Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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35836 Publications

The Impact Ionization MOSFET (IMOS) as Low-Voltage Optical Detector

Schlosser, M.; Iskra, P.; Abelein, U.; Lange, H.; Lochner, H.; Sulima, T.; Wiest, F.; Zilbauer, T.; Schmidt, B.; Eisele, I.; Hansch, W.

The avalanche photodiode (APD) is promoted as an alternative to photomultiplier tubes for optical sensing. When operated in Geiger mode, optically generated electron-hole-pairs trigger an avalanche multiplication, releasing typically about 1E6 charge carriers. However, APDs need operating voltages of about 70 V in order to allow cascaded impact ionization, making them unsuitable for several applications, especially in battery-powered devices. We propose a new device concept based on the vertical Impact Ionization MOSFET (IMOS), which could significantly reduce the operating voltage to about 5 V by using gate control and an additional current-enhancing effect.

Keywords: Impact ionization; MOSFET; Optical Detector

  • Poster
    11th European Symposium on Semiconductor Detectors, NEW DEVELOPMENTS IN RADIATION DETECTORS, 07.-11.06.2009, Wildbad Kreuth, Germany
  • Nuclear Instruments and Methods in Physics Research A 624(2010), 524-527
    DOI: 10.1016/j.nima.2010.05.060

Publ.-Id: 13590

Atomistic simulations of elastic and plastic properties in amorphous silicon

Talati, M.; Albaret, T.; Tanguy, A.

We present here potential-dependent mechanical properties of amorphous silicon studied through molecular dynamics (MD) at low temperature. On average, the localization of elementary plastic events and the co-ordination defect sites appears to be correlated. For Tersoff potential and SW potential the plastic events centered on defect sites prefer 5-fold defect sites, while for modified Stillinger-Weber potential such plastic events choose 3-fold defect sites. We also analyze the non-affine displacement field in amorphous silicon obtained for different shear regime. The non-affine displacement field localizes when plastic events occur and shows elementary shear band formation at higher shear strains.

  • EPL - Europhysics Letters 86(2009), 66005

Publ.-Id: 13589

Temperature Effect on Vibrational Properties of La0.7Sr0.3MnO3

Talati, M.; Jha, P. J.

Temperature dependence of phonons spectra and allied properties of rhombohedral La0.7Sr0.3MnO3 are investigated by using the lattice dynamical method. A tendency of phonon mode to instability causing JT lattice distortion is reflected in a softening of the stretching mode in the phonon dispersion curve of La0.7Sr0.3MnO3 at both 1.6 and 300 K. While the A(1g) mode softens because of gradual decrease in MnO6 rotations, the stretching mode hardens upon reduction in temperature. The distinct features of phonon modes at different temperatures are also reflected in the calculated phonon density of states. Other thermal properties such as specific heat, the Debye temperature, and Gruuneisen parameter are also presented. The decrease in the Debye temperature at 300 K indicates the effect of temperature in lattice softening. Anomalously high value of the Gruneisen parameter points out the presence of anharmonic lattice modes.

Keywords: Phonon dispersion; phonon density of states; colossal magnetoresistance; manganites


Publ.-Id: 13588

Talk on Phase retrieval and differential phase-contrast imaging with low-brilliance x-ray source

Bussmann, M.

In this talk I present the ideas and concepts behind phase contrast imaging with conventional x-ray tubes as presented by F. Pfeifer et al. in their 2006 Nature Physics article (Nature Physics Vol. 2, p. 258-261, April 2006).

Keywords: phase contrast imaging; coherence; grating; x-ray; oncoray journal club

  • Lecture (others)
    OncoRay Journal Club, 07.01.2010, OncoRay, Dresden, Deutscland

Publ.-Id: 13587

Role of soft-iron impellers on the mode selection in the VKS dynamo experiment

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

A crucial point for the understanding of the von-Karman-Sodium (VKS) dynamo experiment is the influence of soft-iron impellers. We present numerical simulations of a VKS-like dynamo with a localized permeability distribution that resembles the shape of the flow driving impellers. It is shown that the presence of soft-iron material essentially determines the dynamo process in the VKS experiment. An axisymmetric magnetic field mode can be explained by the combined action of the soft-iron disk and a rather small $\alpha$-effect parametrizing the induction effects of unresolved small scale flow fluctuations.

Keywords: dynamo; VKS; simulation; permeability; magnetohydrodynamics

Publ.-Id: 13586

HTGR Fuel Element Depletion Benchmark: Stage Three Results

Fridman, E.; Shwageraus, E.

Recently, a new numerical benchmark exercise for High Temperature Gas Cooled Reactor (HTGR) fuel depletion was defined. The purpose of this benchmark is to provide a comparison basis for different codes and methods applied for burnup analysis of HTGRs. The benchmark specifications include three different models: (1) an infinite lattice of tristructural isotropic (TRISO) fuel particles, (2) an infinite lattice of fuel pebbles, and (3) prismatic fuel including fuel and coolant channels. In this paper, we present the results of the third stage of the benchmark obtained with MCNP based depletion code BGCore and deterministic lattice code HELIOS 1.9. The depletion calculations were performed for three-dimensional model of prismatic fuel with explicitly described TRISO particles as well as for two-dimensional model in which double heterogeneity of the TRISO particles was eliminated using reactivity equivalent physical transformation (RPT). Generally good agreement in the results of calculations obtained by different methods and codes was observed.

  • Contribution to proceedings
    PHYSOR 2010 – Advances in Reactor Physics to Power the Nuclear Renaissance, 09.-14.05.2010, Pittsburgh, Pennsylvania, USA
  • Lecture (Conference)
    PHYSOR 2010 – Advances in Reactor Physics to Power the Nuclear Renaissance, 09.-14.05.2010, Pittsburgh, Pennsylvania, USA

Publ.-Id: 13585

HTGR Fuel Element Depletion Benchmark: Stage One Results

Fridman, E.; Shwageraus, E.

Recently, a new numerical benchmark exercise1 for High Temperature Gas Cooled Reactor (HTGR) fuel depletion was defined. The purpose of this benchmark is to provide a comparison basis for different codes and methods applied for burnup analysis of HTGRs.
The benchmark specifications include three different models: (1) an infinite lattice of tristructural isotropic (TRISO) fuel particles, (2) an infinite lattice of fuel pebbles, and (3) prismatic fuel including fuel and coolant channels.
In this summary, we present the results of the first stage of the benchmark.

  • Contribution to proceedings
    2009 ANS Winter Meeting, 15.-19.11.2009, Washington, DC Omni Shoreham Hotel, USA
  • Lecture (Conference)
    2009 ANS Winter Meeting, 15.-19.11.2009, Washington, DC Omni Shoreham Hotel, USA

Publ.-Id: 13584

Ultrafast carrier capture in InGaAs quantum posts

Stehr, D.; Morris, C. M.; Talbayev, D.; Wagner, M.; Kim, H. C.; Taylor, A. J.; Schneider, H.; Petroff, P. M.; Sherwin, M. S.

To explore the capture dynamics of photoexcited carriers in semiconductor quantum posts, optical pump terahertz (THz) probe and time-resolved photoluminescence spectroscopy were performed. The results of the THz experiment show that after ultrafast excitation, electrons relax within a few picoseconds into the quantum posts, which act as efficient traps. The saturation of the quantum post states, probed by photoluminescence, was reached at approximately ten times the quantum post density in the samples. The results imply that quantum posts are highly attractive nanostructures for future device applications.

Keywords: quantum post; terahertz probe; ultrafast; relaxation

Publ.-Id: 13583

X-ray investigation of the interface structure of free standing InAs nanowires grown on GaAs [(1)over-bar(1)over-bar(1)over-bar](B)

Bauer, J.; Pietsch, U.; Davydok, A.; Biermanns, A.; Grenzer, J.; Gottschalch, V.; Wagner, G.

The heteroepitaxial growth process of InAs nanowires (NW) on GaAs [(1) over bar(1) over bar(1) over bar](B) substrate was investigated by X-ray grazing-incidence diffraction using synchrotron radiation. For crystal growth we applied the vapor-liquid-solid (VLS) growth mechanism via gold seeds. The general sample structure was extracted from various electron microscopic and X-ray diffraction experiments. We found a closed GaxIn1-xAs graduated alloy layer at the substrate to NW interface which was formed in the initial stage of VLS growth with a Au-Ga-In liquid alloy. With ongoing growth time a transition from this VLS layer growth to the conventional VLS NW growth was observed. The structural properties of both VLS grown crystal types were examined. Furthermore, we discuss the VLS layer growth process.


Publ.-Id: 13582

Low temperature silicon dioxide by thermal atomic layer deposition: investigation of material properties

Hiller, D.; Zierold, R.; Bachmann, J.; Alexe, M.; Yang, Y.; Gerlach, J. W.; Stesmans, A.; Jivanescu, M.; Müller, U.; Vogt, J.; Hilmer, H.; Löper, P.; Künle, M.; Munnik, F.; Nielsch, K.; Zacharias, M.

SiO2 is the most widely used dielectric material but its growth or deposition involves high thermal budgets or suffers from shadowing effects. The low-temperature method presented here (150 °C) for the preparation of SiO2 by thermal atomic layer deposition (ALD) provides perfect uniformity and surface coverage even into nanoscale pores, which may well suit recent demands in nanoelectronics and nanotechnology. The ALD reaction based on 3-aminopropyltriethoxysilane (APTES), water and ozone provides outstanding SiO2 quality and is free of catalysts or corrosive by-products. A variety of optical, structural and electrical properties are investigated by means of infrared spectroscopy, UV-VIS spectroscopy, secondary ion mass spectrometry, capacitance-voltage- and current-voltage-measurements, electron spin resonance, Rutherford backscattering, elastic recoil detection analysis, atomic force microscopy, and variable angle spectroscopic ellipsometry. Many features, such as the optical constants (n, k), optical transmission and surface roughness (1.5 Å) are found to be similar to thermal oxide quality. Rapid thermal annealing (RTA) at 1000°C is demonstrated to significantly improve certain properties, in particular by reducing the etch rate in hydrofluoric acid, oxide charges and interface defects. Besides a small amount of OH-groups and a few atomic per mille of nitrogen in the oxide remaining from the growth and curable by RTA no impurities could be traced. Altogether, the data point to a first reliable low temperature ALD-growth process for silicon dioxide.

Publ.-Id: 13581

Molecular and Crystal Structures of Plutonyl(VI) Nitrate Complexes with N-Alkylated 2-Pyrrolidone Derivatives: Cocrystallization Potentiality of UVI and PuVI for Uniform MOX Fuel Precursor

Kim, S.-Y.; Takao, K.; Haga, Y.; Yamamoto, E.; Kawata, Y.; Morita, Y.; Nishimura, K.; Ikeda, Y.

Plutonyl(VI) nitrate complexes with N-cyclohexyl-2-pyrrolidone (NCP) and N-neopentyl-2-pyrrolidone (NNpP) were prepared, and their molecular and crystal structures were determined by single crystal X-ray analysis. The obtained compounds have the similar composition, PuO2(NO3)2(NRP)2 (NRP = NCP, NNpP), which are analogous to the corresponding UVI complexes. Both PuO2(NO3)2(NRP)2 complexes show typical structural properties of actinyl(VI) nitrates, i.e., hexagonal-bipyramidal geometry consisting of two NRP molecules and two NO3– ions located in trans positions in the equatorial plane of PuO22+ moiety, Pu=Oax = 1.73 Å, Pu–ONRP = 2.38 Å, Pu–ONO3 = 2.50 Å, and a bond angle between the U–ONRP bond and the carbonyl group of NRP ≈. 135°. The lattice constants and molecular arrangement of PuO2(NO3)2(NCP)2 were completely different from those of UO2(NO3)2(NCP)2. In contrast, these properties of PuO2(NO3)2(NNpP)2 are the same as those of UO2(NO3)2(NNpP)2. These findings provide one of criteria in selection of suitable NRP as a precipitation agent for the spent nuclear fuel reprocessing based on the precipitation method from a viewpoint of crystal engineering.

Keywords: Plutonium nitrate; precipitate; 2-pyrrolidone derivative; reprocessing; single crystal X-ray analysis

  • Crystal Growth & Design 10(2010)5, 2033-2036

Publ.-Id: 13580

Neptunium Carbonato Complexes in Aqueous Solution: An Electrochemical, Spectroscopic, and Quantum Chemical Study

Ikeda-Ohno, A.; Tsushima, S.; Takao, K.; Rossberg, A.; Funke, H.; Scheinost, A.; Bernhard, G.; Yaita, T.; Hennig, C.

The electrochemical behavior and complex structure of Np carbonato complexes, which are of major concern for the geological disposal of radioactive wastes, have been investigated in aqueous Na2CO3 and Na2CO3/NaOH solutions at different oxidation states by using cyclic voltammetry, X-ray absorption spectroscopy, and density functional theory calculations. The end-member complexes of penta- and hexavalent Np in 15 M Na2CO3 with pH = 11.7 have been determined as a transdioxo neptunyl tricarbonato complex. [NpO2(CO3)(3)](n-) (n=5 for Np-V, and 4 for Np-VI). Hence, the electrochemical reaction of the Np-V/VI redox couple merely results in the shortening/lengthening of bond distances mainly because of the change of the cationic charge of Np, without any structural rearrangement. This explains the observed reversible-like feature on their cyclic voltammograms. In contrast, the electrochemical oxidation of Np-V in a highly basic carbonate solution of 2.0 M Na2CO3/1.0 M NaOH (pH > 13) yielded a stable heptavalent Np complex of [(NpO4)-O-VII(OH)(2)](3-), indicating that the oxidation reaction from Np-V to Np-VII in the carbonate solution involves a drastic structural rearrangement from the transdioxo configuration to a square-planar-tetraoxo configuration, as well as exchanging the coordinating anions from carbonate ions (CO32-) to hydroxide ions (OH-).

Keywords: Neptunium; carbonate; redox; EXAFS; structure

Publ.-Id: 13579

Tailoring Magnetic Properties Using Ion Beam Irradiation

Lenz, K.

Magnetism is a collective phenomenon. Hence, local variations on the nanoscale of material properties, which act on the magnetic properties, affect the overall magnetism in an intriguing way. In particular important are the length scales on which a material property changes. These might be related to the exchange length, the domain wall width, a typical roughness correlation length, or a length scale introduced by patterning of the material.
Ion beam erosion can be applied to create well ordered substrate ripples with nanometer periodicity. These artificially created templates serve as a source of a predefined surface morphology and hence allow for the investigation of roughness phenomena. In contrast to that post ion beam irradiation can be used to tailor the magnetic properties of conventional thin films and multilayers. The resulting magnetic properties are neither present in non-implanted nor in homogeneously implanted films. In both cases the magnetic properties depend sensitively on the artificially introduced length scale. Ferromagnetic resonance data of irradiated Py/Ta multilayers as well as Co and Fe thin films on ripple substrates are discussed.

Keywords: FMR; irradiation; ripples; coupling

  • Lecture (others)
    Division seminar of the condensed matter theory group, 15.10.2009, Irvine, CA, USA

Publ.-Id: 13578

Spin dynamics in ferromagnets: Gilbert damping vs. two-magnon scattering

Lenz, K.

There exist several quite different damping mechanisms, which might contribute to the magnetic relaxation processes following the dynamic excitation of the spin system by ferromagnetic resonance (FMR). Most of the thin film magnetism community however seems to consider only Gilbert type damping contributions.
Using FMR and microwave frequencies between 1 and 225 GHz I will show how the different relaxation channels, i.e., dissipative, isotropic Gilbert damping G as well as anisotropic two-magnon scattering , are identified and disentangled by frequency and angle dependent FMR. In the case of Fe3Si films the scattering rates due to two-magnon scattering at crystallographic defects for spin waves propagating in [100] and [110] directions, and the Gilbert damping term are determined. Changing the film thickness from 8 to 40 nm and slightly modifying the Fe concentration influences these relaxation channels.
Finally, for the case of Ne+ irradiated Py/Ta multilayers, I will present how ion beam irradiation can be used to tailor the static and dynamic properties determined by FMR and MOKE.

Keywords: FMR; Gilbert Damping; Two-Magnon Scattering

  • Lecture (others)
    Talk at the electromagnetics group seminar, 13.10.2009, Boulder, Colorado, USA
  • Lecture (others)
    Talk at the Physics Seminar Series, 12.10.2009, Colorado Springs, USA

Publ.-Id: 13577

Determination of the Saturation Magnetization from Perpendicular Magnetic Anisotropy Measurements of Ion Irradiated Multilayers

Lenz, K.; Markó, D.; Strache, T.; Kaltofen, R.; Fassbender, J.

