Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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34122 Publications

Aus alt mach neu – Ripple Pyrometrie für die Blitzlampenausheilung

Reichel, D.; Skorupa, W.; Schumann, T.

Dieser Vortrag befasst sich mit der Temperaturmessung in der Kurzzeitausheilung. Dazu werden die besonderen Anforderungen an die Temperaturmessung in Kurzzeitausheilungsprozessen beleuchtet und historische Lösungen vorgestellt, darunter auch die Ripple Pyrometrie. Letztere wird seit Mitte der Neunziger Jahre erfolgreich für Heißprozesse im Sekundenbereich angewandt. Den Autoren ist es gelungen, diese Methode für Prozesse im Millisekundenbereich (Blitzlampenausheilung) umzusetzen. Experimentelle Ergebnisse werden vorgestellt und hinsichtlich ihres Einflusses auf den Gesamtfehler der Messung analysiert.

Keywords: Ultra-Short Annealing; Temperature Measurement; Ripple Pyrometry; Flash Lamps

  • Lecture (Conference)
    Nutzertreffen Heißprozesse, 23.-24.11.2011, Blaubeuren, Deutschland

Publ.-Id: 16423

3d transition metal diffusion in diluted magnetic semiconductors prepared by pulsed laser processing

Bürger, D.; Seeger, M.; Zhou, S.; Skorupa, W.; Schmidt, H.

High dopant concentrations are often a prerequisite condition for the realization of semiconductors with new functionalities. For example, magnetic dopants can be used to fabricate ferromagnetic semiconductors (FMS) [1] or intermediate band semiconductors for solar cells [2, 3]. The main problem for processing these materials is the very low solubility of magnetic dopants in elementary and III-V semiconductors. Therefore, thermodynamical non-equilibrium conditions have to be applied to overcome these limits. Thereby, the diffusion path during processing has to be as short as possible to reduce clustering processes which would result in a deactivation of dopants.
The diffusion barrier Q of standard shallow donor or acceptor dopants in the solid phase
is generally high which results in very low diffusion coefficients. Therefore, during the fast cooling process after PLA, diffusion or hopping of such shallow dopant atoms in recrystallized Si and GaAs has not been considered in detail and no models were developed which quantify interdiffusion processes of dopants for materials with large bulk diffusion barriers Q. However, 3d transition metal dopants in the most important semiconductors have relatively small bulk diffusion barriers Q that result in higher diffusion rates as compared to standard shallow donors. Therefore, the usual assumption that dopants remain fixed on their initial position during PLA processing has to be verified for each type of magnetic dopant in semiconductor spintronics materials.
In this work, we perform a Monte Carlo Study on a three-dimensional diffusion model to evaluate the kinetics of initial clustering in a simple cubic host:dopant system. In a second step, the temperature quenching process during PLA was calculated for the materials GaAs and Si and conclusions about diffusion and clustering of typical 3d transition metal dopants can be drawn with respect to the PLA parameters. For Mn in GaAs we also consider declustering effects that have to be included for strongly diffusing dopants like Mn in Si.

[1] T. Dietl, H. Ohno, F. Matsukura, J. Cibert, and D. Ferrand, Science 287, 1019 (2000).
[2] A. Luque and A. Marti, Phys. Rev. Lett. 78, 5014 (1997).
[3] J. Olea, M. Toledano-Luque, D. Pastor, G. Gonzáles-Díaz, and I. Mártil, J. Appl. Phys. 104, 016105 (2008).

Keywords: nanoscale clustering; diffusion; diluted magnetic semiconductor

  • Poster
    subtherm 2011, 24.-27.10.2011, Dresden, Deutschland

Publ.-Id: 16422

CFD-Simulations of an impinging jet using a polydispersed multi-field model approach

Hänsch, S.; Lucas, D.; Krepper, E.; Danciu, D.-V.

A new CFD-strategy of a generalized two-phase flow (GENTOP) is presented. The idea of GENTOP combines a multi-field simulation with the recently developed Multiple Size Group (MUSIG) -approach. In the MUSIG-framework, transfers between the different bubble size groups due to bubble coalescence and –breakup are described. By modelling an additional mass transfer between the polydispersed and continuous gas phase, transitions between different gas morphologies can be considered. The continuous gas phase represents the largest gas structures so that for these structures the gas-liquid-interfaces are resolved. This new concept can give a more detailed explanation of complex flow situations, particularly with higher gas fractions, such as the impinging jet being just one application. First results computed by the CFD-code CFX 13.0 are compared to experiments and theoretical data reported in literature.

Keywords: multiphase flow; turbulent impinging jet; free surface; air entrainment; multi-field simulation; MUSIG-model

  • Contribution to proceedings
    6th International Berlin Workshop on Transport Phenomena with Moving Boundaries, 24.-25.11.2011, Berlin, Deutschland
    Proceedings of the 6th International Berlin Workshop on Transport Phenomena with Moving Boundaries
  • Lecture (Conference)
    6th International Berlin Workshop on Transport Phenomena with Moving Boundaries, 24.-25.11.2011, Berlin, Deutschland

Publ.-Id: 16421

Magnetic and optical properties of virgin arc furnace grown MgO crystals

Prucnal, S.; Shalimov, A.; Ozerov, M.; Potzger, K.; Skorupa, W.

Transition metal ions (Mn2+, Cr3+, Fe2+/3+, V2+) as substitutional impurities in cubic crystals play an important role due to their influence on the magneto-optical properties of the virgin crystals. The optical and magnetic properties of commercial MgO(001) single crystals were investigated. The PL spectra of 3d impurity ions (Cr3+ and V2+) show narrow zero phonon lines with decay times in the range of milliseconds and a broad multiphonon sideband decaying in microseconds. The EPR study exhibits hyperfine components corresponding to Mn atoms and to V atoms located in orthorhombic symmetry. The intensity change of the EPR and PL spectra as well as the variation of the decay time with temperature can be explained by electron-spin lattice relaxation due to the Raman process.

Keywords: MgO; Point defects; Magneto-optic materials; Photoluminescence; Magnetism

Publ.-Id: 16420

Determination of secondary ion mass spectrometry relative sensitivity factors for polar and non-polar ZnO

Laufer, A.; Volbers, N.; Eisermann, S.; Potzger, K.; Geburt, S.; Ronning, C.; Meyer, B.

Zinc oxide (ZnO) is regarded as a promising material for optoelectronic devices, due to its electronic properties. Solely, the difficulty in obtaining p-type ZnO impedes further progress. In this connection, the identification and quantification of impurities is a major demand. For quantitative information using secondary ion mass spectrometry (SIMS), so-called relative sensitivity factors (RSF) are mandatory. Such conversion factors did not yet exist for ZnO. In this work, we present the determined RSF values for ZnO using primary (ion implanted) as well as secondary (bulk doped) standards. These RSFs have been applied to commercially available ZnO substrates of different surface termination (a-plane, Zn-face, and O-face) to quantify the contained impurities. Although these ZnO substrates originate from the same single-crystal, we observe discrepancies in the impurity concentrations. These results cannot be attributed to surface termination dependent RSF values for ZnO.

Keywords: ZnO; SIMS

Publ.-Id: 16419

Systematics of azimuthal asymmetries in heavy ion collisions in the 1 A GeV regime

Reisdorf, W.; Leifels, Y.; Andronic, A.; Averbeck, R.; Barret, V.; Basrak, Z.; Bastid, N.; Benabderrahmane, M. L.; Caplar, R.; Crochet, P.; Dupieux, P.; Dzelalija, M.; Fodor, Z.; Gasik, P.; Grishkin, Y.; Hartmann, O. N.; Herrmann, N.; Hildenbrand, K. D.; Hong, B.; Kang, T. I.; Kecskemeti, J.; Kim, Y. J.; Kirejczyk, M.; Kis, M.; Koczon, P.; Korolija, M.; Kotte, R.; Kress, T.; Lebedev, A.; Lopez, X.; Matulewicz, T.; Merschmeyer, M.; Neubert, W.; Petrovici, M.; Piasecki, K.; Rami, F.; Ryu, M. S.; Schuettauf, A.; Seres, Z.; Sikora, B.; Sim, K. S.; Simion, V.; Siwek-Wilczynska, K.; Smolyankin, V.; Stockmeier, M.; Stoicea, G.; Tyminski, Z.; Wisniewski, K.; Wohlfarth, D.; Xiao, Z. G.; Xu, H. S.; Yushmanov, I.; Zhilin, A.

Using the large acceptance apparatus FOPI, we study central and semi-central collisions in the reactions (energies in A GeV are given in parentheses): 40Ca+40Ca (0.4, 0.6, 0.8, 1.0, 1.5, 1.93), 58Ni+58Ni (0.15, 0.25, 0.4), 96Ru+96Ru (0.4, 1.0, 1.5), 96Zr+96Zr (0.4, 1.0, 1.5), 129Xe+CsI (0.15, 0.25, 0.4), 197Au+197Au (0.09, 0.12, 0.15, 0.25, 0.4, 0.6, 0.8, 1.0, 1.2, 1.5). The observables include directed and elliptic flow. The data are compared to earlier data where possible and to transport model simulations. A stiff nuclear equation of state is found to be incompatible with the data. Evidence for extra-repulsion of neutrons in compressed asymmetric matter is found.

Publ.-Id: 16418

Actinide(IV)-oxyhydroxide colloids vs. actinide(IV)-silica colloids: their relevance for environmental conditions

Zänker, H.; Hennig, C.; Weiss, S.

Evidence is provided by PCS, ultrafiltration and ultracentrifugation that uranium(IV) can form silicate-containing colloids. The particles are generated in near-neutral to slightly alkaline solutions containing background chemicals of geogenic nature (carbonate, silicate, sodium ions). They remain stable in aqueous suspension over years. A concentration of up to 10-3 M of colloid-borne U(IV) was observed which is a concentration much higher than the concentrations of truly dissolved or colloidally suspended waterborne An(IV) species hitherto reported for the near-neutral pH range. The prevailing size of the particles is below 20 nm. Laser Doppler velocimetry reveals that the nanoparticles are stabilized in solution by electrostatic repulsion due to a negative zeta potential caused by the silicate. The isoelectric point of the nanoparticles is shifted toward lower pH values by the silicate. Extended X-ray absorption fine structure (EXAFS) spectroscopy showed that U-O-Si bonds, which increasingly replace the U-O-U bonds of the amorphous uranium(IV) oxyhydroxide with increasing silicate concentrations, make up the internal structure of the colloids.
Keywords: uranium(IV), silicate, colloids, near-neutral pH

Keywords: uranium(IV); thorium(IV); silicate; colloids; near-neutral pH

  • Lecture (Conference)
    12. Koordinierungsgespräch HZDR – PSI/LES, 08.-09.12.2011, 08.-09.12.2011, Villigen, Schweiz

Publ.-Id: 16417

Singular surfaces associated with multiple eigenvalues and related physical effects

Kirillov, O.

It is common to consider that generically discrete eigenvalues of an operator are simple. However, in multiparameter operator families multiple eigenvalues are a robust phenomenon. Singular ruled surfaces were studied already by John Wallis, who in 1655 introduced his famous conical wedge known in the modern physical literature under the name of the “double coffee filter”. Later on, due to the efforts of Monge, Catalan, Plücker, Steiner and Cayley, the development of the theory of the ruled surfaces had lead to the formulation of the projective geometry. A first non-trivial physical effect related to the double semi-simple eigenvalue was discovered by Hamilton in 1833, who established that it determines a conical singularity of the dispersion surface – the Hamilton’s diabolical point (DP) – that yields a conical ray surface, which is observable in experiments with birefringent crystals as a conical refraction. In the presence of absorption and optical activity the conical singularities of the dispersion surface can transform into branch points that correspond to double eigenvalues with the Jordan block (exceptional points, EPs). This happens because the matrix determining the dispersion relation becomes a non-Hermitian one, for which an EP has a lower codimension than for a DP. In my presentation I will talk about manifestation of the multiple eigenvalues and the singular surfaces associated with them in modern physical applications such as magnetohydrodynamics dynamo and helical magnetorotational instability where the singularities determine non-trivial scaling laws and help to establish important limits for the critical parameters. I will discuss the role of the singularities in dissipation-induced instabilities on the example of the Brouwer’s problem on a heavy particle in a rotating vessel and show its connection to the modern works on crystal optics, wave propagation and rotor dynamics. Finally, I will touch the issue of the geometric phase in non-Hermitian systems.

Keywords: Instability threshold; parameters; optimization; non-smooth merit functions; multiple eigenvalues; dissipation-induced instabilities

  • Lecture (others)
    Lecture at the seminar of Prof. Roland Ketzmerick, Max-Planck-Institut für Physik komplexer Systeme (MPI-PKS), 21.01.2011, Dresden, Germany


Publ.-Id: 16416

Singular surfaces and multiple eigenvalues in stability and optimization of non-conservative systems

Kirillov, O.

it is common to consider that generically discrete eigenvalues of an operator are simple. However, in multiparameter operator families multiple eigenvalues are a robust phenomenon. Singular ruled surfaces were studied already by John Wallis, who in 1655 introduced his famous conical wedge known in the modern physical literature under the name of the “double coffee filter”. Later on, due to the efforts of Monge, Catalan, Plücker, Steiner and Cayley, the development of the theory of the ruled surfaces had lead to the formulation of the projective geometry. In XXth century the singular surfaces reappeared again in the form of a powerful singularity theory. In my presentation I will talk about multiple eigenvalues and associated singular surfaces in stability and optimization problems for non-conservative systems. First, I consider circulatory systems without damping that describe stability of columns under follower loads and torques, friction-induced instabilities in rotor dynamics as well as aeroelastic stability problems. I present an algorithm for classification of generic singularities on the stability boundary of a circulatory system and list all generic singularities up to codimension 10. I plot generic singularities on the stability boundary for one-, two-, and three-parameter families of circulatory systems and show how to approximate the boundary near the singularities studying perturbation of simple and multiple eigenvalues. I illustrate the general theory by the examples from robotics, rotor dynamics and structural optimization. In the latter case structural optimization of the m-link Ziegler pendulum will be considered and derivation of optimality conditions as well as the connection of the optimal solutions to singularities on the stability boundary will be discussed. Then, I will study the effect of small dissipation on the stability of circulatory systems. In 1952 Ziegler found that an infinitesimally small amount of damping leads to a finite change in the stability domain of a two-link pendulum loaded by the follower force. In 1956 Bottema resolved this destabilization paradox by means of the Whitney umbrella singularity that as he established exists on the stability boundary of the damped Ziegler’s pendulum. I will talk about extensions of this result to general finite dimensional and continuous circulatory systems as well as to the gyroscopic systems with small damping and non-conservative positional forces. Examples of similar paradoxal phenomena from rotor dynamics, soil mechanics and magnetohydrodynamics will be considered in detail.

Keywords: Multiparameter stability problems; stability boundary; singularities; parametric optimization; multiple eigenvalues; dissipation-induced instabilities

  • Lecture (others)
    Lecture at the seminar of Prof. Felix Darve, Laboratoire 3S-R: Sols, Solids, Structures, Risques, 24.02.2011, Grenoble, France


Publ.-Id: 16415

Re-visiting structural optimization of the Ziegler pendulum: singularities and exact optimal solutions

Kirillov, O.

Structural optimization of non-conservative systems with respect to stability criteria is a research area with important applications in fluid-structure interactions, friction-induced instabilities, and civil engineering. In contrast to optimization of conservative systems where rigorously proven optimal solutions in buckling problems have been found, for non-conservative optimization problems only numerically optimized designs were reported. The proof of optimality in the non-conservative optimization problems is a mathematical challenge related to multiple eigenvalues, singularities on the stability domain, and non-convexity of the merit functional. We present a study of the optimal mass distribution in a classical Ziegler’s pendulum where local and global extrema can be found explicitly. In particular, for the undamped case, the two maxima of the critical flutter load correspond to a vanishing mass either in a joint or at the free end of the pendulum; in the minimum, the ratio of the masses is equal to the ratio of the stiffness coefficients. The role of the singularities on the stability boundary in the optimization is highlighted and extension to the damped case as well as to the case of higher degrees of freedom is discussed.

Keywords: Non-conservative systems; oscillatory instabilities; stability boundary; singularity; parametric optimization

Publ.-Id: 16414

Singularities on the boundaries of magnetorotational instabilities and scaling laws

Kirillov, O.; Stefani, F.

In the theory of magnetorotational instability and its modern extensions such as the helical MRI, non-trivial scaling laws between the critical parameters are observed. In case of the standard MRI it is well known that the Reynolds and Hartmann numbers are scaled as Re ∼ Ha2 while for the helical MRI Re ∼ Ha3. What is less known is that the thresholds of SMRI and HMRI plotted as surfaces in the space of parameters, possess singularities that determine the scaling laws. Moreover, the two paradoxes of SMRI and HMRI in the limits of infinite and zero magnetic Prandtl number (Pm), respectively, sharply correspond to the singularities on the instability thresholds. In either case, it is the local Plücker conoid structure that explains the non-uniqueness of the critical Rossby number, and its crucial dependence on the Lundquist number. For HMRI, we have found an extension of the former Liu limit Roc ≃ −0.828 (valid for Lu = 0) to a somewhat higher value Ro ≃ −0.802 at Lu = 0.618 which is, however, still below the Kepler value.

Keywords: Standard Magnetorotational instability; Helical magnetorotational instability; interaction parameter; scaling law

Publ.-Id: 16413

Formation of Soluble Hexanuclear Neptunium(IV) Nano-Clusters in Aqueous Solution: Growth Termination of Actinide(IV) Hydrous Oxides by Carboxylates

Takao, K.; Takao, S.; Scheinost, A.; Bernhard, G.; Hennig, C.

Complexation of NpIV with several carboxylates (RCOO–; R = H, CH3, CHR’NH2; R’ = H, CH3, CH2SH) in moderately acidic aqueous solutions were studied by using UV-vis-NIR and X-ray
absorption spectroscopy. As pH increased, all investigated carboxylates initiated formation of watersoluble hexanuclear complexes, Np6(μ-RCOO)12(μ3-O)4(μ3-OH)4, where the neighboring Np atoms are connected by RCOO– syn-syn bridges and the triangular faces of the Np6 octahedron are capped with μ3-O2–/μ3-OH–. The structure information of Np6(μ-RCOO)12(μ3-O)4(μ3-OH)4 was extracted from the EXAFS data: Np–O2– = 2.22-2.23 Å (coordination number, N = 1.9-2.2), Np–O(RCOO–) and Np–OH– = 2.42-2.43 Å (N = 5.6-6.7 in total), Np···C(RCOO–) = 3.43 Å (N = 3.3-3.9), Np···Np(neighbor) = 3.80-3.82 Å (N = 3.6-4.0), Np···Np(terminal) = 5.39-5.41 Å (N = 1.0-1.2). For the simpler carboxylates, the gross stability constants of Np6(μ-RCOO)12(μ3-O)4(μ3-OH)4 and related monomers, Np(RCOO)(OH)2 +, were determined from the UV-vis-NIR titration data: R = H, log β6,12,–12 = 42.7 ± 1.2, log β1,1,–2 = 2.51 ± 0.05 at I = 0.62 M and 295 K; R = CH3, log β6,12,–12 = 52.0 ± 0.7, log β1,1,–2 = 3.86 ± 0.03 at I = 0.66 M and 295 K.

Publ.-Id: 16412

Dual beam irradiation of nanostructured FeCrAl oxide dispersion strengthened steel

Chen, C. L.; Richter, A.; Kögler, R.; Talut, G.

