Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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39109 Publications

Structural characterization of buried superconducting Ga rich films in Si

Fiedler, J.; Heera, V.; Skrotzki, R.; Herrmannsdörfer, T.; Voelskow, M.; Mücklich, A.; Schmidt, B.; Skorupa, W.; Gobsch, G.; Helm, M.; Wosnitza, J.

Recently it has been shown that heavily p-doped group-IV semiconductors such as diamond, silicon and germanium can become superconducting at low temperatures. Here, we present a study of Ga-implanted Si that becomes superconducting due to precipitation after annealing. Ion implantation allows introducing a high Ga dose (4E16cm-2) in Si that leads to peak concentrations far beyond the solid solubility limit. Rapid thermal annealing (RTA) causes redistribution of the Ga and re-crystallization of the amorphous implanted Si layer. After annealing at temperatures up to 850°C the implanted layers are polycrystalline and contain Ga-rich precipitates. Structural investigations by means of RBS/C measurements and TEM demonstrate a high density of precipitates at the interface of a protective SiO2 layer and the silicon substrate. At optimized annealing conditions (600-700°C) such samples become superconducting with critical temperatures up to 7 K [1].
[1] Skrotzki R. et al. , Appl. Phys. Lett. 97 (2010) 192505

Related publications

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

Publ.-Id: 14919

Acceptor deactivation in individual silicon nanowires: From thick to ultrathin

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

An individual free standing spicular silicon nanowire (NW) fabricated by Ag assisted chemical etching was doped to 1018 dopants/cm-3 by boron ion implantation and annealed at 1000°C. The presented NW is around 900 nm in length and consists of two connected parts, a thicker basis with a diameter of about hundred nm and of a thin top part with an average diameter as thin as 16 nm. This NW was analyzed by scanning spreading resistance microscopy (SSRM). The paper demonstrates that SSRM is capable to spatially and electrically resolve such an ultrathin NW with the thinnest part down to 12 nm in diameter. Experimental results show the dependence of the acceptor deactivation on the diameter of the NW cross section. The doping efficiency of the NW dramatically decreases as the diameter is below 25 nm. Deactivation mechanisms are discussed.

Keywords: nanowire; SSRM; doping; implantation

Related publications

Publ.-Id: 14918

Three-dimensional carrier profiling of individual Si nanowires by scanning spreading resistance microscopy

Ou, X.; Das Kanungo, P.; Kögler, R.; Werner, P.; Gösele, U.; Skorupa, W.; Wang, X.

Individual silicon nanowires (Si NWs) grown by molecular beam epitaxy and in-situ doped with boron were investigated by scanning spreading resistance microscopy (SSRM), a technique based on the conductive atomic force microscopy. The carrier profiles of the NWs were derived from the measured spreading resistance values and calibrated with the known carrier concentration of the underlying epi-layer. The three-dimensional SSRM profile of a NW was obtained by measuring the NW cross sections at different depths along the radial direction. Scanning the same NW with a controlled force on the SSRM tip can abrade material from the cross-sectional surface and the tip moves deeper into the volume of the NW after each image scan. Repeated stripping of the material from the NW results in a "thinning" of the remaining NW segment and a corresponding increase of its resistance which can be addressed by an appropriate data correction. The achieved three-dimensional carrier profile reveals a multi-shell structure of the carrier distribution across the NW diameter which consists of a lower doped core region, a higher doped shell region and a carrier depleted sub-surface region.

Keywords: nanowire; doping; three-dimensional; carrier profile; SSRM

Related publications

Publ.-Id: 14917

Aqueous coordination chemistry and photochemistry of uranium(VI)

Tsushima, S.

We have been exploring aqueous coordination chemistry of uranium(VI) by combining different spectroscopic techniques and computational chemistry, i.e. EXAFS and FTIR spectroscopy and DFT calculations. In uranyl(VI) sulfate system we found sulfate may bound to uranium in both unidentate and bidentate modes.
Whether ligand bind to uranium in unidentate or bidentate might seem to be irrelevant. However the EXAFS and DFT study on uranyl(VI) oxalate system proved that this is entirely not the case and the mode of ligand coordination plays decisive role to the photoreactivity of uranyl(VI) oxalate. Only the uranyl(VI) oxalate having unidentate coordination was found to be photoreactive. The result is consistent with recent UV-Vis absorption spectroscopic study by Görller-Walrand and Servaes.
The validity of the use of DFT on uranium complexes is often disputed. Sophisticated theory such as CASPT2 is proved to be requisite for getting accurate excitation energies of uranyl(VI) complexes. However, DFT calculations were also proved to provide accurate geometries as long as the ground states and the lowest lying triplet states are concerned. Photoluminescence characters of uranium(VI) were also found to be well reproduced by cost-effective DFT calculations.

Related publications

  • Invited lecture (Conferences)
    Seminar at Katholieke Universiteit Leuven, 14.01.2011, Leuven, Belgium

Publ.-Id: 14916

Improved vortex nucleation in truncated soft magnetic cones

Martin, N.; Mönch, I.; Schäfer, R.; Schultz, L.; McCord, J.

Magnetic vortex structures are promising for data storage applications due to the possibility to switch vortex chirality and core orientation independently. Subsequently two bits per element can be stored, which is favorable for high data storage densities. The magnetic vortex state of soft-magnetic nano-disks is stable over a large range of thickness and radii. Nevertheless the formation of a vortex state has to overcome an energy barrier in order to nucleate the vortex at the element’s edge. In the presented work the influence of a large edge tilt on the behavior of vortex nucleation is studied experimentally and by numerical simulations. Single elements and arrays of closely packed elements with a diameter of approx. 300 nm were fabricated by means of nanosphere lithography, by which an element edge tilt of 45° could be achieved. From the simulations it was found that with decreasing edge tilt from 90° (cylindrical dot) to 45° the probability to nucleate a vortex during magnetization reversal increases. For cylindrical elements at the onset of vortex nucleation the out of plane component of magnetization near the edge has opposite signs at the top and bottom of the element. For truncated cones, however, the magnetization points only in one direction and favors the nucleation of a magnetic vortex. Thus, the vortex formation in smaller elements is facilitated by engineering the shape of the dots. For narrowly packed structures it is shown that despite of strong dipolar interactions the magnetization reversal involves a vortex nucleation and annihilation process.

Keywords: magnetic vortex; nanosphere lithography; vortex nucleation

  • Lecture (Conference)
    55th Annual Conference on Magnetism & Magnetic Materials, 14.-18.11.2010, Atlanta, Georgia, USA

Publ.-Id: 14915

Competition of dipolar interactions and lateral exchange spring effect in NiFe elements

Martin, N.; Strache, T.; Mönch, I.; Schultz, L.; Fassbender, J.; McCord, J.

Conventional exchange spring systems consist of directly exchange coupled hard and soft magnetic layers, which characteristic behaviour is related to an interlayer domain wall that is formed during reversal of magnetization. Recently, a similar exchange spring effect was achieved in lateral hard/soft magnetic stripe structures, which were fabricated by means of ion implantation of single layer films [1]. This technique offers the possibility to directly investigate the changes of magnetization in and between the hard/soft phases.

In the presented work, lateral exchange spring structures were prepared on patterned samples to investigate the interplay between structuring and additional dipolar fields. In contrast to extended films, the lateral exchange spring effect only occurs for a higher difference in saturation magnetization Ms between the two magnetic phases. The measured collective magnetization reversal of hard and soft phase is attributed to strong dipolar fields at the element edges that cause a hysteresis behaviour which is comparable to that of a magnetic homogeneous square element. The exchange spring behaviour, occurring with increasing difference in Ms between the two phases is related to an increase in effective shape anisotropy in the high Ms stripes. The magnetization reversal approaches an individual switching of the stripes, with the low Ms stripes switching first. This results in an antiparallel alignment of magnetization of the individual stripes with lateral domain walls in between, which configuration is stabilized by the inter-stripe flux closure. The resulting two-step reversal is modelled, taking the demagnetization and domain wall energy terms into account.

Keywords: ion implantation; thin films; Permalloy; magneto-optical imaging

Related publications

  • Lecture (Conference)
    55th Annual Conference on Magnetism & Magnetic Materials, 14.-18.11.2010, Atlanta, Georgia, USA

Publ.-Id: 14914

Herstellung und Charakterisierung magnetisch heterogener, dünner Schichten

Martin, N.; Schäfer, R.; Fassbender, J.; Schultz, L.; McCord, J.

In der Präsentation werden Methoden vorgestellt, die das Hystereseverhalten dünner magnetischer Schichten gezielt beeinflussen. Insbesondere geht es dabei um lokale Eigenschaftsveränderungen durch Strukturierung mittels lithografischer Techniken und anschließender Ionenimplantation. Der Einfluss der Strukturierung auf das Ummagnetisierungsverhalten der gesamten Schicht wird anhand von magneto-optisch gemessenen Hysteresekurven und Domänenaufnahmen dargestellt und mittels geeigneter Modelle erklärt.

Keywords: thin films; magnetic microstructure; magneto-optical imaging

Related publications

  • Invited lecture (Conferences)
    VAC-Kolloqium, 09.-10.12.2010, Hanau, Deutschland

Publ.-Id: 14913

Lipid Protein Interactions underlie an Evolutionary Conserved Proton Switch in a Transmembrane Peptide derived from Helix-3 of Class-1 GPCRs

Eichler, S.; Madathil, S.; Fahmy, K.

The visual photoreceptor rhodopsin is a proto¬typical class-I (rhodopsin-like) G protein-coupled receptor (GPCR). Photoisomerization of the covalently bound ligand 11-cis-retinal leads to restructuring of the cytosolic face of rhodopsin. The ensuing protonation of Glu-134 in the class-conserved D(E)RY motif at the C-terminal end of trans¬membrane helix-3 promotes the formation of the G-protein-activating state. Glu-134 acts as an autonomous proton switch also in synthetic transmembrane peptides, where lipid protein interactions couple protonation to helix extension and hydrophobic burial of the side chain resulting in an elevated side chain pKa. The implied change in "helical-end-solvation" by interfacial water has been investigated by pulsed hydration experiments. we observed within several seconds (i) lipid/peptide conformational changes by time-resolved Fourier transform infrared (FTIR) difference spectroscopy and (ii) water penetration into the lipidic phase using the simultaneous recording of the fluorescence of a tryptophan (trp) inserted 3 amino acids N-terminally from the ERY motif. Cross-correlation of both monitors reveals the linkage of lipid ester carbonyl hydration to helical end unwinding followed by water penetration into the bilayer one helical turn N-terminally of the conserved ERY motif. Trp-emission further shows that the indole ring is more water-exposed in the ionized than in the protonated state of the adjacent ERY motif evidencing a shift of the lipid/water phase boundary relative to the transmembrane peptide upon proton uptake. The proton-dependent reorganisation of the lipid/peptide/water microdomain N-terminally of the ERY motif is further supported by a pH-sensitive Förster-resonance-energy-transfer from the peptidic trp to 5-(dimethylamino)naphthalene-1-sulfonyl (DANSYL)-labelled lipids. In conclusion, the data reveal a conserved hydration site at the membrane water interface of GPCRs that attracts or repels water in response to protonation, thereby, linking proton uptake to protein conformation and rearrangement of the lipid/peptide/water phase boundary independently of helix-helix interactions.

Keywords: G protein; infrared; spectroscopy; peptide; rhodopsin

  • Contribution to proceedings
    Annual Meeting of the German Biophysical Society 2009, 03.-06.10.2009, Bochum, Deutschland
    Book of Abstracts

Publ.-Id: 14912

Zum Komplexbildungsverhalten ausgewählter Actiniden (U, Np, Cm) mit mikrobiellen Bioliganden

Glorius, M.

Diese Arbeit war ein eigenständiger Teil eines Projektes, welches sich mit der Aufklärung des Einflusses von Mikroorganismen auf die Ausbreitung von Actiniden bei einer Freisetzung dieser aus dem Endlager beschäftigt. Dabei wurde der Einfluss von mikrobiell produzierten Substanzen auf die Mobilisierung ausgewählter Actiniden untersucht. Die in diesem Projekt untersuchten mikrobiell produzierten Substanzen, sogenannte Bioliganden, wurden von Bakterien des Genus Pseudomonas unter speziellen Bedingungen produziert. Die von den Pseudomonaden freigesetzten Bioliganden, hier Siderophore vom Pyoverdin-Typ, haben ein hohes Potential, Metalle, insbesondere Eisen(III), zu komplexieren und so zu transportieren. Es wurde untersucht, in welcher Weise und unter welchen Bedingungen diese Bioliganden in der Lage sind, auch radioaktive Schadstoffe zu komplexieren und damit zu mobilisieren. Für die Untersuchungen wurden die α-strahlenden Actiniden Uran, Curium und Neptunium ausgewählt, weil diese auf Grund ihrer Langlebigkeit und Radiotoxizität von besonderem Interesse sind.
Diese Arbeit beschäftigte sich mit der Wechselwirkung der Actiniden U(VI), Np(V) und Cm(III) mit Modellliganden, die die Funktionalitäten der Pyoverdine simulieren. Für die Metallbindung der Pyoverdine sind die Katecholgruppe des Chromophors und die funktionellen Gruppen der Peptidkette (Hydroxamsäuregruppen und α-Hydroxysäurereste) verantwortlich. Für die Simulation der Hydroxamsäuregruppen kamen dabei die Monohydroxamate Salicylhydroxamsäure (SHA) und Benzohydroxamsäure (BHA) und das natürliche Trihydroxamat Desferrioxamin B (DFO) zum Einsatz und für die Katecholgruppe das 6-Hydroxychinolin (6HQ) und 2,3-Dihydroxynaphthalin (NAP). Als Vergleichsligand wurde außerdem Benzoesäure (BA) untersucht. Für die Bestimmung der Stabilitätskonstanten zur Einschätzung der Stärke der gebildeten Komplexe, die Aufklärung der Struktur der Actinid-Ligand-Verbindungen und die Verfolgung der Änderung der Speziation der Actiniden vor und nach der Wechselwirkung mit den Modellliganden kamen verschiedene spektroskopische Verfahren wie Absorptionsspektroskopie, Laserfluoreszenzspektroskopie,
Röntgenabsorptionsspektroskopie und Schwingungsspektroskopie zum Einsatz. Außerdem wurden erstmals theoretische Modellierungen zur Aufklärung der Struktur der Actinid-Modellligand-Komplexe durchgeführt.
Die Ziele dieser Arbeit waren also die spektroskopische Charakterisierung und Bestimmung der Speziation und Komplexbildungskonstanten sowohl der ausgewählten Modellliganden als auch der gebildeten Actinid-Modellligand-Komplexe, die Aufklärung möglicher Strukturen der Komplexe sowie ein Vergleich der Ergebnisse mit denen der Pyoverdine.
Der Vergleich der Stabilitätskonstanten der untersuchten Liganden mit den drei Actiniden U(VI), Cm(III) und Np(V) ergab im Wesentlichen folgende Reihenfolge der Komplexstärke:
PYO ≥ DFO > NAP > 6HQ > SHA ≥ BHA > BA.
Benzoesäure besitzt als einziger Ligand eine Carboxylfunktionalität und weist mit 103 die geringste Stabilitätskonstante auf. Die beiden Monohydroxamate SHA und BHA bilden mit allen drei Actiniden ähnlich starke 1:1-Komplexe. Bei den 1:2-Komplexen besitzt SHA mit Cm(III) und Np(V) etwas höhere Stabilitätskonstanten als BHA, wahrscheinlich verursacht durch einen stabilisierenden Einfluss der zusätzlichen phenolischen OH-Gruppe. Dieser Trend wurde auch in den theoretischen Modellierungen für die U(VI)-Komplexe beobachtet. Die natürlichen Siderophore DFO und PYO bilden die stärksten Komplexe mit den Actiniden (Stabilitätskonstanten von 1012 bis 1034). Dies liegt in der Struktur und der hohen Anzahl an funktionellen Gruppen begründet; DFO besitzt drei Hydroxamatgruppen, das Pyoverdinmolekül neben den Hydroxamatgruppen noch die Katecholgruppen der Chromophorfunktionalität. Die Modellliganden für die Chromophorfunktionalität, NAP und 6HQ, bilden stärkere Komplexe als die Monohydroxamate SHA und BHA, aber schwächere Komplexe als DFO und PYO. Daraus lässt sich schlussfolgern, dass die Chromophorfunktionalität eine wichtige Rolle bei der Anbindung der Actiniden an die Pyoverdine spielt.
Der Vergleich der Stabilitätskonstanten der Komplexe der Liganden SHA, BHA und 6HQ mit den drei untersuchten Actiniden U(VI), Cm(III) und Np(V) untereinander zeigte, dass die Stärke der Komplexe von U(VI) über Cm(III) zu Np(V) abnimmt. Der Grund dafür liegt in den unterschiedlichen Ladungsdichten der Actinidionen. Während das UO22+-Ion mit einer Koordinationszahl von 5 und einem Ionenradius von ~ 0.6 eine effektive Ladung von + 3.3 besitzt, hat das Cm3+-Ion eine effektive Ladung von + 2.6 und das NpO2+-Ion von + 2.3. Damit besitzt das NpO2+-Ion die geringste Ladungsdichte der untersuchten Actinidionen und bildet damit auch die schwächsten Komplexe mit den niedrigsten Stabilitätskonstanten. Die Stärke der Komplexe der Liganden NAP, DFO und PYO nimmt von Cm(III) über U(VI) zu Np(V) ab. Obwohl Cm(III) eine geringere effektive Ladung als U(VI) hat, bildet es stärkere Komplexe als U(VI). Eventuell sind dafür strukturelle Behinderungen der Koordination durch die lineare O=U=O Einheit verantwortlich.
In einer Kooperation mit dem Institut für Theoretische Chemie der Universität zu Köln wurden für die 1:1- und 1:2-Komplexe der wässrigen U(VI)-SHA-, U(VI)-BHA- und U(VI)-BA-Systeme erstmals theoretische Modellierungen durchgeführt. Dabei wurden die Strukturen der Komplexe sowohl in der Gasphase als auch unter Berücksichtigung der Solvatation optimiert und die relativen Stabilitäten und Anregungsspektren berechnet. Die mit DFT berechneten Bindungsenergien bestätigen die experimentell anhand der Stabilitätskonstanten log β ermittelte Reihenfolge der Komplexstabilitäten (SHA ≥ BHA > BA). Außerdem zeigen die höheren Bindungsenergien der 1:2-Komplexe, dass diese stabiler sind als die 1:1-Komplexe. Dies lässt sich auch anhand der experimentell ermittelten Stabilitätskonstanten nachweisen. Für den 1:1-Komplex des U(VI)-SHA-Systems konnte mit Hilfe der theoretischen Modellierung die strukturelle Anbindung des Uranylions an die Hydroxamsäuregruppe aufgeklärt werden. Der Vergleich der berechneten Strukturen, Bindungsenergien, Bindungslängen und Anregungsspektren der beiden möglichen Anbindungsmodi [O,O] und [N,O’] zeigte deutlich, dass das Uranylion bevorzugt über die beiden Sauerstoffatome der Hydroxamsäuregruppe, also den [O,O]-Modus, gebunden wird. Die Methode der DFT konnte also dazu beitragen, Defizite in der experimentellen Aufklärung der Komplexstruktur im Fall des U(VI)-SHA-Systems zu beheben.
Die Modellliganden und deren Komplexe mit U(VI), Cm(III) und Np(V) wurden zum größten Teil erstmals spektroskopisch charakterisiert sowie deren bisher weitgehend unbekannten Stabilitätskonstanten bestimmt. Außerdem konnte die Struktur der U(VI)-Hydroxamat-Komplexe mit Hilfe der ATR-FTIR-Spektroskopie und der theoretischen Modellierung aufgeklärt werden. Im Vergleich der Ergebnisse der Modellliganden mit denen der Pyoverdine konnte festgestellt werden, dass die Katecholfunktionalität der Pyoverdine eine große Rolle bei der Komplexierung mit den Actiniden spielen wird. Weiterhin ließen sich aus den Ergebnissen Schlussfolgerungen zur Stärke der gebildeten Actinid-Modellligand- und Actinid-Pyoverdin-Komplexe ziehen. Die Pyoverdine bildeten mit U(VI) Komplexe mit Stabilitätskonstanten bis 1030, mit Cm(III) bis 1032 und mit Np(V) bis 1020. Die wichtigsten, in höheren Konzentrationen vorkommenden anorganischen Komplexbildner in natürlichen Wässern sind das Hydroxidion OH- sowie das Carbonation CO32-. Diese besitzen eine hohe Komplexierungsfähigkeit und bilden mit den drei Actiniden U(VI), Cm(III) und Np(V) Komplexe mit Stabilitätskonstanten von 102 bis 1020. Der Vergleich der Konstanten von OH und CO32- mit denen der organischen, mikrobiellen Pyoverdin-Liganden zeigt, dass die Pyoverdine ähnlich starke bzw. teilweise stärkere Komplexe mit den Actiniden bilden als die anorganischen Komplexbildner. Daraus lässt sich ableiten, dass die Pyoverdine selbst in niedrigeren Konzentrationen ein hohes Potential besitzen, Actiniden in natürlichen Wässern zu binden und damit zu transportieren. Die untersuchten Bioliganden sind also in der Lage, bei Anwesenheit in der Natur in bestimmten Konzentrationen im Grundwasser Actiniden, z. B. durch Herauslösen aus Festphasen, zu mobilisieren. Damit können solche Bioliganden das Verhalten der Actiniden in der Umwelt entscheidend beeinflussen. Die Ergebnisse dieser Arbeit tragen dazu bei, den Einfluss der mikrobiellen Liganden auf die Mobilisierung und Ausbreitung der Actiniden besser einschätzen zu können. Damit können die Ergebnisse zur Quantifizierung des Mobilisierungseffekts der Actiniden durch freigesetzte Bioliganden im Nahfeld genutzt werden.

