Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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32180 Publications
Theoretical and numerical approaches to the forward problem and sensitivity calculation of a novel contactless inductive flow tomography
Yin, W.; Peyton, A.; Stefani, F.; Gerbeth, G.;
A completely contactless flow measurement technique based on the principle of EM induction measurements—contactless inductive flow tomography (CIFT)—has been previously reported by a team based at Forschungszentrum Dresden-Rossendorf (FZD). This technique is suited to the measurement of velocity fields in high conductivity liquids, and the possible applications range from monitoring metal casting and silicon crystal growth in industry to gaining insights into the working of the geodynamo. The forward problem, i.e. calculating the induced magnetic field from a known velocity profile, can be described as a linear relationship when the magnetic Reynolds number is small. Previously, an integral equation method was used to formulate the forward problem; however, although the sensitivity matrices were calculated, they were not explicitly expressed and computation involved the solution of an ill-conditioned system of equations using a so-called deflation method. In this paper, we present the derivation of the sensitivity matrix directly from electromagnetic field theory and the results are expressed very concisely as the cross product of two field vectors. A numerical method based on a finite difference method has also been developed to verify the formulation. It is believed that this approach provides a simple yet fast route to the forward solution of CIFT. Furthermore, a method for sensor design selection based on eigenvalue analysis is presented.

Publ.-Id: 13138 - Permalink

Speciation of curium(III) and europium(III) in human urine samples
Heller, A.; Barkleit, A.; Bernhard, G.;
Due to their radiation and heavy metal properties, radionuclides represent a serious health risk to humans in case of incorporation. To understand their toxicity, transport, deposition and elimination in the human organism, it is therefore crucial to elucidate their chemical behavior and properties on a molecular level. For trivalent actinides originating from nuclear power plants knowledge about their metabolism is very limited. In case of incorporation, they tend to accumulate in liver and skeleton and are excreted to maximum 10 – 20 % within the first week. Nevertheless this excretion occurs mainly through the kidneys, which are known to be particularly radiation sensitive.
To address the lack of knowledge, we studied the speciation of curium (as a representative of trivalent actinides) and europium (as the lanthanide analogue) in human urine and their complexation with single constituents. Since both of these heavy metals exhibit unique fluorescence properties, time-resolved laser-induced fluorescence spectroscopy (TRLFS) is an adequate tool for this purpose.
Fresh 24-hours-urine samples were collected from healthy volunteers and analyzed within few days. The inorganic composition of all samples was determined using mass spectrometry with inductive coupled plasma (ICP-MS) and ion chromatography (IC). Then all samples were spiked in vitro with curium or europium and single as well as time-resolved laser-induced fluorescence spectra were measured. We analyzed at least 10 different urine samples and were able to divide all samples into two different groups according to their fluorescence spectra.
We found that all samples with a pH below 5.6 and all samples with a pH above 6.0 each exhibit strikingly similar spectra. Compared to each other the spectra of both groups are very different and therefore easy to distinguish. Furthermore the lifetime of the metals in samples with higher pH is substantially longer than in samples with lower pH. ICP-MS and IC analysis revealed that the inorganic composition of samples which exhibit the same fluorescence spectra can vary broadly within magnitudes. Therefore the most important factor influencing the speciation of metals in human urine does not seem to be the composition but was determined to be the pH.
To identify the dominating species we also recorded the fluorescence spectra of both metals in electrolyte solution containing all inorganic but no organic components of urine. Furthermore we studied the complexation of both metals with urea and citric acid as main organic urine constituents. Comparing the measured spectra and lifetimes with this reference data, we found that at lower pH a complex citric acid species dominates the speciation of both metals while at higher pH the spectra where identical to those in electrolyte solution ruling out any involvement of organic ligands. The exact nature of this inorganic metal species has yet to be clarified.
Keywords: curium(III), europium(III), biofluids, speciation, TRLFS, trivalent actinides, human urine
  • Lecture (Conference)
    Radchem 2010 - 16th Radiochemical Conference, 18.-23.04.2010, Marianske Lazne, Czech Republic

Publ.-Id: 13137 - Permalink

Removal of As (V) from contaminated waters by microorganisms and isolated S-layers
Matys, S.; Stein, R.; Katzschner, B.; Raff, J.; Soltmann, U.; Böttcher, H.; Kießig, G.; Pompe, W.;
With the objective to develop new filter materials for cleaning of arsenic contaminated waters based on sol-gel immobilized microorganisms various bacterial strains and their isolated surface layers were investigated. Interestingly, the binding capacity of four S-layers, namely that of Lysinibacillus sphaericus NCTC 9602, Bacillus soil isolates JG-B 53 and JG-B 62 as well as Geobacillus stearothermophilus ATCC 12980 was 1.5 to 5fold enhanced in comparison to the commercial sorbent Ferrosorp with As(V) model solutions. Thereby, a different binding behaviour between whole cells and their corresponding S-Layers could be observed even in dependence on the used arsenic concentration. AFM investigations revealed more elevated and expanded S-Layer agglomerates in the case of G. stearothermophilus ATCC 12980 after loading with As.
  • Poster
    8th Symposium on remediation in Jena “Jenaer Sanierungskolloqium”: Geo-bio-processes at geochemical barriers, 28.-29.09.2009, Jena, Deutschland