Ion beam irradiation and ion implantation of ferromagnetic films is a smart technique to tailor their magnetic properties and structural composition of multilayers or nanostructured samples [1,2]. Metals like Ta are commonly used as seed and cap layers in spintronic devices like Giant Magneto-Resistance sensors as Ta is chemically stable. However, it is known that 12% of Ta intermixing in Py leads to magnetically dead layers of 0.6-1.2 nm in thickness [3]. These dead layers make it impossible to determine the correct magnetic volume, which is needed to obtain the saturation magnetization from the magnetic moment measured e.g. by SQUID. This is especially true for multilayer samples which typically have a large number of interfaces.
Here we present a method to determine the saturation magnetization of Py/Ta multilayers from VNA-FMR (Vector Network Analyzer Ferromagnetic Resonance) and MOKE (Magneto-optical Kerr Effect) measurements even in the case of interfacial mixing due to ion irradiation, where SQUID magnetometry fails due to the unknown magnetic volume. Three sets of Py/Ta thin film multilayer systems were sputter-deposited on a Si/SiO2 substrate: (1xPy) is a single 20 nm thick Py layer, (5×Py) a multilayer of the structure 31 nm Ta/[4 nm Py/1 nm Ta]5/2 nm Ta and (10xPy) a multilayer of 30.5 nm Ta/[2 nm Py/0.5 nm Ta]10/2.5 nm Ta. The overall Py amount was always 20 nm and the total Ta thickness including seed and cap layer corresponds to 38 nm. Finally, the films have been irradiated with Ne ions at 40 keV with ion fluences in the range of 5×1013 to 5×1016 Ne/cm2. FMR shows that the FMR frequency vs. field dependence is significantly influenced by the amount of irradiation and number of interfaces (see Fig 1). At fluences above 2.5×1015 Ne/cm2 a significant decrease of the resonance frequency can be observed for the 1xPy samples. For the three unirradiated samples the FMR frequency decreases with an increasing number of Py/Ta repetitions, i.e. increasing number of interfaces. This decrease will be even more pronounced if larger numbers of interfaces are used. This can be explained by the higher number of neighboring Ta atoms in those cases. The deleterious effect of Ta on the ferromagnetic properties is becoming much stronger reducing the effective ferromagnetic film thickness by creating magnetically dead layers close to the interface [1,3-6]. This reduction of the saturation magnetization is directly linked to the resonance frequency. This allow to determine not only the uniaxial in-plane anisotropy field K2|| but also the saturation magnetization μ0Ms from the FMR frequency vs. field dependence. However, this can only be done, if there is only shape anisotropy but no uniaxial out-of-plane anisotropy as it is the case for our Py/Ta multilayers. From polar MOKE loops μ0Ms can be obtained by determining the perpendicular anisotropy field of the samples as well. This feature proves to be very useful here since SQUID magnetometry suffers from a major drawback: It requires the exact effective Py volume to calculate μ0Ms from the magnetic moment, which becomes more and more difficult to determine due to the increasing interfacial mixing induced by the ion irradiation and thinner Py layers. In our case, polar MOKE and FMR represent suitable alternatives since they allow μ0Ms to be determined without the knowledge of any film thickness. The good agreement with the SQUID data of the non-irradiated samples supports this (see Fig 2). ...

Keywords: FMR; MOKE, Irradiation

  • Lecture (Conference)
    11th Joint MMM-Intermag Conference, 18.-22.01.2010, Washington DC, USA

Publ.-Id: 13576

Tailoring the Néel- and Interlayer Exchange Coupling of Fe/Cr/Fe Trilayers using Rippled Substrates

Lenz, K.; Körner, M.; Liedke, M. O.; Strache, T.; Dzenisevich, S.; Keller, A.; Facsko, S.; Fassbender, J.

rtificial antiferromagnets made from magnetically coupled trilayer structures are the basis for all types of spintronic devices like MRAM, GMR sensors etc. For years major effort lay on adjusting the coupling strength by changing the spacer thickness or material. Today, nanostructures offer a different approach as they add additional coupling mechanisms like proximity effects or N\'eel orange-peel coupling to the common interlayer exchange coupling (IEC). By means of ion beam erosion techniques it is possible to create well ordered substrate ripples with nanometer periodicity. They are transferred into the films grown on these rippled substrates. Hence, such ripples are a convenient way to induce N\'eel orange-peel coupling [1] and thus allow for tailoring the magnetic properties [2] as well as the coupling strength by varying the ripple periodicity without adjusting the spacer thickness.

We have investigated the influence of rippled vs. flat Si substrates on the interlayer exchange coupling contributions in polycrystalline Fe (4nm)/Cr ($x$ nm)/Fe (4nm) thin film trilayers ($x$=0--5 nm). The substrate surface was periodically modulated (periods of 23 nm and 37 nm) by Ar$^+$ ion beam erosion. The influence of the resulting surface and interface structure on the magnetic properties has been investigated by longitudinal magneto-optical Kerr effect (MOKE) applying a Stoner-Wohlfarth model on the magnetization reversal loops. Using 23 nm period ripples, we find an orange peel type coupling, predicted by N\'eel's theory superimposed on the IEC. In addition due to the morphology of the magnetic layers, a strong uniaxial magnetic anisotropy is induced.
[1] M. Körner, K. Lenz, M.O. Liedke, T. Strache, S. Dzenisevich, A. Keller, S. Facsko, and J. Fassbender, submitted to Phys. Rev. B.
[2] J. Fassbender, T. Strache, M.O. Liedke, D. Mark\'o, S. Wintz, K. Lenz, A. Keller, S. Facsko, I. M\"onch, and J. McCord, submitted to New. J. Phys.

This work is supported by DFG grant FA 314/6-1.

Keywords: MOKE; orange-peel coupling; Neel coupling; interlayer exchange coupling; ripples

  • Poster
    Advances in Magnetic Nanostructures, 04.-09.10.2009, Vail, Colorado, USA

Publ.-Id: 13575

Determination of the Saturation Magnetization from Perpendicular Magnetic Anisotropy Measurements

Lenz, K.; Marko, D.; Strache, T.; Fassbender, J.

Over the last years the modification of magnetic parameters of thin films and multilayers by ion irradiation and implantation has become fashionable. However, especially in multilayer structures ion irradiation can lead to interfacial mixing and thus to a significant reduction of the magnetically active volume, i.e. 'dead' layers. Thus, it can be quite difficult---if not at all impossible---to determine the correct effective magnetic volume, e.g. for measurements of the saturation magnetization by SQUID. Here we show how ferromagnetic resonance (FMR) and magneto-optical Kerr effect (MOKE) measurements can be utilized to determine the saturation magnetization of irradiated Py/Ta multilayers instead and how the magnetic properties change upon irradiation.
We prepared thin films and multilayers of Py/Ta with an overall Py thickness of 20 nm and varying number of Py/Ta stacks and irradiated them with Ne ions at various fluences. FMR, MOKE, and SQUID magnetometry were used for investigation. With both, increasing ion fluences and increasing number of Py/Ta interfaces, a decrease of saturation magnetization and an increase of precessional damping can be observed. The uniaxial anisotropy of the samples is only of small magnitude and remains almost unaffected. There is, depending on the number of interfaces, a critical ion fluence at which ferromagnetic order in the multilayers vanishes.
This work is supported by DFG grant FA 314/3-1.

Keywords: FMR; ion irradiation

  • Poster
    Advances in Magnetic Nanostructures, 04.-09.10.2009, Vail, Colorado, USA

Publ.-Id: 13574

Spin wave excitations: coupling and damping effects in ultrathin films

Lenz, K.; Marko, D.; Strache, T.; Fassbender, J.

Spinwave excitations in thin film ferromagnets control several phenomena starting with spin transfer torque/spin pumping effects, magnetic relaxation and damping, to interlayer exchange coupling (IEC) and its temperature dependence. Most of them are accessible by ferromagnetic resonance (FMR).
There exist several quite different damping mechanisms, which might contribute to the magnetic relaxation processes following the excitation of the spin system. Using a broad range of microwave frequencies, I will show how these different relaxation channels, i.e., dissipative isotropic Gilbert damping as well as anisotropic two-magnon scattering, can be identified and disentangled by frequency and angle dependent FMR on Fe3Si Heusler alloys.
Changing the film thickness from 8 to 40 nm and slightly modifying the Fe concentration influences these relaxation channels [1]. Ion beam irradiation can be used to tailor the damping properties of Py/Ta multilayers after sample preparation [2].
FMR can also be used to study the interlayer exchange coupling. For single crystalline Ni/Cu/Co prototype trilayers the IEC’s temperature dependence was investigated [3]. It follows an effective power law AT n, n ≈ 1.5. The results clearly indicate that the dominant contribution to the temperature dependence is due to the excitation of thermal spin waves. This is corroborated by recently developed theory [4].

[1] Kh. Zakeri et al., Phys Rev. B 76, 104416 (2007).
[2] D. Markó, T. Strache, K. Lenz, J. Fassbender, and R. Kaltofen, submitted
[3] S.S. Kalarickal, X.Y. Xu, K. Lenz, W. Kuch, and K. Baberschke, Phys. Rev. B 75, 224429 (2007).
[4] S. Schwieger, J. Kienert, K. Lenz, J. Lindner, K. Baberschke, and W. Nolting, Phys. Rev. Lett. 98, 057205 (2007).

Keywords: Spin waves; Ferromagnetic Resonance; Interlayer exchange coupling

  • Invited lecture (Conferences)
    448. WE-Heraeus-Seminar: Excitement in magnetism: Spin-dependent scattering and coupling of excitations in ferromagnets, 22.-25.11.2009, Ringberg, Deutsch

Publ.-Id: 13573

Parallel proximal probe arrays with vertical interconnections

Sarov, Y.; Frank, A.; Ivanov, T.; Zöllner, J.-P.; Ivanova, K.; Volland, B.; Rangelow, I. W.; Brogan, A.; Wilson, R.; Zawierucha, P.; Zielony, M.; Gotszalk, T.; Nikolov, N.; Zier, M.; Schmidt, B.; Kostic, I.

This article presents the fabrication and the characteristics of 8x64, parallel, self-actuated, and independently addressable scanning proximal probes with through-silicon via interconnection passing completely through a silicon wafer. The low-resistance highly doped polysilicon through-wafer electrical interconnects have been integrated with scanning proximal probes (SPPs) to enable back side contacts to the application-specific integrated circuit used as an atomic force microscope control circuitry. Every SPP sensor contains a deflection sensor, thermally driven bimetal (bimorph) actuator, and sharp silicon tip. Dry etching-based silicon on insulator three-dimensional-micromachining technique is employed by the creation of the through-silicon vias and the SPP arrays keeping fully complementary metal-oxide semiconductor compatible process regime. The application of the vertical interconnection technology in large-scale two-dimensional cantilever arrays with off-plane bent cantilevers over the chip’s surface, in a combination with the flip-chip packaging technology allow simultaneous approach and parallel scanning of large areas in noncontact mode.

Keywords: AFM probe array; electrical through wafer interconnect; piezoresistive deflection sensor; thermally driven deflection actuator

  • Journal of Vacuum Science & Technology B 27(2009)6, 3132-3138
    DOI: 10.1116/1.3256662

Publ.-Id: 13572

Electrical Characterisation of USJs in doped Si

Ogiewa, M.; Zier, M.; Schmidt, B.

An adaption of the DHE technique, using a stepwise oxidation, as an alternative to e.g. SRP methods as a tool to determine active carrier concentration and mobility depth profiles is presented. As known from the literature, a reduction of dopand activation as well as a decrease of mobility with increasing implantation dose above the solubility limit is observed. The aim is to combine the effects known from the literature in a model system. For industrial purpose, this enables one to find a “sweet spot” of high mobility and active dopand concentration while minimizing the negative effects of a high implantation dose.

Keywords: ultra-shallow pn-junction; charge carrier concentration and mobility; dopand activation

  • Poster
    DPG Frühjahrstagung der Sektion Kondensierte Materie (SKM), 22.-27.03.2009, Dresden, Germany

Publ.-Id: 13571

EFTEM, EELS, and Cathodoluminescence in Si-implanted SiO2 Layers

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

Scanning transmission electron microscopy (STEM) in combination with electron energy loss spectroscopy (EELS) and cathodoluminescence (CL) have been used to investigate Si+-implanted amorphous silicon dioxide layers and the formation of Si nanoclusters.

Keywords: Ion implantation; Si nanoclusters

Publ.-Id: 13570

Ion-erosion-induced pattern as template for layers with magnetic anisotropy and coupling

Fassbender, J.; Liedke, M. O.; Körner, M.; Markó, D.; Lenz, K.; Facsko, S.

Ion-erosion-induced ripples are perfect template systems to systematically investigate the influence of a periodic surface modulation on magnetic properties like magnetic anisotropy in the case of single magnetic films or interlayer exchange coupling in the case of multilayer systems. One of the key advantages of these ripples is that their periodicity can easily be varied in the range between 20 and 60 nm. This matches exactly the range where magnetic properties can be affected by a surface modulation. Two different examples will be discussed: i.) ripple-induced magnetic anisotropies in soft magnetic Permalloy films [1,2] and ii.) the appearance of roughness induced magnetic coupling, e.g. Neel coupling, in multilayer systems [3]. In both cases a significant influence of the surface and interface modulation on the magnetic properties is observed, which drastically depends on the ripple periodicity itself.
[1] M.O. Liedke, B. Liedke, A. Keller, B. Hillebrands, A. Mücklich, S. Facsko, J. Fassbender, Phys. Rev. B 75, 220407 (2007).
[2] J. Fassbender, T. Strache, M.O. Liedke, D. Markó, S. Wintz, K. Lenz, S. Facsko, I. Mönch, J. McCord, New J. Phys. in press.
[3] M. Körner, K. Lenz, M.O. Liedke, T. Strache, A. Mücklich, S. Facsko, J. Fassbender, Phys. Rev. B, submitted.

Keywords: magnetism; ion erosion; templates; nanopatterning; magnetic anisotropy; magnetic damping; magnetic coupling

  • Invited lecture (Conferences)
    2009 MRS Fall Meeting, 30.11.-04.12.2009, Boston, USA

Publ.-Id: 13569

Designing soft magnetic materials by ion irradiation

McCord, J.; Fassbender, J.

The control of the relevant magnetic material parameters like magnetic anisotropy, saturation magnetization as well as the dynamic magnetic properties in ferromagnetic thin films is of significant importance for applications in spin electronics. Commonly, the magnetic anisotropy in ferromagnetic single or multi-layers is initialized either by applying a magnetic field during film deposition or by annealing a magnetic field, which results in an anisotropy aligned along the applied field direction. Another important magnetic parameter, the saturation magnetization, is mainly determined by the film's composition.
We discuss novel ways of patterning magnetic films in terms of laterally varying magnetic properties. The difference of these hybrid property films with respect to conventional ferromagnetic systems is that the magnetic behaviour is strongly influenced by the direct exchange interaction across the regions of different magnetic behaviour. This makes them comparable to magnetic multilayer structures.
Different samples of anisotropy, exchange bias, and saturation magnetization [4] modulated thin films are prepared by local ion irradiation or implantation [1-5]. The magnetization reversal processes in the two-phase materials exhibit unique features, some of them so far only known from multilayer samples. The main emphasis of the presented work is on the role of the magnetic microstructure in stripe-like magnetic hybrid structures on the overall magnetization properties. Unique effects are derived from magnetic property measurements and magnetic domain imaging.
The presented paths of film preparations provide additional degrees of freedom for the tailoring of magnetic properties and functionality of soft-magnetic thin films. The presented methods allow for a local setting of magnetic properties without irreversible structural and magnetic alterations.

[1] J. Fassbender, J. McCord, Magnetic patterning by means of ion irradiation and implantation, J. Magn. Magn. Mat. 320, 579 (2008)
[2] J. McCord, I. Mönch, J. Fassbender, A. Gerber, E. Quandt, Local setting of magnetic anisotropy in amorphous films by Co ion implantation, J. Phys. D: Appl. Phys. 42, 55006 (2009)
[3] J. McCord, L. Schultz, J. Fassbender, Hybrid soft-magnetic lateral exchange spring films prepared by ion irradiation, Adv. Mat. 20, 2009 (2008)
[4] N. Martin, J. McCord, A. gerber, T. Strache, T. Gemming, I. Mönch, N. Farag, R. Schäfer, J. Fassbender, E. Quandt, L. Schultz, Local stress engineering of magnetic anisotropy in soft magnetic thin films, Appl. Phys. Lett. 94, 62506 (2009)

Keywords: magnetism; ion irradiation; magnetic properties; material modification; patterning; microscopy

  • Invited lecture (Conferences)
    XVIII International Materials Research Congress, 16.-20.08.2009, Cancun, Mexiko

Publ.-Id: 13568

Ion Beam Mixing as Basic Technology for a Light-emitting silicon nanocrystal field-effect transistor

Schmidt, B.; Heinig, K.-H.; Beyer, V.; Stegemann, K.-H.