Keywords: Actiniden; Hydroxamsäure; Pyoverdin; Spektroskopie; Komplexierung; actinides; hydroxamic acids; pyoverdin; spectroscopy; complex formation

Related publications

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


Publ.-Id: 14911

Fluence dependence of small-angle neutron scattering in neutron-irradiated Fe-Cr

Bergner, F.; Heintze, C.; Ulbricht, A.

Four Fe-Cr alloys with chromium concentrations ranging from 2.5 to 12.5 at% in three irradiation conditions (0.06, 0.6 and 1.5 displacements per atom) were investigated by means of small-angle neutron scattering. For Fe-12.5 at% Cr, alpha‘–phase particles were unambigiously identified. The size distribution of these particles was estimated and the kinetics of formation were compared with a rate theory model which allows to extrapolate the evolution of the nanostructure to still lower dpa-levels. For 2.5, 5 and 9 at% Cr, the results of the SANS investigation are more complex and the input from other methods, such as APT and TEM, is needed in order to explore the irradiation effects in detail.

Keywords: Fe-Cr alloy; neutron irradiation; SANS

  • Lecture (Conference)
    17th Workshop on Multiscale Modelling and Basic Experiments of Iron-Chromium Alloys for Nuclear Applications, 03.-04.11.2010, Stockholm, Schweden

Publ.-Id: 14910

Investigation of wear-out phenomena in Eu-implanted metal-oxide semiconductor light emitting devices

Lehmann, J.; Rebohle, L.; Kanjilal, A.; Voelskow, M.; Skorupa, W.; Helm, M.

The anomalous wear-out phenomenon of Eu-implanted MOS based light emitting devices (MOSLED’s) was investigated intensively by many different techniques, on samples exposed to different annealing temperatures and times. It will be shown, that in contrast to other rare earth elements the EL intensity of Eu-implanted SiO2 layers can rise under constant current injection before the known EL quenching will start. Under certain circumstances this rise may amount up to two orders of magnitude. The EL behaviour will be correlated with the microstructural and electrical properties of the devices. Transmission electron microscopy (TEM) and Rutherford backscattering spectroscopy (RBS) were used to trace the growth of Eu / Eu oxide clusters and the diffusion of Eu to the interfaces of the gate oxide layer, which are induced by the annealing process. Current-voltage (I(V)) characteristics, EL decay times (τ) and the evolution of the voltage under constant current injection (Vcc) as well as evolution of the EL spectrum with injected charge (EL(Qinj)) were studied with respect to charging and trapping phenomena in the oxide layer in order to reveal details of the EL excitation mechanism. A qualitative model for the anomalous wear-out phenomenon is proposed.

Keywords: Electroluminescence; rare earth; charge trapping; ion implantation; Europium; Si-based light emission; Electroluminescence wear-out; quenching

Related publications

  • Poster
    Nanofair 2010 - 8th International Nanotechnology Symposium, 06.-07.07.2010, Dresden, Deutschland

Publ.-Id: 14909

Wear-out phenomena in Si-based light emitting devices with ion beam implanted europium

Lehmann, J.; Rebohle, L.; Kanjilal, A.; Voelskow, M.; Helm, M.; Skorupa, W.

Recently, it was shown that it is possible to obtain efficient electroluminescence (EL) from UV to IR by implanting lanthanides into the oxide layer of metal-oxide semiconductor (MOS) structures [1]. The best efficiencies could be achieved on a Tb-implanted light emitter with an external quantum efficiency of 16% and a corresponding power efficiency of 0.3%. With these electrically driven Si-based light emitting devices, also called MOSLEDs, it is possible to build an integrated biosensor for the detection of organic molecules like estrogene, e.g. see Ref. [2]. For this purpose, the intensity and stability of the emitted EL are the most critical properties of the light emitters. Usually, lanthanide implanted MOSLEDs show a quenching of the EL-signal with time, which can be attributed to charge trapping in the oxide layer. In contrast to this normal wear-out phenomenon, Eu-implanted MOSLEDs can show a rise in the EL-signal during the operation time of the device [3]. Due to this anomalous wear-out phenomenon, Eu-implanted MOSLEDs offer the possibility to build a device with an extremely stable EL if the occurring processes can be better understood. For this reason, an intensive investigation was performed on Eu-implanted MOSLEDs exposed to different annealing temperatures and times. Transmission electron microscopy (TEM) and Rutherford backscattering spectroscopy (RBS) were used to trace the growth of Eu / Eu oxide clusters and the diffusion of Eu to the interfaces of the gate oxide layer, respectively. Both of them were induced by the annealing process. Resonant nuclear reaction analysis (rNRA) was used to measure the hydrogen depth profile in the dielectric. Current-voltage (I-V) characteristics, the EL decay times (τ) and the evolution of the voltage under constant current injection (Vcc) as well as the evolution of the EL spectrum with injected charge (EL-Qinj) were studied with respect to charging and trapping phenomena in the oxide layer in order to reveal details in the occurring wear-out mechanism of the EL. It will be shown, that for certain annealing conditions the EL intensity of Eu-implanted SiO2 layers can increase during constant current injection which is followed by the known EL quenching. In extreme cases this rise may amount up to two orders of magnitude. The EL behaviour will be correlated with the microstructural and electrical properties of the devices. A qualitative model for the anomalous wear-out phenomenon is proposed.

Keywords: Electroluminescence; rare earth; charge trapping; ion implantation; Europium; Si-based light emission; Electroluminescence wear-out; quenching

Related publications

  • Lecture (Conference)
    Ion Implantation and Other Applications of Ions and Electrons (ION 2010), 14.-17.06.2010, Kazimierz Dolny, Poland

Publ.-Id: 14908

Influence of Al concentration on structure and electrical properties of polycrystalline and epitaxial Al-doped ZnO films grown by reactive pulsed magnetron sputtering

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

Al-doped ZnO (AZO) films which combine maximum carrier mobility (μe), moderate free electron densities (Ne) and high surface roughness are of special interest for application as transparent front electrode in thin film solar cells. They posses high transmission in the near infrared region, close to the bandgap energy of absorber materials like Si (Eg =1.11 eV), and enable a superior light trapping behaviour. A key to tailor AZO film properties is understanding the mechanisms and effects of the Al-dopant incorporation into the ZnO matrix. The present work focuses on investigation of the influence of Al concentration on the electrical properties of AZO and on establishing performance limits with respect to carrier mobility and resistivity (ρ). Polycrystalline and epitaxial AZO films are grown on fused silica and c-axis oriented sapphire substrates, respectively, by reactive pulsed magnetron sputtering using several sets of Zn/Al alloy targets with an Al concentration (cAl) between 0.7 and 8.7 at%. A systematic variation of process parameters such as substrate temperature (Ts) and oxygen partial pressure results in polycrystalline films with μe>45 cm2V-1s-1 and ρ<2.3x10-4 Ωcm at optimum conditions, whereas μe~55 cm2V-1s-1 could be obtained for epitaxial films. It is observed that cAl has a strong influence on the optimum value of Ts, the maximum μe and Ne values and also on film structure and surface roughness. Extensive XRD investigations reveal that Al incorporation in the ZnO matrix has a detrimental effect on in-plane orientation and texture of epitaxial films, even for the lowest cAl used. Furthermore RBS and ERDA confirm a considerable Al enrichment in the films which correlates with deterioration of μe, when Ts is increased above its optimum value. The observed dependence of carrier mobility on Ne in ZnO:Al is discussed in the framework of ionized impurity scattering and clustering as well as grain boundary limited transport which predicts a fundamental physical limit of μe.

Keywords: reactive sputtering; zinc oxide; AZO; mobility; density; resistivity; RBS; ERDA; transparent conductive oxides; ionized impurity scattering

Related publications

  • Poster
    Twelfth International Conference on Plasma Surface Engineering (PSE 2010), 13.-17.09.2010, Garmisch Partenkirchen, Deutschland

Publ.-Id: 14907

A Compton Imager for in-vivo Dosimetry of Proton Beams - A Design Study

Kormoll, T.; Fiedler, F.; Schöne, S.; Wüstemann, J.; Zuber, K.; Enghardt, W.

In-beam SPECT during therapeutic proton beam irradiation is a novel method for three dimensional in-vivo dose verification. For this purpose a Compton camera design is evaluated with respect to the special requirements and conditions that arise from this application. Different concepts are studied by means of simulation concerning the angular resolution and the efficiency. It was found that a cadmium zinc telluride system can perform sufficiently well. For further evaluation the construction of a semiconductor scintillator hybrid system is under way.

Keywords: in-beam SPECT; in vivo dosimetry; ion beam therapy; proton therapy

Publ.-Id: 14906

Lateral straggling and its influence on lateral diffusion in implantation with a focused ion beam

Batabyal, R.; Roy, A.; Roy, S.; Bischoff, L.; Dev, B. N.

Ion implantation plays an important role in semiconductor industry. Different kinds of ions are introduced into semiconductors by implantation in order to form n-type and p-type semiconductors. Nanoscale doped structures are required to be fabricated, usually by a focused ion beam (FIB), for applications in nanoelectronics. However, how closely these structures could be fabricated for an effective device performance would be determined by the limitation imposed by the lateral diffusion of the implanted species. For ion implantation, lateral straggling of the ion beam also produces defects surrounding the implanted region. This would produce radiation enhanced lateral diffusion. It is important to understand the lateral diffusion in FIB-fabricated nanostructures. We present a method based on photoemission electron microscopy (PEEM) for the determination of lateral diffusion coefficient in nanostructures. As an example, we present the investigation of lateral diffusion of Ga in FIB-fabricated structures of Ga-implanted n-type Si. For a set of parallel Ga implanted stripes, the diffusion profiles at the end of the stripes along their length obey the standard diffusion equation and the diffusion coefficient is extracted. However, across the stripes the diffusion profile is more complex, due to the presence of defects due to lateral straggling in the neighbouring stripes.

Keywords: photoemission; focused ion beam; diffusion in nanostructures

Related publications

  • Lecture (Conference)
    24th International Conference on ATOMIC COLLISIONS IN SOLIDS, ICACS-24, 18.-23.07.2010, Krakow, Poland

Publ.-Id: 14905

Spectroscopic studies of arsenic retention onto biotite

Chakraborty, S.; Bardelli, F.; Mullet, M.; Greneche, J.-M.; Varma, S.; Ehrhardt, J.-J.; Banerjee, D.; Charlet, L.

Biotite is a constituent Fe-bearing mineral of Delta subsoils in India and Bangladesh and has been hypothesized as a primary source of arsenic (As). The adsorption behavior of As onto structural Fe(II,III)-bearing biotite fractions (<50 µm) was investigated in the pH range 4-8 under a CO2-free, anoxic condition (O2 <1 ppmv) using X-ray Photoelectron Spectroscopy (XPS) and X-ray Absorption Spectroscopy (XAS). The batch experiments indicate that As adsorption is strongly pH dependent and As(V) adsorbs more efficiently than As(III). X-ray Absorption Near-Edge Structure (XANES) spectra show no oxidation or reduction of As by biotite after 3 days reaction with As(III) or As(V) solutions. Extended X-ray Absorption Fine Structure (EXAFS) spectroscopic results suggest that As(III) forms bidentate mononuclear edge-sharing (2E) and bidentate binuclear corner-sharing (2C) surface complexes at pH 7.7 as indicated by the average As-Fe bond distances at 3.00 ± 0.02 Å and 3.37 ± 0.03 Å respectively. The surface speciation retrieved by XPS does not provide any evidence of reduction of As(V) on biotite after 30 days further confirming the thermodynamic prediction and the XANES results. This study has therefore significant environmental implications for As contaminated areas, where biotite retards the release of As into reducing groundwater. The changes in soil redox condition and weathering of biotite may likely contribute to the occurrence of high As in groundwater.

Keywords: Arsenic; adsorption; biotite; surface complex; reduction

Related publications

  • Chemical Geology 281(2011), 83-92

Publ.-Id: 14904

On the "yl" bond weakening in uranyl(VI) coordination complexes

Tsushima, S.

The U–Oyl triple bonds in the UO22+ aquo ion are known to be weakened by replacing the first shell water with organic or inorganic ligands. Weakening of the U–Oyl bond may enhance the reactivity of “yl” oxygens and uranyl(VI) cation–cation interactions. Density functional theory calculations as well as previously published vibrational spectroscopic data have been used to study the origin of the U–Oyl bond weakening in uranyl(VI) coordination complexes. Natural population analyses (NPA) revealed that the electron localization on the Oyl 2p orbital is a direct measure of the U–Oyl bond weakening, indicating that the bond weakening is correlated to the weakening of the U–Oyl covalent bond and not that of the ionic bond. The Mulliken analysis gives poor results for uranium to ligand electron partitioning and is thus unreliable. Further analyses of molecular orbitals near the highest occupied molecular orbital (HOMO) show that both the sigma and pai donating abilities of the ligands may account for the U–Oyl bond weakening. The mechanism of the bond weakening varies with coordinating ligand so that each case needs to be examined independently.

Publ.-Id: 14903

Influence of humic acids on the actinide migration in the environment: Suitable humic acid model substances and their application in studies with uranium – a review

Sachs, S.; Bernhard, G.

Humic acids (HA) can influence the speciation of metal ions, e.g., actinide ions, and thus their migration in the environment. Therefore, knowledge of the impact of HA on the actinide migration is required to assess their transport in natural systems. However, due to the complex and heterogeneous nature of HA, there are a lot of difficulties in the thermodynamic description of their geochemical interaction behavior. A more basic understanding of the interaction processes of HA can be obtained by investigations applying HA model substances with more defined and specific properties. This work gives a review of selected types of HA model substances (HA-alike melanoidins, synthetic HA with pronounced redox functionality, modified HA with blocked phenolic/acidic OH groups, synthetic humic substance-clay-associates), their synthesis, isotopic labeling, and characterization in comparison to isolated natural HA. Examples for their application in various geochemical studies, such as complexation, redox, sorption and migration studies with uranium as representative for actinides are presented.

Keywords: Humic acids; model substances; synthesis; characterization; labeling; modification; application; uranium; actinides

Publ.-Id: 14902

On the use of different analytical solutions for recalculation of the YALINA-Booster experiment SC3A

Merk, B.; Glivici-Cotruţă, V.; Weiß, F.-P.

The SC3A experiment in the YALINA-Booster facility in Belarus is described and investigated. For this investigation the very special configuration of YALINA-Booster core, consisting of a fast and a thermal zone, decoupled with a neutron ‘valve’ is analyzed in detail based on a full HELIOS model for the calculations. The two region design causes unexpected results in the experiments The special problems for the analysis of the experiments are shown. For an improved representation, a recently developed two group analytical solution for the time dependent diffusion equation obtained by Green’s function method without separation of space and time is used. To model the streaming of neutrons from the thermal area into the fast area an analytical solution for the space-time dependent neutron flux with two sources has been developed from the available Green’s functions for two groups. The space-time dependent thermal and fast neutron flux distributions are discussed. The new analytical solution shows very good agreement in the comparison with the experimental results, even for the unexpected behavior at the outermost detector. Thus analytical solutions without separation of space and time are a very promising tool to develop a new method for the analysis of ADS experiments

Keywords: Yalina; experimental analysis; Green’s function; Two group diffusion equation

Publ.-Id: 14901

Constraining the S factor of 15N(p,g)16O at Astrophysical Energies

Leblanc, P. J.; Imbriani, G.; Goerres, J.; Junker, M.; Azuma, R.; Beard, M.; Bemmerer, D.; Best, A.; Broggini, C.; Caciolli, A.; Corvisiero, P.; Costantini, H.; Couder, M.; Deboer, R.; Elekes, Z.; Falahat, S.; Formicola, A.; Fulop, Z.; Gervino, G.; Guglielmetti, A.; Gustavino, C.; Gyurky, G.; Kaeppeler, F.; Kontos, A.; Kuntz, R.; Leiste, H.; Lemut, A.; Li, Q.; Limata, B.; Marta, M.; Mazzocchi, C.; Menegazzo, R.; O'Brien, S.; Palumbo, A.; Prati, P.; Roca, V.; Rolfs, C.; Rossi Alvarez, C.; Somorjai, E.; Stech, E.; Straniero, O.; Strieder, F.; Tan, W.; Terrasi, F.; Trautvetter, H. P.; Uberseder, E.; Wiescher, M.

The 15N(p,g)16O reaction represents a break out reaction linking the first and second cycle of the CNO cycles redistributing the carbon and nitrogen abundances into the oxygen range. The reaction is dominated by two broad resonances at Ep = 338 keV and 1028 keV and a Direct Capture contribution to the ground state of 16O. Interference effects between these contributions in both the low energy region (Ep < 338 keV) and in between the two resonances (338

Publ.-Id: 14900

Blitzlampentemperung für die Photovoltaik

Skorupa, W.

A review regarding the application of flash lamp annealing for photovoltaic purposes was presented.