Nanostructured ferritic oxide dispersion strengthened (ODS) alloy is an ideal candidate for fission/fusion power plant materials, particularly in the use of a first-wall and blanket structure of a next generation reactor. These steels usually contain a high density of Y–Ti–O and Y–Al–O nanoparticles, high dislocation densities and fine grains. The material contains nanoparticles with an average diameter of 21 nm and was treated by several cold rolling procedures, which modify the dislocation density. Structural analysis with HRTEM shows that the chemical composition of the initial Y2O3 oxide is modified to perovskite YAlO3 (YAP) and Y2Al5O12 garnet (YAG). Irradiation of these alloys was performed with a dual beam irradiation of 2.5 MeV Fe+/31 dpa and 350 keV He+/18 appm/dpa. Irradiation causes atomic displacements resulting in vacancy and self-interstitial lattice defects and dislocation loops. Extended SRIM calculations for ODS steel indicate a clear spatial separation between the excess vacancy distribution close to the surface and the excess interstitials in deeper layers of the material surface. The helium atoms are supposed to accumulate mainly in the vacancies. Additionally to structural changes, the effect of the irradiation generated defects on the mechanical properties of the ODS is investigated by nanoindentation. A clear hardness increase in the irradiated area is observed, which reaches a maximum at a close surface region. This feature is attributed to synergistic effects between the displacement damage and He implantation resulting in He filled vacancies. Fine He cavities with diameters of a few nanometers were identified in TEM images.

Keywords: Irradiation damage; ion implantation; ODS material; irradiation hardening

Publ.-Id: 16411

Irradiation damage in dual beam irradiated nanostructured FeCrAl oxide dispersion strengthened steel

Richter, A.; Chen, C.-L.; Mücklich, A.; Kögler, R.

An oxide dispersion strengthened steel is produced which contains Y-Al-Ti-O nanoparticles with an average diameter of 21 nm. HRTEM analysis shows that the chemical composition of the Y2O3 oxide is modified with perovskite YAlO3 (YAP), Y2Al5O12 garnet (YAG) and Y4Al2O9 monoclinic (YAM) particles. Irradiation of these alloys was performed with a dual ion beam system operating simultaneously with 2.5 MeV Fe+ to 31 dpa and 350 keV He+ to 18 appm/dpa. Ion bombardment causes atomic displacements resulting in vacancy and self-interstitial lattice defects and dislocation loops. TRIM calculations for ODS steel indicate a clear spacial separation between vacancies and self-interstitials at which the vacancy distribution is close to the surface and the interstitials are deposited at a deeper position. The helium atoms mainly accumulate in the vacancies. Fine He cavities with diameters of a few nanometers were identified in HRTEM images. Additionally to structural changes, irradiation generated defects also affect the mechanical properties of the ODS steel. These were investigated by nanoindentation, which is a suitable measuring method as the irradiation damage is created within a thin surface layer. A clear hardness increase in the irradiated depth region was observed, which reaches a maximum close to the surface. This indicates the He condensation in the vacancy dominated region as predicted by the simulations.

Keywords: Irradiation damage; ion implantation; ODS material; radiation hardening of materials

  • Materials Research Society Symposium Proceedings 1298(2011), 141-146
    DOI: 10.1557/opl.2011.47

Publ.-Id: 16410

Doping of Si nanowires by ion implantation

Ou, X.; Geyer, N.; Kögler, R.; Schwen, D.; Werner, P.; Skorupa, W.

Silicon nanowires (Si NWs) have generated enormous scientific interest as building blocks for future nanoelectronics. Due to the quasi-one dimensional structure and a high surface to volume ratio of Si NWs controlled doping to change their electrical properties is challenging. Also, in order to understand the doping mechanism various techniques were used to qualify the spatial distribution and electrical activation of dopant atoms in Si. In our previous work strong surface segregation of implanted phosphorus was found after the rapid thermal annealing (RTA). [1] The studies were carried out for relatively thick Si NWs grown by Molecular Beam Epitaxy (MBE) with a diameter of ~100 nm. However, the preferable size for the future logic application is in the range below 20 nm. This work will also discuss the doping behavior of the thin Si NWs with diameters of sub-20 nanometer fabricated by metal-assisted chemical etching. Electrical characterization of the thin NWs was performed by SSRM of the NW cross section. The issues of the doping of such thin NWs by ion implantation and the diameter dependence of the boron activation in the Si NW are discussed.
[1] Xin Ou et al., Nano Letters, 10 (2010) 171.

Keywords: Nano wires; doping; ion implantation

  • Lecture (Conference)
    Workshop "Ionen- und Positronenstrahlen", 04.07.2011, München, Germany

Publ.-Id: 16409

Laser accelerated protons captured and transported by a pulse power solenoid

Burris-Mog, T.; Harres, K.; Nürnberg, F.; Busold, S.; Bussmann, M.; Deppert, O.; Hoffmeister, G.; Joost, M.; Sobiella, M.; Tauschwitz, A.; Zielbauer, B.; Bagnoud, V.; Herrmannsdoerfer, T.; Roth, M.; Cowan, T. E.

Using a pulse power solenoid, we demonstrate efficient capture of laser accelerated proton beams and the ability to control their large divergence angles and broad energy range. Simulations using measured data for the input parameters give inference into the phase-space and transport efficiencies of the captured proton beams. We conclude with results from a feasibility study of a pulse power compact achromatic gantry concept. Using a scaled target normal sheath acceleration spectrum, we present simulation results of the available spectrum after transport through the gantry.

Keywords: laser acceleration; laser accelerated protons; pulse power; solenoid focusing; beam transport; proton ion cancer therapy

Publ.-Id: 16408

Fresnoite thin films grown by pulsed laser deposition: photoluminescence and laser crystallization

Müller, A.; Lorenz, M.; Brachwitz, K.; Lenzner, J.; Mittwoch, K.; Skorupa, W.; Grundmann, M.; Höche, T.

Fresnoite (Ba2TiSi2O8–BTS) thin films were grown on fused quartz, silicon (100), MgO (100), and aplane sapphire by pulsed laser deposition, and crystallized by subsequent thermal or flash lamp annealing. The corresponding texture evolution of the BTS thin films was studied by X-ray diffraction. The preferential (001) texture of the crystallised BTS films was found to be most pronounced on sapphire substrates. The broad photoluminescence band of the BTS thin films depends only weakly on temperature. The intensity of the BTS luminescence can be as high as that of the most efficient oxide scintillator materials. In order to qualify the fresnoite thin films for photonic applications, we demonstrate infrared-laser direct writing in amorphous BTS films which allows a local crystallisation and patterning. A subsequent considerable enhancement of luminescence intensity can be applied for UV-sensitive marking of nearly any object.

Keywords: pulsed laser deposition; photoluminescence; laser crystallization; flash lamp annealing; Fresnoite

Publ.-Id: 16407

Ion beam synthesis of III-V nanocrystals in silicon

Prucnal, S.; Facsko, S.; Baumgart, C.; Schmidt, H.; Liedke, M. O.; Mücklich, A.; Zhou, S.; Skorupa, W.

Integration of III-V semiconductors with a silicon technology is crucial for the device performance. In this paper we present investigations of the microstructural, optical and electrical properties of III-V quantum dots (InAs, GaAs, InP and GaP) formed in silicon. The III-V QDs were obtained by means of sequential ion implantation and flash lamp annealing (FLA). Conventional selective etching was used to form the n-III-V/p-Si heterojunction. In case of InAs/Si heterostructures, the current-voltage measurement confirms the heterojunction diode formation with the ideality factor of 4.6. Kelvin Probe Force Microscopy measurements indicate a type-II band alignment of n-type InAs NPs on p-type silicon. The main advantage of our method is its integration with large-scale silicon technology, which also allows applying it for Si-based electronic devices.

Keywords: ion implantation; heteroepitaxy; indium arsenide; flash lamp annealing; quantum dots

  • Invited lecture (Conferences)
    46.Deutsches Nutzertreffen Ionenimplantation, 24.11.2011, Blaubeuren, Deutschland

Publ.-Id: 16406

Kelvin probe force microscopy imaging on locally doped silicon nanowires

Baumgart, C.; Habicht, S.; Feste, S.; Helm, M.; Schmidt, H.

Kelvin probe force microscopy (KPFM) [1] is used for the nanoscale characterization of silicon nanowires (NWs). Horizontal NW arrays have been prepared from a silicon-on-insulator (SOI) starting material. After transferring the NW structures into the Si top layer by means of electron-beam lithography and reactive ion etching, the samples have been locally implanted with B and As. Activation of dopants was carried out by a rapid thermal annealing for 5 s at 1000 °C. Athena simulations showed that for the applied implantation and annealing conditions a box-like dopant distribution with comparable concentration of activated dopants can be assumed [2]. Quantitative dopant profiling by means of KPFM is successfully employed to locate the junctions along the B-doped and As-doped Si NWs. In addition, the influence of local intrinsic electric fields [3] is discussed for the investigated SOI structures.
[1] C. Baumgart, M. Helm, H. Schmidt, Phys. Rev. B 80, 085305 (2009). [2] S. F. Feste, J. Knoch, S. Habicht, D. Buca, Q.-T. Zhao, S. Mantl, Solid-State Electronics 53, 1257 (2009). [3] C. Baumgart, A.-D. Müller, F. Müller, and H. Schmidt, Phys. Stat. Sol. A 208, 777 (2011).

  • Poster
    Subtherm 2011, 25.-27.10.2011, Dresden, Deutschland

Publ.-Id: 16405

Gas phase silanization at normal pressure of Si-based integrated light emitters for smart biosensor applications

Germer, S.; Cherkouk, C.; Rebohle, L.; Helm, M.; Skorupa, W.

A different silanization method for SiO2 surfaces has been raised for Si-based light emitter which are considered as light sources in sensors for the detection of harmful biomolecules. This approach uses a special experimental setup for gas phase silanization (GPS) and is based on the evaporation and deposition in nitrogen atmosphere at normal pressure for 15 minutes with different silane volumes. The light emitter has a SiO2 passivation layer on the top which was hydrolyzed in an in situ hybridization chamber and catalyzed with MES (2-(N-morpholino)ethanaesulfone acid hydrate) buffer solution. Afterward, the substrates were silanized with the GPS method using the organosilane (3-Aminopropyl)trimethoxysilane (APTMS). Infrared spectroscopy, X-ray spectroscopy and Atomic force microscopy were used to control and characterize the structure of the SiO2 surface and the APTMS layer. The results demonstrate a successful covalent binding of the coupling agent and the interaction of the deposited molecules with each other. The roughness of the modified surface was investigated by the Atomic force microscopy. The silanized samples show rough and textured surfaces. At last, the suitability of the developed GPS method was verified on light emitters.

Keywords: Si-based light emitter; biosensor; APTMS; silanization; amines

  • Thesis / Students' report
    Technische Universität Freiberg, 2010
    76 Seiten

Publ.-Id: 16404

Investigation of rare earth implanted SiO2 thin films for Down-conversion applications in Photovoltaic's

Germer, S.; Günz, C.; Lehmann, J.; Rebohle, L.; Helm, M.; Skorupa, W.

In this report we present our recent investigations of rare earth (Ce, Tb) implanted SiO2 thin films for Down-conversion (DC) as an application for solar cells. Photovoltaic modules (PV) are showing high losses in the ultra violet range of the incident sunlight, because of band gap losses and front layer absorption. DC layers are applied to the front surface of photovoltaic cells to enhance solar cell efficiency

Keywords: down-conversion; photovoltaic; rare earth atoms; solar cells

  • Poster
    Subsecond thermal processing of Advanced Materials 2011, 24.-28.10.2011, Dresden, Deutschland

Publ.-Id: 16403

Liquid phase processing in the millisecond range for III-V heterostructures in silicon

Prucnal, S.; Facsko, S.; Baumgart, C.; Schmidt, H.; Liedke, M. O.; Mücklich, A.; Zhou, S.; Skorupa, W.

Integration of III-V semiconductors with a silicon technology is crucial for the device performance. In this paper we present investigations of the microstructural, optical and electrical properties of III-V quantum dots (InAs, GaAs, InP and GaP) formed in silicon. The III-V QDs were obtained by means of sequential ion implantation and flash lamp annealing (FLA). Conventional selective etching was used to form the n-III-V/p-Si heterojunction. In case of InAs/Si heterostructures, the current-voltage measurement confirms the heterojunction diode formation with the ideality factor of 4.6. Kelvin Probe Force Microscopy measurements indicate a type-II band alignment of n-type InAs NPs on p-type silicon. The main advantage of our method is its integration with large-scale silicon technology, which also allows applying it for Si-based electronic devices.

Keywords: ion implantation; heteroepitaxy; indium arsenide; flash lamp annealing; quantum dots

  • Invited lecture (Conferences)
    30.Deutsches Nutzertreffen RTP und Heissprozesse, 23.-23.11.2011, Blaubeuren, Deutschland

Publ.-Id: 16402

In-medium operator product expansion for heavy-light-quark pseudoscalar mesons

Zschocke, S.; Hilger, T.; Kämpfer, B.

The operator product expansion (OPE) for heavy-light-quark pseudoscalar mesons (D -mesons and B -mesons) in medium is determined, both for a moving meson with respect to the surrounding medium as well as for a meson at rest. First of all, the OPE is given in terms of normal-ordered operators up to mass dimension 5, and the mass of the heavy quark and the mass of the light quark are kept finite. The Wilson coefficients of such an expansion are infrared (IR) divergent in the limit of a vanishing light-quark mass. A consistent separation of scales necessitates an OPE in terms of non-normal-ordered operators, which implies operator mixing, where the IR-divergences are absorbed into the operators. It is shown that the Wilson coefficients of such an expansion are IR-stable, and the limit of a vanishing light-quark mass is perfomed. Details of the major steps for the calculation of the Wilson coefficients are presented. By a comparison with previous results obtained by other theoretical groups we have found serious disagreements.

Publ.-Id: 16401

Light-emission from rare-earth implanted amorphous silicon dioxide layers

Skorupa, W.; Rebohle, L.

Over the last more than 15 years we have been employing ion beam processing to dope gate-type amorphous silicon dioxide layers grown by thermal oxidation with a variety of species, mostly rare earth elements, to use these layers for the purpose of electroluminescence from a MOS capacitor device based on silicon technology. The main motivation for this work was the integration of optoelectronic functionality into silicon-based electronic circuits as one of the key challenges for future semiconductor applications. Here we report on different rare earth (RE) luminescent centres embedded into the silicon dioxide layer of purpose-designed Metal-Oxide-Silicon-based Light Emitting Devices (MOSLEDs) with advanced electrical performance. Efficient electroluminescence was obtained from UV to infrared with a transparent top electrode made of indium-tin oxide. The electrical and electroluminescence properties of these devices are discussed in respect of possible applications for biosensing. Most of our work was recently published in one of the Springer textbook series [1]. Special devotion will be given in the talk to Akos G.Revesz who died in 2008 [2]. He was one of the pioneers of the physico-chemistry of amorphous silicon dioxide devoted to MOS technology.
[1] L.Rebohle & W.Skorupa “Rare-Earth Implanted MOS Devices for Silicon Photonics”, Springer Series in Materials Science vol.142, 2010

Keywords: silicon dioxide; ion implantation; MOSLED; rare earth atoms; electroluminescence

  • Invited lecture (Conferences)
    EMRS Fall Meeting, Symp.B: Amorphous nanostructure materials, 19.-23.09.2011, Warsaw, Poland

Publ.-Id: 16400

Mikrofluidisches System zum Nachweis von hormonaktiven Substanzen in wässrigen Lösungen

Cherkouk, C.; Rebohle, L.; Howitz, S.; Skorupa, W.

In dieser Arbeit wird ein mikrofluidisches System zum Nachweise von hormonaktiven Substanzen (engl. EDC´s) in wässrigen Lösung vorgestellt. Diese Plattform-Technologie besteht aus vier getrennten mikrofluidischen Einheiten aus Polydimethylsiloxan (PDMS) und Glas, und bietet damit die Möglichkeit einen selektiven Nachweis von mindestens zwei Substanzen pro ein Einweg Chip, dessen Oberfläche mit den jeweiligen Rezeptoren immobilisiert ist. Der Chip selbst enthält eine integrierte Silizium-basierte Lichtquelle. Das Nachweiskonzept basiert auf der direkten Fluoreszenzanalyse. Zur Optimierung der elektrischen Parameter wurden Elektrolumineszenzmessungen (EL) als Funktion der Farbstoffkonzentration( QD800) im Kanal durchgeführt.

Keywords: Si-basierter Lichtemitter; Biosensor; Mikrofluidik; Fluoreszenz; Estrogen; EDC

  • Poster
    10. Dresdner Sensor-Symposium, 05.-07.12.2011, Dresden, Deutschland

Publ.-Id: 16399

Flow field assessment under a plunging liquid jet

Kendil, F. Z.; Danciu, D. V.; Schmidtke, M.; Bousbia, A. S.; Lucas, D.; Krepper, E.; Mataoui, A.

Within the current study, experimental investigations and computational fluid dynamics (CFD) simulations were performed to investigate the flow field structure developed under a turbulent liquid jet plunging into a quiescent pool of water. This topic is still challenging for CFD codes. Indeed, the study of turbulence in two-phase bubbly flows is one domain where experimental, numerical, and theoretical work is being extensively done nowadays. A correct description of closure laws for drag, lift, and interfacial forces is of great importance in numerical simulations.
Most critical with respect to CFD is the impact region between the jet and free surface of the liquid pool. Here, a complex interaction between surface waves and turbulence leads to the entrainment of air. These phenomena occur on very small scales. Up to now, it is not possible to resolve all relevant scales in one simulation due to limited computational resources. Therefore in this work, all phenomena above the pool surface and the impact region are excluded and the focus is set on the development of the flow field below the pool surface. The jet is modeled as a two-phase bubbly flow injecting into the pool.
For this purpose, the Particle Image Velocimetry (PIV) was utilized as measuring technique. Velocity fields for both impinging region and recirculation zone developed in the tank below the free surface were quantified and instantaneous and time-averaged velocity fields were obtained. For test cases where air entrainment occurred, only the recirculation region situated outside the bubble plume was quantified.On the other hand, the numerical simulations were performed using ANSYS-CFX 12.0, a commercial CFD package that solves the Navier-Stokes equations via a finite volume method and a coupled solver. The 2D as well as 3D simulation results are presented and compared with experimental results. Comparisons with the experimental data reveal satisfactory predictions of mean flow quantities, obtained by applying proper models of inter-phase momentum transfer.

Publ.-Id: 16398

Electrical Transport in Individual ZnO Nanorods Studied by Photo-Conductive Atomic-Force Microscopy

Teichert, C.; Beinik, I.; Kratzer, M.; Brauer, G.; Chen, X. Y.; Hsu, Y. F.; Djurisic, A.

One-dimensional ZnO nanostructures exhibit technological potential for many device applications, like efficient low-cost ZnO nanorod-polymer solar cells [1]. Conductive atomic-force microscopy (AFM) is a valuable tool for nanometer-scale electrical characterization of such nanorods [2]. Here, we present a complementary study of electrical transport in individual upright standing ZnO nanorods (NRs) grown by thermal evaporation [4] using conductive AFM (C-AFM) and photoconductive AFM (PC-AFM) [5]. Initially, the electrical properties of the arrays of upright standing ZnO NRs were characterized using two-dimensional current maps measured at different bias voltages applied to the sample contact mode. Further, C-AFM was utilized to determine the local current-to-voltage (I-V) characteristics of the top and side facets of individual upright standing NRs. PC-AFM investigations reveal that I-V curves taken from a single upright standing NR under illumination appear more degraded with respect to the non-illuminated state. Using PC-AFM, we also observed persistent photoconductivity from a single ZnO NR. Both phenomena can be attributed to oxygen desorption/re-adsorption from the ZnO NR surface.
Supported by Austrian Science Fund FWF under project # P19636.
[1] E. Greene, et al., Nano Lett. 5, 1231 (2005).
[2] G. Brauer, et al., Phys. Status Solidi C 6, 2556 (2009).
[4] Y. F. Hsu, et al., Appl. Phys. Lett. 92, 133507 (2008).
[5] H. Sakaguchi, et al., Jpn. J. Appl. Phys. 38, 3908 (1999).

Keywords: ZnO nanostructures; conductive atomic-force microscopy; electrical characterization; photoconductivity

  • Lecture (Conference)
    European Materials Research Society, Spring Meeting, 09.-13.05.2011, Nice, France

Publ.-Id: 16397

Surface complexation of U(VI) at the mineral-water interface probed by time-resolved vibrational spectroscopy – Identification of binary and ternary surface species

Foerstendorf, H.; Müller, K.; Heim, K.; Meusel, T.; Brendler, V.

