Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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33412 Publications

Evaluation of radiation damage using nonlinear ultrasound

Matlak, K.; Wall, J.; Kim, J.-Y.; Qu, J.; Jacobs, L. J.; Viehrig, H.-W.
Nonlinear ultrasound was used to monitor radiation damage in two reactor pressure vessel (RPV) steels. The microstructural changes associated with radiation damage include an increase in dislocation density and the formation of precipitates, and nonlinear ultrasonic waves are known to be sensitive to such changes. Six samples each of two different types of RPV steel were previously irradiated in the Rheinsberg power reactor to two fluence levels, up to 1020 n/cm2. Longitudinal waves were used to measure the acoustic nonlinearity in these samples, and the results show a clear increase in the measured acoustic nonlinearity from the unirradiated state to the medium dose, and then a decrease from medium dose to high dose.
Keywords: reactor pressure vessel steel, neutron irradiation, embrittlement, nonlinear ultrasound, microstructural changes

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Permalink: https://www.hzdr.de/publications/Publ-16550
Publ.-Id: 16550


PT brachistochrone and state discrimination

Günther, U.
In recent work by Bender, Brody, Caldeira and Meister it was shown that the brachistochrone solution of PT Quantum Mechanics (PTQM) can be used to orthogonalize a set of two originally non-orthogonal quantum states. The still remaining draw-back of the proposed technique is in its use of a non-Hermitian PT-symmetric Hamiltonian to achieve the PTQM brachistochrone evolution --- a Hamiltonian which up to now for quantum systems is beyond experimental reach.

We demonstrate that the Bender-Brody-Caldeira-Meister approach can be naturally extended into a higher-dimensional Hilbert space. This allows to interpret the PTQM setup as a very special subsystem of a larger Hermitian system. Moreover we show that this extension can be connected with the standard text-book scheme of unambiguous quantum state discrimination. Technical details of the extension procedure are discussed and ways toward a time-optimal unambiguous state discrimination scheme are indicated.
Keywords: PT quantum mechanics, unambiguous state discrimination, time-optimal state discrimination, PT brachistochrone, extension scheme
  • Invited lecture (Conferences)
    PTQM 2011 symposium, 25.-28.09.2011, Heidelberg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-16549
Publ.-Id: 16549


Mineral dusts - a valuable resource or only dust in the wind?

Renno, A. D.
Rock dust from quarries and from mining operations is a potential valuable resource. Well known and unconventional ways of using are shown. The base for a sustainable use is a very precise chemical and mineralogical characterization of the different dust types.
Keywords: rock dust, sustainable usage of resources, quarry, tailing, mieral dust
  • Invited lecture (Conferences)
    Workshop Internacional Encuentro Alumni DAAD 2012 Geociencias y Energía Desarrollo y Perspectivas de la Cooperación Chileno-Alemana, 18.-21.01.2012, Concepcion, Chile

Permalink: https://www.hzdr.de/publications/Publ-16548
Publ.-Id: 16548


On the use of fine distributed moderating material to enhance feedback coefficients in fast reactors

Merk, B.; Weiß, F.-P.
Recently, the use of moderating materials in fuel assemblies for Sodium cooled fast reactors has been investigated and published in several papers (Annals of Nuclear Energy 38, 5, Annals of Nuclear Energy 38, 11 (2011)). Especially the fine distribution of the moderating material in a layer inside the fuel rod or inside the wire spacer has shown very promising results for the enhancement of the feedback coefficients. The validity of the HELIOS results has been demonstrated in a comparison with MCNP and the transferability of the effect to full core calculations has been shown. The fine distribution of the moderating material is very attractive since it causes only a very limited influence on the safety relevant fuel assembly structure and on the operational parameters like power distribution and end of life burnup distribution. In extension to this published work the influence of the use of moderating materials on systems containing fuels for Minor Actinide transmutation (3% Am, 5% Am, and 2% Np – 2% Am) is examined on the basis of detailed lattice calculations based on 112 energy groups and an unstructured mesh geometry modeling of all fuel assembly details. The influence of the insertion of the Minor Actinides on the fuel temperature and the coolant coefficient is investigated for a reference case and the possibilities of enhancing the feedback coefficients by the insertion of ZrH moderating material are analyzed. The changes in the power and burnup distribution due to the use of the moderating material ZrH will be discussed. Further on, the transmutation potential is compared for the cases with and without moderating material. Neptunium and Americium is slightly more reduced during burnup of the fuel with moderating material only the Curium production rises slightly. A detailed analysis demonstrates that the increase of Cm breeding due to the use of moderating material is lower than the additional amount of destroyed Np and Am. Thus, the results demonstrate that even more Am is burnt with the investigated fuel assembly containing moderating material inside the wire wrapper.
Additionally, a first test of the effect of the use of fine distributed moderating material in a lead cooled fast reactor will be shown. The test is based on preliminary data of the fuel assembly in the GUINEVERE facility. The effect of the moderating material on the neutron spectrum, on the kinf, and on the fuel temperature feedback of the zero power facility is shown and discussed.
Over all, the use of fine distributed moderating material has the potential to open the stage for designable feedback coefficients in fast reactors without creating a major influence on the operational parameters and core coolability.
Keywords: Sodium void effect, SFR, Fast reactor, Zirconium hydride, designable feedback coefficient, transmutation, GUINEVERE, LFR
  • Contribution to proceedings
    Innovative Fast Reactor Designs with Enhanced Negative Reactivity Feedback Features, 27.-29.02.2012, Wien, Österreich
  • Lecture (Conference)
    Innovative Fast Reactor Designs with Enhanced Negative Reactivity Feedback Features, 27.-29.02.2012, Wien, Österreich

Permalink: https://www.hzdr.de/publications/Publ-16547
Publ.-Id: 16547


On the use of moderating material to enhance the feedback coefficients in SFR cores with high minor actinide content

Merk, B.; Weiß, F.-P.
The use of fine distributed moderating material to enhance the feedback effects and to reduce the sodium void effect is described. The consequences of the introduction of fine distributed moderating material into fuel assemblies with fuel configurations foreseen for minor actinide transmutation is analyzed. The degradation of the feedback effects due to the insertion of minor actinides and the compensation by the use of moderating materials is discussed.
Keywords: Sodium void effect, SFR, Fast reactor, Zirconium hydride, designable feedback coefficient, transmutation
  • Contribution to proceedings
    International Congress on Advances in Nuclear Power Plants (ICAPP'12), 24.-28.06.2012, Chicago, USA
  • Lecture (Conference)
    International Congress on Advances in Nuclear Power Plants (ICAPP'12), 24.-28.06.2012, Chicago, USA

Permalink: https://www.hzdr.de/publications/Publ-16546
Publ.-Id: 16546


Solutions without space-time separation for ADS experiments: Overview on Developments and Applications

Merk, B.; Glivici-Cotruţă, V.
The different analytical solutions without space-time separation foreseen for the analysis of ADS experiments are described. The SC3A experiment in the YALINA-Booster facility is described and investigated. For this investigation the very special configuration of YALINA-Booster is analyzed based on HELIOS calculations. The results for the time dependent diffusion and the time dependent P1 equation are compared with the experimental results for the SC3A configuration. A comparison is given for the deviation between the analytical solution and the experimental results versus the different transport approximations. To improve the representation to the special configuration of YALINA- Booster, a new analytical solution for two energy groups with two sources (central external and boundary source) has been developed starting form the Green’s function solution. Very good agreement has been found for these improved analytical solutions.
Keywords: Yalina, experimental analysis, Green’s function, Two group diffusion equation

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Permalink: https://www.hzdr.de/publications/Publ-16545
Publ.-Id: 16545


An analytical solution for the consideration of the effect of adjacent fuel assemblies; extension to hexagonal VVER-440 type fuel assemblies

Merk, B.; Rohde, U.
A new analytical method is described to deal with the Leakage Environmental Effect. The method is based on the one dimensional analytical solution of the two-group diffusion equation for two adjacent fuel assemblies. The quality of the results for this highly efficient method is demonstrated for quadratic fuel assemblies. In additional tests the transferability of the concept to hexagonal VVER-440 type fuel assemblies is shown.
Keywords: VVER, Analytical Solution, Homogenization, Cross Section Preparation, Leakage Assembly Environmental Effect
  • Kerntechnik 4(2012), 230-239

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Permalink: https://www.hzdr.de/publications/Publ-16544
Publ.-Id: 16544


Overview of major HZDR developments for fast reactor analysis

Merk, B.; Glivici-Cotruţă, V.; Duerigen, S.; Rohde, U.; Kliem, S.
The upgrading of the DYN3D code for the application for fast reactors is described. After validation, a diverse code with the possibility for steady state and transient core analysis on the basis of coupled thermal hydraulics/neutronics calculations is available. The work on the use of fine distributed moderating material in SFR cores is discussed with the target on enhancing the feedback coefficients in SFR cores without influencing the operational. Newly developed analytical solutions without separation of space and time for the analysis of ADS experiments are shown with good agreement for the YALINA experiment. The analytical solutions are a very promising tool for the development of a new method for the analysis of ADS experiments.
Keywords: DYN3D, coupled thermalhydraulics/neutronics calculations, Sodium void effect, designable feedback coefficient, analytical solutions, ADS experiments

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Permalink: https://www.hzdr.de/publications/Publ-16543
Publ.-Id: 16543


Curium(III) and europium(III) speciation studies with Mont Terri Opalinus clay isolates

Moll, H.; Bachvarova, V.; Lütke, L.; Geissler, A.; Selenska-Pobell, S.; Bernhard, G.
Microorganisms are ubiquitous also in host rocks of potential nuclear waste disposal sites. In this talk, some results will be presented from the current project about the microbial diversity in Opalinus clay and the interactions of dominant microorganisms with actinides. Especially the interactions of a Sporomusa sp. clay isolate with curium(III) and europium(III) will be shown and discussed.
Keywords: Curium. Europium, Bacteria, TRLFS, Speciation
  • Lecture (others)
    Mont Terri Project: Joint HT-MA-BN-GD-PCC Meeting, 06.-07.02.2012, St. Ursanne, Switzerland

Permalink: https://www.hzdr.de/publications/Publ-16542
Publ.-Id: 16542


DRESDYN: A large scale liquid sodium facility for experiments on dynamo action and related magnetic instabilities

Giesecke, A.; Gerbeth, G.; Gundrum, T.; Kirillov, O.; Seilmayer, M.; Stefani, F.
The DREsden Sodium facility for DYNamo and thermohydraulic studies (DRESDYN), which is presently in the design phase, will comprise a number of large scale liquid sodium experiments devoted to problems of geo- and astrophysical magnetohydrodynamics. A homogeneous dynamo, driven exclusively by precession, will represent the most ambitious compound of DRESDYN.
Another experiment, a sodium filled Taylor-Couette cell, will allow the combined investigation of various versions of the magnetorotational instability and of the Tayler instability. For both experiments, recent results of preparatory studies are presented, and the scientific prospects for the final set-ups are delineated.
Keywords: DRESDYN Dynamo MHD-Instabilities Magnetohydrodynamics Precession Magnetorotational Instability
  • Poster
    European Geosciences Union General Assembly 2012, 23.-27.04.2012, Wien, Austria
  • Open Access Logo Abstract in refereed journal
    Geophysical Research Abstracts 14(2012), EGU2012-2824

Permalink: https://www.hzdr.de/publications/Publ-16541
Publ.-Id: 16541


Shallow-underground accelerator sites for nuclear astrophysics: Is the background low enough?

Szücs, T.; Bemmerer, D.; Cowan, T.; Degering, D.; Elekes, Z.; Fülöp, Z.; Gyürky, G.; Junghans, A.; Köhler, M.; Marta, M.; Schwengner, R.; Wagner, A.; Zuber, K.
In order to reliably estimate the rate of a charged particle induced nuclear reaction in a non-explosive astrophysical scenario, its cross section must be measured far below the Coulomb barrier. However, at the corresponding energies the cross section values are very low, so that the experimental counting rate is dominated by cosmic-ray induced background, even if a suitable anticoincidence shield is applied. This problem can be overcome by performing an accelerator-based experiment in a deep underground site, as has been done with great success at the LUNA 0.4 MV accelerator in Gran Sasso, Italy. Several underground accelerators with higher beam energy are in the planning phase worldwide. All of them are shielded by over 1000 m of rock, a depth at which cosmic-ray effects are negligible for the purposes of nuclear astrophysics experiments. It is shown here that a combined approach, using a shallow underground laboratory below 47 m of rock and an active shield to veto surviving muons in simple detectors, results in a background level that is not far from that of deep underground sites. Data have been obtained using two ”traveling” gamma-detectors. They have been transported both shallow underground, to the Dresden Felsenkeller in Germany, and deep underground, to the Gran Sasso laboratory in Italy. As shallow-underground facilities are more easily accessible than deep-underground ones, the present finding holds the promise of greatly accelerated progress in the field of cross section measurements for nuclear astrophysics.

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Permalink: https://www.hzdr.de/publications/Publ-16539
Publ.-Id: 16539


Dose rate dependence for different dosimeters and detectors: TLD, OSL, EBT films, and diamond detectors

Karsch, L.; Beyreuther, E.; Burris-Mog, T.; Kraft, S.; Richter, C.; Zeil, K.; Pawelke, J.
Purpose: The use of laser accelerators in radiation therapy can perhaps increase the low number of proton and ion therapy facilities in some years due to the low investment costs and small size. The laser-based acceleration technology leads to a very high peak dose rate of about 1011 Gy/s. A first dosimetric task is the evaluation of dose rate dependence of clinical dosimeters and other detectors.
Methods: The measurements were done at ELBE, a superconductive linear electron accelerator which generates electron pulses with 5 ps length at 20 MeV. The different dose rates are reached by adjusting the number of electrons in one beam pulse. Three clinical dosimeters (TLD, OSL and EBT radiochromic films) were irradiated with four different dose rates and nearly the same dose. A faraday cup, an integrating current transformer and an ionization chamber were used to control the particle flux on the dosimeters. Furthermore two diamond detectors were testet.
Results: The dosimeters are dose rate independent up to 4•109 Gy/s within 2 % (OSL and TLD) and up to 15•109 Gy/s within 5 % (EBT films). The diamond detectors show strong dose rate dependence.
Conlusion: TLD, OSL dosimeters and EBT films are suitable for pulsed beams with a very high pulse dose rate like laser accelerated particle beams.

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Permalink: https://www.hzdr.de/publications/Publ-16538
Publ.-Id: 16538


A Tapered Undulator Experiment At The ELBE Far Infrared Hybrid-Resonator Oscillator Free Electron Laser

Lehnert, U.; Michel, P.; Asgekar, V.
A tapered undulator experiment was carried out at the Helmholtz Forschungszentrum Dresden-Rossendorf (ELBE) far-infrared FEL. The oscillator FEL makes use of a hybrid optical resonator. The main motivation was to see whether the presence of a dispersive medium in the form of a waveguide in the resonator has any effect on the outcome. The FEL saturated power and the wavelength shifts have been measured as a function of both positive as well as negative undulator field amplitude tapering. In contrast to the typical high-gain FELs where positive tapering proves beneficial for the output power we observe an improvement of performance at negative taper. During the same experiments we studied the characteristics of the detuning curves. The width of the curves indicate a maximum small-signal gain for zero taper while the output peak power is highest for negative taper. Whereas the saturated power output and the detuning curve characteristics agree with the known theoretical predictions, the wavelength shifts showed deviations from the expected values. Details of the experiment are presented.
Keywords: undulator; hybrid optical resonator; waveguide effect on the outcome; saturated power; positive and negative undulator field; detuning curves

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Permalink: https://www.hzdr.de/publications/Publ-16537
Publ.-Id: 16537


Studies on Boiling Water Reactor design with reduced moderation and analysis of reactivity accidents using the code DYN3D-MG

Rohde, U.; Pivovarov, V. A.; Matveev, Y. A.
The multi-group version of the DYN3D reactor dynamics code was used for calculations for a new concept of a boiling water reactor with tight lattice of fuel rods and reduced neutron moderation. For that purpose, a 5-group cross section library was prepared and connected to the DYN3D code. Comparison calculations with the steady-state finite-difference code ACADEM showed a very good agreement.
The capability of the DYN3D multi-group code in modeling transients in boiling water reactors with tight fuel element lattices was demonstrated by the analysis of two reactivity accidents initiated by the ejection of one control rod and unauthorized withdrawal of a control rod bank from the reactor core. The corresponding analyses were performed for begin of cycle conditions, when the considered control rods are at their maximum insertion depth.
Keywords: high conversion reactor, boiling water reactor, tight fuel lattice, core design, reactor dynamics, reactivity-initiated accidents
  • Kerntechnik 77(2012)4, 240-248

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Permalink: https://www.hzdr.de/publications/Publ-16536
Publ.-Id: 16536


XAS/XMCD studies of Ga+ irradiation driven magnetization reorientation in Pt/Co/Pt nanostructures

