Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

Details on the generation of multiple quasimonoenergetic electron bunches in the self-modulated laser wakefield acceleration SMLWFA regime are presented. This type of laser-plasma interaction can result in pronounced longitudinal laser pulse fragmentation, dependent on plasma density and laser intensity. It is shown by experiments and particle-in-cell simulations that these laser pulse fragments can be powerful enough to trigger nonlinear plasma wave breaking, injection, and acceleration of electrons to quasimonoenergetic energies. With high plasma densities, selfmodulation is promoted, and the advantages of SMLWFA such as especially high accelerating fields and short electron bunches (<5 fs) can be harvested. In addition, more than one quasimonoenergetic electron bunch can be created, with a temporal spacing between each bunch of only few tens of femtoseconds, again governed by plasma density.

A consequence of a loss of coolant accident is that the local insulation material is damaged and maybe transported to the containment sump where it can penetrate and/or block the sump strainers. An experimental and theoretical study, which examines the transport of mineral wool fibers via single and multi-effect experiments is being performed. This paper focuses on the experiments and simulations performed for validation of numerical models of sedimentation and resuspension of mineral wool fiber agglomerates in a racetrack type channel. Three velocity conditions are used to test the response of two dispersed phase fiber agglomerates to two drag correlations and to two turbulent dispersion coefficients. The Eulerian multiphase flow model is applied with either one or two dispersed phases.

We confirm by numerical simulations that the scaling exponents of the dimer model are in agreement with those of the 2+1 dimensional KPZ class.
Surface pattern form if we include Mullins diffusion in the simulation.

We show that a (2+1)-dimensional discrete surface growth model exhibiting Kardar-Parisi-Zhang (KPZ) class scaling can be mapped onto a two-dimensional conserved lattice gas model of directed dimers. The KPZ height anisotropy in the surface model corresponds to a driven diusive motion of the lattice gas dimers. We conrm by numerical simulations that the scaling exponents of the dimer model agree with those of the (2+1)-dimensional KPZ class. This suggests that the dimension dependence has a topological (exclusion) origin. The mapping opens up the possibility of analyzing growth models via reaction-diusion models and allow much more ecient computer simulations (see [1]). In particular we provide very precise surface scaling exponents for d = 2; 3; 4; 5 dimensions obtained by ecient bit-coded algorithms and discuss the problem of the debated upper-critical dimension of KPZ. Furthermore if we supplement this model with conserved, competing surface diusion reactions we can obtain various, coarsening dot or ripple patterns (see image), which are important in self-organizing nano-structure research (see http://www.iom-leipzig.de/for845/).
[1] G. Odor, B. Liedke, and K.-H. Heinig, Phys. Rev. E 79 (2009) 021125.

We show that a 2+1 dimensional discrete surface growth model exhibiting KPZ class scaling can be mapped onto a two dimensional conserved lattice gas model of directed dimers. In case of KPZ height anisotropy the dimers follow driven diffusive motion. We confirm by numerical simulations that the scaling exponents of the dimer model are in agreement with those of the 2+1 dimensional KPZ class. This opens up the possibility of analyzing growth models via reaction-diffusion models, which allow much more efficient computer simulations.

Here is presented and discussed the history, the spectroscopic, the thermo-mechanical and the laser properties of the new old laser crystal Yb:CaF2, of its Sr and Ba isotypes as well as of an Yb and Na codoped compound. It will be shown that Yb:CaF2 is a very particular luminescent material, in which the laser active center probably consists of a complex hexameric cluster, that it is the most promising Yb doped °uoride material for large scale high power and high energy laser systems and that it can compete in several aspects with the currently used Yb doped oxide crystals and glasses. The opportunity of operating the crystals at cryogenic temperatures and the recently achieved improvements in the¯eld of femtosecond pulsed laser operation and high peak power laser amplication is highlighted and evaluated.

Numerical simulations of the kinematic induction equation have been carried out in a setup that resembles the configuration of the VKS dynamo experiment. Primary objective are investigations of the impact of the non-uniform permeability distribution introduced by the ferrous impellers that drive a flow of liquid sodium in the experiment. It is shown that a high-permeability domain favours the axisymetric field mode whereas the first non-axisymmetric mode remains nearly unaffected. However, to circumvent the restrictions of Cowling's theorem, still an alpha-effect is required to explain the axisymmetric field as it is observed in the experiment.

The electronic structures of SmScO3, GdScO3, and DyScO3 are investigated by means of x-ray photoelectron spectroscopy, x-ray emission spectroscopy (XES), and x-ray absorption spectroscopy (XAS). A strong hybridization between Sc 3d and O 2p is found, and a contribution of the rare-earth 5d states to this hybridization is not excluded. The band gaps of the compounds are determined by combining XES and XAS measurements. For SmScO3, GdScO3, and DyScO3 the band gaps were determined to be 5.6, 5.8, and 5.9 eV, respectively. Magnetization versus temperature measurements reveal antiferromagnetic coupling at 2.96 (SmScO3), 2.61 (GdScO3), and 3.10 K (DyScO3). For DyScO3 a Rietveld refinement of a 2 K neutron-diffraction data set gives the spin arrangement of Dy in the Pbnm structure (Shubnikov group: Pbnm).

The origin of the distribution of ion implantation induced point defects in Si and their effect on the oxygen redistribution during SIMOX processing is discussed.

Palladium in its ground-state has a non magnetic fcc structure. We suggest that it can be forced to get ferro-magnetic by an expansion of the lattice constant, or in case of thin films by a varying number of atomic layers. Another option to induce magnetism is to dope the Pd structures with 3d transition metals. We used first principles methods to calculate the magnetization density of different Co doped and undoped Pd structures. Calculations were carried out with the projector augmented waves (PAW) method in the LDA+U approximation and a plane wave basis set. In addition the linear augmented plane waves (LAPW) method was used and compared with the PAW results. Both methods show, that doping with 3d transition metals leads to magnetic moment at the Pd sites of the crystal. In case undoped Pd films the PAW results are similar to existing LAPW calculations.

The studies presented are aiming at a detailed investigation of the behaviour of a VVER-1000/V-320 reactor and the containment structures during a postulated severe accident, including the ways and means by which these accidents may be prevented or mitigated.
A hypothetical station blackout scenario (loss of the offsite electric power system concurrent with a turbine trip and unavailability of the emergency AC power system), belonging to the typical beyond design basis accidents, has been investigated. Station blackout results in reactor shut down, loss of feed water and trip of all reactor coolant pumps. Continuous evaporation of the secondary side leads to steam generators’ depletion followed by heating up of the core. In case of unavailability of essential safety systems the core will be severely damaged and finally the reactor pressure vessel (RPV) might fail.
The analyses are performed using the integral code ASTEC commonly developed by IRSN (Institut de Radioprotection et de Sûreté Nucléaire) and GRS (Gesellschaft für Anlagen- und Reaktorsicherheit mbH).
Code-to-code comparative analyses for the early thermal-hydraulic phase have been performed with the GRS code ATHLET. A large number of sensitivity calculations have been done regarding the axial core power distribution, heat losses, and RPV lower head modelling. The analyses have shown that, despite the considerable differences in the codes themselves, the calculation results are similar in terms of thermal hydraulic response. There are discrepancies in timings of phenomena, which are within the limitations of the physical models and the applied nodalizations.
It was one objective of this investigation to evaluate the Severe Accident Management (SAM) procedures for VVER-1000 reactors, by for instance estimating the time available for taking appropriate decisions and preparing counter-measures. To evaluate the effect of possible operator actions, a SAM procedure (primary side depressurization) is included into the simulation. Without SAMs, the simulation provides plastic rupture of the RPV after approximately 4.3 h, while with SAMs, a prolongation of the vessel failure time is obtained by approximately 90 minutes.
Currently, the late phase of the accident is investigated in more detail by comparing the lower head behaviour as simulated by ASTEC with results from dedicated finite element calculations.
The work contributes to the reliability of the ASTEC code by means of plant applications.

The Master Curve (MC) approach procedure standardised in ASTM E1921 is defined for quasi-static loading conditions. However, the extension of the MC method to dynamic testing is well-established. The effect of loading rate can be broken down into two distinct aspects: 1) the effect of loading rate on Master Curve To values for loading rates within the loading rate range specified in ASTM E1921 for quasi-static loading, and 2) the effect of loading rate on Master Curve To values for higher loading rates. The IAEA CRP8 includes both aspects, but primarily focuses on the second element of loading rate effects, i.e. loading rate ranges above the upper limit of the E1921 standard and it comprises:

• results of a round-robin exercise to validate the application of the Master Curve approach to precracked Charpy (PCC) specimens tested in the ductile-to-brittle transition region using an instrumented pendulum,
• Master Curve data obtained at different loading rates on various RPV steels, in order to assess the loading rate dependence of To and compare it with an empirical model proposed by Wallin, and
• the comparison of results from unloading compliance and monotonic loading in the quasi-static range.

● QPM with ImΠi ≠ 0, plasmons and plasminos from HTL
● extrapolation of lattice QCD to large baryon densities, e.g. CBM@FAIR
● EOS for hydrodynamic phase of heavy-ion collisions (RHIC, LHC, SPS) and quark stars

We present a quasiparticle model based on a two-loop effective action equipped with hard thermal loop (HTL) dispersion relations and an effective running coupling strength. The model allows for an extrapolation of present QCD lattice results at small or zero chemical potential to larger baryon densities. The resulting QCD Equation of State is combined with the hadron sector to arrive at a usable form for hydrodynamical simulations of heavy-ion collisions over a large energy interval. The EoS is shown for several regions of the phase diagram and implications for quark/neutron stars are discussed.

We present a quasiparticle model based on a two-loop effective action equipped with hard thermal loop (HTL) dispersion relations and an effective running coupling strength. The model allows for an extrapolation of present QCD lattice results at small or zero chemical potential to larger baryon densities. The resulting QCD Equation of State is combined with the hadron sector to arrive at a usable form for hydrodynamical simulations of heavy-ion collisions over a large energy interval. The EoS is shown for several regions of the phase diagram and implications for quark/neutron stars are discussed.

Ge2Sb2Te5 (GST) based materials can be easily transformed between amorphous and crystalline phase and vice versa. The dramatic differences in the electrical resistance of these structural states make these materials suitable for non-volatile memory applications (phase change RAM or PCRAM). In order to tune these materials to the desired working point (e.g. low melting temperature, fast crystallization speed), dopants such as Si, N or O are used. In this study, we investigated the influence of PVD deposited Si dopants in 100 nm thin GST films on the crystallisation temperature and on the electrical resistance as well. The dopant concentration was varied between 0% and 3.5% by tunig the RF sputtering power on the SiO2 target. The XRD measurements (ESRF: ROBL beamline @ 12keV) were carried out in a high temperature chamber equipped with a Be dome, that allowed simulaneous determination of the sheet resistance by an electrical 4-point measurement. The samples were heated up to 450°C under vacuum conditions.
All samples were amorphous after deposition. Depending on the Si content, all samples crystallize in a cubic phase in the range between 160°C – 200°C. At the crystallisation temperature the electrical resistance drops by two orders of magnitude. A second transformation to a hexagonal phase was observed only for samples with a Si concentration below 1.0%. The temperature of this phase transformation depends significantly on the Si content. The electrical measurements show a further decline of the resistance upon this phase transformation. The cooling curve of the resistance measurements indicates, that the hexagonal phase exhibits metallic behaviour, whereas the cubic phase exhibits semiconducting properties.

Uranium(IV) is usually regarded as sparingly soluble at near-neutral pH values. It should, therefore, be immobile in anoxic groundwaters. However, indications are that UO2 is able to form stable colloids (nanoparticles) [1] and the question arises if such nanoparticles might counteract the immobility of U(IV) in natural waters. Attempts were made by us to produce U(IV) colloids that are stable at environmentally relevant (i.e. near-neutral or slightly alkaline) pH values. It turned out that U(IV) colloids which are stable over many months can be produced by electrochemical reduction of U(VI) at alkaline pH, adding silicate and titration to the near-neutral region from the alkaline side of the pH scale.

