test-Long Delay Free Recall scores, correlated with the following brain metabolic patterns: scores less than 7 were associated with a typical 18FDG-PET AD pattern, and scores of 7 or higher were associated with hypometabolism in the dorsolateral frontal cortex and no progression to AD. CONCLUSION: These data provide evidence for clinical and functional heterogeneity among subjects with aMCI and suggest that 18FDG-PET findings combined with memory scores may be useful in predicting short-term conversion to AD.
  • Archives of Neurology 62(2005)11, 1728-1733

Publ.-Id: 8079 - Permalink

Pressure vessel investigations of the former Greifswald NPP: Fluence calculations and Nb based fluence measurements
Rindelhardt, U.; Konheiser, J.; Viehrig, H.-W.; Gleisberg, B.;
Pressure vessel integrity assessment after long-term service irradiation is commonly based on surveillance program results. Radiation loading, metallurgical and environmental histories, however, can differ between surveillance and RPV materials. Therefore, the investigation of RPV material from decommissioned NPPs offers the unique opportunity to evaluate the real toughness response. A chance is given now through the investigation of material from the decommissioned Greifswald NPP (VVER-440/230) to evaluate the state of a standard RPV design and to assess the quality of prediction rules and assessment tools.

The operation of the four Greifswald units was finished in 1991 after 12 – 15 years of operation. In autumn 2005 the first trepans (diameter 120 mm) were gained from the unit 1 of this NPP. A new drilling machine was developed and adopted to the actual plant conditions. The drilling machine allows the following remote controlled actions:

• Labeling the position and orientation of the trepan
• Drilling the trepan and ejection of the trepan into the RPV
• Closing the hole in the RPV

Details of the trepanning procedure will be given.

Fluence calculations using the code TRAMO were based on pin-wise time dependent neutron sources and an updated nuclear data base (ENDF/B-VI release 8). The neutron and gamma fluence spectra were determined at the trepan positions. The different loading schemes of unit 1 (standard, with 4 or 6 dummy assemblies) were taken into account. The fluences after the annealing procedure (after cycle 13) were separately determined. The statistical error of the integral fluence values (E > 0.5 MeV) was estimated to be smaller than 1%. The comparison between the calculated fluences and experimental values (determined from excore fluence monitors applied during the 12th cycle) showed a good agreement.
The integral neutron fluence at the inner RPV wall near the critical weld was found to 4.64* 10^18 n*cm-2. The maximum fluence at the RPV is 50 % higher. In addition, it could be shown that the fluence at the designated reference positions can be neglected (3 orders of magnitude smaller). The gamma fluence was calculated to 1.9 *10^20 photons* cm-2 at the critical weld with a similar axial distribution.

The experimental determination of the neutron fluence was based on Niobium activity measurements. The RPV material contains Niobium as trace element. The analysis of the Nb-content is carried out by ICP-MS (inductive coupled plasma mass spectrometry) after dissolution of the material sample. The radiochemical isolation of Nb was done by anion exchange separation. During this separation all other elements of the sample were removed. Finally Nb is stripped from the column. The radiochemical separation is accompanied by determination of the chemical yield of Nb using the above mentioned ICP-MS method.
The measurement of the 93mNb activity is realized by Liquid Scintillation Spectrometry (LSC). A detection efficiency of 91 % was achieved.
Keywords: reactor pressure vessel, NPP, neutron embrittlement, reactor dosimetry
  • Lecture (Conference)
    14th International Conference On Nuclear Energy, 17.-20.07.2006, Miami, United States
  • Contribution to proceedings
    14th International Conference on Nuclear Engineering (ICONE 14), 17.-20.07.2006, Miami, United States
    Proceedings, 0-7918-3783-1, 89578