Keywords: Flash lamp annealing; doping; ion implantation; solar cells

Related publications

  • Lecture (Conference)
    Topical meeting with members of the company Bosch, 10.02.2010, FZ Dresden-Rossendorf, Deutschland

Publ.-Id: 14899

Advances in Si & Ge millisecond processing: From SOI to superconducting Ge

Skorupa, W.; Wündisch, C.; Posselt, M.; Heera, V.; Herrmannsdörfer, T.; Buca, D.; Mantl, D.; Haeberlein, S.; Fendler, R.; Gebel, T.

Recently we could demonstrate that advanced SOI material can be treated in advantageous manner regarding USJ formation [1]. Especially, strained Si and SiGe/Si heterostructures on insulator are promising channel materials for future nanoelectronics devices. Their successful integration into new device architectures depends on the ability of forming ultra shallow and ultra steep junctions. We present results for dopant activation in SOI, sSOI, HOI and sHOI [2]. FLA allows complete suppression of diffusion while obtaining sheet resistances lower than 500 Ω/□ in both, SOI and sSOI. Strained and unstrained SiGe heterostructures indicated significant diffusional broadening of Sb implant profiles and low electrical activation. In contrast, B shows higher activation but significant dopant loss in the near surface region. Moreover, we demonstrate that, after diamond and silicon, the third elemental group-IV semiconductor, germanium, exhibits superconductivity at ambient pressure [3]. For the first time, techniques of the state-of-the-art semiconductor processing as ion implantation and FLA were used to fabricate such material, i.e. a highly Ga-doped Ge (Ge:Ga) layer in near-intrinsic Ge. It is shown that superconductivity can be generated and tailored in the Ge host at temperatures as high as 0.5 K. Results of critical-field measurements demonstrate the quasi-two-dimensional character of superconductivity in the 60 nm thick Ge:Ga layer.
[1] F. Lanzerath, D. Buca, H. Trinkaus, M. Goryll, S. Mantl, J. Knoch, U. Breuer, W. Skorupa, B. Ghyselen, J. Appl. Phys. 104 (2008), 044908
[2] R. A. Minamisava, W. Heiermann, D. Buca, H. Trinkaus, J. Hartmann, W. Skorupa, U. Breuer, B. Ghyselen, S. Mantl, Proc. 215th ECS Meeting, Vol. 19, Issue 1, May 24-29, 2009
[3] T. Herrmannsdörfer, V. Heera, O. Ignatchik, M. Uhlarz, A. Mücklich, M. Posselt, H. Reuther, B. Schmidt, K.-H. Heinig, W, . Skorupa, M. Voelskow, C. Wündisch, R. Skrotzki, M. Helm, J. Wosnitza,
Phys. Rev. Lett., 102 (2009) 217003, Supercond. Sc. & Techn., 23 (2010) 034007

Keywords: ion implantation; flash lamp annealing; SOI; superconduction; germanium; silicon

Related publications

  • Invited lecture (Conferences)
    The VIII-th International Conference on Ion Implantation and other Applications of Ions and Electrons – ION 2010 will be held in Kazimierz Dolny, Poland, between 14-th and 17-th June 2010., 14.-17.06.2010, Kazimierz Dolny, Poland

Publ.-Id: 14898

Doping of Vertical Si Nanowires by Ion Implantation

Skorupa, W.

A review of recent work published in:

ADVANCED MATERIALS Volume: 22 Issue: 36 Pages: 4020-4024
NANO LETTERS Volume: 10 Issue: 1 Pages: 171-175
NANOSCALE RESEARCH LETTERS Volume: 5 Issue: 1 Pages: 243-246

Keywords: ion implantation; silicon nanowires; doping; scanning spreading resistance microscopy

Related publications

  • Invited lecture (Conferences)
    43.Deutsches Nutzertreffen Ionenimplantation, 06.05.2010, Erlangen, Deutschland

Publ.-Id: 14897

Literaturübersicht Temperaturmessung in RTP Mit Augenmerk auf die Blitzlampenausheilung

Reichel, D.; Skorupa, W.; Lerch, W.; Gelpey, J.

No abstract available.

  • Lecture (Conference)
    25. Treffen der Nutzergruppe RTP, 07.05.2009, Erlangen, Deutschland

Publ.-Id: 14896

Application of Large-Eddy Simulation to Pressurized Thermal Shock: assessment of the accuracy

Loginov, M. S.; Komen, E.; Höhne, T.

Pressurized Thermal Shock (PTS) is identied as one of the safety issues where Computational Fluid Dynamics (CFD) can bring real benefits. The turbulence modeling may impact overall accuracy of the calculated thermal loads on the vessel walls, therefore advanced methods for turbulent fows are required. The feasibility and mesh resolution of LES for single-phase PTS are assessed earlier in a companion paper. The current investigation deals with the accuracy of LES approach with respect to the experiment. Experimental data from the Rossendorf Coolant Mixing (ROCOM) facility is used as a basis for validation. Three test cases with dierent ow rates are considered. They correspond to a buoyancy-driven, a momentum-driven, and a transitional coolant mixing pattern in the downcomer. Time- and frequency-domain analysis are employed for comparison of the numerical and experimental data.

Keywords: PTS; CFD; Coolant Mixing; ROCOM

Publ.-Id: 14895

Doping Issues of Si Nanowires

Skorupa, W.

A review of recent work published in:

ADVANCED MATERIALS Volume: 22 Issue: 36 Pages: 4020-4024,
NANO LETTERS Volume: 10 Issue: 1 Pages: 171-175,

Keywords: Doping; ion implantation; scanning spreading resistance profiling; silicon nanowire

Related publications

  • Invited lecture (Conferences)
    27.Deutsches Nutzertreffen RTP und Heissprozesse, 05.05.2010, Erlangen, Deutschland

Publ.-Id: 14894

Biaxial optical anisotropy of self aligned silver nanoparticles and nanowires

Ranjan, M.; Facsko, S.; Möller, W.

In the present study ion beam sputtering has been used for prestructuring of a silicon substrate followed deposition of metal by ebeam evaporation. First a low energy ion beam (Ar+, 500 eV) is incident on the substrate surface at an angle of 67∘ to the surface normal to produce well ordered (20-50 nm) ripple patterns. Then physically vaporized Ag atoms are deposited at grazing angle of 70∘ to the surface normal and normal to the ripples direction. Varying deposition parameters, i.e. ripple periodicity, substrate temperature and atomic flux, we were able to produce well ordered nanoparticles and nanowires. Self-aligned Ag nanoparticles and nanowires deposited on pre-patterned ripple surfaces exhibit strong optical anisotropy. Generalised ellipsometry measurements show that off diagonal Jones matrix elements (Ψ_ps, Δ_ps, Ψ_sp, Δ_sp) are non zero and vary with Eulers angle \phi. This indicates that such a medium is biaxial in nature. A biaxial layer model approach is used to calculate dielectric functions for such a system. Tauc-Lorentz oscillators are used along x and y direction independently and Drude model along z-direction for nanoparticles. This approach provides a very good fitting with the measured Jones matrix element Ψ_pp, Δ_pp, Ψ_ps, Δ_ps, Ψ_sp, Δ_sp. Different cases for ordered nanoparticles and wires will be presented.

Related publications

  • Lecture (Conference)
    DPG Frühjahrstagung der Sektion Kondensierte Materie (SKM) 2010, 21.-26.03.2010, Regensburg, Germany

Publ.-Id: 14892

Self-Organisation of metal nanoparticles and nanowires grown on ripple templates

Ranjan, M.; Oates, T. W. H.; Facsko, S.

Nobel metal nanoparticles exhibit distinct optical properties due to their localized surface plas-mon resonance. Potential applications of these structures can be found in solar cells, nonlinear optical devices, or sensors. Especially for nanoscale optics aligned equidistant chains of metal nanoparticles are favored.
Ion beam sputtered surfaces featuring self-organized ripple patterns have proven to be excellent templates for the alignment of these metal nanoparticles [1]. In the continuous sputtering proc-ess, induced by the bombardment with low-energy ions (100 – 2000 eV), periodic surface pat-terns appear in form of ripples or arrays of hexagonally ordered mounds, which show a very high degree of regularity [2]. The dimension of the pattern is related to the size of the typical collision cascade of a single ion event and lies in the range of ten to tens of nanometers. The periodicity and regularity of the pattern is established by the effective filtering of a narrow band of spatial frequencies on the surface, which results from the interplay between a surface instability caused by the sputtering and surface diffusion processes. Regular ripple morphologies have been pro-duced in this way on very different materials including semiconductors, isolators, and metals, demonstrating the universality of the mechanism [3].
Depending on deposition angle, substrate temperature, beam flux, and deposition time, the metal nanostructures align parallel to the ripples, eventually coalesce forming nanowires [4]. Due to the alignment the nanoparticles exhibit strongly anisotropic optical properties. The difference in the interparticle distance along the parallel and perpendicular direction, respectively, leads to different plasmonic coupling in the respective directions. Therefore a red shift of the plasmon-polariton resonance is observed for light polarized parallel to the ripple direction. In addition, the resonance shifts with the aspect ratio of the nanoparticles. Energy shifts of the plasmon reso-nance of 0.2 eV to 0.7 eV have been determined for aspect ratios in the range of 2 to 5.
This work is partly supported by DFG FOR 845.
1. T.W.H. Oates, A. Keller, S. Facsko , A. Mücklich , Plasmonics 2, 47 (2007).
2. A. Keller, S. Rossbach, S. Facsko, et al., Nanotechnology 19, 135303 (2008).
3. A. Keller, S. Facsko, and A. Moller, Jour. Phys. Cond. Matt. 21, 495305 (2009).
4. T.W. H.Oates, A.Keller, S.Noda, S.Facsko , Appl. Phys. Lett. 93, 063106 (2008

Related publications

  • Poster
    Nanofair 2010, 06.07.-07.11.2010, Dresden, Germany

Publ.-Id: 14891

Self-Organisation of metal nanoparticles on ion beam produced ripple templates

Ranjan, M.; Facsko, S.; Möller, W.

Ion beam sputtering has been used for pre-structuring of the substrate. Low energy ion beam (Ar+, 500 eV) incident on the substrate surface (Si in our case) at an angle of 67o to the surface normal to produce well ordered (20-50 nm) ripple patterns [1, 2]. The periodicity and regularity of the pattern is estab-lished by the effective filtering of a narrow band of spatial frequencies on the surface, which results from the interplay between a surface instability caused by the sputtering and surface diffusion processes. Regular ripple morphologies have been produced in this way on very different materials including semiconductors, iso-lators, and metals, demonstrating the universality of the mechanism [2].
Depending on deposition angle, substrate temperature, beam flux, and deposition time, the metal nanostruc-tures align parallel to the ripples, eventually coalesce forming nanowires [3,4].A very high degree of align-ment not reported so far using the present technique has been achieved. Due to the alignment the nanoparti-cles exhibit strongly anisotropic optical properties. The difference in the interparticle distance along the paral-lel and perpendicular direction, respectively, leads to different plasmonic coupling in the respective direc-tions. Therefore a red shift of the plasmon-polariton resonance is observed for light polarized parallel to the ripple direction. In addition, the resonance shifts with the aspect ratio of the nanoparticles. Energy shifts of the plasmon resonance of 0.2 eV to 0.7 eV have been determined for aspect ratios in the range of 2 to 5.
[1]. Keller.A, Rossbach.S, Facsko.S, Nanotechnology 19(2008) 135303
[2]. Keller.A, Facsko.S,Möller.W, Jour. Phys. Cond. Matt. 21(2009) 495305
[3]. Oates.T.W.H, Keller.A, Facsko.S, A. Mücklich, Plasmonics 2(2007) 47
[4]. Oates.T.W.H, Keller.A, Noda.S, Facsko.S, Appl. Phys. Lett. 93(2008) 063106

Related publications

  • Poster
    Workshop Ion Beam Physics, 29.-31.03.2010, Dresden, Germany

Publ.-Id: 14890

Self-assembled Ag nanoparticles on plasma sputtered hexagonally ordered GaSb nanodots

Ranjan, M.; Fritzsche, M.; Zhou, J.; Facsko, S.; Möller, W.

Low energy ion-irradiation is capable to produce self-organized ripple and dot pattern on surfaces [1, 2].Ion bombardment normal to surface generate hexagonally correlated dot pattern on semiconductor surfaces [2]. Metal film grown on such pre-patterned substrate may lead to highly ordered self-assembled nanoparticles or nanowires [3]. Ordered metal nanoparticles show unique optical properties [4, 5]. In this work negatively biased (-1.2 kV) GaSb substrate was immersed in an inductively coupled RF plasma. Plasma sheath formation around the sample maintained the normal ion incidence. Ion fluence equivalent to 1x1018 cm-2 is sufficient to produce well pronounced hexagonally ordered dot structures. Later oblique incidence PVD growth of silver on such substrate, produce self-assemble nanoparticles fallowing the dots periodicity. Reflection measurement shows a plasmonic splitting and results in two pronounce resonance peak. Such a splitting is arises due to hexagonal arrangement of nanoparticles, not appeared for non-ordered particles. More details study of this work will be presented.


[1] A. Keller, S. Facsko, W. Möller, New J. Phys. 10 (2008) 063004
[2] S.Facsko, T.Dekorsy, C. Koerdt, H. Kurz, A. Vogt, H. Hartnagel, Science 285 (1999)1551
[3] T.W. H.Oates, A.Keller, S.Noda, S.Facsko, Appl. Phy. Lett., 93(2008) 063106.
[4] T.W. H.Oates, A.Keller, S.Facsko, A.Mücklich, Plasmonics 2(2007) 47.
[5] A. Taleb, V. Russier, A. Courty, M. P. Pileni, Phys.Rev.B 59 (1999) 13350

Related publications

  • Poster
    Plasma Surface Engineering (PSE), 13.-17.09.2010, Garmisch-Partenkirchen, Deutschland

Publ.-Id: 14889

Radioökologische Forschung als Basis zur Entwicklung neuer Materialien

Raff, J.

wird nachgereicht

  • Lecture (others)
    Besuch ehemaliger IRC-Mitarbeiter, 19.11.2010, Dresden, Deutschland

Publ.-Id: 14888

Vortex coupling in magnetic multilayer elements

Wintz, S.; Puzic, A.; Strache, T.; Bunce, C.; Körner, M.; Schönherr, T.; Neubert, A.; McCord, J.; Moench, I.; Mattheis, R.; Raabe, J.; Quitmann, C.; Erbe, A.; Fassbender, J.

Spin vortices have attracted much attention due to their chiral nature and the variety of dynamic phenomena associated with them. In this contribution we present experimental findings on vortex coupling in trilayer elements, where two ferromagnetic layers are separated by a nonmagnetic spacer. For such systems the relative configurations of the in-plane flux senses (circulations) as well as the core orientations (polarities) of layered vortices are identified by means of scanning transmission x-ray microscopy (STXM). The dominant coupling mechanisms here are the magneto-dipolar interaction and interlayer exchange coupling (IEC). Remarkably, a modification of the IEC, which can be induced by noble gas ion irradiation, allows to specifically set the circulation configuration of a layered vortex pair to be either an- tiferromagnetic or ferromagnetic. In addition, time-resolved measurements of the response of interlayer coupled vortices to an excitation by sinusoidal magnetic fields will be shown.

Keywords: magnetic vortex; coupling; STXM; interlayer exchange coupling

Related publications

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

Publ.-Id: 14887

Iodine in alluvial platinum–palladium nuggets

Cabral, A. R.; Radtke, M.; Munnik, F.; Lehmann, B.; Reinholz, U.; Riesemeier, H.; Tupinambá, M.; Kwitko-Ribeiro, R.

Synchrotron radiation-induced X-ray fluorescence (SR-XRF) spectrometry was applied to determine iodine concentrations in alluvial Pt–Pd aggregates with delicate morphological features from Córrego Bom Sucesso, Minas Gerais, Brazil. The millimetre-sized botryoidal and rod-shaped grains of alluvial Pt–Pd–Hg intermetallic compounds have surprisingly high concentrations of iodine, in the range from 10 to ~120 µg/g. Because iodine is a strongly biophile element, known to be enriched in peatlands and plant remains in soils by microbial activity, its concentration in the Pt–Pd nuggets suggests biogenic precious-metal fixation in the aqueous alluvial milieu.

Keywords: Iodine; Pt–Pd nuggets; Córrego Bom Sucesso; Minas Gerais; Brazil

Related publications

Publ.-Id: 14886

Magnetically induced electric polarization in an organometallic magnet

Zapf, V. S.; Kenzelmann, M.; Wolff-Fabris, F.; Balakirev, F.; Chen, Y.

The coupling between magnetic order and ferroelectricity has been under intense investigation in a wide range of transition-metal oxides. The most direct coupling is obtained in so-called magnetically induced multiferroics where ferroelectricity arises directly from magnetic order that breaks spatial inversion symmetry. However, it has been difficult to find nonoxide-based materials in which these effects occur. Here we present a study of copper dimethyl sulfoxide dichloride (CDC), an organometallic quantum magnet containing S = 1/2 Cu spins, in which electric polarization arises from noncollinear magnetic order. We show that the electric polarization can be switched in a stunning hysteretic fashion. Because the magnetic order in CDC is mediated by large organic molecules, our study shows that magnetoelectric interactions can exist in this important class of materials, opening the road to designing magnetoelectrics and multiferroics using large molecules as building blocks. Further, we demonstrate that CDC undergoes a magnetoelectric quantum phase transition where both ferroelectric and magnetic order emerge simultaneously as a function of magnetic field at very low temperatures

Publ.-Id: 14885

Breaking Translational Invariance by Population Imbalance: The Fulde-Ferrell-Larkin-Ovchinnikov States

Zwicknagl, G.; Wosnitza, J.

An overview is given of our present understanding of superconductivity with spontaneously broken translation symmetry in polarized Fermi systems. The existence of “crystalline” superconducting phases is considered in a wide range of systems, prominent examples being conduction electrons in metals, ultra-cold atoms in a trap, nuclear matter and dense quark systems. The underlying physics is delineated and theoretical approaches to the inhomogeneous phases and their properties are discussed. From the experimental side, it is argued that superconductivity with imbalance-induced order parameters is realized in layered organic compounds and potentially in heavy-fermion systems.

Publ.-Id: 14884

On-chip superconductivity via gallium overdoping of silicon

Skrotzki, R.; Fiedler, J.; Herrmannsdörfer, T.; Heera, V.; Voelskow, M.; Mücklich, A.; Schmidt, B.; Skorupa, W.; Gobsch, G.; Helm, M.; Wosnitza, J.

We report on superconducting properties of gallium-enriched silicon layers in commercial (100) oriented silicon wafers. Ion implantation and subsequent rapid thermal annealing have been applied for realizing gallium precipitation beneath a silicon-dioxide cover layer. Depending on the preparation parameters, we observe a sharp drop to zero resistance at 7 K. The critical-field anisotropy proofs the thin-film character of superconductivity. In addition, out-of-plane critical fields of above 9 T and critical current densities exceeding 2 kA/cm2 promote these structures to be possible playgrounds for future microelectronic technology

Publ.-Id: 14883

Investigation of conducting nanostructures on ta-C films made by FIB lithography

Philipp, P.; Bischoff, L.