Ferrous iron in clay is a potential natural reductant in anoxic environments. The reduction of UVI by FeII could be an important pathway for the immobilization of uranium in natural subsurface environments as well as in high-level nuclear waste (HLW) repositories. In the present study, we employed three dithionite-bicarbonate-citrate (DCB) treated, Ca-exchanged, Fe-bearing clays viz. montmorillonite (FeSM), Fe-rich smectite (Swa-1) and nontronite (NAu-2) with varying Fe content, and studied the reactivity of structural and readsorbed (surface complexed) Fe(II) species with respect to U sorption and/or reduction at pH 6 in a CO2-free anoxic atmosphere (<1 ppm O2 (v/v)) by using XPS, EXAFS and Mӧssbauer spectroscopies. The surface complexed Fe(II) species on untreated, Ca-exchanged clays were not found to be reactive in uranyl reduction. All three partially (17-45%) reduced, Ca-exchanged clays remove U from solution with a fast rate (minutes-hours), followed by a slow (months) reduction step. EXAFS analysis showed that UVI forms a mononuclear bidentate surface complex with FeIII in the untreated, Ca-exchanged clays which is the pre-requisite of heterogeneous reduction of U by their analogue in DCB treated clays. The adsorbed U was present as partially reduced mixed valence state (UVI and UIV) after 15 and 30 days. After 3 months, XANES spectra showed a substantial increase of UIV (20-50%) at the expense of UVI in case of reduced (DCB treated) FeSM, Swa-1 and complete reduction occurred (100%) in case of reduced NAu-2. The U4f5/2 XPS spectra were deconvoluted into two components, a higher binding energy (393.2±0.2 eV) for UVI and a lower binding energy (391.5±0.2 eV) for UIV. Despite the presence of abundant structural and readsorbed Fe(II) species and favourable reducing condition, the slow reduction of U might be due to (1) the stabilization of Ca in the clay interlayer inhibiting the cation release into solution which is coupled to the electron transfer process (2) that not all structural FeII species are potentially reactive at pH 6 and accessible to U for coordination.

Purpose
The outstanding diversity of cellular properties mediated by neuronal and nonneuronal α7 nicotinic acetylcholine receptors (α7 nAChR) points to the diagnostic potential of quantitative nuclear molecular imaging of α7 nAChR in neurology and oncology. It was our goal to radiolabel the α7 nAChR agonist 4-[5-(4-fluoro-phenyl)-[1,3,4]oxadiazol-2-yl]-1,4-diaza-bicyclo[3.2.2]nonane(NS10743) and to assess the selectivity of [¹⁸F]NS10743 binding site occupancy in animal experiments.

Methods
[¹⁸F]NS10743 was synthesized by nucleophilic substitution of the nitro precursor. In vitro receptor affinity and selectivity were assessed by radioligand competition and autoradiography. The radiotracer properties were
evaluated in female CD-1 mice by brain autoradiography and organ distribution. Target specificity was validated after treatment with SSR180711 (10 mg/kg, intraperitoneal), and metabolic stability was investigated using radio-HPLC.

Results
The specific activity of [18F]NS10743 exceeded 150 GBq/μmol at a radiochemical purity >99%. In vitro, NS10743 and [¹⁸F]NS10743 showed high affinity and specificity towards α7 nAChR. The brain permeation of
[¹⁸F]NS10743 was fast and sufficient with values of 4.83 and 1.60% injected dose per gram and brain to plasma ratios of 3.83 and 2.05 at 5 and 60 min after radiotracer administration. Brain autoradiography and organ distribution showed target-specific accumulation of [¹⁸F]NS10743 in brain substructures and various α7 nAChR-expressing organs. The radiotracer showed a high metabolic stability in vivo with a single polar radiometabolite, which did not cross the blood–brain barrier.

Conclusion
The good in vitro and in vivo features of [¹⁸F] NS10743 make this radioligand a promising candidate for quantitative in vivo imaging of α7 nAChR expression and encourage further investigations.

Structural, magnetic and transport properties of undoped and Mn-doped quasi onedimensional ZnO nano-wires formed as dendrite crystals of different width have been studied. All Mn-doped nanowires (Mn content 16% and 27 %) exhibit a ferromagnetic behavior, which is significantly temperature dependent. A small magnetic signal detected up to the room temperature is supposed to be due to small amounts of magnetic impurities. Analysis of the temperature dependencies of magnetization shows that the observed magnetic properties can be caused by the host ferromagnetic matrix with Curie temperature T_C = 40 K.

By means of single-crystal neutron diffraction, an isostructural transition is observed at the Néel temperature of CsCuCl₃, a quasi-one-dimensional antiferromagnet with a helically modulated crystal structure that is built out of six Cu²⁺ layers. Abrupt atomic displacements of about 0.01 A minimize the ferromagnetic interlayer superexchange interaction via the path Cu-Cl1-Cu that enters also the antiferromagnetic path Cu-Cl1-Cl2-Cu. The latter couples only one pair of Cu²⁺ ions in each chlorine layer since all the other intralayer bonds either have much longer interatomic distances or include more than two intermediate Cl ions and, therefore, can be neglected. Thus, a spatial geometric frustration in this helically modulated stacked triangular lattice is provided by three Cu layers. Influences of the atomic displacements on the exchange energy, as well as the critical behavior of this spatially frustrated material, are discussed.

The synthesis, structural analysis, spectroscopic studies, susceptibility and specific-heat measurements of {[Cu(bmen)₂][Pt(CN)₄]}n (bmen = N,N'-dimethylethylenediamine) are presented. X-ray crystalstructure analysis revealed that the [Pt(CN)₄]^2- building blocks are combined with [Cu(bmen)₂]²⁺ units to form a chain-like structure along the a axis. The Cu(II) atoms are hexacoordinated by four nitrogen atoms in the equatorial plane belonging to two molecules of bidentate bmen ligands with average Cu–N distance of 2.043(18) A . The axial positions are occupied by two nitrogen atoms from bridging [Pt(CN)₄]^2- anions at a longer axial Cu–N distance of 2.490(4) A . The compound is characterized by the presence of a weak antiferromagnetic exchange coupling J/k_B = 0.6 K. Despite the one-dimensional (1D) character of the structure, the analysis of the magnetic properties and specific heat at very low temperatures shows that [Cu(bmen)₂][Pt(CN)₄] behaves as a two-dimensional (2D) square-lattice Heisenberg magnet with weak interlayer coupling.

NiCl₂-4SC(NH₂)₂ (known as DTN) is an S = 1 system with an easy-plane anisotropy dominating over the exchange interaction and exhibiting a field-induced antiferromagnetic ordering with critical fields B_c1 = 2.1 T, B_c2 = 12.6 T and temperature T^max _c = 1.2 K. A systematic study of the low-energy excitation spectrum of DTN in the ordered phase at temperatures down to 0.45 K is presented. It is showed that two observed gapped modes can be consistently interpreted within a four-sublattice antiferromagnet model with a weak isotropic corner-center interaction of magnetic ions in the body-centered tetragonal lattice.

We report results of sound-velocity and sound-attenuation measurements in the quantum S = 1 spin-chain magnet NiCl₂-4SC(NH₂)₂ that shows a field-induced antiferromagnetic (AF) ordering and two corresponding quantum critical points at H_c = 2.1 T and H_s = 12.6 T. The longitudinal acoustic c₃₃ mode modulates the in-chain exchange interaction and shows a softening in the vicinity of the quantum critical points, accompanied by energy dissipation in the acoustic wave. We discuss our results with a model where the main contribution to the spin-lattice interaction arises from the exchange-striction coupling within one-dimensional spin-chains.

Magnetic properties of the S = 1/2 Heisenberg spin-chain material (6MAP)CuCl₃ have been probed by means of magnetization, specific-heat and electron spin resonance (ESR) measurements. A pronounced low-temperature Curie-like tail in the magnetic susceptibility was found at low temperatures. As recently suggested, such a behavior could originate from staggered magnetization effects, responsible also for the field-induced gap opening in S = 1/2 chains with broken translational symmetry. We found a clear anomaly in the specific heat having a broad maximum at T_max = 2.3 K, accompanied by a significant ESR line broadening and g-factor shift. The specific-heat anomaly is magnetic-field independent, indicating that its origin is not related to the field-induced transverse staggered magnetization effects

The geometric and electronic structures of gas phase Mo3nS3n+2 and Mo3n-1S3n+5 clusters are studied experimentally using mass and photoelectron spectroscopy. The experimental results are compared with calculations based on density-functional theory. Although such clusters have been known for decades as main constituents of Chevrel phases, we here report their first gas phase synthesis for sizes up to n=17 (Mo51S53). The smallest entities are Mo6S8 and Mo5S11 with HOMO-LUMO gaps of 0.9eV and 0.5eV. With increasing n, the clusters grow 1-dimensional and form nanowires with a vanishing gap. The sulfur atoms at both ends may easily bind to Au electrodes making these clusters promising components of future nanoelectronic devices.

The formation of interface and border states in metal-oxide-semiconductors structures associated with the generation of embedded germanium nanocrystals in 20 nm SiO2-layers by means of ion implantation and a subsequent annealing was examined. Deep level transient spectroscopy and related time-domain techniques were applied in order to study the charge trapping and emission at the Si-SiO2 interface. A significant dependence of the interface state density Dit on the conditions of the cluster generation was found. Any Ge-implanted sample features a pronounced level at about 0.31 eV above the valence band edge and a concentration above 1e13 /cm²eV, likely related to a Pb-center.
A systematic variation of the filling pulse parameters was utilized in order to separate the response of fast and slow states, and to substantiate the existence of border traps located in the vicinity of the Si-SiO2 interface. The role of interface and border traps for the relaxation of the trapped charge in the nanocrystals is illustrated.

Outstanding scientific results and statistical overview of the Institute of Ion Beam Physics and Materials Research in 2008

The unusual superconducting (SC) phase transitions occuring under competing orbital and spin pair breaking, which characterize clean strongly type-II superconductors at low temperatures, are investigated within a non-perturbative approach, which avoides the difficulties encountered in various perturbative approaches and enables comparison with recent experimental data. It is shown that in a 3D system with strong spin-splitting, a spatial (FFLO) modulation of the order parameter along the magnetic-field direction preserves the continuous nature of the SC transition. However, at a magnetic field slightly below Hc2 the FFLO state becomes unstable, transforming discontinuously into a uniform SC state via a first-order phase transition. Our calculation shows that the entropy jump at the first-order phase transition is siginificantly larger than its total variation in the continuous region between the two transitions, in agreement with recent thermal-conductivity measurements performed on the heavy-fermion compound URu₂Si₂.

WS₂ fullerene particles and nanotubes show a diameter and morphology dependent Raman response, see figure showing response for WS₂ nanotubes of 290 nm and 50 nm diameter. This enables the classification of WS₂ nanotubes, fullerenes, and nanocrystals, and the estimation of geometric properties (Table of Contents).

Experimental studies of the spin-1 Haldane-chain material Ni(C₂H₈N₂)₂NO₂ techniques are reported. The presence of fractional S = 1/2 chain-end states, revealed by ESR and susceptibility measurements is found to be responsible for spin-glass freezing effects. It is suggested that a higher doping with Zn ions suppresses the spin-glass behaviour by creating shorter and isolated chain fragments.

Ziel/Aim:

Für die Therapie mit Y-90-DOTATOC wird obligatorisch eine posttherapeutische Dosimetrie unter Gammakamera durchgeführt, wobei die Nutzung der Bremsstrahlung für die Quantifizierung viele Limitationen mit sich bringt, so dass häufig als Surrogatmarker In-111-DOTATOC verwendet wird. Seit längerer Zeit wird eine prätherapeutische Dosimetrie mit Y-86-DOTATOC favorisiert. Phantom- und Patientenuntersuchungen für singuläre PET-Geräte älterer Bauart existieren. Aber es fehlen dezidierte Untersuchungen für moderne Hybrid-Geräte. An einem PET/CT-Gerät sollen Phantomuntersuchungen die Möglichkeiten zur Dosimetrie aufzeigen.

Methodik/Methods:

Für die Kalibrierung und mögliche Korrekturen wurde ein mit Aktivität füllbares Zylinderphantom (Durchmesser: 20cm, Länge: 20cm) mit 3 inaktiven Zylindereinsätzen (Teflon, Wasser und Luft) verwendet. Die Untersuchung wurde an einem konventionell kalibrierten PET/CT (Normalisierung mit F-18), LSO HiRes Biograph 16 (Siemens, Erlangen) durchgeführt. Zur genauen Aktivitätsbestimmung wurde ein Aktivitätsmessgerät ISOMED 2000 (MED Dresden) über die PTB Braunschweig für Y-86 kalibriert. Das Phantom wurde mit 5,8 kBq/ml Y-86 gefüllt. 3D-Aufnahmen erfolgten mit 10min pro Bettposition, AC-CT, Iterative Rekonstruktion (8i,4s, FWHM=5mm, Streukorrektur).