Publ.-Id: 8078 - Permalink

Retrospective dosimetry of Greifswald VVER 440 RPV: Fluence calculations and Nb based fluence measurements
Rindelhardt, U.; Konheiser, J.; Viehrig, H.-W.; Gleisberg, B.;
The operation of the four Greifswald units (VVER-440/230) finished in 1991 after 12 – 15 years of operation. The investigation of RPV material from the decommissioned Greifswald NPP offers the possibility to evaluate the state of the standard RPV design and to assess the quality of prediction rules and assessment tools. The different operation conditions (irradiated, annealed, and re-irradiated) are a special advantage of the research program.
In autumn 2005 the first trepans (diameter 120 mm) were gained from the unit 1 of this NPP. A new drilling machine was developed and adopted to the actual plant conditions. The drilling machine allows the following remote controlled actions:

• Labeling the position and orientation of the trepan
• Drilling the trepan and ejection of the trepan into the RPV
• Closing the hole in the RPV

Details of the trepanning procedure will be given.
Fluence calculations using the code TRAMO were based on pin-wise time dependent neutron sources and an updated nuclear data base (ENDF/B-VI release 8). The neutron and gamma fluence spectra were determined at the trepan positions. The integral neutron fluence at the inner RPV wall near the critical weld was found to 4.64* 10^18 n*cm-2. The maximum fluence at the RPV is 50 % higher. In addition, it could be shown that the fluence at the designated reference positions can be neglected (3 orders of magnitude smaller). The gamma fluence was calculated to 1.9 *10^20 photons* cm-2 at the critical weld with a similar axial distribution.
The experimental determination of the neutron fluence was based on Niobium activity measurements. The RPV material contains Niobium as trace element. The analysis of the Nb-content is carried out by ICP-MS (inductive coupled plasma mass spectrometry) after dissolution of the material sample. The radiochemical isolation of Nb was done by an anion exchange column. By this separation all other elements were removed.
The measurement of the 93mNb activity is realized by Liquid Scintillation Spectrometry (LSC). Parallel the chemical yield is determined by the above mentioned ICP-MS method.
Keywords: Neutron embrittlement, Greifswald NPP, RPV dosimetry
  • Lecture (Conference)
    9th International Conference on Material Issues inIN Design, Manufactoringand Operation Peration of Nuclear Power Plants Equipment, 05.-09.06.2006, St. Petersburg, Russia
  • Contribution to proceedings
    9th International Conference on Material Issues in Design, Manufactoringand Operation Peration of Nuclear Power Plants Equipment, 06.-09.06.2006, St. Petersburg, Russia
    Proceedings, 241-247

Publ.-Id: 8077 - Permalink

Positron emission tomography in food sciences
Pietzsch, J.; van den Hoff, J.;
kein Abstract verfügbar

Publ.-Id: 8076 - Permalink

Morphology of surfaces bombarded with highly charged ions
Facsko, S.; Kost, D.; Keller, A.; Möller, W.;
The morphology of surfaces after erosion by ion sputtering show very different char-acteristics depending on the ion beam parameters and the material properties. The surface exposed to the ion beam can turn atomically smooth, stochastically or self-affine rough, or can evolve towards regular self-organised patterns, like periodic rip-ples or hexagonally ordered dots [1,2,3]. The structures of these patterns have small sizes in the range of 10 to 100 nm and show a high degree of ordering. Therefore, they have attracted strong interest recently as possible candidates for quantum struc-tures or as templates for deposition or etching processes [3,4].
On materials whose surface turns amorphous during the ion erosion the formation of the periodic patterns relies on at least two interplaying processes: roughening of the surface due to the local variation of sputtering yield and smoothing via diffusion proc-esses [5]. Therefore, the surface morphology depends strongly on the details of the energy deposition by the incoming ions and on the details of the surface diffusion.
At the atomic level, the atomic sputtering, the creation of surface defects, and the influence of the ion beam on surface diffusion processes play a decisive role for the morphology evolution. In the case of single charged ions, the energy deposition is mainly dissipated kinetically in a collision cascade which leads finally to the emission of the sputtered atoms and the creation of defects.
Multiple or highly charged ions carry in addition to their kinetic energy also “potential” energy which is the sum of the ionization energies for getting the higher charge state. Thus, a second energy deposition process takes place, i.e. the release of the poten-tial energy. This dissipation process is mainly electronic and takes place at the direct impact of the ions with the surface. For slow ions at high charge states the potential energy can exceed the kinetic energy thus dominating the ion-solid interaction. It has been demonstrated that at least 30% of the potential energy is retained in the surface and can induce electronic sputtering in the case of insulators [6,7].
We present first investigations of the effect of the potential energy deposition on the surface morphology of insulators and semiconductors. Special emphasis will be given on the characterisation of single ion impacts and the effect of the additional potential energy deposition on self-organised patterns.
Keywords: Highly Charged Ions, Ion Sputtering, Surface Morphology
  • Invited lecture (Conferences)
    348. WE-Heraeus-Seminar: Ions at Surfaces, Patterns and Processes, 19.-23.06.2005, Bad Honnef, Deutschland