A light emitting field-effect transistor (LEFET) which is based on silicon nanocrystals in the gate oxide is demonstrated. The Si nanocrystals in the gate oxide were optimized for a multi-dot floating-gate nonvolatile memory operation. For this aim, ion irradiation through the MOSFET stack of 50 nm poly-Si/15 nm SiO2/Si substrate was performed with 50 keV Si+ ions. The ion beam mixing of the upper poly-Si/SiO2 interface and the lower SiO2/(001)Si interface leads to Si excess in the gate oxide. Subsequent rapid thermal annealing reforms sharp interfaces and separates the excess Si from SiO2. Adjacent to the recovered interfaces, 3-4 nm thick SiO2 zones denuded completely of excess Si have been found, whereas the more distant tails of excess Si form well-aligned narrow layers of nanocrystals with 2-3 nm diameter. LEFETs with an active gate area of 20x20 µm2 were fabricated as nMOSFET devices in a standard 0.6 µm CMOS process line. An AC voltage was applied to the gate in order to inject charges of both polarities into the lower and upper Si nanocrystal layer from the channel and the poly-Si gate of the transistor, respectively. AC voltage and frequency dependent electroluminescence spectra were recorded in the wavelength region of 400-1000 nm as a function of the annealing conditions. The performance of the LEFETs and further possibilities of optimization of efficient light emission will be discussed.

Keywords: Ion beam mixing; Si/SiO2 interface; Si nanocrystals; electroluminesence; MOS-FFET device

  • Lecture (Conference)
    Ionenstrahltreffen 2009, 06.-08.04.2009, Jena, Germany

Publ.-Id: 13567

Ion implantation in AFM cantilever array fabrication

Schmidt, B.; Zier, M.; Potfajova, J.

This paper describes the fabrication of p-type silicon piezoresistive sensing and actuating resistive heater elements monolithically integrated in AFM cantilever arrays using ion implantation for boron doping of all elements including corresponding interconnecting lines between them. Because it has been found that for p-type piezoresistivity the predicted values of the piezoresistive coefficients are approximately two times higher in ultra-shallow boron doped layers with a pn-junction depth < 10 nm than in the silicon p-type bulk material special efforts were done for the realization of ultra-shallow boron profiles using low-energy ion implantation and point defect engineering.

Keywords: Low energy ion implantation; piezoresistor; AFM cantilever array

  • Lecture (Conference)
    54th Internationales Wissenschaftliches Kolloquium, Workshop „PRONANO”,, 10.09.2009, Ilmenau, Germany

Publ.-Id: 13566

Bildrekonstruktion für die ultraschnelle Limited-Angle-Röntgen-Computertomographie von Zweiphasenströmungen

Bieberle, M.

Die ultraschnelle Röntgentomographie ist eine Messmethode, die speziell für die Untersuchung von transienten Zwei- und Mehrphasenströmungen entwickelt wurde. Speziell angepasste Bildrekonstruktionsalgorithmen ermöglichen die direkte Rekonstruktion von Phasengrenzflächen.

Keywords: Röntgen; Computertomographie; Zweiphasenströmungen; Messtechnik

  • Lecture (others)
    KOMPOST Doktorandenseminar, 10.12.2009, Dresden, FZD, Deutschland

Publ.-Id: 13565

Ultrafast electron-beam x-ray computed tomography for multi-phase flow measurement

Bieberle, M.

Ultrafast x-ray computed tomography is an imaging technique that has been optimized for transient flow measurements. Special image reconstruction algorithms enable the direct reconstruction of the physical phases of the investigated two-phase-flows.

Keywords: x-ray tomography; flow measurement; image reconstruction

  • Lecture (others)
    FZD Doktorandenseminar, 16.-18.09.2009, Krögis, Deutschland

Publ.-Id: 13564

Compositional, structural and morphological modifications of N-rich Cu3N films induced by irradiation with Cu8+ at 42 MeV

Gordillo, N.; Rivera, A.; Grötzschel, R.; Munnik, F.; Güttler, D.; Crespillo, M. L.; Agulló-López, F.; González-Arrabal, R.

N-rich Cu3N films were irradiated with Cu8+ at 42 MeV in the fluence range from 4×1011 to 1×1014 cm-2. The radiation-induced changes in the chemical composition, structural phases, surface morphology and optical properties have been characterised as a function of fluence, substrate temperature and angle of incidence of the incoming ion by means of ion beam analysis (IBA), X-ray diffraction (XRD), atomic force microscopy (AFM), profilometry and Fourier transform IR spectrophotometry (IRFT). IBA techniques reveal a very efficient sputtering of N whose yield (5×103 at/ion) is almost independent of substrate temperature (RT-300ºC) but slightly depends on the incidence angle of the incoming ion. The area density of Cu remains essentially constant within the investigated fluence range. All data suggest an electronic mechanism to be responsible for the N depletion. The release of nitrogen and the formation of Cu2O and metallic Cu are discussed on the basis of existing models.

Keywords: Copper nitride; ion beam modification of materials; ion beam mixing; swift heavy ion irradiation; electronic sputtering

Publ.-Id: 13563

Combined effects of humic matter and surfactants on PAH solubility: Is there a mixed micellization?

Lippold, H.

1. Introduction
It has been recognized that solid-liquid distribution and transport of hydrophobic contaminants such as PAH (polycyclic aromatic hydrocarbons) are governed by their interaction with mineral-bound and dissolved humic matter, acting as a sink or a mobilizing agent, respectively. As surface-active compounds, humic substances are often compared to surfactants. Emerging environmental technologies involve a deliberate application of surfactants to enhance the sorption capacity of soils and aquifer materials, or to increase the efficiency of soil washing procedures and pump-and-treat operations for groundwater decontamination. Whereas contaminant binding to humics as well as to surfactants has been extensively studied, there is a notable lack of literature on their combined action in mixed systems. This topic is, however, important because environmental influences of surfactants are inevitably associated with the effects of the ubiquitous natural organics. Since both are amphiphilic, it seems conceivable that mixed micelles can be formed, involving synergistic or antagonistic effects in the solubilization of organic compounds.
In this study, we have examined the joint influence of humic acid and surfactants (cationic, anionic) on the water solubility of pyrene as a representative of PAH, at surfactant concentrations below and above the critical micelle concentration (CMC). In order to detect and characterize interaction processes, we have investigated the octanol-water partitioning of humic acid in the presence of various surfactants, using radiolabelled humic material. In particular, the hypothesis of a micellar nature of dissolved humic substances has been addressed.

2. Materials and Methods: omitted here

3. Results and Discussion
The water solubility of pyrene is increased in the presence of humic acid, which acts as a carrier due to hydrophobic interaction of both components. When adding the cationic surfactant dodecyltrimethylammonium bromide (DTAB), this solubility enhancement was found to be cancelled; the humic colloids were precipitated as a consequence of charge compensation by the organo-cations.
Interestingly, an antagonistic effect was also observed on addition of an anionic surfactant, sodium dodecylsulfate (SDS). While no precipitation was induced in this case, the solubility of pyrene was reduced by half and remained constant on further addition. Only at surfactant concentrations above the CMC, the solubility increased sharply owing to micellar incorporation. The presence of HA did not cause any change in the CMC of SDS, as is normally observed on addition of a second amphiphilic compound. Furthermore, the effects of HA and micellar SDS on pyrene solubility turned out to be strictly additive. Consequently, they are based on distinct processes, occurring independently of each other, i.e., there is no mixed micellization with humic molecules acting as a co-surfactant.
The octanol-water partition ratios of HA changed significantly in the presence surfactants. The partitioning equilibrium was shifted towards the organic phase on addition of cationic surfactants, and towards the aqueous phase on addition of anionic surfactants. Based on these findings, different modes of interaction could be identified, providing an explanation for the decline in pyrene solubilization in systems of HA and SDS. Obviously, a competitive situation arises in the hydrophobic binding of the PAH and the surfactant tail groups. The fact that the pyrene molecules cannot be displaced completely supports the proposition that different binding sites exist in humic colloids: weak near-surface sites and strong inner sites.
The size distribution of the colloids was found to be unaffected by the association with anionic as well as with cationic surfactants. A general micellar character is thus unlikely since a co-aggregation should then entail substantial disruptions and rearrangement processes.

4. Conclusions: omitted here

  • Poster
    15th meeting of the International Humic Substances Society (IHSS 15), 27.06.-02.07.2010, Tenerife, Espana

Publ.-Id: 13562

Role of impurities and dislocations for the unintentional n-type conductivity in InN

Darakchieva, V.; Barradas, N. P.; Xie, M.-Y.; Lorenz, K.; Alves, E.; Schubert, M.; Persson, P. O. A.; Giuliani, F.; Munnik, F.; Hsiao, C. L.; Tu, L. W.; Schaff, W. J.

We present a study on the role of dislocations and impurities for the unintentional n-type conductivity in high-quality InN grown by molecular beam epitaxy. The dislocation densities and H profiles in films with free electron concentrations in the low 1017 cm-3 and mid 1018 cm-3 range are measured, and analyzed in a comparative manner. It is shown that dislocations alone could not account for the free electron behavior in the InN films. On the other hand, large concentrations of H sufficient to explain, but exceeding substantially, the observed free electron densities are found. Furthermore, enhanced concentrations of H are revealed at the film surfaces, resembling the free electron behavior with surface electron accumulation. The low-conductive film was found to contain C and it is suggested that C passivates the H donors or acts as an acceptor, producing compensated material in this case. Therefore, it is concluded that the unintentional impurities play an important role for the unintentional n-type conductivity in InN. We suggest a scenario of H incorporation in InN that may reconcile the previously reported observations for the different role of impurities and dislocations for the unintentional n-type conductivity in InN.

Publ.-Id: 13561

Numerical simulation of the insulation material transport in a PWR core under loss of coolant conditions

Höhne, T.; Grahn, A.; Kliem, S.; Rohde, U.; Weiss, F.-P.

In 1992, strainers on the suction side of the ECCS pumps in Barsebäck NPP Unit 2 became partially clogged with mineral wool after a safety valve opened because steam impinged on the thermally-insulated equipment and released mineral wool. This event pointed out that strainer clogging in the course of a loss-of-coolant accident is an issue and induced many investigations to understand and prevent strainer clogging effects.

Modifications of the insulation material, the strainer area and mesh size were carried out in most of the German NPPs. Moreover, back flushing procedures to remove the mineral wool from the strainers and differential pressure measurement were implemented to assure the performance of emergency core cooling during the containment sump recirculation mode.

Nevertheless, it cannot be completely ruled out, that a limited amount of the smaller fractions of insulation material could be transported into the RPV. During a postulated cold leg LOCA with hot leg ECC injection, the fibres enter the upper plenum and can accumulate at the fuel element spacer grids, preferably at the uppermost grid level. This effect might affect the ECC flow into the core and could result in degradation of core cooling.

It was the aim of the numerical simulations presented to study where and how many mineral wool fibers are deposited at the upper spacer grid. The 3D, time dependent, multi-phase flow problem was modelled by applying the CFD code ANSYS CFX.

The spacer grids were modeled as a strainer, which completely retains all the insulation material that reaches the uppermost spacer level. There, the accumulation of the insulation material gives rise to the formation of a compressible fibrous layer, the permeability of which to the coolant flow is calculated in terms of the local amount of deposited material and the local value of the superficial liquid velocity.

Before the switch over of the ECC injection from the flooding mode to the sump mode, the coolant circulates in an inner convection loop in the core extending from the lower plenum to the upper plenum. The CFD simulations have shown that after starting the sump mode, the ECC water injected through the hot legs flows down into the core via so-called "brake through channels" located in the outer core region where the downward leg of the convection role had established. The hotter, lighter coolant rises in the center of the core. As a consequence, the insulation material is preferably deposited at the uppermost spacer grids positioned in the break through zones. This means that the fibres are not uniformly deposited over the core cross section.

When the inner recirculation stops later in the transient, insulation material can also be collected in other regions of the core cross section at the level of the upper spacer grids. Nevertheless, with a total of 2.7 kg fiber material deposited at the uppermost spacer level, the pressure drop over the fiber cake is not higher than 8 kPa and all the ECC water could still enter the core. The CFD calculation does not yet include steam production in the core and also does not include re-suspension of the insulation material during reverse flow. This will certainly further improve the coolability of the core.

Keywords: CFD; Fibre; Core; PWR

  • Contribution to proceedings
    18th International Conference on Nuclear Engineering, 17.-21.05.2010, Xi'an, China
  • Lecture (Conference)
    18th International Conference on Nuclear Engineering, 17.-21.05.2010, Xi'an, China

Publ.-Id: 13560

Temperature dependence of the crossover between the near-infrared Er and defect-related photoluminescence bands of Ge-rich Er-doped SiO2 layers

Kanjilal, A.; Rebohle, L.; Prucnal, S.; Voelskow, M.; Skorupa, W.; Helm, M.

Temperature-dependent photoluminescence of Ge-rich SiO2 in the presence or absence of Er shows a crossover between defect-related (15–150 K) and Er-related (150–295 K) emission within 1525 and 1440 nm. The origin of the near-infrared defect-related bands is discussed in the light of recombination of localized excitons in luminescence centers at the Ge cluster/SiO2 interface. Time-resolved photoluminescence further enables us to illustrate the observed 1.53 um Er emission above 150 K in terms of a phonon-assisted nonradiative energy-transfer process from the luminescence centers to the Er3+ ions.

Keywords: PL; Er; Ge clusters

Publ.-Id: 13559

Establishing the mechanism of thermally induced degradation of ZnO:Al electrical properties using synchrotron radiation

Vinnichenko, M.; Gago, R.; Cornelius, S.; Shevchenko, N.; Rogozin, A.; Kolitsch, A.; Munnik, F.; Möller, W.

X-ray absorption near edge structure and x-ray diffraction studies with synchrotron radiation have been used to relate the electrical properties of ZnO:Al films to their bonding structure and phase composition. It is found that Al-sites in an insulating metastable homologous (ZnO)3Al2O3 phase are favored above a certain substrate temperature (Ts) leading to deterioration of both the crystallinity and the electrical properties of the films. The higher film resistivity is associated with lower carrier mobility due to increased free electron scattering. Lower metal to oxygen flux ratios during deposition expand the range of Ts at which low-resistivity films are obtained.

Keywords: transparent conductive oxides; Al-doped ZnO; reactive pulsed magnetron sputtering; electrical properties; XANES

Publ.-Id: 13558

DREAMS - a universal AMS facility based on the 6 MV - TandetronTM at FZD in Dresden

Akhmadaliev, S.; Kolitsch, A.; Merchel, S.; Möller, W.

A new accelerator mass spectrometry (AMS) system has been installed at the Forschungszentrum Dresden-Rossendorf (FZD). The system is based on a 6 MV-TandetronTM accelerator produced by High Voltage Engineering Europe (HVEE). The AMS facility is specified for measurements of 10Be, 14C, 26Al, 36Cl, 41Ca and 129I with isotopic ratios of 10-10 - 10-16 and precision better than 0.3% for 14C/12C.
The system uses a bouncer sequential injector with two Cs-sputter ion sources and a 54°-electrostatic analyser (ESA). On the high-energy site it has a 90°-analysing magnet, Faraday-Cups for stable nuclides, a 35°-ESA, a post-stripper foil, and a 30°-vertical magnet for suppression of interfering species, and gas ionisation chamber for detection of radionuclides [1].
The Cockroft-Walton type high voltage generator provides a terminal voltage of up to 6 MV. The system is additionally equipped with a multipurpose ion injector containing a third Cs-sputter ion source and a duoplasmatron for high-energy ion implantation and ion-beam materials analysis.

[1] M. Arnold et al., accepted for Nucl. Instr. and Meth. B (Proceedings
of IBA-2009).

Keywords: Accelerator mass spectrometry; AMS

  • Lecture (Conference)
    DPG Frühjahrstagung der Sektion AMOP (SAMOP), 08.-12.03.2010, Hannover, Deutschland


Publ.-Id: 13557

Comparison among MCNP-based depletion codes applied to burnup calculations of pebble-bed HTR lattices

Bomboni, E.; Cerullo, N.; Fridman, E.; Lomonaco, G.; Shwageraus, E.

The double-heterogeneity characterising pebble-bed high temperature reactors (HTRs) makes Monte Carlo based calculation tools the most suitable for detailed core analyses. These codes can be successfully used to predict the isotopic evolution during irradiation of the fuel of this kind of cores. At the moment, there are many computational systems based on MCNP that are available for performing depletion calculation. All these systems use MCNP to supply problem dependent fluxes and/or microscopic cross sections to the depletion module. This latter then calculates the isotopic evolution of the fuel resolving Bateman's equations.
In this paper, a comparative analysis of three different MCNP-based depletion codes is performed: Montburns2.0, MCNPX2.6.0 and BGCore. Monteburns code can be considered as the reference code for HTR calculations, since it has been already verified during HTR-N and HTR-N1 EU project. All calculations have been performed on a reference model representing an infinite lattice of thorium-plutonium fuelled pebbles. The evolution of k-inf as a function of burnup has been compared, as well as the inventory of the important actinides.
The k-inf comparison among the codes shows a good agreement during the entire burnup history with the maximum difference lower than 1%. The actinide inventory prediction agrees well. However significant discrepancy in Am and Cm concentrations calculated by MCNPX as compared to those of Monteburns and BGCore has been observed. This is mainly due to different Am-241 (n,γ) branching ratio utilized by the codes.
The important advantage of BGCore is its significantly lower execution time required to perform considered depletion calculations. While providing reasonably accurate results BGCore runs depletion problem about two times faster than Monteburns and two to five times faster than MCNPX.