Publ.-Id: 13136 - Permalink

Antiproliferative effect of ferrocifen drug candidateson malignant pleural mesothelioma cell lines
Zanellato, I.; Heldt, J.-M.; Vessieres, A.; Jaouen, G.; Osella, D.;
The purpose of this study was to investigate the antiproliferative potential of two novel bio-organometallic drug candidates, based on hydroxyl-phenyl-but-1-ene skeleton and containing the ferrocenyl (Fc) moiety, namely ferrociphenol (Fc-diOH) and ferrocifen (Fc-OH-TAM), on two cell lines, named BR95 (epithelial-like) and MM98 (sarcomatous-like), obtained from pleural effusions of previously untreated malignant pleural mesothelioma (MPM) patients. In vitro chemosensitivity of MPM cells towards the title compounds was evaluated by cell viability assay, alkaline Single Cell Gel Electrophoresis (Comet test) and western blotting evaluation of p53 induction. The two bio-organometallic derivatives were found to be more potent in inhibiting cell proliferation than the reference metallo-drug cisplatin (CDDP). This antiproliferative effect cannot be attributed to estrogenic/antiestrogenic activity, since both cell lines resulted to be estrogen insensitive (ER−). Fc-diOH and CDDP were able to upregulate wild type p53 present in MM98 cell line, while Fc-OH-TAM was not. Similarly, Fc-diOH and CDDP induced early DNA damage, while Fc-OH-TAM did not. This indicates that, albeit the similar structures, the two ferrocifens exhert different mechanisms of cytotoxicity on MPM cells.
Keywords: Malignant mesothelioma, Antiprloliferative activity, Ferrocifens, Bio-orgometallic chemistry

Publ.-Id: 13135 - Permalink

The French accelerator mass spectrometry facility ASTER: Improved performance and developments
Arnold, M.; Merchel, S.; Bourlès, D. L.; Braucher, R.; Benedetti, L.; Finkel, R. C.; Aumaître, G.; Gottdang, A.; Klein, M.;
After the installation and acceptance test of the French 5 MV AMS facility ASTER, the focus has been on improving 10Be and 26Al routine measurements. Quality assurance was established by introducing traceable AMS standards for each nuclide, self-monitoring by taking part in round-robin exercises and proficiency testing, and surveillance of long- and short-time variability of blank and reference materials. A background level of 3x10-14 makes ASTER well-suited for measuring 41Ca/40Ca in the 10-12 region, which is sufficient for a wide range of applications. Routine AMS measurements of volatile elements like 36Cl and 129I are most likely feasible in the very near future after sophisticated ion source improvements took place.
Keywords: accelerator mass spectrometry, terrestrial cosmogenic nuclides (TCN), calibration

Publ.-Id: 13133 - Permalink

Visualization of microorganisms in acidophilic biofilms
Brockmann, S.; Arnold, T.;
Biofilms are ubiquitous and so they can also be found in regions with high concentrations of heavy metals. Due to their ability to change geochemical parameters e.g. O2-concentrations, Eh, pH, and by generating metabolites they are very important for the investigation of transport processes of heavy metals in nature. However, the influence of biofilms on the migration of uranium in contaminated environments, e.g. the former uranium mining areas in eastern Germany, was disregarded so far. In the former underground uranium mine in Königstein thick biofilms in form of streamers were observed in the mine adit drainages and in form of dripstone-like biofilms with slimy endings.
The biofilm structure was visualized by confocal laser scanning microscopy (CLSM). Fluorescent dyes were used for staining the microorganisms and the extracellular polymeric substances (EPS). Unfortunately, the biofilms from acid mine drainages (AMD) have pH-values not higher than 3 and the most common fluorescent dyes are not stable below pH-values of 4. Hence, the first step in this study was to find new acid-stable fluorescent dyes to stain the acidophilic microorganisms without any increase of the pH. For this purpose a variety of new fluorescent dyes were tested and the most suitable ones were compared with the common fluorescent dyes DAPI and SYTO 59. It was found that the selected new fluorescent dyes did very well stain acidophilic biofilm microorganisms whereas DAPI and SYTO 59 fail.
  • Poster
    8th Symposium on remediation in Jena “Jenaer Sanierungskolloquium”: Geo-bio-processes at geochemical barriers, 28.-29.09.2009, Jena, Deutschland