The identification of the molecular interactions occurring at solid-liquid interfaces is of great significance to the assessment of the migration behavior of heavy metal ions in the environment. In particular, the dissemination of radioactive metals, such as uranium (U), in soils and groundwater aquifers is determined by sorption and desorption processes at mineral surfaces.
The molecular structures of the sorption complexes are mainly obtained by means of spectroscopic investigations of batch samples. These experiments provide no molecular information about the dynamic processes occurring during complex formation at the solid-liquid interface. However, such information, in particular about the early sorption steps, is expected to improve the understanding of the sorption processes. Therefore, we applied attenuated total reflection Fourier-transform infrared (ATR FT-IR) spectroscopy for in situ studies of the molecular processes at solid-liquid interfaces in real time with time resolution in the sub minute range and under selective conditions approaching near environmental relevant conditions [1].
In this work, we provide vibrational spectroscopic data from binary and ternary sorption systems, namely U(VI)/TiO2 and U(VI)/atm. CO2/ferrihydrite(Fh), respectively. From the binary U(VI)/TiO2-system the subsequent formation of two different surface species was observed [2]. These species were identified as inner and outer sphere uranyl complexes substantiating basic principles of surface complexation modeling which are based on thermodynamic approaches.
The spectral data obtained from in situ sorption experiments of U(VI) onto Fh demonstrate the formation of a unique U(VI) surface species irrespective of the absence or presence of atmospherically derived CO2. In contrast, the surface speciation of the carbonate anions significantly changes upon U(VI) sorption strongly suggesting the formation of ternary surface species. Moreover, the online monitoring of the sorption and desorption reactions allows the analysis of the sorption kinetics. Because of the different reaction rates found for carbonate sorption and desorption reactions on pristine Fh and Fh pretreated with U(VI), it is shown that carbonate sorption is a faster reaction than the sorption of U(VI). From the structural information of the ternary sorption complex derived from the spectroscopic results, molecular structures of the surface species are proposed [3].

[1] Voegelin, A. et al. (2003) Environ. Sci. Technol. 37, 972-978.
[2] Müller, K. et al. (2012) Geochim. Cosmochim. Acta 76, 191-205.
[3] Foerstendorf, H. et al. (2012) Journal of Colloid and Interface Science, submitted.

  • Lecture (Conference)
    'Uranium biogeochemistry: transformations and applications', 11.-16.03.2012, Ascona, Schweiz

Publ.-Id: 16396

Photoresponse in Materials for Solar Cell Applications studied by Means of Photoconductive Atomic-Force Microscopy

Beinik, I.; Kratzer, M.; Lorbek, S.; Wachauer, A.; Brauer, G.; Chen, X.; Hsu, Y. F.; Djurisic, A.; Montaigne-Ramil, A.; Bliznyuk, V.; Usluer, O.; Egbe, D.; Sariciftci, N. S.; Teichert, C.

Conductive probe based atomic force microscopy techniques like conductive atomic-force microscopy (C-AFM) [1,2], photoconductive AFM (PC-AFM) [3, 4], and photo-assisted Kelvin probe force microscopy (PA-KPFM) [5,6] provide an opportunity to study electronic and optoelectronic properties of surfaces and interfaces with nanometer resolution.
Here, we present our results on investigations of: 1) photoconductivity of single upright standing ZnO nanorods (NRs) grown by thermal evaporation [7], and 2) photoresponse in thin organic semiconductor films, namely AnE-PVstat:PCBM blends. The measurements have been performed in ambient or under N2 atmosphere using MFP3D from Asylum Research and in UHV with room temperature AFM/STM from Omicron extended with an external illumination system employing lock-in detection.
First, a novel PC-AFM setup which has been implemented to study the optoelectronic properties of individual upright standing ZnO NRs under illumination from the top will be presented. Using this setup we investigated transient photocurrent behavior and recorded photocurrent spectra from single upright standing ZnO NRs. A persistent photoconductivity from single ZnO NRs for the time intervals up to 1800 s has been observed. Simultaneously, the photoconductivity spectra (Fig. 1) revealed that the minimum photon energy sufficient for photocurrent excitation is 3.1 eV, which is at least 100 mV less than the energy sufficient for the band-to-band excitation. The mechanism of the persistent photoconductivity in ZnO is discussed in the frame of existing theoretical models.
In the second part, the results on investigations of the photoresponse in AnE-PVstat:PCBM blends spin-coated on PEDOT:PSS/ITO/ will be presented. The AnE-PVstat:PCBM blend acts as an active layer where the charge generation (by illumination) and charge separation processes take place. The charge separation in this structure occurs due to the presence of the effective electric field between AnE-PVstat, which serves as a donor, and PCBM which serves as an acceptor. The heterogeneity of the films, in turn, impacts the charge carrier generation, separation, and transport. Here, we analyzed the correlation between the heterogeneity and efficiency of the light-to-electricity conversion for (1:1), (1:2) and (1:3) AnE-PVstat to PCBM blend ratios. The 2D current maps recorded under illumination reveal the regions of high photoresponse for the case of (1:3) blend ratio, which is also confirmed by PA-KPFM and local current-to-voltage characteristics. The results on local photoresponse characterization of the samples with different blend ratios are correlated with the data on the light-to-electricity conversion efficiency obtained macroscopically.

1 S. Kremmer, C. Teichert, E. Pischler, H. Gold, F. Kuchar, and M. Schatzmayr, Surf. Interface Anal. 33, 168-172 (2002).
2 C. Teichert and I. Beinik, in Scanning Probe Microscopy in Nanoscience and Nanotechnology 2, edited by B. Bhushan (Springer, Berlin Heidelberg, 2011), pp. 691-721.
3 H. Sakaguchi, F. Iwata, A. Hirai, A. Sasaki, and T. Nagamura, Jpn. J. Appl. Phys. 38, 3908-3911 (1999).
4 D.C. Coffey, O.G. Reid, D.B. Rodovsky, G.P. Bartholomew, and D.S. Ginger, Nano Letters 7, 738-744 (2007).
5 L. Kronik and Y. Shapira, Surface Science Reports 37, 1-206 (1999).
6 E.J. Spadafora, R. Demadrille, B. Ratier, and B. Grévin, Nano Letters 10, 3337-3342 (2010).
7 Y.F. Hsu, Y.Y. Xi, A.B. Djurišić, and W.K. Chan, Applied Physics Letters 92, 133507 (2008).

Keywords: ZnO nanorods; organic semiconductor films; Photoconductive Atomic-Force Microscopy

  • Lecture (Conference)
    International Workshop on Scanning Probe Microscopy for Energy Applications, 08.-10.06.2011, Mainz, Deutschland

Publ.-Id: 16395

Electrical Transport in Individual ZnO Nanorods Studied by Photo-Conductive Atomic-Force Microscopy

Teichert, C.; Beinik, I.; Kratzer, M.; Brauer, G.; Chen, X. Y.; Hsu, Y. F.; Djurisic, A.

One-dimensional ZnO nanostructures exhibit technological potential for many device applications, like efficient low-cost ZnO nanorod-polymer solar cells [1]. Conductive atomic-force microscopy (AFM) is a valuable tool for nanometer-scale electrical characterization of such nanorods [2]. Here, we present a complementary study of electrical transport in individual upright standing ZnO nanorods (NRs) grown by thermal evaporation [4] using conductive AFM (C-AFM) and photoconductive AFM (PC-AFM) [5]. Initially, the electrical properties of the arrays of upright standing ZnO NRs were characterized using two-dimensional current maps measured at different bias voltages applied to the sample contact mode. Further, C-AFM was utilized to determine the local current-to-voltage (I-V) characteristics of the top and side facets of individual upright standing NRs. Further, we pioneered the application of PC-AFM to resolve the photoconductivity spectra measured from a single as-grown ZnO NR. PC-AFM is similar in concept to C-AFM: the sample surface is biased and additionally irradiated from a Xe light source connected to a monochromator. The current through the AFM tip is measured as a function of illumination intensity and/or wavelength. PC-AFM investigations reveal that I-V curves taken from a single upright standing NR under illumination appear more degraded with respect to the non-illuminated state. Analyzing the photoconductivity spectra it has been found that the band gap of ZnO NR is reduced by about 220 meV with respect to the known value of 3.37 eV at room temperature. Using PC-AFM, we also observed persistent photoconductivity from a single ZnO NR. We believe that both phenomena can be attributed to the processes of oxygen desorption/re-adsorption from the ZnO NR surface. Moreover, these observations are in good agreement with theoretical predictions of the influence of oxygen vacancies on the electronic structure of ZnO [6].
Supported by Austrian Science Fund FWF under project # P19636.
[1] E. Greene, et al., Nano Lett. 5, 1231 (2005).
[2] G. Brauer, et al., Phys. Status Solidi C 6, 2556 (2009).
[3] C. Teichert and I. Beinik, in “Scanning Probe Microscopy in Nanoscience and Nanotechnology”, Vol. 2,
Edited by B. Bhushan, (Springer, Heidelberg, 2011).
[4] Y. F. Hsu, Y. Y. Xi, A. B. Djurišić, W. K. Chan, Appl. Phys. Lett. 92, 133507 (2008)
[5] H. Sakaguchi, et al., Jpn. J. Appl. Phys. 38, 3908 (1999).
[6] S. Lany and A. Zunger, Physical Review B 72, 035215 (2005).

Keywords: ZnO Nanorods; Photo-Conductive Atomic-Force Microscopy; electrical transport

  • Poster
    Materials Research Society (MRS), Spring Meeting, 25.-29.04.2011, San Francisco, USA

Publ.-Id: 16394

Model experiments to the magnetic field effect on the continuous casting process

Timmel, K.; Eckert, S.; Gerbeth, G.

Die Magnetfeldwirkung auf die Stahlströmung im kontinuierlichen Stranggussverfahren wurde experimentell an einem verkleinerten Flüssigmetallmodell untersucht. In vorangegangenen Messungen mit dem Ultraschall-Doppler-Verfahren zeigte sich bereits ein Einfluss des Magnetfeldes sowohl auf die gemittelte Strömung als auch auf die zeitlichen Geschwindigkeitsschwankungen. Mittels einer schnelleren Ultraschall-Konfiguration und dem Einsatz von Potentialsonden wurde das Zeitverhalten der Strömung nun näher untersucht und ein Überblick über die ersten Ergebnisse gegeben.

Keywords: continuous casting; liquid metal model; magnetic field; Ultrasound Doppler Method; potential probes

  • Lecture (Conference)
    Symposium on Simulation and Modeling of Metallurgical Processes "SymSim", 07.-10.12.2011, Planner Alm, Österreich

Publ.-Id: 16393

Photooxidation in Combination with Nanotechnologies - Principles, Developments and R&D Approaches of an Advanced Technology for Water and Air Treatment - Uviblox®

Seitz, F.; Pollmann, K.; Mackenzie, K.; Opiolka, S.

Many organic and oxidizable inorganic substances are main targets for oxidation and destruction during treatment, purification and disinfection of contaminated ground water, waste water, air, soil and waste gas and odor. Uviblox® technology uses the effects of photooxidation and photocatalytical processes by middle and low pressure UV lamps for technical systems. There are many possibilities for combination and optimisation of photooxidation with other technologies like nanotechnologies. Degradation processes can be enforced by nano structures of photocatalysts significantly. Different approaches are strongly pursued in research & development projects like NanoAqua, Fe-NANOSIT and nanoblox. These projects search for different ways of applying and handling the photocatalytical nano particles like TiO2 and ZnO. Biological surface layers, magnetite, transparent and reflecting materials are tested for suspending nano particle solids as well as for coating fixtures. Research results are very promising and economic application of nano photocatalysts in water and gas phase for purification seems likely. Any presumed ecotoxicity was not found for the examined nanoparticles so far.

Keywords: photooxidation; photocatalysis; nanoparticle

  • Journal of Advanced Oxidation Technologies 14(2011)2, 260-265

Publ.-Id: 16392

Electrical Transport of Single ZnO Nanorods studied by Photo-Conductive AFM

Kratzer, M.; Beinik, I.; Teichert, C.; Brauer, G.; Chen, X. Y.; Durisic, A. B.; Hsu, Y. F.

Semiconductor nanomaterials have come into the focus of research due to their potential for electronic and optoelectronic applications. Their properties strongly depend on their size, morphology, and dimension. In this work, we concentrate on the electrical and optoelectric properties of individual nanorods (NRs) in arrays of upright standing ZnO NRs. ZnO is a wide band gap semiconductor with potential application in solar cells [1] and gas sensors [2]. The NRs under investigation were grown via thermal evaporation (TE) and via hydrothermal synthesis (HT) [3,4]. In order to investigate such small structures atomic force microscopy (AFM) based methods have been applied. We utilized conventional conductive atomic force microscopy (C-AFM) [5] and additionally realized a photo conductive atomic force microscopy (PC-AFM) [6, 7] setup for our measurements. Examination of the current-to-voltage (I-V) characteristics measured for the top and side facets of individual TE grown NRs yielded Schottky like behavior with different barrier heights and ideality factors for both facet types [8]. The PC-AFM measurements on the top facet of TE grown NRs revealed a clear photo-response upon illumination with white light. Additionally, persistent photo-conductivity could be observed, manifesting itself by a very slow recovery to the initial dark conductivity level after light is switched off. Comparison of the dark and illuminated I-V characteristics revealed an increase in p-type conductivity for the illuminated case. The results will be discussed referring to the current models.

[1] M. Law, L. E. Greene, J. C. Johnson, R. Saykally, P. Yang, Nat. Materials 4, 455 (2005).
[2] H.-J. Lim, D. Y. Lee, Y.-J. Oh, Sensors and Actuators A: Physical 125, 405 (2006).
[3] A.B. Djurisic, Y. H. Leung, Small 2, 944 (2006).
[4] Y. F. Hsu, Y. Y. Xi, A. B. Djurišić, W. K. Chan, Appl. Phys. Lett. 92, 133507 (2008).
[5] C. Teichert, I. Beinik, in Scanning Probe Microscopy in Nanoscience and Nanotechnology, (vol. 2) edited by B. Bhushan (Springer, Heidelberg, 2011).
[6] H. Sakaguchi, F. Iwata, A. Hirai, A. Sasaki, T. Nagamura, Jpn. J. Appl. Phys. 38, 3908 (1999).
[7] D. C. Coffey, O. G. Reid, D. B. Rodovsky, G. P. Batholomew, D. S. Ginger, Nano Lett. 7, 738 820 (2007).
[8] I. Beinik, M. Kratzer, A. Wachauer, L. Wang, R. T. Lechner, C. Teichert, C. Motz, W. Anwand,
G. Brauer, X. Y. Chen, Y. F. Hsu, A. B. Djurišić, J. Appl. Phys. accepted .

Keywords: Electrical Transport of Single ZnO Nanorods; Photo-Conductive AFM

  • Lecture (Conference)
    3rd International Workshop on Epitaxial Growth and Fundamental Properties of Semiconductor Nanostructures, 11.-16.09.2011, Traunkirchen, Austria

Publ.-Id: 16391

On the T2 deep level in zinc oxide thin films

Schmidt, M.; Karsthof, R.; Schmidt, F.; von Wenckstern, H.; Ellguth, M.; Pickenhain, R.; Grundmann, M.; Brauer, G.

For the majority of deep levels studied in n - type conducting ZnO by means of capacitance spectroscopy only the activation energy and the high temperature limit of the electron capture cross - section are known since these quantities can be evaluated easily from the temperature dependence of the trap’s thermal electron emission rate. We focused on the T2 level occuring in pulsed laser deposition grown ZnO thin films. In order to tune the T2 concentration in the samples, we employed different growth and annealing conditions as well as the implantation of oxygen and zinc ions, respectively. The physical properties of T2 were studied by sophisticated deep level transient spectroscopy and photo - capacitance experiments. These experiments revealed a strong dependence of the thermal activation energy, 185meV < Ea < 280meV, on the concentration of T2 in the sample as well as on the electric field (Poole - Frenkel effect). T2 was found to be preferentially generated under zinc rich conditions as both, the implantation of zinc ions and thermal annealing at low oxygen partial pressures increase its concentration. From photo - capacitance transients the photo - ionisation cross - section spectrum was calculated.

Keywords: T2 deep level in zinc oxide thin films

  • Lecture (Conference)
    DPG Frühjahrstagung der Sektion AMOP (SAMOP) und der Sektion Kondensierte Materie (SKM)2011, 13.-18.03.2011, Dresden, Deutschland

Publ.-Id: 16390

Basic structures of photonic integrated circuits for smart biosensor applications

Germer, S.; Rebohle, L.; Skorupa, W.; Helm, M.

In this report we present our recent developments for utilizing the Si-based light emitter consisting of a MOS structure for the detection of organic pollutants. In the latest approach the light emitters are intended to serve as light sources in smart biosensors [1, 2]. In fluid media the device is placed beneath the dye-labeled sample exciting the dye. This light emission can be recorded by an external detector. It was shown that the silanization of the device surface was successfully based on the covalent binding of the organosilane [3]. The harmlessness of the silanization method to the integrated light emitters was proved by comparing the electroluminescence spectra of Tb-based MOSLEDs before and after silanization. We further showed that the transparency is maintained. Similarly, the human estrogen receptor hERα could be immobilized effectively on the coated surface [3]. We also discuss our concept of an integrated light emitter and a receiver in a dielectric waveguide structure below the bioactive layer for the detection of harmful substances, like synthetic estrogens or plasticizer in drinking water. Optical properties of waveguides, e.g. the transmission, are very sensitive to changes of the effective refraction index, which might be induced by the immobilization of biomolecules on the waveguide surface or in cavity structures, e.g. photonic crystals. This lab-on-a-chip system provides fast light transmission without using of any additional lenses and achieves further portability and miniaturization.

[1] L. Rebohle, C. Cherkouk, S. Prucnal, M. Helm, W. Skorupa, Vacuum 83, 24 (2009)
[2] L. Rebohle, T. Gebel, R.A. Yankov, T. Trautmann, W. Skorupa, J. Sun, G. Gauglitz, R. Frank, Optical Materials 27, 1055 (2005)
[3] C. Cherkouk, L. Rebohle, W. Skorupa, T. Strache, H. Reuther and M. Helm, Journal of Colloid and Interface Science 337, 375 (2009)

Keywords: biosensor; waveguide; silanization; organosilane; photonic crystals

  • Poster

Publ.-Id: 16389

Si-based integrated photonic circuits: first approach

Germer, S.; Rebohle, L.; Helm, M.; Skorupa, W.

In this report we present our recent developments for utilizing the Si-based light emitter consisting of a MOS structure for the detection of organic pollutants. In the latest approach the light emitters are intended to serve as light sources in smart biosensors [1,2]. Now we discuss our concept of an integrated light emitter and a receiver in a dielectric waveguide structure below the bioactive layer for the detection of harmful substances, like synthetic estrogens or plasticizer in drinking water. Optical properties of waveguides, e.g. the transmission, are very sensitive to changes of the effective refraction index, which might be induced by the immobilization of biomolecules on the waveguide surface or in cavity structures, e.g. photonic crystals. The guiding of the light depends on the geometry and material composition of the waveguide. First waveguides were fabricated through plasma enhanced chemical vapor deposition (PECVD) and optical photolithography with following etching steps. Afterwards the layer thicknesses were analyzed by ellipsometry and the surface roughness via scanning electron microscopy (SEM). However, the investigation of the different waveguides will be allowed through finite element method (FEM) simulations (COMSOL) and experimentally through a setup for the optical transmission measurement. In summary, this lab-on-a-chip system provides fast light transmission without using of any additional lenses and achieves further portability and miniaturization.