Tetrahedral amorphous carbon (ta-C) films with high sp3 content produced by mass filtered vacuum arc deposition were modified by Ga+ FIB irradiation. Surface swelling occurs as a function of fluence, caused by ion induced conversion of sp3 to sp2 hybridized carbon atoms. A model [1] for diamond swelling was applied to ta-C films to estimate the swelling for fluences up to 1 x 1016 cm-2. For higher fluences data from TRIDYN simulations were included due to sputtering in a good agreement with the experiments. Van der Pauw structures were produced by means of Ga+ FIB lithography. A decrease of the sheet resistance with increasing fluence due to the evolution of graphitic regions was observed. The lowest value of 290 Ohm/sq was achieved at 1.6 x 1017 cm-2. Additionally, conducting graphitic wires were produced (length: 10 µm, width: 300 nm to 5 µm). The wire resistivity was measured within 130 kOhm (5 µm width) and 3 GOhm (300 nm width). Ion induced graphitization of ta-C films by FIB offers prospective applications in nano technology to fabricate conductive nanostructures in an insulating thin film.
[1] F. Bosia et al. Nucl. Instrum. Meth. B 268 (2010) 2991.

Keywords: tetrahedral amorphous carbon; ta-C; FIB lithography; graphitization; nano structures

Related publications

  • Poster
    75. Jahrestagung der DPG und DPG Frühjahrstagung, 13.-18.03.2011, Dresden, Deutschland

Publ.-Id: 14882

Freestanding Si nanowires fabricated by Ga+ FIB implantation and subsequent anisotropic etching

Böttger, R.; Bischoff, L.; Schmidt, B.; Krause, M.

Localized Ga+ ion implantation in silicon-on-insulator substrates (top layer 2 µm) by focused ion beam and subsequent anisotropic and selective wet etching has been used to fabricate freely suspended nanowires with reproducible widths between 20 and 200 nm.
The dependence of the resulting nanowire width on the implanted fluence has been investigated and is supported by a numerical model reproducing the experimental data and enabling an a priori estimation of the nanowire width as a function of the implanted fluence. Moreover, the temperature dependence of the nanowires’ resistivity and the activation energy for electrical current flow were investigated before and after direct current annealing in air and in vacuum ambient. Annealed nanowires showed a decrease of their resistivity up to two orders of magnitude, indicating a partial recrystallization of the nanowires through self-heating and a change in the conduction mechanism. The assumption of recrystallization is supported by scanning electron microscopy and Raman spectroscopy.
The comprehension of the pinpointed fabrication of such Si nanostructures establishes a broad range of application in the field of nano-electro-mechanical systems.

Keywords: silicon-on-insulator; Ga focused ion beam implantation; nanowire; anisotropic etching; width; resistivity; phase change; annealing; Raman spectroscopy

Related publications

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

Publ.-Id: 14881

Complex formation of trivalent americium with salicylic acid at very low concentrations

Müller, M.; Acker, M.; Taut, S.; Bernhard, G.

For the first time, the complexation of americium(III) with salicylic acid was studied at trace metal concentrations using a 2.0 m Long Path Flow Cell for UV–vis spectroscopy. The detection limit of Am(III) in aqueous solution at pH 3.0 was found to be 5 9 10-9 M. Two Am(III)-salicylate complexes were formed at pH 5.0 in 0.1 M NaClO4, indicated by a clear red shift of the absorption maximum. The absorption spectra obtained from spectrophotometric titration were analyzed by means of factor analysis and complex stabilities were calculated to be log b110 = 2.56 ± 0.08 and log b120 = 3.93 ± 0.19.

Keywords: Americium; Long path flow cell; UV–vis; Detection limit; Complexation; Salicylic acid

Publ.-Id: 14880

Development of a high resolution and high dispersion Thomson Parabola

Jung, D.; Hoerlein, R.; Kiefer, D.; Letzring, S.; Gautier, D. C.; Schramm, U.; Huebsch, C.; Oehm, R.; Albright, B. J.; Fernandez, J. C.; Habs, D.; Hegelich, B. M.

Here we report on the development of a novel high resolution and high dispersion Thomson Parabola for simultaneously resolving protons and low-Z ions of more than 100 MeV/nucleon necessary to explore novel laser-ion-acceleration schemes. High electric and magnetic ¯elds enable energy resolutions of ¢E=E < 5% at 100 MeV/nucleon and impede premature merging of di®erent ion species at low energies on the detector plane. First results from laser driven ion acceleration experiments performed at the Trident Laser facility demonstrate high resolution and superior species and charge state separation of this novel Thomson parabola for ion energies of more than 30 MeV/nucleon.

Keywords: laser ion acceleration; ino spectrometer

Publ.-Id: 14879

Sicherheitstechnische Fragestellungen im Reaktorbetrieb am Beispiel eines DWR

Schäfer, F.; Tusheva, P.; Weiss, F.-P.

Der Vortrag erläutert grundlegende Prinzipien der nuklearen Sicherheit, gibt einen Überblick zu Betriebstransienten und hypothetischen Störfällen in einem DWR und diskutiert die verschiedenen Methoden, welche für Untersuchungen zur Reaktorsicherheit angewendet werden.

Keywords: Nuclear Reactor; Reactor Safety

  • Invited lecture (Conferences)
    3. VDI-KTG Kolloquium "Perspektiven der Kernenergie", 26.10.2010, Dresden, Deutschland

Publ.-Id: 14878

Spatial manipulation of magnetic damping in ferromagnetic-antiferromagnetic films by ion irradiation

McCord, J.; Strache, T.; Mönch, I.; Mattheis, R.; Fassbender, J.

The effective magnetic damping parameter in ferromagnetic-antiferromagnetic-ferromagnetic NiFe/IrMn/NiFe try-layer structures is set over a wide range. Ultra-thin antiferromagnetic systems in combination with low fluence Ni-ion irradiation are used to control the magnetic damping parameter by two independent mechanisms. Changing the ferromagnetic-antiferromagnetic interface the initially strongly increased damping parameter is reduced. Applying the method locally, results in a magnetic layer with spatially distributed regions of different damping. The overall relaxation time of the mixed property film is found to be a direct superposition of the individual relaxation time contributions and thus determined by the ratio of phases with individual damping parameter.

Related publications

Publ.-Id: 14877

Realization of radiobiological in vitro cell experiments at conventional X-ray tubes and unconventional radiation sources

Beyreuther, E.

More than hundred years after the discovery of X-rays different kinds of ionizing radiation are ubiquitous in medicine, applied to clinical diagnostics and cancer treatment as well. Irrespective of their nature, the widespread application of radiation implies its precise dosimetric characterization and detailed knowledge of the radiobiological effects induced in cancerous and normal tissue. Starting with in vitro cell irradiation experiments, which define basic parameters for the subsequent tissue and animal studies, the whole multi-stage process is completed by clinical trials that translate the results of fundamental research into clinical application. In this context, the present dissertation focuses on the establishment of radiobiological in vitro cell experiments at unconventional, but clinical relevant radiation qualities.
In the first part of the present work the energy dependent biological effectiveness of photons was studied examining low-energy X-rays (≤ 50 keV), as used for mammography, and high-energy photons (≥ 20 MeV) as proposed for future radiotherapy. Cell irradiation experiments have been performed at conventional X-ray tubes providing low-energy photons and 200 kV reference radiation as well. In parallel, unconventional quasi-monochromatic channeling X-rays and high-energy bremsstrahlung available at the radiation source ELBE of the Forschungszentrum Dresden-Rossendorf were considered for radiobiological experimentation. For their precise dosimetric characterization dosimeters based on the thermally stimulated emission of exoelectrons and on radiochromic films were evaluated, whereas just the latter was found to be suitable for the determination of absolute doses and spatial dose distributions at cell position. Standard ionization chambers were deployed for the online control of cell irradiation experiments. Radiobiological effects were analyzed in human mammary epithelial cells on different subcellular levels revealing an increasing amount of damage for decreasing photon energy. For this reason, the assumed photon energy dependence was reconfirmed for a cell line other than human lymphocytes, an important finding that was discussed on the 2007 Retreat of the German Commission on Radiological Protection.
After successful finalization of the photon experiments the focus of the present dissertation was directed to the realization of in vitro cell irradiation experiments with laser-accelerated electrons. This research was carried out in the frame of the project onCOOPtics that aims on the development of laser-based particle accelerators, which promise accelerators of potentially compact size and more cost-effectiveness suitable for a widespread medical application, especially for high precision hadron therapy. The unique properties, i.e., the ultrashort bunch length and resultant ultrahigh pulse dose rate, of these unconventional particle accelerators demand for extensive investigations with respect to potential effects on the dosimetric and radiobiological characterization. Based on the experiences gained at ELBE first experiments on the radiobiological characterization of laser-accelerated electrons have been performed at the Jena Titanium:Sapphire laser system. After beam optimization, a sophisticated dosimetry system was established that allow for the online control of the beam parameters and for the controlled delivery of dose to the cell sample. Finally, worldwide first systematic in vitro cell irradiation experiments were carried out resulting in a reduced biological effectiveness for laser-accelerated electrons relative to the 200 kV X-ray reference, irrespectively on the biological effect and cell lines examined. These successful results are the basis for future in vivo studies and experiments with laser-accelerated protons.

Keywords: X-ray tubes; radiation sources

Related publications

  • Open Access Logo Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; FZD-540 2010
    ISSN: 1437-322X


Publ.-Id: 14876

Time resolved spectroscopy on quantum dots and graphene at the FELBE free-electron laser

Winnerl, S.; Stehr, D.; Wagner, M.; Schneider, H.; Helm, M.; Seidel, W.; Michel, P.; Zibik, E. A.; Carpenter, B. A.; Porter, N. E.; Skolnick, M. S.; Wilson, L. R.; Grange, T.; Ferreira, R.; Bastard, G.; Orlita, M.; Plochocka, P.; Kossacki, P.; Potemski, M.; Sprinkle, M.; Berger, C.; de Heer, W. A.

The free-electron laser FELBE at the Forschungszentrum Dresden-Rossendorf enables experiments with spectral, temporal, and, by means of near-field microscopy, also high spatial resolution. FELBE delivers picosecond IR and THz pulses in a wavelength range from 5 µm to 280 µm. Operation in a continous pulsing regime and synchronization to various tabletop laser sources allows for two-color pump-probe experiments. Here we review the potential of the laser and focus on two highlight pump-probe experiments. In the first experiments, the relaxation dynamics in self assembled InGaAs quantum dots at energies below the Reststrahlen band is studied. Long intradot relaxation times (1.5 ns) are found for level separations of 14 meV (3.4 THz), decreasing very strongly to 2 ps at 30 meV (7 THz). The results are in very good agreement with our microscopic theory of the carrier relaxation process, taking into account polaron decay via acoustic phonons [1]. In the second experiment, the relaxation dynamics in graphene is investigated at photon energies E = 20 – 250 meV. For excitations below the phonon energy of the G-mode, long relaxation times (20 – 40 ps) are observed. While the pump-induced transmission is positive for E > 30 meV, pump-induced absorption occurred for E < 20 meV. The increased transmission for E > 30 meV is caused by bleaching of the interband transition. We attribute the induced absorption to heating of carriers by intraband free-carrier absorption for E < 2E_F (E_F: Fermi energy).

[1] E. A. Zibik et al. Nature Materials 8, 803 - 807 (2009).

Keywords: Quantum dots; graphene; relaxation dynamics; polarons; terahertz; infrared; pump-probe spectroscopy

Related publications

  • Invited lecture (Conferences)
    SPIE Photonics West, 22.-27.01.2011, San Francisco, USA
  • Proceedings of SPIE 7937(2011), 793708
    DOI: 10.1117/12.873702


Publ.-Id: 14875

Relaxation dynamics in epitaxial graphene probed at low excitation energies

Winnerl, S.; Orlita, M.; Plochocka, P.; Schneider, H.; Helm, M.; Kossacki, P.; Potemski, M.; Sprinkle, M.; Berger, C.; de Heer, W. A.

The relaxation dynamics of graphene has been investigated in various degenerate as well as two-color pump-probe studies at excitation energies E = 1.6 eV [1-5]. We report on degenerate pump-probe spectroscopy at much lower energies (E = 20 – 250 meV; radiation source: free-electron laser) on graphene multilayers grown by thermal decomposition. Relaxation times between 20 and 40 ps are found for photon energies E < 70 meV, where only acoustic phonons can contribute to the relaxation dynamics. At 245 meV a much faster relaxation with two time constants (tau_1 ≈ 1.2 ps, tau_2 = 4 – 8 ps) is observed and attributed to contributions of optical phonons. While the pump-induced transmission is positive for E > 30 meV, pump-induced absorption occurred for E < 20 meV (Fig. 1). The increased transmission for E > 30 meV is caused by bleaching of the interband transition. We attribute the induced absorption to heating of carriers by intraband free-carrier absorption for E < 2E_F (E_F: Fermi energy).
[1] J.M. Dawlaty et al., Appl. Phys. Lett. 92, 042116 (2008).
[2] D. Song et al., Phys. Rev. Lett. 101, 157402 (2008).
[3] P.A. George et al., Nano Lett. 8 ,4248 (2008).
[4] H. Wang et al., Appl. Phys. Lett., 96, 081917 (2010).
[5] D. Sun et al., Phys. Rev. Lett. 104, 136802 (2010).

Keywords: Relaxation dynamics; graphene; infrared; terahertz

Related publications

  • Poster
    2nd International Symposium on the Science and Technology of Epitaxial Graphene, 14.-17.09.2010, Amelia Island, USA

Publ.-Id: 14874

Compositional depth profiling of TaCN thin films

Adelmann, C.; Conard, T.; Franquet, A.; Brijs, B.; Munnik, F.; Burgess, S.; Witters, T.; Meersschaut, J.; Kittl, J. A.; Vandervorst, W.

The composition profiling of thin TaCN films was studied. For the composition profile determination using x-ray photoemission spectrometry (XPS) in combination with Ar sputtering, preferential sputtering effects of N with respect to Ta and C were found to lead to inaccurate elemental concentrations. Sputter yield calculations for the given experimental conditions allowed for the correction of a part of the error, leading to fair accuracy by reference-free measurements. Further improvement of the accuracy was demonstrated by the calibration of the XPS compositions against elastic recoil detection analysis (ERDA) results. For Auger electron spectrometry (AES) in combination with Ar sputtering, accurate results required the calibration against ERDA. Both XPS and AES allowed for a reliable and accurate determination of the compositional profiles of TaCN-based thin films after calibration. Time-of-flight secondary-ion mass spectrometry was also used to assess the composition of the TaCN films. However, the analysis was hampered by large matrix effects due to small unintentional oxygen contents in the films. Energy-dispersive x-ray spectrometry is also discussed, and it is shown that an accurate reference-free measurement of the average film concentration can be achieved.

Keywords: TaC; TaN; TaCN; XPS; AES; ToF-SIMS; ERDA; EDX; composition profile

Related publications

Publ.-Id: 14873

Speciation of Uranium in Seepage and Pore Waters of Heavy Metal-Contaminated Soil

Baumann, N.; Arnold, T.; Lonschinski, M.

The uranium speciation in natural occurring seepage water samples, and in soil water samples, all samples from test site “Gessenwiese”, were analyzed by Time-resolved Laser-induced Fluorescence Spectroscopy (TRLFS). Test site Gessenwiese was installed as a part of a research program of the Friedrich Schiller University Jena for investigations within the area of a recultivated former uranium mining heap close to Ronneburg (Eastern Thuringia).
Those investigations revealed that the uranium speciation in that seepage water is dominated by the uranium (VI) sulfate species UO2SO4(aq). The analyses were performed to compare presented results in a later stage with the uranium speciation in plants, which grow on the grassland test site Gessenwiese. It was showed that TRFLS is a useful tool for clearing up the speciation of uranium in water, which is affiliated by plants.

  • Book chapter
    Kothe, Erika; Varma, Ajit: Bio-Geo Interactions in Metal-Contaminated Soils, Berlin: Springer, 2012, 978-3-642-23326-5, 131-142

Publ.-Id: 14872

Reversals and the turbulent alpha-effect in kinematic simulations of natural and experimental dynamos

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

From paleomagnetic observations, numerical simulations and -- meanwhile -- also experiments, it is evident that reversing dynamos are a quite common phenomenon. An easy access to the examination of reversing dynamos is provided by simplifying mean field simulations where the induction effects of helical small scale turbulence are parametrized by the so called α-effect.

In a geodynamo-like α2-model reversing solutions are obtained only for a highly restricted class of radial α-profiles which are characterized by a proximity of oscillating and non-oscillating state. The required properties of the α-effect, indeed, have been found from local simulations of rotating magnetoconvection in a Cartesian box (Giesecke et al. 2005, PEPI 152, 90-102). Essential properties of the field reversals can be assigned to the behavior of so called exceptional points in the spectrum of the dynamo-operator where two different non-oscillatory field eigenmodes merge and continue as one oscillatory eigenmode (Stefani et al. 2005, PRL, 94, 184506). The connection between oscillating solutions and irregular occurring reversals arises from fluctuations of the α-effect, which causes a sporadic switching from steady to the oscillatory regime and vice versa. In this picture a reversal is an inevitable consequence of the behavior of the instantanous growthrate in conjuction with fluctuations of the driving source.

Recent results of the French von-Kármán-Sodium (VKS) dynamo offer a possibility for detailed investigations of reversing magnetic fields. In the VKS experiment a turbulent flow of liquid sodium is driven by two counter rotating soft iron impellers located close to the endplates of a cylindrical vessel. The geometric structure of the observed magnetic field is dominated by an axisymmetric dipole that exhibits regular and irregular reversals if the impellers rotate with different frequencies. Recent simulations show that the induction process is essentially determined by the material properties of the flow driving impellers (high permeability) because of internal boundary conditions for the magnetic field on the interface between fluid and impeller (Giesecke et al. 2010, PRL 104, 044503). However, only the combined interaction of soft iron disks and a comparatively small α-effect allows to explain the dominating axisymmetric field. Contributions of dipole and quadrupole type fields deduced from the equatorial symmetry show nearly the same growth rate supporting the reversal model presented by Pétrélis & Fauve (2009, PRL 102, 144503) that is based on the coupling between these two modes.

Keywords: Dynamo; Geodynamo; alpha-effect; Simulations

  • Poster
    AGU Fall Meeting 2010, 13.-17.12.2010, San Francisco, USA
  • Contribution to proceedings
    AGU Fall Meeting 2010, 13.-17.12.2010, San Francisco, USA
    Reversals and the turbulent α-effect in simulations of natural and experimental dynamos

Publ.-Id: 14871

High permeability material and dynamo action

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

A prescribed flow of liquid sodium provides an energy source for self-generation of a magnetic field. The influences of non-uniform material properties on the dynamo process are examined by means of kinematic simulations of the electromagnetic induction equation.

High permeability material even if localized in a small volume like the flow driving impellers in the French VKS dynamo experiment, essentially determines the field generation process (decrease of the effective critical magnetic Reynolds number and enforcement of internal boundary conditions on material interfaces). Permeability caused facilitation of dynamo action might be important as well for the helical flow in cooling circuits of fast breeders. Preliminary simulations for a model flow in and around soft-iron sub-assemblies (that comprise the nuclear fuel pins) show a reduction of the critical magnetic Reynolds number for the onset of dynamo action by a factor of 2.

Keywords: Dynamo; Permeability

  • Poster
    MHDDAYS 2010, 22.-23.11.2010, Dresden, Germany

Publ.-Id: 14870

Multiple active mirror concept for high energy short-pulse lasers

Loeser, M.; Kroll, F.; Röser, F.; Siebold, M.; Schramm, U.; Sauerbrey, R.