Publ.-Id: 8075 - Permalink

Interaction of Highly Charged Ions with the Surface of Insulators
Facsko, S.; Kost, D.; Keller, A.; Möller, W.; Pesic, Z.; Stolterfoht, N.;
The interaction of highly charged ions (HCIs) with surfaces has been the subject of in-tense scientific research in the last years. Special attention was paid to the interaction with the surface of metals, where the formation of hollow atoms and their relaxation dynamics has been studied in detail [1]. From theses studies the interaction scenario for metal surfaces has been revealed and found to be consistent with the classical-over-barrier-model [2]. In contrast, the study of the interaction of HCIs with insulating surfaces is not as complete and still lacks some understanding [3].
The main differences between metals and insulators can be found in the higher work function, the lower density of electrons in the conduction band, and the much lower conduc-tivity. Therefore, the microscopic and macroscopic charging of insulating surfaces, which constitutes an important part of the interaction mechanisms, makes these studies difficult. Different methods can be used to overcome this difficulty. Using thin layers of a deposited material is one of the possibilities and will be presented here for the interaction of highly charged Ne ions with the SiO2 surface. Secondary electron emission from these layers and the calorimetric determination of the potential energy retention in these layers will be compared to results on Au surfaces.
In addition, the main aspects of the interaction of HCIs with insulating surfaces will be reviewed briefly. By means of the emission of x-rays and secondary electrons the formation and relaxation of hollow atoms above insulating surfaces will be discussed. Furthermore, the more applicative aspects of the interaction of HCIs with insulators like potential sputtering and single ion induced surface tracks and modifications will be covered.
Keywords: Highly Charged Ions, Insulator Surfaces, Electron Spectroscopy, Calorimetry
  • Invited lecture (Conferences)
    3rd Conference on Elementary Processes in Atomic Systems (CEPAS), 31.08.-2.09.2005, Miskolc, Hungary
  • Radiation Physics and Chemistry 76(2007)3, 387-391

Publ.-Id: 8074 - Permalink

Self-Organized Ordered Nanostructures by Ion Beam Sputtering
Facsko, S.; Rossbach, S.; Keller, A.; Gago, R.; Möller, W.;
There is a high demand of lateral structures with dimensions from some nanometers to tens of nanometers in the fields of electronics, magnetic storage, and biology. This has triggered research activities in self-organization and self-assembling mechanisms for their fabrication which can successfully complement the classical methods of lithography. These self-organization processes, classified as “bottom-up” approaches, in contrast to the “top-down” approaches of lithography, will join more and more the nanotechnology.
In the series of self-organized processes for the fabrication of nanostructures the pattern formation during ion erosion of surfaces has attracted much interest in the last years. In the continuous sput-tering process, induced by the bombardment with low-energy ions, periodic surface patterns ap-pear in form of ripples under off-normal incidence or regular arrays of hexagonally ordered dots at normal incidence. The dimension of the patterns is related to the size of the typical collision cascade and lies in the range of ten to tens of nanometers, depending primary on ion energy, inci-dence angle, and surface temperature. The self-organization mechanism relies on the interplay between a surface instability caused by the sputtering and surface diffusion processes. Regular ripple and dot morphologies have been produced in this way on very different materials including semiconductors, and metals, demonstrating the universality of this mechanism.
Keywords: Ion Sputtering, Nanostructures, Quantum Dots
  • Invited lecture (Conferences)
    Joint Meeting of the German Vacuum Society (DVG) and the Polish Vacuum Society (PTP), 26.-29.10.2005, Krakow, Polen