[1] L. Rebohle, C. Cherkouk, S. Prucnal, M. Helm, W. Skorupa, Vacuum 83, 24 (2009)
[2] L. Rebohle, T. Gebel, R.A. Yankov, T. Trautmann, W. Skorupa, J. Sun, G. Gauglitz, R. Frank, Optical Materials 27, 1055 (2005)

Keywords: biosensor; waveguide; photonic crystals

  • Lecture (Conference)
    PhD Seminar HZDR, 26.09.2011, Dresden, Deutschland
  • Poster
    6th PhD seminar, 05.-07.10.2011, Rabenberg, Deutschland
  • Lecture (Conference)
    PhD Seminar HZDR, 07.05.2012, Dresden, Deutschland
  • Lecture (Conference)
    PhD Seminar, 16.09.2013, Dresden, Deutschland
  • Lecture (Conference)
    HZDR PhD Seminar, 07.-09.10.2013, Bautzen, Deutschland

Publ.-Id: 16388

Kelvin probe force microscopy on doped semiconductor nanostructures with local, carrier-depleted space charge regions

Baumgart, C.; Müller, A.-D.; Müller, F.; Helm, M.; Schmidt, H.

Failure analysis and optimization of semiconducting devices require knowledge of their electrical properties. Kelvin probe force microscopy (KPFM) is the most promising non-contact electrical nanometrology technique to meet the demands of today‘s semiconductor industry. We present its applicability to locally doped silicon structures. Quantitative dopant profiling by means of KPFM measurements is successfully demonstrated on a conventional static random access memory (SRAM) cell and on cross-sectionally prepared Si epilayers by applying a recently introduced new explanation of the measured KPFM signal [1]. Additionally, the influence of local, carrier-depleted space charge regions and of the electric fields across them is discussed. It is explained how drift and diffusion of injected charge carriers in intrinsic electric fields influence the surface region of the investigated semiconductor and thus may disturb the detected KPFM bias.
[1] C. Baumgart, M. Helm, H. Schmidt, Phys. Rev. B 80, 085305 (2009).

  • Lecture (Conference)
    DPG Frühjahrstagung der Sektion AMOP (SAMOP) und der Sektion Kondensierte Materie (SKM) 2011, 13.-18.03.2011, Dresden, Duetschland

Publ.-Id: 16387

Positron annihilation at planar defects in oxides

Kuriplach, J.; Brauer, G.; Melikhova, O.

Transition metal oxides are interesting materials with important prospective applications. Planar defects like stacking faults and grain boundaries are often present in such materials and may affect their properties. In particular, it has been recently shown that a zinc oxide (ZnO) single crystal contain a large amount of stacking faults [1]. Furthermore, nanocrystalline materials based on zirconia (ZrO2) are also frequently studied and their characteristics are significantly influenced by grain boundaries [2]. The planar defects just mentioned exhibit free volumes which, in principle, are detectable using positron annihilation spectroscopy. In this contribution, we present a preliminary theoretical study of positron interaction with planar defects in oxides.
First, we examine several stacking faults (SFs) in ZnO, following their structural investigation presented in [3]. It is found that studied SFs represent rather shallow positron traps with the corresponding positron lifetime exceeding the bulk one slightly only. It might be necessary to consider interactions of SFs with other defects (vacancies, impurities) in order to characterize more precisely their effect on materials’ properties, including positron response.
Second, we perform the case study of the Sigma 5 (310) [001] symmetric tilt grain boundary [4,5] in ZrO2. In this case, positrons also localize at the grain boundary, but such localization is affected by the presence of yttrium (Y3+) ions which are often added to zirconia to improve its mechanical properties. The reason is that Y3+ ions influence the charge state of the grain boundary studied.

[1] W. Anwand et al., J. Appl. Phys. 109, 063516 (2011).
[2] J. Čížek et al., Phys. Rev. B 81, 024116 (2010).
[3] Y. Yan et al., Phys. Rev. B 70, 193206 (2004).
[4] Z. Mao et al., J. Am. Ceram. Soc. 85, 1594 (2002).
[5] T. Oyama et al., Phys. Rev. B 71, 224105 (2005).

Keywords: ZnO; stacking faults; positron annihilation

  • Poster
    Tenth International Workshop on Positron and Positronium Chemistry (PPC-10), 05.-09.09.2011, Smolenice Castle, Slovakia

Publ.-Id: 16386

Effect of Sintering on Defects in Yttria Stabilised Zirconia

Prochazka, I.; Cizek, J.; Melikhova, O.; Anwand, W.; Brauer, G.; Konstantinova, T. E.; Danilenko, I. A.

A variable energy slow positron beam was utilised to investigate depth dependent effects of sintering on the tetragonal yttria stabilised zirconia nanopowders. Positron implantation was combined with the determination of Doppler broadened profiles of annihilation radiation. The results are consistent with recent positron lifetime data showing that sintering at elevated temperatures leads to a disappearance of pores and a significant grain growth, which is demonstrated by a strong suppression of positronium formation and a substantial decrease in concentration of open volume defects at triple points, respectively, with increasing sintering temperature. An existence of a subsurface layer of a relatively high content of defects was shown in sintered samples and tentatively attributed to arise from a diffusion of open volume defects from the sample interior toward the surface or from a sintering-induced surface modification.

Keywords: Yttria stabilised zirconia; sintered nanopowders; slow positron implantation spectroscopy

  • Lecture (Conference)
    Tenth International Workshop on Positron and Positronium Chemistry (PPC-10), 05.-09.09.2011, Smolenice Castle, Slovakia
  • Materials Science Forum 733(2013), 236-239
    DOI: 10.4028/

Publ.-Id: 16385

Structural Pattern of Cinnamic Acid on Different Substrates Probed by Slow Positron Beam Technique

Ganguly, B. N.; Anwand, W.; Brauer, G.; Wagner, A.

Cinnamic acid (phenyl acrylic acid) is an essential constituent of Cinnamon oil, and is well known for its medicinal values. The compound comprises of hydrogen bonded supra molecular structure due to strong hydrogen bonding between the carboxylic groups and other intermolecular hydrogen bonding as well. On the whole it forms a crystalline layered structure in solid state. In order to study its structural organization and orientation of the molecular functional groups it has been our astute interest if we could form thin layers of these molecules on suitable substrates. Thus, thin layer characteristics of cinnamic acid (CINN) on the two commonly used substrates namely: fused quartz plate and on silicon substrate has been attempted and they were subjected to Doppler broadening of positron annihilation radiation (DB) line shape analysis by slow positron beam on the range of 30 – 1200 eV energy to study the near surface properties. While CINN on quartz substrate showed a periodic pattern (the rippled nature) significant from the point of view of the layer structure, as compared to the pure solid state analysis, the results on the pure silicon substrate were not so regular, it is rather apparent that a strong substrate dependent property was noticed with the layer formation . The cause of this effect was also identified through coincidence DB analysis and another complementary technique XPS in corroboration and shall be presented.
The discussion on the organization of CINN on the quartz substrate as revealed from the DB will be presented.

Keywords: Cinnamic acid; thin layer characteristics; XPS; PAS

  • Poster
    Tenth International Workshop on Positron and Positronium Chemistry (PCC-10), 05.-09.09.2011, Smolenice Castle, Slovakia

Publ.-Id: 16384

Bestimmung langlebiger Radionuklide zur Datierung in den Geowissenschaften und der Kosmochemie

Merchel, S.; Rugel, G.; Akhmadaliev, S.

Keywords: accelerator mass spectrometry; AMS; geomorphology

  • Lecture (others)
    Dresdener Geowissenschaftliches Kolloquium, 15.05.2012, Dresden, Deutschland

Publ.-Id: 16383

Characterization of quenched-in vacancies in Fe-Al alloys

Cizek, J.; Lukac, F.; Prochazka, I.; Kuzel, R.; Jiraskova, Y.; Janickovic, D.; Anwand, W.; Brauer, G.

Physical and mechanical properties of Fe-Al alloys are strongly influenced by atomic ordering and point defects. In the present work positron lifetime (LT) measurement combined with slow positron implantation spectroscopy (SPIS) were employed for investigation of quenched-in vacancies in Fe-Al alloys with Al content ranging from 18 to 49 at.%. Interpretation of positron annihilation data was performed using ab-inito theoretical calculations of positron parameters. Quenched-in defects were identified as Fe-vacancies.
It was found that the lifetime of positrons trapped at quenched-in defects increases with increasing Al content due to increasing number of Al atoms surrounding vacancies. The concentration of quenched-in vacancies strongly increases with increasing Al content from ~10e-5 in Fe82Al18 (i.e. the alloy with the lowest Al content studied) up to ~ 10e-1 in Fe51Al49 (i.e. the alloy with the highest Al content studied in this work).

Keywords: Fe-Al alloys; vacancies; positron annihilation

  • Lecture (Conference)
    Seventh International Workshop on Positron Studies of Defects (PSD-11), 28.08.-02.09.2011, Delft, Niederlande

Publ.-Id: 16382

THEREDA - Thermodynamische Referenzdatenbasis. Abschlussbericht

Altmaier, M.; Brendler, V.; Bube, C.; Marquardt, C.; Moog, H. C.; Richter, A.; Scharge, T.; Voigt, W.; Wilhelm, S.

A long term safety assessment of a repository for radioactive waste requires evidence, that all relevant processes, which might have a significant positive or negative impact on its safety, are known and understood. In the case of brine intrusion into the disposal area, it has to be demonstrated, that the initiated chemical reactions don’t lead to an undue release of radionuclides into the biosphere. The starting point for this is to assess the solubility of contaminants in the solutions interacting with the waste. Solubility estimations can either be based on experimental data determined at conditions closely resembling those in the repository or on thermodynamic calculations.
A so called “thermodynamic database” created from experimental data is the basis for thermodynamic model calculations. Several research institutions in Germany are working on an improvement of the thermodynamic database. This work comprises investigations into fundamental thermodynamic data (such as vapour pressures or solubili-ties) as well as the application of sophisticated analytical or spectroscopic tools, which allow insight into aqueous speciation or structural details of surface complexes as basis for correct chemical and thermodynamic models.
Experience teaches that thermodynamic equilibrium calculations performed by different experts readily become difficult to compare and evaluate. This is only in part due to ill-defined (and -documented!) boundary conditions imposed on the calculations, but is frequently related to the use of different thermodynamic data or different conceptual models underlying them. Further difficulties arise by the fact that thermodynamic data used for a calculation actually are strongly interrelated; modification of an individual value without adapting the dependent values leads to “inconsistent” data. If applied in a calculation, this may lead to erroneous results, often unnoticed by the user.
As a result, in different institutions various databases exist that are appropriate for spe-cific tasks. However, they might lead to different results when they are applied to the same problem. This situation is unacceptable, both from a scientific point of view and considering the special public awareness for the final disposal of radioactive waste.
In 2002, a working group of five institutions was established for the creation of a com-mon thermodynamic database for nuclear waste disposal in deep geological formations (HZDR, GRS, TU BAF, KIT, AF-Consult). The common database was named THEREDA: Thermodynamic Reference Database.
It was agreed that the newly created database should be operated jointly by all members of the working group. In the mean term it is intended, that its usage becomes mandatory for geochemical model calculations for nuclear waste disposal in Germany. Furthermore, it was agreed that the new database should be developed along the guidelines long-term usability, easy access, applicability, internal consistency, comprehensiveness, documentation.
Activities within the time for which this report is valid cover a wide range of aspects. At first, a data model had to be designed from scratch which allows for the storage of thermodynamic data, at the same time facilitating export into code-specific parameter files. Creating the data model emphasis was laid upon its long term usage. Thus, a degree of abstraction was chosen which exceeds todays necessities and allows for future extensions. Technically the databank is implemented on a web server. Programs were created, which permit reading and writing access to the data. From the created webpages programs can be called that produce code specific parameter files ready for download upon specific request by the user.
THEREDA can thus be thought of as a databank in conjunction with a suite of peripheral programs, which aims at administrating, processing and extracting data. The data export is intended for the use in programs that calculate thermodynamic equilibria in aqueous solutions at temperatures which are of potential interest for hydrogeochemical systems in general and solutions containing hazardous contaminants like radionuclides or heavy metals in particular. As such, THEREDA is not designed to hold primary experimental data, neither data concerning any liquid other than aqueous solu-tion, e. g. melts or other substances which are stable under conditions beyond those where aqueous solutions may exist. Emphasis is laid on the correct calculation of ex-perimentally determined solubilities and aqueous speciation. Accompanying the above mentioned activities the working group agreed upon guide-lines which are to be followed upon selection and assessment of data. A system of quality assuring measure was set up; this comprises technical aspects relating to the databank as well as criteria determining how data are to be internally reviewed prior to release (auditing). As an external measure of quality assurance an internet forum was established to feedback questions and requirements from realistic problems into the project. A handbook was written to guide users in the handling of THEREDA (for the time being in german only).
Finally, thermodynamic data were entered. They comprise the system of oceanic salts as well as species and solid phase of a variety of radio-toxic and chemo-toxic ele-ments. This piece of work is on-going. At present, benchmark calculations are prepared. The first release of data will cover the system of oceanic salts (apart from C).

Keywords: THEREDA; thermodynamic reference database; repository; radioactive waste; equlibrium calculations; hydrogeochemical modelling

  • Other report
    Braunschweig: Gesellschaft für Reaktorsicherheit und Strahlenschutz (GRS) mbH, 2011
    876 Seiten

Publ.-Id: 16381

A comparative glance into the HAVAR alloy by PAS and TEM methods

May-Tal Beck, S.; Anwand, W.; Wagner, A.; Harush, M.; Eisen, Y.; Beck, A.; Ocherashvili, A.; Hen, O.

The HAVAR alloy was originally developed in the late 1940. It is a high strength, nonmagnetic and corrosion resistant material. One of its applications is in the medical industry, in the process of fluorodeoxyglucose (FDG) production for Positron Emission Tomography (PET). The 18F positron emitting isotope is produced by the reaction 18O(p,n)18F in proton cyclotrons. In Soreq NRC, 25 µm foils of HAVAR are used as a window material for the 18O enriched water targets, contained in Al vessels. With the increasing demand for 18F-FDG, an accelerated production rate is planned, with much higher intense proton beam from the new SARAF accelerator at Soreq NRC [1]. This initiated a research effort to study radiation damage in HAVAR that can predict its radiation hardness in the ~2-4 mA SARAF proton beam.
We measured four 25 µm thick HAVAR samples: cold rolled (CR), cold rolled and heat treated (HT), annealed (AN) and CR irradiated (IR). The latter was a window taken apart from the target 7 years ago after irradiation in the cyclotron to 10MeV protons of total charge 1mA-h. The first three samples were metallurgically characterized by means of Transmission Electron Microscope (TEM). Positron Annihilation Spectroscopy (PAS) measurements were preformed on all four samples. These included Doppler Broadening (DB) and Positron Annihilation Lifetime ( PAL) measurements in the slow positron beam and in the table top lifetime spectrometer at HZDR [2]. We present preliminary results from these PAS measurements, that show clear differences between the four samples. Positron lifetimes of the HAVAR types change between ~80ps for the annealed sample to ~175ps for the irradiated sample. The positron diffusion length changes from (8 ± 1) nm (CR) to (66 ± 1) nm (AN) in these samples. We also compare between the metallurgical characteristics of the different types of HAVAR measured with TEM to PAS results. The PAS measurements show a clear increase of the mean lifetime with the increase of the density of dislocations in the CR sample compared to that of AN HAVAR foils.

[1] L. Weissman et al., "The Status of the SARAF Linac Project", WE102 in Proceedings of Linac 2010, Tsukuba, September 12-17, 2010
[2] W. Anwand, H. - R. Kissener, and G. Brauer, Acta Phys. Pol. A 88, 7 (1995).

Keywords: HAVAR alloy; PET; proton irradiation; defect characterization; Transmission Electron Microscopy; Positron Annihilation Spectroscopy

  • Lecture (Conference)
    Seventh International Workshop on Positron Studies of Defects (PSD-11), 28.08.-02.09.2011, Delft, Niederlande
  • Lecture (Conference)
    26th Conference of the Nuclear Societies in Israel, 21.-23.02.2012, Dead Sea, Israel

Publ.-Id: 16380

Intelligente Sensorpartikel zur Strömungsuntersuchung in Rührbehältern

Reinecke, S.; Pöpping, U.; Hampel, U.

Die räumliche Erfassung relevanter Prozessparameter wird bei einer Vielzahl industrieller Anwendungen durch den begrenzten Zugang zum Prozess erschwert. Beispiele sind Reaktoren mit Rührwerken, Bioreaktoren, Fermenter und Schüttgutbehälter. In solchen Behältern ist die Installation von fest angebrachten Sensoren und Kabelverbindungen oft nicht realisierbar oder unerwünscht. Zudem sind räumlich auflösende Apparate, wie Kameras oder Tomografiemesssysteme, meist nicht anwendbar. Daher bietet die Überwachung der räumlichen Verteilung relevanter Prozessparameter ein hohes Potential für die verbesserte Untersuchung und die Optimierung der Anlagen und Prozesse. Zur Erfassung räumlich verteilter Parameter in Prozessbehältern wurde ein Konzept autonomer Sensorpartikel entwickelt und getestet. Das Messsystem beinhaltet mehrere autonome Sensorpartikel und eine Basiseinheit.

  • Poster
    10. Dresdner Sensor-Symposium, 05.-07.12.2011, Dresden, Deutschland

Publ.-Id: 16379

Defect induced ferromagnetism in 4H-SiC single crystals

Li, L.; Hua, W.; Prucnal, S.; Yao, S.; Shao, L.; Potzger, K.; Zhou, S.

We have demonstrated the feasibility of using ion irradiation to induce ferromagnetism in 4H-SiC. Upon Ne+ ion irradiation to a fluence of 5×1014 /cm2, ferromagnetism is observed up to room temperature, while the virgin sample only shows diamagnetism. Sample characterization by using both Rutherford backscattering/channeling spectrometry and Raman spectroscopy shows defect generation and the partial loss of crystalline structures by ion irradiation. With further increased fluences to reach complete amorphization in SiC, the magnetic moments are still observed. The defect-induced ferromagnetism is stable upon thermal annealing at 1400 °C.

Keywords: Ion irradiation; 4H-SiC; Defect; Ferromagnetism

Publ.-Id: 16378

Ultrafast full-angle volumetric X-ray tomography

Bieberle, M.; Stürzel, T.; Menz, H.-J.; Hampel, U.

Ultrafast electron beam X-ray computed tomography has seen considerable progress in the last few years. Beginning with a limited-angle approach, single-plane, dual-plane and multi-plane tomography arrangements have been studied. Based on these proofs of principle, a single-plane full-angle tomography system has been built up and was used to image and analyze various two-phase flow scenarios. Lately, the dual-plane tomography has also been realized as a full-angle setup, which is now able to measure phase distributions as well as velocity profiles within the object of interest.
Now, we present a full-angle volumetric X-ray computed tomography setup, which comprises eight circular X-ray source paths distributed on a vertically expanded target and one ring of 320 detector elements surrounding the target. The resulting reverse cone-beam geometry allows three-dimensional reconstruction of the imaged object volume using Feldkamp-type reconstruction algorithms. The electron beam is guided consecutively along all circular source paths, which takes 500 µs per path, while the detector elements simultaneously measure the X-ray projections with 1 MHz sampling rate. This results in 500 discrete source positions per revolution and a volume rate of 250 s-1.
The performance of the setup has been demonstrated in phantom as well as two-phase flow experiments, which revealed detailed structures and flow dynamics in 3-D.