Mazalski, P.; Maziewski, A.; Liedke, M. O.; Fassbender, J.ORC; Ferré, J.; Mougin, A.; Baczewski, L. T.; Wawro, A.; Rogalev, A.; Wilhelm, F.
The magnetic properties of ultrathin films are usually tuned by the varying film thickness, chemical composition or structure (see e.g. [1,2]). It has been demonstrated that the magnetic properties of thin films with perpendicular magnetic anisotropy of interfacial origin may be also tuned by ions irradiation [3]. A Pt/Co/Pt trilayer irradiated by different ions exhibits an out-of-plane to in-plane magnetization reorientation phase transition. Moreover, an ion irradiation-driven intermixing and disordering at the Co–Pt interfaces was shown to lead to a reduction of the anisotropy, coercivity, and Curie temperature.
In our recent paper [4] we presented new effect - remarkable oscillation of the magnetic anisotropy in the Pt/Co(2.6 nm)/Pt (deposited by sputtering technique) induced by an uniform low fluence Ga+ ion irradiation at 30 keV. Increasing fluence F magnetization rotates from in-plane to out-of-plane state and then back to in-plane state. Similar effect, driven by Ga+ ion irradiation, has been recently observed in Pt/Co/Pt deposited by molecular beam epitaxy.
The key question is the origin of observed out-of-plane magnetization state induced by ions irradiation. Ion irradiation driven creation of strongly anisotropic Co-Pt L10 phase is proposed. This hypothesis is supported by measurement of K-edge X-ray absorption (XAS) and X-ray magnetic circular dichroism (XMCD) on the ID12 ERSF beamline. The study was done on: Pt/Co/Pt samples both as deposited film and irradiated one with fluence creating out-of-plane magnetization state, reference sample - L10 Co0.5Pt0.5 thin film. The XMCD spectrum of the irradiated sample is interpreted as the superposition of pure Co and L10 CoPt alloy contributions. TRIDYN [5] simulations, for different Ga ion fluence, were performed for results discussion.
This work was supported by the following projects: SPINLAB - EU programme Innovative Economy, Priority 2.2, SPIRIT European Community - contract no. 227012, ESRF/73/2006.
References
[1] - M. Kisielewski et al., Phys. Rev. Lett. 89, 87203 (2002)
[2] - A. Stupakiewicz et al., Phys. Rev. Lett. 101, 217202 (2008)
[3] - C. Chappert et al., SCIENCE 280, 1919 (1998)
[4] - J. Jaworowicz et al., Appl. Phys. Lett. 95, 022502 (2009)
[5] - W. Möller et al., Comp. Phys. Commun. 51, 355 (1988).
Keywords: XAS/XMCD studies of Ga+ irradiation driven magnetization reorientation in Pt/Co/Pt nanostructures
  • Lecture (Conference)
    ESRF Users' Meeting 2012, 06.-09.02.2012, Grenoble, France

Permalink: https://www.hzdr.de/publications/Publ-16535
Publ.-Id: 16535


Interaction of dislocationswith Cu-Ni-vacancy clusters in Fe

Terentyev, D.; Malerba, L.; Bonny, G.; Al-Motasem, A. T.; Posselt, M.
not available, please contact authors
Keywords: dislocations, iron, Cu-Ni-vacancy clusters, Monte Carlo simulations, molecular dynamics
  • Lecture (Conference)
    16th Meeting of International Group on Radiation Damage Mechanisms in Pressure Vessel Steels (IGRDM-16), 04.-09.12.2011, Santa Barbara, USA

Permalink: https://www.hzdr.de/publications/Publ-16534
Publ.-Id: 16534


X-ray investigations on CoSi2 nano wires manufactured by focused ion beam synthesis

Grenzer, J.; Roshchupkina, O.; Fritzsche, M.; Mücklich, A.; Bischoff, L.
Nanowires and chains of nanoparticles are of emerging interest in nanoelectronics, nano-optics and plasmonics as well as for their monolithic integration into microelectronic devices. Epitaxial buried or surface CoSi2 layers in silicon can be formed by implanting Co in stoichiometric concentration and subsequent annealing. Ion beam synthesis allows the fabrication of submicron pattern, which can be formed either directly by a mass separated writing Co focused ion beam (FIB) or indirectly by a Ga FIB in combination with a thin Co film on the rear side of the Si wafer, providing the Co for the nanowire formation by diffusion.

We have studied the strain of the Si host lattice around a single nanostructure depending on their crystallographic orientation using high-resolution x-ray diffraction and TEM. The X-ray experiment was carried out using a highly focused beam (~0.5µm) at the beam line ID01 at ESRF. Surrounding a wire a peak was found indicating a tensile strain of approx. -1.4%.

The CoSi2 peak intensity is strongly modulated by moving from one wire to another. Moreover the diffuse scattered intensity around the Si bulk reflection is increased and is getting even more enhanced between the wires. A possible mechanism lying behind the CoSi2 structure formation is the lattice relaxation by stable dislocation loops. A zigzag like defect structure, characteristic for the formation of 311 defects, was identified by TEM at the grain boundary between the CoSi2 nanowires and the Si bulk.
  • Poster
    E-MRS 2011 SPRING MEETING, 09.-13.05.2011, Nice, France

Permalink: https://www.hzdr.de/publications/Publ-16533
Publ.-Id: 16533


Material science towards the fs range: What we can do?

Grenzer, J.
Material science towards the fs range:
What we can do?
  • Lecture (others)
    Workshop on Petawatt-Lasers at Hard X-Ray Light Sources, 05.-09.09.2011, Helmholtz-Zentrum Dresden-Rossendorf, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-16532
Publ.-Id: 16532


The ROBL Upgrade: in-situ investigations for material science

Grenzer, J.; Baehtz, C.; von Borany, J.
Werkstoffcharakterisierung mit Strahllinien
  • Lecture (others)
    DGM Fachausschusssitzung, BAM Berlin, 27.05.2011, Berlin, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-16531
Publ.-Id: 16531


Material science towards the fs range: Experimental challanges using an XFEL

Grenzer, J.
Seminar Series:
"Understanding advanced materials and processes on the atomic level:
Materials research with ultrashort, intense and coherent X-ray pulses and high-power lasers"
  • Lecture (others)
    Seminar Serie - HZDR, 04.11.2011, Helmholtz-Zentrum Dresden-Rossendorf, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-16530
Publ.-Id: 16530


High-Electron-Mobility InN Layers Grown by Boundary-Temperature-Controlled Epitaxy

Wang, X.; Liu, S.; Ma, N.; Feng, L.; Chen, G.; Xu, F.; Tang, N.; Huang, S.; Chen, K. J.; Zhou, S.; Shen, B.
A boundary-temperature-controlled epitaxy, where the growth temperature of InN is controlled at its maximum, is used to obtain high-electron-mobility InN layers on sapphire substrates by molecular beam epitaxy. The Hall-effect measurement shows a recorded electron mobility of 3280 cm^2 V^-1 s^-1 and a residual electron concentration of 1.47×10^17 cm^-3 at room temperature. The enhanced electron mobility and reduced residual electron concentration are mainly due to the reduction of threading dislocation density. The obtained Hall mobilities are in good agreement with the theoretical modelling by the ensemble Monte Carlo simulation.
  • Applied Physics Express 5(2012), 015502
    DOI: 10.1143/APEX.5.015502
  • Communication & Media Relations
    News release at Semiconductor Today 30.01.2012

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Permalink: https://www.hzdr.de/publications/Publ-16529
Publ.-Id: 16529


Actinide(IV)-silica colloids and their potential geochemical implications

Zänker, H.; Weiss, S.; Hennig, C.; Dreissig, I.
Due to their low solubility, tetravalent actinides, An(IV), are usually assumed to be immobile in natural waters. However, it is also well known that insoluble precipitation products can be mobile if they occur as colloids. For An(IV) oxyhydroxides this phenomenon has thoroughly been studied [1-3]. Here (see also [4]) we describe the formation of a new type of An(IV) colloids.
Evidence is provided by photon correlation spectroscopy (PCS), ultrafiltration and ultracentrifugation that uranium(IV) and Th(IV) can form silicate-containing colloids. The An(IV)-silica 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 An(IV) was observed which is a concentration significantly 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. The size of the < 20 nm particles depends on silicate concentration and pH. The higher the silicate concentration and the pH, the smaller (and obviously the more stable) are the particles that are formed (however, silicate at the concentrations tested does not form particles in the absence of the actinides).
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.
The mechanism of colloidal stabilization can be regarded as “sequestration” by silicate, a phenomenon well known from trivalent heavy metal ions of high ion potential such as iron(III) [5, 6) or curium(III) [7], but never reported for tetravalent actinides so far. Extended X-ray absorption fine structure (EXAFS) spectroscopy on the U(IV)-silica nanoparticles 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. The next-neighbor coordination of U(IV) in the U(IV)-silica colloids is comparable with that of coffinite, USiO4.
The assessment of actinide behavior in the aquatic environment should take the possible existence of An(IV)-silica colloids into consideration. Their occurrence might influence actinide migration in anoxic waters.
[1] Neck, V. et al., Radiochim. Acta 90, 485 (2002).
[2] Bitea, C. et al., Colloids Surf., A 217, 63 (2003).
[3] Altmaier, M. et al., Radiochim. Acta 92, 537 (2004).
[4] Dreissig, I. et al., Geochim. Cosmochim. Acta 75, 352 (2011).
[5] Browman, M. G. et al., Environ. Sci. Technol. 23, 566 (1989).
[6] Robinson, R. B. et al., J. Am. Water Works Assn. 84, 77 (1992).
[7] Panak, P. J. et al., Radiochim. Acta 93, 133 (2005).
Keywords: Colloids, nanoparticles, uranium, thorium, silica, anoxic groundwater
  • Lecture (Conference)
    E-MRS 2012 SPRING MEETING, 15.-17.05.2012, Strasbourg, France

Permalink: https://www.hzdr.de/publications/Publ-16528
Publ.-Id: 16528


Pyrrolovesamicols - Synthesis, structure and VAChT binding of two 4-fluorobenzoyl regioisomers

Wenzel, B.; Li, Y.; Kraus, W.; Sorger, D.; Sabri, O.; Brust, P.; Steinbach, J.
This letter describes the synthesis of two regioisomers of a new class of vesamicol analogs as possible ligands for imaging the vesicular acetylcholine transporter in future PET studies. The reaction mechanism of the synthesis of these two pyrrolovesamicols was studied by HPLC and the molecular structures were determined by X-Ray structure analysis. Binding affinities to VAChT were evaluated by competitive binding analysis using a cell line stably transfected with ratVAChT.
Keywords: Pyrrolovesamicol Vesamicol VAChT Pyrrole

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Permalink: https://www.hzdr.de/publications/Publ-16527
Publ.-Id: 16527


Scalable Microstructured Photoconductive Terahertz Emitters

Winnerl, S.
The development of scalable emitters for pulsed broadband terahertz (THz) radiation is reviewed. Their large active area in the 1 – 100 mm^2 range allows for using the full power of state-of-the-art femtosecond lasers for excitation of charge carriers. Large fields for acceleration of the photogenerated carriers are achieved at moderate voltages by interdigitated electrodes. This results in efficient emission of single-cycle THz waves. THz field amplitudes in the range of 300 V/cm and 17 kV/cm are reached for excitation with 10 nJ pulses from Ti:sapphire oscillators and for excitation with 5 μJ pulses from amplified lasers, respectively. The corresponding efficiencies for conversion of near-infrared to THz radiation are 2.5 × 10^-4 (oscillator excitation) and 2 × 10^-3 (amplifier excitation). In this article the principle of operation of scalable emitters is explained and different technical realizations are described. We demonstrate that the scalable concept provides freedom for designing optimized antenna patterns for different polarization modes. In particular emitters for linearly, radially and azimuthally polarized radiation are discussed. The success story of photoconductive THz emitters is closely linked to the development of mode-locked Ti:sapphire lasers. GaAs is an ideal photoconductive material for THz emitters excited with Ti:sapphire lasers, which are widely used in research laboratories. For many applications, especially in industrial environments, however, fiber-based lasers are strongly preferred due to their lower cost, compactness and extremely stable operation. Designing photoconductive emitters on InGaAs materials, which have a low enough energy gap for excitation with fiber lasers, is challenging due to the electrical properties of the materials. We discuss why the challenges are even larger for microstructured THz emitters as compared to conventional photoconductive antennas and present first results of emitters suitable for excitation with ytterbium-based fiber lasers. Furthermore an alternative concept, namely the lateral photo-Dember emitter, is presented. Due to the strong THz output scalable emitters are well suited for THz systems with fast data acquisition. Here the application of scalable emitters in THz spectrometers without mechanical delay stages, providing THz spectra with 1 GHz spectral resolution and a signal-to-noise ratio of 37 dB within 1 s, is presented. Finally a few highlight experiments with radiation from scalable THz emitters are reviewed. This includes a brief discussion of near-field microscopy experiments as well as an overview over gain studies of quantum-cascade lasers.
Keywords: Terahertz, scalable emitter

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Publ.-Id: 16526


Elastische Rückstoßatomspektrometrie leichter Elemente mit Subnanometer-Tiefenauflösung

Kosmata, M.
In der vorliegenden Arbeit wird erstmals das QQDS-Magnetspektrometer für die höchstauflösende Ionenstrahlanalytik leichter Elemente am Helmholtz-Zentrum Dresden-Rossendorf umfassend vorgestellt. Zusätzlich werden sowohl alle auf die Analytik Einfluss nehmenden Parameter untersucht als auch Methoden und Modelle vorgestellt, wie deren Einfluss vermieden oder rechnerisch kompensiert werden kann.
Die Schwerpunkte dieser Arbeit gliedern sich in fünf Bereiche.
Der Erste ist der Aufbau und die Inbetriebnahme des QQDS-Magnetspektrometers, der zugehörige Streukammer mit allen Peripheriegeräten und des eigens für die höchstauflösende elastische Rückstoßanalyse entwickelten Detektors. Sowohl das umgebaute Spektrometer als auch der im Rahmen dieser Arbeit gebaute Detektor wurden speziell an experimentelle Bedingungen für die höchstauflösende Ionenstrahlanalytik leichter Elemente angepasst und erstmalig auf einen routinemäßigen Einsatz hin getestet. Der Detektor besteht aus zwei Komponenten. Zum einen befindet sich am hinteren Ende des Detektors eine Bragg-Ionisationskammer, die zur Teilchenidentifikation genutzt wird. Zum anderen dient ein Proportionalzähler, der eine Hochwiderstandsanode besitzt und direkt hinter dem Eintrittsfenster montiert ist, zur Teilchenpositionsbestimmung im Detektor.
Die folgenden zwei Schwerpunkte beinhalten grundlegende Untersuchungen zur Ionen-Festkörper-Wechselwirkung. Durch die Verwendung eines Magnetspektrometers ist die Messung der Ladungszustandsverteilung der herausgestreuten Teilchen direkt nach einem binären Stoß sowohl möglich als auch für die Analyse notwendig. Aus diesem Grund werden zum einen die Ladungszustände gemessen und zum anderen mit existierenden Modellen verglichen. Außerdem wird ein eigens entwickeltes Modell vorgestellt und erstmals im Rahmen dieser Arbeit angewendet, welches den ladungszustandsabhängigen Energieverlust bei der Tiefenprofilierung berücksichtigt. Es wird gezeigt, dass ohne die Anwendung dieses Modells die Tiefenprofile nicht mit den quantitativen Messungen mittels konventioneller Ionenstrahlanalytikmethoden und mit der Dickenmessung mittels Transmissionselektronenmikroskopie übereinstimmen, und damit falsche Werte liefern würden. Der zweite für die Thematik wesentliche Aspekt der Ionen-Festkörper-Wechselwirkung, sind die Probenschäden und -modifikationen, die während einer Schwerionenbestrahlung auftreten. Dabei wird gezeigt, dass bei den hier verwendeten Energien sowohl elektronisches Sputtern als auch elektronisch verursachtes Grenzflächendurchmischen eintreten. Das elektronische Sputtern kann durch geeignete Strahlparameter für die meisten Proben ausreichend minimiert werden. Dagegen ist der Einfluss der Grenzflächendurchmischung meist signifikant, so dass dieser analysiert und in der Auswertung berücksichtigt werden muss. Schlussfolgernd aus diesen Untersuchungen ergibt sich für die höchstauflösende Ionenstrahlanalytik leichter Elemente am Rossendorfer 5-MV Tandembeschleuniger, dass die geeignetsten Primärionen Chlor mit einer Energie von 20 MeV sind. In Einzelfällen, wie zum Beispiel der Analyse von Bor, muss die Energie jedoch auf 6,5 MeV reduziert werden, um das elektronische Sputtern bei der notwendigen Fluenz unterhalb der Nachweisgrenze zu halten.
Der vierte Schwerpunkt ist die Untersuchung von sowohl qualitativen als auch quantitativen Einflüssen bestimmter Probeneigenschaften, wie beispielsweise Oberflächenrauheit, auf die Form des gemessenen Energiespektrums beziehungsweise auf das analysierte Tiefenprofil. Die Kenntnis der Rauheit einer Probe an der Oberfläche und an den Grenzflächen ist für die Analytik unabdingbar. Als Resultat der genannten Betrachtungen werden die Einflüsse von Probeneigenschaften und Ionen-Festkörper-Wechselwirkungen auf die Energie- beziehungsweise Tiefenauflösung des Gesamtsystems beschrieben, berechnet und mit der konventionellen Ionenstrahlanalytik verglichen. Die Möglichkeiten der höchstauflösenden Ionenstrahlanalytik werden zudem mit den von anderen Gruppen veröffentlichten Komplementärmethoden gegenübergestellt.
Der fünfte und letzte Schwerpunkt ist die Analytik leichter Elemente in ultradünnen Schichten unter Berücksichtigung aller in dieser Arbeit vorgestellten Modelle, wie die Reduzierung des Einflusses von Strahlschäden oder die Quantifizierung der Elemente im dynamischen Ladungszustandsnichtgleichgewicht. Es wird die Tiefenprofilierung von Mehrschichtsystemen, bestehend aus SiO2-Si3N4Ox-SiO2 auf Silizium, von Ultra-Shallow-Junction Bor-Implantationsprofilen und von ultradünnen Oxidschichten, wie zum Beispiel High-k-Materialien, demonstriert.
Keywords: ERD, IBA, mass spectrometry, high resolution, charge state
  • Open Access Logo Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; HZDR-016 2012
    ISSN: 2191-8708

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Permalink: https://www.hzdr.de/publications/Publ-16525
Publ.-Id: 16525


High precision X-ray polarimetry

Marx, B.; Schulze, K. S.; Uschmann, I.; Kämpfer, T.; Lötzsch, R.; Wehrhan, O.; Wagner, W.; Detlefs, C.; Roth, T.; Härtwig, J.; Förster, E.; Stöhlker, T.; Paulus, G. G.
The polarization purity of 6.457- and 12.914-keV X- rays has been improved to the level of 2.4E-10 and 5.7E-10. The polarizers are channel-cut silicon crystals using six 90° reflections. Their performance and possible applications are demonstrated in the measurement of the optical activity of a sucrose solution.
Keywords: X-ray polarimetry, diffraction, channel-cut silicon crystal