Publ.-Id: 8073 - Permalink

How to increase the MHD drag reduction efficiency for turbulent flows
Shatrov, V.; Gerbeth, G.;
Recently, permanent magnets and high electric current densities are often used to achieve reasonable Lorentz forces for a magnetohydrodynamic (MHD) flow control. This choice, however, usually leads to a low energetic efficiency for the flow control of seawater. We present results of direct numerical simulations of turbulent channel flow drag reduction using electromagnetic forces. The Lorentz force is created by a permanent magnetic field and an electric current from electrodes placed at the bottom wall. We consider the two cases of a spanwise oscillating force and a streamwise steady force. The main result is that a significant efficiency improvement is possible if load factors k ~ 1 are used. The application of the streamwise Lorentz force leads to a much more effective drag reduction if we consider the drag as a full force applied to the body. The skin-friction drag increases but the full drag may be strongly reduced with a good efficiency.
  • Lecture (Conference)
    Whither Turbulence Prediction and Control, 26.-29.03.2006, Seoul, Korea
  • Contribution to proceedings
    Whither Turbulence Prediction and Control, 26.-29.03.2006, Seoul, Korea
    Proceedings, 80-81

Publ.-Id: 8072 - Permalink

Synthesis of cobalt-disilicide nanowires using fine-focused ion beam
Akhmadaliev, C.; Schmidt, B.; Bischoff, L.;
No abstract required
Keywords: CoSi2,FIB, nanowires, ion beam synthesis
  • Lecture (others)
    DFG Priority Program 1165 Workshop: Nanowires and Nanotubes, 04.-09.09.2005, Kleinwalsertal, Germany

Publ.-Id: 8071 - Permalink

Focused ion beam synthesis of CoSi2 nanowires
Akhmadaliev, C.; Bischoff, L.; Schmidt, B.;
No abstract required
Keywords: FIB, ion beam synthesis, nanowires, CoSi2
  • Lecture (others)
    342. WE-Heraeus Seminar "Science and Technology of Inorganic Nanowires", 13.-16.02.2005, Bad Honnef, Germany

Publ.-Id: 8070 - Permalink

Quantum well infrared photodetectors: Physics and applications
Schneider, H.;
This seminar talk reports on the physics and applications of quantum well infrared photodetectors.
Keywords: infrared, photodetector, intersubband, QWIP
  • Lecture (others)
    Seminarvortrag, 12.01.2006, TU Dresden, Deutschland

Publ.-Id: 8069 - Permalink

FIB ion implantation into Si for CoSi2 nanowire growth
Schmidt, B.; Akhmadaliev, C.; Bischoff, L.;
No abstract required
Keywords: CoSi2, ion beam synthesis, FIB, nanowires
  • Lecture (others)
    Annual Meeting of the DFG Priority Program 1165: Nanowires and Nanotubes, 02.-04.04.2005, Fulda, Germany

Publ.-Id: 8068 - Permalink

Thin highly sensitive piezoresitive cantilevers - implantation technology
Schmidt, B.;
No abstract required
Keywords: Low energy ion implantation, RTA annealing, boron depth profiles
  • Lecture (others)
    EU-IP 515739: Technology for the production of massively parallel intelligent cantilever- probe platforms for nanoscale analysis and synthesis, PRONANO WP1 Technical Meeting, 28.-29.11.2005, Kassel, Germany

Publ.-Id: 8067 - Permalink

Resistivity of boron implanted p++ and piezoresistor layers
Zier, M.; Schmidt, B.;
No abstract required
Keywords: shallow pn-junction, sheet resistance, piezresistors
  • Lecture (others)
    EU-IP 515739: Technology for the production of massively parallel intelligent cantilever- probe platforms for nanoscale analysis and synthesis, PRONANO WP1 Technical Meeting, 28.-29.11.2005, Kassel, Germany