Publ.-Id: 13132 - Permalink

TRLFS investigation on seepage waters of the Gessenbach grassland
Baumann, N.; Arnold, T.;
Laser fluorescence techniques possess some superior features, above all a very high sensitivity for fluorescent heavy metal ions. The predominance of TRLFS compared to other spectroscopic techniques, e.g. XRD and IR was showed in Baumann N. et al. (2008) in analyzing the speciation of U(VI) in a thin layer of an alteration product formed on depleted uranium. With their high sensitivity TRLFS is also suited to identify the U(VI) speciation in plant constituents. Long delay steps in time-resolved measurements avoid annoying fluorescence emission caused by organic substances.
Uranium speciation in seepage water of the Gessenbach grassland was determined by TRLFS. This was done to compare it in a later stage with the uranium speciation in plants, which grow on that grassland and ingest the same uranium contaminated water during their growth. The uranium content in those samples GB 3 and GB 6 was 75.1 and 291 ppb, respectively, and both samples delivered an evaluable fluorescence signal for TRLFS. The positions of the six peak maxima from these signals are in both water samples in concordance with data for uranium sulfate species published in the literature, e. g. in Bernhard G. et al. (1996) at 477, 493, 513, 537, 562 and 591 nm. Moreover, the time-resolved fluorescence signals of both water samples possess a mono-exponential decay, indicating the presence of one species only. These two characteristics, i.e. positions of peak maxima and lifetimes revealed without doubt that the uranium speciation in the seepage water is dominated by uranium (VI) sulfate species.
TRLFS measurements with plant compartments (e.g. roots, leaves, shoots) which grow in association with the seepage water will be carried out in future investigations. U(VI) components could be extracted from the plant compartments by centrifugation as cell sap, or as solid milled plant compartment sample and subsequently studied by TRLFS. Information in preparation of the plant compartments for TRLFS analyses has been reported in Günther A. et al. (2003) and were further refined. As suggested by Carrière M. et al. (2005) reactivity and toxicity of uranium depend on the speciation of heavy metals and accordingly have to be considered as important possible risk factor as uranium may enter economic plants and eventually arrives in the food chain.

Baumann N. et al. Environ. Sci. Technol. 42 8266-8269 (2008)
Bernhard G. et al. Radiochim. Acta 74 87-91(1996)
Günther A. et al. Radiochim. Acta 91 319-328 (2003)
Carrière M. et al. Nucl. Instrum. Methods Phys. Res. Sect. B-Beam Interact. Mater. Atoms 231, 268-273 (2005)
  • Lecture (Conference)
    8th Symposium on remediation in Jena “Jenaer Sanierungskolloquium”: Geo-bio-processes at geochemical barriers, 28.-29.09.2009, Jena, Deutschland

Publ.-Id: 13131 - Permalink

On the coupled solution of a combined population balance model using the least-squares spectral element method
Zhu, Z.; Dorao, C. A.; Lucas, D.; Jakobsen, H. A.;
In this work, a cross-sectional averaged two-fluid model combined with a population balance model is applied to simulate the flow field and the bubble size distributions in a two-phase bubble column. The Martinez-Bazan breakage kernel and a modified Prince and Blanch coalescence kernel have been chosen to describe bubble breakage and bubble coalescence, respectively. In the present study, we discuss the use of a higherorder spectral element methodsthe least-squares methodsto compute the system of equations in a coupled manner. The least-squares method is highly accurate and has a number of advantages over the conventional numerical methods like the finite difference and finite volume methods. In contrast to the finite volume method, when desinging an overall solution algorithm, this least-squares method ensures that all the continuity equations are satisfied individually and it deals with both the convective and diffusive terms stably and accurately. The novel iterative algorithm solves the flow and the population balance equation in a coupled manner. The model has been validated against experimental data obtained for two-phase flow in a bubble column. The predicted bubble size distribution and other flow quantities are in good agreement with the experimental data.
Keywords: population balance, bubble, coalescence, breakup
  • Industrial & Engineering Chemistry Research 48(2009), 7994-8006

Publ.-Id: 13130 - Permalink

Uranium speciation in biofilms studied by Laser fluorescence techniques
Arnold, T.; Großmann, K.; Baumann, N.;
Biofilms may immobilize toxic heavy metals in the environment and thereby influence their migration behavior. The mechanisms of these processes are currently not understood. This is due to the complexity occurring in such biofilms creating many discrete geochemical microenvironments which may differ from the surrounding bulk solution in their bacterial diversity, their prevailing geochemical parameters, e.g. pH and dissolved oxygen concentration, their presence of organic molecules, e.g. metabolites, and many more. All of them may affect the metal speciation. To obtain such information, which are necessary for performance assessments studies or the development of new cost effective strategies for cleaning waste waters, it is however very important to develop new non-invasive methods applicable to study the interactions of metals within biofilm systems. Laser fluorescence techniques possess some superior features above all a very high sensitivity for fluorescent heavy metals. An approach of combining confocal laser scanning microscopy and laser induced fluorescence spectroscopy to study the interactions of biofilms with uranium is presented and it was found that the coupling of these techniques is a promising tool to study in situ in non-invasive fashion fluorescent heavy metals within biofilm systems. Information on uranium speciation and uranium redox states can be generated.
Keywords: biofilm, uranium, confocal laser scanning microscopy (CLSM), laser-induced fluorescence spectroscopy (LIFS)