Ytterbium-doped gain media are preferably utilized in high-energy, diode-pumped lasers due to their comparably long fluorescence lifetime, absence of excited state absorption, and quenching effects. Despite exhibiting a low quantum defect, thermal lensing and stress birefringence within the amplifying medium limits the maximum repetition rate of large aperture lasers. Furthermore, the quasi-three-level scheme of Yb3+ leads to re-absorption losses at room temperature especially when operating at low fluences. Here, we present a novel approach combining longitudinal cooling of a disk-laser design with the energy storage capability of a rod amplifier. Therefore, a multiple active mirror amplifier is presented for improved optical-to-optical conversion efficiency and reduced thermally induced aberrations at high repetition rates. Multi-passing both pump and extraction beams through the gain medium, which is well known from thin-disk lasers, also reduces the re-absorption losses. However, energy scaling of a single thin-disk design is limited by parasitic lasing due to a high aspect ratio between longitudinal and transverse gain. We also introduce simulation results on a multiple active mirror short-pulse amplifier employing various Ytterbium-doped gain media such as Yb:YAG, Yb:CaF2, Yb:glass, and Yb:silica. Furthermore, time resolved measurements of thermally induced aberrations at pulse-pumped operation are illustrated.

Keywords: Diode-pumped lasers; Ytterbium-doped solid state lasers

  • Lecture (Conference)
    DPG Frühjahrstagung der Sektion AMOP 2010, 08.-12.03.2010, Hannover, Deutschland

Publ.-Id: 14869

Ion-beam induced hydrogen redistribution in a-Si:H-based triple layer structures

Pantchev, B.; Danesh, P.; Schmidt, B.; Grambole, D.; Bischoff, L.

Ion-beam induced hydrogen migration has been studied in triple layer structures, a-Si/a-Si:H/a-Si and SiO2/a-Si:H/SiO2. Nuclear reaction analysis has been used for simultaneous irradiation with MeV ions and measurement of hydrogen distribution in the structures. It has been established that there is no hydrogen loss from SiO2/a-Si:H/SiO2 structures, but an asymmetric redistribution due to hydrogen penetration into the bottom SiO2 layer. Hydrogen loss has been observed from the a-Si/a-Si:H/a-Si structures. The inspection of the surface of these samples by means of atomic force microscope has shown that it proceeds by bubble formation and blistering at the inner interface. The observed ion-beam induced selective penetration of hydrogen into the underlying material can be used as a tool for preparation of microcavity and microchannel arrays.

Keywords: a-Si:H; ion implantation; hydrogen migration

Related publications

  • Lecture (Conference)
    16 th International School on Condensed Matter Physics “Progress in Solid State and Molecular Electronics, Ionics and Photonics”, 29.08.-03.09.2010, Varna, Bulgaria
  • Open Access Logo Journal of Physics: Conference Series 253(2010), 012055
    DOI: 10.1088/1742-6596/253/1/012055
    Cited 1 times in Scopus

Publ.-Id: 14868

Nanoindentation-induced pile-up in hydrogenated amorphous silicon

Pantchev, B.; Danesh, P.; Wiezorek, J.; Schmidt, B.

Nanoindentation-induced material extrusion around the nanoindent (pile-up) leads to an overestimation of elastic modulus, E, and nanohardness, H, when the test results are evaluated using the Oliver and Pharr method. Factors affecting the pile-up during testing are residual stresses in film and ratio of film and substrate mechanical properties. Nanoindentation of hydrogenated amorphous silicon (a-Si:H) films has been carried out with the aim to study the effect of residual compressive stress on the pile-up in this material. To distinguish the contribution of compressive stress to the appearance of pile-up ion implantation has been used as a tool, which reduces the compressive stress in a-Si:H. Scanning probe microscope has been used for the imaging of the indent and evaluation of the pile-up. The values of E and H have been obtained from the experimental load-displacement curves using depth profiling with Berkovich tip, which has created negligible pile-up. A sharper cube corner tip has been used to study the pile-up. It has been established that pile-up is determined by the material plasticity, when the compressive stress is below 200 MPa. The contribution of mechanical stress to the pile-up is essential for the stress as high, as about 500 MPa.

Keywords: Nanoindentation; silicon hardness; ion implantation

Related publications

  • Lecture (Conference)
    16 th International School on Condensed Matter Physics “Progress in Solid State and Molecular Electronics, Ionics and Photonics”, 29.08.-03.09.2010, Varna, Bulgaria
  • Open Access Logo Journal of Physics: Conference Series 253(2010), 012054
    DOI: 10.1088/1742-6596/253/1/012054
    Cited 4 times in Scopus

Publ.-Id: 14867

Effect of hydrogen on hardness of amorphous silicon

Danesh, P.; Pantchev, B.; Wiezorek, J.; Schmidt, B.; Grambole, D.

A comparative study of hardness of thin films of hydrogenated amorphous silicon (a-Si:H) and hydrogen-free amorphous silicon (a-Si) was carried out to reveal the role of hydrogen in the plastic properties of amorphous silicon. In addition, the effect of hydrogen on hardness was established by changing hydrogen concentration in the material using post-deposition processing of the samples. The hydrogen concentration in a-Si:H was decreased by thermal annealing. In a-Si hydrogen was introduced by plasma hydrogenation. The values of hardness of the as-prepared a-Si and a-Si:H films were determined by nanoindentation using depth profiling. Low-depth indentation was applied to evaluate the effect of post-hydrogenation. The results obtained show that the presence of hydrogen in the amorphous silicon network leads to the increase in hardness. The conducted experiments demonstrate that plasma hydrogenation can be used as an effective tool to increase the hardness of amorphous silicon. Hardness of a-Si:H of about 12.3–12.7 GPa is as high as of crystalline silicon, suggesting a-Si:H can be a substitute for crystalline silicon in some MEMS.

Keywords: Hydrogenated amorphous silicon; Ion implantation; Elastic modulus; Hardness

Related publications

Publ.-Id: 14866

Effect of keV ion irradiation on mechanical properties of hydrogenated amorphous silicon

Danesh, P.; Pantchev, B.; Wiezorek, J.; Schmidt, B.

The susceptibility of mechanical properties of hydrogenated amorphous silicon (a-Si:H) to the implantation-enhanced disorder has been studied with the aim to extend the application field of this material in the technology of micro-electromechanical systems. Effect of keV ion irradiation on the elastic modulus, E, of hardness, H, and of root-mean-squared roughness to silicon ion implantation has been determined. The mechanical properties were evaluated by nanoindentation testing. E of 119 GPa and H of 12.3 GPa were determined for the as-prepared a-Si:H film. The implantation of silicon ions leads to a decrease in E and H, evaluated for a series of the implantation fluences in the range of 1.0x1013–5.0x1016 cm-2. Surface smoothing has been observed at high fluences and low ion energy of 18 keV, suggesting that ion beam may be used as a tool to reduce the roughness of the a-Si:H surface, while keeping intact the mechanical properties inside the film. The conducted experiments show that it is possible to prepare a-Si:H films with hardness and smoothness comparable to crystalline silicon.

Keywords: Hydrogenated amorphous silicon; Ion implantation; Elastic modulus; Hardness

Related publications

Publ.-Id: 14865

Magnetic hybrid films - magnetic property patterning by ion irradiation

McCord, J.; Hamann, C.; Strache, T.; Martin, N.; Mönch, I.; Mattheis, R.; Kaltofen, R.; Quandt, E.; Fassbender, J.

Ion irradiation and implantation allows for a focussed materials modification in the range of a few nanometer. Effects of periodic patterning of the physical properties circumventing topographic patterning in the conventional sense are exploited. Magnetic materials with mixed hybrid magnetic properties are created. An overview over ongoing activities at the FZD will be given.

Related publications

  • Invited lecture (Conferences)
    „Struktur und Eigenschaften kondensierter Materie“ Seminar der TU Chemnitz, 23.11.2010, TU Chemnitz, Germany

Publ.-Id: 14864

Electrical characterization of oxygen vacancies in oxides by means of space charge spectroscopy

Schmidt, H.

The development of new materials for cool devices, e.g. memristive and spintronics devices, needs non-destructive techniques to characterize defects in new materials. The knowledge on defects is strongly desired and will help to prevent device degredation. The non-destructive characterization of certain defects is possible by means of positron annihilation spectroscopy (PAS) if open volume-defects are large and electrically neutral/negatively charged, if segregations are attractive for positrons and change the annihilation rate, and/or if the electron density and with that annihilation rate changes during phase transitions. The complementary, destructive characterization of defects in semiconductors prepared as diodes by means of space charge spectroscopy is possible if the defects are charged/decharged in response to electrical pulses applied to the diode.

Keywords: defects; space charge spectroscopy; positron annihilation spectroscopy

Related publications

  • Lecture (Conference)
    Workshop on Positron Annihilation Spectroscopy, 19.10.2010, FZD, Germany

Publ.-Id: 14862

Electrical characterization of semiconductors on the mm-nm length scale

Schmidt, H.

The electrical conductivity of semiconductors is controlled by the activated dopant level and the intrinsic carrier concentration. Semiconductor devices are prepared with either holes or electrons as the majority charge carriers. Hall effect measurements yield carrier concentration and mobility and estimates of scattering mechanisms. The use of Hall effect measurements and of capacitance-voltage and deep level transient spectroscopy measurements for profiling depth dependent free carrier concentrations and for identifying deep traps within the forbidden gap of semiconductors, respectively, yields a potent suite of characterization techniques on the mm-mum length scale. Insight into the electrical properties of doped semiconductor nanostructures may be obtained from scanning spreading resistance microscopy and Kelvin probe force microscopy measurement. Dielectric semiconductor conductivities on the nm scale may be obtained from scanning probe microscopy measuremens. Examples of current investigations by means of the presented electrical characterization techniques are given.

Keywords: space charge spectroscopy; electrical nanometrology

  • Invited lecture (Conferences)
    IZFP-Kolloquium, 25.10.2010, Saarbrücken, Germany

Publ.-Id: 14861

Temperature Measurement in Rapid Thermal Annealing

Reichel, D.; Skorupa, W.; Lerch, W.; Gelpey, J.

Microelectronics Industry and consequently semiconductor research have developed into pillars of modern technology. Industrial demands for short process times at low cost are steadily increasing. Considerable attention is thereby drawn to ultra-short annealing cycles on the order of just a few milliseconds.
One major application for thermal annealers is to anneal damage caused by ion implantation. For this purpose temperatures above 600 °C are preferred, although a high diffusion rate of the dopants ought to be avoided. Therefore, short heating periods with steep ramp rates are desired.
This is where Flash Lamp Annealing comes into play. It allows for directed thermal treatment of surfaces within just a few milliseconds without or with drastically reduced thermal stress of the bulk material. Due to the selected wavelength range in the visible and near infrared region the lightpulse is absorbed by the near-surface layers and diffusion into the bulk is limited by the ultra-short time span. Thereby temperatures up to 2000°C are achieved dependent on the energy of the lightpulse and the optical properties of the sample. Cooling takes place by heat conduction into the bulk.
The applications are numerous, especially in thermal treatment of semiconductor surfaces where doping concentrations far beyond the solubility limit are desired, e.g. for ultra shallow implantation profiles. Similarily, highly doped layers are required when studying small scale effects like superconductivity brought about by the implanted dopant.
Due to the high energy density on the sample even high melting points can be achieved for defect annealing during recrystallization of the melt.
The response of various materials to subsecond thermal treatment, however, is not well understood for most cases, especially the temperature dependence of many material parameters is unknown to a large extent. Clearly, for deeper investigation into the subject a real-time temperature measurement with a high temperature resolution (ΔT << 5K), is crucial and is regarded as a key component in order to achieve rapid and reliable processing.
For this purpose traditional means of temperature measurement, e.g. thermocouples, must be excluded. Not only do they lead to wafer contamination but their long response time contradicts the ultra-fast annealing time of the Flash Lamp Device.
In the framework of the presentation previous non-contact approaches to rapid temperature measurement will be discussed with special regard to temperature resolution and industrial mass production.

Keywords: Temperature Measurement; Rapid Thermal Annealing; Flash Lamp Annealing

  • Lecture (Conference)
    9th International Workshop on Subsecond Thermophysics, 22.-24.09.2010, Graz, Österreich

Publ.-Id: 14860

Rückbau des Zyklotrons U-120 am Forschungszentrum Dresden-Rossendorf

Naumann, B.; Friedrich, M.; Matz, W.

Der Beitrag gibt einen Überblick über den Stand des Rückbaus des Zyklotrons U-120, das von 1958 bis 1999 eines der größten experimentellen Anlagen im Forschungszentrum Rossendorf war. Der Rückbau der Beschleunigeranlage begann im Jahr 2001. Bis zum November 2010 sind alle Anlagenteile und Experimentaufbauten radiologisch bewertet und größtenteils entsorgt worden. Der Beitrag beschreibt u. a. die Verfahren zur Bewertung der Aktivierung großer Bauteile des Zyklotrons.

  • Invited lecture (Conferences)
    4. Symposium Stilllegung und Rückbau kerntechnischer Anlagen, 02.-03.11.2010, Hannover, Deutschland

Publ.-Id: 14859

A trigonal nodal solution approach to the multi-group simplified P3 equations in the reactor code DYN3D

Duerigen, S.; Grundmann, U.; Mittag, S.; Merk, B.; Fridman, E.; Kliem, S.

The neutronics model of the nodal reactor dynamics codeDYN3D developed for 3-D analyses of steady states and transients in light-water reactors has been extended by a simplified P3 (SP3) neutron transport option to overcome the limitations of the diffusion approach. To provide a method being applicable to reactors with hexagonal fuel assemblies and furthermore allowing flexible mesh refinement, the nodal SP3 method has been developed on the basis of a flux expansion in trigonal-z geometry. In this paper, the derivation of the trigonal SP_3 method is presented and preliminary assessment of the methodology is performed.

Keywords: simplified P3; SP3; nodal method; trigonal; triangular; hexagonal

  • Contribution to proceedings
    International Conference on Mathematics and Computational Methods Applied to Nuclear Science and Engineering (M&C 2011), 08.-12.05.2011, Rio de Janeiro, Brazil, 978-85-63688-00-2
  • Lecture (Conference)
    International Conference on Mathematics and Computational Methods Applied to Nuclear Science and Engineering (M&C 2011), 08.-12.05.2011, Rio de Janeiro, Brazil

Publ.-Id: 14858

Preparation of laser-accelerated proton beams for radiobiological applications

Metzkes, J.; Cowan, T. E.; Karsch, L.; Kraft, S. D.; Pawelke, J.; Richter, C.; Richter, T.; Zeil, K.; Schramm, U.

This paper presents the concept of transport and filtering of laser-accelerated proton pulses used for the first cell irradiation experiments performed with the Dresden 150 TW laser DRACO. Based on a simple non-focusing magnetic dipole equipped with two apertures the concept makes use of an energy dependent angular asymmetry of the proton spectra. For micron thin target foils protons of interest with energies above 7 MeV are observed to be significantly oset from target normal where low energy emission is dominantly centered. As the eect can be controlled via the target rotation with respect to the incoming light, it can be used to optimize the transport efficiency for high energy protons while simultaneously suppressing background radiation.

Keywords: laser acceleration of ions; target normal sheath acceleration; magnetic energy filter; radiobiological studies

Publ.-Id: 14857

Bispidine-derivatives for radiopharmaceutical applications

Fähnemann, S.

kein Abstract verfügbar

  • Lecture (others)
    Seminarvortrag School of Chemistry, Monash University, 07.10.2010, Melbourne, Australia

Publ.-Id: 14856

Correlation between the microstructure and the degradation of rare earth implanted Si-based light emitters

Rebohle, L.; Nazarov, A.; Tyagulskii, S.; Tyagulskii, I.; Lehmann, J.; Skorupa, W.

The degradation of rare earth (RE)-implanted light emitters based on a Si-SiO2-SiON-ITO structure was investigated using the example of Tb and Eu as a function of their microstructural, electrical and electroluminescence (EL) properties. As shown by transmission electron microscopy and Rutherford backscattering spectroscopy the different implantation and annealing conditions lead to two different types of microstructures: devices with small RE oxide clusters and devices with large RE oxide clusters and strong RE agglomerations at the SiO2 interfaces. The electrical and EL properties of the devices were characterized by constant current injection measurements, in which the EL and the applied voltage is monitored with time, and IV, CV and EL spectrum measurements. As a result of these investigations it is shown that devices with small RE oxide clusters normally exhibit a high EL intensity and degrade in a two-step process characterized by a negative and a positive net charge trapping. In contrast to this, devices with large RE oxide clusters have a lower EL intensity, but the first step of degradation is suppressed resulting in lower quenching cross sections and thus a longer operation life time. The degradation is explained by a defect shell model in which the RE oxide clusters are surrounded by defect regions of different extensions leading to the different behavior of devices with small and large RE oxide clusters.

Keywords: Electroluminescence; rare earth; MOS capacity; charge trapping; ion implantation

Related publications

  • Lecture (Conference)
    3rd Int. Meeting on Recent Developments in the study of Radiation Effects in Matter, 24.-28.10.2010, Gramado, Brazil

Publ.-Id: 14855

Comparison of the stability of Y-90-, Lu-177- and Ga-68- labeled human serum albumin microspheres (DOTA-HSAM)

Wunderlich, G.; Schiller, E.; Bergmann, R.; Pietzsch, H.-J.


Microparticles derived from denatured human serum albumin (DOTA-derivatized human serum albumin microspheres, or DOTA-HSAM) are attractive carriers of radionuclides for both therapeutic and diagnostic purposes. In this article, we describe a labeling procedure for diagnostic (Ga-68) and therapeutic (Y-90, Lu-177) radionuclides and report on the results of stability studies of these products.


DOTA-HSAM was labeled in 0.5 M ammonium acetate buffer, pH 5.0, containing 0.02 mg/ml detergent. After adding the radionuclide, the mixture was shaken for 15 min at 90°C. Labeling yields and in vitro stability were determined by thin-layer
chromatography. For determination of the in vivo stability of Ga-68 and Y-90 DOTA-HSAM, the particles were injected intravenously in Wistar rats.


Labeling yields up to 95% in the case of Ga-68 and Lu-177 were achieved. Ga-68-labeled DOTA-HSAM showed high in vitro and in vivo stability. The amount of particle-bound radioactivity of Lu-177 DOTA-HSAM declines slowly in a linear manner to approximately 72% after 13 days. For Y-90, the labeling yield decreased with increasing radioactivity level. We presume radiolysis as the reason for these findings.


The labeling of DOTA-HSAM with different radionuclides is easy to perform. The radiation-induced cleavage of the labeled chelator together with the rather short half-life of radioactivity fixation in vivo (3.7 days) is, in our opinion, opposed to therapeutic applications of DOTA-HSAM. On the other hand, the high stability of Ga-68 DOTA-HSAM makes them an attractive candidate for the measurement of regional perfusion by PET.