Keywords: X-ray; computed tomography; ultrafast; 3-D

  • Contribution to proceedings
    6th International Symposium on Industrial Process Tomography (ISPT6), 26.-28.03.2012, Cape Town, South Africa
  • Poster
    6th International Symposium on Industrial Process Tomography (ISPT6), 26.-28.03.2012, Cape Town, South Africa

Publ.-Id: 16377

Study of exclusive one-pion and one-eta production using hadron and dielectron channels in pp reactions at kinetic beam energies of 1.25 GeV and 2.2 GeV with HADES

Agakishiev, G.; Alvarez-Pol, H.; Balanda, A.; Bassini, R.; Böhmer, M.; Boyard, J. L.; Cabanelas, P.; Chernenko, S.; Christ, T.; Destefanis, M.; Dohrmann, F.; Dybczak, A.; Eberl, T.; Fabbietti, L.; Fateev, O.; Finocchiaro, P.; Friese, J.; Fröhlich, I.; Galatyuk, T.; Garzon, J. A.; Gernhäuser, R.; Gilardi, C.; Golubeva, M.; Gonzalez-Diaz, D.; Guber, F.; Gumberidze, M.; Hennino, T.; Holzmann, R.; Iori, I.; Ivashkin, A.; Jurkovic, M.; Kämpfer, B.; Kanaki, K.; Karavicheva, T.; Koenig, I.; Koenig, W.; Kolb, B. W.; Kotte, R.; Kozuch, A.; Krizek, F.; Kühn, W.; Kugler, A.; Kurepin, A.; Lang, S.; Lapidus, K.; Liu, T.; Maier, L.; Markert, J.; Metag, V.; Michalska, B.; Moriniere, E.; Mousa, J.; Müntz, C.; Naumann, L.; Otwinowski, J.; Pachmayer, Y. C.; Pechenov, V.; Pechenova, O.; Pietraszko, J.; Przygoda, W.; Ramstein, B.; Reshetin, A.; Roy-Stephan, M.; Rustamov, A.; Sadovsky, A.; Sailer, B.; Salabura, P.; Sanchez, M.; Schmah, A.; Schwab, E.; Sobolev, Y. G.; Spataro, S.; Spruck, B.; Ströbele, H.; Stroth, J.; Sturm, C.; Tarantola, A.; Teilab, K.; Tlusty, P.; Toia, A.; Traxler, M.; Trebacz, R.; Tsertos, H.; Wagner, V.; Wisniowski, M.; Wüstenfeld, J.; Yurevich, S.; Zanevsky, Y.

We present exclusive measurements of π+, π0 and ω production in pp reactions at 1.25 GeV and 2.2 GeV beam kinetic energy, in hadronic and dielectron channels. Using the former, high statistics invariant mass and angular distributions within the HADES acceptance are obtained for π+ and π0 exclusive production, as well as acceptance corrected distributions, which are compared to a resonance model. The sensitivity of the data to the Δ(1232) production angular distribution and to the contribution of higher lying baryon resonances is shown and an improved parameterization of the data is proposed. Cross sections are extracted especially in the case of pp->ppη at 2.2 GeV (σ=0.142 ± 0.022 mb) for which only old and controversial data existed. Using the dielectron channels, the π0 and η Dalitz decay signals could be reconstructed, with yields fully consistent with the hadronic channels. The electron invariant masses and acceptance corrected helicity angle distributions are found in good agreement with model predictions.

Publ.-Id: 16376

Inclusive dielectron production in proton-proton collisions at 2.2 GeV beam energy

Agakishiev, G.; Alvarez-Pol, H.; Balanda, A.; Bassini, R.; Böhmer, M.; Boyard, J. L.; Cabanelas, P.; Chernenko, S.; Christ, T.; Destefanis, M.; Dohrmann, F.; Dybczak, A.; Eberl, T.; Fabbietti, L.; Fateev, O.; Finocchiaro, P.; Friese, J.; Fröhlich, I.; Galatyuk, T.; Garz´On, J. A.; Gernhäuser, R.; Gilardi, C.; Golubeva, M.; Gonzalez-Diaz, D.; Guber, F.; Gumberidze, M.; Hennino, T.; Holzmann, R.; Iori, I.; Ivashkin, A.; Jurkovic, M.; Kämpfer, B.; Kanaki, K.; Karavicheva, T.; Koenig, I.; Koenig, W.; Kolb, B. W.; Kotte, R.; Kozuch, A.; Krizek, F.; Kühn, W.; Kugler, A.; Kurepin, A.; Lang, S.; Lapidus, K.; Liu, T.; Maier, L.; Markert, J.; Metag, V.; Michalska, B.; Moriniere, E.; Mousa, J.; Müntz, C.; Naumann, L.; Otwinowski, J.; Pachmayer, Y. C.; Pechenov, V.; Pechenova, O.; Pietraszko, J.; Przygoda, W.; Ramstein, B.; Reshetin, A.; Roy-Stephan, M.; Rustamov, A.; Sadovsky, A.; Sailer, B.; Salabura, P.; Sanchez, M.; Schmah, A.; Schwab, E.; Sobolev, Y. G.; Spataro, S.; Spruck, B.; Ströbele, H.; Stroth, J.; Sturm, C.; Tarantola, A.; Teilab, K.; Tlusty, P.; Toia, A.; Traxler, M.; Trebacz, R.; Tsertos, H.; Wagner, V.; Wisniowski, M.; Wüstenfeld, J.; Yurevich, S.; Zanevsky, Y.

Data on inclusive dielectron production are presented for the reaction 2.2 GeV p + p measured with the High Acceptance DiElectron Spectrometer (HADES). Our results supplement data obtained formerly in this bombarding energy regime by DLS and HADES. The comparison with the DLS data for the reaction p + p at 2.09 GeV is shown. The reconstructed e+e− distributions are compared with a simulated pair cocktail, which points to an excess yield of invariant masses at around 0.5 GeV/c2. Inclusive cross sections of neutral pion and eta production are obtained as well.

Publ.-Id: 16375

Tailoring the magnetism of GaMnAs via defect engineering by energetic ions

Zhou, S.; Li, L.; Chen, L.; Rushforth, A. W.; Fassbender, J.; Helm, M.; Zhao, J.; Campion, R. P.; Gallagher, B. L.; Schmidt, H.

Ion irradiation of semiconductors is a well understood method to tune the carrier concentration in a controlled manner. For dilute magnetic semiconductors (DMS), the free carriers mediate the local magnetic moments and develop the long-range ferromagnetic coupling. Therefore, ion irradiation should provide a tool to engineer the magnetic properties of DMS. In this contribution, we show the possibility of fine tailoring the magnetism of highly conducting virgin GaMnAs films by ion irradiation. With increasing the displacement per atom (ion fluence), the GaMnAs films become more insulating step by step and only paramagnetic at the end. The coercivity can be increased by several times [1]. The approach can be used to tailor GaMnAs films with different coercivities, Curie temperatures (TC) as well as saturation magnetization. On the other hand one can use the approach to understand the conduction and magnetic coupling mechanism [2]. For relatively thick 25nm GaMnAs films with a high TC of 150 K [3] where the electrical gating is difficult due to the large hole concentration, ,we can decrease the hole concentration gradually. We found a linear dependence of Tc with increasing the compensation of holes by ion irradiation. This observation favours a valence band picture of ferromagnetic GaMnAs with high Mn concentrations.
1. L. Li, et al., J. Phys. D 44 099501 (2011);
2. T. E. Winkler, et al., Appl. Phys. Lett. 98, 012103 (2011).
3. Y. Nishitani, et al., Phys. Rev. B 81, 045208 (2010).

Keywords: Diluted magnetic semiconductor; GaMnAs; Ion irradiation

  • Poster
    6th International School and Conference on Spintronics and Quantum Information Technology (SPINTECH6), 01.-05.08.2011, Matsue, Japan

Publ.-Id: 16373

Ion implantation and short-time annealing for spintronics

Zhou, S.

Doping of semiconductors is an essential issue for device fabrication. Ion implantation followed by annealing is a well-established method to dope Si and Ge. This approach has been maturely integrated with the IC industry production line. Nowadays, the demands for functional spintronics/photovoltaic materials require a supersaturated doping of semiconductors. For instance, regarding spintronics applications one needs to prepare magnetic semiconductors which are doped with up to 5-10% Mn. As a non-equilibrium process, ion implantation can introduce enough dopants as required. However, the activation of dopants remains challenging due to the clustering of implanted ions during post-annealing. The solubility limit is a fundamental barrier for dopants incorporated into a specific semiconductor. On the other hand, one notes that the solubility limit in the liquid phase is generally much larger than that in the solid phase. Short-time annealing in the millisecond or nanosecond regime allows the epitaxial growth from a liquid phase. Shallow dopants in Si and Ge, mainly the elements from the III or V columns of the periodic table, have been successfully built in by ion implantation and pulsed laser annealing [1]. The carrier concentration can reach values as high as 1021 cm-3. Such a platform combining ion implantation and short-time annealing has been established at Helmholtz-Zentrum Dresden-Rossendorf (HZDR) [2]. In this contribution, we will give an overview of the platform and particularly of its application in the preparation of Mn doped Ge [3, 4].

[1] C. W. White, et al., J. Appl. Phys. 51, 738 (1980).
[2] W. Skorupa, et al., J. Electrochemical Soc. 152, G436 (2005).
[3] S. Zhou, et al., Phys. Rev. 81, 165204 (2010).
[4] S. Zhou, et al., Appl. Phys. Lett. 96, 202105 (2010).

  • Invited lecture (Conferences)
    Seminar at Univ. Jena, 30.06.2011, Jena, Germany
  • Lecture (Conference)
    Workshop „Ionen- und Positronenstrahlen“, 04.-05.07.2011, München, Germany

Publ.-Id: 16372

Ion implantation-induced defects in Oxide Dispersion Strengthened (ODS) steel probed by positron annihilation spectroscopy

Anwand, W.; Butterling, M.; Brauer, G.; Wagner, A.; Richter, A.; Chen, C.-L.; Kögler, R.

Oxide Dispersion Strengthened (ODS) steel is a promising candidate for an application in fission and fusion power plants of a new generation because of its advantageous properties as stability and temperature resistance. A microscopic understanding of the physical reasons of the mechanical and thermal properties as well as the behaviour of the material under irradiation is an important pre-condition for such applications. The investigated ODS FeCrAl alloy “PM2000” has been produced in a powder metallurgical way by means of hot isostatic pressing and hot rolling. Neutron-induced damage at ODS steel was simulated by He+ and Fe2+ co-implantation with energies of 2.5 MeV and 400 keV, respectively, and different fluences. The implantation has been carried out with a dual ion beam which enables a simultaneous implantation of both ion types. Thereby the Fe2+ implantation was used for the creation of radiation defects, and He+ was implanted in order to reproduce He bubbles as they are expected to appear by neutron irradiation. The implantation-induced damage was investigated by depth dependent Doppler broadening (DB) measurements using a variable energy slow positron beam. In addition, as-received, deformed and annealed ODS samples were characterized by DB and positron lifetime measurements for comparison.

Keywords: ODS steel; irradiation-induced damage; simultaneous He and Fe implantation; positron annihilation

  • Lecture (Conference)
    Workshop "Ionen- und Positronenstrahlen", 04.-05.07.2011, München/Neubiberg, Deutschland
  • Lecture (Conference)
    Deutsche Physikalische Gesellschaft Frühjahrstagung der Sektion Kondensierte Materie, 25.-30.03.2012, Berlin, Deutschland

Publ.-Id: 16371

Ion irradiation as a controllable approach to study the defect-induced ferromagnetism

Zhou, S.; Potzger, K.; Yang, Z.; Helm, M.; Fassbender, J.

Recently, ferromagnetism was observed in nonmagnetically doped, but defective semiconductors or insulators, including TiO2 [1] and ZnO [2-5] (see a review by Coey et al. [6]). This kind of observation challenges the conventional understanding of ferromagnetism, which is rather due to spin-split states or bands. Often the defect-induced ferromagnetism has been observed in samples prepared under non-optimized condition, i.e. by accidence or by mistake. To understand the mechanism of the defect-induced ferromagnetism, one needs a better controlled method to create defects in the crystalline materials. As a nonequilibrium and reproducible approach of inducing defects, ion irradiation provides such a possibility. Energetic ions displace atoms from their equilibrium lattice sites, thus creating mainly vacancies, interstitials or antisites. The amount and the distribution of defects can be controlled by the ion fluence and energy. By ion irradiation, we have generated defect-induced ferromagnetism in TiO2 [1] and SiC [7]. The saturation magnetization rises and falls with increasing the ion fluence due to the interplay between the amount of defects and the crystalline quality. Using electron spin resonance and positron annihilation spectroscopies, one can determine where the unpaired electrons are located and the concentration of defects. Ion irradiation combined with proper characterizations of defects could allow us to clarify the local magnetic moments and the coupling mechanism in defective semiconductors. Otherwise we may have to build a new paradigm to understand the defect-induced ferromagnetism.

[1] S. Zhou, et al., Phys. Rev. B 79, 113201 (2009).
[2] S. Zhou, et al., J. Phys. D 41, 105011 (2008).
[3] K. Potzger, et al., Appl. Phys. Lett. 92, 182504 (2008).
[4] S. Zhou, et al., Appl. Phys. Lett. 93, 232507 (2008).
[5] Q. Xu, et al., Appl. Phys. Lett. 92, 082508 (2008).
[6] J. M. D. Coey, et al., New J. Phys. 12, 053025 (2010).
[7] L. Li, et al., Appl. Phys. Lett. 98, 222508 (2011).

  • Invited lecture (Conferences)
    China-Germany Symposium on "Electronic structure calculations and their application in material science", 08.-11.11.2011, Chengdu, China
  • Poster
    The 56th Magnetism and Magnetic Materials Conference, 30.10.-03.11.2011, Phoenix / Scottsdale, USA
  • Invited lecture (Conferences)
    Invited seminar at the Institute of Solid State Physics, Chinese Academy of Sciences, 13.10.2011, Hefei, China

Publ.-Id: 16370

EXAFS and DFT Investigations of Uranyl-Arsenate Complexes in Aqueous Solution

Gezahegne, W. A.; Hennig, C.; Tsushima, S.; Planer-Friedrich, B.; Scheinost, A. C.; Merkel, B. J.

Uranium and arsenic often co-occur in nature, for example, in acid mine drainage waters. Interaction with arsenic is thus important to understand uranium mobility in aqueous solutions. For the present study, EXAFS spectroscopy was used to investigate the formation and identify the structure of aqueous uranyl arsenate species at pH 2. The nearest U−As distance of 3.39 Å, observed in shock-frozen liquid samples, was significantly shorter than that observed in solid uranyl arsenate minerals. The shorter bond length indicated that the solution contained a bidentate-coordinated species, in contrast to the monodentate coordination in solid uranyl arsenate minerals. The U−As coordination number of 1.6 implied that two uranyl arsenate species with U:As ratios of 1:1 and 1:2 formed in nearly equal proportions and that the hydrated uranyl ion was present only as a minor component. The two uranyl arsenate species could not be differentiated spectroscopically, since their U−As distances were equal. A comparison based on DFT modeling indicated for both the 1:1 and the 1:2 species, that the bidentate arsenates were bound to uranium with one of the binding oxygen atoms being protonated. Based on the present spectroscopic study, the two species that will have to be considered in acidic uranium−arsenic-rich solutions are thus
UO2H2AsO4+, and UO2(H2AsO4)20.

Publ.-Id: 16369

Identification of defect properties by positron annihilation in Te-doped GaAs after Cu in-diffusion

Elsayed, M.; Krause-Rehberg, R.; Anwand, W.; Butterling, M.; Korff, B.

Positron lifetime measurements and Doppler-broadening spectroscopy were combined to investigate the defect properties during Cu diffusion in Te-doped GaAs. The diffusion of Cu was performed during an annealing step at 1100°C under two different arsenic vapor pressures. The samples were quenched into room temperature water. During a subsequent isochronal annealing experiment, it was found that vacancy clusters were generated and grown, and finally they disappeared. The lifetime results show that, in addition to deep positron traps of vacancy type, positron trapping with a lifetime close to the bulk value of 228 ps occurs. The positron lifetime results give direct evidence of positron localization at shallow traps in GaAs:Te. Due to the Cu contamination during the annealing process, the shallow trap is believed to be the Cu2−Ga double acceptor. The concentration of shallow traps is determined and found to be in good agreement with the concentration determined by Hall measurement. It decreases up to saturation with increasing annealing. The positron binding energy to these negative nonopen volume trap centers is determined to be 79 meV. It is found to be in agreement with the calculated value.Moreover, coincidence Doppler-broadening spectroscopy shows clearly that Cu atoms are bound in the direct vicinity of the observed vacancy-like defects. Theoretical calculations of momentum distribution predicted that one Cu atom incorporated into a Ga site surrounds the observed open-volume defects.

Keywords: positron lifetime and Doppler broadening spectroscopy; Te-doped GaAs; Cu diffusion; defect properties

Publ.-Id: 16368

Magneto-optical coupling in ferromagnetic thin films investigated by VMOGE

Mok, K. M.; Scarlat, C.; Kovacs, G. J.; Li, L.; Zviagin, V.; McCord, J.; Helm, M.; Schmidt, H.

We investigated the magneto-optical coupling in ferromagnetic thin films (Fe, Ni20Fe80, Co, Ni80Fe20, Ni) in the spectral range from 300 to 1100 nm. We performed Mueller matrix ellipsometry measurements in a magnetic field of arbitrary orientation and magnitude up to 400 mT at room temperature with a set-up vector-magneto-optical generalized ellipsometer (VMOGE). We extracted the magneto-optical dielectric tensor of the ferromagnetic thin films under saturated in-plane magnetization conditions. The off-diagonal elements of the magneto-optical dielectric tensor depend on the net spin polarization and the electronic band structure of the magnetized material. For ferromagnetic Fe, Co, and Ni, the converted magneto-optical dielectric tensor agrees well with reported experimental optical conductivity data. With additional measurements on the magnetization of the ferromagnetic thin films, we extracted the magnetic field independent magneto-optical coupling constant Q, which is a useful parameter for characterization of magneto-optical materials.
Reference: K. Mok et al., Phys. Rev. B 84, 094413 (2011)

Keywords: Mueller matrix; generalized ellipsometry; ferromagnet

  • Lecture (Conference)
    DPG Frühjahrstagung der Sektion Kondensierte Materie (SKM), 25.-30.03.2012, Berlin, Germany
  • Lecture (Conference)
    7th Workshop Ellipsometry, 05.-07.03.2012, Leipzig, Germany

Publ.-Id: 16367

Magneto-optical dielectric tensor of Co, Fe, Ni, and of NiFe alloys under saturated magnetization conditions

Mok, K. M.; Du, N.; Schmidt, H.

Magneto-optical generalized ellipsometry (MOGE) has become extensively important for characterization the magneto-optical response of single and multilayer materials. We setup a Vector-Magneto-Optical Generalized Ellipsometer (VMOGE) in the spectral range from 250 nm to 1100 nm using an octupole magnet, to perform VMOGE measurements of the Mueller matrix in a magnetic field of arbitrary orientation and magnitude up to 0.4 T at room temperature. The VMOGE features a new "field orbit" measurement that can be performed without physically moving the sample, which is useful to study magnetic multilayer or nanostructure samples. An optical model based on the 4 x 4 matrix formalism is required to evaluate and fit the experimental Mueller matrix data. Searching the best match model between experimental and calculated VMOGE data, the magneto-optical dielectric tensor of each layer in a multilayer sample system can be determined. In this work, we investigate the magneto-optical properties of the elemental ferromagnets Co, Fe, and Ni, as well as of NiFe alloys. We extracted the wavelength dependence of the magneto-optical dielectric tensor under saturated magnetization conditions.

Keywords: Mueller matrix; generalized ellipsometry; ferromagnet

  • Lecture (Conference)
    DPG Frühjahrstagung der Sektion AMOP (SAMOP) und der Sektion Kondensierte Materie (SKM) 2011, 13.03.2011, Dresden, Germany

Publ.-Id: 16366

Extension of the wall boiling model by using the MUSIG approach

Krepper, E.; Rzehak, R.

The report describes the capabilities of CFD simulatin wall boiling coupled with a population balance model. For the demonstration DEBORA tests were used. Instead of water at high pressure in the DEBORA tests Dichlorodifluoromethane (R12) was used as the working fluid. Similar conditions in terms of the relevant non-dimensional numbers have been realized. This facilitated measurements of radial profiles for gas volume fraction, gas velocity, liquid temperature and bubble size.
Essential for the momentum, mass and energy exchange between the phases is an adequate description of the interfacial area or respectively the bubble size. In the present work a population balance approach coupled to a wall boiling model is used, where bubbles are generated at the wall with a certain size that subsequently evolves due to both condensation / evaporation and coalescence / fragmentation processes. The paper shows the potential of this approach which is able to describe the observed bubble size increase caused by bubble coalescence after leaving the wall as well as the change of gas fraction profile from wall to core peaking with increasing inlet temperature respective decreasing liquid subcooling and consequently enhanced vapour generation.