Publ.-Id: 13129 - Permalink

Characterization of single ZnO nanorods by conductive atomic force microscopy
Beinik, I.; Kratzer, M.; Wang, L.; Brauer, G.; Anwand, W.; Teichert, C.;
  • Poster
    Joint Annual Meeting of the Austrian Physical Society (ÖPG), 02.-04.09.2009, Innsbruck, Austria

Publ.-Id: 13128 - Permalink

Characterisation of ZnO single crystals – a challenge to positron annihilation spectroscopy
Brauer, G.;
  • Lecture (others)
    Seminar am Institut für Kristallzüchtung Berlin, 17.08.2009, Berlin, Germany
  • Lecture (others)
    Seminar an der Charles University Prague, 02.11.2009, Prague, Czech Republic

Publ.-Id: 13127 - Permalink

Pattern rotation in the anisotropic Kuramoto-Sivashinsky equation
Keller, A.; Nicoli, M.; Cuerno, R.; Facsko, S.; Möller, W.;
The formation of regular nanopatterns during low energy ion sputtering of solid surfaces has become a topic of intense research. This research is mainly motivated by promising applications of nanopatterned surfaces e.g. in thin film growth. On the other hand, these surfaces represent an interesting example of spontaneous pattern formation in non-equilibrium systems exhibiting different features like wavelength coarsening or a transition to spatiotemporal chaos. Different pattern types are observed for different experimental conditions, i.e. wavelike ripple patterns and hexagonally ordered dot arrays under oblique and normal ion incidence, respectively [1].
According to the model of Bradley and Harper (BH) [2], the regular patterns result from the competition between curvature dependent roughening and diffusional smoothing of the surface. Since the local erosion rate is higher in troughs than on crests, the eroded surface is unstable against any periodic perturbances. In the presence of a smoothing mechanism, however, wave vector selection occurs and a periodic pattern with a characteristic spatial frequency is observed. During recent years, several nonlinear extensions of the linear BH model have been proposed with the stochastic Kuramoto-Sivashinsky (KS) equation having played a prominent role [3]. However, although most experimental investigations on ion-induced pattern formation were performed under oblique ion incidence, only few theoretical studies focused on the corresponding anisotropic KS (aKS) equation.
In this work, we have investigated the influence of anisotropy on the morphology evolution in numerical integrations of the aKS equation. For a strong nonlinear anisotropy, a rotation by 90° of the initially formed ripple pattern was observed for intermediate and long integration times. Comparison with analytical predictions indicates that the observed rotated ripple pattern arises from anisotropic renormalization properties of the aKS equation. This result may also offer an explanation for the recent observation of transient structures in high-temperature experiments on Si(111) [4].

[1] W. L. Chan and E. Chason, J. Appl. Phys. 101, 121301 (2007)
[2] R. Bradley and J. Harper, J. Vac. Sci. Technol. A 6, 2390 (1988)
[3] R. Cuerno and A.-L. Barabási, Phys. Rev. Lett. 74, 4746 (1995)
[4] A.-D. Brown, J. Erlebacher, W.-L. Chan, and E. Chason, Phys. Rev. Lett. 95, 056101 (2005)
  • Poster
    Workshop Nanoscale Modification of Surfaces and Thin Films, 30.08.-03.09.2009, Rathen, Germany

Publ.-Id: 13125 - Permalink

The use of Th in HTR: state of the art and implementation in Th/Pu fuel cycles
Mazzini, G.; Bomboni, E.; Cerullo, N.; Fridman, E.; Lomonaco, G.; Shwageraus, E.;
Nowadays nuclear power is the only greenhouse-free source that can contribute appreciably to the solution of the increasing world-wide energy demand problem. The use of Thorium in the nuclear energy production may offer some unique advantages to accomplish this task. Extensive research and development on the thorium fuel cycle has been conducted in many countries around the world. Starting from the current nuclear waste policy as well as from the (V)HTR good capabilities of Pu burning, the EU PUMA project focus on core physics investigations, in order to further demonstrate the potential benefits of using the HTR core as a Pu/MA transmuter. In this paper the following aspects have been analyzed:
– The state of art about the studies focusing on the use of Th in different core concepts
– The use of Th in HTRs, with a particular emphasis on Th-Pu fuel cycles
– An original assessment of Th-Pu fuel cycles in HTR, on the basis, the energy produced totally, per initial Pu and the ratio between discharged and loaded Pu mass
Some aspects related to Thorium exploitation were outlined, with a particular emphasis on its suitability for working in pebble-bed HTR as a fertile element in a Th-Pu fuel cycle, that is a promising kind of fuel considered in the framework of the EU PUMA project. Particularly, the influence of the Th/Pu weight fraction at BOC in a typical HTR pebble was analyzed as far as the reactivity trend vs. burn-up, the energy produced per Pu unit mass, and the Pu isotopic composition at EOC are concerned. The obtained results suggest us that there is not a best composition for the PBMR Pu/Th fuel. However deeper investigations need to be performed in order to draw final conclusions. Thus, at the moment it is possible to state that some optimized Th percentage in the initial Pu/Th fuel could be suggested on the basis of the aim we are trying to reach.
  • Open Access LogoScience and Technology of Nuclear Installations 2009(2009), 749736