Keywords: Human serum albumin microspheres; Stability; Radiolabeled particles; Radiolysis; Thiourea bond

Publ.-Id: 14854

Production of Lambda and Sigma(0) hyperons in proton-proton collisions

Abdel-Bary, M.; Abdel-Samad, S.; Brinkmann, K.-T.; Clement, H.; Dietrich, J.; Doroshkevich, E.; Dshemuchadse, S.; Ehrhardt, K.; Erhardt, A.; Eyrich, W.; Filges, D.; Filippi, A.; Freiesleben, H.; Fritsch, M.; Gast, W.; Georgi, J.; Gillitzer, A.; Gottwald, J.; Hesselbarth, D.; Jaeger, H.; Jakob, B.; Jaekel, R.; Karsch, L.; Kilian, K.; Koch, H.; Krapp, M.; Kress, J.; Kuhlmann, E.; Lehmann, A.; Marcello, S.; Marwinski, S.; Mauro, S.; Meyer, W.; Michel, P.; Moeller, K.; Morsch, H. P.; Moertel, H.; Naumann, L.; Paul, N.; Pinna, L.; Pizzolotto, C.; Plettner, C.; Reimann, S.; Richter, M.; Ritman, J.; Roderburg, E.; Schamlott, A.; Schoenmeier, P.; Schroeder, W.; Schulte-Wissermann, M.; Sefzick, T.; Stinzig, F.; Steinke, M.; Sun, G. Y.; Teufel, A.; Ullrich, W.; Wagner, G. J.; Wagner, M.; Wenzel, R.; Wilms, A.; Wintz, P.; Wirth, S.; Wuestner, P.; Zupranski, P.

This paper reports results on simultaneous measurements of the reaction channels pp → pK+Λ and pp → pK+Σ0 at excess energies of 204, 239, and 284MeV (Λ) and 127, 162, and 207MeV (Σ0). Total and differential cross-sections are given for both reactions. It is concluded from the measured total cross-sections that the high-energy limit of the cross-section ratio is almost reached at an excess energy of only about 200MeV. From the differential distributions observed in the overall CMS as well as in the Jackson and helicity frames, a significant contribution of interfering nucleon resonances to the Λ production mechanism is concluded while resonant Σ0 production seems to be of lesser importance and takes place only through specific partial waves of the entrance channel. The data also indicate that kaon exchange plays a minor role in the case of Λ but an important role for Σ0 production. Thus the peculiar energy dependence of the Λ/Σ0 cross-section ratio appears in a new light as its explanation requires more than mere differences between the pΛ and the pΣ0 final-state interaction. The data provide a benchmark for theoretical models already available or yet to come.

Publ.-Id: 14853

Characterization of microstructural defects in melt grown ZnO single crystals

Anwand, W.; Brauer, G.; Grynszpan, R. I.; Cowan, T. E.; Schulz, D.; Klimm, D.; Čížek, J.; Kuriplach, J.; Procházka, I.; Ling, C. C.; Djurišić, A. B.; Klemm, V.; Schreiber, G.; Rafaja, D.

Various nominally undoped, hydrothermally or melt grown (MG) ZnO single crystals have been investigated by standard positron lifetime measurements. Furthermore, optical transmission measurements and structural characterizations have been performed; the content of hydrogen in the bound state was determined by nuclear reaction analysis.
A positron lifetime of 165-167 ps, measured for a brownish MG ZnO sample containing (0.30 +/- 0.03) at.-% of bound hydrogen, matches perfectly the value found for colorless MG ZnO crystals. The edge shift, observed in the "blue light domain" of the optical absorption for the former sample with respect to the latter samples, is estimated to be 0.70 eV, and found equal to a value reported previously. The possible role of zinc interstitials as well as nitrogen-related defects is considered and discussed. Microstructure analysis by X-ray diffraction and transmission electron microscopy revealed the presence of stacking faults in MG crystals in a high concentration, which suggests these defects to be responsible for the observed positron lifetime.

Keywords: zinc oxide; microstructure defects; positron annihilation; optical transmission; X-ray diffraction; transmission electron microscopy

Publ.-Id: 14852

Bakterielle Wechselwirkungen ausgewählter Actinide vor dem Hintergrund der Endlagerung von radioaktivem Abfall

Moll, H.

Bakterien, ubiquitär vorkommende Mikroorganismen, können signifikant die Speziation und damit das Verhalten von Schwermetallen in der Umwelt beeinflussen. Detaillierte Kenntnisse der Wechselwirkungsprozesse von Bakterien mit Actiniden sind z. B. für Langzeitsicherheitsanalysen für zukünftige Endlager hochradioaktiver Abfälle sowie zur Sanierung kontaminierter Flächen und Einrichtungen erforderlich. Das Interesse an mikrobiellen Prozessen der Actinide ist in den letzten Jahren stetig gestiegen. Dennoch sind die Kenntnisse zur mikrobiellen Diversität an möglichen Endlagerstandorten von nuklearem Abfall relativ begrenzt.
Im Vortrag werden am Beispiel ausgewählter Actinide detaillierte Untersuchungen zur Aufklärung von deren Speziation mit speziellen Bakterien vorgestellt. Ein kurzer Überblick zur Bestimmung der mikrobiellen Diversität in Umweltproben wird gegeben. Der Hauptschwerpunkt liegt auf direkten und indirekten Wechselwirkungsprozessen der Actinide mit Bakterien.

Keywords: bacteria; actinides; nuclear waste disposal

Related publications

  • Invited lecture (Conferences)
    Seminar für Kern- und Radiochemie am Institut für Kernchemie der Johannes Gutenberg-Universität Mainz, 29.11.2010, Mainz, Deutschland

Publ.-Id: 14851

Surface Modification on KBr (001) with Slow Highly Charged Ions

Wilhelm, R. A.; Heller, R.; El-Said, A. S.; Facsko, S.

Highly Charged Ions (HCI) carry an enormous amount of potential energy (up to 100 keV for Xe50+) which is defined as the sum of the binding energies of all missing electrons. This unique parameter offers new ways of surface modifications without a significant bulk damage.
During neutralization and de-excitation processes of the HCI the potential energy is released into electronic excitations within the solid (creation of electron hole pairs). These electron hole pairs get rapidly self-trapped due to strong electron-phonon coupling in the ionic lattice and decay into color centers (mainly H, F and F*-centers).
Finally these color centers lead to a desorption of K and Br neutralized atoms at the surface site, which after a agglomeration of many of these color centers forms a pit-like nanostructure on atomically flat KBr(001) surfaces.
The influence of kinetic and potential energy effects will be discussed.

Keywords: HCI; DIET; KBr; electron-hole pair; pit; nanostructures; color center

Related publications

  • Lecture (Conference)
    International Symposium on Electron Beam Ion Sources and Traps, EBIST2010, 07.-10.04.2010, Stockholm, Sverige
  • Poster
    International Symposium on Electron Beam Ion Sources and Traps, EBIST2010, 07.-10.04.2010, Stockholm, Sverige

Publ.-Id: 14850

The traceless Staudinger ligation with fluorine-18: a novel and versatile labeling technique for the synthesis of PET-radiotracers

Pretze, M.; Wuest, F.; Peppel, T.; Köckerling, M.; Mamat, C.

The development of rapid radiolabeling techniques under mild reaction conditions involving the short-lived positron emitter fluorine-18 remains a special challenge in organic PET chemistry. This work describes a novel and facile application of the traceless Staudinger ligation as a mild and versatile labeling method for preparation of various radiotracers labeled with fluorine-18.

Keywords: Radiolabeling; Traceless Staudinger ligation; Bioorthogonal; Fluorine-18

Publ.-Id: 14849

The speciation of U(VI) in aqueous solution and sorbed onto TiO2 studied by in situ vibrational spectroscopy

Müller, K.; Meusel, T.; Brendler, V.; Foerstendorf, H.; Bernhard, G.

The migration behavior of uranium in the environment is controlled by prominent molecular phenomena such as hydrolysis and complexation reactions in aqueous solutions as well as the diffusion and sorption onto minerals present along groundwater flow paths. These reactions significantly influence the mobility and bioavailability of the metal ions in the environment, in particular at water-mineral interfaces. Hence, for the assessment of migration processes the knowledge of the mechanisms occurring at interfaces is crucial. The required structural information can be obtained using various spectroscopic techniques.
In the present study, the speciation of uranium(VI) at the TiO2-water interface has been investigated by the application of attenuated total reflection Fouriertransform infrared (ATR FT-IR) spectroscopy. Moreover, the distribution of the hydrolysis products in micromolar aqueous solutions of U(VI) at ambient atmosphere has been characterized for the first time, by a combination of ATR FT-IR spectroscopy, near infrared (NIR) absorption spectroscopy, and speciation modeling applying updated thermodynamic databases.

  • Lecture (others)
    Seminar at the Department of Nuclear Engineering, Kyoto University, 29.06.2010, Kyoto, Japan

Publ.-Id: 14848

Speciation of actinyl ions in aqueous solution and at water-mineral interfaces. A vibrational spectroscopic approach

Müller, K.

The migration behavior of actinides in the environment is controlled by prominent molecular phenomena such as hydrolysis and complexation reactions in aqueous solutions as well as the diffusion and sorption onto minerals present along groundwater flow paths. These reactions significantly influence the mobility and bioavailability of the metal ions in the environment, in particular at water-mineral interfaces. Hence, for the assessment of migration processes the knowledge of the mechanisms occurring at interfaces is crucial. The required structural information can be obtained using various spectroscopic techniques.
In the present study, the speciation of uranium(VI) and neptunium(V) at environmentally relevant mineral-water interfaces of oxides of titania, alumina, silica, iron, zinc, and alumosilicates has been investigated by the application of attenuated total reflection Fouriertransform infrared (ATR FT-IR) spectroscopy.
Moreover, the distribution of the hydrolysis products in micromolar aqueous solutions of U(VI) and Np(V/VI) at ambient atmosphere has been characterized for the first time, by a combination of ATR FT-IR spectroscopy, near infrared (NIR) absorption spectroscopy, and speciation modeling applying updated thermodynamic databases.

  • Lecture (others)
    Jahresseminar des Graduiertenkollegs 826/3, 08.11.2010, Burg Schönburg in Oberwesel, Deutschland

Publ.-Id: 14847

Uranium sorption on various forms of titanium dioxide – influence of surface area, surface charge and impurities

Comarmond, M. J.; Payne, T. E.; Harrison, J. J.; Thiruvoth, S.; Wong, H. K.; Aughterson, R. D.; Lumpkin, G. R.; Müller, K.; Foerstendorf, H.

Titanium dioxide (TiO(2)) has often served as a model substrate for experimental sorption studies of environmental contaminants. However, various forms of Ti-oxide have been used, and the different sorption properties of these materials have not been thoroughly studied. We investigated uranium sorption on some thoroughly characterized TiO(2) surfaces with particular attention to the influence of surface area, surface charge, and impurities. The sorption of U(VI) differed significantly between samples. Aggressive pretreatment of one material to remove impurities significantly altered the isoelectric point, determined by an electroacoustic method, but did not significantly impact U sorption. Differences in sorption properties between the various TiO(2) materials were related to the crystallographic form, morphology, surface area, and grain size, rather than to surface impurities or surface charge. In-situ attenuated total reflection Fourier-transform infrared (ATR FT-IR) spectroscopic studies showed that the spectra of the surface species of the TiO(2) samples are not significantly different, suggesting the formation of similar surface complexes. The data provide insights into the effect of different source materials and surface properties on radionuclide sorption.

Publ.-Id: 14846

Preparation, 99mTc-labeling and biodistribution studies of a PNA oligomer containing a new ligand derivative of 2,2′-dipicolylamine

Gasser, G.; Jäger, K.; Zenker, M.; Bergmann, R.; Steinbach, J.; Stephan, H.; Metzler-Nolte, N.

A new azido derivative of 2,2′-dipicolylamine (Dpa), 2-azido-N,N-bis((pyridin-2-yl)methyl)ethanamine, (Dpa-N3) was readily prepared from the known 2-(bis(pyridin-2-ylmethyl)amino)ethanol (Dpa-OH). It was demonstrated that Dpa-N3 could be efficiently labeled with both [Re(CO)3(H2O)3]Br and [99mTc(H2O)3(CO)3]+ to give [Re(CO)3(Dpa-N3)]Br and [99mTc(CO)3(Dpa-N3)]+, respectively. Furthermore, Dpa-N3 was successfully coupled, on the solid phase, to a Peptide Nucleic Acid (PNA) oligomer (H-4-pentynoic acid-spacer-spacer-tgca-tgca-tgca-Lys-NH2; spacer = –NH–(CH2)2–O–(CH2)2–O–CH2–CO–) using the Cu(I)-catalyzed [2 + 3] azide/alkyne cycloaddition (Cu-AAC, often referred to as the prototypical “click” reaction) to give the Dpa-PNA oligomer. Subsequent labeling of Dpa-PNA with [99mTc(H2O)3(CO)3]+ afforded [99mTc(CO)3(Dpa-PNA)] in radiochemical yields > 90%. Partitioning experiments in a 1-octanol/water system were carried out to get more insight on the lipophilicity of [99mTc(CO)3(Dpa-N3)]+ and [99mTc(CO)3(Dpa-PNA)]. Both compounds were found rather hydrophilic (log Do/w values at pH = 7.4 are −0.50: [99mTc(CO)3(Dpa-N3)]+ and −0.85: [99mTc(CO)3(Dpa-PNA)]. Biodistribution studies of [99mTc(CO)3(Dpa-PNA)] in Wistar rats showed a very fast blood clearance (0.26 ± 0.1 SUV, 1 h p.i.) and modest accumulation in the kidneys (5.45 ± 0.45 SUV, 1 h p.i.). There was no significant activity in the thyroid and the stomach, demonstrating a high in vivo stability of the 99mTc-labeled Dpa-PNA conjugate.

Keywords: Bio-organometallic chemistry; Click chemistry; Nuclear medicine; Peptide nucleic acid (PNA); Rhenium compounds; Technetium compounds

Publ.-Id: 14845

Characterization of Si nanowires fabricated by Ga+ FIB implantation and subsequent selective wet etching

Böttger, R.; Bischoff, L.; Schmidt, B.; Krause, M.

Local gallium (Ga) ion implantation in silicon (Si) by focused ion beam (FIB) and subsequent anisotropic and selective wet etching has been used to fabricate freely suspended nanowires (NWs) with reproducible widths between 20 and 200 nm. The dependence of the resulting NW width on the implanted fluence has been investigated and is supported by a numerical model reproducing the experimental data and enabling an a priori estimation of the NW width as a function of the implanted fluence. Furthermore, the resistance of the NWs, its temperature response and the activation energy for electrical current flow were investigated before and after direct current (DC) annealing in air and in vacuum. Annealed NWs showed a decrease of their resistivity up to two orders of magnitude, indicating a partial re-crystallization of the NWs through self-heating and a change in the conduction. The assumption of recrystallization is supported by scanning electron microscopy (SEM) and Raman spectroscopy.

Keywords: silicon-on-insulator; Ga focused ion beam implantation; nanowire; anisotropic etching; width; resistivity; phase change; annealing; Raman spectroscopy

Related publications

Publ.-Id: 14844

A method to estimate the planar, instantaneous body force distribution from velocity field measurements

Albrecht, T.; Weier, T.; Gerbeth, G.; Metzkes, H.; Stiller, J.

We present a simple method to derive a planar, instantaneous body force distribution from a given 2-D velocity field without knowledge of the pressure field. If the body force consists of one component only, spatial integration completely recovers this component.
Particle Image Velocimetry and Direct Numerical Simulations of a wall jet induced by a known body force were conducted to validate the method, demonstrating a good agreement of the original and reconstructed force fields.

Publ.-Id: 14843

Präzisionsmessung der Photodissoziation des Deuterons bei Energien im Bereich der Big-Bang-Nukleosynthese

Hannaske, R.; Bemmerer, D.; Beyer, R.; Birgersson, E.; Grosse, E.; Hartmann, A.; Junghans, A. R.; Kempe, M.; Kosev, K.; Marta, M.; Massarczyk, R.; Matic, A.; Schilling, K.-D.; Schwengner, R.; Sobiella, M.; Wagner, A.

Die für die primordiale Nukleosynthese wichtige Reaktion d(γ,n)p wurde am supraleitenden Elektronen-Linearbeschleuniger ELBE mit Bremsstrahlung bei einer Endpunktenergie von 5,0 MeV untersucht.
Der Photonenfluss wurde mit Hilfe der resonanten Streuung an Aluminiumkernen bei Energien von 2,2 und 3,0 MeV bestimmt. Die Effektivität der verwendeten Germanium-Detektoren wurde mit Hilfe von Referenzstrahlern und Simulationsrechnungen ermittelt. Mit beidseitig ausgelesenen Szintillationsdetektoren wurden Flugzeit und -strecke der Neutronen bestimmt. Wegen der niedrigen Nachweisschwelle der Detektoren kann der Wirkungsquerschnitt für Neutronenenergien von 50 keV bis 1,4 MeV bestimmt werden. Die erreichte statistische Unsicherheit beträgt 5 %, die Energieauflösung 4 %. Bisher untersuchte systematische Unsicherheiten werden diskutiert.

Keywords: Big Bang nucleosynthesis; bremsstrahlung; gamma-ray spectroscopy; neutron time-of-flight; nuclear astrophysics; photon scattering

Related publications

  • Lecture (Conference)
    74. Jahrestagung der DPG und DPG Frühjahrstagung, 15.-19.03.2010, Bonn, Deutschland

Publ.-Id: 14842

Investigation of the beltline welding seam and base metal of the Greifswald WWER-440 Unit 1 reactor pressure vessel

Schuhknecht, J.; Viehrig, H.-W.; Rindelhardt, U.

The investigation of reactor pressure vessel (RPV) materials from decommissioned nuclear power plants (NPPs) offers the unique opportunity to scrutinize the irradiation behavior under real conditions. Material samples taken from the RPV wall enable a comprehensive material characterization. The paper describes the investigation of trepans taken from the decommissioned WWER-440 first generation RPVs of the Greifswald NPP. Those RPVs represent different material conditions such as irradiated (I); irradiated and recovery annealed (IA); and irradiated, recovery annealed, and reirradiated (IAI). The working program is focused on the characterization of the RPV steels (base and weld metal) through the RPV wall. The key part of the testing is aimed at the determination of the reference temperature T0 following the American Society for Testing of Materials (ASTM) Test Standard E1921–08 to determine the fracture toughness of the RPV steel in different thickness locations. In a first step, the trepans taken from the RPV Greifswald unit 1 containing the X-butt multilayer submerged welding seam and from base metal ring 0.3.1 both located in the beltline region were investigated. Unit 1 represents the IAI condition. It is shown that the master curve (MC) approach as adopted in ASTM E1921 is applicable to the investigated original WWER-440 weld metal. The evaluated T0 varies through the thickness of the welding seam. The lowest T0 value was measured in the root region of the welding seam representing a uniform fine grain ferritic structure. Beyond the welding root T0 shows a wavelike behavior. The highest T0 of the weld seam was not measured at the inner wall surface. This is important for the assessment of ductile-to-brittle temperatures measured on subsize Charpy specimens made of weld metal compact samples removed from the inner RPV wall. Our findings imply that these samples do not represent the most conservative condition. Nevertheless, the Charpy-V transition temperature TT41J estimated with results of subsize specimens after the recovery annealing was confirmed by the testing of standard Charpy-V-notch specimens. The evaluated TT41J shows a better accordance with the irradiation fluence along the wall thickness than the master curve reference temperature T0. The evaluated T0 from the trepan of base metal ring 0.3.1 varies through the thickness of the RPV wall. The KJc values generally follow the course of the MC, although the scatter is large. The reembrittlement during two campaign operations can be assumed to be low for the weld and base metal.

Keywords: nuclear power plant; decommisioning; reactor pressure vessel; testing; fracture toughness; Master Curve; integrity assessment

Publ.-Id: 14841

Experimental and numerical modeling of the steel flow in a continuous casting mould under the influence of a transverse DC magnetic field

Timmel, K.; Miao, X.; Eckert, S.; Lucas, D.; Gerbeth, G.