Publ.-Id: 8066 - Permalink

Quantum well infrared photodetectors: quantum structures for high-performance thermal imaging
Schneider, H.; Maier, T.; Fleissner, J.; Walther, M.; Koidl, P.; Weimann, G.; Cabanski, W.; Finck, M.; Menger, P.; Rode, W.; Ziegler, J.;
Intersubband transitions in GaAs/AlGaAs heterostructures are increasingly used in cameras for the thermal infrared regime. An excellent thermal resolution has been achieved in particular in the 8 - 12 µm spectral range. We report on the basic properties of these quantum well infrared photodetectors (QWIPs) and on the properties of cameras based on these devices in comparison to other detector materials. Finally we address a few applications for which QWIPs are the material of choice.
Keywords: thermal imaging, intersubband, infrared, QWIP
  • Invited lecture (Conferences)
    International Symposium on Advanced Electronics for Future Generations - “Secure-Life Electronics” for Quality Life and Society, 11.-12.10.2005, Tokyo, Japan

Publ.-Id: 8065 - Permalink

Thin highly sensitive piezoresitive cantilevers - fabrication of ultra-shallow pn-junctions
Schmidt, B.; Zier, M.;
No abstract required
Keywords: boron implantation, low energy implantation, RTA annealing, piezoresistors, SIMS profiles
  • Lecture (others)
    EU-IP 515739: Technology for the production of massively parallel intelligent cantilever- probe platforms for nanoscale analysis and synthesism, PRONANO Meeting, Vienna, 18.-19.10.2005, Vienna, Austria

Publ.-Id: 8064 - Permalink

Thin highly sensitve pizoresistive cantilevers - fabrication of ultra-shallow pn-junctions
Schmidt, B.;
No abstract required
Keywords: Low-energy ion implantation, ultra-shallow boron layers, piezorestistors
  • Lecture (others)
    EU-IP 515739: Technology for the production of massively parallel intelligent cantilever- probe platforms for nanoscale analysis and synthesis, Kick-Off Meeting, 19.-20.04.2005, Erlangen, Germany

Publ.-Id: 8063 - Permalink

Ion beam synthesis of CoSi2 for nanoscale interconnects
Schmidt, B.;
No abstract was required
Keywords: CoSi2, nanowares, nanochains, ion beam synthesis, FIB
  • Lecture (others)
    Seminar INFINEON Dresden, 16.12.2005, Dresden, Germany

Publ.-Id: 8062 - Permalink

Ionenstrahltechnik und Nano-Technologie
Schmidt, B.;
No abstract was required
Keywords: Ion implantation, ion beam synthesis, nanoparticles, nanowires
  • Lecture (others)
    URANIA Vortragszentrum e.V. Dresden, 14.10.2005, Rossendorf, Germany

Publ.-Id: 8061 - Permalink

Ion beam synthesis of CoSi2 for nano-interconnects
Schmidt, B.;
No abstract was required
Keywords: Ion beam synthesis, Fib, Co++-implantation, nanowires
  • Lecture (others)
    Seminar FhG Center of Nanotechnology Dresden, 13.10.2005, Dresden, Germany

Publ.-Id: 8060 - Permalink

Was können Ionenstrahlen in der Nanotechnologie bewirken?
Schmidt, B.;
No abstract was required
Keywords: Ion beam synthesis, nanostructures, nanocrystals, nanowires
  • Lecture (others)
    Sonderseminar Universität der Bundeswehr, 06.10.2005, München-Neubiberg, Germany

Publ.-Id: 8059 - Permalink

Nano-Technologie - Materialien für die Zukunft
Schmidt, B.;
No abstract was required
Keywords: Nanotechnology, Nanostructures, Nanodots, Nanowires, Ion beam synthesis, FIB
  • Lecture (others)
    Lange Nacht der Wissenschaften, 01.07.2005, Dresden, Germany