Ergebnisse/Results:

Die ROI-Auswertung am Phantom ergab eine Überbewertung ("falsche" Aktivitätsanreicherung) in den inaktiven Zylindern, bezogen auf die Aktivitätskonzentration im aktiven Zylinderbereich (Teflon +0,3%, Luft +22% und Wasser +2%). Mit der konventionellen PET-Normalisierung, Schwächungs- und Streukorrektur wurde die zu erwartende Aktivitätskonzentration im Zylinder um 45% reduziert wiedergegeben. Ein Rekonstruktionsvergleich mit und ohne Streukorrektur zeigte, dass der konventionelle Streukorrekturalgorithmus für Y-86 falsche Ergebnisse liefert. Für die weitere Quantifizierung ohne Streukorrektur wurde eine Crosskalibrierung vorgenommen und ein Kalibrierfaktor von 0,9 cps(Siemens)/Bq für Y-86 bestimmt.

Schlussfolgerungen/Conclusions:

Für eine prätherapeutische Dosimetrie mit Y-86 an einem PET/CT-Gerät, kann mit der konventionellen Kalibrierung (Normalisierung mit F-18) eine Quantifizierung vorgenommen werden. Die besten Ergebnisse sind bei Rekonstruktion ohne Streukorrektur (artefaktfrei) zu erreichen. Eine separate Crosskalibrierung für Y-86 ist notwendig. Die Überbewertung bei Luft ist sicherlich auf das ungünstige Emissionsspektrum von Y-86 zurückzuführen. Die gemessenen Überbewertungen (Reko: ohne Streukorrektur) für dieses 3D-PET Gerät (PET/CT, LSO) ist moderater als dies Pentlow [1] für einen 3D-BGO-GE-Scanner (Advance) (Teflon +161%, Luft -20%% und Wasser +56%) ermittelt hat.

Literatur/References:

[1] Pentlow, K.S., Finn, R.D., Larson, St.M. et.al., Quantitative Imaging of Y-86 with PET: The Occurrence and Correction of Anomalous Apparent Activity in High Density Regions; Clinical Positron Imaging, Vol.3, No.3, 2000

Ziel/Aim:

Für Multi-Center Studien mit unterschiedlichen PET-Scannern ist ein einfach anwendbares und robustes Verfahren zur Bestimmung der rekonstruierten Bildauflösung entscheidend um vergleichbare Ergebnisse bei der quantitativen Auswertung und Volumenbestimmung zu erzielen. Ziel dieser Arbeit war deshalb die präzise Bestimmung der Auflösung innerhalb des rekonstruierten Bildes mit Hilfe von Messungen am weit verbreiteten IEC/NEMA Ganzkörperphantom in Abhängigkeit vom Target zu Hintergrund Kontrast und der Zählstatistik.

Methodik/Methods:

Datengrundlage bildeten Messungen eines IEC Ganzkörperphantoms (Kugeleinsätze 10-37mm Durchmesser) an 7 Scannersystemen (2 BGO-, 3 LSO- und 2 GSO-Scanner) die im 3D und, wenn möglich, 2D Modus für unterschiedliche Messzeiten (1 bis 10min) und Kontrastverhältnisse zwischen Kugeln und Hintergrund (1:0,6:1/3:1/1,5:1) akquiriert und jeweils mit dem herstellerseitig empfohlenen Ganzkörperprotokoll rekonstruiert wurden. Die rekonstruierte Ortsauflösung im Bild wurde für jede der 5 Kugeln im Phantom durch Anpassung des entsprechenden Modells, d.h. durch Faltung der Objektfunktion (Kugel+Wand+Untergrund) mit einer Gauss-förmigen Point Spread Function an die vollständigen als Radialprofil aufgetragenen 3D-Messdaten (je nach Größe der Kugel ca. 10³-10⁴Datenpunkte pro Kugel) bestimmt.

Ergebnisse/Results:

Mit dem vorgestellten Regressionsverfahren kann unter klinikähnlichen Messbedingungen die rekonstruierte Bildauflösung FWHM [mm] anhand der Kugeln mit einer sehr hohen statistischen Genauigkeit von (2,8 +/- 0,1)% bestimmt werden (Mittelwert über 593 Kugeln). Für kleine Kugeln von 10-16mm Durchmesser ist die stat. Genauigkeit mit 3-5% etwas schlechter als mit ~2% für große Kugeln mit 22-37mm Durchmesser. Die Resultate zeigen, dass mit dem Ganzkörper-Standardprotokoll die rekonstruierte Bildauflösung bei allen Systemen deutlich unter der mit NEMA spezifizierten Geräteauflösung liegt. Sie ist i.w. unabhängig von der Messzeit (1-10min), sinkt aber mit fallendem Target zu Hintergrund Kontrast (gegenüber dem 1:0 Kontrast um 30% bei Kontrast 6:1, um 54% bei Kontrast 3:1 und um 80% bei Kontrast 1,5:1). Diese Auflösungsverschlechterung hat bei Strukturengrößen unterhalb dem Dreifachen der Bildauflösung direkten Einfluss auf die Quantifizierung und auf die das Volumen repräsentierende Aktivitätsschwelle.

Schlussfolgerungen/Conclusions:

Um eine auch für kleine Zielstrukturen über unterschiedliche Scanner gültige Quantifizierung und valide Methode zur Volumenbestimmung in der PET zu etablieren, muss zwingend die tatsächliche, rekonstruierte Bildauflösung einbezogen werden. Der hier beobachteten Abhängigkeit der Ortsauflösung vom Kontrast ist dabei Rechnung zu tragen.

We report results of ultrasonic investigations of the quantum S = 1 spin-chain magnet NiCl₂-4SC(NH₂)₂, also known as DTN, in magnetic fields up to 18 T and temperatures down to 0.3 K. A field H along the [001] direction induces a transition into an antiferromagnetic phase with T^max _N = 1.2 K. Accordingly, at T = 0 there are two quantum critical points at ~2.1 T and at ~12.6 T. The acoustic c₃₃ mode, propagating along the spin chains, shows a pronounced softening close to the phase transition, accompanied by energy dissipation of the sound wave. The H-T phase diagram obtained from our measurements is compared with results from other experimental investigations and the low-temperature acoustic anomalies are traced up to T > T_N. We also report frequency-dependent effects, which open the possibility to investigate the spin fluctuations in the critical regions. Our observations show an important role of the spin-phonon coupling in DTN.

Since 2007, the Dresden High Magnetic Field Laboratory (Hochfeld-Magnetlabor Dresden, HLD) operates as a user facility, providing unique experimental possibilities in pulsed fields. The HLD offers various experimental techniques, such as electrical transport, magnetization, ultrasound, and magnetic resonance. A particular feature of the laboratory is the next-door free-electron-laser installation used for high-field infrared spectroscopy and electron spin resonance in pulsed fields. Additionally, nuclear magnetic resonance and specific-heat measurement techniques are being developed in pulsed magnetic field. As the only laboratory in Europe, the HLD has reached magnetic fields of about 87 T allowing now to perform experiments in this field range for modern materials research. Several 60 and 70 Tesla magnets are regularly used by researchers. A two-coil 100 T prototype magnet and a long-pulse (1000 ms) 60 T magnet are ready for their first tests. Some recent scientific results will be highlighted.

Multiferroic HoMnO₃ is ferroelectric below T_c = 875 K and antiferromagnetically ordered below T_N(Mn) = 75 K (Mn subsystem). In addition, at T_N(Ho) approximately 5 K the Ho subsystem undergoes a transition into an antiferromagnetically ordered state. The coupling between the ferroelectric and antiferromagnetic order parameters in HoMnO3 has not yet been unambiguously explained, revealing the importance of geometrical frustrations and a complex interplay between the Ho and Mn magnetic subsystems. High-quality single-crystalline samples of HoMnO₃ were studied by means of X-band (9.3 GHz) electron spin resonance spectroscopy. A relatively strong absorption was found below 5 K, which corresponds to the temperature of the magnetic ordering of the Ho subsystem. The observed mode exhibits a very pronounced anisotropic behavior and can be interpreted as an excitation within the antiferromagnetically ordered Ho subsystem.

The successful use of picosecond-pulse free-electron-laser (FEL) radiation for the continuous-wave THz-range electron spin resonance (ESR) spectroscopy has been demonstrated. The unique combination of two linac-based FELs (covering the wavelength range of 4 - 250 μm) with high magnetic fields at the Research Center Dresden-Rossendorf (FZD) allows for tunable-frequency ESR spectroscopy in an extraordinary broad frequency range of 1.2 - 75 THz in magnetic fields up to ~70 T. The new approach is of particular importance for studying magnetic excitations in materials exhibiting field-induced phenomena (including magnetic phase transitions) and in spin systems with a large zero-field splitting. The performance of the spectrometer is illustrated with ESR spectra obtained in the low-dimensional organic material (C₆H₉N₂)CuCl₃ and the multiferroic compound YMnO₃ This work was made in collaboration with R. Wünsch, W. Seidel, H.D. Zhou, C. Wiebe.

Scattering methods (x-rays or neutrons) as well as capacitive dilatometry can be used to investigate the magnetostriction (i.e. the change of length or shape) of solids with high accuracy and sensitivity (resolution limit for relative length changes about 10⁻⁹). The experimental range of scattering methods, especially, was extended to high magnetic fields of about 30 T in the last years. Therefore, these methods accompany the traditional dilatometry which was developed to work well up to the highest available fields (45 T in constant field magnets and 60 T in pulsed field systems). As examples, thermal expansion (investigated by x-ray diffraction and dilatometry), magnetostriction and magnetization measurements on the rare-earth based compounds Gd₅Ge₃, Tb₅Ge₃ and GdSi are discussed. The magnetoelastic behaviour of both Gd-containing substances shows an unexpected magnetic anisotropy which is caused by exchange striction effects. The complete set of (complementary) experimental methods resulted in a clear knowledge of the phase transitions from which, at least, the magnetic phase diagrams were constructed.

We have measured the temperature and frequency-dependant transmission and phase shift through LuNi₂B₂C thin films on MgO substrates at terahertz frequencies. From the measured data, we could accurately determine the complex dielectric constant, epsilon, the complex optical conductivity, sigma, and the penetration depth, lambda. Comparing our measured results with theory, we find strong deviations from the standard one-band BCS predictions. These deviations can be attributed to the multiband nature of the superconducting state in LuNi₂B₂C.

We have studied the de Haas-van Alphen (dHvA) effect of the borocarbide superconductor LuNi₂B₂C both in the normal and in the superconducting state by use of the field-modulation method in high magnetic fields up to 15 T and at low temperatures down to 0.5 K. In the superconducting state we observed an additional damping of the dHvA oscillation amplitudes compared to the normal state for different dHvA frequencies. This is due to the opening of the superconducting gap and, therefore, enables us to determine the magnetic-field-dependent gap for different bands from this experiment. The possibility to perform the measurements at various crystal orientations in the magnetic field allows to examine the angular dependence of the superconducting gap parameter.

We studied the charge ordered (CO) state of the quasi 1-D S = 1/2 quantum spin chains (TMTTF)₂X (X=SbF₆ and AsF₆) by comprehensive W-Band (95 GHz), Q-band (34 GHz) and X-Band (9.5 GHz) ESR experiments between 4 and 300 K in order to explore the nature of the exchange interaction in the CO state. At high temperatures, both compounds show a linear decrease of the linewidth with decreasing temperature; this behavior does not depend on the applied microwave frequency as well as the anisotropy of both, linewidth and g-value. Below T_CO, the breaking of the inversion symmetry of the (TMTTF)₂- dimers results in additional contributions DeltaH_CO to the ESR linewidth. While the linewidth is frequency independent along the three principle magnetic axes a, b', and c*, it is substantially enhanced for the Q- and W-band measurements along the diagonal of a − b' plane. The enhanced linewidth along 45° in the a − b' plane below T_CO shows a quadratic frequency dependence which is characteristic for anisotropic Zeeman interaction. From this finding we can conclude that the charge order leads to two inequivalent magnetic sites. We will compare this result to one obtained on anion-ordered TMTTF salts where a different charge-order pattern was proposed.

Ziel/Aim:

Das auf T-Zellen lokalisierte Antigen CD4 stellt ein therapeutisches Target der Therapie der rheumatischen Arthritis dar. Bisher konnte diese Zielstruktur bildgebend jedoch nicht dargestellt werden. Ziel dieser Pilotstudie war es, die Verträglichkeit und Verteilung eines neuen murinen Tc-markierten Anti-CD4-Antikörperfragmentes bei Patienten mit rheumatischer Arthritis und dessen Eignung als Aktivitätsmarker einzuschätzen.