Keywords: CFD; two-phase flow; wall boiling; population balance models; MUSIG

  • Article, self-published (no contribution to HZDR-Annual report)
    Forschungszentrum Rossendorf 2011
    33 Seiten
    ISSN: 1437-322X

Publ.-Id: 16365

Decomposition kinetics in Ti1-xAlxN coatings as studied by in-situ X-ray diffraction during annealing

Wüstefeld, C.; Rafaja, D.; Dopita, M.; Motylenko, M.; Baehtz, C.; Michotte, C.; Kathrein, M.

The influence of the microstructure of the as-deposited cathodic arc evaporated Ti1-xAlxN coatings and, in particular, the influence of the intrinsic lattice strains on their thermal stability were investigated by insitu synchrotron high temperature glancing angle X-ray diffraction (HT-GAXRD) experiments up to 850 °C. The microstructure of the as-deposited coatings was adjusted by the bias voltage (UB=−40 V, UB=−80 V and UB=−120 V) and by the [Al]/([Ti]+[Al]) ratio (0.4, 0.5 and 0.6) of the used Ti–Al targets. The microstructure evolution during annealing was described in terms of the phase composition of the coatings, the aluminium content, aluminium distribution and residual lattice strains in fcc-(Ti,Al)N. Independent of the deposition parameters ([Al]/([Ti]+[Al]) ratio and bias voltage), all coatings contained a mixture of fcc-(Ti, Al)N, fcc-AlN and w-AlN after annealing at 850 °C. The [Al]/([Ti]+[Al]) ratio was found to control the amount of fcc-(Ti,Al)N, whereas the bias voltage was mainly responsible for the relative amount of fcc-AlN and w- AlN. Finally, the interplay between lattice strains and the kinetics of the spinodal decomposition of fcc-(Ti, Al)N was illustrated.

Keywords: Ti–Al–N Cathodic arc evaporation Thermal stability Microstructure X-ray diffraction Bias voltage

Publ.-Id: 16364

In Situ Characterization of Alloy Catalysts for Low-Temperature Graphene Growth

Weatherup, R. S.; Bayer, B. C.; Blume, R.; Ducati, C.; Baehtz, C.; Schlögl, R.; Hofmann, S.

Low-temperature (∼450 °C), scalable chemical vapor deposition of predominantly monolayer (74%) graphene films with an average D/G peak ratio of 0.24 and domain sizes in excess of 220 μm2 is demonstrated via the design of alloy catalysts. The admixture of Au to polycrystalline Ni allows a controlled decrease in graphene nucleation density, highlighting the role of step edges. In situ, time-, and depthresolved X-ray photoelectron spectroscopy and X-ray diffraction reveal the role of subsurface C species and allow a coherent model for graphene formation to be devised.

Keywords: Graphene; chemical vapor deposition (CVD); alloy catalyst; in situ metrology; XPS; XRD

Publ.-Id: 16363

Influence of high permeability disks in an axisymmetric model of the Cadarache dynamo experiment

Giesecke, A.; Nore, C.; Stefani, F.; Gerbeth, G.; Leorat, J.; Herreman, W.; Luddens, F.; Guermond, J. L.

Numerical simulations of the kinematic induction equation are performed on a model configuration of the Cadarache von-K\'arm\'an-Sodium dynamo experiment. The effect of a localized axisymmetric distribution of relative permeability mur that represents soft iron material within the conducting fluid flow is investigated. The critical magnetic Reynolds number Rmc for dynamo action of the first non-axisymmetric mode roughly scales like Rmcμ-Rmc ∝ μr-1/2 i.e. the threshold decreases as μr increases. This scaling law suggests a skin effect mechanism in the soft iron disks. More important with regard to the Cadarache dynamo experiment, we observe a purely toroidal axisymmetric mode localized in the high permeability disks which becomes dominant for large μr.
In this limit, the toroidal mode is close to the onset of dynamo action with a (negative) growth-rate that is rather independent of the magnetic Reynolds number. We qualitatively explain this effect by paramagnetic pumping at the fluid/disk interface and propose a simplified model that quantitatively reproduces numerical results.
The decise role of the high permeability disks for the mode selection in the Cadarache dynamo experiment cannot be inferred from computations using idealized pseudo-vacuum boundary conditions (H ✕ n =0).

Keywords: dynamo; VKS; permeability; soft iron

Publ.-Id: 16362

Synthese und In-vitro-Charakterisierung neuer Aminobenzovesamicol-Analoga als potentielle Liganden für den vesikulären Acetylcholintransporter im Gehirn

Barthel, C.

  • Thesis / Students' report
    Hochschule Zittau/Görlitz, Fakultät Mathematik/Naturwissenschaften, Fachgruppe Chemie, 2011
    78 Seiten

Publ.-Id: 16361

Radiosynthesis, In Vitro and In Vivo Evaluation of a 6-(2-[18F]Fluoroethoxy)-7-methoxy-pyrrolidinylquinazoline for PET Imaging of Phosphodiesterase 10A in Brain

Funke, U.; Deuther-Conrad, W.; Barbar Asskar, G.; Scheunemann, M.; Fischer, S.; Hiller, A.; Briel, D.; Brust, P.

1. Introduction

Phosphodiesterase 10A (PDE10A) is a key enzyme that mediates neural signal transduction by regulating intracellular concentration of the cyclic nucleotides adenosine (cAMP) and guanosine monophosphate (cGMP) and is mainly present in brain. Particularly high PDE10A expression and activity was observed in brain regions of dopaminergic and GABAergic neurotransmission. As these relations are not fully understood and PDE10A hypofunction is supposed to correlate with neuropsychiatric disorders such as schizophrenia, obsessive-compulsive disorders, Parkinson’s disease, and Huntington’s disease, there is an ongoing interest in PDE10A as target for molecular imaging by PET.
For the pharmacological treatment of schizophrenia, a highly PDE10A inhibiting, selective and brain penetrable 6,7-dimethoxy-4-pyrrolidinylquinazoline has been designed (Ki=4 nM [1]). Based on this structure we developed fluorine-18 labeled derivatives as potential PET radiotracers for imaging PDE10A in brain [2]. Herein we report on the radiosynthesis and radiotracer properties of the 6-[18F]fluoroethoxy derivative [18F]2 (Figure 1).

2. Materials & Methods

The non-radioactive reference compound 2 and the 7-tosyloxy precursor 1 were prepared in multi-step syntheses, and 2 was screened for its PDE10A inhibitory potency (Ki=32 nM) as well as selectivity in enzyme activity studies [2]. The automated radiosynthesis of [18F]2 was carried out on a TRACERlabTM FX F-N synthesizer. Aqueous n.c.a. [18F]Fluoride was transferred to MeCN via a Chromafix® 30-PS-HCO3 cartridge, dried azeotropically and converted to its K[18F]F-K2.2.2-carbonate complex. Nucleophilic 18F-for-OTs substitution was performed with ~2 mg of 1 in 750 µL MeCN at 85°C within 15 min. Purification of [18F]2 was carried out by SPE (SepPak®Plus C-18, MeCN), followed by semi-preparative RP-HPLC (e.g. on ReproSil-Pur® C18 AQ, 7 µm; 5010 + 15010 mm, 42% MeCN, 20 mM NH4OAc, 4 mL/min; tR=30.3 min). Formulation of [18F]2 was done by SPE, removal of organic eluent and dissolution in physiological saline.
Radioligand stability (EtOH, MeCN, physiological saline and phosphate buffer solution, 40 and 80°C, 5-120 min) and lipophilicity (logD7.0-7.4, shake-flask) were determined. Further characterization in vitro of [18F]2 included the determination of stability in rat plasma (37°C, 30 and 60 min), PDE10A affinity (KD, PDE10A transfected SF21 cells) and autoradiographic imaging of sagittal female rat brain slices, incubated with [18F]2 alone, together with 2 or highly PDE10A-specific MP-10, respectively. Evaluation in vivo of [18F]2 in female CD-1 mice was carried out by the determination of biodistribution and brain uptake as well as metabolism studies and ex vivo brain autoradiography, with validation of specificity by pre-treatment with MP-10 (1mg/kg at 15 min before radiotracer).

Figure 1. Radiosynthesis of [18F]2 and its binding at a sagittal rat brain slice in vitro.

3. Results

Radiosynthesis of [18F]2 resulted in labeling efficiencies of 76-94%, a radiochemical yield of 41.210.3% (n=6, 2 h, based on [18F]F-), a radiochemical purity of ≥99% and specific activities of 80-1030 GBq/mol. [18F]2 remained stable during heating in organic solvents (97% of [18F]2, 120 min, 80°C), and showed moderate stability in aqueous buffer solutions (95% of [18F]2, 60 min, 40°C) and rat plasma (94% of [18F]2, 60 min, 37°C). A logD7.0-7.4 of ~2.5, was determined, and by homologous competition a KD of 24 nM (n=2) was estimated. By autoradiography in vitro, a heterogeneous distribution of [18F]2 in rat brain was observed (Figure 1), which was partially inhibited by MP-10. Biodistribution studies revealed an initial brain uptake of 1.6%ID/g at 5 min p.i.. Striatal uptake at 60 min p.i. was not inhibited by MP-10, which was confirmed by ex vivo autoradiography. Only 41%, 64% and 20% of the radioactivity measured in plasma, brain and liver, respectively, at 30 min p.i. corresponded to parent radioligand. An evidence for slight defluorination was observed because in femur uptake values increased by 25% at 60 min p.i. after removal of the bone marrow.

4. Discussion/Conclusion

A convenient radiosynthesis and satisfactory radiochemical results, as well as moderate lipophilicity and PDE10A affinity initially indicated [18F]2 to be a suitable radiotracer. However, the heterogeneous but non-displaceable binding of [18F]2 in vitro provides evidence for binding affinity to another target. Reasonable high uptake of [18F]2 in mice brain was found, which was non-specific and non-selective. The radioligand stability in vivo is comparably low and the presence of brain metabolites is inappropriate for molecular imaging.
In conclusion, a structural revision of our pharmaceutical lead is needed to improve the in vivo properties and to develop an applicable radiotracer for neuroimaging of PDE10A with PET.

Research Support: European Regional Development Fund (ERDF).

References: [1] Chappie TA, Humphrey JM, Allen MP et al. [2007] J.Med.Chem. 50: 182-185.
[2] Nieber K, Erdmann S, Briel D et al. [2010] Patent Appl. P1014WO.

  • Poster
    ESRR 2012 - 16th European Symposium on Radiopharmacy and Radiopharmaceuticals, 26.-29.04.2012, Nantes, France

Publ.-Id: 16360

Implementation of microbial processes in the performance assessment of spent nuclear fuel repositories

Behrends, T.; Krawczyk-Bärsch, E.; Arnold, T.

Present strategies for the long-term disposal of high-level nuclear wastes are based on the construction of repositories hundreds of meters below the earth surface. Although the surrounding host-rocks are relatively isolated from the light at the earth surface they are by no means lifeless. Microorganisms rule the deep part of the biosphere and it is well established that their activity can alter chemical and physical properties of these environments. Microbial processes can directly and indirectly affect radionuclide migration in multiple ways. Within 6th FP IP FUNMIG the interplay between microbial biofilms and radionuclides and the effect of microbially induced redox transformations of iron on radionuclide mobility have been investigated. For the first time, formation of U(V) as a consequence of microbial U(VI) reduction in a multi-species biofilm was detected in vivo by combining laser fluorescence spectroscopy and confocal laser scanning microscopy. Furthermore, it was demonstrated that addition of U(VI) can lead to increased respiratory activity in a biofilm. Increased respiration in a biofilm can create microenvironments with lower redox potential, and hence induce reduction of radionuclides. Transient mobilisation of uranium was observed in experiments with iron oxides containing adsorbed U(VI) in which the activity of sulphate reducing organisms was mimicked by sulphide addition. Faster reaction of sulphide with iron oxides compared to U(VI) reduction, and decreasing U(VI) adsorption due to the transformation of iron oxides into FeS can explain the observed intermittent U mobilisation. The presented research on microbe-radionuclide interactions performed within FUNMIG addresses only a few aspects of the potential role of microorganisms in the performance assessment of nuclear waste repositories. For this reason, this article provides additionally a cursory overview of microbial processes which were not studied within the FUNMIG project but are relevant in the context of performance assessment. Following aspects are presented: a) the occurrence and metabolic activity of microorganisms of several proposed types of host-rocks b) the potential importance of microorganisms in the near-field of nuclear waste repositories, c) indirect effects of microbial processes on radionuclide mobility in the repository far-field, d) binding of radionuclides to microbial biomass, e) microbial redox transformations of radionuclides, and f) the implementation of microbial processes in reactive transport models for radionuclide migration.

Keywords: microbial processes; radionuclides; repositories

Publ.-Id: 16359

Anomalous hysteretic Hall effect in a ferromagnetic, Mn-rich, amorphous Ge:Mn nano-network

Bürger, D.; Zhou, S.; Höwler, M.; Ou, X.; Kovacs, G.; Reuther, H.; Mücklich, A.; Skorupa, W.; Helm, M.; Schmidt, H.

The read out of the magnetization state in magnetic semiconductors by electrical Hall resistance measurements makes it possible to use ferromagnetic semiconductors in nonvolatile memories. In a previous work [1], we fabricated ferromagnetic Ge:Mn by Mn ion implantation and pulsed laser annealing (PLA) and observed hysteretic Hall resistance below 10 K. By applying different PLA conditions we fabricated a percolating, Mn-rich, amorphous Ge:Mn nano-network with hysteretic Hall resistance up to 30K. This nano-network is embedded in crystalline Ge:Mn between 5 nm and 40 nm under the sample surface.
We applied chemical and physical etching to confirm the contribution of the nano-network to the magnetic properties. The nano-network has a significant influence on the correlation between magnetism and anomalous Hall resistance. In the future such nano-networks may be used to spin-polarize free charge carriers in semiconductors at room temperature.
[1] S. Zhou et al., Phys. Rev. B 81, 165204 (2010)

Keywords: percolation; anomalous Hall effect; ferromagnetic semiconductors; pulsed laser annealing

  • Lecture (Conference)
    DPG Frühjahrstagung der Sektion Kondensierte Materie (SKM) 2012, 25.-30.03.2012, Berlin, Deutschland
  • Poster
    DPG Frühjahrstagung der Sektion Kondensierte Materie (SKM) 2012, 25.-30.03.2012, Berlin, Deutschland

Publ.-Id: 16357

Table-top supercomputers for not-quite-table-top radiation source

Bussmann, M.

Laser-driven sources of proton, electron and x-ray beams can provide for new insights into the dynamics of matter on the picosecond to femtosecond time scale. However, for real-world applications such as tumor therapy with laser-driven ion beams or material probing with X-ray Thomson scattering sources our understanding and control of beam properties has to improved. In my talk I will show how modern supercomputing hardware such as GPUs can help us find optimum scenarios for laser-driven radiation sources. Besides showing pretty movies I will focus on the challenges of modern laser plasma simulations and possible ways to overcome them. The talk will conclude with two examples that explore laser matter interaction which illustrate why a pen, some paper and a lot of thinking are always better than all hardware you can possibly buy.

Keywords: laser acceleration; gpu; simulation

  • Lecture (others)
    Trident Seminar, 27.10.2011, Los Alamos, NM, United States of America
  • Lecture (others)
    Seminar Materials Division, 25.10.2011, Livermore, CA, United States of America

Publ.-Id: 16356

A scalable implementation of the Particle-in-Cell Algorithm on GPU Clusters

Bussmann, M.; Burau, H.; Widera, R.; Berninger, F.; Hübl, A.; Kluge, T.; Debus, A.; Schramm, U.; Cowan, T. E.; Schmitt, F.; Hönig, W.; Juckeland, G.; Nagel, W.; Kilian, P.; Ganse, U.; Siegel, S.; Spanier, F.; Ragan-Kelley, B.; Verboncoeur, J.

We present PIConGPU, an implementation of the particle-in-cell algorithm for relativistic laser-plasma interactions. PIConGPU is currently used to simulate laser-wakefield acceleration of electrons as a model for strongly anisotropic many-particle systems. We discuss caveats when porting the particle-in-cell algorithm to GPUs and lessons learned from extending the code from a single-GPU version to a multiple-GPU version.

Keywords: pic; particle-in-cell; simulation; gpu

  • Lecture (Conference)
    Workshop Programming of Heterogeneous Systems in Physics, 05.-07.10.2011, Jena, Deutschland

Publ.-Id: 16355

The speciation of curium(III) bound by the Mont Terri opalinus clay isolate Sporomusa sp. and to the Äspö strain Pseudomonas fluorescens

Moll, H.; Bachvarova, V.; Lütke, L.; Geissler, A.; Selenska-Pobell, S.; Bernhard, G.

It is known that microorganisms exist in host rocks of potential nuclear waste disposals. In this talk, some results will be presented from the current project about the microbial diversity in clay (opalinus clay) and the interactions of dominant microorganisms with actinides. Especially the interactions of two bacteria a Sporomusa sp. clay isolate and a Äspö strain P. fluorescens with curium(III) will be shown and discussed

Keywords: curium(III); TRLFS; bacteria; speciation

  • Lecture (others)
    12. Koordinierungsgespräch HZDR - PSI/LES, 08.-09.12.2011, Paul Scherrer Institut (PSI), Villingen, Schweiz

Publ.-Id: 16354

Messung und Simulationen anisotroper Diffusion in Opalinuston

Schikora, J.; Joseph, C.; Kulenkampff, J.; Brendler, V.; Lippmann-Pipke, J.

Es ist kein Abstract vorhanden.

  • Lecture (others)
    PSI-Meeting, 08.-09.12.2011, Villigen, Schweiz

Publ.-Id: 16353

Spectral properties of oscillatory and non-oscillatory α2-dynamos.

Giesecke, A.; Stefani, F.; Gerbeth, G.

The eigenvalues and eigenfunctions of a linear α2-dynamo have been computed for different spatial distributions of an isotropic α-effect. Oscillatory solutions are obtained when α exhibits a sign change in the radial direction. The time-dependent solutions arise at so called exceptional points where two stationary modes merge and continue as an oscillatory eigenfunction with conjugate complex eigenvalues. The close proximity of oscillatory and non-oscillatory solutions may serve as the basic ingredient for reversal models that describe abrupt polarity switches of a dipole induced by noise.

Whereas the presence of an inner core with different magnetic diffusivity has remarkable little impact on the character of the dominating dynamo eigenmodes, the introduction of equatorial symmetry breaking considerably changes the geometric character of the solutions. Around the dynamo threshold the leading modes correspond to hemispherical dynamos even when the symmetry breaking is small. This behavior can be explained by the approximate dipole-quadrupole degeneration for the unperturbed problem.

More complicated scenarios may occur in case of more realistic anisotropies of α- and β-effect or through non-linearities caused by the backreaction of the magnetic field (magnetic quenching).

Keywords: dynamo; alpha-effect; mean-field theory; reversal

Publ.-Id: 16352

Ionenenergieverteilung während der ZnO-Abscheidung durch Magnetronsputtern: keramisches vs. metallisches Target

Wilde, C.

ad hoc short-notice report. No abstract was necassary

Keywords: ion energy distribution; sputtering; magnetron; mass spectrometry; TCO; AZO

  • Lecture (Conference)
    Transparente leitfähige Oxide - Festkörperphysikalische Grundlagen und Technologie, 16.-17.05.2011, Dresden, Deutschland

Publ.-Id: 16351

DC magnetron sputtering of ZnO:Al from metallic and reduced ceramic targets: comparison of ion energy distributions

Wilde, C.; Vinnichenko, M.

Magnetron sputtering is a common technique for deposition of transparent conductive oxides (TCO) such as Al-doped ZnO (AZO). The film growth using either metallic (reactively) or reduced ceramic targets often show different properties and morphology even in case of optimized processes. Therefore it is crucial to understand differences in magnetron plasma leading to such variations of properties.

The energy of ions emitted from the target in these processes is important, because it influences nucleation and the quality of the TCO.
The negative ions with energies high enough to damage the growing film are of special interest.