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Publ.-Id: 16524


Channeling radiation at impact of resonant acoustic waves

Azadegan, B.; Grigoryan, L. S.; Wagner, W.
A consistent classical approach is presented which permits to reveal the influence of acoustic lattice vibrations on important features of planar positron channeling radiation. It is shown that a resonance effect occurs if the wave number of the acoustic field approaches dedicated values corresponding to the wave number of the oscillatory motion of the channeled particle. Modulation of its trajectory and velocity causes an enhancement of the radiation intensity.
Keywords: channeling radiation, positron channeling, acoustic superlattice
  • Invited lecture (Conferences)
    International Conference on Electron, Positron, Neutron and X-ray Scattering under External Influences, 16.-22.10.2011, Yerevan-Meghri, Armenia
  • Contribution to proceedings
    International Conference on Electron, Positron, Neutron and X-ray Scattering under External Influences, 16.-22.10.2011, Yerevan-Meghri, Armenia
    Proceedings of the International Conference on Electron, Positron, Neutron and X-ray Scattering under External Influences, Yerevan: IAPP Print, 978-99941-2-710-8, 44-51

Permalink: https://www.hzdr.de/publications/Publ-16523
Publ.-Id: 16523


Relaxation dynamics in graphene close to the Dirac point

Winnerl, S.; Schneider, H.; Helm, M.; Orlita, M.; Plochocka, P.; Kossacki, P.; Potemski, M.; Winzer, T.; Malic, E.; Knorr, A.; Sprinkle, M.; Berger, C.; de Heer, W. A.
The carrier dynamics in epitaxially grown graphene is studied in pump-probe experiments with photon energies in the range from 10 – 250 meV. A strong increase of the relaxation time is observed as the photon energy is decreased to values below the optical phonon energy. The underlying processes dominating the relaxation are identified by a comparison of the experimental results with microscopic calculations. Variation of the photon energy between 20 meV and 30 meV results in a change from induced transmission for larger photon energies to induced absorption for lower photon energies. An interplay of interband and intraband processes is responsible for this behavior.
  • Invited lecture (Conferences)
    International Symposium on THz nanoscience (TeraNano 2011), 24.-25.11.2011, Osaka, Japan

Permalink: https://www.hzdr.de/publications/Publ-16522
Publ.-Id: 16522


Planar positron channeling radiation on an acoustic superlattice

Azadegan, B.; Grigoryan, L. S.; Wagner, W.
Planar positron channeling in an acoustic superlattice and the stimulation of the emission of channeling radiation at resonance of the particle motion with the acoustic field excited in a PbTiO3 single crystal is considered in the framework of classical mechanics and electrodynamics. Based on computed particle trajectories, spectral-angular distributions of channeling radiation influenced by resonant ultrasound have been simulated. The presented method explains the influence of ultrasonic waves on the intensity of channeling radiation in a rather simple and descriptive manner.
Keywords: channeling radiation, superlattice, hypersound
  • Lecture (Conference)
    Radiation from Relativistic Electrons in Periodic Structures (RREPS-11), 12.-16.09.2011, Egham, United Kingdom
  • Open Access Logo Journal of Physics: Conference Series 357(2012), 012025
    DOI: 10.1088/1742-6596/357/1/012025

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Publ.-Id: 16521


Planar channeling radiation by relativistic electrons in different structures of silicon carbide

Azadegan, B.; Dabagov, S. B.; Wagner, W.
Spectral distributions of channelling radiation by relativistic electrons in different planes of different types of polytype silicon carbide crystals such as hexagonal, zincblende, and rombohedral are presented. For every structure we have found the planes from which channeling radiation of relativistic electrons is possible. Using Doyle-Turner approximation to the atomic scattering factor and taking in to account thermal vibrations of atoms, the continuum potentials for different planes of different structure of polytype SiC single crystal were calculated. In the frame of quantum mechanic, the theory of channeling radiation has been applied to calculate the transverse electron states in the continuum potential of the planes and to study transition energies, linewidths, depth dependence for population of quantum states and spectral radiation distributions. At electron energies higher than 100 MeV the spectral distributions of radiation are calculated by classical calculations. The trajectories, velocities and accelerations of electrons are obtained and in the frame of classical electrodynamics. The spectral-angular distribution of radiation has been calculated using real trajectories, velocities and acceleration of electrons. Specific properties of planar channeling radiation in different structures of SiC are discussed.
Keywords: channeling radiation, relativistic electrons, X-rays

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Publ.-Id: 16520


Novel unipolar nanodiodes for room-temperature THz detection

Balocco, C.; Kasjoo, S. R.; Lu, X. F.; Zhang, L. Q.; Alimi, Y.; Winnerl, S.; Song, A. M.
We report on the room-temperature electrical rectification at 1.5 THz with novel non-linear asymmetric nanochannels. The planar layout facilitates the integration of microfabricated THz antennas without introducing parasitic elements, and enables ultra-high operation frequencies. This is the highest speed reported for nanorectifiers to date.
Keywords: Nanodetector, terahertz
  • Lecture (Conference)
    36th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz 2011), 02.-07.10.2011, Houston, USA
  • Contribution to proceedings
    36th International Conference on Infrared, Millimeter and Terahertz Waves (IRMMW-THz 2011), 02.-07.10.2011, Houston, USA
    Proceedings of the 36th International Conference on Infrared, Millimeter and Terahertz Waves (IRMMW-THz 2011)

Permalink: https://www.hzdr.de/publications/Publ-16519
Publ.-Id: 16519


Self-amplified Cherenkov radiation from a relativistic electron in a waveguide partially filled with a laminated material

Grigoryan, L. S.; Mkrtchyan, A. R.; Khachatryan, H. F.; Arzumanyan, S. R.; Wagner, W.
The radiation from a relativistic electron uniformly moving along the axis of cylindrical waveguide filled with laminated material of finite length is investigated. Expressions for the spectral distribution of radiation passing throw the transverse section of waveguide at large distances from the laminated material are derived with no limitations on the amplitude and variation profile of the layered medium permittivity and permeability.
Numerical results for layered material consisting of dielectric plates alternated with vacuum gaps are given. It is shown that at a special choice of problem parameters, Cherenkov radiation generated by the relativistic electron inside the plates is self-amplified. The visual explanation
of this effect is given and a possible application is discussed.
Keywords: Cherenkov radiation, relativistic particle, waveguide, periodic medium

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Publ.-Id: 16518


Adsorption kinetics of cell wall components of gram positive bacteria on technical surfaces studied by QCM-D

Suhr, M.; Günther, T.; Raff, J.; Pollmann, K.
In general, the cell wall components of gram-positive bacteria e.g. single lipid bilayer, peptidoglycan, Surface-layer proteins (S-layer) and other biopolymers are well studied. These cell wall components are interesting for several bio-induced technical applications such as biosorptive materials. Although biosorption processes have been intensively investigated, the investigation of metal interaction with biomolecules as well as adsorption processes on substrates on molecular level remains challenging.
In our work we used the quartz crystal microbalance with dissipation monitoring (QCM-D) in order to study the layer formation of cell wall compounds and interaction processes on the nano scale range.
This analytical method allows the detailed detection of array formation of bacterial S-layer proteins and gives a better understanding of the self-assembling processes. S-layer proteins as a part of the outer cell envelope of many eubacteria and archaea form paracrystalline protein lattices in strain depended geometrical structures [1]. Once isolated the proteins exhibit the ability to form these lattices on different kinds of interfaces and possesses equal to the bacteria cells high metal binding capacities. These properties open a wide spectrum of applications e.g. ultrafiltration membranes for organic and inorganic ions and molecules, templates for the synthesis of catalytic nanoparticles and other bio-engineered materials [2, 3].
By performing different experiments with and without modification of technical surfaces with adhesive promoters e.g. polyelectrolytes it is possible to make exact statements regarding coating kinetics, layer stability and interaction with metals. Subsequent atomic force microscopy (AFM) studies enable the imaging of bio nanostructures and reveal complex information of structural properties. Aim of these investigations is the assembly of a simplified biological multilayer based on cell compounds of gram positive bacteria in order to clarify sorption processes in a complex system. The understanding of coating, biological and biological-metal interaction processes is interesting for different technical applications.

1. U.B. Sleytr et al., Prog. Surf. Sci. 68 (2001), 231-278.
2. K. Pollmann et al., Biotechnology Advances 24 (2006), 58– 68.
3. J. Raff et al., Chem. Mater. 15 (2003), 240-244.
Keywords: QCM-D, S-Layer, bacteria, multi layer, AFM
  • Poster
    Annual Conference of the Association for General and Applied Microbiology (VAAM), 18.-21.03.2012, Tübingen, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-16517
Publ.-Id: 16517


ASL perfusion quantification: a comparison with PET and Optical Imaging techniques using double labeled microspheres

Bos, A.; Bergmann, R.; Hofheinz, F.; van den Hoff, J.
Purpose/Introduction: Regional tissue perfusion is a fundamental physiological parameter controlling delivery of oxygen and nutrients to tissue which provides valuable information for cancer research and radiation therapy planning. There do exist established methods in nuclear medicine for perfusion assessment and quantification (e.g. O-15 PET), however, the truly quantitative procedures in general require arterial blood sampling making them ill-suited for routine clinical application.. In contrast, the Arterial Spin Labeling (ASL) MRI technique is absolutely non- invasive, but its quantitative accuracy in small animals is not well investigated. The purpose of this work was to assess accuracy of ASL perfusion measurements in rat brain by a comparison with microspheres derived regional perfusion information using dedicated small animal Positron Emission Tomography (PET) and ex vivo Optical imaging (OI).

Subjects and Methods: 20 µm microspheres were double-labeled with either Cu-64 or Ga-68 for PET and X-sight 670 LSS for OI. They were administered through a catheter to the left ventricle of the heart and a reference blood sample was extracted from the left femoral artery. ASL measurements were performed in a 7T animal system (Bruker Biospin 70/30), using a Flow-sensitive Alternating Inversion Recovery (FAIR) sequence with an adiabatic hyperbolic secant inversion pulse (sech120) and Echo Planar Imaging (EPI) acquisition. Global and selective T1 maps of two measured slices (Hemisphere in caudate putamen region and Cerebellum), PET data and correspondingly cut brain sections were used for calculation of the perfusion. All relevant physiological parameters were monitored. Perfusion of the whole brain (PET, OI) and two dedicated slices (PET, OI, MRI) were analyzed. The results of the different methods were compared.

Results: The perfusion dependency of PET vs. OI was fitted with a linear model resulting in a slope of 0.96 and a Pearson correlation factor (PCF) of 0.97. Since water cannot be considered freely diffusible at elevated perfusion levels, Renkin-Crone formula (y = 1- exp(- PS / x) was used for the fitting of MRI vs. PET data. For the model being used, the sensible value for the surface area product (PS) of 182mL/g/min for water in brain tissue was yielded. .

Discussion/Conclusion: The results of this study show that it is possible to obtain quantitative perfusion values with ASL in the brain of the rat using the EPI-FAIR technique .
Keywords: ASL, PET, IO, perfusion, microspheres
  • Lecture (Conference)
    European Society for Magnetic Resonance in Medicine and Biology 2011, 06.-8.10.2011, Leipzig, Germany

Permalink: https://www.hzdr.de/publications/Publ-16516
Publ.-Id: 16516


Quantitative Perfusion Measurements: A Comparison of MRI Using Arterial Spin Labeling (ASL) with Radioactive and Fluorescence Microspheres

Bos, A.; Bergmann, R.; van den Hoff, J.
Aim: Arterial Spin Labeling (ASL) is a Magnetic Resonance Imaging (MRI) technique for perfusion evaluation, which is based on spin inversion in the arterial blood and observation of relaxation effects. However, quantitative accuracy of ASL measurements in small animals is not well investigated. The purpose of this work was to assess accuracy of quantitative ASL perfusion measurements in rat brain by comparison with microspheres derived regional perfusion information using dedicated micro Positron Emission Tomography (PET) and ex vivo Optical imaging (OI).
Methods: Catheters were implanted through the right carotid artery in the left ventricle of the heart for administration of labeled microspheres (diameter 20 µm) and in the left femoral artery for blood sampling. Microspheres were double-labeled with either Cu-64 or Ga-68 for PET and X-sight 670 LSS for OI. ASL measurements were performed in a 7T small animal system using a Flow-sensitive Alternating Inversion Recovery (FAIR) sequence with an adiabatic hyperbolic secant inversion pulse (length-bandwidth product: 80) and Echo Planar Imaging (EPI) acquisition. Global and selective T1 images, correspondingly cut brain sections, and PET data were used for perfusion values calculation. All the crucial physiological parameters were monitored. Perfusion of the whole brain (PET, OI) and two dedicated slices (PET, OI, MRI) were estimated independently with specified methods. The consistency of OI compared to PET for whole brain was used as criterion for inclusion of the respective animal into further data evaluation.
Results: A mean perfusion of the whole brain was 88.8 mL/100g/min. In slices measured with ASL (cerebellum with pons and hemispheres in caudate putamen region) perfusion was calculated with each technique separately. Results from MRI and PET were considered for Cu-64, Ga-68 and for whole data set. The estimated correlation factor for MRI vs. PET is 0.91 and Renkin-Crone model fitting yields a plausible Permeability Surface product (PS) for water (182 mL/g/min). The same data was fitted also with linear regression forced to zero-point (y=0.76x). The left-right disparity in Cortex, Thalamus and Cerebellum was observed because of catheter implantation, namely for 73% of animals perfusion in the left part of the brain was higher.
Conclusions: The quantitative perfusion measurements in the rat brain using ASL are possible but require thorough data analysis. Overall regional contrast provided by ASL is concordant with regional distribution of microspheres in the rat brain. However, deviations from linear correlation are visible and are the subject of further investigations. In order to be useful for routine application in small animal imaging, ASL data acquisition and data evaluation needs to be further optimized. A final calibration via a quantitative comparison with radio- and fluorescent-labeled microspheres seems mandatory.
Keywords: Perfusion, ASL, PET, OI, microspheres
  • Poster
    World Molecular Imaging Congress 2011, 02.-10.09.2011, San Diego, USA
  • Contribution to proceedings
    World Molecular Imaging Congress 2011, 02.-10.09.2011, San Diego, USA
    Proceedings of the World Molecular Imaging Congress 2011, S721

Permalink: https://www.hzdr.de/publications/Publ-16515
Publ.-Id: 16515


Physical characterization of PECVD and PEALD Ru(-C) films and comparison with PVD Ruthenium film properties

Wojcik, H.; Junige, M.; Bartha, W.; Albert, M.; Neumann, V.; Merkel, U.; Peeva, A.; Gluch, J.; Menzel, S.; Munnik, F.; Liske, R.; Utess, D.; Richter, I.; Klein, C.; Engelmann, H. J.; Ho, P.; Hossbach, C.; Wenzel, C.
PECVD and PEALD of ruthenium films using RuEtcp2 as a precursor andN2/H2/Ar plasma as a reducing agent were characterized. A self-adjusting process to overcome the previously reported inhibition of Ru PEALD on TaN substrates was investigated. Ellipsometric modelling of Ru films was demonstrated providing information on both film thickness and estimated Ru content. The physical properties of PECVD/PEALD Ru films were compared to characteristics of sputtered Ru films within the categories resistivity, impurites, crystal structure, conformity and Cu plating. As a result, ToFSIMS, ERDA and 3D atomprobe revealed the presence of carbon impurities in PECVD and PEALD Ru films, dependent on deposition temperature and plasma power. Nevertheless, highly conductive Ru-C films were produced via PECVD and PEALD achieving resistivities equal to PVD Ru. For all types of Ru films, the size effect played a significant role at thicknesses below 10 nm; Cu plating and crystallization behaviour appeared similar. Direct Cu fill potential of different Ru films was discussed for damascene structures and through silicon vias.