Methodik/Methods:

In die Studie wurden 3 weibliche und 2 männliche Patienten im Alter von 58 bis 71Jahren untersucht. Jeweils 30min, 1, 2, 4, 8 und 24 Stunden nach i.v. Applikation von 585 +/- 115 MBq wurden planare Ganz- und Teilkörper-Szintigraphien angefertigt und visuell in jeweils 68 Gelenken ausgewertet. Eine aktive Entzündung wurde klinisch durch Schwellung und Schmerz in mindestens einem Gelenk definiert (Gold-Standard). Die Patienten wurden bis 7 Tage p.i. klinisch nachuntersucht.

Ergebnisse/Results:

Nebenwirkungen konnten weder akut noch im weiteren Verlauf beobachtet werden. Ein Anstieg des humanen Anti-Murinen-Antikörper-Titers wurde ebenfalls nicht verzeichnet.

Bei allen 5 Patienten zeigten sich szintigraphisch positive Befunde in 25 von 37 klinisch mit Schmerz und Schwellung betroffenen Gelenken. Szintigraphisch positiv waren 19 von 277 Gelenken ohne klinisch nachweisbare Schmerz oder Schwellung. Somit errechnet sich eine Rate falsch-positiver Befunde von 7% und falsch-negativer Befunde von 32%.

Schlussfolgerungen/Conclusions:

Die Tc-99m-Anti-CD4-mAb-Fragment-Szintigraphie ist eine vielversprechende neue Technik zur Evaluierung der Lymphozytenaktivität im chronischen und akuten Stadium einer rheumatischen Arthritis, wobei offenbar die Spezifität höher ist als die Sensitivität. Ob damit auch eine Prognoseabschätzung möglich ist, müssen die Folgestudien mit längerem Follow-Up zeigen.

Since the beginning of 2007, the new Dresden High Magnetic Field Laboratory (Hochfeld-Magnetlabor Dresden, HLD) at the Forschungszentrum Dresden-Rossendorf, is accepting proposals for magnet time and is hosting user groups. Pulsed magnetic fields up to about 70 T (with 150 ms pulse duration in a 24 mm bore) as well as smaller ones (60-65 T, with 25-50 ms pulse durations) are available for users. Recently, the European record field of 87.2 T (10 ms in a 20 mm bore) has been reached in a newly designed double-coil system. Besides the ultimate goal of a pulsed magnet reaching 100 T for a timescale of 10 ms in a bore of 20 mm, further large-scale magnets (e.g. 60 T, 1 s, 40 mm) are planned. The necessary energy for the pulsed coils is provided by a world-unique 50 MJ capacitor bank. A free-electron-laser facility next door allows high-brilliance radiation to be fed into the pulsed field cells of the HLD, thus making possible unique high-field magneto-optical experiments in the range 4-250 µm. Cryotechniques and different sample probes for a broad range of experimental techniques, custom designed for the pulsed magnets, are readily available for users. In-house research of the HLD focuses on electronic properties of strongly correlated materials at high magnetic fields. Some examples of the scientific work being carried out will be highlighted.

In the so-called FFLO state, named after Fulde, Ferrell, Larkin, and Ovchinnikov, the superconducting state can survive even at high magnetic fields above the Pauli paramagnetic limit. The quasi-two-dimensional (2D) organic superconductors have been suggested as good candidates for exhibiting the FFLO state. When applying the magnetic field exactly parallel to the conducting layers the orbital pair breaking is greatly suppressed and the Pauli limit is reached. We performed high-resolution specific-heat and torque-magnetization experiments in magnetic fields up to 32 T for such 2D organic superconductors. In a very narrow region close to parallel orientation we observe additional anomalies below the upper critical field signalling the existence of an additional superconducting phase. The specific-heat data for k-(BEDT-TTF)₂Cu(NCS)₂ with T_c = 9.1 K show that the superconducting transition becomes first order for fields above 21 T indicating that the Pauli limit is reached. Below about 3 K, the upper critical field increases sharply and a second first-order transition appears within the superconducting phase. Our results give strong evidence for the realization of the FFLO state in organic superconductors.
Work done in cooperation with R. Lortz, B. Bergk, Y. Wang, A. Demuer, I. Sheikin, G. Zwicknagl, and Y. Nakazawa.

es hat kein Abstrakt vorgelegen

es hat kein Abstrakt vorgelegen

Ziel/Aim:

Die posttherapeutische Dosimetrie bei der Therapie neuroendokriner Tumore mit Y-90-DOTATOC kann mittels der Y-90-Bremsstrahlungsbilder einer Gammakamera durchgeführt werden, wobei die eingeschränkte Bildqualität jedoch Unsicherheiten birgt. Alternativ kann eine prätherapeutischen Dosimetrie mit Y-86-DOTATOC am PET/CT durchgeführt werden. Ziel dieser Untersuchung war es, Übereinstimmungen oder Differenzen zur Y-90-Bremsstrahlungsdosimetrie zu finden.

Methodik/Methods:

Die Untersuchungen erfolgten bei bisher 5 Patienten an einem LSO-PET/CT-Tomographen (Biograph 16, Siemens Medical). Appliziert wurden 136 (110-153) MBq Y-86-Dotatoc, die Datenakquisition erfolgte 0,5/2,5/5/21/28 und 45 Stunden p.i. als Teilkörper in 7 Bettpositionen (3 bzw. 4 min/Bett). Pro Scan wurde ein Low-Dose-CT zur Schwächungskorrektur angefertigt. Zeitaktivitätskurven für die Nieren, die Milz, sowie der gesamten Leber wurden ermittelt. Die Residenzzeiten für Y-86 wurden ermittelt und mittels OLINDA für die nachfolgende Therapie die zu erwarteten Organdosen bestimmt.

Die Y-90-Dosimetrie erfolgte posttherapeutisch 14 Tage später durch Auswertung der Bremsstrahlungsaufnahmen an einer Doppelkopf-Gammakamera (80 keV + 140 keV, 30% Energiefenster, HEPG-Kollimator, Forte, Phillips).

Ergebnisse/Results:

Die mit Y-86-DOTATOC erzeugten PET-Aufnahmen zeigten gegenüber den Bremsstrahlungsbildern eine deutlich bessere Abgrenzung der Nieren, Leber, Milz und ermöglichten zudem die eindeutige Tumorlokalisation. Die kinetischen Daten konnten überlagerungsfrei aus VOIs gewonnen werden, während ausgeprägte Metastasierungen der Leber keine Abschätzung der Dosis für das gesunde Lebergewebe erlaubte. Die mit Y-86 ermittelten Organdosen der Nieren (2,3 Gy/GBq) ergaben einen übereinstimmenden Wert wie bei Y-90 (2,3 Gy/GBq). Für die Milz ergab die Y-86-Dosimetrie einen um 30% niedrigeren Wert während für die Leber ein um 40% höherer Wert gegenüber der Y-90-Dosimetrie errechnet wurde.

Schlussfolgerungen/Conclusions:

Y-86-DOTATOC erlaubt die Detektion von Tumorläsionen, welche das therapeutische Radiopharmakon aufnehmen, obwohl die Bildqualität nicht dem vom Ga-68-DOTATOC gewohnten Standard entspricht. Eine Abschätzung der Nierendosis als kritischem Organ erlaubt auch die Festlegung einer maximalen Aktivitätsmenge. Die Nierendosis wird durch beide Methoden in ähnlicher Höhe ermittelt, was die Nutzung der Y-90-Bremsstrahlung zur Dosimetrie anstelle eines Surogatparameters (In-111-Pentetreotide) erlaubt.

Literatur/References:

Gefördert durch das Bundesministerium für Bildung und Forschung.

The measured thermodynamic phase diagram of the quasi-two-dimensional magnet [Cu(HF₂)(pyz)₂]BF₄ (pyz=pyrazine=N₂C₄H₄) exhibits an unusual nonmonotonic dependence of the Neel temperature T_N as a function of magnetic field H. The nonmonotonic behavior of T_N(H) results from two competing effects induced by the field: while H suppresses the amplitude of the order parameter by polarizing the spins along a given direction, it also reduces the phase fluctuations by changing the order parameter space from the sphere S² to the circle S¹. The latter effect dominates at low fields only if the system is close enough to its lower critical dimension (d_c = 2), i.e., when fluctuations become important. Our theoretical results reproduce the measured phase diagram and demonstrate that this unusual effect is realized in [Cu(HF₂)(pyz)₂]BF₄.

Ziel/Aim:

Sigma-Rezeptoren sind eine eigenständige Rezeptorklasse und werden in zwei Subtypen σ1 und σ2 unterteilt. σ1-Rezeptoren spielen eine bedeutende Rolle bei der Signalübertragung im Gehirn. Wegen ihrer Beteiligung an neurodegenerativen Prozessen sind σ1-Rezeptoren ein interessantes Target für das Neuroimaging mittels PET. Bisher ist kein σ1-Radiotracer bekannt, der für die klinische Anwendung genutzt wird.
Kürzlich wurde von uns eine neuartige Substanzgruppe mit einer Spiro[2]benzofuran-1,4'-piperidin-Leitstruktur beschrieben (1), die eine hohe Affinität und Spezifizität (σ1 vs. σ2) besitzt. Wir stellen erste Ergebnisse zur Synthese von drei F-18 markierten Radioliganden vor, die sich vom 1'-Benzyl-3H-spiro[[2]benzofuran-1,4'piperidin] ableiten.

Methodik/Methods:

Als Strategie für die Radiosynthese von 1 (F-18-Bn; -OMe in Pos. 3) wurde die F-18 Markierung eines 4-Nitrobenzoyl-bzw. 4-Trimethylammonium-triflat-Präkursors mit anschließender Reduktion der Benzoylgruppe und von 2 (F-18-Bn, -CN in Pos. 3) die reduktive Aminierung von 4-[F-18]Fluorbenzaldehyd mit dem freien Amin gewählt. Die Darstellung von 3 (-Bn; F-18- Propyl in Pos.3) durch F-18 Markierung in der Seitenkette des Spiro[2]benzofuran erfolgte durch nucleophile Substitution eines Tosylat-Präkursors.

Ergebnisse/Results:

Die Radiosynthese von 1 wurde bisher nicht weiter verfolgt, da bei nicht-radioaktiven Voruntersuchungen die Reduktion der Benzoylgruppe auf große Probleme stieß und sich die Substanz als säurelabil erwies. Nach zahlreichen Experimenten zur Optimierung der reduktiven Aminierung konnte 2 mit NaBH3CN/MeOH in Gegenwart von HOAc nur in geringer radiochemischer Ausbeute (RCA) erhalten werden. Demgegenüber wurde das F-18- Fluorpropylderivat 3 in einer Eintopfreaktion (K[F-18]F/K222, MeCN, 85°C, 30 min) mit ≥ 60% Markierungsausbeute erhalten, wobei nur wenige Nebenprodukte auftraten.

Die Optimierung der Reaktion ergab reproduzierbar folgende Parameter: RCA 35-48% (n=11), Synthesezeit 90-120 min, radiochem. Reinheit >99,5%, chem. Reinheit ≥99,7%, spezifische Aktivität 150-238 GBq/µmol. Die Abtrennung von 3 erfolgte mittels HPLC (RP-Phase, wässr. MeCN als Eluent) und SPE. Die Synthese ist für eine Automatisierung konzipiert. In ersten Tierexperimenten an Mäusen konnte eine spezifische Anreicherung im Gehirn, eine günstige Organverteilung und eine ausreichende metabolische Stabilität des Radioliganden 3 nachgewiesen werden.

Schlussfolgerungen/Conclusions:

Zur Radiosynthese eines F-18 markierten σ1-Liganden mit Spiropiperidin-Struktur wurden drei Kandidaten untersucht. Für das Fluorpropylderivat 3 konnte eine optimierte Radiosynthese etabliert werden. Ausgehend von den biologischen und metabolischen Daten wird gegenwärtig am fine-tuning der Struktur zur weiteren Verbesserung der Eigenschaften gearbeitet.

Literatur/References:

(1) Maier, CA, Wünsch, B, J Med Chem 2002, 45, 4923-4930.

We present de Haas–van Alphen measurements of the nonmagnetic borocarbide superconductor LuNi₂B₂C. The electronic band structure is extracted from the magnetic quantum oscillations in the normal state. In accordance with previous investigations we find a complex band structure with different open and closed Fermi-surface sheets. From the temperature dependence of the oscillations amplitude the effective mass of the single bands can be determined. Due to many-body interactions we observe enhancements of the effective masses compared to the results by full-potential-density-functional calculations. Therefore, we are able to determine the angular dependence of the interaction strength for the different bands separately.