In this contribution we report results of comparative analysis of ion energy distributions in a broad energy range for DC magnetron sputtering using metallic and ceramic targets. The energy distributions
of low-energy ions show a similar behaviour for both processes, while in case of high-energy negative ions and fragments of them, they are substantially different . Moreover, magnetron plasma in case of metallic target sputtering shows substantially lower fraction of negatively charged ions with high energy. The observed differences indicate the potential of reactive magnetron sputtering to produce AZO films with less damage, and as a result, with improved properties.

Keywords: Sputtering; Magnetron; Ion Energy Distribution; TCO; mass spectrometry

  • Lecture (Conference)
    DPG Frühjahrstagung der Sektion Kondensierte Materie (SKM) 2012, 25.-30.03.2012, Berlin, Deutschland

Publ.-Id: 16350

Fluence calculation and activity determination at the reactor pressure vessel and their Support of VVER reactors

Konheiser, J.; Borodkin, G.; Borodkin, P.

In the first part, Niobium, nickel and technetium isotopes from RPV trepans of the decommissioned NPP Greifswald (VVER-440) have been analyzed. The activities were determined by TRAMO (Monte-Carlo) fluence. The ratios of calculated to measured (C/E) 93mNb gamma activities for several trepan samples are between 0.43 and 0.97. Up to 20 to 40% lesser fluences have been computed for Nickel and Technetium. The fact that all C/E ratios are below unity suggests that the measured values may have been additionally heightened by activities from other nuclides.
In the second part, VVER reactor support structures (RSS) and reactor pressure vessel (RPV) welds should be undergone the neutron dosimetry analysis to understand their status of criticality relatively a problem of reactor equipment integrity. DORT synthesis and TRAMO Monte Carlo neutron transport calculations were used for fast neutron fluence rates and reaction rates evaluations. Neutron activation measurements by iron foils in ex-vessel cavity near RPV and RSS points of interest are used for testing calculation results. The study has shown that neutron load parameters of RSS and RPV may be enough reason to require the analyses of the resistance against the brittle fracture of these components.

Keywords: activation; Niobium; nickel; technetium; reactor dosimetry; support structures; VVER-440; VVER-1000

  • Lecture (Conference)
    11. AAA Usergroup Meeting, 05.12.2011, Garching bei München, Deutschland

Publ.-Id: 16349

Dose Controlled Radiobiological Experiments with Ultra-short Pulse Laser Accelerated Proton Pulses - and the future of the Dresden laser lab

Schramm, U.


  • Lecture (others)
    MLL Kolloquium der TU und LMU München, 01.12.2011, Garching, Deutschland

Publ.-Id: 16348

Spectroscopic investigation of the interaction between uranium(VI) and schiff bases

Lindner, K.; Günther, A.; Bernhard, G.

Presentation of the complexation of Uranium(VI) with selected Schiff bases in methanol investigated by UV/Vis spectroscopy and ATR FT-IR spectroscopy.

Keywords: Uranium(VI); Schiff bases; UV/Vis; ATR FT-IR

  • Poster
    Doktorandenseminar - Kompetenzzentrum Ost für Kerntechnik, 08.12.2011, Zittau, Deutschland

Publ.-Id: 16347

The Influence of Temperature and Clay Organics on the Retention Behavior of Opalinus Clay concerning Radionuclides

Schott, J.; Schmeide, K.; Acker, M.; Barkleit, A.; Brendler, V.; Bernhard, G.

Presently, argillaceous rock formations are under investigation as potential host rocks for nuclear waste repositories. The sorption of radionuclides on mineral phases is an important physicochemical process in a nuclear waste repository in the case of a water inleakage. Concerning the required long-term safety and risk assessment of the storage of high-level radioactive waste the understanding of this process is essential. Opalinus Clay (OPA) is a complex composed argillaceous rock. This natural occurring clay rock is discussed as host rock formation for nuclear waste repositories. In a repository based on argillaceous rock an initial temperature of around 100°C is expected. But although elevated temperatures are able to influence the sorption behaviour of radionuclides on mineral phases the temperature effect is still investigated insufficiently. Due to the fact that natural organic matter was found in the OPA the influence of organic matter on the radionuclide sorption hast to be investigated. The investigations concentrated on the sorption of Eu(III) and U(VI) on OPA under realistic OPA pore water conditions (OPA pore water medium, pH 7.6, I = 0.4 mol•L-1) up to 50°C. In addition to the temperature dependent investigations the influence of small organic molecules (e.g. lactate, acetate, propionate, tartrate, citrate) on the Eu(III) and U(VI) sorption on OPA was studied up to 50°C.
The Eu(III) sorption is characterized by a strong binding of Eu(III) and the U(VI) sorption is characterized by a weak binding of U(VI) to the clay surface. A significant temperature dependency for the Eu(III) and U(VI) sorption was observed. In the presence of the organic matter the Eu(III) and U(VI) sorption decreases with rising ligand concentration due to a complexation of the metal ions by the ligands in solution. The mobilization of Eu(III) and U(VI) correlates with the complex formation strength of the organic ligands.

Keywords: sorption; Eu(III); U(VI); Opalinus Clay; temperature; organics

  • Lecture (Conference)
    12. Koordinierungsgespräch HZDR-PSI/LES, 08.-09.12.2011, Villigen, Schweiz

Publ.-Id: 16346

Photon scattering by nuclei

Grosse, E.; Junghans, A. R.

Most information about the micro-world has been obtained by light microscopy, i.e. observations with photons and our knowledge about the structure of atoms and molecules mainly originates from electromagnetic spectroscopy.

  • Book chapter
    H. Schopper: Landolt-Börnstein - Numerical Data and Funktional Relationships in Science and Technology, Vol. I /25D, Berlin: Springer, 2013, 4-39

Publ.-Id: 16345

Description of dipole strength in heavy nuclei in conformity with their quadrupole degrees of freedom

Grosse, E.; Junghans, A. R.; Massarczyk, R.; Schwengner, R.; Schramm, G.

In conformity to new findings about the widespread occurrence of triaxiality arguments are given in favor of a description of the giant dipole resonance in heavy nuclei by the sum of three Lorentzians. This TLO parameterization allows a strict use of resonance widths {\Gamma} in accordance to the theoretically founded power law relation to the resonance energy. No additional variation of {\Gamma} with the photon energy and no violation of the sum rule are necessary to obtain a good agreement to nuclear photo-effect, photon scattering and radiative capture data. Photon strength other than E1 has a small effect, but the influence of the level density on photon emission probabilities needs further investigation.

  • Open Access Logo Contribution to proceedings
    Third International Workshop on Compound Nuclear Reactions and Related Topics, 19.-23.09.2011, Prague, Czech Republic
    EPJ Web of Conferences 21 (2012) 04003

Publ.-Id: 16344

Rare-earth plasma extreme ultraviolet sources at 6.5-6.7 nm

Otsuka, T.; Kilbane, D.; White, J.; Higashiguchi, T.; Yugami, N.; Yatagai, T.; Jiang, W.; Endo, A.; Dunne, P.; O'Sullivan, G.

We have demonstrated a laser-produced plasma extreme ultraviolet source operating in the 6.5-6.7 nm region based on rare-earth targets of Gd and Tb coupled with a Mo/B4C multilayer mirror. Multiply charged ions produce strong resonance emission lines, which combine to yield an intense unresolved transition array. The spectra of these resonant lines around 6.7 nm (in-band: 6.7 nm +/-1%) suggest that the in-band emission increases with increased plasma volume by suppressing the plasma hydrodynamic expansion loss at an electron temperature of about 50 eV, resulting in maximized emission.

Publ.-Id: 16343

In-Medium Modifications of Scalar Charm Mesons in Nuclear Matter

Hilger, T.; Kaempfer, B.

Employing QCD sum rules the in-medium modifications of scalar charm mesons in a cold nuclear matter environment are estimated. The mass splitting of D* - (D) over bar* is quantified.

Publ.-Id: 16342

Determination of 41Ca with LSC and AMS: method development, modifications and applications

Hampe, D.; Gleisberg, B.; Köhler, M.; Akhmadaliev, S.; Rugel, G.; Merchel, S.

The isotope 41Ca is produced by neutron capture of the stable and most abundant calcium nuclide 40Ca in concrete of the bioshield around nuclear reactors. Because of its long half-life (1.04*105 a) the declaration of 41Ca in concrete is often requested for radioactive waste disposal.
The radioanalytical 41Ca determination by liquid scintillation counting (LSC) is still a reasonable option for laboratories involved in decommissioning of nuclear installations despite the emission of only low-energy Auger electrons (ca. 3.6 keV) and the difficulty of obtaining a certificated standard. Besides accelerator mass spectrometry (AMS), being the most sensitive analytical technique not only for 41Ca, is increasingly gaining broader accessibility and applicability. Herein, we present a radiochemical separation procedure developed for 41Ca determination with LSC and AMS in varying materials. The radioanalytical isolation consists of anion exchange and extraction chromatography as well as carbonate precipitation and recrystallization from organic solvents. Thereby, disturbing radionuclides as 55Fe, 60Co, 90Sr, 137Cs, 152Eu or 241Pu are removed with decontamination factors of 102-104. Quench curves for determining the measurement efficiency are generated with a 41Ca solution gained from the 41Ca/40Ca certified reference material ERM-AE701. In routine application the procedure is characterized by chemical yields of 25-80%, measurement efficiencies of 1-10% and detection limits of 0.05 Bq*g-1 ash and 0.3 Bq*l.1. Aliquot solutions of LSC can be easily converted into CaF2-AMS-targets by successive oxalate and fluoride precipitation. Pros and cons for both measurement techniques are addressed based on 41Ca results from LSC and AMS for the same material.

Keywords: LSC; accelerator mass spectrometry; nuclear waste disposal

  • Poster
    Ninth International Conference METHODS AND APPLICATIONS OF RADIOANALYTICAL CHEMISTRY (MARC IX), 25.-30.03.2012, Kailua-Kona, Hawaii, USA

Publ.-Id: 16340

Using Table-top Supercomputers for Simulating Table-top Radiation Sources

Bussmann, M.; Burau, H.; Widera, R.; Berninger, F.; Hübl, A.; Steiniger, K.; Kluge, T.; Debus, A.; Metzkes, J.; Zeil, K.; Kraft, S.; Jochmann, A.; Schlenvoigt, H. P.; Siebold, M.; Schramm, U.; Cowan, T. E.; Schmitt, F.; Hönig, W.; Juckeland, G.; Nagel, W.; Kilian, P.; Ganse, U.; Siegel, S.; Spanier, F.; Ragan-Kelley, B.; Verboncoeur, J.

Designing laser-driven radiation sources requires realistic simulations, new ideas and good modeling. For inventing a design, a thorough analysis of existing designs is of great help. For planing designs, the fundamentals of the radiation generation process must be well understood. For testing designs, a fast return of results and the possibility to perform surveys of a large landscape of parameters is essential. In my talk I will address all steps in the source design using three examples from our recent research
* Scaling of hot electron energies with laser intensity in laser-solid interaction
* Laser-driven x-ray sources with tunable energy and bandwidth
* Fast computation of laser-plasma interaction with new computation hardware

Keywords: laser particle acceleration

  • Invited lecture (Conferences)
    2nd ELI Beamlines Scientific Challenges Meeting, 05.-06.10.2011, Praha, Česká republika

Publ.-Id: 16339

PIConGPU A scalable implementation of the Particle-in-Cell Algorithm for GPU Clusters

Bussmann, M.; Burau, H.; Berninger, F.; Kluge, T.; Debus, A.; Schramm, U.; Cowan, T. E.; Schmitt, F.; Widera, R.; Hönig, W.; Juckeland, G.; Nagel, W.

We present PIConGPU, a performant implementation of the particle-in-cell algorithm for GPUs that is scalable on GPU clusters. PIConGPU is used for fast-response simulations of laser-plasma interaction, including laser wakefield acceleration using the sliding-window technique. We discuss lessons learned from going from the initial two-dimensional PICimplementation to a full 3D implementation, focusing on data storage on the GPU and data communication between GPU nodes in a cluster. We show how communication and data storage can be efficiently hidden from users who want to extend the code by adding new physics so that users can assume to be working in a singledata single-instruction environment without deeper knowledge of GPU programming. As an example we show how the far field of relativistic electrons performing betatron oscillations in a laser-driven wakefield can be calculated from macro-particle trajectories on the GPU and subsequently stored in CPU. First simulation results obtained with PIConGPU are shown to illustrate the advantage of fast response simulations for large parameter scans.

Keywords: gpu; pic; particle-in-cell; simulation

  • Lecture (Conference)
    ICNSP 2011, 07.-09.09.2011, Long Branch, NJ, United States of America

Publ.-Id: 16338

A scalable, performant, highly-parallel particle-in-cell code for fast simulations of large laser-plasma experiments

Bussmann, M. H.; Burau, H.; Berninger, F.; Debus, A.; Irman, A.; Jochmann, A.; Hönig, W.; Schmitt, F.; Widera, R.; Juckeland, G.; Nagel, W.; Schramm, U.; Cowan, T. E.

A scalable, performant, highly-parallel Particle-in-Cell code for fast simulations of large Laser-Plasma experiments. Investigating parameters for optimizing laser particle acceleration is a timeconsuming task since realistic simulations of laser plasma interactions using the particle-in-cell technique can require the computation of several hundred million particle trajectories on a grid of several ten million cells. The computational effort needed to investigate the dependence of the performance of new acceleration scenarios on only a few parameters thus normally requires the use of large-scale high-performance computing systems only available at central super computing centres. Thus, parameter scans are usually performed by reducing the system size, the particle density, the computation time and the dimensionality of the problem. Such a scan is then at best complimented by a small number of more realistic large-scale simulations with parameters closer to the experimental parameters. Recently, general purpose graphical processing units (GPGPUs) have entered the stage of high performance computing. This new hardware offers a computational power exceeding that of standard CPU-based computers by several orders of magnitude at much lower investment and maintenance costs. Making good use of this computational power is only possible if the algorithm can run on a massively parallel system consisting of a huge number of independently working processors. However, the memory on a single GPGPU and thus the system size that can be computed on it is limited We present PIConGPU [1], a particle-in-cell algorithm that can run efficiently on a cluster of GPGPU nodes. PIConGPU can run largescale, realistic simulations by mapping the physical system onto many GPGPUs. Thus, the time needed to calculate the evolution of the large system is comparable to the time it takes to compute the small sub-region that can fit on a single GPU and therefore can lead to turnaround times of only a few hours for a hundred thousand time steps and single time steps of under a nanosecond per macro-particle [2].
If computational stability and dispersion is treated appropriately, using GPGPUs to simulate for example laser wakefield acceleration of electrons can greatly enhance the study of large parameter spaces while at the same time using simulation parameters resembling those of the experimental system studied. We focus on real-world examples of using PIConGPU for the simulation of laser electron acceleration scenarios investigated with the DRACO laser system at the Forschungszentrum Dresden-Rossendorf and show how the fast response time of GPGPU-based simulations can open up the path for optimizing experimental parameters.

Keywords: GPU; PIC; particle-in-cell; simulation; parallel

  • Lecture (Conference)
    SPIE Optics + Optoelectronics, 18.-21.04.2011, Praha, Česká republika

Publ.-Id: 16337

New direction in Melos obsidian characterization

Eder, F.; Neelmeijer, C.; Pearce, N. J. G.; Sterba, J. H.; Bichler, M.; Merchel, S.

In 2006, Arias et al.[1] chemically characterized a new obsidian source on the island of Melos. This third obsidian source, obsidian blocks inside the volcanoclastic deposits at Agios Ioannes, was claimed to be well distinguishable from the two well-known sources Agia Nychia and Demenegakion.
Following a sampling campaign in 2010, investigations of samples collected from all three Melos obsidian finding spots (Agia Nychia, Demenegakion, Agios Ioannes) were performed by three complementary analytical techniques (Neutron Activation Analysis, Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry, Ion Beam Analysis). Unfortunately, investigations had to be conducted on rubblestones, since the obsidian blocks described by Arias et al. could not be located. The “chemical fingerprint” composed of 43 elements clearly separates the rubblestones into the two known groups of Agia Nychia and Demenegakion. Elevated Sb concentrations already mentioned in Arias et al. could be confirmed but are probably attributed to a local contamination.

References: [1] Arias et al., J. Radioanal. Nucl. Chem. 268 (2006) 371–386.

Keywords: ion beam analysis; archaeometry; PIXE; PIGE

  • Poster
    „Archäometrie und Denkmalpflege 2012“, 28.-31.03.2012, Tübingen, Deutschland

Publ.-Id: 16336

Experimental characterisation of the interfacial structure during counter-current flow limitation in a model of the hot leg of a PWR

Vallée, C.; Nariai, T.; Futatsugi, T.; Tomiyama, A.; Lucas, D.; Murase, M.

In order to investigate the two-phase flow behaviour during counter-current flow limitation in the hot leg of a pressurised water reactor, dedicated experiments were performed in a scaled down model of the Kobe University. The structure of the interface was observed from the side of the channel test section using a high-speed video camera. An algorithm was developed to recognise the stratified interface in the camera frames after background subtraction. The evolution of the water level along the hot leg is analysed in function of the liquid and gas flow rates.

Keywords: counter-current flow limitation; CCFL; hot leg; stratified two-phase flow; interfacial structure; image processing

Publ.-Id: 16335

Elektronik für einen Strahllagemonitor (BPM)

Büchner, A.

Die geplante Elektronik für einen neuen Strahllagemonitor (BPM) an ELBE wird vorgestellt. Der neue Strahllagemonitor soll einen wesentlich höheren Dynamikbereich haben und gleichzeitig die alten Differenzstrommonitore (DCM) ablösen. Dazu werden die einzelnen Signale vom Stripline-Monitor aufbereitet, digitalisiert und in einem FPGA verarbeitet. Die Strahllage und der Strahlstrom werden bestimmt und sowohl analog wie auch digital ausgegeben. Die Differenz des Strahlstromes zweier Strahllagemonitore wird gebildet und für das Maschinenschutzsystem überwacht.

Keywords: ELBE; Beam Position Monitor; BPM; Stripline-Monitor; Differential Current Monitor; DCM

  • Invited lecture (Conferences)
    102. Tagung der Studiengruppe elektronische Instrumentierung, 21.-23.03.2011, Darmstadt, Deutschland

Publ.-Id: 16334

Development of a PET ligand for imaging PDE10A in brain - synthesis, potency, metabolism and radiochemistry of a 7-(2-fluoroethoxy)-6-methoxy-quinazoline derivative

Schwan, G.; Funke, U.; Deuther-Conrad, W.; Egerland, U.; Birkemeyer, C.; Scheunemann, M.; Nieber, K.; Sträter, N.; Brust, P.; Briel, D.

The phosphodiesterase (PDE) 10A plays an important role in neurotransmission by regulating intracellular levels of the cyclic nucleotides cAMP and cGMP in dopaminergic neurons. In consequence, PDE10A is associated with dopamine-related central nervous diseases such as Huntington’s disease and schizophrenia. Thus, PDE10A is a promising candidate for drug development with a variety of selective PDE10A inhibitors published during the last decade [1, 2]. The aim of the presented work is the development of a positron emission tomography (PET)
radiotracer for imaging of PDE10A in vivo.
Based on a lead structure (IC50PDE10A = 8 nM), published for therapeutic applications [3], three nonradioactive fluoroalkoxy derivatives (1, 2, 3) were enantioselectively synthesized over 11-14 steps and characterized regarding their potency and selectivity to inhibit PDE10A in a cAMP competition assay. Prolongation of the alkyl chain from 1 to 3 by one methylene group each resulted in decreased inhibitory potency from IC50 = 24 nM over 106 nM to 144 nM. Metabolic stability of 2 was determined in comparison to the lead compound in an in-vitro metabolism assay using rat liver S9-fractions. Metabolites were structurally characterized using ESI-MS-MS coupling techniques.
With regard to radiochemical accessibility, derivative 2 appeared as the most promising candidate for radioligand investigation. Initially, a two-step synthesis of [18F]2, consisting of 18F-labelling of 1,3-bistosyloxyethane and following coupling with phenolic precursor 4, was carried out. For the 18F-fluoroalkylation step labeling yields (LY) of 30-45% were achieved. Consequently, in a one-step procedure the tosylethoxy precursor 5 was used for 18Flabelling, improving LY up to 42-72%. Biodistribution studies in female CD-1 mice revealed high initial brain uptake of [18F]2. However, it was not significantly inhibited by competition with 2 or by pre-treatment with MP-10, a high PDE10A specific inhibitor, indicating lack of specificity in vivo. In conclusion, these results motivate for further structural variation of the lead compound to make it suitable for neuroimaging of PDE10A with PET.
Acknowledgements: We would like to thank J. Ortwein (Institute of Pharmacy, University of Leipzig) and the team of L. Hennig (Institute for Analytical Chemistry, University of Leipzig) for their analytical support. This project was financed by resources of the European Fond for Regional Development (EFRE) and the Free State of Saxony.
1. Chappie et al., Current Opinion in Drug Discovery & Development 2009, 12, 458–467.
2. Kehler and J. P. Kilburn, Expert Opinion on Therapeutic Patents 2009, 19, 1715–1725.
3. Chappie et al., J. Med. Chem. 2006, 50, 182–185.