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Permalink: https://www.hzdr.de/publications/Publ-16514
Publ.-Id: 16514


Recombinant production of genetically modified S-layer proteins in different expression systems

Lederer, F.; Kutschke, S.; Pollmann, K.
Surface layer (S-layer) are proteins which cover the outermost of many prokaryotes and are probably the basic and oldest forms of bacterial envelope. These proteins are mostly composed of protein and glycoprotein monomers and have the ability to self-assemble into two-dimensional arrays on interfaces. Several characteristics like their work as molecular sieve, as virulence factor or the protection of the cell from toxic heavy metal ions make S-layer proteins interesting for their usage as ultrafiltration membranes, drug microcontainers, filter materials or patterning structures in nanotechnology.
Heterologous expression of S-layer proteins is not simple and depends on the used vector and the expression system. Equally the S-layer protein size, genetic specifics, and the existence of adapted signal peptides influence the expression. To enable an efficient and economical protein production protein secretion is the most favoured method.
In this work we describe the recombinant production of different S-layer variants and characterize the differences of the used protein expression systems.
We used four different S-layer genes of Lysinibacillus sphaericus JG-A12, Bacillus spec. JG-B12 and Lactobacillus acidophilus and expressed their proteins in Escherichia coli, Pichia pastoris and Lactococcus lactis. Some of these proteins were genetically modified to adapt the construct to the used S-layer expression system.
Our work identified Lactococcus lactis as the best expression system for the used S-layer genes.
  • Poster
    Annual Conference of the Association for General and Applied Microbiology (VAAM), 18.-21.03.2012, Tübingen, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-16513
Publ.-Id: 16513


On the feasibility of automatic detection of range deviations from in-beam PET data

Helmbrecht, S.; Santiago, A.; Enghardt, W.; Kuess, P.; Fiedler, F.
In-beam PET is a clinically proven method for monitoring ion beam cancer treatment. The objective is predominantly the verication of the range of the primary particles. Due to dierent processes leading to dose and activity, evaluation is done by comparing measured data to simulated. Up to now, the comparison is performed by well trained observers (clinicians, physicists). This process is very time consuming and low in reproducibility. However, an automatic method is desirable. A one dimensional algorithm for range comparison has been enhanced and extended to three dimensions. System inherent uncertainties are handled by means of a statistical approach. To test the method a set of data was prepared. Distributions of +-activity calculated from treatment plans were compared to measurements performed in the framework of the German Heavy Ion Tumor Therapy Project at GSI Helmholtz Centre for Heavy Ion Research Darmstadt, Germany. Articial range deviations in the simulations served as test objects for the algorithm. Range modications of dierent depth (4 mm, 6mm and 10mm water equivalent path length) can be detected. Even though sensitivity and specicity of a visual evaluation is higher, the method is feasible as basis for the selection of patients from the data pool for retrospective evaluation of treatment and treatment plans and correlation with follow up data. Furthermore, it can be used for the development of an assistance tool for a clinical application.
Keywords: in-beam PET, dose monitoring in ion therapy, in-vivo dosimetry, ion therapy

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Permalink: https://www.hzdr.de/publications/Publ-16512
Publ.-Id: 16512


Development Strategies for Creating a Suite of Reference Materials for the In-situ Microanalysis of Non-conventional Raw Materials

Renno, A. D.; Merchel, S.; Michalak, P. P.; Munnik, F.; Wiedenbeck, M.
The availability of reference materials (RM) for microanalytical methods is decreasing. According to currently exist no materials for which the chemical composition has been certified at the μm sampling scale. Many labs use in-house „standards“ as a temporary measure.
Recent economic trends regarding the supply of rare metals readily justify scientific research into non-conventional raw materials, where a particular need is a better understanding of the relationship between mineralogy, microstructure and the distribution of key metals within ore deposits (geometallurgy). Non-conventional raw materials include everything different from what most people consider to be usual or normal, the geometallurgy concept aims to close the gap between ore body exploration/ exploitation (mining) on the one hand, and mineral processing and metallurgy on the other hand. This interface is widely regarded as an interdisciplinary divide that holds significant potential to utilize non-renewable mineral resources more efficiently and sustainably. Achieving these goals will require an extensive usage of in-situ microanalytical techniques capable of spatially resolving material heterogeneities which can be key for understanding better resource utilization. The availability of certified reference materials (CRMs) is an essential prerequisite for
(1) validating new analytical methods,
(2) demonstrating data quality to the contracting authorities,
(3) supporting method development and instrument calibration, and
(4) establishing traceability between new analytical approaches and existing data sets.
This need has led to the granting of funding by the European Union and the German Free State of Saxony for a program to develop such reference materials .
This effort will apply the following strategies during the selection of the future CRMs:
(1) We will use exclusively synthetic minerals, thereby providing large volumes of homogeneous starting material, following the idea “one CRM for all methods”.
(2) We will focus on matrices which are capable of incorporating many ‘important’ elements while avoid exotic compositions which would not be optimal matrix matches.
(3) We will prefer those phases which remain stable during the various microanalytical procedures.
We decided to synthesize a Fe-S phase, a mineral of the feldspar group, and a phase of the columbite-tantalite solid solution series. As far as possible, both definitive methods as well as methods involving matrix corrections will be used for determining the compositions of the individual materials.
The following methods are considered in our planned studies thus far:
- Electron microprobe analysis (EPMA)
- Laser ablation - ICP-MS (LA-ICP-MS)
- Secondary Ion Mass Spectrometry (SIMS)
- Micro-XRF (μ-XRF)
- Synchrotron-based XRF (S-XRF)
- Particle-induced X-Ray Emission analysis (PIXE)
- Particle-induced γ-Ray-Emission (PIGE)
- Rutherford Backscattering Spectrometry (RBS)
- Elastic Recoil Detection Analysis (ERDA)
- Nuclear Reaction Analysis (NRA)
A critical challenge for the certification process will be the validation of the determination of analytes concentrations as sub-μg sampling masses.
This initiative will assess the homogeneity of the reference materials at sampling sizes ranging between 50 and 1 μm. It is intended to document crystal structural and crystal chemical homogeneity too, knowing that these features may potentially impact specific analytical methods, by affecting diffusion, ion conductivity, and subsurface charging. Both spectroscopic and diffractometric methods will be used, like Raman microspectroscopy, FT-IR microspectroscopy, cathodoluminescence spectroscopy, as well as Electron backscatter diffraction (EBSD).
It is planned to cooperate with those who are interested in the development of such reference materials and we invite them to take part in round-robin exercises.
Keywords: Reference Materials, Geochemistry
  • Invited lecture (Conferences)
    Microscopy and Microanalysis 2011, 07.-11.08.2011, Nashville, USA

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Permalink: https://www.hzdr.de/publications/Publ-16511
Publ.-Id: 16511


Structure and electrical properties of transparent conductive doped ZnO grown by reactive magnetron sputtering

Cornelius, S.; Vinnichenko, M.; Munnik, F.; Heller, R.; Kolitsch, A.; Möller, W.
No abstract available.
Keywords: Al-doped ZnO transparent conductive oxide zinc oxide magnetron sputtering doping activation
  • Invited lecture (Conferences)
    IOP Workshop "Plasmas, Surfaces and Thin Films", 08.06.2011, London, England

Permalink: https://www.hzdr.de/publications/Publ-16510
Publ.-Id: 16510


The Rossendorf beamline BM20 at the ESRF: overview and perspectives

Shalimov, A.; Baehtz, C.; Grenzer, J.; von Borany, J.
The Rossendorf beamline (ROBL) BM20 at the European Synchrotron Radiation Facility in Grenoble is operated by Helmholtz Zentrum Dresden Rossendorf since 1999. ROBL belongs to Collaborative Research Group (CRG) of beamlines and provides two third parts of beamtime for users from HZDR, while the one third of beamtime is offered to external users selected by ESRF advisory committee. Two experimental stations are placed at the beamline: one is dedicated to materials research, while the second station is designed for spectroscopic investigations of actinides and other radionuclide’s. Material Research Hutch (MRH) is equipped with high precision heavy duty 6-circle diffractometer used for structural characterization of thin layers, nanoparticles, interfaces and analysis of other structural properties of solid state materials. Experimental installations allow users to perform different types of complex experiments including in-situ deposition, annealing in vacuum or gas environment, spectroscopic measurements, following (electro) chemical reactions or morphology transformations using available fast detectors and supplementary devices. Radiochemistry Hutch (RCH) possesses highly specialized safety system making possible investigations of alpha-emitting radionuclides by x-ray absorption spectroscopy (XAS) methods. (More information at www.hzdr.de).
Extensive upgrade of beamline optics, which assets in gain of beam brilliance, homogeneity and accessible energy range is scheduled in 2011. According to our calculation, new monochromator combined with toroidal x-ray mirrors will increase beam intensity up to 3 orders of magnitude in respect to the present value. Energy tunable in the range from 6 up to 35 keV allows users to realize element sensitive spectroscopic measurements like XANES and EXAFS, as well as x-ray scattering investigations (XRD, XRR, GID or GISAX) in anomalous mode. MRH detector installations include novel 1D position sensitive and 2D image Dectris detectors, two modern energy dispersive detectors from KETEK and Bruker Axes, as well as traditional scintillator counters. Besides of that, experimental setup can be tailored with equipment loaned from ESRF instrument pool.
Summarizing the overview of Rossendorf beamline, we would admit broad spectrum of research feasible at ROBL stations: all possible diffraction measurements combined with spectroscopic analysis can be performed during in-situ experiments involving film deposition, different types of annealing, chemical reactions etc. Upcoming modernization of x-ray optics will significantly improve brilliance of the beam, giving outstanding possibilities for researchers in their most challenging experiments.
  • Poster
    IX Krajowe Sympozjum Użytkowników Promieniowania Synchrotronowego, KSUPS 2011, 26.-27.09.2011, Warsaw, Poland

Permalink: https://www.hzdr.de/publications/Publ-16509
Publ.-Id: 16509


Aktivierung des Al Donators in reaktiv Magnetron-gesputterten ZnO Schichten

Cornelius, S.; Vinnichenko, M.; Munnik, F.; Heller, R.; Kolitsch, A.; Möller, W.
Al dotiertes ZnO ist eines der am häufigsten untersuchten Ersatzmaterialien für Sn dotiertes In2O3 (ITO) für transparente leitfähige Elektroden. Jedoch wurde bisher nur in wenigen Publikationen versucht zu messen, welcher Anteil des eindotierten Al tatsächlich elektrisch aktiv ist. Basierend auf systematischer Variation von Substrattemperatur und Targetzusammensetzung wurden in dieser Arbeit die elektrischen Eigenschaften aus Hall-Messungen und die mittels Ionenstrahlanalytik bestimmte Zusammensetzung der AZO-Schichten zueinander in Beziehung gesetzt.
Es konnte gezeigt werden, dass für geringe Al Konzentrationen eine maximale effektive Al Aktivierung erreicht wird. Während ab einer gewissen kritischen Al Konzentration die Aktivierung schnell abfällt und die elektrische Leitfähigkeit der Schichten abnimmt.
Keywords: Al-doped ZnO transparent conductive oxide zinc oxide magnetron sputtering doping activation
  • Lecture (Conference)
    EFDS Workshop "Transparente leitfähige Oxide; Festkörperphysikalische Grundlagen, Materialien und Technologie", 16.05.2011, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-16508
Publ.-Id: 16508


Self – organized FePt nanoparticles in MgO synthesized by ion-implantation and high-temperature annealing

Shalimov, A.; Akhmadaliev, S.; Baehtz, C.; Potzger, K.
The formation of FePt nanoparticles (NPs) in MgO crystals after sequential ion implantation and high temperature annealing has been observed and analyzed by means of structural and magnetic characterization. Self-organized FePt NPs were synthesized by an implantation of Fe and Pt ions to the depth of ~90 nm under the MgO surface and post-implantation annealing at 800°C. Structural and magnetic properties of produced NPs have been investigated using x-ray diffraction (XRD), magetometry measurements, and theoretical calculations of ion distributions and magnetization behavior. FePt NPs represent preferential orientation to MgO matrix with a relation of FePt[001]||MgO[001] and FePt[110]||MgO[100]. Using the Preisach formalism of magnetization, the spontaneous moment of FePt was estimated to be in a range ~600 – 3500 mu_B depending on the ion fluences, and corresponds to the NP’s size of 3.5 – 20 nm obtained from XRD study. Several structural phases of FePt NPs, such as, FePt3, disordered fcc and ordered L10 phase were observed in different samples. The evident tendency of L10 ordering after high fluence ion implantation and high-temperature annealing is demonstrated. Optimized regimes of implantation and annealing processes are reported in addition to physical properties of FePt NPs.
  • Poster
    E-MRS 2011 Fall Meeting - Symposium A, 19.-23.09.2011, Warsaw, Poland

Permalink: https://www.hzdr.de/publications/Publ-16507
Publ.-Id: 16507


Incorporation of Al in ZnO by reactive pulsed magnetron sputtering: electrical properties and dopant activation

Cornelius, S.; Vinnichenko, M.; Munnik, F.; Heller, R.; Kolitsch, A.; Möller, W.
Al-doped ZnO (AZO) films which combine maximum carrier mobility (μe), moderate free electron densities (Ne) and high surface roughness are of special interest for application as transparent front electrode in thin film solar cells. They posses high transmission in the near infrared region, close to the bandgap energy of absorber materials like Si (Eg =1.11 eV), and enable a superior light trapping behaviour. A key to tailor AZO film properties is understanding the mechanisms and effects of the Al-dopant incorporation into the ZnO matrix. The present work focuses on investigation of the influence of Al concentration on the electrical properties of AZO and on establishing performance limits with respect to carrier mobility and resistivity (ρ). Polycrystalline and epitaxial AZO films are grown on fused silica and c-axis oriented sapphire substrates, respectively, by reactive pulsed magnetron sputtering using several sets of Zn/Al alloy targets with an Al concentration (cAl) between 0.7 and 8.7 at%. A systematic variation of process parameters such as substrate temperature (Ts) and oxygen partial pressure results in polycrystalline films with μe>45 cm2V-1s-1 and
<2.3x10-4 Ωcm at optimum conditions, whereas μe~55 cm2V-1s-1 could be obtained for epitaxial films. It is observed that cAl has a strong influence on the optimum value of Ts, the maximum μe and Ne values and also on film structure and surface roughness. The observed dependence of carrier mobility Ne in AZO is discussed in the framework of ionized impurity scattering and clustering as well as grain boundary limited transport which predicts a fundamental physical limit of μe.
Rutherford Backscattering (RBS) and elastic recoil detection analysis (ERDA) confirm a considerable Al enrichment in the films when Ts is increased above its optimum value which correlates with the deterioration of their electrical properties. Combining ion beam analysis and Hall-effect measurements allows to estimate the fraction of electrically active Al dopants, which is rarely reported in a quantitative and systematic manner. The influence of intrinsic defects and charge compensation complicate the interpretation of the results. Nevertheless the target Al concentration as well as the substrate temperature are shown to have an impact on the dopant activation.
Keywords: Al-doped ZnO transparent conductive oxide zinc oxide magnetron sputtering doping activation
  • Lecture (Conference)
    MRS Spring Meeting 2011 (Symposium S: Plasma-assisted Materials Processing and Synthesis), 25.-29.04.2011, San Francisco, USA

Permalink: https://www.hzdr.de/publications/Publ-16506
Publ.-Id: 16506


Determination of the electrically active Al fraction in Al doped ZnO grown by pulsed reactive magnetron sputtering

Cornelius, S.; Vinnichenko, M.; Munnik, F.; Heller, R.; Kolitsch, A.; Möller, W.
Al-doped ZnO (AZO) films which combine maximum carrier mobility (µe), moderate free electron densities (Ne) and high surface roughness are of special interest for application as transparent front electrode in thin film solar cells. They posses high transmission in the near infrared region, close to the bandgap energy of absorber materials like Si (Eg=1.11 eV), and enable a superior light trapping behaviour.
A key to tailor AZO film properties is understanding the mechanisms and effects of the Al-dopant incorporation into the ZnO matrix. It is well accepted that the mobilities in degenerately doped AZO are limited by ionized impurity scattering. A way to overcome this limitation would be to reduce the density of ionized impurities which either don’t donate electrons themselves or compensate the Al donor. This is equivalent to increasing the fraction of electrically active Al in the ZnO host material. Systematic and quantitative investigations on this topic are rarely reported in literature. Therefore this work focuses on quantification of the Al concentration by ion beam analysis methods in conjuction with Hall-effect measurements for AZO films grown by reactive pulsed magnetron sputtering. The influence of parameters like target composition and substrate temperature on the Al activation will be discussed.
Keywords: Al-doped ZnO transparent conductive oxide magnetron sputtering activation doping
  • Lecture (Conference)
    DPG Spring Meeting, 13.-18.03.2011, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-16505
Publ.-Id: 16505


Nonlinear terahertz spectroscopy of semiconductor quantum structures

Schneider, H.
There is no abstract.
Keywords: infrared/terahertz spectroscopy, nonlinear quadratic detection, semiconductor quantum wells, intersubband transsitions
  • Invited lecture (Conferences)
    2. IR-ON Symposium: InfraRed Optical Nanostructures, 10.03.2011, Wien, Österreich

Permalink: https://www.hzdr.de/publications/Publ-16504
Publ.-Id: 16504


Voigt effect measurements on PLD grown nickel oxide thin films

Scarlat, C.; Mok, K. M.; Zhou, S.; Lorenz, M.; Grundmann, M.; Helm, M.; Schubert, M.; Schmidt, H.
NiO has great potential applications in spin valves, magnetooptical sensors, optical fibers, solar thermal absorbers, or in non-volatile resistive random memories [1]. In our study NiO, NiMnO, and NiMnLiO thin films have been grown on double-side polished r-plane sapphire substrates by pulsed laser deposition. We measured the complex Voigt angle using the polarized light from a HeCd laser, a Glan Taylor polarizer, a Hinds PEM-100 and two LockIns [2]. The Voigt effect is a second-order magneto-optic effect [3]. The polarization state of light after transmission through a sample consisting of ca. 1 μm thick, weak ferromagnetic and diamagnetic NiO thin films on purely diamagnetic r-plane sapphire substrates has been modelled using the 4x4 matrix formalism [2] in dependence of an external magnetic field applied in-plane, i.e. in Voigt configuration. The modelling results revealed that for the bare diamagnetic substrate the Voigt angle depends parabolically on the external magnetic field and that the weak ferromagnetic and diamagnetic NiO thin films changed the parabolic dependence of the Voigt angle in the range of ±0.3 T to a flat-top shape in agreement with the experimentally determined Voigt angle. Furthermore, due to the NiO thin films the Voigt angle increased ca. (1±i)10-5 deg for an external in-plane field of ±0.3 T.
[1] U. Russo, D. Ielmini, A.L. Lacaita, A. Pirovano, F. Pellizer and R. Bez, IEEE Electron Device Lett. 25 (2004) 507-509.
[2] C. Scarlat, K. M. Mok, S. Zhou, M. Vinnichenko, M. Lorenz, M. Grundmann, M. Helm, M. Schubert, H. Schmidt, Phys. Stat. Sol. (C) 7 (2010) 334-337.
[3] R. Carey and B.W.J. Thomas, J. Phys.: D: Appl. Phys. 7 (1974) 2362-2368.
  • Lecture (Conference)
    DPG Spring Meeting, 13.-18.03.2011, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-16503
Publ.-Id: 16503


Optical and magnetic properties of Cr-implanted indium oxides thin films

Scarlat, C.; Zhou, S.; Vinnichenko, M.; Kolitsch, A.; Helm, M.; Schmidt, H.
Dilute magnetic oxides using the electron spin rather than its charge as information carrier are expected to play a key role in the development of spinelectronics. As it has been shown recently, indium oxide (IO), a transparent conducting material, is of potential importance also as a material for spintronics. Polycrystalline and amorphous (ca. 300 nm thick) n-type conductive IO films were grown on SiO2/Si substrates using reactive magnetron sputtering. The films were implanted with Cr+ ions in order to reach Cr concentrations of 1, 2, 3, 4 and 5 at%. The implantation energy was 120 keV. Cr is chosen as a dopant because of its large magnetic moment in the ionic state, and the antiferomagnetic nature of Cr metal segregations. It is non-trivial to form any ferromagnetic secondary phase of Cr oxide. Highly oxygen deficient 2%Cr:IO co-evaporated films revealed ferromagnetism. Here we study the effect of the post-growth treatment on the structural, electrical, magnetic, and optical properties of Cr-implanted IO films. It is shown that only the 2%Cr:IO implanted film is weakly ferromagnetic at 5 K. A reasonable model for the Cr:IO implanted films has been developed to extract optical constants from spectroscopic ellipsometry data below 3 eV in dependence on the Cr concentration.
  • Poster
    DPG Spring Meeting, 13.-18.03.2011, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-16502
Publ.-Id: 16502


Infrared photodetectors based on quantum wells

Schneider, H.
There is no abstract.
Keywords: infrared/terahertz detector, semiconductor quantum well, GaAs/AlGaAs, thermal imaging
  • Invited lecture (Conferences)
    Workshop on Infrared Technology, 05.-09.12.2011, Rio de Janeiro, Brasil

Permalink: https://www.hzdr.de/publications/Publ-16501
Publ.-Id: 16501


Annealed, stress-free, and ferromagnetic Mn-doped indium tin oxide films

Scarlat, C.; Xu, Q.; Zhou, S.; Potzger, K.; Salvan, G.; Helm, M.; Schmidt, H.; Iacomi, F.
Indium tin oxide (ITO) is a transparent semiconductor and can be highly conductive at room temperature (RT) when doped, making ferromagnetic ITO films attractive candidates for magnetooptical and spintronic devices. Undoped and Mn doped indium tin oxide (ITO) thin films have been grown on SiO2/Si substrates by vacuum thermal evaporation (VTE) technique using targets with the atomic ratio In:Sn:Mn=114:12:13, 109:12:7, 122:12:4 and 122:12:0. In order to have practically stress-free samples [1] all the samples were annealed at 450 oC for 2 hours in air. Magnetotransport measurements revealed negative magnetoresistance and no anomalous Hall effect is observed. The ITO doped films exhibit RT ferromagnetism after annealing. The samples were investigated by magnetooptical Kerr effect (MOKE) spectroscopy measurements.