Ziel/Aim:

5-Cyanindol-3-ylcyclohexylamine wurden neben zahlreichen anderen Verbindungen hinsichtlich ihrer antidepressiven Eigenschaften in der Entwicklung neuer selektiver Serotonin-Reuptake-Inhibitoren (SSRI) untersucht (1,2). Die beschriebenen guten Affinitäten zum Serotonintransporter (SERT) und Selektivitäten bezüglich h5HT_1A- und α₁-Rezeptoren waren ausschlaggebend für unsere Entwicklung von cis-3-(4-(6-(3-[F-18]Fluorpropoxy)-3,4-dihydroisochinolin-2(1H)-yl)cyclohexyl)-1H-indol-5-carbonitril (F-18-Ic) als potentiellem PET-Radiotracer.

Methodik/Methods:

Die nichtradioaktiven Referenzverbindungen wurden in Mehrstufen-Synthesen dargestellt, die cis- und trans-Isomere säulenchromatographisch isoliert und ihre Affinität und Selektivität bezüglich des SERT in kompetitiven Radioligand-Bindungsstudien ermittelt. Hierfür wurden transfizierte HEK293-Zellen (hSERT, hNET und hDAT) und Membranhomogenat des Rattenkortex (r5HT_1A-Rezeptor) eingesetzt.
Die Synthese der phenolischen Präkursoren für die Radiosynthese, IIc und IIt, erfolgte über Demethylierung des entsprechenden 6-Methoxydihydroisochinolin-cis- bzw. -trans-Derivates mit Hilfe von BBr₃. 1,3-Bistosyloxypropan wurde nach einem Standardverfahren zu 3-[F-18]Fluorpropyltosylat ([F-18]III) umgesetzt und direkt für die Veretherung von IIc bzw. IIt (2 mg; K₂CO₃, MeCN/80°C) zum F-18-markierten cis- bzw. trans-Derivat, [F-18]Ic bzw. [F-18]It, verwendet. Nach Aufarbeitung mit SPE folgte semipräparative Radio-HPLC (RP-18, 50% MeCN + 0,2% TFA).

Ergebnisse/Results:

Alle Referenzverbindungen binden selektiv an den hSERT mit K_i-Werten zwischen 4 und 327 nM, wobei die cis-Isomere eine signifikant höhere Affinität zum hSERT und besonders geringe Affinitäten zu hNET und r5HT_1A aufweisen. [H-3]Citalopram-Assays ergaben bis zu 140-fach höhere Affinitäten zum hSERT als [H-3]Paroxetin-Assays, entsprechend aktueller Veröffentlichungen über unterschiedliche Bindungsstellen spezifischer SERT-Liganden.
N.c.a. [F-18]III konnte in 10-15 Minuten (Markierungsausbeute (MA) 60-80%) synthetisiert werden. Die Veretherung zu [F-18]Ic bzw. [F-18]It ergab in 8-10 min eine MA von 40-50% und eine radiochemische Ausbeute von 11-22% (2,5 h total). Radiochemische und chemische Reinheit wurden mit ≥99% (HPLC, TLC) und die spezifische Aktivität mit ≥50 GBq/µmol (HPLC) bestimmt. Die Radiosynthese lässt sich auf ein automatisiertes Verfahren übertragen.

Schlussfolgerungen/Conclusions:

Radiochemische und physikochemische Ergebnisse sowie In-vitro-Daten weisen [F-18]Ic als einen vielversprechenden Radiotracer für die Darstellung des SERT aus. Weiterführende Experimente sind geplant, um die Hirnaufnahme und In-vivo-Bindung von [F-18]Ic zu untersuchen.

Literatur/References:

(1) Meagher K L et al, Bioorg Med Chem Lett 2001;11:1885-1888.
(2) Deskus A J et al, Bioorg Med Chem Lett 2007;17:3099-3104.

Ziel/Aim:

Zur quantitativen Analyse des F-18-DOPA-PET bei IPS wird in der Regel die Dopamin-Einstromrate (ki) in einem 90min PET-Protokoll bestimmt. Der Effektive Verteilunsgvolumen-Quotient (EDVR), als ein Maß für den F18-DOPA-Umsatz, wurde als sensitiverer Parameter postuliert (1), erfordert jedoch eine 4h-Meßzeit. Levodopa ist ein Standardmedikament, um den absoluten Dopamin-Mangel beim IPS auszugleichen. Neuere Ergebnisse favorisieren den Einsatz von Dopaminrezeptor-Agonisten wie z. B. Cabergolin. Kann anhand des EDVR ein Unterschied im Verlauf der IPS-Erkrankung im Vergleich zweier Medikations-Regime differenziert werden?

Methodik/Methods:

36 Patienten mit neu diagnostiziertem idiopathischen Parkinsonsyndrom (25 Männer, 11 Frauen, Alter 62+/- 9 Jahre, Hohn &Yahr Stad 1- 2,5)). Positives BfS-Gutachten und Ethikvotum. PET I vor Beginn der Studien-Medikation, PET II erfolgte nach 3-monatiger Medikamenteneinnahme. Die Medikation war gegenüber dem Nuklearmediziner verblindet. PET-Protokoll: Prämedikation mit 150 mg Carbidopa per os 60 min vor Untersuchungsbeginn. Dynamisches F18-DOPA-Hirn-PET (ECAT EXACT HR+ (Siemens/CTI)) : 10 min Transmision, Injektion von 185 MBq F-18-DOPA i.v., Emission bis 90 min p.i., 2x 40 min Emission ab 120 min und 190 min p.i. nach je 10 min Transmission. Rekonstruktion und Zusammenfügen der Datensätze. Positionierung von VOIs vordefinierter Größe und Anzahl über Nucl. Caudatus, Putamen, Referenzgewebe occipital (freie Positionierung in allen 3 Raumebenen (Softwarepaket ROVER, ABX Radeberg)). Es wurden die Einstromraten ki und das EDVR nach Sossi et al.(1) für beide Putamina ohne Seitentrennung bestimmt.

Ergebnisse/Results:

19 Patienten wurden mit Levodopa behandelt, 17 Patienten erhielten Cabergolin. Weder zu Beginn der Studie noch nach 3 Monaten gab es signifikante Unterschiede zwischen den Mittelwerten der Parameter ki und EDVR beider Behandlungsgruppen. In der Levodopa-Gruppe zeigte sich von PET I zu PET II eine sign. Abnahme von ki (von 0,0117 auf 0,0110) und eine sign. Zunahme des EDVR (1,257 auf 1,335). In der Cabergolin-Gruppe fand sich keine Änderung des ki (0,0116 auf 0,0115) aber eine sign. Zunahme des EDVR (1,137 auf 1,331). Die Mittelwerte der Differenzen von PET I zu PET II zeigten für ki keinen sign. Unterschied zwischen Levodopa (0,0007) und Cabergolin (0,0001), jedoch bezüglich des EDVR mit deutlich größerer Differenz in der Cabergolin-Gruppe (Levodopa -0,078, Cabergolin -0,194).

Schlussfolgerungen/Conclusions:

EDVR erscheint als sensiblerer Parameter im Vergleich zu ki, um diskrete Änderungen im Verlauf des frühen IPS unter Medikationsbedingungen zu differenzieren. Auf Grund des langen Untersuchungsprotokolles erscheint diese Methode jedoch nicht für die Routine zur generellen Klärung des Vorliegens einer Störung im dopaminergen System geeignet.

Literatur/References:

(1) Sossi V, de la Fuente-Fernandez R, Holden JE et al. J Cereb Blood Flow Metab 22:232-239, 2002.

Ziel/Aim:

Untersuchung zur prognostischen Wertigkeit von F18-Misonidazol-PET (F18-MISO) bezüglich der Heilungswahrcheinlichkeit im Tumor-Xenograft-Model des humanen Plattenepithel-Karzionms (hSCC) FaDu auf Nacktmäusen vor Einzeitbestrahlung.

Methodik/Methods:

Das humane Plattenepithel-Karzinom wurde subcutan auf das Hinterbein von 70 Nacktmäusen transplantiert. Bei einem Tumordurchmesser von 7-9mm wurde eine F18-MISO-PET (11MBq i.v., Micro-PET P4, CTI Molecular Imaging Inc., gemessene Schwächungskorrektur, Emission in Anaesthesie über 30min ab 210min p.i.) durchgeführt. Die Auswertung erfolgte mittels 3D-regions of interest über dem Tumor ("ROIFinder automatic mode", ROVER software ABX Radeberg, Germany). Bestimmt wurden das hypoxische Volumen (HV) und der maximale standard uptake value (SUV_max). Nach dem PET wurde eine Einzeitbestrahlung von 25 Gy oder 35 Gy unter normalem Blutfluß appliziert (200 kV Röntgenstrahlung, 0,5mm Cu, ca. 1,2 Gy/min). Der Studienendpunkt waren lokale Tumorkontrolle bzw. Zeitpunkt des Rezidivs.

Ergebnisse/Results:

Tumorkontrollraten nach 25 Gy waren geringer als nach 35 Gy (22% versus 69%, log rank p<0,0001). Der mediane SUV_max betrug 2,54 (range: 0,19-6,83). Das HV reichte von 38 mm³ bis 353 mm³ (median 112 mm³, 95%CI: 92-128 mm³). In Tumoren mit einem HV geringer als dem Median betrug die Tumorkontrolle 33% nach 25 Gy und 82% nach 35 Gy. In Tumoren mit einem HV größer als dem Median betrug die Tumorkontrolle 15% nach 25 Gy und 53% nach 35 Gy. In der multivariaten COX Analyse ergab sich nach Korrektur für Dosis und Tumorvolumen eine signifikante prognostische Aussage bezüglich des HV für die Tumorkontrolle. Die Bestrahlungsdosis hatte einen signifikanten Einfluß auf die Rezidivwahrscheinlichkeit (p<0,0005), das Tumorvolumen und der SUV_max waren bezüglich der Prognose der Heilungswahrscheinlichkeit nicht relevant.

Schlussfolgerungen/Conclusions:

Das F-18-MISO HV ist eine signifikanter Prädiktor für das outcome nach Bestrahlung mit hoher Einzeldosis im FaDu hSCC Tumormodell in der Nacktmaus. Von der Intensität der F18-MISO-Anreicherung, gemessen als SUV_max, konnte in dieser Studie keine prognostische Aussage abgeleitet werden.

Diese Arbeit wurde im 6.EU-Rahmenprogrammes Projekt BioCare proposal#505785 durchgeführt.

This study is focused on tailoring Nb2O5 film porosity during reactive pulsed magnetron sputtering. Dense amorphous films with closed nanopores have been formed onto unheated substrates at high growth rates. The films have a high refractive index n_400=2.54, a low extinction coefficient, k_400~6x10^-4, a low mechanical stress (-90 MPa) and a negligible thermal shift. The specific depth distribution of the nanopores is believed to be the reason for the high film density combined with a low mechanical stress.

The influence of rippled vs. flat Si substrates on the interlayer exchange coupling of polycrystalline Fe/Cr/Fe thin films is studied. The rippled substrates with ripple wavelengths of 22 and 37 nm where created by means of ion beam erosion. Using lambda=22 nm ripple substrates we find a Néel coupling superimposed on the interlayer exchange coupling in Fe/Cr/Fe trilayers associated with a strong uniaxial anisotropy induced by the substrate topography. These results are obtained by applying a Stoner-Wolfarth model on magnetic reversal loops obtained via longitudinal magneto-optical Kerr effect magnetometry.

Polydispersed bubbly flows with wide range of bubble size are commonly encountered in many industrial fields. The use of population balance models coupled with the two-fluid model presents the most viable way of handling such complex flow structures. The main focus of this paper is to access the capabilities of two population balance models – namely Average Bubble Number Density (ABND) and Inhomogeneous MUlti-SIze-Group (MUSIG) model; in resolving the dynamical changes of void fraction and bubble size distribution under polydispersed flow conditions. Numerical predictions are validated against two polydispersed flow measurements. Special attentions are directed towards the performance of the two models in capturing the behavioral transition of “wall peak” to “core peak” void fraction profile. Applicability and drawbacks of the two population balance models for industrial applications are also discussed.