Keywords: HTR; Pebble-bed; MCNP; Monte-Carlo depletion codes; MCNPX; Monteburns; BGCore

  • Nuclear Engineering and Design 240(2010), 918-924

Publ.-Id: 13556

Silicon Cluster Aggregation in Silica Layers

Fitting, H.-J.; Fitting Kourkoutis, L.; Salh, R.; Kolesnikova, E. V.; Zamoryanskaya, M. V.; von Czarnowski, A.; Schmidt, B.

Scanning transmission electron microscopy (STEM) in combination with electron energy loss spectroscopy (EELS) and cathodoluminescence (CL) have been used to investigate Si+-implanted amorphous silicon dioxide layers and the formation of Si nanoclusters. The microstructure of the Si doped silica films was studied by energy filtered transmission electron microscopy (EFTEM) in a 200 kV FEI Tecnai F20 TEM. The samples were amorphous, thermally grown 500 nm SiO2 layers on Si substrate doped by Si+ ions with an energy of 150 keV up to an atomic dopant fraction of about 4 at%. A thermal post-annealing leads to formation of silicon clusters with sizes 1-5 nm and concentrations of about 1018 cm-3. Respective cathodoluminescence spectra in the near IR region indicate such structural changes by appearance of an additional band at 1.35 eV as well as additional emission bands in the visible green-yellow region.

Keywords: Si ion implantation; Nanoclusters; Understoichiometric silica; Cathodoluminescence

Publ.-Id: 13554

Parallel Hardware-accelerated Particle in Cell (PiC) Physics using MPI, pThreads and CUDA: Implementing a Prototype

Juckeland, G.; Bussmann, M.

Presentation of the parallel communication scheme implemented by PIConGPU

Keywords: particle-in-cell; algorithm; parallel; pic; simulation; gpu; cluster; network; mpi; threads; pthreads; message-passing-interface; laser; plasma

  • Invited lecture (Conferences)
    Herausforderungen des HPC in Deutschland, 29.09.2009, Leogang, Österreich

Publ.-Id: 13553

New approaches investigating production rates of in-situ produced terrestrial cosmogenic nuclides

Merchel, S.; Braucher, R.; Benedetti, L.; Bourlès, D.

In-situ produced cosmogenic nuclides have proved to be valuable tools for environmental and Earth sciences. However, accurate application of this method is only possible, if terrestrial production rates in a certain environment over a certain time period and their depth-dependence within the exposed material are exactly known. Unfortunately, the existing data and models differ up to several tens of percent.
Thus, one of the European project CRONUS-EU goals is the high quality calibration of the 36Cl production rate by spallation at independently dated surfaces. As part of fulfilling this task we have investigated calcite-rich samples from four medieval landslide areas in the Alps: Mont Granier, Le Claps, Dobratsch, and Veliki Vrh (330-1620 m, 1248-1442 AD).
For investigating the depth-dependence of the different nuclear reactions, especially, the muon- and thermal neutron-induced contributions, we have analysed mixtures of carbonates and siliceous conglomerate samples - for 10Be, 26Al, and 36Cl - exposed at different shielding depths and taken from a core drilled in 2005 at La Ciotat, France (from surface to 11 m shielding).
AMS of 36Cl was performed at LLNL and ETH, 10Be and 26Al at ASTER.

Acknowledgments: Thanks to V. Alfimov, M. Arnold, G. Aumaître, J. Borgomano, R. Finkel, I. Mrak, and J.M. Reitner.

Keywords: accelerator mass spectrometry; cosmogenic nuclides; TCN

  • Lecture (Conference)
    DPG Frühjahrstagung des Arbeitskreises Atome, Moleküle, Quantenoptik und Plasmen (AMOP), 08.-12.03.2010, Hannover, Deutschland

Publ.-Id: 13552

Die Jagd nach dem Feldrekord - Forschung in hohen Magnetfeldern

Wosnitza, J.

es hat kein Abstract vorgelegen!

  • Invited lecture (Conferences)
    Studium Generale "Naturwissenschaft Aktuell", 03.12.2009, Dresden, Deutschland

Publ.-Id: 13551

Die Jagd nach dem Feldrekord - Forschung in hohen Magnetfeldern

Wosnitza, J.

Was sind Magnetfelder? Wo findet man sie? Wie erzeugt man sie und zu was sind sie nutze? Antworten auf diese Fragen sollen in dem Vortrag durch Vorstellung der weltweiten Bestrebungen, immer höhere Magnetfelder zu erreichen, gegeben werden. Ähnlich wie z. B. Druck und Temperatur haben magnetische Felder einen tief greifenden Einfluss auf den Zustand und Zustandsänderungen der Materie. Untersuchungen von Materialien in hohen Magnetfeldern sind daher mittlerweile Standard und eine Vielzahl von Anwendungen in unserem täglichen Leben sind ohne Magnetfeldeffekte undenkbar. In der Forschung wird der stetig wachsende Bedarf an möglichst großen Magnetfeldstärken durch Hochfeldlaboratorien abgedeckt. In dem neu aufgebauten Hochfeld-Magnetlabor Dresden sollen demnächst gepulste Magnetfelder bis zu 100 Tesla erzeugt werden. Erste Hochfeldmagnete sind in Betrieb und seit 2007 hat neben der Eigenforschung der Nutzerbetrieb begonnen. Der momentane Status des Labors, die Schwierigkeiten, die zur Erzeugung so hoher Magnetfelder überwunden werden müssen, und exemplarische wissenschaftliche Ergebnisse aus Hochfeldstudien sollen vorgestellt werden.

  • Invited lecture (Conferences)
    Technische Universität München, 13.11.2009, München - Garching, Deutschland

Publ.-Id: 13550

Research at the new Dresden High Magnetic Field Laboratory

Wosnitza, J.

High magnetic fields are one of the most powerful tools available to scientists for the study, modification, and control of the state of matter. The application of magnetic fields, therefore, has become a commonly used instrument for condensed-matter physics. For the observation of many phenomena very high magnetic fields are essential. Consequently, the demand for the highest possible magnetic-field strengths is increasing. At the Dresden High Magnetic Field Laboratory (Hochfeld-Magnetlabor Dresden, HLD), that in 2007 has opened its doors for external users, pulsed magnetic fields up to 70 T are available and a European record field of 87.2 T have been reached. The laboratory has set the ambitious goal of reaching 100 T on a 10 ms timescale. As a unique feature, a free-electron-laser facility next door allows high-brilliance radiation to be fed into the pulsed field cells of the HLD, thus making possible high-field magneto-optical experiments in the range 3-250 µm. Cryotechniques and different sample probes for a broad range of experimental techniques custom designed for the pulsed magnets are readily available for users. In-house research of the HLD focuses on electronic properties of strongly correlated materials at high magnetic fields. Besides introducing some highlights of the HLD experimental infrastructure, some recent scientific research results will be presented. This includes e.g. the detection of Shubnikov-de Haas oscillations in electron-doped high-temperature superconductors that allowed to unravel a drastic change of the Fermi-surface topology upon doping [1]. Furthermore, pulsed-field experiments at the HLD allowed to observe the field-induced conductance switching in single-walled carbon nanotubes

  • Invited lecture (Conferences)
    6th International Symposium on High Magnetic Field Spin science in 100T, 07.-09.12.2009, Sendai, Japan

Publ.-Id: 13549

Optical spectroscopy of superconductors in terahertz frequency range

Pronin, A.

es hat kein Abstract vorgelegen

  • Invited lecture (Conferences)
    Universität Göttingen, 16.11.2009, Göttingen, Deutschland

Publ.-Id: 13548

Exploring the spin-1/2 frustrated square lattice model with high-field magnetization studies

Tsirlin, A. A.; Schmidt, B.; Skourski, Y.; Nath, R.; Geibel, C.; Rosner, H.

We report on high-field magnetization measurements for a number of layered vanadium phosphates that were recently recognized as spin- 1/2 frustrated square lattice compounds with ferromagnetic nearest-neighbor couplings (J1) and antiferromagnetic next-nearest-neighbor couplings (J2). The saturation fields of the materials lie in the range from 4 to 24 T and show excellent agreement with the previous estimates of the exchange couplings deduced from low-field thermodynamic measurements. The consistency of the high-field data with the regular frustrated square lattice model provides experimental evidence for a weak impact of spatial anisotropy on the nearest-neighbor couplings in layered vanadium phosphates. The variation in the J2 /J1 ratio within the compound family facilitates the experimental access to the evolution of the magnetization curve upon the change in the frustration magnitude. Our results support the recent theoretical prediction by Thalmeier et al. [Phys. Rev. B 77, 104441 (2008)] and give evidence for the enhanced bending of the magnetization curves due to the increasing frustration of the underlying spin system

  • Physical Review B 80(2009), 132407

Publ.-Id: 13547

Interplay of frustration and magnetic field in the two-dimensional quantum antiferromagnet Cu(tn)Cl-2

Orendacova, A.; Cizmar, E.; Sedlakova, L.; Hanko, J.; Kajnakova, M.; Orendac, M.; Feher, A.; Xia, J.; Yin, L.; Pajerowski, D.; Meisel, M.; Zelenak, V.; Zvyagin, S.; Wosnitza, J.

Specific heat and ac magnetic susceptibility measurements, spanning low temperatures (T >= 40 mK) and high-magnetic fields (B <= 14 T), have been performed on a two-dimensional (2D) antiferromagnet Cu(tn)Cl-2 (tn=1,3-diaminopropane=C3H10N2). The compound represents a S = 1/2 spatially anisotropic triangular antiferromagnet realized by a square lattice with nearest-neighbor (J/kB = 3 K), frustrating next-nearest-neighbor (0 < J'/J < 0.6), and interlayer (|J''/J| approximate to 10-3) interactions. The absence of long-range magnetic order down to T = 60 mK in B = 0 and the T-2 behavior of the specific heat for T <= 0.4 K and B >= 0 are considered evidence of a high degree of 2D magnetic order. In fields lower than the saturation field, Bsat = 6.6 T, a specific heat anomaly, appearing near 0.8 K, is ascribed to bound vortex-antivortex pairs stabilized by the applied magnetic field. The resulting magnetic phase diagram is remarkably consistent with the one predicted for a square lattice without a frustrating interaction, expect that Bsat is shifted to values lower than expected. Potential explanations for this observation, as well as the possibility of a Berezinski-Kosterlitz-Thouless (BKT) phase transition in a spatially anisotropic triangular magnet with the collinear Neel ground state, are discussed.

  • Physical Review B 80(2009), 144418

Publ.-Id: 13546

Effects of two gaps and paramagnetic pair breaking on the upper critical field of SmFeAsO0.85 and SmFeAsO0.8F0.2 single crystals

Lee, H.-S.; Bartkowiak, M.; Park, J.-H.; Lee, J.-Y.; Kim, J.-Y.; Sung, N.-H.; Cho, B. K.; Jung, C.-H.; Kim, J. S.; Lee, H.-J.

We investigated the temperature dependence of the upper critical field [Hc2(T)] of fluorine-free SmFeAsO0.85 and fluorine-doped SmFeAsO0.8F0.2 single crystals by measuring the resistive transition in low static magnetic fields and in pulsed fields up to 60 T. Both crystals show that Hc2(T)’s along the c axis [Hc2 c(T)] and in an ab-planar direction [Hc2 ab(T)] exhibit a linear and a sublinear increase, respectively, with decreasing temperature below the superconducting transition. Hc2(T)’s in both directions deviate from the conventional one-gap Werthamer-Helfand-Hohenberg theoretical prediction at low temperatures. A two-gap nature and the paramagnetic pair-breaking effect are shown to be responsible for the temperature-dependent behavior of Hc2 c and Hc2 ab, respectively.

  • Physical Review B 80(2009), 144512

Publ.-Id: 13545

Modifications in structural and optical properties of Mn-ion implanted CdS thin films

Chandramohan, S.; Kanjilal, A.; Strache, T.; Tripathi, J. K.; Sarangi, S. N.; Sathyamoorthy, R.; Som, T.

In this paper, we report on modifications in structural and optical properties of CdS thin films due to 190 keV Mn-ion implantation at 573 K. Mn-ion implantation induces disorder in the lattice, but does not lead to the formation of any secondary phase, either in the form of metallic clusters or impurity complexes. The optical band gap was found to decrease with increasing ion fluence. This is explained on the basis of band tailing due to the creation of localized energy states generated by structural disorder. Enhancement in the Raman scattering intensity has been attributed to the enhancement in the surface roughness due to increasing ion fluence. Mn-doped samples exhibit a new band in their photoluminescence spectra at 2.22 eV, which originates from the d–d (4T1 → 6A1) transition of tetrahedrally coordinated Mn2+ ions.

Keywords: CdS thin films; Mn-ion implantation; Structural properties; Optical properties

Publ.-Id: 13544

Ion irradiation of permalloy: From thin magnetic films to lateral exchange spring nanostructures

Strache, T.; Reichel, L.; Wintz, S.; Fritzsche, M.; Mönch, I.; Raabe, J.; Martin, N.; McCord, J.; Körner, M.; Markó, D.; Romstedt, F.; Fassbender, J.

Due to its low coercivity and negligible magnetostriction, permalloy (Ni80Fe20) is one of the most used materials in thin film and micro/nano magnetism. By means of ion irradiation the magnetic properties can be modified [1], and in combination with a lithographically defined mask or the use of a focused ion beam magnetic patterning can be achieved [2]. The changes of the magnetic properties due to ion-solid- interaction must be related to different origins, e.g. direct implantation, surface sputtering and interfacial mixing. Their respective influence depends strongly on the chosen multilayer system as well as on the implantation conditions.
Here we present a systematic study of irradiation of permalloy with common ion species. Special emphasis is put on the separation of the effect of direct implantation from mixing and sputtering. By transferring this knowledge to laterally resolved irradiation, direct exchange coupled magnetic stripes of submicron width are created. The magnetization reversal process of this lateral exchange spring structures depends on the interaction between adjacent soft and hard magnetic stripes. By scaling the stripe sizes down, fundamental questions regarding the maximum domain wall density and the domain–wall interaction may be addressed.

[1] J. Fassbender et al., Physical Review B 73, 184410 (2006).
[2] J. McCord et al., Advanced Materials 20, 2090 (2008).

  • Lecture (Conference)
    Workshop Ionenstrahlphysik, 06.-08. April 2009, Friedrich-Schiller-Universität Jena, 06.04.2009, Jena, Deutschland

Publ.-Id: 13543

Tuning Coercivity in CoCrPt-SiO2 Hard Disk Material

Strache, T.; Tibus, S.; Springer, F.; Rohrmann, H.; Albrecht, M.; Lenz, K.; Fassbender, J.

In order to increase the storage density of modern computer disk drives and to push the superparamagnetic limit to the smallest achievable bit sizes further, smaller grains with even larger magnetic anisotropies are required, which are accompanied by large coercive fields obstructing the writing process. One route to overcome this problem is to independently reduce the coercive field without altering anisotropy and remanence by tailoring the intergranular exchange in granular CoCrPt-SiO2 films. Here we demonstrate that by means of ion implantation of Co and Ne a continuous reduction of the coercive field can be achieved without significant modification of the remaining magnetic parameters. In addition to the magnetization reversal behavior of the entire film investigated by magneto-optic Kerr effect and SQUID magnetometry, also the magnetic domain configuration in the demagnetized state is imaged by magnetic force microscopy.

Keywords: magnetism; ion irradiation; magnetic storage; hard disk; coercivity; anisotropy; magnetic domains

  • Lecture (Conference)
    DPG Spring Meeting of the Condensed Matter Section, March 22-27, 2009, Dresden, Germany, 25.03.2009, Dresden, Deutschland

Publ.-Id: 13542

Hochintensitätslaser und ihre Anwendungen

Bussmann, M.; Kroll, F.

Der Vortrag gibt einen Überblick über die nichtlinearen optischen Effekte die im Aufbau und der Diagnostik hochintensiver Kurzpulslaser eine Rolle spielen sowie über die Anwendungen moderner Hochleistungslaser in der Strahlenphysik.

The talk gives an overview of those nonlinear optical effects which are important for building high-intensity short-pulse lasers and their diagnostics as well as the application of high-power lasers in beam physics.

Keywords: high-intensity lasers; nonlinear optics; diagnostics; ultra-short laser pulses; particle acceleration; beam physics; radiation sources

  • Invited lecture (Conferences)
    Lectures on laser and plasma physics, 16.12.2009, TFH Wildau, Berlin, Germany

Publ.-Id: 13541

Di-Electrons from Resonances in Nucleon-Nucleon Collisions

Kaptari, L. P.; Kämpfer, B.