[1] L Kerkache et al, J. Phys. D: Appl. Phys. 39 184–189, (2006).
  • Poster
    subtherm 2011, 25.-27.10.2011, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-16500
Publ.-Id: 16500


Magnetic Mn-doped indium tin oxide films prepared by vacuum thermal evaporation

Scarlat, C.; Xu, Q.; Mok, K.; Shalimov, A.; Fronk, M.; Salvan, G.; Zahn, D. R. T.; Helm, M.; Schmidt, H.; Iacomi, F.
Indium tin oxide (ITO) can be made a highly conductive transparent coating contact in photovoltaics by doping. Undoped and Mn doped indium tin oxide (ITO) thin films were grown on SiO2/Si substrates by vacuum thermal evaporation (VTE) using sources with atomic ratios of In:Sn:Mn=114:12:13, 109:12:7, 122:12:4, and 122:12:0. In order to have practically stress-free ITO films [1], all the samples were annealed at 450 oC for 2 hours in air. Magnetotransport measurements reveal negative magnetoresistance while no anomalous Hall effect is observed. The Mn-doped ITO films exhibit room temperature ferromagnetism after annealing. We analyzed the magnetization data from SQUID measurements using simulations based on the Preisach approach and derived the magnetic parameters of nanoparticles in the Mn-doped ITO films, namely, the magnetization of individual particles and the distributions of coercive and interparticle interaction fields. The samples were also investigated by magneto-optical Kerr effect spectroscopy and Vector Magnetooptical Generalized Ellipsometry measurements to explore possible combined functionalities in photovoltaics and magnetooptics.

[1] L Kerkache et al., J. Phys. D: Appl. Phys. 39 184–189, (2006).
  • Poster
    Next Generation Solar Energy From Fundamentals to Applications, 12.-14.12.2011, Erlangen, Germany

Permalink: https://www.hzdr.de/publications/Publ-16499
Publ.-Id: 16499


ROssendorf BeamLine II - New experimental possibilities for in-situ diffraction experiments

Baehtz, C.; Shalimov, A.; Grenzer, J.; von Borany, J.
New experimental possibilities of the upgraded ROBL-beamline will be represented as well as results of the in-situ growth investigation of carbon nano tubes and graphene.
Keywords: Synchrotron radiation, in-situ diffracton, carbon nano tubes
  • Lecture (others)
    7. Wissenschaftliches Seminar des Dresdner Fraunhofer-Clusters Nanoanalytik, 27.01.2012, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-16498
Publ.-Id: 16498


Bildung von Nanolöchern auf KBr-Oberflächen durch Beschuss mit hochgeladenen Ionen

Wilhelm, R. A.
Hochgeladene Ionen tragen eine große Menge potentieller Energie (bis zu 100 keV), die als Summe der Bindungsenergien der fehlenden Elektronen definiert ist. Mit Hilfe dieser potentiellen Energie können auf Festkörperoberflächen Strukturen im Bereich von einigen Nanometern erzeugt werden, wobei durch geringe kinetische Energien der Ionen (weniger als 100 eV) Schaden im Festkörpervolumen vermieden werden kann. Die Produktion von Nanolöchern auf KBr(001)-Oberflächen durch den Beschuss mit einzelnen hochgeladenen Ionen wurde bereits untersucht. Diese Arbeit befasst sich aufbauend auf bekannten Ergebnissen mit des Einflusses hoher Fluenzen hoch- und niedriggeladener Ionen auf den Lochbildungsprozess. Diese Untersuchungen sind von Bedeutung um den Mechanismus der defektinduzierten Desorption als treibende Kraft für die Bildung von Nanolöchern zu identifizieren. Ergebnisse von Bestrahlungen von KBr(001)-Oberflächen mit hoch- und niedriggeladenen (4 ≤ q ≤ 54) Ionen bei hohen Fluenzen von (10^10..10^15) cm^−2 und verschiedenen Temperaturen werden in dieser Arbeit vorgestellt. Das zugrunde liegende Modell der defektinduzierten Desorption wird anhand der vorliegenden Ergebnisse diskutiert.

Highly charged ions carry a large amount of potential energy (up to 100 keV), which is defined as the sum of the binding energies of all missing electrons. This energy can be used to modify surfaces on the nano-scale, and due to very low kinetic energies (less than 100 eV), significant bulk damage can be avoided. The production of nanometer sized pit-like structures on KBr(001) surfaces by the impact of single highly charged ions was previously studied in detail. Therefore, investigations of high fluence effects of highly and lowly charged ions are important to clearly identify the mechanism of defect mediated desorption as the driving force for the creation of pit-like nanostructures on ionic crystals like KBr. Results of high fluence compared to low fluence irradiations in range of (10^10..10^15) cm^−2 with highly charged ions (4 ≤ q ≤ 54) and the influence of the temperature on the nanostructure production on KBr(001) surfaces are shown. Moreover, the defect mediated desorption model is discussed.
  • Thesis / Students' report
    TU Dresden, 2010
    58 Seiten

Permalink: https://www.hzdr.de/publications/Publ-16497
Publ.-Id: 16497


In-Situ Analysis of Nanostructures Induced by Slow Highly Charged Ions

Wilhelm, R. A.; Heller, R.; Facsko, S.
The sum of the binding energies of all missing electrons (potential energy) of highly charged ions can induce surface modifications on the nanometer scale. We present results of a set-up for slow highly charged ion irradiations and scanning probe microscopy studies under in-situ conditions. A Dresden-EBIT is used to provide ions of different species with charge states up to q=40 (e.g. for Xe). An electrostatic deceleration lens system allows to vary the kinetic energies of the ions in the range of 10eV· q up to 5keV· q. Furthermore, we studied surface nanostructures on various substrates by an Omicron ultra high vacuum (UHV) scanning probe microscope, which is directly connected to the ion source. The size and the shape of nanostructures created by the deposition of potential energy and analyzed in-situ under UHV conditions are discussed and compared to those observed by recent studies under ex-situ conditions.
  • Lecture (Conference)
    DPG Frühjahrstagung der Sektion Kondensierte Materie (SKM), 25.-30.03.2012, Berlin, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-16496
Publ.-Id: 16496


Surface Modification on KBr(001) with Slow Highly Charged Ions in High Fluence and High Potential Energy Regime

Wilhelm, R. A.; Heller, R.; Facsko, S.
Highly charged ions (HCI) have an unique property, their potential energy, which can induce modifications on surfaces on the nano-scale without a significant bulk damage. The potential energy, defined as the sum of the binding energies of all missing electrons, can exceed 100 keV, e.g. for Xe50+ or Au60+. This amount of energy is mainly released by the emission of electrons with energies of several 10 eV as described by the classical over the barrier model. The release of the HCI’s potential energy as emission of electrons right in front of the surface or in the first nanometers of the solid leads to a strong interaction with the electronic system of the solid. Especially in ionic crystals like KBr many electron-hole pairs are created near the impact site of the HCI. Due to a strong electronphonon coupling in ionic crystals these excitons become self-trapped and can either recombine or decay into so called colour centres. In KBr F and H-centres are created. H-centres are defined as an interstitial molecular halide atom and a F-center is an electron at an anion site. F-centres, which were produced near the surface, can recombine with surface ions (K+) and lead to their neutralisation and desorption. Also a Br-atom desorption occurs when the H-centre recombines with the surface.
Recently nano-pits on KBr surfaces induced by single ion impacts were investigated and a potential as well as a kinetic energy-threshold for their formation was found. The depths of the pits produced by a single ion impact was found to be one atomic monolayer for Xe charge states up to q = 40 and various kinetic energies. Low charge state (q>10) irradiations, in contrast, show pits as well, but only for much higher fluences (several 10^13 cm^-2). We present studies of high fluence irradiations with highly (q>10) and lowly (q<10) charged Xe ions. For high charge states a deepening of the pits (with increasing fluence) was found, while for low charge state irradiations a depletion region close to low coordinated sites like step edges has been observed. For irradiations with highest charges states, i.e. Au54+ ions and low fluences (<10^10 cm^-2) pit structures could be observed with double monolayer depths for single impacts. This indicates a second energy-threshold for the desorption of the second monolayer by a single ion impact. A qualitative model will be discussed to describe and identify the observed potential and kinetic energy effects.
  • Poster
    XXVII International Conference on Photonic, Electronic and Atomic Collisions, 27.07.-02.08.2011, Belfast, United Kingdom

Permalink: https://www.hzdr.de/publications/Publ-16495
Publ.-Id: 16495


Nanostructures induced by slow highly charged ions on KBr(001) surfaces

Wilhelm, R. A.; Heller, R.; Facsko, S.
Highly charged ions carry a large amount of potential energy (up to 100 keV) which is defined as the sum of all binding energies of all missing electrons. This energy can be used to modify surfaces on the nano-scale and due to very low kinetic energies (less than 100 eV) significant bulk damage can be avoided. The production of nanometer sized pit-like structures on KBr(001) surfaces by the impact of single highly charged ions was studied in detail previously. The investigation of high fluence effects of highly and lowly charged ions is important to clearly identify the mechanism of defect mediated desorption as the driving force for the creation of pit-like nanostructures on ionic crystals like KBr. Results of high fluence compared to low fluence irradiations will be shown and kinetic and potential energy effects will be discussed.
  • Lecture (Conference)
    DPG Frühjahrstagung der Sektion Kondensierte Materie (SKM), 17.03.2011, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-16494
Publ.-Id: 16494


Pit formation on poly(methyl methacrylate) due to ablation induced by individual slow highly charged ion impact

Ritter, R.; Wilhelm, R. A.; Ginzel, R.; Kowarik, G.; Heller, R.; El-Said, A. S.; Papaléo, R. M.; Rupp, W.; Crespo López-Urrutia, J. R.; Ullrich, J.; Facsko, S.; Aumayr, F.
We report the formation of nano-sized pits on poly(methyl methacrylate) after exposure to slow highly charged ion beams. The pits are formed on the polymer surface as a direct result of individual ion impacts. Intermittent contact mode atomic-force microscopy was employed to study the size evolution of the pits in dependence of potential and kinetic energies of the incident ions. A potential energy threshold value of approximately 7 keV was found for pit formation. Above this value an increase in potential energy results in an increasing pit volume, while the pit shape can be tuned by varying the kinetic energy.

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Permalink: https://www.hzdr.de/publications/Publ-16493
Publ.-Id: 16493


Ferromagnetic Ge:Mn prepared by ion implantation and pulsed laser annealing

Zhou, S.; Bürger, D.; Li, L.; Skorupa, W.; Helm, M.; Oesterlin, P.; Schmidt, H.
We report the fabrication of Ge:Mn ferromagnetic semiconductors by Mn-ion implantation into Ge followed by
pulsed laser annealing. The implanted Ge layer was recrystallized during annealing. We observed that the longitudinal and
Hall resistances exhibit the same hysteresis as the magnetization, which is usually considered as a sign of carrier-mediated
ferromagnetism.
Keywords: Magnetic semiconductors, Spin polarized transport in semiconductors, Elemental semiconductors, Magnetotransport phenomena; materials for magnetotransport

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Permalink: https://www.hzdr.de/publications/Publ-16492
Publ.-Id: 16492


Microbial synthesis of core/shell gold/palladium nanoparticles for applications in green chemistry

Deplanche, K.; Merroun, M. L.; Casadesus, M.; Tran, D. T.; Mikheenko, I. P.; Bennett, J. A.; Wood, J.; Jones, I. P.; Attard, G. A.; Selenska-Pobell, S.; Macaskie, L. E.
We report a novel biochemical method based on the sacrificial hydrogen strategy to synthesise bimetallic Au/Pd nanoparticles (NPs) with a core/shell configuration. The ability of E. coli cells supplied with H2 as electron donor to rapidly precipitate Pd(II) ions from solution is used to promote the reduction of soluble Au(III). Pre-coating cells with Pd(0) (bioPd) dramatically accelerated Au(III) reduction, with the Au(III) reduction rate being dependent upon the initial Pd loading by mass on the cells. Following Au(III) addition, the bioPd/Au(III) mixture rapidly turned purple indicating the formation of colloidal gold. Mapping of bio-NPs by energy dispersive X-ray microanalysis (EDX) suggested Au-dense core regions and peripheral Pd but only Au was detected by X-ray diffraction analysis. However surface analysis of cleaned NPs by cyclic voltammetry (CV) revealed largely Pd surface sites, suggesting, since XRD shows no crystalline Pd component, that layers of Pd atoms surround Au NPs. Characterisation of the bimetallic particles using X-ray absorption spectroscopy (XANES and EXAFS) confirmed the existence of Au-rich core and Pd-rich shell type bimetallic biogenic NPs. These showed comparable catalytic activity to chemical counterparts with respect to the oxidation of benzyl alcohol, in air, and at a low temperature (90 oC).
Keywords: bioreduction, bimetallic catalysts, catalysis, core/shell, Escherichia coli, gold, palladium

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Permalink: https://www.hzdr.de/publications/Publ-16491
Publ.-Id: 16491


Biomineralization of Uranium in Natural Environments

Selenska-Pobell, S.; Reitz, T.; Geissler, A.; Merroun, M.
Prokaryotic microorganisms (bacteria and archaea) are the most ubiquitous organisms in terrestrial and aquatic environments. They play a major role in deposition and weathering of a large variety of minerals enriched with or consisting mainly of different metals, such as iron, manganese, copper, gold, and even radionuclides (e.g. uranium). The structure of biologically synthesized minerals is strongly influenced by the metabolic properties of the bacterial or archaeal strains involved in their production and also by the different metal binding potential of their cell wall components.
The talk will focus on cell wall dependent accumulation and biomineralization of uranium by particular Gram-positive and Gram-negative bacteria recovered from uranium mining wastes. By using TEM, EXAFS and TRLF we were able to demonstrate that the Gram-negative and most of the Gram-positive bacteria inhabiting the oligotrophic uranium mining waste pile environments immobilize U(VI) at their cell walls or extracellularly in a form of uranyl phosphate compounds. Particular Gram-positive bacterial isolates, possessing highly ordered proteinaceous surface layers (S-layers), are immobilizing U(VI) by both phosphate groups of their thick peptidoglycan and of their phosphorylated S-layer and also by the carboxylic groups of the aspartate and glutamate stretches of their S-layers.
In contrast to bacteria, archaeal diversity is not very high in uranium polluted environments. In addition, these prokaryotic organisms interact with uranium in a significantly different way then bacteria. We were able to demonstrate that some archaeal organisms, indigenous for the uranium mining wastes, are not able to accumulate high amounts of uranium and that the mechanisms of uranium binding differ significantly from those of all studied bacteria. The latter is related to the unusual cell wall structure of the studied archaeal cells.
  • Lecture (Conference)
    Uranium biogeochemistry: transformations and applications, 11.-16.03.2012, Monte Verita, Ascona, Switzerland

Permalink: https://www.hzdr.de/publications/Publ-16488
Publ.-Id: 16488


In-situ characterization of the carbon nanotube growth process by X-ray diffraction

Baehtz, C.; Wirth, T. C.; Bayer, B. C.; Hofmann, S.; von Borany, J.
In the last few years carbon nanotubes (CNT) attract more and more attention due to their interesting physical properties especially in the field of micro electronics. Synthesis of CNTs with tailored properties is still a critical point, especially for their applications as interconnects. The growth of CNT by chemical vapor deposition (CVD) is an established synthesis route and it was used in this study.
In-situ X-ray diffraction experiments during growth conditions are performed at the beamline BM20 at the ESRF operated by the Helmholtz-Zentrum Dresden-Rossendorf using a high temperature annealing chamber suitable for reactive gases. Acetylene was used as carbon precursor for the CVD of CNT. Different catalyst systems were studied. For iron nano-particles acting as CNT catalyst, there is still a debate which species can be catalytically active: metallic iron and/or iron carbide. The formation of the metal nano-particles by dewetting and respective crystallisation of the initial thin film was followed by X-Ray reflectivity (XRR) and diffraction (XRD) measurements. We proved that CNT growth can occur without the presence of Fe3C. In general two reaction pathways denoted by a high and low (or zero) iron carbide concentration were observed. Which route the growth follows depends in a statistical way on the ratio of different iron phases (α- and γ-Fe) present in the nano-particles. This can be influenced also by the reaction conditions like temperature and kind of the buffer layer supporting the catalyst film. One challenge is to grow CNT on a conducting support without scarifying the CNT yield and structural quality of the grown CNTs.
Using a Co-buffer layer in-between Si-support and Fe-catalyst leads to the formation of conductive CoSi2 via CoSi by subsequent silicidation during the growth process. Herby a high yield of CNT was obtained.
CoSi2 support is more promising than Ta support, but we used Ta as model system to explain all possible interactions, all occurring phases during processing by side reactions were recorded. Notable CNT yield triggered by high catalytic activity of iron at low temperatures ~550C was observed.
This study shows that in-situ diffraction experiments are a powerful tool to investigate catalytic reactions. The understandings of these processes are the basis of tailoring future materials.
Keywords: Carbon nano tubes, synchrotron radiation, in-situ diffraction
  • Lecture (Conference)
    IUCr2011 - XXII Congress and General Assembly, 22.-30.08.2011, Madrid, Spain