  • Poster
    Joint Meeting of the Austrian and German Pharmaceutical Science, 20.-23.09.2011, Innsbruck, Österreich

Publ.-Id: 16333

Pharmacological and toxicological properties of a novel selective PDE10A ligand

Siegert, F.; Erdmann, S.; Schwan, G.; Scholz, S.; Brust, P.; Sträter, N.; Altenburger, R.; Briel, D.; Nieber, K.

The phosphodiesterase 10A (PDE10A) has an important role in neurotransmission regulating the intracellular cyclic nucleotides especially in dopaminergic neurons. The PDE10A is a promising candidate for drug development and inhibiton of the PDE10A could be an interesting therapeutic stategy for treatment of brain dysfunctions, such as schizophrenia. The present study was designed to examine pharmacological and toxicological properties of a potent and selective brain permeable inhibitor of PDE10A (Ki = 31.9 nM) as nonradioactive derivative for the development of a radiotracer for positron emission tomography (PET).
The lead compound (3006) and the fluoric substituted derivative with prolonged alkyl chain by one methylen group (3039) had no effect on basal intracellular calcium concentration [Ca+]i in human neuroblastoma cells (SH-SY5Y). High concentrations (100 μM) of 3039 but not 3006 increased potassium-induced calcium mobilisation. Electrophysiological investigations on rat brain slices indicated no effect of 3039 or 3006 on postsynaptic membrane parameters and synaptic transmission up to 100 μM. After long-term incubation (48 h) 3039 and 3006 enhanced metabolic activity and reduced LDH-release of SH-SY5Y cells up to 1 μM whereas at high concentration (100 μM) metabolic activity was decreased due to slightly increased cell damage. Using the zebrafish embryo toxicity test mortality was observed at concentration of 100 μM for 3039 and ≥ 1μM for 3006 after incubation of 48 h.
The results suggest a different pharmacological profile of 3039 in comparison to its lead compound 3006 possibly by distinct binding characteristics to the PDE10A enzyme. Both compounds had no toxic effects in concentrations relevant for PET ligands. 3039 seems to be an appropriate candidate for developing a PET probe for studying distribution of PDE10A in vivo.

  • Poster
    Joint Meeting of the Austrian and German Pharmaceutical Science, 20.-23.09.2011, Innsbruck, Österreich

Publ.-Id: 16332

Radiolabelling of engineered nanomaterials as a tool for sensitive particle tracking - Cyclotron facility – Radionuclide production

Franke, K.; Hildebrand, H.

Vortrag im Rahmen eines Workshops, kein Abstract vorhanden

  • Lecture (Conference)
    7th annual CYCLEUR workshop on cyclotron research and radio-labelled nanoparticles, 28.-29.11.2011, Ispra, Italia

Publ.-Id: 16331

Realistic Integration of Sorption Processes in Long-term Safety Assessments

Schikora, J.

Vortrag für das Kompetenzzentrum OST 2011 in Zittau. Inhalt ist die realitätsnahe Integration von Sorptionsprozessen in Langzeitsicherheitsanalysen. Nach einer kurzen Erläuterung zur Motivation und der Vorstellung des Projektes ESTRAL wird die konzeptionelle Vorgehensweise zur realitätsnahen Integration von Sorptionsprozessen exemplarisch am Standort Gorleben vorgestellt. Für die verwendeten smart-Kd Matrizen werden am Beispiel des oberen Grundwasserleiters anschließend Sensitivitäts- und Unsicherheitsanalysen vorgestellt. Ein Ergebnis dieser Analysen ist die Identifikation von wichtigen Einflussfaktoren. Für den Kd-Wert von U(VI) sind dies zum Beispiel der DIC-Gehalt und die Konzentration an Calciumionen.

  • Lecture (Conference)
    Kompetenzzentrum OST 2011, 08.12.2011, Zittau, Deutschland

Publ.-Id: 16330

The Search for Supernova-produced Radionuclides in Terrestrial Deep-sea Archives

Feige, J.; Wallner, A.; Winkler, S. R.; Merchel, S.; Fifield, L. K.; Korschinek, G.; Breitschwerdt, D.

An enhanced concentration of 60Fe was found in a deep ocean's crust in 2004 in a layer corresponding to an age of ~2 Myr. The conrmation of this signal in terrestrial archives as supernovainduced and detection of other supernova-produced radionuclides is of great interest. We will investigate a marine sediment from the South Australian Basin to search for live 26Al, 60Fe, 53Mn, 60Be and the pure r-process element 244Pu. A possible nding of these radionuclides in a sediment core might allow us to improve the time resolution of the signal and thus to link the signal to a supernova event in the solar vicinity ~2 Myr ago. Furthermore, we might get an insight on nucleosynthesis scenarios in massive stars, the condensation into dust grains and transport mechanisms from the supernova-shell into the solar system.

Keywords: intersteller medium; supernova remnants; nucleosynthesis; ISM; accelerator mass spectrometry

  • Open Access Logo Publications of the Astronomical Society of Australia (PASA) 29(2012), 109-114
    DOI: 10.1071/AS11070

Publ.-Id: 16329

The Molecular Structure of 1,2:5,6-Di-O-isopropylidene-3-O-toluenesulfonyl-a-D-glucofuranose

Mamat, C.; Peppel, T.; Köckerling, M.

The crystal and molecular structure of 1,2:5,6-Di-O-isopropylidene-3-O-toluenesulfonyl-a-D-glucofuranose is reported. This compound crystallizes from a petroleum ether/ethyl acetate mixture with the chiral orthorhombic space group P212121 with four molecules in the unit cell. The unit cell parameters are: a = 9.7945(7), b = 10.1945(7), and c = 21.306(1), and V = 2127.4(2) Å3. Bond lengths and angles of this tosyl-protected glucofuranose are typical

Publ.-Id: 16328

1D-confinement of polyiodides inside single-wall carbon nanotubes

Chorro, M.; Kane, G.; Alvarez, L.; Cambedouzou, J.; Paineau, E.; Rossberg, A.; Kociak, M.; Aznar, R.; Pascarelli, S.; Launois, P.; Bantignies, J. L.

1D-confinement of polyiodides inside single-wall carbon nanotubes (SWCNT) is investigated. Structural arrangement of iodine species as a function of the SWCNT diameters is studied. Evidence for long range one dimensional ordering of the iodine species is shown by x-ray and electron diffraction experiments independently of the tube diameter. The structure of the confined polyiodides is investigated by x-ray absorption spectroscopy. The confinement influences the local arrangement of the chains. Below a critical diameter Φc of 1 nm, long linear polyiodides are evidenced leading to a weaker charge transfer than for nanotube diameter above Φc. A shortening of the polyiodides is exhibited with the increase of the nanotube diameter leading to a more efficient charge transfer. This point reflects the 1D-confinement of the polyiodides inside the nanotubes.

Publ.-Id: 16327

Korrekturen für nichtreine und hochenergetische Positronenstrahler in der Kleintierbildgebung unter Verwendung von Monte-Carlo Simulationen

Sauerzapf, S.; Zakhnini, A.; Weber, W.; Pietrzyk, U.; Mix, M.

Das Isotop I-124 besitzt zusätzlich zum β+-Zerfall γ−Linien, die in sogenannten „falschen“ Koinzidenzen resultieren und eine bildverschlechternde Hintergrundaktivität verursachen. Wegen der maximalen Positronenzerfallsenergie von 2,1MeV besitzt I-124 eine hohe Reichweite, die die Ortsauflösung reduziert. Ziel dieser Arbeit war die Implementation einer Korrektur, die beide Effekte korrigiert.
Methodik/ Methods:
Ausgehend von optimalen Akquisitionseinstellungen wurde eine sinogrammbasierte Hintergrundsubtraktion sowie ein Rekonstruktionsalgorithmus mit Auflösungsrückgewinnung implementiert. Messungen wurden am MicroPET Focus 120 durchgeführt und mit GATE [1] Monte-Carlo (MC) Simulationen für verschiedene Phantome verglichen (Mausvoxelphantom, NEMA Image Quality Phantom (IQ) und ein selbstgebautes Mini-NEMA Schwächungsphantom). Die Bildrekonstruktion erfolgte mit Hilfe eines modifizierten OSEM-Algorithmus aus der STIR Library [2]. Über die MC-Simulationen lassen sich die Anteile der falschen zu wahren Koinzidenzen separieren und bei der Korrektur berücksichtigen. Für die Auflösungsrückgewinnung wurden Punktquellen in verschiedenen Schwächungsmaterialien simuliert und über die Reichweitenhistogramme materialabhängige Faltungskerne berechnet. Diese sind über den Vorwärtsprojektor in den Algorithmus integriert.
Ergebnisse/ Results:
Simulationen und vergleichende Messungen zeigen, dass am MicroPET durch Verkleinerung des Energiefensters von 350-650keV auf 400-550keV eine deutliche Reduktion der störenden Hintergrundaktivität und eine Verbesserung der Bildqualität erzielt werden kann. Die Anteile falscher zu wahrer Koinzidenzen sind außerhalb des Objektes homogen und nicht aktivitätsabhängig: 0,76 (MC: IQ, 90MBq, 50s) bzw. 0,77 (MC: IQ, 9MBq, 70s). Innerhalb existiert ein aktivitätsabhängiger Anteil von 0,29 bzw. 0,18, der über Gauß-Fits in der sinogrammbasierten Hintergrundsubtraktion berücksichtigt wird. Als Resultat ergeben sich quantitativ genauere und kontrastreichere Bilder. Simulationen eines realistischen Mausphantoms mit I-124, Ga-68 und F-18 zeigen, dass der dominante Effekt für die Bildverschlechterung in der Kleintierbildgebung der Auflösungsverlust durch die hohe Positronenzerfallsenergie ist. Die Anwendung der o.g. Entfaltungsmethode verbessert bei I-124 die Ortsauflösung von 4,9mm FWHM vor der Korrektur auf 2,5mm nach der Korrektur (IQ, Insert mit d=5mm, nach 20 Iterationen). Kritisch bei dieser Korrektur ist die genaue Definition des Abbruchkriteriums, da für höhere Iterationen eine Überkorrektur mit Artefakten entsteht.

Schlussfolgerungen/ Conclusions:
Unter Berücksichtigung von MC-Simulationen wurden Korrekturen für die Bildrekonstruktion von nichtreinen, hochenergetischen Positronenstrahlern erarbeitet. Die Ergebnisse der Simulationen konnten verifiziert und erfolgreich auf reale Daten übertragen werden.

[1]Jan et al. Med. Biol. (56) (2011) 881-901
[2]Thielemans et. al. IEEE NSS & MIC Record 2006

  • Poster
    Die 50. Jahrestagung der Deutschen Gesellschaft für Nuklearmedizin, 25.-28.04.2012, Bremen, Deutschland

Publ.-Id: 16326

A Simulation study to determine the influence of low-energy bremsstrahlungs photons on the acquisition of very rare coincidence events from Yttrium-90 decay.

Thomas, L.; Sauerzapf, S.; Mix, M.; Zakhnini, A.; Gaens, M.; Axer, M.; Pietrzyk, U.

In the course of treating liver cancer, frequently SIRT (selective internal radiation therapy) with Yttrium-90 is applied. In order to study the bio-distribution, often SPECT or SPECT/CT imaging is used, based on the detection of low-energy bremstrahlung photons. However, there is also another imaging option, namely through observation of the very rare internal pair production of Y-90, leading to an experimental situation well suited for PET (2). The aim of this study is to study the influence of the low-energy bremsstrahlung photons, which come at relatively high count-rate, but at the same time preserving the PET signal, i.e. the two gammas originating from the e+-e- annihilation, since only 32 out of one million decays of Yttrium-90 happen via internal pair production.

The normal decay channel, the emission of therapeutically used electrons with high energy, comes with the production of low energy bremsstrahlung photons. Despite their relatively low energy (only a fraction of 16,6% of such photons exceeds more than 300 keV), the high-count rate could lead to saturation effects (via pulse pile-up) of the PET detector electronics. To absorb these low-energy photons, it was suggested to insert a copper ring into the gantry (1). To analyze a) where or not such a ring is required and b) which material might be best suited, we simulated a Siemens MicroPET Focus 120 and the PET part of a Philips Gemini TOF PET-CT with GATE (2) with different ring materials and a contrast medium filled phantom. Results from simulations were compared with experimental data obtained from measurements under condition comparable to the simulation.

First preliminary results from the simulation showed, that a 0.5 cm thick copper ring absorbs the low-energy bremsstrahlung, while preserving those at higher energy around 511 keV. In contrast, a ring of 0.5 cm of lead also absorbs many of the gammas around 511 keV. However, so far it is not certain, whether such a ring made of copper or lead would be required at all. Further studies are needed, especially with taking into account the signal processing chain as offered by GATE to differentiate further options in improving the detection of very rare signals for PET. Additional measurements might also provide more details of what exactly the PET-images show, because a superposition of the bremsstrahlung photons from interacting electrons with the true coincidence signals cannot be ruled out.
Our first results of distributions of simulated and measured events from Y-90 internal pair production look promising. The PET-images show very clear distributions of Y-90, yet need further confirmation, especially studying the influence of pile-up, dead-time effects on the rare coincidence signal.

(1) R Lhommel et al: Eur J Nucl Med Mol Imaging (2009) 36:1696.
(2) S Jan et al: GATE V6. Phys. Med. Biol. (2011) 56 881-901.

  • Poster
    Die 50. Jahrestagung der Deutschen Gesellschaft für Nuklearmedizin, 25.-28.04.2012, Bremen, Deutschland

Publ.-Id: 16325

Experiments on air entrainment under a vertical circular impinging jet: Measurement of the entrained air quantity

Danciu, D.-V.; Beyer, M.; Lucas, D.

The paper presents an experimental investigation regarding the phenomenon of air entrainment as a result of a jet impinging into a tank filled with water. The main objective of the work consists of gathering information about the concentration of the entrained void fraction, bubble velocities and the entrainment rate. For this purpose, a measuring technique based on wire-mesh sensors was used. For distinct combinations of nozzle exit velocity, jet length and immersion depth, the concentration and distribution of the entrained void fraction, as well as bubble size distributions and velocities were acquired. The corresponding calculated entrainment rate was found to increase linearly with both jet exit velocity and length, and to be smaller than predicted by literature. The experiments aim to provide an extensive database for air entrainment under plunging jets, needed for validation of Computational Fluid Dynamics (CFD) codes.

Keywords: air entrainment; impinging jet; high temporal resolution; experiments; wire-mesh sensor; void fraction; bubble velocities

  • Contribution to proceedings
    6th International Berlin Workshop on Transport Phenomena with Moving Boundaries, 24.-25.11.2011, Berlin, Germany
    Proceedings of the 6th International Berlin Workshop on Transport Phenomena with Moving Boundaries

Publ.-Id: 16324

Doping of silicon by ion implantation and annealing

Prucnal, S.

Multicrystalline p-type silicon wafers were used for the implantation of phosphorous. After ion implantation the silicon is strongly disordered or amorphous within the ion range. Therefore subsequent annealing is required to remove the implantation damage and to activate the doping element. The influence of the annealing types (furnace annealing - FA, rapid thermal annealing – RTA and Flash-lamp-annealing – FLA) on the optical and electrical properties of mc-Si solar cell was investigated. FLA offers here an alternative route for the emitter formation at an overall low thermal budget. During FLA, only the wafer surface is heated homogeneously to very high temperatures at ms time scales, resulting in the annealing of the implantation damage and an electrical activation of the phosphorous. However, a variation of the pulse time also allows to modify the degree of annealing of the bulk region to some extent as well, which can have an influence on the gettering behaviour of metallic bulk impurities.

Keywords: mc-Si; solar cells; FLA; PIII

  • Lecture (Conference)
    62th Freiberger Research Conference, 15.-17.06.2011, Freiberg, Germany

Publ.-Id: 16323

Solar cell emitters fabricated by PIII and flash lamp millisecond annealing

Prucnal, S.; Endler, R.; Henke, D.; Kolitsch, A.; Abendroth, B.; Krockert, K.; König, K.; Möller, H. J.; Skorupa, W.

Cost reduction is the overall goal in the further development of solar cell technologies. Multicrystalline silicon has attracted considerable attention because of its high stability against light soaking. In case of Solar Grade (SoG) mc-Si the rigorous control of metal impurities is desirable for solar cell fabrication. The main source of degradation of the photovoltaic effect in p-type mc-Si is iron present as interstitials (Fei) and Fe-B pairs. Processing solar cells at lower temperatures helps reducing the energy cost and in thin film technologies may also facilitate the use of less temperature stable substrates such as normal glass or polymers foils. In the present work a new technique will be presented and explored, which allows the implantation of the doping element by a plasma process and the subsequent annealing by a short time light pulse (Flash Lamp Annealing). Plasma Immersion Ion Implantation (PIII) technique can be used for the emitter formation of solar cells. It is much easier to handle and has the potential for mass production. A dedicated PIII - machine has been built suitable for the implantation of doping impurities into silicon.
The phosphorous implanted and annealed SoG mc-Si wafers were characterised by means of μ-Raman spectroscopy, temperature dependent photoluminescence (PL), surface photo-voltage method (SPV) and four-point probe resistor measurements. It could be demonstrated that FLA at 1000°C for 3 ms even without preheating is sufficient to recrystallize implanted silicon and to electrically activate the phosphorous. The sheet resistance (SR) of FLA samples shows values of about 40 μ/sq. Moreover, the minority carrier diffusion length for the FLA samples is in the range of 80 m. This is up to one order of magnitude higher than that observed from RTA or FA samples.

Keywords: Raman spectroscopy; photoluminescence; FLA; mc-Si

  • Poster
    11th International Workshop on Plasma-Based Ion Implantation & Deposition, 08.-12.09.2011, Harbin, China

Publ.-Id: 16322

III-V/Si heterostructures fully integrated into silicon

Prucnal, S.; Facsko, S.; Baumgart, C.; Schmidt, H.; Liedke, M. O.; Mücklich, A.; Zhou, S. Q.; Skorupa, W.

Integration of III-V semiconductors with a silicon technology is crucial for the devices performance. In this paper we present investigations of the microstructural, optical and electrical properties of III-V quantum dots (InAs, GaAs, InP and GaP) formed in silicon. The III-V QDs were obtained by means of sequential ion implantation and flash lamp annealing (FLA). Conventional selective etching was used to form the n-III-V/p-Si heterojunction. In case of InAs/Si heterostructures, the current-voltage measurement confirms the heterojunction diode formation with the ideality factor of n=4.6. Kelvin Probe Force Microscopy measurements indicate a type-II band alignment of n-type InAs NPs on p-type silicon. The main advantage of our method is its integration with large-scale silicon technology, which also allows applying it for Si-based electronic devices.

Keywords: III-V; flash lamp annealing; heterojunction; ion implantation

  • Lecture (Conference)
    Subsecond thermal processing of Advanced Materials 2011 (subtherm-2011), 25.-27.10.2011, Dresden, Germany

Publ.-Id: 16321

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