The contribution of the low-lying nucleon resonances P-33(1232), P-11(1440), D-13(1520), and S-11(1535) to the invariant-mass spectra of di-electrons stemming from the exclusive processes pp -> pp e(+)e(-) and pn -> pn e(+)e(-) is investigated within a fully covariant and gauge-invariant diagrammatical approach. We employ, within the one-boson exchange approximation, effective nucleon-meson interactions including the exchange mesons pi, eta, sigma, omega, and rho as well as excitations and radiative decays of the above low-lying nucleon resonances. The total contribution of these resonances is dominant; however, bremsstrahlung processes in pp and, in particular, pn collisions at beam energies of 1-2 GeV are still significant in certain phase-space regions.

Publ.-Id: 13540

Surface nanostructures by single highly charged ions

Facsko, S.; Heller, R.; El-Said, A.; Meissl, W.; Aumayr, F.

It has recently been demonstrated that the impact of individual, slow but highly charged ions on various surfaces can induce surface modifications with nanometer dimensions. Generally, the size of these surface modifications (blisters, hillocks, craters or pits) increases dramatically with the potential energy of the highly charged ion, while the kinetic energy of the projectile ions seems to be of little importance. This paper presents the currently available experimental evidence and theoretical models and discusses the circumstances and conditions under which nanosized features on different surfaces due to the impact of slow highly charged ions can be produced.

Keywords: nanostructures; highly charge ions; AFM

Publ.-Id: 13538

Interaction of uranium(VI) towards glutathione - an example to study different functional groups in one molecule

Frost, L.; Geipel, G.; Viehweger, K.; Bernhard, G.

Glutathione, the most abundant thiol compound of the cell, has a great binding potential towards heavy metal ions. Hence it might influence the distribution of actinides on a cellular level. The unknown strength of the interaction of uranium(VI) with glutathione at physiologically relevant pH is subject of this paper and was studied with UV-vis spectroscopy and time-resolved laser-induced fluorescence spectroscopy (TRLFS). The complex stability constant of UO2H2GS+ at 0 ionic strength, log β121 , was calculated to be 39.09 ± 0.15 and 39.04 ± 0.02 in case of UV-vis spectroscopy and TRLFS respectively. Therefore the average formation constant for UO22+ + H2GS- = UO2H2GS+ at 0 ionic strength can be assigned to be log K11 = 19.83±0.15.
Furthermore it was demonstrated, that derivatization of the ligand associated with an enhancement of the ligand’s spectroscopic properties can be used for the determination of complex stability constants and to assess the coordination chemistry more detailed. Using UV-vis spectroscopy, the stability constant of the complex between UO22+ and glutathione pyruvate S-conjugate, a well absorbing ligand in contrast to glutathione, was calculated to be > 39.24 ± 0.08. Furthermore the interaction of UO22+ with glutathione derivatized with the fluorescent label monobromobimane was examined with femtosecond laser fluorescence spectroscopy. Thereby the stability constant of the 1:1 complex was determined to be > 39.35 ± 0.02. Although the thiol group of glutathione was blocked a strong coordination was found. Thus a significant involvement of the thiol group in the coordination of U(VI) can be excluded.

Keywords: Uranium; Glutathione; Complexation; Derivatization; UV-vis spectroscopy; TRLFS

  • Contribution to proceedings
    APSORC'09, 29.11.-04.12.2009, Napa, USA
  • Open Access Logo Proceedings in Radiochemistry 1(2011), 357-362
    DOI: 10.1524/rcpr.2011.0063

Publ.-Id: 13537

Phase separation in carbon:transition metal nanocomposite thin films

Berndt, M.

kein Abstract vorhanden

  • Open Access Logo Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; FZD-527 2009
    ISSN: 1437-322X


Publ.-Id: 13536

Visualization of freckle formation induced by forced melt convection in solidifying GaIn alloys

Boden, S.; Eckert, S.; Gerbeth, G.

A bottom-up solidification of a Ga-25%In alloy under the influence of buoyancy-driven and electromagnetically driven convection was investigated by X-ray radioscopy. The main effect of the flow on the solidification is determined by the flow-induced redistribution of solute concentration which results in a change of the growth direction of the dendrites and the preference of secondary branches for an accelerated or decelerated growth. The experiments demonstrate how the interdendritic flow contributes to the formation of spacious segregation freckles.

Keywords: directional solidification; dendritic growth; convection; segregation; X-ray radioscopy

  • Materials Letters 64(2010), 1340-1343

Publ.-Id: 13534

Advanced spectroscopic synchrotron techniques to unravel the intrinsic properties of dilute magnetic oxides: the case of Co:ZnO

Ney, A.; Opel, M.; Kaspar, T. C.; Ney, V.; Ye, S.; Ollefs, K.; Kammermeier, T.; Bauer, S.; Nielsen, K.-W.; Goennenwein, S. T. B.; Engelhard, M. H.; Zhou, S.; Potzger, K.; Simon, J.; Mader, W.; Heald, S. M.; Cezar, J. C.; Wilhelm, F.; Rogalev, A.; Gross, R.; Chambers, S. A.

The use of synchrotron-based spectroscopy has revolutionized the way we look at matter. X-ray absorption spectroscopy (XAS) using linear and circular polarized light offers a powerful toolbox of element-specific structural, electronic, and magnetic probes that is especially well suited for complex materials containing several elements. We use the specific example of Zn1−xCoxO (Co:ZnO) to demonstrate the usefulness of combining these XAS techniques to unravel its intrinsic properties. We demonstrate that as long as phase separation or excessive defect formation is absent, Co:ZnO is paramagnetic. We can establish quantitative thresholds based on four reliable quality indicators using XAS; samples which show ferromagnet-like behaviour fail to meet these quality indicators, and complementary experimental techniques indeed prove phase separation. Careful analysis of XAS spectra is shown to provide quantitative information on the presence and type of dilute secondary phases in a highly sensitive, non-destructive manner.

  • Open Access Logo New Journal of Physics 12(2010), 013020

Publ.-Id: 13533

Capped Colloidal Particular: A Model System for Spin Arangements

Erbe, A.

no abstract submitted

Keywords: colloids; soft matter; model systems

  • Invited lecture (Conferences)
    SPP 1296 Workshop, 13.-14.10.2009, Bayreuth, Deutschland

Publ.-Id: 13531

Colloids: Mesoscopic model systems of matter on a nano scale

Leiderer, P.; Erbe, A.

Colloidal suspensions consist of small particles in (mostly) aqueous medium, which allow to model phenomena in condensed matter on a mesoscopic scale. Due to the dominant length and time scales such systems are readily accessible by means of video microscopy. In this talk examples for both the structure of colloidal particle ensembles and transport phenomena in colloidal systems will be discussed. In the case of structure formation, e.g., configurations of particles with a mesoscopic "spin" will be presented, realized by colloidal spheres with permanent magnetic caps, which allow one to model the spin configurations of magnetic clusters. The transport investigations focus on phenomena in narrow channels and on "active swimmers", i.e. capped magnetic particles which are propelled through the surrounding liquid by a catalytic reaction and can be steered by an external magnetic field.

Keywords: colloids; soft matter; model systems

  • Invited lecture (Conferences)
    Juelich Soft Matter Days 2009, 10.-13.11.2009, Bonn, Deutschland

Publ.-Id: 13530

Confined longitudinal acoustic phonon modes in free-standing Si membranes coherently excited by femtosecond laser pulses

Hudert, F.; Bruchhausen, A.; Issenmann, D.; Schecker, O.; Waitz, R.; Erbe, A.; Scheer, E.; Dekorsy, T.; Mlayah, A.; Huntzinger, J.-R.

In this Rapid Communication we report the first time-resolved measurements of confined acoustic phonon modes in free-standing Si membranes excited by fs laser pulses. Pump-probe experiments using asynchronous optical sampling reveal the impulsive excitation of discrete acoustic modes up to the 19th harmonic order for membranes of two different thicknesses. The modulation of the membrane thickness is measured with fm resolution. The experimental results are compared with a theoretical model including the electronic deformation potential and thermal stress for the generation mechanism. The detection is modeled by the photoelastic effect and the thickness modulation of the membrane, which is shown to dominate the detection process. The lifetime of the acoustic modes is found to be at least a factor of 4 larger than that expected for bulk Si.

Keywords: Elemental semiconductors and insulators; Time resolved luminescence; Mechanical modes of vibration; Free films

Publ.-Id: 13529

Molecular Electronics: A Review of Experimental Results

Erbe, A.; Verleger, S.

Molecular electronics aims for scaling down electronics to its ultimate limits by choosing single molecules as the building blocks of active devices. The advantages of this approach are the high reproducibility of molecular synthesis on the nanometer scale, the ability of molecules to form large structures by self-assembly, and the huge versatility of molecular complexes. On the other hand, conventional contacting techniques cannot form contacts on the single molecule scale and imaging techniques nowadays cannot provide a detailed image of such junctions. Therefore, the fabrication has to rely to some degree on self-organization of the constituents. The proof that a molecule has been contacted successfully can only be given by indirect methods, for example by measuring the current transport through the junctions. Here we give an overview of various techniques that were used successfully to contact molecules and to characterize them electrically. The techniques range from methods to contact single molecules to such which can be used to characterize ensembles of molecules. Especially, the comparison between such different techniques shows that a single measurement is always prone to artefacts originating from the unknown microscopic details of the junctions. It is therefore necessary to perform a statistically relevant number of measurements in order to resolve molecular properties. Various properties of the molecules can be studied. Special examples axe the influence of conformational changes of the molecules, differences between various coupling endgroups of the molecules and effects of light-irradiation onto the molecular junctions.

Keywords: Molecular electronic devices; Nanoelectronic devices; Electronic transport in nanoscale materials and structures

  • Open Access Logo Acta Physica Polonica A 115(2009), 455-461

Publ.-Id: 13528

Applying contactless inductive flow tomography to a continuous casting model

Wondrak, T.; Galindo, V.; Gerbeth, G.; Gundrum, T.; Stefani, F.; Timmel, K.

The contactless inductive flow tomography (CIFT) is able to reconstruct the velocity field in electrically conducting melts by measuring the induced magnetic field outside the melt. In this paper, we apply this method to the flow field in a small model of a continuous casting mould. It is shown that the flow structure in general, and the jet position and the intensity in particular, can be reliably determined, using a moderate number of sensors.

Keywords: continuous casting; industrial tomography; liquid metal flow measurement

  • Lecture (Conference)
    12th MHD Days, 08.-9.12.2009, Potsdam, Germany

Publ.-Id: 13527

Alfven wave experiments with liquid rubidium

Gundrum, T.; Hüller, J.; Stefani, F.; Gerbeth, G.; Herrmannsdörfer, T.; Putzke, C.; Arnold, F.

We present first experiments at the Dresden High Magnetic Field Laboratory, with liquid rubidium inserted into a high pulsed magntic field and describe the resulting effects when the Alfven velocity crosses the sound speed.

Keywords: Alfven; Rubidium; Alkali metal; High Magnetic Field; MHD

  • Lecture (Conference)
    12. MHD-Tag, 08.-9.12.2009, Potsdam, Germany

Publ.-Id: 13526

Cyclin-dependent kinases Cdk4 and Cdk6: targets for cancer treatment and visualization.

Graf, F.; Köhler, L.; Mosch, B.; Steinbach, J.; Pietzsch, J.

Cancerogenesis is closely associated with deregulated cell proliferation and, consequently, aberrant cell cycle control. The first phase of the cell cycle (G1) comprises important steps for initiation of DNA replication and subsequent cell division. The activation and coordination of G1 phase is accomplished by enzymes of serine/threonine kinase family. As members of this protein family and important regulators of early cell cycle machinery, cyclin-dependent kinases 4 and 6 (Cdk4/6) associate with regulatory protein cyclin D, and phosphorylate retinoblastoma protein pRb. Hyperphosphorylated pRb dissociates from E2F transcription factors and triggers transcription of genes required for further G1 phase progression. Hence, Cdk4/6 were identified as essential and critical activators of G1 phase in human embryogenesis, homeostasis, and cancer development; G1 phase progression in cell cycle by phosphorylation of retinoblastoma protein pRb and thua, activation of gene transcription.
In 80% of human tumors the Cdk4/6-cyclin D/ pRb/ E2F pathway is altered provoked by multiple mechanisms. In tumor formation, hyperactivation of Cdk4/6 is often a result of overexpression, silencing, and epigenetic alteration of their regulators or substrates. On the other hand, disruption of Cdk4/6-associated cell cycle control in cancer is also caused directly by mutations and amplification of Cdk4/6 themself. Cdk4/6 protein amplification was found in a wide spectrum of solid tumors and blood cell cancer, e.g., gliomas, lymphomas, melanomas, carcinomas, and leukemias. In consequence, Cdk4/6 were considered to be attractive targets for pharmacological anti-cancer drug development. In the recent years, Cdk4/6 inhibitors of high potency and selectivity against other kinases, especially other cyclin-dependent kinases, were developed and evaluated. One of these compounds, a pyrido[2,3-d]pyrimidine-7-one derivative currently is undergoing clinical trials for cancer therapy.
Though, potent and selective pyrido[2,3-d]pyrimidine-7-one Cdk4/6 inhibitors are not only promising new compounds for cancer therapy, but also for visualization and functional characterization of human tumors. Radiolabeled Cdk4/6 inhibitors could be of particular interest for the assessment of Cdk4/6 protein status and Cdk4/6 activity of human tumors by non-invasive imaging technique positron-emission-tomography (PET). PET affords the opportunity of three-dimensional imaging of physiological processes in vivo. Additionally, PET would provide pharmacological data of radiolabeled Cdk4/6 inhibitors, which may help to estimate the applicability of the compounds for tumor therapy. In this regard, positron-emitting Cdk4/6 inhibitors were designed, synthesized and characterized in our institute for the first time. The radiolabeled compounds and their nonradioactive analogs are based on the lead structure of pyrido[2,3-d]pyrimidine-7-one CKIA.
First, iodine-containing pyrido[2,3-d]pyrimidine-7-one derivatives CKIA and CKIB were evaluated concerning their efficacy and suitability as Cdk4/6 inhibitors in human tumor cell lines. The compounds showed both significant and specific inhibition of tumor cell proliferation and G1 phase arrest by targeting the Cdk4/6-cyclin D/ pRb/ E2F signaling pathway [2]. The iodine substituent of CKIA and CKIB represents an attractive site for an isotopic substitution with the positron emitter iodine-124 (124I). 124I-labeled Cdk4/6 inhibitors [124I]CKIA and [124I]CKIB were evaluated concerning their radiopharmacological properties in cellular radiotracer uptake studies, biodistribution studies, and small animal PET studies in NMRI nu/nu mice bearing the human squamous cell carcinoma tumor FaDu [3]. With 4.18 d half-life, 124I affords extended radiopharmacological evaluation and imaging studies using PET. Nevertheless, high positron energy and minor positron emission (26%) are disadvantages, especially for the resolution of PET images. ....

  • OncoPost & OncoPeople The official Newspaper of the ECCO 15 – 34th ESMO Congress 3(2009), 10

Publ.-Id: 13524

Applying the contactless inductive flow tomography to a model of continuous steel casting

Stefani, F.; Wondrak, T.; Gundrum, T.; Gerbeth, G.

We utilize the contactless inductive flow tomography (CIFT) for visualizing the flow of GaInSn in a model of continuous steel casting. Since for thin slab casting the velocity can be assumed to be mainly two-dimensional it is sufficient to apply only one external magnetic field and to measure the induced fields at the narrow faces of the mould. In a first step we show that a numerically determined flow field can be reconstructed by CIFT with an empirical correlation coefficient of about 75 per cent. Then we apply the method to various single-phase and two-phase flows in the real model and show that typical flow features can be reliably detected.

  • Lecture (Conference)
    GAMM 2010, 22.-26.03.2010, Karlsruhe, Germany

Publ.-Id: 13522

Functionalized Mineral Surfaces: Sorption Mechanisms of Growth Proteins on the Surface of Bone Replacement Materials (BioMin)

Fischer, H.; Koczur, K.; Lindner, M.; Jennissen, H. P.; Meissner, M.; Zurlinden, K.; Mueller-Mai, C.; Seifert, G.; Oliveira, A.; Morawetz, K.; Gemming, S.