Permalink: https://www.hzdr.de/publications/Publ-16487
Publ.-Id: 16487


Nanostrukturierte Verschleißschutzschichten für den Automobilbau - von der Konzeption zur Anwendung

Fassbender, J.ORC; Möller, W.; Beyer, E.; Seifert, G.; Zellbeck, H.; Abrasonis, G.; Gemming, S.; Hübner, M.; Joswig, J.-O.; Krause, M.; Kunze, T.; Leson, A.; Makowski, S.; Posselt, M.; Weihnacht, V.
Optimierte, leichte, aber widerstandsfähige Werkstoffe eröffnen dem Fahrzeugbau die Möglichkeit, Energieeffizienz- und Klimaschutzziele mit einer Verbesserung der funktionalen Fähigkeiten des Fahrzeugs zu verbinden. Ziel des Projekts ist die Herstellung und Optimierung der dafür erforderlichen neuartigen, nanoskalig strukturierten, harten und selbstschmierenden Schichten für verschleißbelastete Motorenteile. Konventionelle dünne Funktionsschichten auf Kohlenstoffbasis werden in der Regel durch Niederdruck-Beschichtungsverfahren hergestellt. In den letzten Jahren sind neue Ansätze zur Weiterentwicklung dieser Materialklasse entstanden, die besonders auf nanoskalig strukturierte Systeme fokussieren, und die in Teilprojekt D1 ‘NanoCarbCoat’ für den automobilen Leichtbau erschlossen werden sollen. Dazu verbindet das betont interdisziplinär ausgerichtete Teilprojekt die Expertise von Partnern aus Natur- und Ingenieurwissenschaften zur Abscheidung und physikalischen Charakterisierung kohlenstoffbasierter Schichten, zur Modellierung der tribologischen Vorgänge an Schichten im Kontakt miteinander und mit einem Schmierstoff und zum Test der Beschichtung unter realistischen Bedingungen im Verbrennungsmotor.
Keywords: tribology, wear-resistant coatings, nanotribology, multiscale modeling, motor
  • Contribution to external collection
    W.A. Hufenbach: ECEMP – European Centre for Emerging Materials and Processes, Hightech – Made in Germany – Created in Saxony, Auerbach: Verlag Wissenschaftliche Skripten, 2011, 3000221093, 179-190

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Permalink: https://www.hzdr.de/publications/Publ-16486
Publ.-Id: 16486


Phase Separation and Size Controlled Nanocrystal Formation in GeO

Sahle, C. J.; Sternemann, C.; Nyrow, A.; Schwamberger, A.; Wieland, F.; Zschintzsch, M.; von Borany, J.; Hohl, A.; Tolan, M.
Semiconducting group IV nanocrystals (NC), such as Ge- and Si-NC, have drawn a lot of attention in recent years because of their potential use in new generations of light emitting diodes, fast and stable non-volatile flash memories or highly efficient solar cells. Although intensive research has been conducted regarding the photoluminescence and charge storage properties of readily produced oxide embedded NCs little is known about the phase separation and NC formation process. Here, we present in and ex situ X-ray absorption near edge structure (XANES) spectroscopy data of the temperature induced disproportionation, i.e phase separation of GeOx (x ≈ 1) into Ge and GeO2, which leads to the formation of Ge NCs embedded in a Ge oxide matrix. The formation of size controlled Ge NCs is achieved using a GeOx–SiO2 superlattice approach. The influence of reducing hydrogen in the annealing ambient on the phase separation process and resulting NC density is discussed.
  • Lecture (Conference)
    DPG Spring Meeting, Dresden, Germany Symposium: Condensed Matter: Semiconductor Physics, 13.-18.03.2011, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-16485
Publ.-Id: 16485


Charge carrier depth profiling at ultra-shallow pn-junctions

Schmidt, B.; Philipp, P.; Zier, M.
According to the continuously shrinking of semiconductor device dimensions the fabrication of ultra-shallow pn-junctions is the essential requirement for modern CMOS technology. Therefore the importance of measurement techniques for dopant depth profiles is rising and the demands in resolution and accuracy are continuously increasing. The established methods like SIMS and spreading resistance profiling become less suitable for these applications because of their disadvantages at measurements close to the silicon surface. The Stepwise Oxidation Profiling (SWOP) is a new measurement technique for ultra shallow boron doped layers with pn-junction depths less than 20 nm. SWOP is based on the continuous anodic oxidation technique (CAOT) proposed by S. Prusin [1] and was applied to boron doped layers formed by ion implantation with rapid thermal annealing and by a new doping technique called flash lamp diffusion (FLD).
[1] S. Prussin, AIP Conference Proceedings 931, 275 (2007).
Keywords: ultra-shallow doping profiles, charge carrier depth profiling
  • Invited lecture (Conferences)
    Workshop "Moderne Methoden der Oberflächen- und Dünnschichtanalytik", 30.11.2011, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-16484
Publ.-Id: 16484


Nitrogen Implanted GaAs as a Promising Photovoltaic Material

Gao, K.; Prucnal, S.; Skorupa, W.; Helm, M.; Yastrubchak, O.; Gluba, L.; Zhou, S.
As a III-V photovoltaic material, gallium arsenide has promising prospects in aerospace applications and concentrator cells in virtue of its high efficiency, outstanding thermal stability, as well as the resistance to radiation damage.
In order to further increase the efficiency of GaAs based solar cells, one reasonable method is to modify its bandgap thereby the absorption range. A cell with a GaAs base can have several layers of slightly different compositions that allow a cell designer to precisely control the generation and collection of electrons and holes. Alloying is one method to tailor the properties of semiconductor materials for specific applications. The introduction of nitrogen into the GaAs matrix allows to vary the band gap energy in a broad energy range from ~3.4 eV (GaN) to ~0.8 eV (GaN0.15As0.85)1.
Here we present the synthesis of GaNxAs1-x layers using ion implantation and millisecond flash lamp annealing (FLA) techniques. After nitrogen implantation the GaAs wafer is amorphous within the implantation range and N atoms are located mainly in the interstitial position. Post-implantation thermal annealing restores the initial properties of the matrix and leads to the GaNxAs1-x layers formation. The optical properties of the GaNxAs1-x layers were investigated by -Raman spectroscopy, temperature dependence photoluminescence and photoreflectance spectroscopy. It is shown that during milliseconds range FLA nitrogen can be efficiently incorporated into the GaAs matrix. The band gap of nitrogen reach GaAs layer can be easily tuned from 1.34 down to 1 eV by varying the nitrogen fluence and annealing parameters.
Keywords: GaN(x)As(1-x), Ion Implantation, Flash Lamp Annealing
  • Poster
    Next Generation Solar Energy, 12.-14.12.2011, Erlangen, Germany

Permalink: https://www.hzdr.de/publications/Publ-16483
Publ.-Id: 16483


Extremely large-scale simulation of a Kardar-Parisi-Zhang model using graphics cards

Kelling, J.; Ódor, G.
The octahedron model introduced recently has been implemented onto graphics cards, which permits extremely large-scale simulations via binary lattice gases and bit-coded algorithms. We confirm scaling behavior belonging to the two-dimensional Kardar-Parisi-Zhang universality class and find a surface growth exponent: β=0.2415(15) on 217×217 systems, ruling out β=1/4 suggested by field theory. The maximum speedup with respect to a single CPU is 240. The steady state has been analyzed by finite-size scaling and a growth exponent α=0.393(4) is found. Correction-to-scaling-exponent are computed and the power-spectrum density of the steady state is determined. We calculate the universal scaling functions and cumulants and show that the limit distribution can be obtained by the sizes considered. We provide numerical fitting for the small and large tail behavior of the steady-state scaling function of the interface width.
Keywords: 05.70.Ln, 05.70.Np, 82.20.Wt

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Permalink: https://www.hzdr.de/publications/Publ-16482
Publ.-Id: 16482


Imaging of spin-torque induced magnetization dynamics in lateral spin injector configuration

Buhl, M.; Bernert, K.; Wintz, S.; Henschel, T.; Mattheis, R.; Raabe, J.; Grebing, J.; Potzger, K.; Erbe, A.; Fassbender, J.ORC
Electrical transport characteristics of structures consisting of normal metals and ferromagnetic materials depend strongly on the magneti- zation direction of the ferromagnets. Thus, different spin polarizations can lead to different resistance values of such structures. The absorp- tion of spin polarized electrons in a ferromagnetic material (spin transfer torque) by domain/domain walls leads to magnetization switching or domain wall movement. This can be achieved by driving a current perpendicular to the plane of the ferromagnet (CPP) or in the plane (CIP). In this experiment we investigate the magnetization behavior of ferromagnetic nanopillars located between two lateral spin injectors in the CIP configuration. Using Scanning Transmission X-ray Mircoscopy (STXM) these studies will give more insights in the switching behav- ior and dynamics. Technological applications can mostly be found in memory structures, where the magnetization can be stored and read out.
Keywords: current in plane, CIP, spin transfer torque, STT, scanning transmission x-ray microscopy, STXM, spin polarization, lateral spin injection, ferromagnetism, Cobalt, Co
  • Poster
    DPG Spring Meeting Dresden 2011, 14.-18.03.2011, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-16481
Publ.-Id: 16481


Estimation of carbon ion induced activity distributions with the yield approach

Priegnitz, M.; Enghardt, W.; Laube, K.; Fiedler, F.
Phantom irradiation with pencil-like beams of carbon ions have been performed at GSI Darmstadt. The induced β+-activity has been monitored by means of the dedicated in-beam PET scanner mounted at the irradiation site. On the basis of the yield approach ion beam induced positron emitter distributions have been predicted for these irradiation and activity distributions have been estimated. The comparison of predicted and measured activity profiles provides promising results.
  • Contribution to external collection
    in: GSI Scientific Report 2011, Darmstadt: GSI Helmholtzzentrum für Schwerionenforschung, 2012, 533

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Permalink: https://www.hzdr.de/publications/Publ-16480
Publ.-Id: 16480


Manipulation of Ge quantum dot ordering in alumina matrix by deposition conditions

Buljan, M.; Baehtz, C.; Holý, V.; Radić, N.; Roshchupkina, O.; Prucnal, S.; Mücklich, A.; Valeš, V.; Bernstorff, S.; Grenzer, J.
We present an investigation of ordering and PL properties of Ge QDs in an alumina matrix formed by magnetron-sputtering deposition of (Ge+Al2O3)/Al2O3 multilayers. The self-assembly process occurs during the deposition and results with the formation of three-dimensional quantum dots lattices. We investigate the dependencies of the size and ordering properties on the deposition temperature, rotation of the substrate holder and direction of the incoming flux of Ge during the deposition process. The results of the investigation show that tuning the deposition temperature enables manipulation with QD sizes and their mutual distances. We show that the ordering of QDs obtained by deposition on fixed substrate holder leads to the formation of a quantum dot crystal, while the rotation of substrate holder leads to randomly rotated domains with regular ordering. The observed phenomenon is explained by a combination of the surface morphology effect on the nucleation positions of Ge quantum dots with a lateral inhomogeneity of the ad-atom flux. In addition, we show that the resulting quantum-dot lattices have size-dependent PL properties.
  • Lecture (Conference)
    DPG-Frühjahrstagung der Sektion Kondensierte Materie, 25.-30.03.2012, Berlin, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-16479
Publ.-Id: 16479


In-situ observation of the Self-assembled growth of ordered Ge nanocrystals embedded within a dielectrical matrix

Grenzer, J.; Buljan, M.; Roshchupkina, O.; Baehtz, C.; Holý, V.
We report on an in-situ X-ray investigation of a self-assembled growth of Ge nanocrystals embedded in a dielectrical matrix forming a BCC-like super structure. Such a material could be a key element for the development of a new generation of solar cells extending the spectral range for energy conversion. Using small angle scattering techniques and X-ray diffraction the formation of crystalline Ge nanoparticles during growth and annealing was studied in-situ at the BM20 beam line at that ESRF using a process chamber for magnetron sputter deposition and annealing that can be inserted into the goniometer. A single some 100nm thick Ge+Al2 O3 layer using magnetron sputtering was deposited at an elevated substrate temperature. The self-assembly during growth or subsequent annealing results in the formation of a well ordered three-dimensional BCC-like quantum dot lattice within the whole deposited volume. The formed nanocrystals are very small in size (< 4.0𝑛𝑚 with a very narrow size distribution and a large spatial density. The parameters of the formed super structure can be directly influenced by changing the deposition parameters. The self-ordering of the quantum dots is explained by diffusion mediated nucleation and surface morphology effects.
  • Lecture (Conference)
    DPG-Frühjahrstagung der Sektion Kondensierte Materie, 25.-30.03.2012, Berlin, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-16478
Publ.-Id: 16478


The 25Mg(p,γ)26Al reaction at low astrophysical energies

Strieder, F.; Limata, B.; Formicola, A.; Imbriani, G.; Junker, M.; Bemmerer, D.; Best, A.; Broggini, C.; Caciolli, A.; Corvisiero, P.; Costantini, H.; Dileva, A.; Elekes, Z.; Fülöp, Z.; Gervino, G.; Guglielmetti, A.; Gustavino, C.; Gyürky, G.; Lemut, A.; Marta, M.; Mazzocchi, C.; Menegazzo, R.; Prati, P.; Roca, V.; Rolfs, C.; Rossi Alvarez, C.; Somorjai, E.; Straniero, O.; Terrasi, F.; Trautvetter, H. P.
In the present work we report on a new measurement of resonance strengths in the reaction 25Mg(p,gamma)26Al at E_cm= 92 and 189 keV. This study was performed at the LUNA facility in the Gran Sasso underground laboratory using a 4pi BGO summing crystal. For the first time the 92 keV resonance was directly observed and a resonance strength omega-gamma=(2.9+/-0.6)x10E-10 eV was determined. Additionally, the gamma-ray branchings and strength of the 189 keV resonance were studied with a high resolution HPGe detector yielding an omega-gamma value in agreement with the BGO measurement, but 20% larger compared to previous works.

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Permalink: https://www.hzdr.de/publications/Publ-16477
Publ.-Id: 16477


Phase sensitive monitoring of electron bunch form and arrival time in superconducting linear accelerators

Kaya, C.; Schneider, C.; Al Shemmary, A.; Seidel, W.; Kuntzsch, M.; Bhattacharyya, J.; Mittendorff, M.; Evtushenko, P.; Winnerl, S.; Staats, G.; Helm, M.; Stojanovic, N.; Michel, P.; Gensch, M.
In this letter we present a simple approach for monitoring electron bunch form and arrival time combining electro-optic sampling and phase and frequency sensitive signal de-tection. The sensitivity of the technique allows on line diagnostic to be performed down to bunch charges in the femtocoulomb regime. The concept has high impact for the develop-ments of the next generation of 4th Generation X-ray light sources working with long pulse trains or continuous wave mode of operation.
Keywords: electro-optic sampling, arrival time monitor, srf, accelerator, electron bunch diagnostic

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Permalink: https://www.hzdr.de/publications/Publ-16476
Publ.-Id: 16476


Ungeduldige Forscher träumen mit DREAMS Bestimmung langlebiger Radionuklide mit Beschleunigermassenspektrometrie

Merchel, S.; Akhmadaliev, S.; Pavetich, S.; Rugel, G.
Das Helmholtz-Zentrum Dresden-Rossendorf hat sein Spektrum ionenanalytischer Verfahren um eine weitere hochsensitive Methode erweitert: die Beschleunigermassenspektrometrie (accelerator mass spectrometry = AMS). Die AMS ist prädestiniert zur Bestimmung langlebiger Radionuklide (Halbwertszeit ≥ 100 Jahre). Diese werden nicht, wie allgemein üblich, mittels Zerfallszählung detektiert. Vielmehr bestimmen die „ungeduldigen Forscher“ die noch nicht zerfallenen Nuklide wesentlich effizienter massenspektrometrisch.
Keywords: AMS, Radionuklide
  • GIT Labor-Fachzeitschrift 56(2012)Februar, 88-90

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Publ.-Id: 16475


Status von AMS–Messungen an DREAMS

Rugel, G.; Akhmadaliev, S.; Merchel, S.; Pavetich, S.
Am Helmholtz–Zentrum Dresden–Rossendorf wurde im Jahr 2010 die Dresdner Accelerator Mass Spectrometry (DREAMS) Anlage mit einem 6 MV Beschleuniger installiert. Für die Routinemessungen mit 10Be und 26Al wurden Vergleichsmessungen mit anderen Laboren vorgenommen.
Ausserdem wurden die verwendeten in–house–Standards an sogenannte Primärstandards ankalibriert. Von Testmessungen an volatilen Elementen wie Chlor (36Cl) berichtet S. Pavetich [1]. AMS–Messungen von 41Ca/Ca–Verhältnissen wurden an Proben aus dem Rückbau nuklearer Anlagen und an Meteoritenproben (siehe [2]) vorgenommen. In Kooperation mit externen Partnern wurden bisher zahlreiche terrestrische Proben auf 10Be und 26Al untersucht.
Danksagung: Wir danken dem Verein für Kernverfahrenstechnik und Analytik Rossendorf e. V. für die Bereitstellung von Probenmaterial.
Ref.: [1] S. Pavetich et al., diese Tagung. [2] S. Merchel et al., diese Tagung.
Keywords: accelarator mass spectrometry, radionuclide, AMS
  • Lecture (Conference)
    DPG Frühjahrstagung des Arbeitskreises Atome, Moleküle, Quantenoptik und Plasmen (AMOP), 12.-16.03.2012, Stuttgart, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-16474
Publ.-Id: 16474