Publ.-Id: 8058 - Permalink

Correlation of structural and physical properties of metastable Fe-Cr phases
Gorbunov, A.; Levin, A. A.; Meyer, D. C.; Bischoff, L.; Eckert, D.; Köhler, B.; Mertig, M.; Weissbach, T.; Wieser, E.; Pompe, W.;
This paper contributes to the studies of physical properties of metastable Fe-Cr phases which have been discovered recently in the thin films deposited from the hyperthermal Fe and Cr particle beams. The electrical resistance and the magnetic remanence are correlated with the crystallographic parameters and phase composition of the samples. It is demonstrated that the focused ion-beam induced phase transformation in the unusual metastable Fe-Cr alloys can be used for the fabrication of ferromagnetic arrays.
Keywords: metastable Fe-Cr phases, ferromagnetic arrays, FIB
  • Crystal Research and Technology 40(2005), 106

Publ.-Id: 8057 - Permalink

Präparation und Charakterisierung von Strukturen für die Nanotechnologie
Schmidt, B.;
No abstract was required
Keywords: Nanocrystals, Nanowires, FIB, Ion beam synthesis
  • Lecture (others)
    Sonderseminar im Rahmen des Graduiertenkollegs, 27.06.2005, Rostock, Germany

Publ.-Id: 8056 - Permalink

Schmidt, B.;
No abstract was required
Keywords: Nanotechnology, Nanocrystals, Nanowires, Ion beam Synthesis, FIB
  • Lecture (others)
    Lehrerfortbildungsseminar Rossendorf, 12.02.2005, Forschungszentrum Rossendorf, Germany

Publ.-Id: 8055 - Permalink

Ionenstrahlanalytik an den Rossendorfer Beschleunigern
Grötzschel, R.; Grambole, D.; Güttler, D.; Herrmann, F.; Kreißig, U.; Neelmeijer, C.;
Das Ionenstrahllabor des Forschungszentrums Rossendorf als Teil des Institutes für Ionenstrahlphysik und Materialforschung betreibt Materialanalytik mit MeV Ionenstrahlen an 3 Beschleunigern, dem 5 MV Tandem, dem 3 MV Tandetron und dem 2 MV van de Graaff-Beschleuniger.
Insgesamt sind für diese Arbeiten 12 Experimentierplätze installiert, mit denen alle ionenstrahlanalytischen Techniken in hoher Qualität zur Verfügung stehen.
Neben Standardtechniken wie RBS/channeling, ERDA, PIXE und NRA, die wegen spezifischer Vorteile inzwischen unverzichtbar zum Instrumentarium der physikalischen Dünnschicht- Charakterisierung gehören, werden Verfahren eingesetzt und weiterentwickelt, die von hoher Relevanz bei der Entwicklung moderne funktioneller Schichten und deren Abscheidung sind.
Dazu gehört vor allem die quantitative Analytik von Oberflächen und ultradünnen Schichten mit Tiefenauflösungen im sub-nm – Bereich durch den Einsatz von Magnetspektrometern für die hochauflösende Teilchenspektrometrie. Begleitet wird diese methodische Entwicklung von Grundlagenarbeiten zur Abbremsung und zum Ladungsaustausch von leichten Schwerionen in Festkörpern.
Eine andere Richtung wird verfolgt bei der in situ – Ionenstrahlanalytik transienter Prozesse in „Echtzeit“, also während eines Prozessverlaufes.
Im Vortrag werden nach einer kurzen Vorstellung des Ionenstrahllabors die Arbeiten zur Höchstauflösung vorgestellt und ein in situ-Experiment zur Targetvergiftung beim reaktiven Magnetronsputtern beschrieben.
  • Invited lecture (Conferences)
    Zukunftsperspektiven und Anwendungen von Ionenstrahlen, 17.10.2005, Berlin, Deutschland