This paper is concerned with numerical and experimental investigations focusing on the fluid flow in the continuous casting process under the influence of an external DC magnetic field. Systematic measurements of the mould flow were carried out using the eutectic alloy GaInSn inside a plexiglass model at room temperature. The jet flow discharging from the submerged entry nozzle was exposed to a level magnetic field spanning across the entire wide side of the mould. The ultrasound Doppler velocimetry (UDV) was applied to obtain a detailed experimental data base with respect to the mean values and transient properties of the velocity fields occurring in the mould. Numerical calculations were performed by means of the software package CFX with an implemented RANS-SST turbulence model. The comparison between our numerical calculations and the experimental results displays a very well agreement. An important outcome of this study is the feature that the magnetic field does not provide a smooth reduction of the velocity fluctuations at the nozzle outlet.

Keywords: continuous casting; electromagnetic brake; experimental modeling; numerical simulation

  • Magnetohydrodynamics 46(2010), 437-448

Publ.-Id: 14840

Experimental facility for two- and three-dimensional ultrafast electron beam X-ray computed tomography

Stürzel, T.; Bieberle, M.; Laurien, E.; Hampel, U.; Barthel, F.; Menz, H.-J.; Mayer, H.-G.

An experimental facility is described which has been designed to perform ultrafast two- and three-dimensional electron beam computed tomography. As a novelty a specially designed transparent target enables tomography with no axial offset for 2D imaging and high axial resolution three-dimensional im-aging employing the cone-beam tomography principles. The imaging speed is 10,000 frames per second for planar scanning and more than 1000 frames per second for 3D imaging. The facility serves a broad spectrum of potential applications primarily the study of multiphase flows, but also in principle non-destructive testing or small animal imaging. In order to demonstrate the aptitude for these applications static phantom experiments at a frame rate of 2000 fps were performed. Resulting spatial resolution was found to be 1.2 mm and better for a reduced temporal resolution.

Keywords: three-dimensional tomography; electron beam tomography; X-ray tomography; multiphase flow measurement

Publ.-Id: 14839

Editorial on the special issue on imaging systems and techniques

Karras, D. A.; Giakos, G. C.; Hampel, U.

Imaging systems and techniques have found widespread application in medical and biological imaging, security and surveillance systems, remote sensing, biometrics, non-destructive testing, computer sciences, materials research, and most recently also in various types of customer products. Imaging systems may be based on different physical measuring principles, such as optical, infrared, acoustic, microwave, terahertz, electrical, X-ray and gamma ray sensing techniques, for example. But behind the imaging sensor there is strong common ground in electronics concepts and circuits for signal conversion, processing, acquisition, and storage as well as algorithms for image enhancement, image reconstruction and image analysis. Imaging systems are increasingly complex and therefore challenge electronic engineers and computer scientists. Concurrently to an ongoing trend of increasing the spatial and temporal resolution of such systems, there is a growing demand for hardware-supported image processing, multi-modality imaging, data reduction as well as improved sensitivity, specificity and robustness.

Keywords: imaging systems and techniques

  • International Journal of Signal and Imaging Systems Engineering 3(2011)3, 145-147

Publ.-Id: 14837

Stand und Perspektiven der Kernenergie in Deutschland und „Umgebung“

Lucas, D.; Weiß, F.-P.

In einem Überblicksvortrag werden aktuelle Fakten und Entwicklungen zur Kernenergienutzung in Deutschland und der Welt vorgestellt und diskutiert. Das schließt auch die Darstellung aktueller Forschungsschwerpunkte für gegenwärtige und zukünftige Reaktoren ein.

Keywords: Nuclear energy

  • Invited lecture (Conferences)
    3. VDI-KTG-Kolloquium "Perspektiven der Kernenergie", 26.10.2010, Dresden, Deutschland

Publ.-Id: 14836

A moderation layer to improve the safety behavior of sodium cooled fast reactors

Merk, B.; Weiß, F.-P.

The nature of the sodium void effect in an infinite lattice is discussed with all different contributions. In a next step, the insertion of a layer consisting of moderating material for a reduction of the effect is proposed. The effect of three different moderating layers on the sodium void defect, the neutron spectrum, and the kinf over burnup is investigated. Special emphasis is given to the influence of the moderation layer on the feedback effects. Especially the uranium-zirconium hydride UzrH layer causes a strong reduction of the sodium void effect. Additionally this layer improves the fuel temperature effect and the coolant effect of the system significantly. All changes cause by the insertion of the UZrH layer lead to a significant increase in stability of the fast reactor system against transients. The moderating layers have only a small influence on the breeding effect and on the production of minor actinides. The insertion of the moderating layer does not imply any constraints on the core design and the power distribution in the fuel element an. Thus the use of a moderation layer gives the opportunity of designable feedback effects in a fast reactor core.

Keywords: Sodium Void Effect; SFR; Fast Reactor; Uranium-Zirconium Hydride; Boron Carbide

  • Contribution to proceedings
    International Conference on Mathematics and Computational Methods Applied to Nuclear Science and Engineering (M&C 2011), 08.-12.05.2011, Rio de Janeiro, Brazil, ISBN 978-85-63688-00-2
  • Lecture (Conference)
    International Conference on Mathematics and Computational Methods Applied to Nuclear Science and Engineering (M&C 2011), 08.-12.05.2011, Rio de Janeiro, Brazil

Publ.-Id: 14835

Application of a two energy group analytical solutions to the YALINA experiment SC3A

Merk, B.; Glivici-Cotruţă, V.; Weiß, F.-P.

The SC3A experiment in the YALINA-Booster facility in Belarus is described and investigated. For this investigation the very special configuration of YALINA-Booster core, consisting of a fast and a thermal zone, decoupled with a neutron ‘valve’is analyzed based on a full HELIOS model for the calculations. The effect of the two region design on the experimental results at different detector positions is leading to unexpected results and the special problems for the analysis of the experiments have been shown. For a more detailed representation, a recently developed two group analytical solution for the time dependent diffusion equation obtained by Green’s function method without separation of space and time was used. To model the above mentioned streaming of neutrons from the thermal area into the fast area an analytical solution for the time dependent neutron flux with two sources has been developed from the available Green’s functions for two groups. In addition to the central source pulse of the external source a source at the boundary of the system has been introduced. The new analytical solution shows very good agreement with the experimental results, even for the unexpected behavior of the outermost deterctor. Thus analytical solution without separation of space and time are a very promising tool to develop a new method for the analysis of ADS experiments.

Keywords: Yalina; experimental analysis; Green’s function; Two group diffusion equation

  • Contribution to proceedings
    The International Conference on Mathematics and Computational Methods applied to Nuclear Science and Engineering (MC 2011), 08.-12.05.2011, Rio de Janeiro, Brazil, ISBN 978-85-63688-00-2
  • Lecture (Conference)
    International Conference on Mathematics and Computational Methods Applied to Nuclear Science and Engineering (M&C 2011), 08.-12.05.2011, Rio de Janeiro, Brazil

Publ.-Id: 14834

Investigation of coolant mixing in reactor VVER-1000

Lisenkov, A.; Bezrukov, Y. A.; Ulianovskiy, D. V.; Zaytsev, D. V.; Bykov, M. A.; Shishov, A. V.; Höhne, T.; Rohde, U.; Gallori, D.

This paper presents arrangement of the problem, methodology of experiment performance and results of experimental investigation of coolant mixing in downcomer and lower plenum of VVER-1000. Three groups of experiments simulating coolant mixing were executed: in conditions of RCP start-up, during natural circulation recovery in the course of SB LOCA and in conditions of stable operation of different amount of RCPs. Results of experiments are used for validation of codes.

Keywords: CFD; VVER-1000

  • Contribution to proceedings
    ICAPP11 (2011 International Congress on Advances in Nuclear Power Plants "Performance & Flexibility: The Power of Innovation"), 02.-05.05.2011, Nice, France
  • Lecture (Conference)
    ICAPP11 (2011 International Congress on Advances in Nuclear Power Plants "Performance & Flexibility: The Power of Innovation"), 02.-05.05.2011, Nice, France

Publ.-Id: 14833

Experimental investigation of in-vessel mixing phenomena in a VVER-1000 scaled test facility during unsteady asymmetric transients

Moretti, F.; Melideo, D.; Del Nevo, A.; D’Auria, F.; Höhne, T.; Lisenkov, E.; Bucalossi, A.; Gallori, D.

In-vessel turbulent mixing phenomena affect the time and space distribution of coolant properties (e.g. boron concentration and temperature) at the core inlet which impacts consequently the neutron kinetics response. For reactor safety evaluation purposes and to characterize these phenomena it is necessary to set and validate appropriate numerical modelling tools to improve the current conservative predictions. With such purpose, an experimental campaign was carried out by OKB Gidropress, in the framework of the European Commission Project “TACIS R2.02/02 - Development of safety analysis capabilities for VVER-1000 transients involving spatial variations of coolant properties (temperature or boron concentration) at core inlet”. The experiments were conducted on a scaled facility representing the primary system of a VVER-1000 including a detailed model of the Reactor Pressure Vessel with its internals. The simulated transients involved perturbations of coolant properties distribution providing a wide validation matrix. The main achievements of the set of experiments featuring transient asymmetric pump behaviour are presented in this paper. The potential of the obtained experimental database for the validation of thermal fluid dynamics numerical simulation tools is also discussed and the role of computational fluid dynamics in supporting the experimental data analysis is highlighted.

Keywords: CFD; turbulent mixing

Publ.-Id: 14832

Highly anisotropic effective dielectric functions of silver nanoparticle arrays

Oates, T. W. H.; Ranjan, M.; Facsko, S.; Arwin, H.

Variable-angle and Mueller matrix spectroscopic ellipsometry measurements of highly anisotropic plasmonic materials composed of random and aligned silver nanoparticles and nanorods are presented. We show that the effective dielectric tensors of randomly dispersed particles are uniaxially anisotropic and those of aligned particles are biaxially anisotropic, with the anisotropy predominantly at the plasmonic resonances. The strong resonances in nanorod arrays result in the real part of the effective in-plane permittivities being opposite in sign over a significant range in the visible, suggesting the potential to design materials that display tunable negative-refraction.

Keywords: metamaterial; left-handed medium; extreme anisotropy; photonic crystals; indefinite materials

Related publications

  • Open Access Logo Optics Express 19(2011)3, 2014-2028

Publ.-Id: 14831

Pygmy Dipole Strength in Exotic Nuclei and the Equation of State

Klimkiewicz, A.; Paar, N.; Adrich, P.; Fallot, M.; Le Bleis, T.; Rossi, D.; Boretzky, K.; Aumann, T.; Alvarez-Pol, H.; Aksouh, F.; Benlliure, J.; Berg, T.; Boehmer, M.; Casarejos, E.; Chartier, M.; Chatillon, A.; Cortina-Gil, D.; Datta Pramanik, U.; Elze, T. W.; Emling, H.; Ershova, O.; Fernando-Dominguez, B.; Geissel, H.; Gorska, M.; Heil, M.; Hellstrom, M.; Johansson, H.; Jones, K. L.; Junghans, A.; Kiselev, O.; Kratz, J. V.; Kulessa, R.; Kurz, N.; Labiche, M.; Lemmon, R.; Litvinov, Y.; Mahata, K.; Maierbeck, P.; Nilsson, T.; Nociforo, C.; Palit, R.; Paschalis, S.; Plag, R.; Reifarth, R.; Simon, H.; Summerer, K.; Surowka, G.; Vretenar, D.; Wagner, A.; Walus, W.; Weick, H.; Winkler, M.

A concentration of dipole strength at energies below the giant dipole resonance was observed in neutron-rich nuclei around 132Sn in an experiment using the FRS-LAND setup. This so-called “pygmy” dipole strength can be related to the parameters of the symmetry energy and to the neutron skin thickness on the grounds of a relativistic quasiparticle random-phase approximation. Using this ansatz and the experimental findings for 130Sn and 132Sn, we derive a value of the symmetry energy pressure of p-bar0 = 2.2±0.5 MeV/fm3. Neutron skin thicknesses of Rn−Rp = 0.23±0.03 fm and 0.24±0.03 fm for 130Sn and 132Sn, respectively, have been determined. Preliminary results on 68Ni from a similar experiment using an improved setup indicate an enhanced cross section at low energies, while the results for 58Ni are in accordance with results from photoabsorption measurements.

  • Contribution to proceedings
    NUCLEAR STRUCTURE AND DYNAMICS '09: Proceedings of the International Conference, 04.-08.05.2009, Dubrovnik, Croatia
    Pygmy Dipole Strength in Exotic Nuclei and the Equation of State: AIP Conference Proceedings, 978-0-7354-0702-2, 181-184

Publ.-Id: 14830

Influence of hydrogen on the thermally induced phase separation in GeO/SiO2 multilayers

Sahle, C. J.; Zschintzsch, M.; Sternemann, C.; von Borany, J.; Nyrow, A.; Jeutter, N. M.; Wagner, R.; Frahm, R.; Tolan, M.

The influence of the annealing atmosphere on the temperature induced phase separation of Ge oxide in GeOx/SiO2 multilayers (x ~ 1) leading to size controlled growth of Ge nanocrystals is explored by means of x-ray absorption spectroscopy at the Ge K-edge. Ge sub-oxides contained in the as-deposited multilayers diminish with increasing annealing temperature, showing a complete phase separation at approximately 450 °C using inert N2 ambient. The use of reducing H2 in the annealing atmosphere influences the phase separation even in an early stage of the disproportionation. In particular, the temperature regime where the phase separation occurs is lowered by at least 50 °C. At temperatures above 400 °C the sublayer composition and thus the density of the Ge nanocrystals can be altered by making use of the reduction of GeO2 by H2.

Related publications

  • Nanotechnology 22(2011)12, 125709

Publ.-Id: 14829

Simulation der Teilchenbeschleunigung auf mehreren GPUs mittels CUDA

Knüpfer, A.; Bussmann, M.

Präsentation von PIConGPU

Keywords: particle in cell; pic; gpu

  • Invited lecture (Conferences)
    Herbsttreffen des ZKI-Arbeitskreises "Supercomputing", 27.-28.10.2010, Göttingen, Deutschland

Publ.-Id: 14828

pp and ππ intensity interferometry in collisions of Ar+KCl at 1.76A GeV

Agakishiev, G.; Balanda, A.; Bannier, B.; Bassini, R.; Belver, D.; Belyaev, A.; Blanco, A.; Böhmer, M.; Boyard, J. L.; Cabanelas, P.; Castro, E.; Chernenko, S.; Christ, T.; Destefanis, M.; Diaz, J.; Dohrmann, F.; Dybczak, A.; Eberl, T.; Epple, E.; Fabbietti, L.; Fateev, O.; Finocchiaro, P.; Fonte, P.; Friese, J.; Froehlich, I.; Galatyuk, T.; Garzon, J. A.; Gernhaeuser, R.; Gil, A.; Gilardi, C.; Golubeva, M.; Gonzalez-Diaz, D.; Guber, F.; Gumberidze, M.; Heilmann, M.; Heinz, T.; Hennino, T.; Holzmann, R.; Huck, P.; Iori, I.; Ivashkin, A.; Jurkovic, M.; Kaempfer, B.; Kanaki, K.; Karavicheva, T.; Kirschner, D.; Koenig, I.; Koenig, W.; Kolb, B. W.; Kotte, R.; Krizek, F.; Kruecken, R.; Kuehn, W.; Kugler, A.; Kurepin, A.; Lang, S.; Lange, J. S.; Lapidus, K.; Liu, T.; Lopes, L.; Lorenz, M.; Maier, L.; Mangiarotti, A.; Markert, J.; Metag, V.; Michalska, B.; Michel, J.; Mishra, D.; Moriniere, E.; Mousa, J.; Muentz, C.; Naumann, L.; Otwinowski, J.; Pachmayer, Y. C.; Palka, M.; Parpottas, Y.; Pechenov, V.; Pechenova, O.; Perez-Cavalcanti, T.; Pietraszko, J.; Przygoda, W.; Ramstein, B.; Reshetin, A.; Roy-Stephan, M.; Rustamov, A.; Sadovsky, A.; Sailer, B.; Salabura, P.; Schmah, A.; Schwab, E.; Siebenson, J.; Sobolev, Y. G.; Spataro, S.; Spruck, B.; Stroebele, H.; Stroth, J.; Sturm, C.; Tarantola, A.; Teilab, K.; Tlusty, P.; Traxler, M.; Trebacz, R.; Tsertos, H.; Wagner, V.; Weber, M.; Wendisch, C.; Wisniowski, M.; Wojcik, T.; Wuestenfeld, J.; Yurevich, S.; Zanevsky, Y.; Zhou, P.; Zumbruch, P.

Results on pp, π+π+, and π-π- intensity interferometry are reported for collisions of Ar+KCl at 1.76$A$~GeV beam energy, studied with the High Acceptance Di-Electron Spectrometer (HADES) at SIS18/GSI. The experimental correlation functions as a function of the relative momentum are compared to model calculations allowing the determination of the space-time extent of the corresponding emission sources. The π π source radii are found significantly larger than the pp emission radius. The present radii do well complement the source-size excitation functions of the collision system of size $A+A \simeq 40+40$. The pp source radius at fixed beam energy is found to increase linearly with the cube root of the number of participants. From this trend, a lower limit of the pp correlation radius is deduced.

Publ.-Id: 14827

Irradiation Response of Greifswald Unit 8 RPV Steels

Viehrig, H.-W.; Gillemot, F.; Horvat, M.; Acosta, B.; Debarberis, L.

Base and weld metal and cladding of the not commissioned SKODA reactor pressure vessel of Greifswald Unit 8 was investigated. Tensile, Charpy size SE(B) and 0.5T-C(T) specimens were irradiated at the LYRA and BAGIRA irradiation rigs with different neutron fluxes. The main focus was on fracture toughness testing according to the Mater Curve approach and crack extension curves. With these tests the reference temperature T0 and fracture toughness values for ductile tearing according to the ASTM test standards ASTM E1921 and ASTM E1820, respectively, were determined.
The irradiation in the LYRA rig with a neutron flux of about 1.57•1012 n/cm2 results in shifts of the reference temperature ΔT0 which correspond with the prediction according to the Russian WWER-440 code. In contrast the BAGIRA irradiation with a neutron flux of about 68.6•1012 n/cm2 results in remarkable higher ΔT0 values then predicted. For weld metal from multilayer welding seams the orientation of the specimens is crucial for the direct measurement of the fracture toughness by using the MC concept. The evaluation of J-R curves measured on Charpy size SE(B) specimens is demanding because of the unsteady developing through the different structures of the cladding.

Keywords: reactor pressure vessel steel; neutron; neutron irradiation; fracture toughness; Master Curve approach; crack extension curve; neutron embrittlement

  • Lecture (Conference)
    IAEA Specialists’ Meeting on Irradiation Embrittlement and Life Management of Reactor Pressure Vessels, 18.-22.10.2010, Znojmo, Czech Republic

Publ.-Id: 14826

Previous results of the investigation on the decommissioned reactor pressure vessels of the Greifswald NPP

Viehrig, H.-W.; Houska, M.