Publ.-Id: 13124 - Permalink

Preliminary evaluation of a nuclear scenario involving innovative gas cooled reactors
Vezzoni, B.; Cerullo, N.; Forasassi, G.; Fridman, E.; Lomonaco, G.; Romanello, V.; Shwageraus, E.;
In order to guarantee a sustainable supply of future energy demand without compromising the environment integrity, some actions for a substantial reduction of CO2 emissions are nowadays deeply analyzed. One of them is the improvement of the nuclear energy use. In this framework, innovative gas-cooled reactors, both the thermal and the fast solutions, seem to be very attractive for the electricity production point of view and for the potential industrial use along the high temperature processes (e.g. H2 production by steam reforming or I-S process). This work focuses on a preliminary (and conservative) evaluation of possible advantages that a symbiotic cycle (EPR-PBMR-GCFR) could entail, with special regard to the reduction of the HLW inventory and the optimization of the exploitation of the fuel resources. The comparison between the symbiotic cycle chosen and the reference one (once-through scenario – EPR-SNF directly disposed) shows a reduction of the time needed to reach a fixed reference level from ~170000 years to ~1550 years, time comparable with typical human times and for this reason more acceptable by the public opinion. In addition, this cycle enable to have a more efficient use of resources involved, obtaining that the total electric energy produced becomes equal to 630.54 TWh/year (instead of only 529.62 TWh/year, case of only EPR) without consuming additional raw materials.
  • Open Access LogoScience and Technology of Nuclear Installations 2009(2009), 940286

Publ.-Id: 13123 - Permalink

Interactions of Sulfolobus acidocaldarius with uranium
Reitz, T.; Merroun, M. L.; Rossberg, A.; Selenska-Pobell, S.;
Interactions of the acidothermophilic archaeon Sulfolobus acidocaldarius DSM 639 with U(VI) were studied by using a combination of wet chemistry, X-ray absorption spectroscopy (XAS), and time-resolved laser-induced fluorescence spectroscopy (TRLFS). We demonstrated that at pH 2 this archaeal strain possesses a low tolerance to U(VI) and that its growth is limited to a uranium concentration below 1.1 mM. At similarly high acidic conditions (pH 1.5 and 3.0), covering the physiological pH growth optimum of S. acidocaldarius, at which U(VI) is soluble and highly toxic, rapid accumulation of the radionuclide by the cells of the strain occurred. About half of the uranium bind-ing capacity was reached by the strain after an incubation of five minutes and nearly total saturation of the binding sites was achieved after 30 minutes. Both, EXAFS- and TRLF-spectroscopic analyses showed that the accumulated U(VI) was complexed mainly through organic phosphate groups. The EXAFS measurements revealed that U(VI) is coordinated to the organic phosphate ligands of the archaeal cells in a monodentate binding mode with an average U-P bond distance of 3.60 ± 0.02 Å.
Keywords: Uranium, Archaea, Tolerance, Biosorption, EXAFS, TRLFS
  • Radiochimica Acta 98(2010), 249-257

Publ.-Id: 13119 - Permalink

System Solution for In-Beam Positron Emission Tomography Monitoring of Radiation Therapy
Shakirin, G.;
In-beam Positron Emission Tomography (PET) is a system for monitoring high precision radiation therapy which is in the most cases applied to the tumors near organs at risk. High quality and fast availability of in-beam PET images are, therefore, extremely important for successful verification of the dose delivery. Two main problems make an in-beam PET monitoring a challenging task. Firstly, in-beam PET measurements result in a very low counting statistics. Secondly, an integration of the PET scanner into the treatment facility requires significant reduction of the sensitive surface of the scanner and leads to a dual-head form resulting in imaging artifacts. The aim of this work is to bring the imaging process by means of in-beam PET to optimum quality and time scale. The following topics are under consideration:
- analysis of image quality for in-beam PET;
- image reconstruction;
- solutions for building, testing, and integration of a PET monitoring system into the dedicated treatment facility.
Keywords: in-beam PET, radiation therapy
  • Book (Editorship)
    Dresden: TUDPress, 2009
    112 Seiten
    ISBN: 978-3-941298-33-0