Publ.-Id: 8054 - Permalink

Nano-Drähte durch Ionenbeschuss
Schmidt, B.; Bischoff, L.; Akhmadaliev, C.; Heinig, K.-H.;
Die fortschreitende Miniaturisierung mikroelektronischer Strukturen sowie deren Kombination mit optischen, mechanischen oder magnetischen Komponenten erfordern laufend neue physikalische und technologische Ansätze. Im Forschungszentrum Rossendorf wird im Rahmen von zwei Projekten, getragen von der Deutschen Forschungsgemeinschaft (DFG), intensiv an der Entwicklung und Untersuchung von Nanostrukturen für die Elektronik der Zukunft gearbeitet. So beschäftigt sich das FZR-Institut für Ionenstrahlphysik und Materialforschung u. a. mit der reproduzierbaren Herstellung von maßgeschneiderten Nano-Drähten, die möglichst passfähig zur herkömmlichen Silizium-Techologie sein sollen.

Die Herstellung dieser Drähte beruht auf der Ionenstrahlsynthese, schematisch in Abb. 2 dargestellt. Hierzu werden feine Linien von Cobalt-Ionen mit dem Fokussierten Ionenstrahl (FIB; Focussed Ion Beam) in ein Silizium-Substrat bei erhöhten Temperaturen implantiert und in einem folgenden Ausheilprozess zu einem Cobaltdisilizid-Draht (CoSi2) synthetisiert. Dabei wird die Kombination zweier wesentlicher Aspekte ausgenutzt. Zum einen wird der geringe Drahtdurchmesser durch die hohe Fokussierbarkeit des FIB auf kleiner als 50 Nanometer erreicht, auch als „top-down“-Ansatz bezeichnet. Zum anderen führen selbst-organisierende Prozesse, der „bottom-up“-Ansatz, zu einer weiteren Konzentration der implantierten Cobalt-Verteilung. Dies ermöglicht die Synthese von Nanostrukturen mit einem Durchmesser von 10 bis 20 Nanometer.

Der Schwerpunkt der Arbeiten konzentriert sich zunächst auf das zur Mikroelektronik-Technologie kompatible Cobaltdisilizid. Dieses Material ist metallisch, weist eine sehr gute Leitfähigkeit auf und ist hinsichtlich der Gitterstruktur der des Siliziums sehr ähnlich. Die ersten Ergebnisse sind vielversprechend, nun gilt es, die Reproduzierbarkeit sowie die genaue „Platzierung“ der Drähte im Material zu gewährleisten. Auf dem Weg hin zu neuen Nano-Bauelementen für die Mikroelektronik ist also noch viel zu tun.
Keywords: nano-wire, CoSi2, ion beam synthesis
  • Dresdner Transferbrief 2(2005), 13-13

Publ.-Id: 8053 - Permalink

Metabolite analysis in positron emission tomography studies: examples from food sciences
Pawelke, B.;
Substances of various chemical structures can be labelled with appropriate positron emitting isotopes and applied as tracer compounds in PET examinations. Using dynamic data acquisition protocols, time-activity curves of radioactivity uptake in organs can be derived and the measurements of tissue tracer concentrations can be translated into quantitative values of tissue function. However, analysis of metabolites of these tracers regarding their nature and distribution in the living organism is an essential need for the quantitative analysis of PET measurements. In addition, metabolite analysis contributes to the interpretation of the images obtained as well as to the identification of pathological changes in metabolic pathways. This paper reports on representative examples of radiolabelled compounds which might be of importance in food science (e.g., amino acids, polyphenols, and model compounds for advanced glycation end products (AGEs)). Typical procedures of analysis (radio-HPLC, radio-TLC) including pre-analytical sample preparation are described. Specific challenges of the method, e.g., trace amounts of radiolabelled compounds and the influence of the often very short half-lives of positron-emitting nuclides used are highlighted. Representative results of analyses of plasma, urine, and tissue samples are presented and discussed in terms of the metabolic fate of the tracers.
Keywords: Positron emission tomography – Metabolite analysis – Tracer – Amino acids – Advanced glycation endproducts – Polyphenols