In the field of biomaterials, more specifically of materials which are used for medical implants, recent research is focused on the interface between implant material and biological environment. Among crystalline and glassy bone substitutes calcium- and phospho­rus-based oxides are of special interest, because their chemical composition can be adjusted to natural bone. Materials containing an appropriate ratio of oxides of calcium, phos­phorus and other physiologically compat­ible constitutents such as silicate and alkalis are bioactive and degradable in vivo. Therefore, the strategy in using such bone substitute implants is that these materials are slowly degraded inside the body and successively substituted by natural bone tissue.
Especially granular media with particles from appropriate calcium alkali orthophosphates, such as [Ca2KNa(PO4)2], exhibit a strongly en­han­ced biodegradability, but the sponge-like structure of the bone can not be remodelled with granulates. Yet, gene­ra­tive manufacturing techniques (rapid proto­typing) nowadays allow to build up even large, three-dimensional structures that are adapted to macro-/microscopic structural bone charac­te­ristics.
However, the natural bioactivity of calcium phosphates and related inorganic compounds is limited. bone remodelling is impeded, in particular when larger bone defects are to be restored by this class of material. Yet, the growth of bone tissue can significantly be stimulated by so-called Bone Morphogenetic Proteins (BMPs), proteins that are synthesized during build-up of bone tissue by the human body. Since a couple of years it has become possible to produce BMPs synthetically and couple them to surfaces of bone replacement materials. After the successful bioactivation of metallic Titanium-based prosthetic surfaces with BMP, the present study is devoted to elucidating the mechanism of protein coupling and especially the desorption kinetics of BMP on mineral surfaces.
Those experimental studies are accompanied by a scale-bridging simulation of the BMP sorption process from physiologic solution as a function of the local pH-value and the structure formation at the solid-liquid interface. With this knowledge the project BioMin yields a significant contribution to develop and manufacture tailored bone substitute implants, so that degradation of the substitute material and build-up of new bone tissue can go hand-in-hand in vivo.

Keywords: bone replacement; apatite; phosphate; BMP; molecular modeling

  • Lecture (Conference)
    GeoDresden 2009, 30.09.-02.10.2009, Dresden, Deutschland

Publ.-Id: 13521

Simulation of bone replacement materials

Gemming, S.

In the field of biomaterials, more specifically of materials which are used for medical implants, recent research is focused on the interface between implant material and biological environment. Among crystalline and glassy bone substitutes calcium- and phospho­rus-based oxides are of special interest, because their chemical composition can be adjusted to natural bone. Materials containing an appropriate ratio of oxides of calcium, phos­phorus and other physiologically compat­ible constitutents such as silicate and alkalis are bioactive and degradable in vivo. Therefore, the strategy in using such bone substitute implants is that these materials are slowly degraded inside the body and successively substituted by natural bone tissue.
Especially granular media with particles from appropriate calcium alkali orthophosphates, such as [Ca2KNa(PO4)2], exhibit a strongly en­han­ced biodegradability, but the sponge-like structure of the bone can not be remodelled with granulates. Yet, gene­ra­tive manufacturing techniques (rapid proto­typing) nowadays allow to build up even large, three-dimensional structures that are adapted to macro-/microscopic structural bone charac­te­ristics.
However, the natural bioactivity of calcium phosphates and related inorganic compounds is limited. bone remodelling is impeded, in particular when larger bone defects are to be restored by this class of material. Yet, the growth of bone tissue can significantly be stimulated by so-called Bone Morphogenetic Proteins (BMPs), proteins that are synthesized during build-up of bone tissue by the human body. Since a couple of years it has become possible to produce BMPs synthetically and couple them to surfaces of bone replacement materials. After the successful bioactivation of metallic Titanium-based prosthetic surfaces with BMP, the present study is devoted to elucidating the mechanism of protein coupling and especially the desorption kinetics of BMP on mineral surfaces.
Those experimental studies are accompanied by a scale-bridging simulation of the BMP sorption process from physiologic solution as a function of the local pH-value and the structure formation at the solid-liquid interface. With this knowledge the project BioMin yields a significant contribution to develop and manufacture tailored bone substitute implants, so that degradation of the substitute material and build-up of new bone tissue can go hand-in-hand in vivo.

Keywords: bone replacement; biomaterials; bioglasses; apatite; calcium phosphate; molecular modeling

  • Invited lecture (Conferences)
    Seminar on Topical Problems in Theoretical Physics, 16.12.2009, Chemnitz, Deutschland

Publ.-Id: 13520

Density-functional theory in materials science

Gemming, S.

Simulations of materials behaviour are an important component of materials development when measurements are indirect and gain from theoretical interpretation, when the 'ideal' experiment is impeded by technological limitations, or when novel concepts and possible routes to their practical implementation are explored. Empirical physical models can be specifically tailored and have been employed successfully for the first two tasks, but the transfer to new tasks beyond the original application requires careful parameter reassessment. Quantum mechanical models, on the other hand, afford an a priori parameter-free access to materials properties on the nanoscale. In particular the density-functional theory provides computationally efficient access to the electronic structure of materials in the electronic ground state. Derived quantities such as forces, stresses, and responses to external electric or magnetic fields allow for the calculation of atom arrangements, lattice constants, elastic tensors, polarisabilities, dielectric and piezoelectric constants, or conductivity of nanosized systems or of systems with nanoscale building blocks. After a short introduction to the fundamentals of density-functional theory the applicability and the limitations of the approach for condensed matter systems will be discussed.

Keywords: density-functional theory; materials science; electronic structure calculations

  • Lecture (others)
    FZD Theory Seminar Series, 17.12.2009, Dresden-Rossendorf, Deutschland

Publ.-Id: 13519

Quasiantiferromagnetic 120° Néel state in two-dimensional clusters of dipole-quadrupole-interacting particles on a hexagonal lattice

Mikuszeit, N.; Baraban, L.; Vedmedenko, E.; Erbe, A.; Leiderer, P.; Wiesendanger, R.

The magnetostatic interactions of colloidal particles, “capped” with radially magnetized Co/Pt multilayers, are modeled. Motivated by experiment the particles are arranged in microscopic two-dimensional clusters on a hexagonal lattice and are free to rotate. The thermodynamically stable states of clusters containing up to 108 particles are calculated theoretically by means of Monte Carlo simulations in the framework of multipole expansion. It is shown analytically that radially magnetized hemispheres have higher-order multipole moments beyond the dipole. Depending on geometrical details also even order moments appear. The even order moments break the inversion symmetry of the magnetic potential of a single particle. For a specific mixing ratio of dipole and quadrupole moments, the experimentally observed antiferromagnetic 120° Néel state in the clusters is found.

Keywords: Magnetostatics; General theory and models of magnetic ordering; Magnetic liquids

Publ.-Id: 13518

Overview of Superconducting Photo Injectors

Arnold, A.; Teichert, J.

The success of most of the proposed electron accelerator projects for future FELs, ERLs or 4th generation light sources is contingent upon the development of an appropriate source to generate the electrons with an unprecedented combination of high-brightness, low emittance and high average current.
An elegant way is to combine the high brightness of RF guns with the superconducting technology. This concept was first proposed at the University of Wuppertal*. In 2002, the successful operation of a SRF photo-injector could be demonstrated at FZD for the 1st time**. However, this type of injectors is still in the R&D phase.
Challenges are the design of the cavity with its specific geometry, the choice of the photocathode type, its life time, a possible cavity contamination, the problems on coupling of high-average power into the cavity and the risk of beam excitation of higher order cavity modes.
During the last years several R&D projects have been launched. Most of them pursue different approaches to deal with these issues. This contribution gives an overview on the progress of the SRF photo-injector development based on the most prominent projects in the world.

Keywords: RF gun combine with superconducting technology; SRF photo injector; photocathode; overview

  • Invited lecture (Conferences)
    Overview of Superconducting Photo Injectors, 20.-25.09.2009, Berlin, Deutschland
  • Contribution to proceedings
    14th International Workshop on RF Superconductivity (SRF09), 20.-25.09.2009, Berlin, Germany
    Overview of Superconducting Photo Injectors, 20-26


Publ.-Id: 13517

Low Emittance Polarized Electron Source Based on FZD Superconducting RF Gun

Xiang, R.; Arnold, A.; Michel, P.; Murcek, P.; Teichert, J.

The state-of-art DC guns with GaAs type photocathodes have been successfully operated as polarized electron sources for accelerators, but the beam emittance is regretfully very high because of the bunch
compressing after the gun. Though not all of the high energy physics experiments using polarized beams are sensitive to the source emittance, but a new source with lower emittance can simplify the injector
system and lower radiation load during the beam transport. Normal conducting rf gun can produce beams with low emittance, but the limit on vacuum is still an open question for the currently designed RF guns. In
this paper a new type of polarized source is reported: FZD polarized SRF gun, i.e. FZD superconducting rf gun with GaAs-type photocathode. The SRF gun is able to produce 1mA CW beam with 9.5MeV energy
and 1 mm mrad emittance. It has higher accelerating field and thus lower emittance than DC guns, at the same time much better vacuum condition than RF guns. Based on the successful running experience
in last two years, SRF gun applied with GaAs type cathode is considered as a promising alternative for current polarized guns. Some interesting questions will be discussed here, including the back bombardment
on cathode, cathode dielectric loss in strong RF field and the cathode time response.

Keywords: state of art DC guns; GaAs Type photocathodes; SRF gun

  • Lecture (Conference)
    The XIIIth International Workshop on Polarized Sources, Targets & Polarimetry, 07.-11.09.2009, Ferrara, Italien

Publ.-Id: 13516

CFD-simulations and experiments on steam condensation in polydisperse bubbly flows

Schmidtke, M.; Krepper, E.; Lucas, D.; Beyer, M.

Bubble condensation in sub-cooled water is a complex process, to which various phenomena contribute. Since the condensation rate depends on the interfacial area density, bubble size distribution changes caused by breakup and coalescence play a crucial role.
To investigate the involved phenomena and their complex interplay, new experiments on steam bubble condensation in vertical co-current steam/water flows have been have been carried out in the TOPFLOW test facility in Dresden, which consists of an 8m long vertical DN200 pipe (inner diameter: 195mm). Steam is injected into the pipe and the development of the bubbly flow is measured at different height levels with a wire mesh sensor. By varying the steam nozzle diameter (1mm or 4 mm) the initial bubble size can be influenced. Larger bubbles come along with a lower interfacial area density and therefore they condensate slower (see figure). In addition to previous experiments (Lucas & Prasser, 2007) also the steam velocity is measured by correlating the signals of two wire mesh sensors installed in a small distance to each other. In the new experiment also the pressure drop along the pipe is measured as well as the temperature at selected points (Lucas et al., 2009). The additional sensors allow for choosing a defined gas inflow pressure as well as a distinct sub-cooling temperature at the injection location. Here steam pressures between 1-2 MPa and sub-cooling temperatures from 2 to 4 Kelvin were applied. Due to the pressure drop along the pipe, the saturation temperature falls towards the upper pipe end. This affects the sub-cooling temperature and can even cause re-evaporation in the upper part of the test section.
In second part of the present contribution, the new TOPFLOW condensation experiments are compared with simulations using an extended MUSIG approach. This approach has been developed in cooperation with ANSYS-CFX for the computation of condensation in polydispersed bubbly flows with CFD. This extended MUSIG approach includes the transition of bubbles to smaller size groups due to condensation as well as the shift of the bubble size distribution due to pressure changes. In the second part of the present contribution, simulations with the extended MUSIG approach are compared with the new TOPFLOW condensation experiments. The new CFD approach is able to catch all relevant phenomena qualitatively, such as bubble condensation and evaporation (if the saturation temperature falls below the water temperature) and radial bubble size segregation. Crucial for the condensation simulations is the modeling of coalescence and breakup, which still needs to be improved. The presented condensation experiments and the extended MUSIG approach are a useful basis for validating models for polydispersed bubbly flows.

Keywords: water/steam flow; condensation; polydisperse; MUSIG; TOPFLOW

  • Contribution to proceedings
    Jahrestagung Kerntechnik 2010, 04.-06.05.2010, Berlin, Deutschland
  • Lecture (Conference)
    Jahrestagung Kertnechnik 2010, 04.-06.05.2010, Berlin, Deutschland

Publ.-Id: 13515

The Properties of Normal Conducting Cathodes in FZD Superconducting Cavity

Xiang, R.; Arnold, A.; Buettig, H.; Janssen, D.; Justus, M.; Lehnert, U.; Michel, P.; Murcek, P.; Schamlott, A.; Schneider, C.; Schurig, R.; Teichert, J.; Staufenbiel, F.

The superconducting rf photoinjector (SRF photoinjector) is one of the latest application of SC technology in the accelerator field. Since superconducting cathodes with high QE are not available up to now, normal conducting cathode material is the main choice for the SRF photoinjectors. However, the compatibility between the cathode and the cavity is one of the challenges for this concept. The SRF gun with Cs2Te cathode has been successfully operated under the collaboration of BESSY, DESY, FZD, and MBI. In this paper, some experience gained in the gun commissioning will be concluded. The results of the properties of Cs2Te photo cathodes in the cavity will be presented, such as the Q.E., life time, regeneracy, dark current and thermal emittance. At the same time, the cavity quality is showed to be steady before and after the cathode working.

Keywords: Superconducting RF Photoinjector; SC technology; Accelerator; SRF Gun; Cs2Te cathode

  • Poster
    14th International Conference on RF Superconductivity (SRF 2009), 20.-25.09.2009, Berlin, Deutschland

Publ.-Id: 13514

Hydrogen depth profiling with nanometre resolution

Munnik, F.; Heller, R.; Neelmeijer, C.

The amount of hydrogen in semiconductors can highly influence electrical, physical and chemical properties on a microscopic as well as on a macroscopic scale. Many applications in the micro electronics industry, in solar cell research and in surface science require the precise knowledge of the actual hydrogen concentration and its concentration distribution near the surface. Nuclear Reactions Analysis (NRA) has been successfully established as a standard technique in chemical analysis within recent decades. In the particular case of hydrogen depth profiling the so-called 15N-method became one of the most successful, non-destructive and standard-free analysing technique. This method is based on the nuclear reaction 15N(1H,αγ)12C, which is characterized by a pronounced resonance at 6.385 MeV. By variation of the initial 15N-ion energy the depth in the sample where the 15N resonance energy is reached can be easily adjusted according to the particular ion stopping in the material. Thus, a depth sensitive measurement of the absolute H-concentration becomes feasible. Using grazing incident angles the depth resolution near the surface can reach 1 nm. Detection limits under optimum conditions are as low as 0.05 at%. Fundamentals of the 15N-method and experimental set-up at the 6 MV accelerator at the FZD as well as particular examples of hydrogen depth profiling in ongoing state-of-the-art experiments are presented.

Keywords: NRA; high-resolution; hydrogen

  • Poster
    2nd International Conference on Functional Nanocoatings, 28.-31.03.2010, Dresden, Germany

Publ.-Id: 13513

Enhancement in the photocatalytic nature of nitrogen-doped PVD-grown titanium dioxide thin films

Tavares, C. J.; Marques, S. M.; Viseu, T.; Teixeira, V.; Carneiro, J. O.; Alves, E.; Barradas, N. P.; Munnik, F.; Girardeau, T.; Rivière, J.-P.

Nitrogen-doped titanium dioxide semiconductor photocatalytic thin films have been deposited by unbalanced reactive magnetron physical vapor deposition on glass substrates for self-cleaning applications. In order to increase the photocatalytic efficiency of the titania coatings, it is important to enhance the catalysts absorption of light from the solar spectra. Bearing this fact in mind, a reduction in the titania semiconductor band-gap has been attempted by using nitrogen doping from a coreactive gas mixture of N2:O2 during the titanium sputtering process. Rutherford backscattering spectroscopy was used in order to assess the composition of the titania thin films, whereas heavy-ion elastic recoil detection analysis granted the evaluation of the doping level of nitrogen. X-ray photoelectron spectroscopy provided valuable information about the cation-anion binding within the semiconductor lattice. The as-deposited thin films were mostly amorphous, however, after a thermal annealing in vacuum at 500 °C the crystalline polymorph anatase and rutile phases have been
developed, yielding an enhancement in the crystallinity. Spectroscopic ellipsometry experiments enabled the determination the refractive index of the thin films as a function of the wavelength, while from the optical transmittance it was possible to estimate the semiconductor indirect band-gap of these coatings, which has been proven to decrease as the N-doping increases. The photocatalytic performance of the titania films has been characterized by the degradation rate of an organic reactive dye under UV/visible irradiation. It has been found that for a certain critical limit of 1.19 at. % of nitrogen doping in the titania anatase crystalline lattice enhances the photocatalytic behavior of the thin films and it is in accordance with the observed semiconductor band-gap narrowing to 3.18 eV. By doping the titania lattice with nitrogen, the photocatalytic activity is enhanced under both UV and visible light.

Publ.-Id: 13512

Running Experience of the Superconducting RF Photoinjector at FZD

Xiang, R.; Buettig, H.; Janssen, D.; Justus, M.; Lehnert, U.; Michel, P.; Murcek, P.; Schamlott, A.; Schneider, C.; Arnold, A.; Teichert, J.; Schurig, R.; Kamps, T.; Rudolph, J.; Schenk, M.; Staufenbiel, F.; Will, I.; Klemz, G.