Publ.-Id: 13118 - Permalink

In-situ X-ray scattering investigations at ROBL
Baehtz, C.; Jeutter, N.; Grenzer, J.; von Borany, J.;
The beamline BM20 operated by the Forschungszentrum Dresden-Rossendorf is located at ESRF storage ring and divided into two stations for spectroscopy and diffraction in the range of 6 to 30 keV. The core competences of material research station are different in-situ X-ray scattering and diffraction investigations also combined with X-ray spectroscopy using a dual magnetron sputtering deposition chamber. Hereby the syntheses of SiO2/GeOx multilayers to create Ge nanocrystalls with well defined sizes by thermal decomposition afterward or directly by sputtering at elevated temperature were investigated. These are promising materials is in the field of solar cells. On the other side by the use a hemispherical Beryllium dome (optional with electrical resitivity four-point setup) the catalyst formation for the carbon nano tubes synthesis was characterized by in-situ diffraction experiment under controlled reactive atmosphere. By in-situ investigations process were characterized on-line and structural und functional properties are correlated directly with each other, which increase the comprehension of synthesis and processing of functional materials.
Keywords: in-situ, diffraction, carbon nano tubes, magnetron sputtering
  • Poster
    Euromat 2009, 07.-10.09.2009, Glasgow, UK

Publ.-Id: 13117 - Permalink

Comparison of PET Concepts for Dose Delivery Monitoring of Particle Therapy
Kunath, D.; Braess, H.; Fiedler, F.; Laube, K.; Parodi, K.; Priegnitz, M.; Shakirin, G.; Enghardt, W.;
Tumor therapy using particle beams is highly precise and requires methods for monitoring of dose delivery. Solutions based on positron emission tomography (PET) are successfully implemented for the radiation therapy with carbon ions and protons at the Gesellschaft für Schwerionenforschung, Darmstadt, Germany, at the Heavy Ion Medical Accelerator at Chiba, Japan, at the Massachusetts General Hospital, Boston, USA, at the Hyogo Ion Beam Medical Center, Japan as well as at the National Cancer Center Kashiwa, Japan. Furthermore, the PET monitoring technique has been tested experimentally for 3He, 7Li, and 16O. The main requirements for the PET monitoring are (1) to produce images containing relevant information for the evaluation of dose delivery and (2) to reduce the additional time required for imaging as much as possible. There are three technical realizations: (1) In-beam PET (measurement during the irradiation), (2) In-room PET (measurement immediately after the irradiation of each portal using a PET scanner placed in the therapy room), (3) Off-line PET (measurement after the complete irradiation by means of a PET scanner located in a different room). These three concepts have been evaluated concerning workflow, counting statistics, and imaging. The treatment workflow is mostly affected by off-line PET. In the case of in-room and off-line PET, the counting statistics is approximately one half of that for in-beam PET if reasonable measuring times (<= 15 min) are assumed. Furthermore, there is an information loss using off-line PET. Thus, in-beam and in-room PET are the most feasible concepts to integrate PET into the particle therapy for dose monitoring.
Keywords: Positron emission tomography, dose monitoring, particle therapy
  • Contribution to proceedings
    Medical Physics and Biomedical Engineering World Congress, 07.-12.09.2009, München, Deutschland, Berlin Heidelberg New York: Springer, 978-3-642-03897-6
  • Lecture (Conference)
    Medical Physics and Biomedical Engineering World Congress, 07.-12.09.2009, München, Deutschland

Publ.-Id: 13116 - Permalink

Simulation des Boreinspeisesystems und seiner Reaktivitätswirksamkeit in einem Siedewasserreaktor (SWR)
Laczkó, G.;
Der vorliegende Bericht befasst sich mit der Modellierung des Vergiftungssystems TW und der Simulation von auslegungsüberschreitenden Störfalltransienten, in denen eine Boreinspeisung erfolgt. Die Modellierung des Vergiftungssystems beinhaltet die Simulation des Transports und der Reaktivitätswirksamkeit des Bors während einer beliebigen Transiente. Das Modell berücksichtigt den Verlust des Boranteils, der in die Dampfphase übergeht (Dampfflüchtigkeit des Bors) und damit im Hinblick auf den Neutronenhaushalt verloren geht. Um die Dampfflüchtigkeit des Bors quantitativ zu berücksichtigen, wurden die aktuellen Messdaten der TU Dresden herangezogen. Diese Arbeit wurde im Rahmen eines gemeinsamen Förderprogramms zwischen dem Forschungszentrum Dresden-Rossendorf (FZD) und der Vattenfall Europe Nuclear Energy (VENE) durchgeführt.
  • Article, self-published (no contribution to HZDR-Annual report)
    Forschungszentrum Rossendorf 2009
    112 Seiten