Publ.-Id: 8052 - Permalink

Small animal positron emission tomography in food sciences
Bergmann, R.; Pietzsch, J.;
Positron emission tomography (PET) is a 3-dimensional imaging technique that has undergone tremendous developments during the last decade. Non-invasive tracing of molecular pathways in vivo is the key capability of PET. It has become an important tool in the diagnosis of human diseases as well as in biomedical and pharmaceutical research. In contrast to other imaging modalities, radiotracer concentrations can be determined quantitatively. By application of appropriate tracer kinetic models, the rate constants of numerous different biological processes can be determined. Rapid progress in PET radiochemistry has significantly increased the number of biologically important molecules labelled with PET nuclides to target a broader range of physiologic, metabolic, and molecular pathways. Progress in PET physics and technology strongly contributed to better scanners and image processing. In this context, dedicated high resolution scanners for dynamic PET studies in small laboratory animals are now available. These developments represent the driving force for the expansion of PET methodology into new areas of life sciences including food sciences. Small animal PET has a high potential to depict physiologic processes like absorption, distribution, metabolism, elimination and interactions of biologically significant substances, including nutrients, ‘nutriceuticals’, functional food ingredients, and foodborne toxicants. Based on present data, potential applications of small animal PET in food sciences are discussed.
Keywords: Positron emission tomography – Food sciences – Small animal PET scanners – PET tracer

Publ.-Id: 8051 - Permalink

Principles of quantitative positron emission tomography
van den Hoff, J.;
The central distinguishing feature of positron emission tomography (PET) is its ability to investigate quantitatively regional cellular and molecular transport processes in vivo with good spatial resolution. This review wants to provide a concise overview of the established principles underlying quantitative data evaluations of the acquired PET images. Especially, the compartment modelling framework is discussed on which virtually all quantification methods utilized in PET are based. The aim of the review is twofold: first, to provide the reader with an idea of the theoretical framework and mathematical tools and second, to enable an intuitive grasp of the possibilities and limitations of a quantitative approach to PET data evaluation. This should facilitate an understanding of how PET measurements translate into quantities such as regional blood flow, volume of distribution, and metabolic rates of specific substrates.
Keywords: Positron emission tomography – PET – Tracer kinetics – Compartment modelling

Publ.-Id: 8050 - Permalink

Ge/Si quantum dot nanostructures grown with low-energy ion beam-assisted epitaxy
Dvurechenskii, A. V.; Smagina, J. V.; Groetzschel, R.; Zinovyev, V. A.; Armbrister, V. A.; Novikov, P. L.; Teys, S. A.; Gutakovskii, A. K.;
Scanning tunneling microscopy (STM) and reflection high-energy electron diffraction (RHEED) experiments were performed to study growth modes induced by hyperthermal Ge+ ion action during molecular beam epitaxy (MBE) of Ge on Si(100). The continuous and pulsed ion beams were used. These studies have shown that ion beam bombardment during heteroepitaxy leads to decrease in critical film thickness for transition from two-dimensional (2D) to three-dimensional (3D) growth modes, enhancement of 3D island density, and narrowing of island size distribution, as compared with conventional MBE experiments. Moreover, it was found that ion beam assists the transition from hut- to dome-shaped Ge islands on Si(100). The crystal perfection of Ge/Si structures with Ge islands embedded in Si was analyzed by Rutherford backscattering/channeling technique,(RBS) and transmission electron microscopy (TEM). The studies of Si/Ge/Si(100) structures indicated defect-free Ge nanopaticles and Si layers for the initial stage of heteroepitaxy (five monolayers of Ge) in pulsed ion beam action growth mode at 350 degrees C. Continuous ion beam irradiation was found to induce dislocations around Ge clusters. The results of kinetic Monte Carlo (KMC) simulation have shown that two mechanisms of ion beam action can be responsible for stimulation of 2D-3D transition: (1) surface defect generation by ion impacts, and (2) enhancement of surface diffusion.
Keywords: ion beam-assisted epitaxy; nanoparticles; self-assembling effects
  • Surface & Coatings Technology 196(2005)1-3, 25-29

Publ.-Id: 8049 - Permalink

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