More and more electron accelerator projects for FELs, ERLs or 4th generation light sources require “super” electron beams with high brightness, low emittance, and high average current. Under this background, much attention is paid on the research and development of new electron sources. A Superconducting RF photoinjector within a collaboration of HZB, DESY, FZD, and MBI is designed to improve the beam quality for ELBE IR-FEL users, and at the same time to test this kind of promising injector concept. The main design parameters of this gun are the final electron energy of 9.5 MeV, 1 mA average current, and transverse normalized emittances (rms) of 1 mm mrad at 77 pC and 2.5 mm mrad at 1 nC bunch charge. In this paper the results of the RF and beam parameter measurements with Cs2Te photo cathodes will be presented, and the experience for the gun running gained at the first beam experiment will be concluded, including the life time and the compatibility of the normal conducting photocathode in SC cavity, the cavity properties after the cathode’s inserting.

Keywords: electron accelerator for FEL; 4th generation; high brightness; low emittance; high average; new electron source; superconducting RF photoinjector

  • Lecture (Conference)
    The 31st International Free Electron Laser Conference FEL 2009,, 23.-28.08.2009, Liverpool, UK

Publ.-Id: 13511

Interstitial-Mediated Diffusion in Germanium under Proton Irradiation

Bracht, H.; Schneider, S.; Klug, J. N.; Liao, C. Y.; Lundsgaard Hansen, J.; Haller, E. E.; Nylandsted Larsen, A.; Bougeard, D.; Posselt, M.; Wündisch, C.

We report experiments on the impact of 2.5 MeV proton irradiation on self-diffusion and dopant diffusion in germanium (Ge). Self-diffusion under irradiation reveals an unusual depth independent broadening of the Ge isotope multilayer structure. This behavior and the observed enhanced diffusion of B and retarded diffusion of P demonstrates that an interstitial-mediated diffusion process dominates in Ge under irradiation. This fundamental finding opens up unique ways to suppress vacancy-mediated diffusion in Ge and to solve the donor deactivation problem that hinders the fabrication of Ge-based nanoelectronic devices.

Keywords: Germanium; dopant diffusion; proton irradiation

  • Physical Review Letters 103(2009), 255501

Publ.-Id: 13510

New fluorine-18 radiolabeled Cdk4/6 inhibitors: potential radiotracers for tumor imaging by positron emission tomography.

Graf, F.; Köhler, L.; Mosch, B.; Pietzsch, J.

Cyclin-dependent kinases 4 and 6 (Cdk4/6) are important components of cell cycle activation in G1 phase and play critical roles in dysfunction of growth control during cancerogenesis. The aim of our study was the evaluation of new fluorine containing pyrido[2,3 d]pyrimidin-7-one derivatives (CKIC, CKID and CKIE) concerning their efficacy and suitability as Cdk4/6 inhibitors and, after fluorine-18 radiolabeling, as radiotracers for imaging of tumors by positron emission tomography (PET).

Materials and methods
Small molecule inhibitors CKIC, CKID and CKIE were analyzed concerning their biological and radiopharmacological properties in human tumor cell lines HT-29, FaDu and THP-1. Cell cycle distribution of cells was determined by flow cytometry DNA analysis and effects on cell growth were measured. Phosphorylation of retinoblastoma protein (pRb) at Ser780 was analyzed by Western blotting. mRNA expression of the pRb affected genes E2F-1 and PCNA was measured with quantitative RT-PCR. Stability and radiotracer uptake studies with [18F]CKIE were performed.

Cell cycle analyses showed a concentration-dependent (50 nM to 10 µM) increment of percentage of tumor cells in G1 phase after 24 h of incubation with CKIC, CKID and CKIE, with CKIE to be more potent than CKIC and CKID. Cell growth studies indicated reduced tumor cell numbers after 48 h of treatment with 1 µM (< 75%) and 10 µM (< 30%) CKIE and 10 µM (< 70%) CKIC or respectively CKID. Cdk4 specific phosphorylation at pRb Ser780 is decreased in a concentration dependent manner after 24 h of incubation with CKIE. Downregulation of E2F-1 and PCNA mRNA expression could be demonstrated after treatment with CKIE. [18F]CKIE indicated high stability in physiological buffer and cell culture medium. Cellular radiotracer uptake using [18F]CKIE increased with time amounting to 46.3±11.2 %ID/mg protein in HT-29 and 46.2±13.8 %ID/mg protein in FaDu cells, respectively, after 60 min at 37°C. Uptake of [18F]CKIE could be blocked with nonradioactive CKIE dependent on concentration (e.g., 23.5±3.7 %ID/mg protein with 5 µM CKIE after 60 min at 37°C).

CKIE was identified as the most potent fluorine containing pyrido[2,3 d]pyrimidin-7-one derivative analyzed in our study causing arrest of tumor cells in G1 phase due to inhibition of the Cdk4/6/ pRb/ E2F pathway. In vitro radiotracer uptake studies using [18F]CKIE demonstrated tumor cell uptake, which is an important prerequisite for further PET studies in tumor-bearing mice.

  • Lecture (Conference)
    European Cancer Organisation (ECCO) 15 – 34th European Society for Medical Oncology (ESMO) Multidisciplinary Congress, 20.-24.09.2009, Berlin, D
  • Abstract in refereed journal
    European Journal of Cancer Suppl. 7(2009)2, 120-121

Publ.-Id: 13509

Neue tetradentate S4-Liganden auf der Basis verbrückter Dimercaptomaleinsäurederivate (DMMS) zur stabilen Komplexierung von Re-188

Förster, C.; Pietzsch, H.-J.; Steinbach, J.

Das Ziel dieser Forschungsarbeiten ist die Entwicklung eines neuen bifunktionellen Chelatorsystemes für eine stabile Komplexierung thiophiler Radiometallnuklide wie Re 188 oder Tc 99m. Neben der Radionuklidfixierung soll dieses Ligandsystem reaktive Zentren (z. B. Aktivester, Maleinimid, Isothiocyanat) zur kovalenten Bindung an verschiedene zielsuchende Einheiten (Antikörper, -fragmente, Peptide, usw.) besitzen. Je nach verwendetem Radionuklid und gebundenem biologisch aktiven Adressmolekül können verschiedene Krankheitsbilder diagnostiziert (Tc-99m) und therapiert (Re 188) werden.
Ausgehend von Verbindung 1 können über die Bildung des Anhydrids 3 und anschließen-der Reaktion mit sekundären Aminen (u. a. Morpholin, 1 Aza-kronenether) unter-schiedliche thiolgeschützte Derivate 4 synthetisiert werden. Hierbei besteht die Möglichkeit, mittels ent-sprechender Amine die pharmakologischen Eigenschaften des späteren Konjugates zu beeinflussen. Die Ausbeuten bis Verbindung 4 sind nahezu quantitativ. Durch Überführung von 4 in das Carbonsäurechlorid, Verbrückung mit boc-geschütztem Norspermidin (Ausbeute 72 %) und Entschützung der einzelnen Schutzgruppen (quant.) erhält man die tetradendaten Liganden 6.
Es gelang zudem, dieses Ligandsystem durch die Reaktion von Bernstein-säureanhydrid mit dem sekundären Amin und Überführung der terminalen Carboxylgruppe in einen Aktivester an eine 5‘-hexylamin-modifizierte DNA zu binden. Beginnende radioaktive Markierungsstudien mit Tc-99m und Re-188 werden zeigen, ob diese 188Re-DMMS-DNA-Konjugate für etwaige Pretargeting-Ansätze zur Therapie von Tumorerkrankungen verwendet werden können.

  • Poster
    GDCh-Wissenschaftsforum Chemie 2009, 30.08.-02.09.2009, Frankfurt am Main, D

Publ.-Id: 13508

Influence of substrate temperature and oxygen partial pressure on the electrical properties of Al-doped ZnO grown by reactive pulsed magnetron sputtering

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

The study is focused on improvement of the free electron mobility in Al-doped ZnO films grown by reactive pulsed magnetron sputtering. At optimum growth conditions low-absorbing films are obtained with a Hall mobility of 46 cm2 V −1s−1, a free electron density of 6.0x1020 cm−3, and an electrical resistivity of 2.26x10−4 cm. The relation between the mobility and free electron density for different growth conditions is discussed in terms of ionized impurity scattering, impurity clustering, and grain boundary limited transport.

Keywords: magnetron sputtering; transparent conductive oxides; Al doped zinc oxide; free electron mobility; electrical properties

  • Lecture (Conference)
    DPG Frühjahrstagung der Sektion Kondensierte Materie (SKM)2009,, 22.-27.03.2009, Dresden, Deutschland

Publ.-Id: 13507

Electrical properties of reactively sputtered ZnO thin films with a wide range of Al impurity concentrations

Cornelius, S.; Vinnichenko, M.; Kolitsch, A.; Möller, W.

Despite the fact, that thin films of transparent conductive oxides (TCOs) are already in use as transparent electrodes for thin film solar cells, there are still questions whether it is possible to further improve their electrical and optical properties. Moreover the fundamental mechanisms that govern the incorporation and activation of dopants in the host lattice are only partially understood. Therefore this study is focused on Al doped ZnO (AZO) as one of the most used TCOs. By relating parameters of film growth to structure and properties the abovementioned questions were addressed. In particular it is of big interest to increase the Hall mobility while maintaining a high free carrier concentration to obtain highly conductive films which show low absorption in the near IR and visible spectral range.

The AZO films were grown using reactive pulsed magnetron sputtering (RPMS) on fused silica and sapphire substrates. The oxygen partial pressure during deposition was precisely controlled by exploiting the gettering of the reactive gas by the sputtered metal at constant oxygen gas flow. This was combined with different substrate temperatures (T_S=RT-550 °C) and Al concentrations (c_Al=0.5-8.7 at %). The film structure was studied by X-ray diffraction (XRD), cross-sectional TEM and atomic force microscopy, while the elemental composition was determined by elastic recoil detection analysis. Further characterization was done by spectroscopic ellipsometry and Hall-effect measurements in van-der Pauw geometry.

It was shown for every Al concentration there is a maximum Hall mobility which can be reached at a certain optimum substrate temperature and oxygen partial pressure which are interrelated. The recent achievement of a high Hall mobility of 46 cm2/Vs at a free electron density of 6.0x1020 cm-3 in reactive pulsed magnetron sputtered (RPMS) ZnO:Al demonstrates that the RPMS technique is suitable for the production of high quality TCO films [1].

A comparison of the results with data from other publications reveals an underlying physical limit of mobility in polycrystalline TCO films in general. For different growth conditions and target Al concentrations the relation between the mobility and free electron density can be explained in terms of ionized impurity scattering, impurity clustering and grain boundary limited transport.
Moreover epitaxial undoped and Al doped ZnO films were grown on sapphire substrates and studied by extensive XRD analysis. It was found that these films possess a high degree of in-plane orientation with a rotation of their hexagonal lattice by 30° with respect to the substrate.

[1] S. Cornelius et al, Appl. Phys. Letters 94, 042103 (2009)

Keywords: magnetron sputtering; transparent conductive oxide; Al doped zinc oxide; free electron mobility; electrical properties

  • Poster

Publ.-Id: 13506

PIConGPU: A fully relativistic particle-in-cell code for a GPU cluster.

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

The particle-in-cell algorithm (PIC) is one of the most widely used algorithms in computational plasma physics. With the advent of graphical processing units (GPUs) large-scale plasma simulations on inexpensive GPU clusters are in reach. We present an implementation of a fully relativistic plasma PIC algorithm for GPUs based on the NVIDIA CUDA library. It supports a hybrid architecture consisting of single computation nodes interconnected in a standard cluster topology, each node carrying one or more GPUs. The inter-node communication is realized using the Message Passing Interface (MPI). The simulation code PIConGPU presented in this work is to our knowledge the first scalable GPU cluster implementation of the PIC algorithm in plasma physics.

Keywords: particle-in-cell; algorithm; laser wakefield acceleration; message-passing-interface; pic; mpi; graphical processing unit; gpu; cuda; performance; vampir

Publ.-Id: 13505

Radiolabelling of proteins with fluorine-18 via click chemistry

Ramenda, T.; Knieß, T.; Bergmann, R.; Steinbach, J.; Wüst, F.

The study describes for the first time the application of Cu(I)-mediated 1,3-dipolar [3+2]cycloaddition for the labelling of proteins with the short-lived positron emitter fluorine-18 as exemplified with azide-functionalized human serum albumin (HSA).

Publ.-Id: 13504

Validation of a generalized model for bubble coalescence and breakup in MUSIG approach

Liao, Y.; Lucas, D.; Krepper, E.

Flow fields in the safety research of nuclear reactors are usually complex and often involve two-phase (gas-liquid) flows, where one of the phases is continuous and the other phase consists of disperse bubbles. It is well-known that bubble coalescence and breakup can lead to significant variations in the bubble size distribution, which influences the relative motion of bubbles, i.e. the redistribution of gas-liquid interface. To model the dynamic evolution of the disperse gaseous phase, the population balance equation (PBE) has to be solved together with the classical hydrodynamic Euler/Euler simulation. The Inhomogeneous MUSIG (MUltiple-Size-Group) model implemented in the CFX 12.0 commercial CFD code is one kind of efficient method for the solution of the PBE [1, 2]. However, the closure models for bubble coalescence and breakup were diagnosed as one weak point in the application of this approach [3, 4].
In the previous work, a generalized model was proposed for the modeling of bubble coalescence and breakup, which considers all important mechanisms, e.g. turbulent fluctuation, laminar shear, wake entrainment and eddy capture and interfacial slip velocity. The first test in a 1D Test Solver has shown that the new model is capable of tracing the evolution of bubble size distribution and radial gas volume fraction in vertical pipe flow [5, 6].
In the present study, the new model was implemented into CFX 12.0 through user FORTRAN subroutines and serves as new constitutive relations of the MUSIG approach. Two-dimensional axisymmetric multi-fluid simulations were performed for air-water flows in a large vertical pipe (DN 200). Simulation results for the evolution of bubble size distribution, radial gas volume fraction, Sauter mean bubble diameter as well as gas velocity were compared to the TOPFLOW experiment. The extents of the calculation grid are, x: 0~0.1m, z: 0.221~1.021m. The flow is in the z-direction.

Keywords: A generalized model; Bubble coalescence and breakup; MUSIG approach; CFX

  • Contribution to proceedings
    Jahrestagung Kerntechnik 2010, 04.-06.05.2010, Berlin, Germany
  • Lecture (Conference)
    Jahrestagung Kerntechnik 2010, 04.-06.05.2010, Berlin, Germany

Publ.-Id: 13503

Silicon based microcavity enhanced light emitting diodes

Potfajova, J.

  • Open Access Logo Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; FZD-526 2009
    ISSN: 1437-322X


Publ.-Id: 13502

Hyperthermal ion induced self-organization during the growth of carbon-transition metal films

Abrasonis, G.; Kovacs, G. J.; Oates, T. W. H.; Tucker, M.; Munnik, F.; Bilek, M. M. M.; Möller, W.

Spatial self organization of metal nanoparticles and quasi-continuous multilayers in carbon-transition metal (TM=Co, Ni and Cu) composite thin films as a function of metal content, metal type and incoming flux energy is investigated. Films were grown by pulsed filtered cathodic vacuum arc (PFCVA) which produces a flux of film forming species in the form of ions with ‘natural’ hyperthermal energies in the range of ~20-50 eV. Since each arc pulse deposits less than one monolayer of ions, by rapidly alternating between cathodes it is possible to deposit compounds or nanocomposites. The metal content (nominal 10-50 at.%) was varied by changing the metal to carbon pulse ratio while the incoming beam energy was controlled by applying substrate bias of 0 V, -15 V and -30 V. The structure of the films was investigated by means of transmission electron microscopy and grazing incidence small angle x-ray scattering while the film composition was determined by elastic recoil detection analysis. The results demonstrate that the vertical self-organization occurs in all type of films. At low metal contents the formation of un-correlated encapsulated nanoparticles occurs. The increase in the metal content results in the formation of a vertically layered separated nanoparticle structure with well pronounced diagonal metal nanoparticle correlations, while the further increase in the metal content results in the formation of quasi-continuous metal/carbon multilayers. The periodicity of the vertical structure strongly depends on the film composition and the incoming ion energy. The observed vertical ordering is broken down by the thermal activation of the surface diffusivity by an additional thermal heating during the deposition. The results are discussed on the interplay of stochastic thermal effects and ion induced ballistic effects.

Keywords: self organization; metal nanoparticles; composite films; pulsed filtered cathodic vacuum arc; PFCVA; hyperthermal ion energy; transmission electron microscopy; TEM; grazing incidence small angle x-ray scattering; GISAXS; elastic recoil detection analysis; ERDA

  • Poster
    2009 MRS Fall Meeting, 30.11.-04.12.2009, Boston MA, USA

Publ.-Id: 13501

Scaling of proton energies in ultra-short pulse laser plasma acceleration and future projects at FZ Dresden-Rossendorf

Schramm, U.