Cosmogenic nuclides in meteorites

Merchel, S.; Akhmadaliev, S.; Rugel, G.; Cartwright, J. A.; Ott, U.; Faestermann, T.; Fimiani, L.; Korschinek, G.; Ludwig, P.
After successful installation of the Dresden Accelerator Mass Spectrometry (DREAMS) facility [1], determinations of the lighter radionuclides 10Be, 26Al, and 41Ca are now easily attainable in Germany. Accompanied by data for the heavier radionuclides (i.e. 53Mn and 60Fe) that can be measured at the 14 MV tandem at Munich and stable nuclides such as 21,22Ne and 38Ar from noble gas mass spectrometry at MPI Mainz, complete and unique exposure histories of extraterrestrial material can be reconstructed.
For example, recent analyses of the 100th Martian meteorite Ksar Ghilane 002 [2] and four samples from the nickel-rich ataxite Gebel Kamil [3] show interesting features revealing amazing stories.
Ackn.: A. Bischoff and L. Folco are thanked for providing meteorite material and data for bulk chemical data.
Ref.: [1] G. Rugel et al., this meeting. [2] J. Llorca et al., submitted to Meteorit. Planet. Sci.. [3] L. Folco et al., Science 329 (2010) 804.
Keywords: accelerator mass spectrometry, meteorite, radionuclides, noble gases
  • Lecture (Conference)
    DPG Frühjahrstagung des Arbeitskreises Atome, Moleküle, Quantenoptik und Plasmen (AMOP), 12.-16.03.2012, Stuttgart, Deutschland

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Publ.-Id: 16473


The 100th Martian meteorite Ksar Ghilane 002 (KG 002): Noble gases and radionuclides point to a strong relationship with Los Angeles

Cartwright, J. A.; Merchel, S.; Rugel, G.; Fimiani, L.; Ludwig, P.; Llorca, J.; Ott, U.
Ksar Ghilane 002 (KG 002) is the 100th Martian meteorite to be catalogued by the Meteoritical Bulletin, and the first to be recovered from Tunisia (January, 2010). The single stone, weighing 538 g, is a coarse-grained basaltic shergottite that shows remarkable petrological and compositional similarities with evolved shergottite Los Angeles [1,2].
By performing noble gas and radionuclide analysis on KG 002, we aim to contribute further in determining the extent of its similarity with Los Angeles. In particular, we investigate the potential for a launch-pairing of these two meteorites by comparison of cos-mic ray exposure (CRE) ages, where preferred CRE ages for Los Angeles of 3.10 ± 0.70 and 3.35 ± 0.30 Ma have been previously suggested [3,4].
References: [1] Llorca J. et al. (subm.) MAPS. [2] Roszjar J. et al. (2011) LPSC XLIII, this conf. [3] Terribilini, D. et al. (2000) MAPS, 35:A155-A156. [4] Eugster, O. et al. (2002) MAPS, 37:1345-1360.
Keywords: accelerator mass spectrometry, meteorite, noble gases, radionuclides
  • Poster
    43rd Lunar and Planetary Science Conference, 19.-23.03.2012, The Woodlands, Texas, United States

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Permalink: https://www.hzdr.de/publications/Publ-16472
Publ.-Id: 16472


Shock wave synthesis of γ-Si3[O,N]4 in the new Freiberg blasting facility under different conditions

Renno, A. D.; Schlothauer, T.; Schwarz, M. R.; Heide, G.; Kroke, E.
The new subterranean blasting facility at the TU Bergakademie Freiberg allows experiments at elevated capacities of 20 kg C4-equivalent. The new installation permits the investigation of phase transitions of γ Si3N4 under dynamic loading.
We studied the influence of plate thickness (shock duration) and different precursor-pressure powder (Cu, NaCl) mixtures at charge masses between 2000 and 20.000 g C4.
Systematic studies showed that the Mach-reflection (so called “upstreaming jetting phenomena”) is of vital importance for the synthesis success, due to the fact that the T-p ratio will increase dramatically [Milyavskii et al., 2006].
We synthesized pure γ-Si3[O,N]4 from H-bearing precursors at pressures > 25 GPa [Schlothauer et al., 2011].
The phase transition Si2N2NH into γ-Si3[O,N]4 is completely reconstructive and requires a high temperature-pressure-ratio of 176 K/GPa at pressures up to 35 GPa. Despite the high energy density during the shock wave synthesis process it will be inevitable to prepare the samples under an inert nitrogen atmosphere.
Keywords: Shock wave experiments, Mineral Physics
  • Poster
    AGU Fall Meeting 2011, 05.-09.12.2011, San Francisco, USA

Permalink: https://www.hzdr.de/publications/Publ-16471
Publ.-Id: 16471


Magnetic model for A2CuP2O7 (A = Na, Li): One-dimensional versus two-dimensional behavior

Lebernegg, S.; Tsirlin, A. A.; Janson, O.; Nath, R.; Sichelschmidt, J.; Skourski, Y.; Amthauer, G.; Rosner, H.
We report magnetization measurements, full-potential band-structure calculations, and microscopic modeling for the spin-1/2 Heisenberg magnets A2CuP2O7 (A = Na, Li) involving complex Cu-O-O-Cu superexchange pathways. Based on a quantitative evaluation of the leading exchange integrals and the subsequent quantum Monte Carlo simulations, we propose a quasi-one-dimensional magnetic model for both compounds, in contrast to earlier studies that conjectured on a two-dimensional scenario. The one-dimensional nature of A2CuP2O7 is unambiguously verified by magnetization isotherms measured in fields up to 50 T. The saturation fields of about 40 T for both Li and Na compounds are in excellent agreement with the intrachain exchange J1 is about 27 K extracted from the magnetic susceptibility data. The proposed magnetic structure entails spin chains with the dominating antiferromagnetic nearest-neighbor interaction J1 and two inequivalent, nonfrustrated antiferromagnetic interchain couplings of about 0.01J1 each. A possible long-range magnetic ordering is discussed in comparison with the available experimental information

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Permalink: https://www.hzdr.de/publications/Publ-16470
Publ.-Id: 16470


Singlet–Triplet Excitations and High-Field Magnetization in CuTe2O5

Wang, Z.; Schmidt, M.; Goncharov, Y.; Skourski, Y.; Wosnitza, J.; Berger, H.; Krug Von Nidda, H.-A.; Loidl, A.; Deisenhofer, J.
By measuring the THz electron spin resonance (ESR) transmission spectra and high-field magnetization on the spingapped system CuTe2O5, we identified the singlet–triplet excitations in the dimerized non-magnetic ground state. The determined spin-gap value of hnu0 = 4.94 meV at the Gamma point (Q = 0) is significantly smaller than the strongest antiferromagnetic exchange interaction between the Cu ions predicted by theoretical investigations. We also observed the critical field Ha*c1 = 37.6 T for H perp bc-plane and Hbcc1 = 40.6 T for H parallel bc-plane at the onset of non-zero magnetization, consistent with the gap value and corresponding anisotropic g-factors determined previously. The observed singlet–triplet excitations in Faraday and Voigt configurations suggest a mixing of the singlet state with the Sz = 0 triplet state and the Sz = plus/minus 1 triplet states, respectively, due to the Dzyaloshinskii–Moriya (DM) interaction with a DM vector perpendicular to the crystalline bc-plane.

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Permalink: https://www.hzdr.de/publications/Publ-16469
Publ.-Id: 16469


Enhancement of the upper critical field in codoped iron-arsenic high-temperature superconductors

Weickert, F.; Nicklas, M.; Schnelle, W.; Wosnitza, J.; Leithe-Jasper, A.; Rosner, H.
We present the first study of codoped iron-arsenide superconductors of the 122 family (Sr/Ba)1-xKxFe2-yCoyAs2 with the purpose to increase the upper critical field Hc2 compared to single doped Sr/BaFe2As2 materials. Hc2 was investigated by measuring the magnetoresistance in high pulsed magnetic fields up to 64 T. We find, that Hc2 extrapolated to T = 0 is indeed enhanced significantly to approx 90 T for polycrystalline samples of Ba0:55K0:45Fe1:95Co0:05As2 compared to approx 75 T for Ba0.55K0.45Fe2As2 and BaFe1.8Co0.2As2 single crystals. Codoping thus is a promising way for the systematic optimization of iron-arsenic based superconductors for magnetic-field and high-current applications.

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Publ.-Id: 16468


Research at Hihgh Magnetic Fields - Activities at the Dresden High Magnetic Field Laboratory

Wosnitza, J.
  • Invited lecture (Conferences)
    Science Vision for the European Spallation Source, 10.-12.10.2011, Bad Reichenhall, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-16467
Publ.-Id: 16467


The impact of the Äspö ground water bacterium Pseudomonas fluorescens on the speciation of plutonium

Moll, H.; Lütke, L.; Sachs, S.; Schmeide, K.; Bernhard, G.
Bacteria are widely distributed in nature and they can strongly influence the behaviour of actinides in the environment. This presentation focuses on the unknown interaction between plutonium (Pu(VI) and Pu(IV)-polymers) and cells of the ground water bacterium Pseudomonas fluorescens isolated from the Äspö site, Sweden. Accumulation experiments were performed in order to obtain information about the amount of Pu bound by the cells in dependence on the contact time and the initial plutonium concentration. We used solvent extraction and UV-vis-NIR absorption spectroscopy to determine the speciation of Pu oxidation states. The Pu oxidation state distributions will be discussed in detail and a model which describes the ongoing processes in the system Pu–P. fluorescens will be presented.
Keywords: Plutonium, Bacteria, Speciation
  • Contribution to proceedings
    Plutonium Futures - The Science 2012, 15.-20.07.2012, Cambridge, UK
  • Lecture (Conference)
    Plutonium Futures - The Science 2012, 15.-20.07.2012, Cambridge, UK

Permalink: https://www.hzdr.de/publications/Publ-16466
Publ.-Id: 16466


Strain Relaxation and Vacancy Creation in Thin Platinum Films

Gruber, W.; Chakravarty, S.; Baehtz, C.; Leitenberger, W.; Bruns, M.; Kobler, A.; Kübel, C.; Schmidt, H.
Synchrotron based combined in situ x-ray diffractometry and reflectometry is used to investigate the role of vacancies for the relaxation of residual stress in thin metallic Pt films. From the experimentally determined relative changes of the lattice parameter a and of the film thickness L the modification of vacancy concentration and residual strain was derived as a function of annealing time at 130 °C. The results indicate that relaxation of strain resulting from compressive stress is accompanied by the creation of vacancies at the free film surface. This proves experimentally the postulated dominant role of vacancies for stress relaxation in thin metal films close to room temperature.
Keywords: Synchrotron radiation, Pt thin films, reflectometry

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Imaging measurement techniques for the LIMMCAST continuous casting model

Franke, S.; Wondrak, T.; Räbiger, D.; Timmel, K.; Büttner, L.; Czarske, J.; Eckert, S.; Gerbeth, G.
The properties of the mould flow are significant for the casting quality at the continuous casting of steel. To investigate the flow behaviour model experiments were performed using liquid metal melts with a low melting temperature. Thereto adequate imaging measuring techniques for liquid metal flows are required. We will present three methods: the Ultrasound Doppler Velocimetry (UDV) and the Contactless Inductive Flow Tomography (CIFT) to measure two-dimensional velocity fields in the mould and the Mutual Inductance Tomography (MIT) to measure the two-phase flow distribution in the SEN. The UDV method by means of ultrasonic array transducers provides spatial- and time-resolved measurements at a measuring area of 24 × 24 voxel with frame rates up to 30 fps. A method based on the application of ultrasonic wave guides is presented to extend the limited temperature range of conventional ultrasonic transducers (up to 200°C) to temperatures up to about 700°C. CIFT facilitate measurements of the global flow structure with frame rates of 1 fps. Due to its feature as a contactless measuring method it can be applied at facilities operating at room temperature as well as much higher temperatures. The MIT as well a contactless measuring principle may resolve the two-phase flow distribution in the SEN with up to 20 fps. All three methods were successfully applied at a small-scale continuous casting model based on the metal alloy GaInSn liquid at room temperature and are currently adapted to a large-scale casting model applying the alloy BiSn in a temperature range of 200°C to 350°C.
Keywords: Ultrasound Doppler Velocimetry, Contactless Inductive Flow Tomography, Mutual Inductance Tomography, continuous casting, liquid metal model, mould flow, flow measurements, two-phase flow
  • Lecture (Conference)
    Symposium on Simulation and Modeling of Metallurgical Processes "SymSim", 07.-10.12.2011, Planner Alm, Österreich

Permalink: https://www.hzdr.de/publications/Publ-16464
Publ.-Id: 16464


Classification of bubbles in vertical gas–liquid flow: Part 1 – An analysis of experimental data

Qi, F. S.; Yeoh, G. H.; Cheung, S. C. P.; Tu, J. Y.; Krepper, E.; Lucas, D.
In consideration of the practical importance regarding the application of gas–liquid flow in a vertical pipe and the quest towards the development of more robust physical models to accurately predict the essential interfacial parameters of the two-phase flow, comprehensive analysis of the characteristics and phase distribution patterns of such a flow have been performed on both experimental measurements and theoretical predictions. In this first part, analysis of experimental data in a large diameter pipe with an inner diameter of 195.3 mm via the wire-mesh senor measuring technique was presented. The experiments were performed at the TOPFLOW facility of Helmholtz-Zentrum Dresden-Rossendorf. In the present paper, measurements of local interfacial parameters which included the void fraction, volume equivalent bubble diameter, bubble size distribution and interfacial velocities were discussed. Test points covering flow regimes from bubbly to cap to slug to churn-turbulent flow were selected to investigate the flow of different bubble shapes and sizes and the significant bubble coalescence and break-up mechanism throughout the large vertical pipe. The radial and axial evolutions of the local flow structure were interpreted in terms of the classifications of different groups of bubbles (Group-1 and Group-2). In addition, the phase distribution patterns were analyzed through the concept of skewness, which essentially identified two fundamental patterns, namely, wall peak and core peak. In general, Group-1 bubbles being smaller spherical bubbles have shown to exhibit a wall peaking distribution while Group-2 bubbles being larger non-spherical bubbles corresponded to a core peaking distribution. The classification of bubbles that have been performed in this present study can be employed for the development of bubble coalescence and break-up mechanistic kernels and other interfacial force closure models for a two bubble group approach in the context of computational fluid dynamics.
Keywords: Gas–liquid flow, Large diameter pipe, Phase distribution patterns, Skewness

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Publ.-Id: 16463


Joint Project: Interaction and transport of actinides in natural clay rock with consideration of humic substances and clay organics - Investigations of temperature dependence of complexation and sorption of trivalent actinides (Am(III)) in the system actinide-NOM-natural clay rock-aquifer (Final Report BMWi Project No.: 02 E 10417)

Acker, M.; Barkleit, A.; Müller, M.; Schott, J.; Bernhard, G.
The main objective of this project was to study the interaction processes between An(III)/Ln(III), (representated by Am(III) and Eu(III), respectively), organic model ligands, and Opalinus Clay at elevated temperature (until 80°C). The thermodynamic data (log, ΔG, ΔH and ΔS) for the complexation and sorption processes have been derived and led to an enhancement of the thermodynamic database by data at elevated temperatures.

The complexation of Am(III)/Eu(III) with small organic ligands (pyromellitic, salicylic, lactic, acetic, citric, and tartaric acid) that serve as model ligands for natural organic material, like humic substances or clay organic was investigated by temperature dependent UV-Vis and time-resolved laser-induced fluorescence spectroscopy (TRLFS).
For the first time, the UV-Vis absorption spectroscopy utilizing a Long Path Flow Cell (LPFC) has been established for speciation analysis of Am(III) at trace concentrations. A detection limit of 5*10-9 mol/l-1 Am(III) was determined with an 2 m LPFC.
Several Am(III)/Eu(III)-organic ligand complexes were spectroscopically and thermodynamically characterized. General, all studied complexation reactions are endothermic and driven by entropy.
Furthermore, the interaction of Eu(III) with pyromellitc acid (1,2,4,5-benzene-tetracarboxylic acid) had been studied in detail with additional methods like isothermal titration calorimetry (ITC) and Fourier-transform infrared spectroscopy in combination with density function theory (DFT) calculations. At elevated temperature and higher concentration (> 5 mM Eu(III) and pyromellitic acid) a temperature-dependent polymerization was observed. It had been shown that predominantly chelating coordination with two carboxylic groups in the monomeric complex and monodentate binding of a single carboxylic group in the polymeric complex of the polycarboxylate with Eu(III) occurs.