Publ.-Id: 13115 - Permalink

Efficient THz sideband generation in GaAs/AlGaAs multi quantum wells
Wagner, M.; Schneider, H.; Winnerl, S.; Helm, M.; Roch, T.; Andrews, A. M.; Schartner, S.; Strasser, G.;
We have investigated the third-order nonlinear mixing process between a near-infrared laser and a free-electron laser in an undoped symmetric GaAs/AlGaAs multi quantum well. AC THz electric fields which couple strongly with intraband excitations in semiconductors can lead to spectral sidebands of simultaneous interband excitation. In this nonlinear mixing process a near-infrared (NIR) laser beam is mixed with the THz beam to generate sidebands around the NIR frequency with a frequency spacing equal to the THz frequency or multiples of it: ω = ω_NIR ± n × ω_THz (with integer n). We have investigated the third-order nonlinear mixing process between a near-infrared laser and a free-electron laser (FEL) in an undoped symmetric GaAs/AlGaAs multi quantum well. The sample is studied in transmission under illumination by FELBE, the free-electron laser (FEL) of the Forschungszentrum Dresden-Rossendorf. We use the tunability of the FEL to study the dependence of the mixing efficiency on THz wavelength. We find resonances related to heavy- to light-hole transitions, but also to the heavy-hole intra-exciton 1s-2p transition. It turns out that the conversion efficiency of the n=+2 sideband is largest (up to 0.1 %) for the 1s-2p intra-exciton transition, which is comparable to values previously reported for n=+1.
Keywords: THz sidebands, nonlinear mixing, intraexcitonic transition
  • Poster
    EDISON16, 24.-28.08.2009, Montpellier, Frankreich

Publ.-Id: 13112 - Permalink

On the spectrum of the magnetohydrodynamic mean field α2-dynamo operator
Günther, U.; Langer, H.; Tretter, C.;
The existence of magnetohydrodynamic mean-field α2-dynamos with spherically symmetric, isotropic helical turbulence function α is related to a non-self-adjoint spectral problem for a coupled system of two singular second oder ordinary differential equations. We establish global estimates for the eigenvalues of this system in terms of the profile α and its derivative α'. They allow us to formulate an anti-dynamo theorem and a non-oscillation theorem. The conditions of these theorems, which again involve α and α', must be violated in order to reach overcritical and oscillatory regimes, respectively.
Keywords: magnetohydrodynamics, MHD, alpha-dynamo, anti-dynamo theorem, oscillation, polarity reversal, field reversal, oscillating dynamo, operator theory, non-self-adjoint operator, resolvent estimates

Publ.-Id: 13111 - Permalink

Fano profile in the intersubband THz response of photoexcited GaAs/AlGaAs quantum wells
Wagner, M.; Golde, D.; Stehr, D.; Schneider, H.; Helm, M.; Andrews, A. M.; Roch, T.; Strasser, G.; Kira, M.; Koch, S. W.;
In our work we probe the conduction intersubband transition of an undoped GaAs/Al0.34Ga0.66As multiple quantum well via broadband terahertz pulses after resonant photoexcitation at the 1s heavy-hole exciton. The pump-induced change in the transmitted terahertz field shows a strong beating. In the frequency domain this results in an asymmetric Fano-like line shape for the intersubband resonance and an additional broad low-frequency peak. However, the total THz absorption shows only the single symmetric peak of the intersubband transition. In our microscopic theory these signatures unambiguously originate from the phase sensitive superposition of ponderomotive and terahertz intersubband currents.
Keywords: Fano profile, THz probe, intersubband transition
  • Lecture (Conference)
    EDISON16, 24.-28.08.2009, Montpellier, Frankreich
  • Open Access LogoJournal of Physics: Conference Series 193(2009), 012073
    DOI: 10.1088/1742-6596/193/1/012073

Publ.-Id: 13110 - Permalink

Absorptions- und Emissionsspektroskopische Messungen an Chlorophyll und entsprechenden Derivaten
Jentsch, A.;
Ziel dieser Arbeit ist es, die Wechselwirkung von Chlorophyll a mit Uranylionen zu untersuchen. Es wurde eine methanolische Chlorophylllösung mittels Absorptionsspektroskopie charakterisiert. Das Absorptionsmaxima befindet sich bei 665,1 nm. Anschließend wurde das Zentralatom aus dem Komplex entfernt. Das Absorptionsmaximum der erhaltenen Pheophytinlösung liegt bei 653,1 nm. Nach Zugabe von Uranylnitrat war eine bathochrome Verschiebung des Peakmaxima nach 691,3 nm zu beobachten. Die aufgenommenen Emissionsspektren deuten ebenfalls darauf hin, dass der Uranylchlorophyll-Komplex synthetisiert werden konnte. Bei ausreichendem Überschuss an Uranylionen wird das Magnesium im Chla-Molekül durch UO22+ ersetzt.
Anhand der Absorptionspektren wurde versucht, die Assoziationskonstante K für die Bildung des U-Chla-Komplexes aus Pheophytin a zu ermitteln. Man erhält log K = 4,70 ± 0,35.
Keywords: chlorophyll, pheophytin
  • Other report
    TU Dresden: Bachelorarbeit (Studiengang Chemie), 2009
    40 Seiten