Keywords: laser proton acceleration

  • Invited lecture (Conferences)
    Plasma Physics Seminar GSI, 01.12.2009, Darmstadt, Deutschland

Publ.-Id: 13500

Kelvin probe digs deep

Baumgart, C.

News Item: Kelvin probe force microscopy (KPFM) now has a good explanation, thanks to Christine Baumgart of the nanospintronics group at the Forschungszentrum Dresden-Rossendorf (FZD), Germany.

  • TRAC-Trends in analytical chemistry 28(2009)10, vi-viii

Publ.-Id: 13499

Modified 3½-Cell SC Cavity Made of Large Grain Niobium for the FZD SRF Photoinjector

Murcek, P.; Buettig, H.; Michel, P.; Moeller, K.; Arnold, A.; Teichert, J.; Xiang, R.; Freitag, M.; Kneisel, P.

An SRF photoinjector has been successfully tested in FZD under the collaboration of BESSY, DESY, FZD, and MBI. In order to improve the gun cavity quality and thus reach a higher gradient, a new 3+1/2 superconducting cavity is being fabricated in cooperation with JLab. The modified cavity is made of large grain niobium, composed of one filter choke, one special designed half-cell (gun-cell) and three TESLA cavities. In this paper, the main updates of the new cavity design will be explained in detail. The deformation of the filter choke and the gun-cell, which is caused by pressure fluctuation in the He-line and also by the effect of the Lorentz force, will be minimized by stiffening between the filter choke and the gun-cell. Meanwhile, the cathode hole in the choke and gun-cell is enlarged for better rinsing. To simplify assembly, the NbTi pick-up will be welded directly on the wall of filter choke.

  • Poster
    SRF 2009 Conference, 20.-25.09.2009, Berlin and Dresden, Germany
  • Contribution to proceedings
    SRF 2009 Conference, 20.-25.09.2009, Berlin and Dresden, Germany

Publ.-Id: 13496

ERL 2009 WG1 Summary Paper: Drive Lasers and RF Gun Operation and Challenges

Lewellen, J. W.; Bluem, H.; Burrill, A.; Grimm, T. L.; Kamps, T.; Legg, R.; Liu, K.; Rao, T.; Smedley, J.; Teichert, J.; Zhang, S.

Working Group I of the 2009 Energy Recovery Linac Workshop focused on high-brightness, high-power electron beam sources for energy recovery linacs (ERLs), and relevant technology such as development of drive lasers. The WG1 summary paper was broken into two parts: DC guns and loadlocks; and RF guns and drive lasers. This was done both to retain more manageable paper sizes, and because SRF guns are in an earlier stage of development than DC guns. This paper describes the advances, concepts, and thoughts for the latter topics presented at the workshop.
There are many challenges to the successful operation of SRF guns as high-brightness, high-average-current beam sources. These combine the set of challenges for high-current SRF cavities (fabrication, cleaning and processing, HOM extraction, etc.), with challenges for high-average-current photocathode sources (photocathode fabrication, quantum efficiency and lifetime, drive laser technology, etc.). New challenges also arise from this combination, such as the requirement for having removable cathodes in an SRF cavity. Practical approaches have been, and are currently being, found to address the problems, and the base of knowledge and experience continues to grow.
Alternate ideas are also beginning to make inroads. Hybrid DC-SRF guns, pioneered by Peking University, offer promise for combining the best features of both technologies. Quarter-wave SRF cavities offer compact size for a given frequency, potentially easier fabrication than elliptical cells, and very high transit-time factors for quasi-DC operation. Also, the use of normal-conducting cavities, usually dismissed out of hand due to the required RF power consumption, may become practical with advanced cavity designs.
This paper summarizes the state-of-the-art of drive lasers, cathode development and RF gun-based injectors for ERL beam sources The focus in the field has been on DC and SRF guns to date, but interesting approaches for hybrid DC/SRF guns and normal-conducting RF guns are also presented. The paper concludes with discussions of operational issues and concerns, technical issues related to beam source realization, and future concepts.

  • Contribution to proceedings
    Energy Recovery Linac Workshop ERL´09, 08.-12.06.2009, Ithaca, USA

Publ.-Id: 13495

FZD SRF Gun Development and Testing

Teichert, J.; Arnold, A.; Büttig, H.; Janssen, D.; Justus, M.; Lehnert, U.; Michel, P.; Moeller, K.; Murcek, P.; Schneider, C.; Schurig, R.; Staats, G.; Staufenbiel, F.; Tietze, H.; Xiang, R.; von der Horst, B.; Matheisen, A.; Stephan, J.; Kamps, T.; Rudolph, J.; Schenk, M.; Klemz, G.; Will, I.; Volkov, V.

kein Abstract verfügbar.

  • Invited lecture (Conferences)
    Energy Recovery Linac Workshop ERL´09, 08.-12.06.2009, Ithaca, USA

Publ.-Id: 13494

Quantum Chemical Calculation for the Nuclear Safety Research: Complementary Tool to Spectroscopy and Electrochemistry

Tsushima, S.

Quantum chemical calculations is capable of predicting various physicochemical properties of ions and molecules and may assist to further explore experimental chemistry. Among several different available theories, density functional theory (DFT) is a reasonable compromise between accuracy and computational time, and is nowadays widely used for the studies in physics, chemistry, and material science.
I will present several examples how DFT calculations can be used to better understand experimental actinide chemistry. The first example shows the calculations of luminescence properties of uranium(VI). The quenching of uranium(VI) luminescence in the presence of some types of organic and inorganic compounds are well reproduced by the DFT calculations and the quenching mechanism has been postulated. In another example, redox potentials of the actinide couple An(VI)/An(V) was studied for An = U, Np, Pu, Am. The unsolved question "What is the highest oxidation state of plutonium?" was discussed from theoretical viewpoint. The structures of various actinide complexes were also studied and they were disucussed together with EXAFS spectroscopy measurements at the Rossendorf Beamline in ESRF, France.

  • Lecture (Conference)
    Theory Seminar Series in FZD, 10.12.2009, FZD, Dresden, Germany
  • Lecture (Conference)
    Seminar talk at the Institute of Scientific and Industrial Research, Osaka University, 28.12.2010, Osaka, Japan

Publ.-Id: 13493

Photochemistry and fluorescence of uranium(VI): A density functional theory approach

Tsushima, S.

no abstract for this talk

  • Lecture (Conference)
    Helmholtz Koordinierungstreffen 2009, 22.10.2009, FZD, Dresden, Germany

Publ.-Id: 13492

Room temperature transparent ferromagnetism in 200 keV Ni2+ ion implanted PLD grown ZnO/sapphire film

Pandey, B.; Ghosh, S.; Srivastava, P.; Kumar, P.; Kanjilal, D.; Zhou, S.; Schmidt, H.

Intrinsic ferromagnetism at room temperature has been observed in ZnO/sapphire films by implantation of 200 keV Ni2+ ions with fluences 6 × 1015, 8 × 1015, 1 × 1016 and 2 × 1016 ions/cm2. Crystalline phases are identified by glancing angle X-ray diffraction (GAXRD), which shows no extra phase in the implanted films. Highest saturation magnetization (Ms) is observed in the film implanted with the fluence of 8 × 1015 ions/cm2 as examined by SQUID magnetometry. This film has almost 80% transmittance across visible wavelength range and hence a potential candidate of transparent ferromagnetic semiconductor [TMS]. Defect like oxygen vacancies in the films are studied by X-ray photoelectron spectroscopy (XPS). Ferromagnetism of the films is explained on the basis of bound magnetic polaron (BMP) model.

Publ.-Id: 13491

Modifizierung von radioaktiv markierbaren, komplementären L-Oligonukleotiden zur Beeinflussung ihrer Pharmakokinetik für Pretargeting-Technologien

Förster, C.; Bergmann, R.; Schubert, M.; Közle, I.; Walther, M.; Pietzsch, H.-J.; Vonhoff, S.; Klussmann, S.; Pietzsch, J.; Steinbach, J.

kein Abstract verfügbar

  • Lecture (Conference)
    17. Jahrestagung der AG Radiochemie/Radiopharmazie der DGN, 24.-26.09.2009, Schellerhau, D

Publ.-Id: 13490

PROMISEs, fulfillments, and prospects

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

We give a survey about the recent experiments on the helical magnetorotational instability (MRI) in the framework of the Potsdam ROssendorf Magnetic InStability Experiment (PROMISE). By comparing the experimental results with numerical simulations we show that the observed instability is indeed a global instability rather than a noise-triggered convective one. We also delineate the plans for further experiments on the azimuthal MRI and on the Tayler instability.

  • Lecture (Conference)
    12th MHD Days, 08.-09.12.2009, Potsdam, Germany

Publ.-Id: 13489

On the relation of standard and helical magnetorotational instability

Kirillov, O.; Stefani, F.

The magnetorotational instability (MRI) plays a crucial role for cosmic structure formation by enabling turbulence in Keplerian disks which would be otherwise hydrodynamically stable. With particular focus on MRI experiments with liquid metals, which have small magnetic Prandtl numbers, it has been shown that the helical version of this instability (HMRI) has a scaling behaviour that is quite different from that of the standard MRI (SMRI). We discuss the relation of HMRI to SMRI by exploring various parameter dependencies. We identify the mechanism of transfer of instability between modes through a spectral exceptional point that explains both the transition from a stationary instability (SMRI) to an unstable travelling wave (HMRI) and the excitation of HMRI in the inductionless limit. For certain parameter regions we find new islands of the HMRI.

  • Lecture (Conference)
    12th MHD Days, 08.-09.12.2009, Potsdam, Germany
  • Open Access Logo Astrophysical Journal 712(2010), 52-68
    DOI: 10.1088/0004-637X/712/1/52

Publ.-Id: 13488

Shortest electron bunch duration measurements from laser-accelerated electrons using single-shot THz time-domain interferometry

Debus, A. D.; Bussmann, M.; Schramm, U.; Sauerbrey, R.; Murphy, C. D.; Major, Z.; Hörlein, R.; Veisz, L.; Schmid, K.; Schreiber, J.; Witte, K.; Jamison, S. P.; Gallacher, J. G.; Jaroszynski, D. A.; Kaluza, M. C.; Hidding, B.; Kiselev, S.; Heathcote, R.; Foster, P. S.; Neely, D.; Divall, E. J.; Hooker, C. J.; Smith, J. M.; Ertel, K.; Langley, A. J.; Norreys, P.; Collier, J. L.; Karsch, S.

Laser-plasma wakefield based electron accelerators are expected to deliver ultrashort electron bunches with unprecedented peak currents. However, their actual pulse duration has never been directly measured in a single-shot experiment.
We present measurements of the ultrashort duration of such electron bunches by means of THz time-domain interferometry. With data obtained using a 0.5J, 45fs, 800nm laser and a ZnTe-based electro-optical setup we demonstrate the duration of laser-accelerated, quasi-monoenergetic electron bunches at a best fit of 32fs (FWHM) with a 90% upper confidence level of 38fs.

Keywords: electron bunch length measurement coherent transition radiation laser plasma wakefield acceleration

  • Poster
    4th Graduate Student Seminar, 16.-18.09.2009, Krögis, Deutschland

Publ.-Id: 13487

A method of determining narrow energy spread electron beams from a laser plasma wakefield accelerator using undulator radiation

Gallacher, J.; Anania, M.; Brunetti, E.; Budde, F.; Debus, A.; Ersfeld, B.; Haupt, K.; Islam, M.; Jackel, O.; Pfotenhauer, S.; Reitsma, A.; Rohwer, E.; Schlenvoigt, H.; Schwoerer, H.; Shanks, R.; Wiggins, S.; Jaroszynski, D.

In this paper a new method of determining the energy spread of a relativistic electron beam from a laser-driven plasma wakefield accelerator by measuring radiation from an undulator is presented. This could be used to determine the beam characteristics of multi-GeV accelerators where conventional spectrometers are very large and cumbersome. Simultaneous measurement of the energy spectra of electrons from the wakefield accelerator in the 55-70 MeV range and the radiation spectra in the wavelength range of 700-900 nm of synchrotron radiation emitted from a 50 period undulator confirm a narrow energy spread for electrons accelerated over the dephasing distance where beam loading leads to energy compression. Measured energy spreads of less than 1% indicates the potential of using a wakefield accelerator as a driver of future compact and brilliant ultrashort pulse synchrotron sources and free-electron lasers that require high peak brightness beams.

Publ.-Id: 13486

All-optical Femtosecond Bunch Length Measurement of Laser-accelerated Electron Beams

Debus, A.; Bussmann, M.; Schramm, U.; Sauerbrey, R.; Murphy, C. D.; Major, Z.; Hörlein, R.; Veisz, L.; Schmid, K.; Schreiber, J.; Witte, K.; Jamison, S. P.; Gallacher, J. G.; Jaroszynski, D. A.; Kaluza, M. C.; Hidding, B.; Kiselev, S.; Heathcote, R.; Foster, P. S.; Neely, D.; Divall, E. J.; Hooker, C. J.; Smith, J. M.; Ertel, K.; Langley, A. J.; Norreys, P.; Collier, J. L.; Karsch, S.

Electron bunches accelerated in the wakefield of a laser beam are expected to have pulse lengths below a hundred femtoseconds. Such pulse lengths cannot be measured by established accelerator diagnostics. However, with laser-driven electron beam generation it becomes possible to perform an all-optical measurement of the electron pulse length on a single-shot basis.
We present the analysis of data taken in 2005 at the ASTRA laser. A 400 mJ, 45 fs laser pulse is focused to a spot size of 8 mum FWHM using an f/16 parabolic mirror to accelerate electrons in a gas jet of 2 mm length. Terahertz transition radiation created in the passage of these electrons through a 50 mum Al foil is focused onto a 200 mum thick ZnTe crystal and brought into overlap with part of the ASTRA pulse negatively chirped to 5 ps.
The Terahertz pulse induces transient birefringence in the crystal via the electro-optical Pockels effect while the ASTRA pulse probes the resulting change in polarization and therefore the temporal structure of the Terahertz pulse.
We will focus on the details of the data analysis and show that the observed temporal signal can clearly distinguish between the quasi-monoenergetic electron bunch and the quasi-thermal tail of the electron distribution in a manner which is consistent with the measured electron spectra.

  • Lecture (Conference)
    ULIS 2009 - Ultra-intense Laser Interactions Science 2009, 24.-29.05.2009, INFN - Laboratori Nazionali di Frascati, Italien

Publ.-Id: 13485

Komplexierung von Eu(III) mit verschiedenen Aminosäuren

Rönitz, O.

In dieser Arbeit sollte die Komplexierung von Europium(III) mit verschiedenen Aminosäuren untersucht, Komplexstabilitätskonstanten bestimmt und Aussagen über die Bindungsstärke dieser Liganden getroffen werden. Dazu wurden die proteinogenen Aminosäuren Tryptophan, Tyrosin, Phenylalanin, Threonin und Alanin ausgewählt und die Komplexierung mittels UV/VIS und zeitaufgelöster Laserfluoreszenzspektroskopie untersucht. Dabei wurde Europium als Analogelement für dreiwertige Actinide ausgewählt, da es nicht radioaktiv und dadurch einfach handhabbar ist. Da dreiwertige Lanthanide und Actinide sehr ähnliche Eigenschaften aufweisen, können Erkenntnisse mit dreiwertigen Lanthaniden in erster Nährung auf das Verhalten von dreiwertigen Actiniden übertragen werden. Die sehr guten Fluoreszenzeigenschaften des Europium(III) schaffen darüber hinaus die Voraussetzung zur Untersuchung der Bindung und Komplexierung mit unterschiedlichen Liganden in biologisch relevanten, niedrigen Konzentrationsbereichen. Anhand der ermittelten Komplexstabilitätskonstanten sollte abschließend die Speziation des Europiums in wässrigen Aminosäurelösungen ermittelt und der Beitrag dieser Stoffklasse zur Bindung von Schwermetallen in Biofluiden beurteilt werden.

Keywords: Europium(III); TRLFS; Aminosäuren; Speziation; Komplexierung

  • Other report
    Dresden: Hochschule für Technik und Wirtschaft Dresden: Diplomarbeit (Studiengang Chemieingenieurwesen), 2009
    66 Seiten

Publ.-Id: 13484

Übersicht über Modellumfang, Verifikations- und Validierungsstand sowie Einsatzgebiete verschiedener russischer Störfallcodes

Kliem, S.

Im Rahmen einer Literaturrecherche wurden Informationen über Modellumfang, Verifikations- und Validierungsstand sowie Einsatzgebiete verschiedener russischer Störfallcodes zusammengestellt. Dabei handelt es sich um die Programmgruppen KORSAR, TRAP, BIPR sowie das Programm TIGR und um die zur Erzeugung von reaktorphysikalischen Daten notwendigen Programme.

  • Article, self-published (no contribution to HZDR-Annual report)
    Forschungszentrum Rossendorf 2009
    76 Seiten
    ISSN: 1437-322X

Publ.-Id: 13483

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