Experimental determination of the thermophysical properties conductivity, viscosity, and surface tension of lithium iodide was carried out in the temperature range starting slightly above the melting point and up to about 950~K. These measurements are motivated by the search for a transparent substance, the Prandtl number Pr of which approaches or is even less than unity, and which shows a stable Marangoni effect with respect to a potential pollution of the melt. Such a combination of material properties is mandatory in the attempt of a physical modelling of laser welding processes where optical access to the bulk of the fluid is needed in order to measure the flow field. In an extension to these basic studies, also the electrical conductivity and the influence of the admixture of other iodides on Pr was studied exemplarily.

Clusters in Cobalt implanted Boron pre-doped ZnO

Nitrilotriacetic acid, commonly known as NTA (N(CH2CO2H)3), can be considered a representative of the polyaminocarboxylic family. The results presented in this paper describe the thermodynamical complexation and structural investigation of An(IV) complexes with NTA in aqueous solution. In the first part, the stability constants of the An(IV) complexes (An ) Pu, Np, U, and Th) have been determined by spectrophotometry. In the second part, the coordination spheres of the actinide cation in these complexes have been described using extended X-ray absorption fine structure spectroscopy and compared to the solid-state structure of (Hpy)2[U(NTA)2] · (H2O). These data are further compared to quantum chemical calculations, and their evolution across the actinide series is discussed. In particular, an interpretation of the role of the nitrogen atom in the coordination mode is proposed. These results are considered to be model behavior of polyaminocarboxylic ligands such as diethylenetriamine pentaacetic acid, which is nowadays the best candidate for a chelating agent in the framework of actinide decorporation for the human body.

Practicing engineers are constantly confronted with the prospect of solving complex gas-liquid bubbly flow problems in real industrial systems. The use of population balance models coupled with the two-fluid model presents the most viable way of handling such flows. The homogeneous MUltiple-SIze-Group (MUSIG) model has recently become a widely adopted population balance approach whereby the continuous bubbles size range can be represented by a series of discrete classes. The improved inhomogeneous MUSIG model extends the capability of accounting different bubble shapes and travelling gas velocities. Conversely, the Average Bubble Number Density (ABND) model represents another simpler approach in handling bubble interactions in complex gas-liquid bubbly flow. The capability of these three population balance models is assessed. Particular emphasis is directed towards the possible handling of bubbly-to-slug transition flow conditions. Numerical predictions are compared against experimental data obtained from Lucas et al. [1] and Hibiki et al. [2]. Shortcomings and applicability of these models for industrial applications are also discussed.

Spektri emissii i wosbuschdenia photoluminescencii pri komnatnoi temperature plenok Si3N4 implantirovannich plenok Ge+ i Ar+, issledovanui v savisimosti ot dosui ionov i temperaturui posledujuschego otschiga.

The phenomenon of air entrainment as a result of an impinging water jet was experimentally studied by means of videometry and image processing methods. A series of experiments at different conditions was performed and evaluated. Each experiment consisted of a 10s recorded sequence with a frequency of 200Hz. Jet lengths varied between 0.01m and 0.2m and jet exit velocities ranged between 0.8m/s and 2.5m/s. Image processing algorithms were applied to extract information about jet penetration depth, width of the bubble plume and bubble size distribution. Therefore, images were subdued to background subtraction, binarization and averaging. Bubble sizes were estimated from single images by subsequent background subtraction, cell segmentation, bubble detection and bubble size calculation by means of a Hough-transform based algorithm. It was found that the bubble sizes were in accordance to the data present in the literature. The penetration depth of the plume was compared to an empirical formula presented by Bin in the literature. It was established that in addition to the impact velocity, the amount of entrained gas has a significant effect on the penetration depth.

The accuracy of numerical predictions for gas/liquid two phase flows using Computational Multiphase Fluid Dynamics (CMFD) methods strongly depends on the formulation of models governing the interaction between the continuous liquid field and bubbles of different sizes. The purpose of this paper is to develop, test and validate a multifield model of adiabatic gas/liquid flows at intermediate gas concentrations (e.g., churn turbulent flow regime), in which multiple-size bubbles are divided into a specified number of groups, each representing a prescribed range of sizes. The proposed modeling concept uses transport equations for the continuous liquid field and for each bubble field. The overall model has been implemented in the NPHASE-CMFD computer code. The results of NPHASE-CMFD simulations have been validated against the experimental data from the TOPFLOW test facility. Also, a parametric analysis on the effect of various modeling assumptions has been performed.

Metodami photolumineszensii, kombinirovannove rassejania i spektroskopii obratnogo rasseania alpha tschastiz issledovano formirovanie zentrov rekombinationnogo uslutschenia pri otschige sloev SiO₂, implantirovannich ionami Ge.

Air entrainment as a result of a water jet plunging into a pool of water was studied by means of visualization techniques. Image processing algorithms were used to analyze the recorded sequences of the phenomenon. Data regarding the penetration depth and bubble size distribution was gathered for different jet impact velocities and jet lengths. The accumulated results are further used to validate the models implemented in computational fluid dynamics (CFD) codes.

A hydrodynamic model of two-phase, churn-turbulent flows is being developed using the computational multiphase fluid dynamics (CMFD) code, NPHASE-CMFD. The numerical solutions obtained by this model are compared with experimental data obtained at the TOPFLOW facility of the Institute of Safety Research at the Forschungszentrum Dresden-Rossendorf. The TOPFLOW data is a high quality experimental database of upward, co-current air-water flows in a vertical pipe suitable for validation of computational fluid dynamics (CFD) codes. A five-field CMFD model was developed for the continuous liquid phase and four bubble size groups using mechanistic closure models for the ensemble-averaged Navier-Stokes equations. Mechanistic models for the drag and non-drag interfacial forces are implemented to include the governing physics to describe the hydrodynamic forces controlling the gas distribution. The closure models provide the functional form of the interfacial forces, with user defined coefficients to adjust the force magnitude. An optimization strategy was devised for these coefficients using commercial design optimization software. This paper demonstrates an approach to optimizing CMFD model parameters using a design optimization approach. Computed radial void fraction profiles predicted by the NPHASE-CMFD code are compared to experimental data for four bubble size groups.

A basis model was proposed in this work, which considers bubble coalescence and breakup due to different mechanisms, including coalescence due to turbulence, laminar shear, wake entrainment and eddy capture, and breakup due to turbulent fluctuation, laminar shear and interfacial slip velocity. The basis model was implemented into an efficient 1D Test Solver, which is developed specially for bubbly flows in a round vertical pipe. For the first step, the new model was validated with the high quality experimental data for the case of air-water mixtures, which were obtained at the TOPFLOW facility. Simulation results showed that at relatively low superficial gas velocities, the initial bubble size was small and had a narrow distribution, and coalescence dominates the evolution; with the increase in the superficial gas velocity, large bubbles appear near injection position, and result in a much wider bubble size distribution, and breakup became predominant. The radial air volume fraction was redistributed from the injection position at wall to the whole cross section, and the stable peak remains near the wall for small bubbles while migrating towards the pipe centre for large bubbles. The comparison of simulation results with experimental data showed encouraging agreements, which affirmed the feasibility and capability of the basis model and indicated also the requirements for adjustments and improvements.

Bubble condensation plays an important role e.g. in sub-cooled boiling or steam injection into pools. Since the condensation rate is proportional to the interfacial area density, bubble size distributions have to be considered in an adequate modeling of the condensation process. The effect of bubble sizes was clearly shown in experimental investigations done at the TOPFLOW facility of FZD. Steam bubbles were injected into a sub-cooled upward pipe flow via orifices in the pipe wall located at different distances from measuring plane. 1 mm and 4 mm injection orifices were used to vary the initial bubble size distribution. Measurements were done using a wire-mesh sensor. Condensation is clearly faster in case of the injection via the smaller orifices, i.e. in case of smaller bubble sizes. In a previous work a simplified test solver, developed especially to test models for vertical pipe flow was used to simulate these effects. Now the results will be transferred to the CFD code CFX from ANSYS. Recently the Inhomogeneous MUSIG model was implemented into the code enabling the simulation of poly-dispersed flows including the effects of separation of small and large bubbles due to bubble size dependent lift force inversion. It allows to divide the dispersed phase into size classes regarding the mass as well as regarding the momentum balance. Up to now transfers between the classes in the mass balance can be considered only by bubble coalescence and breakup (population balance). Now an extension of the model is proposed to include the effects due to phase transfer. The paper discusses the necessary extensions of the Inhomogeneous MUSIG model and presents the new experimental setup for the investigation on steam bubble condensation.

The visual photoreceptor rhodopsin is a prototypical 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 transmembrane helix-3 promotes the formation of the G-protein-activating state. Using transmembrane segments derived from helix-3 of bovine rhodopsin, we show that lipid protein interactions play a key role in this cytosolic "proton switch". Infrared- and fluorescence-spectroscopic pKa determinations reveal that the D(E)RY motif is an autonomous functional module coupling side chain neutralization to conformation and helix positioning as evidenced by side chain to lipid headgroup Förster-resonance-energy-transfer. The free enthalpies of helix stabilization and hydrophobic burial of the neutral carboxyl shift the side chain pKa into the range typical of Glu-134 in photoactivated rhodopsin. The lipid-mediated coupling mechanism is independent of interhelical contacts allowing its conservation without interference with the diversity of ligand-specific interactions in class-I GPCRs.

Comparisons of uranium (U) accumulation and tolerance were conducted in terrestrial versus laboratory trials using an endemic, on a former U mining site growing Arabidopsis halleri.
Sequential extractions combined with ICP-MS measurements were used for determining the soil content of different metals and the U accumulation in plants, respectively. Root elongation tests, investigations of photosynthetic traits via absorption and fluorescence spectroscopy enabled estimations of U tolerance.
Hydroponically grown plants accumulated 100 fold more U in roots and 10 fold more in shoots compared with plants growing in their native habitat. Despite this elevated U uptake, the root elongation was not affected. However, impairments of the photosynthetic machinery could clearly be proven.
These facts are important indications for a pronounced decreasing U tolerance under laboratory conditions. The occasional different bioavailability of U and essential metals such as iron in the two approaches is one of the key factors affecting U accumulation, transport, tolerance or toxicity development. The described “uranophyte” Arabidopsis halleri could be a versatile tool for such unequal objects.

Photoabsorption cross sections sigma_gamma up to the neutron-separation energy S_n were measured for the stable even-mass isotopes 92-100Mo in photon-scattering experiments at the ELBE accelerator. As a consequence of the high level density at excitation energies close to S_n a huge number of resolved transitions and in addition an even greater intensity portion in an unresolved continuum have been observed. Simulations of gamma-ray cascades were performed to estimate the intensity distribution of inelastic transitions to low-lying levels and, hence, to deduce intensities and branching ratios of the ground-state transitions needed for the determination of sigma_gamma. The combination of the present data with (gamma,n) data allows us to obtain sigma_gamma in the energy range from about 4 MeV up to the giant dipole resonance. The experimental cross sections are compared with predictions of a new approach called Instantaneous Shape Sampling that calculates dipole strengths by means of QRPA for instantaneous shapes of the nucleus with probabilities obtained from IBA. The calculated sigma_gamma reproduce very well the experimental values around S_n.

Vorgestellt werden aktuelle Ergebnisse zur Komplexierung von dreiwertigem Americium mit den Liganden Pyromellitsäure, Citronensäure und Salicylsäure. Mit TRLFS und UV-vis-Spektroskopie konnten für die Systeme belastbare Komplexbildungskonstanten bestimmt werden. Erste Ergebnisse zu temperaturabhängigen Messungen und Sorptionexperimenten werden präsentiert.

Zinc oxide is getting an enormous attention due to its potential applications in a variety of fields such as optoelectronics, spintronics and sensors. The renewed interest in this wide band gap oxide semiconductor relies on its direct high energy gap (Eg~3.437 eV at low temperatures) and large exciton binding energy. However to reach the stage of device production the difficulty to produce in a reproducible way p-type doping must be overcome.
In this study we discuss the structural and optical properties of ZnO films doped with nitrogen, a potential p-type dopant. The films were deposited by magnetron sputtering using different conditions and substrates. The composition and structural properties of the films were studied combining X-ray diffraction (XRD), Rutherford backscattering (RBS), and heavy ion elastic recoil detection analysis (HI-ERDA). The results show an improvement of the quality of the films deposited on sapphire with increasing radio-frequency (RF) power with a preferentially growth along the c-axis. The ERDA analysis reveals the presence of H in the films and a homogeneous composition over the entire thickness. The photoluminescence of annealed samples evidences an improvement on the optical quality as identified by the well structured near band edge recombination.