The sorption of Eu(III) on Opalinus Clay was investigated in absence and presence of the small organic ligands citric and tartaric acid at different temperatures and under synthetic pore water conditions (I = 0.4 M, pH = 7.6) by batch experiments. Time-resolved laser-induced fluorescence spectroscopy was used for analysis of the Eu(III) speciation in the binary system Eu(III)-Opalinus Clay and ternary system Eu(III)-Opalinus Clay-small organic ligand under pore water conditions.
The Eu(III) sorption was found to increase generally with temperature in a considerably endothermic reactions with enthalpies of about 50 kJ/mol 1. In presence of tartrate or citrate the Eu(III) sorption decreases with increasing ligand concentration due to a complex formation of Eu(III) in solution. This complex formation was verified by TRLFS investigations. The detected Eu(III) surface species on Opalinus Clay with a luminescence lifetime of (201  9) µs is no influenced by the presence of the studied organic ligands.
Keywords: Americium, Europium, Opalinus clay, organic model ligands, complexation, sorption, elevated temperature, thermodynamics
  • Other report
    Dresden: TU Dresden, 2011
    49 Seiten

Permalink: https://www.hzdr.de/publications/Publ-16462
Publ.-Id: 16462


In-situ X-ray Scattering: A Tool for Investigation of Nanostructure Formation

Grenzer, J.
Nowadays, the development of new materials is often associated with specific properties of functionalized nanostructures. X-ray investigations are a very important tool to find the link between the functional (magnetism, luminescence) and the corresponding structural properties (size, orientation etc.) that are generating this function and to explain the underlying physical processes. This knowledge makes it possible to design new materials with specific properties. We report on (in-situ) X-ray studies that are focused on ion-beam sputtering techniques (IBS) creating nanostructures either by ion beam erosion or by sputter deposition processes.
With IBS the roughness of solid surfaces can be modified on lateral scales of a few nanometers to micrometers or even further. In a defined parameter set IBS leads to a surface smoothing, whereas at other parameters the roughness is increased, leading eventually to periodic patterns, i.e. ripple and hexagonal dot patterns. In-situ measurements of the surface roughness during IBS of GaSb surfaces give insight into the detailed mechanisms; especially, if the early time regime is addressed. Modern synchrotron sources give us the possibility to study the nanostructure growth during deposition. A sputtering chamber mounted on a six-circle goniometer allows an insight into the growth of nanostructures using different scattering and diffraction methods. We have investigated the growth of FePt islands incorporated into an Ag matrix. The high brilliance of the synchrotron source had made it possible to obtain a reliable GISAXS signal and to control the cluster morphology during growth even at the initial stage. By depositing 6 nm Ag layer directly on the SiO2 substrate, we obtained well defined FePt clusters. FePt nanoislands have been achieved without degradation of the magnetic properties. We obtained a magnetic asymmetry with magnetic moments preferentially oriented parallel to the layer surface.
  • Invited lecture (Conferences)
    8th Autumn School on X-ray Scattering from Surfaces and Thin Layers, 04.-07.10.2011, Smolenice Castle, Slovakia

Permalink: https://www.hzdr.de/publications/Publ-16459
Publ.-Id: 16459


Silicon ripple structures produced by Xe+ irradiation at medium energies

Grenzer, J.; Hanisch, A.; Facsko, S.; Mücklich, A.; Biermanns, A.; Pietsch, U.
We report on the evolution of wave-like nanopatterns induced by Xe+ ion irradiation at high fluences in an energy range between 5 keV and 70 keV. By means of atomic force microscopy a statistical analysis of the ripple amplitude and wavelength was carried out showing that the periodicity and the amplitude of the rippled structures follow a linear dependence on the energy.
However, the evolution of the rippled patterns clearly differs for the lower and higher ion energies. For energies below 25 keV we observed almost no fluence dependence of the wavelength and amplitude in the investigated range of 1...8·1017 cm-2. But for energies above 25 keV and fluences above 1·1017 cm-2 coarsening was found. At energies larger than 50 keV Xe the ripple structures display a saturation regime for fluences higher than 5·1017 cm-2.
Investigations with cross-sectional high resolution transmission electron microscopy and energy-dispersive X-ray spectroscopy revealed the appearance of Xe filled inclusions at ion energies above 25 keV. This result correlates with an almost stable ratio of the ripple wavelength to the ripple amplitude of about 30 occurring above a threshold fluence of 2·1017 cm-2 and above 25 keV.
These results indicate that there is a certain threshold energy and fluence above which a stable form of the investigated wave-like structure is build up. This is possibly caused by the formation of noble gas inclusions at higher ion energies.
  • Poster
    International Workshop on "NANOSCALE PATTERN FORMATION AT SURFACES", 18.-22.09.2011, El Escorial, Spain

Permalink: https://www.hzdr.de/publications/Publ-16458
Publ.-Id: 16458


Structural investigations of ion beam doped silicon nanowires

Grenzer, J.; Roshchupkina, O.; Kögler, R.; Das Kanungo, P.; Werner, P.
For the development of nano-optical devices nano wires (NW) are of emerging interest. One of the most important steps in the fabrication of Si devices is doping using ion beam implantation. However, this may lead to a distortion of the NW’s crystalline structure or even to an amorphization. A subsequent annealing procedure is necessary to recover the crystalline structure. The advantage of implanted Si NW’s is that the electrical conductivities are significantly higher than MBE-grown in-situ doped ones [1]. NW’s of about 100nm in diameter and 100..400 nm in length, nominally undoped, were MBE grown on Si(111) using Au as a growth-initiator. We followed the structural changes of the NW’s caused by implantation and annealing. We used rapid thermal annealing up to a temperature of 1100∘ C of about 30 seconds to remove a possible damage induced by implantation. Diffraction experiments were carried out at the ID01 ESRF beamline using a microfocused X-ray beam in combination with a 2D detector to obtain 3D diffraction patterns. Our experiments have shown that defect structure and form of the investigated NW’s change after implantation and annealing.
  • Lecture (Conference)
    DPG Spring Meeting, 13.-18.03.2011, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-16457
Publ.-Id: 16457


Serpent Monte Carlo code: new methods for few-group cross section generation

Fridman, E.; Leppänen, J.
The Serpent Monte Carlo (MC) code has been developed since 2004, and publicly distributed since 2009. One of the main applications for the code is the production of homogenized multi-group constants, which can still be considered a relatively unexplored field for the MC method. The calculation techniques required for this task have been implemented and refined during the seven years of Serpent development, with valuable feedback, contribution and new ideas from the user community. This paper presented two such topics: homogenization in leakage-corrected criticality spectrum and group constant generation in reflector regions. The implemented methods were verified and demonstrated by numerical examples. It is concluded that the new methodology improves the results of the deterministic calculation, and paves the way for Monte Carlo based group constant generation.
  • Contribution to proceedings
    Jahrestagung Kerntechnik 2012, 22.-24.05.2012, Stuttgart, Germany
  • Lecture (Conference)
    Jahrestagung Kerntechnik 2012, 22.-24.05.2012, Stuttgart, Germany

Permalink: https://www.hzdr.de/publications/Publ-16456
Publ.-Id: 16456


Chemical fingerprinting of Hungarian and Slovakian obsidian using three complementary analytical techniques

Eder, F. M.; Neelmeijer, C.; Pearce, N. J. G.; Sterba, J. H.; Bichler, M.; Merchel, S.
The natural volcanic glass obsidian is one of the classical objects of archaeometrical analyses. Reliable provenancing by means of its highly specific chemical composition, the “chemical fingerprint”, can provide information about economy, policy and the social system of ancient societies.

Although Mediterranean obsidian have mainly been the focus of characterization since the pioneer work of Cann and Renfrew (1964), provenancing of Central and Eastern Europe obsidian sources attracts increasing attention in the past decades. Fingerprinting of Hungarian and Slovakian obsidian sources is of great interest especially for Central European sites where obsidian has been widely used (Williams-Thorpe et al., 1984, Kasztovszky et al., 2008, Biró, 2009).

The application of three complementary analytical techniques on the same set of raw material samples allows both, a more complete characterization of obsidian sources and a comparison of analytical results. The aim of this multi-methodical approach is to apply three different analytical methods, in particular:

• Instrumental Neutron Activation Analysis (INAA),
• Ion Beam Analysis (IBA) comprising of Particle Induced X-ray Emission (PIXE) and Particle Induced Gamma-ray Emission (PIGE)
• Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry (LA-ICP-MS)

to detect a maximum element spectrum and to compare element concentrations determined with at least two analytical techniques. This way a check of self-consistency of analytical results is possible. Furthermore, it allows the identification of a maximum of compositional differences between Hungarian and Slovakian sources by revealing the most characteristic “chemical fingerprint” composed of more than 40 elements.

For this study, NAA, IBA and LA-ICP-MS measurements are scheduled to be applied to 25 raw material samples from sources from Hungary and Slovakia in cooperation with the Natural History Museum Vienna (Hammer, V. and Seemann, R., Department of Mineralogy and Petrography) and the Vienna Lithothek (Trnka, G., Department of Prehistoric and Protohistoric Archaeology).

Up to now, IBA studies have already been carried out using the external 4 MeV proton beam of the 6 MV Tandem accelerator of the Ion Beam Centre of Helmholtz-Zentrum Dresden-Rossendorf. Further NAA investigations will be performed at the TRIGA Mark II 250 kW research reactor of the Atominstitut in Vienna. LA-ICP-MS measurements will be conducted using the Thermo Element 2 ICP-MS coupled to an ArF gas Excimer laser system at the Aberystwyth University.

CANN, J.R. AND RENFREW, C, 1964. The characterization of obsidian and its application to the Mediterranean Region. Proceedings of the Prehistoric Society 30, 111-131.

WILLIAMS-THORPE, O., WARREN, S.E. and NANDRIS, J.G., 1984. The distribution and provenance of archaeological obsidian in central and eastern Europe. Journal of Archaeological Science 11, 183-212.

KASZTOVSZKY, Z., BIRÓ, K., MARKÓ, A. and DOBOSI, V., 2008. Prompt gamma activation analysis for non-destructive characterization of chipped stone tools and raw materials. Journal of Radioanalytical and Nuclear Chemistry 278, 293-298.

BIRÓ, K.T., 2009. Sourcing Raw Materials for Chipped Stone Artifacts: The State-of-the-Art in Hungary and the Carpathian Basin. In: Adams, B. and Blades, B.S. (Eds.) Lithic Materials and Paleolithic Societies (eds B. Adams and B. S. Blades), Wiley & Blackwell, 47-53.
Keywords: ceramics, glazes, glass and vitreous materials, ion beam analysis, neutron activation analyis, ICP-MS
  • Poster
    39th International Symposium on Archaeometry: “50 years of ISA”, 28.05.-01.06.2012, Leuven, Belgium

Permalink: https://www.hzdr.de/publications/Publ-16455
Publ.-Id: 16455


Entwicklung von Feldbusknoten für den wissenschaftlichen Gerätebau

Kaever, P.
Mit der Entwicklung spezialisierter Feldbusknoten lässt sich eine für den wissenschaftlichen Gerätebau in vielen Fällen sinnvolle Aufteilung zwischen selbst entwickelten und kommerziell verfügbaren Komponenten unter konsequenter Nutzung vorhandener Automatisierungssysteme erreichen. Im Folgenden wird vorgestellt, welche Schritte dabei erforderlich sind und welche Möglichkeiten sich mit diesem Ansatz ergeben.
Keywords: Automatisierung, Feldbus, Feldbusgeräte, wissenschaftlicher Gerätebau
  • Open Access Logo Contribution to proceedings
    102. Tagung der Studiengruppe elektronische Instrumentierung im Frühjahr 2011, 21.-23.03.2011, Darmstadt, Deutschland
    Peter Göttlicher (DESY): 102. Tagung der Studiengruppe elektronische Instrumentierung im Frühjahr 2011, Hamburg: Deutsches Elektronen-Synchrotron, 978-3-935702-58-4, 213-223

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Permalink: https://www.hzdr.de/publications/Publ-16454
Publ.-Id: 16454


Segregation-induced hardening by dislocation loops in bcc FeCr alloys

Terentyev, D.; Bergner, F.; Bonny, G.; Zhurkin, E. E.; Malerba, L.
Enrichment of Cr on both <100> and ½<111> dislocation loops has been reported under ion, electron and neutron irradiation in Fe-xCr with x=9-15 at.%. Cr enrichment in Fe-9,12Cr around edge of loops is predicted by atomistic Monte Carlo simulations. MC simulations indicate that Cr clustering on loops disappears above equilibrium solubility limit (ΔT~100-150K). MD simulations indicate that Cr enrichment at loops enhances their strength in a range of specific loading conditions.
  • Lecture (Conference)
    16th Meeting of the International Group on Radiation Damage Mechanisms in Pressure Vessel Steels (IGRDM-16), 04.-09.12.2011, Santa Barbara, USA
  • Contribution to proceedings
    IGRDM-16, 04.-09.12.2011, Santa Barbara, USA
    Proceedings of IGRDM-16

Permalink: https://www.hzdr.de/publications/Publ-16453
Publ.-Id: 16453


Small-angle neutron scattering in neutronirradiated Fe-Cr alloys

Bergner, F.; Heintze, C.; Ulbricht, A.; Kuksenko, S.; Pareige, C.; Pareige, P.
The objectives are to report data for Fe2.5Cr, Fe5Cr, Fe9Cr, Fe12Cr irradiated up to 0.06, 0.6, 1.5 dpa; to calculate nuclear scattering from features reported by Kuksenko et al. based on APT; and to compare with measured nuclear SANS. We have found that the NiSi-enriched clusters observed by APT are not responsible for the observed SANS intensities. Possible sources of the apparent discrepancy between SANS and APT for Fe12Cr are discussed. The dominant source is the overestimation of the Fe fraction in the Cr-rich clusters by APT.
  • Lecture (Conference)
    16th Meeting of the International Group on Radiation Damage Mechanisms in Pressure Vessel Steels (IGRDM-16), 04.-09.12.2011, Santa Barbara, USA
  • Contribution to proceedings
    IGRDM-16, 04.-09.12.2011, Santa Barbara, USA
    Proceedings of the IGRDM-16

Permalink: https://www.hzdr.de/publications/Publ-16452
Publ.-Id: 16452


SANS applied to RPV weld material from decommissioned NPP Greifswald taking into account atom probe data

Bergner, F.; Ulbricht, A.; Viehrig, H.-W.; Wagner, A.; Nishida, K.; Soneda, N.
SANS data are presented for as-irradiated, irradiated and annealed, and re-irradiated weld material from units 4, 2, and 1, respectively, of the decommissioned NPP Greifswald. The unirradiated reference condition is represented by a data scatter band obtained for several unirradiated weld materials of the same kind. The effects or irradiation, annealing and re-irradiation are worked out. Comparison of the SANS data with available atom probe data for the same material from unit 4 indicates an apparent discrepancy between both methods. Possible reasons are carefully discussed. The dominant reason is the overestimation of the Fe fraction in the irradiation-induced clusters by APT due to trajectory overlaps.
  • Lecture (Conference)
    16th Meeting of the International Group on Radiation Damage Mechanisms in Pressure Vessel Steels (IGRDM-16), 04.-09.12.2011, Santa Barbara, USA
  • Contribution to proceedings
    IGRDM-16, 04.-09.12.2011, Santa Barbara, USA
    Proceedings of IGRDM-16

Permalink: https://www.hzdr.de/publications/Publ-16451
Publ.-Id: 16451


Solved and unsolved issues in the interpretation of SANS results obtained for neutron-irradiated Fe-Cr alloys

Bergner, F.; Heintze, C.; Ulbricht, A.
Full set of nuclear and magnetic SANS data for a number of four Cr levels, three dpa levels each, is presented. The results are given in terms of concentration, size and A-ratio as function of Cr and dpa. A consistent understanding is obtained for Fe12Cr in terms of alpha‘ phase formation. For Fe2.5Cr, Fe5Cr and Fe9Cr, the presence of a second kind of scatterers is indicated, to which impurity elements such as Ni, Si, and C must contribute. The nature of scatterers in Fe2.5Cr, Fe5Cr and Fe9Cr is among the unsolved issues. Candidates are Cr-C-enriched clusters and/or Cr-Si-P-Ni-enriched clusters detected by atom probe tomography. There is an inconsistency between composition reported for APT and composition assumed in the SANS analysis with respect to Cr/Fe-fraction.
  • Lecture (Conference)
    19th Workshop on Multiscale Modelling and Basic Experiments of Iron-Chromium Alloys for Nuclear Applications, 08.-09.11.2011, Sala, Schweden

Permalink: https://www.hzdr.de/publications/Publ-16450
Publ.-Id: 16450


Modification to the central-cell correction of germanium acceptors

Drachenko, O.; Schneider, H.; Helm, M.; Kozlov, D.; Gavrilenko, V.; Wosnitza, J.; Leotin, J.
In this paper, we report a correction to the model potential of the Ga acceptor in germanium, evidenced by high-magnetic-field photoconductivity measurements. We found that under high magnetic fields the chemical shift of the binding energy of Ga acceptors vanishes, contrary to the results given by the generally accepted theory. To fit our data, we found that the central-cell correction should contain a repulsive part (i.e., it must be bipolar), in contrast to the purely attractive screened point-charge potential widely used in the literature.
Keywords: Germanium, acceptor, chemical shift, central-cell correction, high magnetic field

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Permalink: https://www.hzdr.de/publications/Publ-16449
Publ.-Id: 16449


Die tertiären Vulkanite Sachsens - neue mineralogische und geochemische Daten zu 'Alten Bekannten'

Renno, A. D. Keywords: petrology, mineralogy, geochemistry, Saxony, Erzgebirge, Lausitz, Tertiary volcanic rocks
  • Lecture (others)
    Dresdner Geowissenschaftliche Kolloquien, 10.01.2012, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-16448
Publ.-Id: 16448


The trigonal nodal SP3 method of the code DYN3D — verification on pin level

Duerigen, S.; Bilodid, Y.; Fridman, E.
The neutronics model of the nodal reactor dynamics code DYN3D developed for 3D analyses of steady states and transients in Light-Water Reactors has been extended by a simplified P3 (SP3) neutron transport option – to overcome the limitations of the diffusion approach at regions with significant anisotropy effects. To provide a method being applicable to reactors with hexagonal fuel assemblies and to furthermore allow flexible mesh refinement, the nodal SP3 method has been developed on the basis of a flux expansion in trigonal-z geometry. In this paper, a verification of the methodology on quasi-pin level is performed by means of a single-assembly test example. The corresponding pin-wise few-group cross sections were obtained by the deterministic lattice code HELIOS. The power distributions were calculated using both the trigonal DYN3D diffusion and SP3 solver and compared to the HELIOS reference solutions. Close to regions with non-negligible flux anisotropies, e.g., caused by the presence of a strong absorbing material, the power distribution calculated by DYN3D-SP3 shows a significant improvement in comparison to the diffusion method.
Keywords: simplified P3, SP3, nodal method, trigonal, triangular, hexagonal, mesh refinement, pin level
  • Contribution to proceedings
    Jahrestagung Kerntechnik, 22.-24.05.2012, Stuttgart, Deutschland
  • Lecture (Conference)
    Jahrestagung Kerntechnik, 22.-24.05.2012, Stuttgart, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-16447
Publ.-Id: 16447


Gamma-induced Positron Annihilation Spectroscopy

Butterling, M.; Anwand, W.; Wagner, A.; Krause-Rehberg, R.
The setup and idea of the Gamma-induced Positron Spectroscopy (GiPS) using the superconducting LINAC ELBE is presented. Features of a setup using bremsstrahlung to create positrons by pair production as well as the advantages of the characteristics of the ELBE beam will be shown and discussed. The measurement of the positron and positronium lifetime of water at various temperatures is an example for investigation and the connection of theory and experiment and will also show the perfect function of the GiPS setup.
Keywords: Positron Annihilation Spectroscopy, Bremsstrahlung, Positronium
  • Lecture (others)
    Seminar talk as part of a DAAD contract (507 556 28) with Charles University Prague, 12.12.2011, Prague, Czech Republic

Permalink: https://www.hzdr.de/publications/Publ-16445
Publ.-Id: 16445


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