The investigation of reactor pressure vessel (RPV) material from the decommissioned Greifswald NPP representing the first generation of Russian type WWER-440/V-230 reactors offers the opportunity to evaluate the real toughness response. The Greifswald RPVs represent different material conditions viz. irradiated, irradiated and annealed and irradiated, annealed and re-irradiated.
The paper presents test results measured on the trepan taken from the beltline welding seam located in the reactor core region of the Unit 4 RPV. This unit was shut down after 11 years of operation and represents the irradiated condition. The working program comprises chemical analysis, microstructure investigations (by means of metallography and SEM), mechanical testing (hardness and tensile), and fracture mechanics testing. The key part of the testing is focused on the determination of the reference temperature T0 following the ASTM test standard E1921-10. The KJc values measured on TS oriented pre-cracked and side-grooved Charpy size SE(B) specimens from defined thickness locations of the welding seam approximately follow the course of the Master Curve but with a large scatter. Reference temperatures T0 through the thickness of the RPV beltline welding seam runs almost opposite to the trend predicted by the Russian code for the decrease of the neutron fluence from 5.1•E19 n/cm2 to 1.1•E19 n/cm2 (E>0.5MeV). T0 varies between 6°C from near the welding root at ¼ wall thickness to 117°C at ¾ wall thickness. The scatter of T0 beyond the welding root is about 40 K and depends strongly on the structure at the crack tip. The results are also evaluated according to integrity assessment procedures based on the Master Curve concept.

Keywords: reactor pressure vessel; welding seam; specimen orientation; fracture toughness; Master Curve approach; integrity assessment

  • Lecture (Conference)
    IAEA Specialists’ Meeting on Irradiation Embrittlement and Life Management of Reactor Pressure Vessels, 18.-22.10.2010, Znojmo, Czech Republic

Publ.-Id: 14825

Shaping of submicrometer-structures by swift heavy ion irradiation

Ferhati, R.; Guilliard, N.; Weishaar, T.; Amirthapandian, S.; Fritzsche, M.; Bischoff, L.; Bolse, W.

Processing of small structures on µm- or nm-scales using swift heavy ions of some MeV/u energy (SHI) has become an important research topic because of the unique features of the ion irradiation technique. Each single ion impact in the solid results in a highly excited (some eV per atom), almost one-dimensional excitation, which because of its cold surrounding lasts for only a few tens of picoseconds. In many crystalline materials (especially insulators) this rapidly quenched local excitation manifests itself in a highly disordered or even amorphous cylinder of the above mentioned dimensions. The irradiation was carried out in our new in-situ high resolution scanning electron microscope (HRSEM), which we have recently installed at the new UNILAC accelerator of the Helmholtz Gesellschaft für Schwerionenforschung (GSI) in Darmstadt. This setup enables us to perform sequences of combined ion irradiation and HRSEM analysis steps at one and the same spot on target surface throughout the whole experiment and allows us to investigate the evolution of individual objects during ion irradiation with a lateral resolution of a few nm. The specimen consisted of a 100 nm thick NiO film, which has been deposited onto an oxidized Si substrate by of reactive magnetron sputtering. The film was prestructured with a grid of 50 x 50 right-angled trenches by means of a focused ion beam (FIB) at the Forschungszentrum Dresden-Rossendorf. The trenches extended from the surface down to the NiO/SiO2 interface and had a width of about 100 nm. The distances were varied from 0.2 µm to 5 µm, with always 5 trenches having the same distance. This way NiO-blocks of 100 nm height were created, having quadratic (along the diagonal of the grid) respectively rectangular cross sections (off-grid elements). The specimen was then irradiated with 5.9 MeV/u U-ions under grazing incidence (tilt angle 80) and continuous azimuthal rotation (angular velocity 1.45_/s). We have investigated the reshaping of µm- to nm-sized rectangular NiO-blocks by SHI irradiation under grazing incidence and continuous azimuthal rotation. While initially small blocks form single pillar-like structures, blocks of larger dimensions rearrange into tooth-like objects. Below a certain size (~100 nm in diameter) the structures become instable and start to move and coalesce. The plastic deformation and the formation of the pillars can be understood in terms of the hammering effect (or better: in terms of isotropic tensile in-plane stresses due to the irradiation). The observed saturation effect and the instability until now remain unexplained and need further experiments for their clarification.

Keywords: oxide films; FIB; swift heavy ions; submicron structures

Related publications

  • Contribution to external collection
    Prof. Dr. Peter Michler, Prof. Dr. Wolfgang Bolse: Annual Report 2009, Institut für Halbleiteroptik und funktionale Grenzflächen, Universität Stuttgart, Stuttgart: Universität Stuttgart, 2010, 48-49

Publ.-Id: 14824

A Common Approach to Image Reconstruction for Different Applications of Compton Cameras

Schöne, S.; Shakirin, G.; Kormoll, T.; Herbach, C.-M.; Pausch, G.; Enghardt, W.

Compton camera imaging is a promising technique for the measuring of high energetic gamma rays. Potential applications of Compton cameras are homeland security and medical imaging.
Up to now the only method for the monitoring of ion radiation therapy is positron emission tomography (PET). The main disadvantage of the PET technique is the distortion of the measured β+-activity by metabolism and blood flow due to a half-live of up to 20 min for the therapy relevant positron emitters. This problem can be overcome by measuring the prompt photons of wide energies using Compton cameras. Compton cameras can also be used in homeland security for location and nuclide identification of remote radiation sources.
We developed an application independent method for representation and calculation of the system matrix (SM) for Compton cameras. The method provides a structured approach for the SM creation which simplifies the software development process and the optimization of the computational performance. Additionally, the SM calculation is completely independent of the reconstruction algorithm itself.
The first reconstruction results based on this unified SM calculation approach for medical imaging and homeland security applications are presented.

  • Poster
    2010 Nuclear Science Symposium and Medical Imaging Conference, 30.10.-06.11.2010, Knoxville TN, USA
  • Contribution to proceedings
    2010 Nuclear Science Symposium and Medical Imaging Conference, 30.10.-06.11.2010, Knoxville TN, USA
    Conference Record 2010 Nuclear Science Symposium and Medical Imaging Conference

Publ.-Id: 14823

Requirements on the instrumentation of a prompt gamma measuring device

Fiedler, F.; Kormoll, T.; Müller, A.; Enghardt, W.

no abstract available

Keywords: in-beam SPECT; in vivo dosimetry; Compton camera

  • Lecture (Conference)
    2010 Nuclear Science Symposium and Medical Imaging Conference, 29.10.-06.11.2010, Knoxville, USA
  • Contribution to proceedings
    2010 Nuclear Science Symposium and Medical Imaging Conference, 29.10.-06.11.2010, Knoxville, USA, 29.10.-06.11.2010, Knoxville, USA
    Proceedings to NSS MIC 2010

Publ.-Id: 14822

Eu3+-Mediated Polymerization of Benzenetetracarboxylic Acid Studied by Spectroscopy, Temperature-Dependent Calorimetry, and Density Functional Theory

Barkleit, A.; Tsushima, S.; Savchuk, O.; Philipp, J.; Heim, K.; Acker, M.; Taut, S.; Fahmy, K.

Thermodynamic parameters for the complexation of Eu3+ with pyromellitic acid (1,2,4,5-benzenetetracarboxylic acid, BTC) as a model system for polymerisable metal-complexing humic acids were determined using temperature-dependent time-resolved laser-induced fluorescence spectroscopy (TRLFS) and isothermal titration calorimetry (ITC). At low metal and ligand concentrations (<50 µM Eu3+, <1 mM BTC), a 1:1 monomeric Eu-BTC complex was identified in the range of 25-60°C. At elevated concentrations (>500 µM Eu3+ and BTC) a temperature-dependent polymerization was observed. The two methods lead to consistent thermodynamic data (ΔH = 18.5 ± 1.5/16.5 ± 0.1 kJ mol-1; ΔS = 152 ± 5/130 J mol-1 K-1; TRLFS/ITC) in the absence of polymerisation. With the onset of polymeristaion, TRLFS reveals the water coordination number of the lanthanide, whereas calorimetry is superior in determining the thermodynamic data in this regime. Evaluating the heat uptake kinetics, the monomer and polymer formation steps could be separated by "time-resolved" ITC, revealing almost identical binding enthalpies for the sequential reactions. Structural features of the complexes were studied by Fourier-transform infrared (FTIR) spectroscopy in combination with density functional theory (DFT) calculations showing predominantly monodentate binding of a single carboxylate group in both the monomeric and the polymeric complexes of the polycarboxylate with Eu3+. The data show that pyromellitic acid is a suitable model for the study of metal-mediated polymerisation as a crucial factor in determining the effect of humic acids on the mobility of radionuclides in soils.

Publ.-Id: 14820

Comparative characterization of two natural humic acids from the Pearl River Basin, China, and their environmental implications

Liu, J.; Wang, J.; Chen, Y.; Lippold, H.; Lippmann-Pipke, J.

Two humic acids (HAs) were isolated from contaminated river sediments present under comparative conditions in the Pearl River Basin, China. YFHA (the HA extracted at an open pyrite mining area in Yunfu) exhibits a lower absorption intensity for certain bands in the Fourier Transform Infrared spectra, a lower E4/E6 value (the UV absorbances at 465 nm (E4) and 665 nm (E6)), a lower apparent molecular weight, a lower polarity index and a lower oxygen functionality in comparison with GZHA (the HA isolated at an urban living area in Guangzhou). All these differences generally indicate a higher degree of humification of YFHA than GZHA. Overall, the enrichment patterns of permanent heavy metals in the studied HAs are similar to those in the corresponding sediments. In particular, YFHA exhibits high enrichment of trace element Tl, a characteristic concomitant from the mining of the pyrite minerals. The adsorption isotherms of two HAs for goethite and pyrolusite--two representative geological materials generally conform to the Langmuir equation. Based on the qualitative relationships between the Langmuir constants of the adsorption isotherms and the chemical characteristics of HAs, the main mechanism of HA adsorption on these materials is suggested to be hydrophobic interaction. This study highlights the promising use of HA as a peculiar bio-indicator of uncommon trace metal contaminations. The HA adsorption mechanism on representative geological materials further provides a theoretical basis for the study on the unusual metal behavior in complex environmental settings.

Keywords: humic acid; permanent metal load; adsorption; goethite; pyrolusite

Publ.-Id: 14819

European activities on cross-cutting nuclear thermal-hydraulics

Cheng, X.; Boudier, P.; Class, A.; Hampel, U.; Ma, W. M.; Meloni, P.; Papukchiev, A.; Prasser, M.; Roelofs, F.; van Tichelen, K.

For the long-term development of nuclear power, innovative nuclear systems such as Gen-IV reactors and transmutation systems need to be developed for meeting future energy challenges. Thermal-hydraulics is recognized as a key scientific subject in the development of innovative reactor systems. In Europe, a consortium is established consisting of more than 20 institutions of research centers, universities and nuclear industries with the main objectives to identify and to organize research activities on important crosscutting thermal-hydraulic issues encountered in various innovative nuclear systems. A large-scale integrated research project is proposed to FP7 of European Commission and expected to start in the near future.
The main topics considered in the THINS (Thermal-Hydraulics of Innovative Nuclear Systems) project are (a) Advanced reactor core thermal-hydraulics; (b) Single phase mixed convection; (c) Single phase turbulence; (d) Multiphase flow; (e) Numerical code coupling and qualification. The main objectives of the project are:

  • Generation of a data base for the development and validation of new models and codes describing the selected crosscutting thermal-hydraulic phenomena. This data base contains both experimental data and data from direct numerical simulations (DNS).
  • Development of new physical models and modelling approaches for more accurate description of the crosscutting thermal-hydraulic phenomena such as heat transfer and flow mixing, turbulent flow modelling for a wide range of Prandtl numbers, and modelling of flows under strong influence of buoyancy.
  • Improvement of the numerical engineering tools and establishment of a numerical platform for the design analysis of the innovative nuclear systems. This platform contains numerical codes of various classes of spatial scales, i.e. system analysis, sub-channel analysis and CFD codes, their coupling and the guidelines for their applications.
The project will achieve optimum usage of available European resources in experimental facilities, numerical tools and expertise. It will establish a new common platform of research results and research infrastructure. The main outcomes of the project will be a synergized infrastructure for thermal-hydraulic research of innovative nuclear systems in Europe.
This paper summarizes some key crosscutting thermal-hydraulics issues and corresponding ongoing research activities in Europe. The technical and management structure of the THINS project will be described. Examples of results achieved so far will be presented.

Keywords: generation IV nuclear reactors; nuclear thermal hydraulics

  • Contribution to proceedings
    14th International Topical Meeting on Nuclear Reactor Thermalhydraulics (NURETH-14), 25.-29.09.2011, Toronto, Canada
    Proceedings of the 14th International Topical Meeting on Nuclear Reactor Thermalhydraulics (NURETH-14)
  • Lecture (Conference)
    14th International Topical Meeting on Nuclear Reactor Thermalhydraulics (NURETH-14), 25.-30.09.2011, Toronto, Canada

Publ.-Id: 14818

New 18F-labelled alkyl-substituted spirocyclic piperidines for imaging of σ1 receptors: radiolabelling and preliminary biological evaluation

Maisonial, A.; Fischer, S.; Hiller, A.; Große Maestrup, E.; Deuther-Conrad, W.; Scheunemann, M.; Schepmann, D.; Steinbach, J.; Wünsch, B.; Brust, P.

Ziel: It is accepted that at least two σ receptor subtypes exist, termed σ1 and σ2 [1, 2]. Of these, σ1 receptor, the best characterized up to now [3], is assumed to be involved in several neurological diseases. PET imaging using specific σ1 receptor radioligands could be very helpful to obtain a target validation during drug development, a quantitative in vivo mapping of σ1 receptors as well as an improvement of our understanding of all the processes in which σ1 receptors are involved. Recently, a new class of spirocyclic piperidines with high affinity and selectivity for σ1 receptor binding site has been developed. Within this series, [18F]WMS1813 ([18F]1’-benzyl-3-(3-fluoropropyl)-3H-spiro[[2]benzofuran-1,4’-piperidine]) has been successfully developed and used for detection of central σ1 receptors in mice [4]. Further structure-activity relationship studies on the linear ω-fluoroalkyl chain provided three other promising analogues, bearing either fluoromethyl- (WMS1850), fluoroethyl- (WMS1828) or fluorobutyl- (WMS1847) moieties. Herein, we report on the radiosynthesis and preliminary biological evaluation of these new candidates for PET imaging of σ1 receptors.
Methoden: [18F]WMS1850, [18F]WMS1828, and [18F]WMS1847 were synthesized by direct aliphatic nucleophilic substitution of the corresponding tosylate precursors by using the K[18F]F-K222-carbonate complex. For each radiotracer studied, solvent, temperature, reaction time and precursor concentration were optimized. Preliminary experiments on lipophilicity, chemical stability, organ distribution and metabolic stability in CD-1 mice were performed.
Ergebnisse: Optimisation of radiofluorination parameters provided high labelling efficiencies of 61-88% using acetonitrile or DMSO as solvent, at 83 °C or 150°C respectively, with precursor concentrations between 2.0 and 3.0 mg/mL. [18F]WMS1850, [18F]WMS1828, and [18F]WMS1847 were obtained with radiochemical yields of 43-50%, 35-45%, and 45-53%, respectively, radiochemical purities of >98.5%, and high specific activities, generally ≥150 GBq/µmol. Distribution coefficients determined experimentally (Log D = 2.39-3.16, pH = 7.2), underline the moderate lipophilic character of the three radiotracers. The radiolabeled compounds also show appropriate chemical stabilities in acetonitrile, PBS, TRIS-HCl, and Dulbecco buffer.
No radiometabolites permeated into the brain of mice up to 60 min p.i. Metabolic profiles in liver, plasma, and urine were also investigated. By ex vivo autoradiography, the highest target (facial nucleus)-to-nontarget (olfactory bulb) tissue ratio has been determined for [18F]WMS1828 with a value of 4.69 at 45 min p.i. [18F]WMS1828 was superior also in organ distribution studies with a value of brain uptake of 4.71 ± 1.39 %ID/g in comparison to [18F]WMS1813 (3.18 ± 0.68 %ID/g), and [18F]WMS1847 (1.78 ± 0.16 %ID/g), and [18F]WMS1850 (2.65 ± 0.68 %ID/g) at 30 min p.i.
Schlussfolgerungen: For the three radiotracers studied, optimised protocols led to very efficient radiosyntheses. With respect to first biological data, [18F]WMS1828 appears to be the most promising candidate for PET imaging of σ1 receptors, with even better pharmacological profile than the lead compound. Hence, [18F]WMS1828 radiosynthesis is selected for transfer onto an automated radiosynthesis module with a view to further clinical development.
[1] Quirion, R.; Bowen, W. D.; Itzhak, Y.; Junien, J. L.; Musacchio, J. M.; Rothman, R. B.; Su, T. S.; Tam, S. W.; Taylor, D. P. Trends Pharmacol Sci. 1992; 13: 85-86.
[2] Hayashi, T. ; Su, T. P. Current Neuropharmacology. 2005; 3: 267-280.
[3] van Waarde, A.; Ramakrishnan, N. K.; Rybczynska, A. A.; Elsinga, P. H.; Ishiwata, K.; Nijholt, I. M.; Luiten, P. G. M.; Dierckx, R. A. Behavioural Brain Research. 2010; doi:10.1016/j.bbr.2009.12.043.
[4] Maestrup, E. G.; Fischer, S.; Wiese, C.; Schepmann, D.; Hiller, A.; Deuther-Conrad, W.; Steinbach, J.; Wünsch, B.; Brust, P. J. Med. Chem. 2009; 52: 6062-6072.

Keywords: σ1 receptor; 18F; radiolabelling; imaging

  • Lecture (Conference)
    18. Jahrestagung der Arbeitsgemeinschaft Radiochemie / Radiopharmazie der DGN, 16.-18.09.2010, Bad Boll, Deutschland

Publ.-Id: 14817

Synthesis, pharmacological activity and structure affinity relationships of spirocyclic σ1 receptor ligands with a (2-fluoroethyl) residue in 3-position

Große Maestrup, E.; Wiese, C.; Schepmann, D.; Brust, P.; Wünsch, B.

In order to develop a fluorinated radiotracer for imaging of σ1 receptors in the central nervous system a series of (2-fluoroethyl) substituted spirocyclic piperidines 3 has been prepared. In the key step of the synthesis 2-bromocinnamaldehyde acetal 5 was added to piperidones 6 with various substituents at the N-atom. Unexpectedly, this reaction led to 2-benzoxepines 8, which were contracted with acid to afford the spirocyclic 2-benzofuranacetaldehydes 9. The best yields were obtained, when the transformations up to the alcohols 10 were performed without isolation of intermediates. Generally the (2-fluoroethyl) derivatives 3 have higher σ1 affinity and σ1/σ2 selectivity than the corresponding (3-fluoropropyl) derivatives 2. The most promising candidate for the development as radiotracer is the (2-fluoroethyl) derivative 3a (WMS-1828, fluspidine, 1’-benzyl-3-(2-fluoroethyl)-3H-spiro[[2]benzofuran-1,4’-piperidine]), which shows subnanomolar σ1 affinity (Ki = 0.59 nM) and excellent selectivity over the σ2 subtype (1331-fold) as well as some other receptor systems. The novel synthetic strategy also allows the systematic pharmacological evaluation of intermediate alcohols 10. Despite their high σ1 affinity (Ki = 6-32 nM) and selectivity the alcohols 10 are 10-30-fold less potent than the bioisosteric fluoro derivatives 3.

Keywords: σ1 receptor ligands; spirocyclic piperidines; [18F] radiotracer; neuroimaging; structure affinity relationships; ring contraction

Publ.-Id: 14816

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