A new route for tuning the magnetic anisotropy of ultrathin Co films by Ga+ ion irradiation is presented. The magnetic anisotropy of a Pt/Co(2.6 nm)/Pt film is first changed from in-plane to out-of-plane by uniform low dose Ga+ ion irradiation at 30 keV. When increasing the dose, a second spin reorientation transition towards the sample plane is also evidenced. This could be an elegant way to design magnetic nanowires with perpendicular anisotropy, embedded in an in-plane magnetized environment, either by uniform irradiation through a mask or focused ion beam. Tentative explanations
on the origin of these two successive spin reorientations are proposed.

Using a combination of computer simulations based on the binary collision approximation and molecular dynamics simulations the (meta)stable defect structure formed after a single ion impact into single crystalline silicon is obtained. Characteristics of the defect morphology such as the ratio between isolated and clustered defects are mainly determined by mass of the incident ion.

Strained Si and SiGe/Si heterostructures on insulator are promising channel materials for future nanoelectronics devices. The successful integration of these materials into new MOSFETs architectures depends on the ability of forming ultra shallow and ultra steep junctions for the source/drain regions. Here, we present results using flash lamp annealing for dopant activation in SOI, sSOI, HOI and sHOI. Flash lamp annealing technique allows complete suppression of diffusion while obtaining sheet resistances lower than 500 Ω/□, in both, SOI and sSOI. First investigations of strained and unstrained SiGe heterostructures after flash lamp annealing 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.

The manganites La_1-xSr_xMnO₃ exhibit a remarkable rich phase diagram as function of temperature, doping concentration and magnetic field, accompanied by attractive properties like colossal magneto resistance (CMR). Furthermore lightly doped La_1-xSr_xMnO₃ (around x = 0.125) shows an unusual ferromagnetic insulating (FMI) ground state which can not be explained by the conventional double exchange model. We studied the magnetic properties of a La_0.875Sr_0.125MnO₃ single crystal by means of temperature dependent magnetometry and applied x-ray circular magnetic dichroism (XMCD) at the Mn L_2,3 edges. In contrast to previous results reported [1] we do not find a significant Mn orbital moment, neither in the FMI phase (T < 180 K) nor in the high temperature paramagnetic insulating phases (T > 180 K). The experimental XMCD results are compared with charge transfer multiplet calculations.

Im Vortrag werden die Synthese und Charakterisierung schwefelhaltiger Huminsäure-Modellverbindungen sowie Ergebnisse zur Untersuchung des Einflusses von Huminsäureschwefelfunktionalitäten auf die U(VI)-Komplexierung diskutiert. Weiterhin werden Ergebnisse zur U(VI)-Sorption an Opalinuston vorgestellt.

The question of the nature of superconductivity in boron-doped diamond (synthesized at high pressures and high temperatures) is still open. Here we present consistent measurements of resistivity and specific-heat on two samples containing pure ¹³C and ¹²C, revealing a 0.2 K shift of the superconducting transition temperature T_c. Hallcoefficient measurements confirm equal charge-carrier concentrations in both samples. The results are interpreted as a carbon-isotope effect more than two times larger than expected from the most simple BCS model for phonon-mediated superconductivity. Additional analyses of microstructure and exact boron content of the superconducting material show the presence of highly boron-enriched amorphous boundaries between the grains. For these investigations highresolution transmission-electron microscopy and electron-energy-loss spectroscopy were used.

We report on results of sound-velocity and sound-attenuation measurements in the triangular-lattice quasi-2D spin-1/2 antiferromagnet (AFM) Cs₂CuCl₄ (T_N = 0.6 K), in magnetic fields up to 18 T applied along the a axis and at low temperatures from 5 down to 0.3 K. Below T_N this material displays a 3D incommensurate spiral longrange AFM order, which is stable up to B_s ≈ 8.5 T for fields applied along the a axis. Above this field all spins are polarized. For the AFM phase a possibility for the Bose-Einstein condensation of magnons has been suggested whereas beyond the AFM phase at low temperatures a proximity to the spin liquid (SL) state is considered in this compound. The longitudinal c₁₁ acoustic mode, which has a propagation direction along the a axis, shows pronounced anomalies in sound velocity and attenuation in discussed temperature and field range indicating spinstrain interaction. It also demonstrates frequency-dependent effects indicating the presence of relaxation processes. The ultrasonic results are analyzed with a theory based on exchange-striction coupling. There is a good qualitative agreement between theory and experiment.

High-spin states in 83Rb were populated in the reaction 11B + 76Ge at beam energies of 45 and 50 MeV. Gamma rays were detected with the spectrometer GASP. The level scheme of 83Rb was extended up to 13.9 MeV. Mean lifetimes of 23 levels were determined using the Doppler-shift-attenuation method. Among the bands newly established is a sequence including intense M1 transitions and cross-over E2 transitions. This sequence turns out to be irregular and thus shows that magnetic rotation observed in the neighboring odd-odd isotopes cannot be sustained in this odd-even nuclide. Excited states in 83Rb were interpreted in terms of the shell model using the model space pi (0f5/2, 1p3/2, 1p1/2, 0g9/2) nu (1p1/2, 0g9/2). The configuration predicted for the M1 sequence is analogous to the one predicted for the M1 band in the neighbor 84Rb and reproduces the transition strengths at high spin.

We have investigated Py-Ta thin film systems with varying numbers of interfaces, but a constant overall thickness of 20 nm Py and 38 nm Ta. The samples have been irradiated with Ne⁺ ions at various fluences in order to modify their magnetic properties, that have been probed using ferromagnetic resonance (FMR), magneto-optical Kerr effect (MOKE), and SQUID magnetometry. The saturation magnetization M_s decreases both with increasing number of Py-Ta inferfaces and with increasing ion fluences. The uniaxial anisotropy of the samples is only of small magnitude and remains almost unaffected. There is a critical fluence depending on the number of interfaces for which ferromagnetism vanishes.

Regarding electronic materials there is a clear and increasing interest in energy pulse modification of materials, especially also thermal processing far below one second, i.e. the lower limit of RTP (Rapid Thermal Processing) called spike annealing. It is the world of processing in the millisecond or nanosecond range. In the past, this was mainly driven by the need of suppressing the so-called Transient Enhanced Diffusion for advanced boron-implanted shallow pn-junctions in the front-end silicon chip technology. Meanwhile the interest in flash lamp annealing (FLA) in the millisecond range spread out into other fields than just “classical” silicon electronics. This paper reports shortly about the restart in flash lamp annealing and further on recent experiments regarding shallow junction engineering in germanium and SOI (silicon-on-insulator), annealing of ITO (Indium Tin Oxide) layers on glass and plastic foil interesting for low cost electronics as well as investigations which we did during the last years in the field of wide band gap semiconductor materials (SiC, ZnO). Moreover recent achievements in the field of silicon-based light emission basing on Metal-Oxide-Semiconductor Light Emitting Devices will be reported. Finally it will be demonstrated that the basic principle of short time thermal processing, i.e. surface heating on a colder bulk, features also advantages regarding the casting of lead sheets to produce organ pipes in the spirit of the 17th century.

The photocapacitance (PC) has been probed on MOS diodes with an Eu-implanted SiO2 layer. In general, rare earth implanted SiO2 layers in MOS diodes are of great interest for possible applications in integrated metal-oxide-semiconductor light emitting devices (MOSLEDs). For example, green and ultraviolet electroluminescence has been probed on SiO2:Tb-MOSLEDs and SiO2:Gd-MOSLEDs, respectively. MOSLEDs reach external quantum efficiencies between 1% and 16%, and the electroluminescence peaks are typically ascribed to 4f-intrashell transitions of trivalent rare earth ions. A clear capacitance change has been observed for different wavelengths under monochromatic illumination. Some of the detected peaks correspond to the energies of 4f-intrashell transitions of the Eu ions. According to this, the number of active luminescence centers in MOSLEDs may be determined from PC measurements. Some 4f-intrashell transitions have been also observed by means of electroluminescence measurements on the same MOSLEDs. To emphasize the physical significance of the PC data recorded on SiO2:Eu-MOSLEDs, we also compare PC data recorded on different MOSLEDs implanted with other rare earth ions.

NiO has great potential applications in gas sensors, optical fibers, solar thermal absorbers, or in non-volatile resistive random memories. In our study NiO, NiMnO, and NiMnLiO have been grown on double-side polished r-plane sapphire substrates by pulsed laser deposition. In contrast to the antiferromagnetic behaviour of bulk NiO, we probed weak ferromagnetism with a coercivity ranging between 150 and 250 Oe by means of SQUID magnetometry. We measured the complex Voigt angle using a HeCd laser, a Glan Taylor polarizer, a Hinds PEM-100 and two LockIns. The polarization state of light after transmission through a sample consisting of ca. 1 μm thick, weak ferromagnetic and diamagnetic NiO thin films on diamagnetic r-plane sapphire substrates has been modelled using the 4*4 matrix formalism in dependence of an external magnetic field applied in-plane. The modelling results revealed that for the bare diamagnetic substrate the Voigt angle depends parabolically on the external magnetic field and that the weak ferromagnetic and diamagnetic NiO thin films changed the parabolic dependence of the Voigt angle in the range of ±0.1 T to a flat-top shape in agreement with the experimentally determined Voigt angle.

We have investigated the interlayer exchange coupling in Fe (4nm)/Cr (x nm)/Fe (4nm) thin film trilayers (x=0–5 nm) deposited on rippled armorphous silicon substrates. The substrate surface was periodically modulated (periods of 20 nm, 35 nm, and 50 nm) by Ar+ ion erosion. The influence of the resulting surface and interface structure on the magnetic properties has been investigated by magneto-optical Kerr effect (MOKE). We found an orange peel type coupling, predicted by Néel’s theory and, due to the morphology of the magnetic layers, a strong uniaxial magnetic anisotropy in the system.
This work is supported by DFG grant FA 314/6-1.

During a Lost of Coolant Accident (LOCA) cold Emergency Core Cooling (ECC) water can be injected into the cold leg of the primary loop of PWR. A relevant problem occurring in this situation is the development of wavy stratified flows which can lead to slug generation. Because slug flow cannot be predicted with the required accuracy and spatial resolution by the one-dimensional system codes, the stratified flows are increasingly modelled with computational fluid dynamics (CFD) codes. In CFD, closure models are required that must be validated. The recent improvements of the multiphase flow modelling in the ANSYS CFX code make it now possible to simulate these mechanisms in detail. In order to validate existing and further developed multiphase flow models, high-resolution measurement data is needed in time and also in space.

For the experimental investigation of co-current air/water flows, the HAWAC (Horizontal Air/Water Channel) was built. The channel allows in particular the study of air/water slug flow under atmospheric pressure. Parallel to the experiments, CFD calculations were carried out. A picture sequence recorded during slug flow was compared with the equivalent CFD simulation made. The two-fluid model was applied with a special turbulence damping procedure at the free surface. An Algebraic Interfacial Area Density (AIAD) model on the basis of the implemented mixture model was introduced, which allows the detection of the morphological form of the two phase flow and the corresponding switching via a blending function of each correlation from one object pair to another. As a result this model can distinguish between bubbles, droplets and the free surface using the local liquid phase volume fraction value.

The behaviour of slug generation and propagation at the experimental setup was qualitatively reproduced by the simulation, while local deviations require a continuation of the work. The creation of small instabilities due to pressure surge or an increase of interfacial momentum should be analysed in the future. Furthermore, experiments with pressure and velocity measurements are planned and will allow quantitative comparisons, also at other superficial velocities.

Cathodoluminescence (CL), scanning transmission electron microscopy (STEM), and energy dispersive X-ray analysis (EDX) have been used to investigate Si and Ge cluster formation in amorphous silicon dioxide layers and their respective luminescence behavior.
Commonly, CL emission spectra of pure SiO2 are identified with particular defect centers within the atomic network of silica including the non-bridging oxygen-hole center (NBOHC) associated with the red luminescence (R) at 650 nm (1.9 eV) and the oxygen deficient centers (ODC) with the blue (B) (460 nm; 2.7 eV) and ultraviolet UV (295 nm; 4.2 eV) bands. In GeC ion implanted SiO2 an additional violet (V) Ge related emission band is identified at (410 nm; 3.1 eV). A post-implantation thermal annealing at temperatures Ta = 700-1100 °C in dry nitrogen leads up to 900 °C to a huge increase of the violet luminescence, followed by a decrease towards 1100 °C. The strong increase of the violet luminescence is associated with formation of low-dimension Ge aggregates like dimers, trimers and higher formations; the following decay of luminescence is due to further growing to Ge nanoclusters.

Metal-oxynitride-oxide-silicon (MONOS) structures containing SiO2 layer implanted with different concentrations of ytterbium atoms were investigated. The electroluminescence (EL) measurements show that the MONOS:Yb devices can operate as blue or near infrared light emitters depending on the Yb concentration and annealing time. For an Yb concentration of up to 1.5% and annealing times of 30 min the near infrared EL with a peak at 975 nm corresponding to the 2F5/2→2F7/2 transition dominates. The short time annealed (6 s) sample containing 3% of Yb atoms exhibits mainly the blue EL due to co-operative up-conversion emission in the Yb3+-Yb3+ system. An enhancement of the red EL at 650 nm due to up-conversion energy transfer from the 2F5/2 excited state to the nonbridging oxygen hole center (NBOHC) is also presented.

Magnetic semiconductors with high Curie temperatures and large coercivity are very promising materials for spintronic applications. An approach to fabricate GaMnAs is the Mn-implantation of GaAs followed by pulsed laser annealing (PLA). We investigated the influence of Mn concentration and PLA conditions, e.g. number of pulses, pulse length, and pulse energy, on the structural and magnetic properties of GaMnAs. Using SQUID magnetometry, we revealed a strong decrease of the saturation magnetization with increasing number of pulses. HRXRD-measurements revealed a lattice expansion normal to the surface after implantation. PLA leads either to a strain decrease (1 pulse) or even to a strain over compensation (10 pulses). We conclude that Mn implantation into GaAs followed by PLA is not sufficient for increasing the Curie temperature in GaMnAs. In addition, the drawback of the Mn implantation is the loss of As from the GaAs surface as detected by means of Auger electron spectroscopy. Heat transfer calculations and coimplantation with suitable elements are possible approaches to enhance the properties of GaMnAs.

The request for room-temperature diluted magnetic semiconductors resulted in a large interest in GaN containing transition metals. Recent investigations have shown that beside of the real dilute state spinodal decomposition as well as the formation of secondary phases may play an important role in the discussion of the origin of the ferromagnetism [1, 2].
In this study, the dynamics of formation of secondary phases is investigated on GaN epilayers deposited on sapphire and implanted with 57Fe+ ions (3, 8 and16 • 1016 cm−2) at room temperature. Samples were annealed at 750° – 1200° C in N2 and Ar flow for durations between some ms and some minutes.
The formation of secondary phases in Fe implanted GaN upon annealing a N2-flow was detected ex-situ by means of x-ray diffraction and Mössbauer spectroscopy and supported by SQUID magnetometry. During annealing in reduced N2 atmosphere the reversal phase change from Fe3N at room temperature to Fe2.4N at 1023 K was observed by means of in-situ x-ray diffraction. Samples, annealed by a flash lamp in an Ar flow show the formation of different secondary phases depending on annealing time and temperature.

[1] Bonanni et al., PRL 101, (2008) 135502
[2] Li et al., Journal of Crystal Growth 310, (2008) 3294–3298

INTRODUCTION
Radiolabelled particles are an attractive tool in the therapy of malignancies of the liver. Hepatic tumours receive their blood supply mainly from the arterial circulation, unlike normal liver tissue which is supplied by the portal vein. The intra-arterial application of microspheres with particle size > 10 m are trapped in the capillary bed and release a local radiotoxic dose with low levels of toxicity to the normal liver (1). The aim of this study was to determine the in vitro (incubation in human plasma and DTPA-Challenge) and in vivo characteristics of radiolabelled human serum albumin (HSA) microspheres and the valuation of suitability for radiotherapeutical treatment of liver malignancies. Covalent attachment of DOTA chelators onto the surface of the spheres opens up an easy access to Y-86-radiolabelled HSA microspheres. For in vivo experiments the labelled spheres were injected into the tail vein of Wistar rats. After 1, 12, 24 and 48 h the animals were sacrificed and the radioactivity concentration of isolated organs and tissue was determined. Furthermore, to investigate the influence of the surface structure we have used three different batches of HSA microspheres (smooth to rough; diameter 20-30 µm).

RESULTS AND DISCUSSION
Approximately 25 DOTA molecules per molecule HSA could be attached as estimated from elemental analysis of DOTA-HSA microspheres, independently of the surface characteristics of the spheres. They were Y-86 labelled under optimized conditions in 96 ± 1 % yield. No significant differences between smooth- and rough-surfaced spheres were found. In DTPA challenge experiments 98 % of the radioactivity was still particle-associated after 24 hours incubation at 37 °C. In vitro studies in human plasma resulted in 95 ± 4 % particle-associated radioactivity after 48 h incubation at 37 °C. In the in vivo experiments radiolabelled smooth and rough microspheres were completely trapped in the lungs, which served in our experiments as model for the vascular system of a solid tumour. Biodistribution of radioactivity was determined up to 48 h p.i. The estimated activity in the urine was below 1 %ID at 1 and 12 h p.i., and below 9 %ID at 24 and 48 h. Radioactivity level of other organs and tissues was marginal (< 2 %ID at all time points). The three batches of particles differed considerably in their radioactivity recovery in the lungs. For the clearance of radioactivity from the lungs decay-corrected half-lives of 85 h (rough microspheres) and 187 h (smooth microspheres) were calculated (2).
We found a strong dependency between the in vivo stability of radiolabel fixation on the surface and the roughness of the particle. We concluded that for the preparation of HSA-derived microspheres for radiotherapeutic application smooth-surfaced spheres are superior to rough spheres due to their higher in vivo stability.

REFERNCES
1. Murthy R et al., Yttrium-90 microsphere therapy for hepatic malignancy: devices, indications, technical considerations, and potential complications. Radiographics 25 (2005), 41-55.
2. Schiller E, Bergmann R, Pietzsch J, Noll B, Sterger A, Johannsen B, Wunderlich G, Pietzsch H-J, Yttrium-86-labelled human serum albumin microspheres: relation of surface structure with in vivo stability, Nucl. Med. Biol., doi: 10.1016/j.nucmedbio.2007.10.008.

The generation of dilute magnetic semiconductors (DMS) by ion-beam implantation of magnetic centres into semiconducting materials has experienced renewed interest since the generation of magnetic thin films from the Cobalt-doped wide-gap semiconductor TiO2. Since the magnitude of the magnetic moment in such films is strongly varying and since the implementation in a standard, Silicon-based semicon ductor device is challenging, we have concentrated on the binary and fully integrable system Vanadium:Silicon. At higher doping concentrations, Vanadium and Silicon form several binary compounds; the most well characterised structures have the compositions V:Si= 3:1, 5:3, 6:5, 1:2, and bear the potential to exhibit magnetism. At higher dilution, Vanadium may form point defects in the crystalline Silicon host matrix. Here, we investigate different combinations of substitutional and interstitial vanadium atoms in a silicon crystal matrix.

As a result of continued scaling and the emphasis on low power and low voltage operation, silicon-oxide-nitride-oxide-silicon (SONOS) nonvolatile memory has received more attention recently. In this talk we investigate the charge decay characteristics of SONOS devices at elevated temperatures. Based on the thermal emission model as the dominant charge loss mechanism, the trap density energy distribution is determined. Furthermore we present an advanced model which includes the influence of subsequent tunneling through the bottom oxide after thermal excitation in the conduction band of the nitride.

The morphology of different amorphous or amorphized SiO2 surfaces, including thermally grown films, fused silica, and single crystalline quartz, during low energy ion sputtering has been investigated by means of atomic force microscopy. For all three materials, the formation of periodic ripple patterns oriented normal to the direction of the ion beam is observed at intermediate incident angles. At near-normal incidence, the SiO2 surfaces remain flat, whereas a rotation of the ripple patterns is observed at grazing incidence. At intermediate angles, the patterns on the different surfaces exhibit wavelength coarsening of different strengths, which can be attributed to different amounts of near-surface mass transport by the surface-confined ion-enhanced viscous flow. In the framework of the recent hydrodynamic model of ion erosion, the observed differences in ripple coarsening are consistent with this interpretation and indicate that the surface energies of thermally grown SiO2 and amorphized quartz are lower and higher than that of fused silica, respectively.

no abstract available

As the size of semiconductor devices is decreasing permanently, new techniques are required to probe their dopant profile reliably on a nanometer scale. Kelvin probe force microscopy (KPFM) and scanning capacitance microscopy (SCM) are the most promising techniques for this demand. KPFM (LevelAFM from Anfatec) enables the detection of the contact potential difference (CPD) between tip and sample and SCM (DI3100 from Veeco Instruments) probes the capacitance of the metal oxide structures formed in contact. In order to demonstrate the complementary information obtained by KPFM and SCM measurements, we used the pn junction in a static random access memory integrated circuit device where the n-well with a donor concentration of 2E17 cm⁻³ has been fabricated by implanting the p-epi with a nominal acceptor concentration of 2E16 cm⁻³ with P+ ions of energy 900 keV and a fluence of 1.7E13 cm⁻² [1]. As expected, KPFM yields a smooth variation of the CPD between the p-epi and the n-well amounting to 230 meV. SCM clearly shows the boxlike doping profile of this pn junction. The CPD variation can be modelled by assuming a partially compensated donor concentration in the n-well.
[1] M.W. Nelson et al., Electrochemical and Solid-State Letters 2 (1999) 475.

The simple operability of stable and compact fiber lasers motivated research on photoconductive THz emitters based on substrates that allow interband excitation with wavelengths up to 1.55 μm. Low-temperature grown InGaAs and ion-irradiated InGaAs, both grown lattice-matched on InP, have been used as substrate materials for dipole emitter antennas [1,2]. However, the resistivity of these materials is still too low for large-area emitters with interdigitated electrodes [3]. These structures prevent carrier excitation in every second spacing by an additional metallization or by etching of the substrate [4]. Hereby the excited elementary THz waves interfere constructive in the far field. These emitter designs combine the advantages of high bias fields and large active areas. Furthermore detection with elements of similar electrode geometry based on GaAs substrates with sub-picosecond carrier lifetimes and resistivity in the 106 Ω cm range has been demonstrated [5]. Here we present such large-area emitters based on InGaAsN which show efficient THz emission for excitation wavelengths up to 1.35 μm.
The substrate material consists of a 1000 nm Ga1-yInyAs1-xNx (y=0.11 and x=0.04) layer grown by molecular-beam epitaxy on semi-insulating GaAs. On top there is an additional 60 nm thick Al0.3Ga0.7As barrier layer followed by a 5 nm GaAs cap layer. Transmission measurements with a Fourier spectrometer reveal a bandgap corresponding to a wavelength of 1.5 μm. The esistance of a complete device with an active area of 1 mm2 is 0.3 MΩ. This allows operation with high bias fields (30 kV/cm) without being limited by heating. For excitation an optical parametric oscillator (OPO), tunable between 1.1 μm and 1.5 μm, is used. The pulse duration is 280 fs. The THz signal is detected by electro-optical sampling using a 1 mm thick ZnTe crystal. The gating beam (λ = 820 nm) for detection is split off from a Ti:sapphire oscillator which drives the OPO.
The THz transient is measured with lock-in technique and has a signal-to-noise ratio of 400 obtained with 100 ms integration time constant. The bandwidth of the emitted radiation is 2.5 THz and is limited by the pulse duration of the OPO. Varying the OPO wavelength at fixed excitation power results in constant THz signals for wavelengths below 1.3 μm. For excitation wavelengths of 1.4 μm the signals are about 5 times smaller as compared to the shorter wavelengths. Furthermore we compare the InGaAsN emitter with an emitter based on semi-insulating (SI) GaAs when both are excited at 800 nm. Here the SI-GaAs emitter shows an 8 time higher THz field then the InGaAsN emitter at the same excited carrier density. We attribute this to the high electron obility in the SI-GaAs substrate.
In summary the THz emission indicates a high transient conductance of the InGaAsN material. The high resistivity makes it suitable for large area antennas with interdigitated electrode geometry.
References
[1] M. Suzuki and M. Tounouchi, Appl. Phys. Lett. 86, 163504, 2005
[2] A. Takazato, M. Kamakura, T. Matsui, J. Kitagawa, and Y. Kadoya, Appl. Phys. Lett. 91, 011102 ,2007
[3] A. Dreyhaupt, S. Winnerl, T. Dekorsy, and M. Helm, Appl. Phys. Lett. 86, 121114, 2005
[4] M. Awad, M. Nagel, and H. Kurz, Appl. Phys. Lett. 91, 181124, 2007
[5] F. Peter, S. Winnerl, S. Nitsche, A. Dreyhaupt, H. Schneider, and M. Helm, Appl. Phys. Lett. 91, 081109, 2007