Publ.-Id: 13109 - Permalink

Laser Cooling at ESR, CSR and FAIR
Bussmann, M.; Schramm, U.; Dimopoulou, C.; Kozhuharov, C.; Kuehl, T.; Noertershaeuser, W.; Steck, M.; Stoehlker, T.; Winters, D.; Ma, X.; Wen, W.; Zhang, D.; Geppert, C.; Novotny, C.; Birkl, G.; Walther, T.;
Laser cooling of ion beams is a promising technique to achieve ultracold ion beams of unprecedented brilliance in storage rings. Recent experiments at the ESR/GSI have shown that laser cooling at relativistic beam energies is feasible, opening the route towards laser cooling at future storage rings such as SIS300/FAIR. In this talk we present recent results on laser cooling of C3+ ion beams at the ESR. The results presented show that with laser-cooling space-charge dominated ion beams are observed with at least one order of magnitude smaller momentum spread than attained with electron cooling. This allows to reach the regime of strong coupling, which is a prerequisite for beam crystallization. Based on these results we present new experiments planned at ESR and CSR which will take full advantage of all-optical beam diagnostics that will allow to overcome the limited resolution of standard ion beam diagnostics. In combination with all-optical cooling schemes which do not rely on initial electron cooling of the ion beam, laser cooling is one of the most promising candidates for cooling ion beams at ultra-relativistic energies accessible at the future FAIR facility.
Keywords: laser cooling, relativistic ion beam, esr, csr, fair, optical diagnostics, pulsed laser, schottky pickup, momentum spread, strongly coupled plasma, crystalline ion beam
  • Invited lecture (Conferences)
    International workshop on beam cooling and related topics, COOL'09, 31.08.-04.09.2009, Lanzhou, China

Publ.-Id: 13108 - Permalink

Radiosynthesis of New [90Y]-DOTA-Based Maleimide Reagents Suitable for the Prelabeling of Thiol-Bearing L-Oligonucleotides and Peptides
Schlesinger, J.; Fischer, C.; Közle, I.; Vonhoff, S.; Klussmann, S.; Bergmann, R.; Pietzsch, H.-J.; Steinbach, J.;
We describe the radiosynthesis of two new [90Y]-DOTA-based maleimide reagents, suitable for the mild radiolabeling of L-RNAs and peptides modified with thiol-bearing linkers. The synthesis procedure of both maleimide-bearing 90Y complexes, [{(2S)-2-[4-(2,5-dioxo-2,5-dihydro-1H-pyrrol-1-yl)benzyl]-1,4,7,10-tetraazacyclododecane-1,4,7,10-tetrayl}tetraacetato][90Y]yttrate(1-)([90Y]3) and [{(2S)-2-(4-{[4-(2,5-dioxo-2,5-dihydro-1H-pyrrol-1-yl)butanoyl]amino}benzyl)-1,4,7,10-tetraaza-cyclododecane-1,4,7,10-tetrayl]tetraacetato}[90Y]yttrate(1-)([90Y]4), was optimized in terms of an easy purification method via solid-phase extraction (SPE). Application as well as reactivity of both maleimide reagents were initially evaluated by the prelabeling of glutathione (GSH) and a thiol-modified 12mer L-RNA as model substances. In comparison to the N-aryl maleimide-bearing complex [90Y]3, N-alkyl maleimide-bearing complex [90Y]4 showed an increased hydrolytic stability at pH g 7. A slightly higher reactivity was found for [90Y]3 by prelabeling of 0.1 and 1 μg glutathione, respectively, in phosphate buffer (pH 7.2) at room temperature. In terms of very high radiochemical yields, the direct radiolabeling of DOTA-L-RNA conjugate with [90Y]YCl3 proved to be more suitable than the prelabeling of the thiol-modified 12mer L-RNA derivative with [90Y]4.

Publ.-Id: 13107 - Permalink

Radiopharmaceutical basic principles of 18F-DOPA in nuclear medicine
Füchtner, F.;
kein Abstract verfügbar
  • Invited lecture (Conferences)
    International Congress congenital hyperinsulinism and pancreatic tumors in childhood, 16.-18.09.2009, Greifswald, D

Publ.-Id: 13106 - Permalink

Synthesis if new [Y-90]-DOTA based Meleimides for the prelabeling of thiol-bearing L-oligonucleotides and peptides
Pietzsch, H.-J.; Schlesinger, J.; Fischer, C.; Közle, I.; Vonhoff, S.; Klussmann, S.; Bergmann, R.; Steinbach, J.;
Objectives: A common chelator for radioisotopes of Y and the lanthanides is DOTA. However, the elevated temperatures necessary to achieve sufficient radiochemical yields may be a drawback, especially for the radiolabeling of thermally sensitive molecules such as DOTA-modified antibodies. A promising alternative to the “direct” radiolabeling of DOTA conjugates (“postlabeling”) is the use of so-called “prelabeling” agents. Here, we present the synthesis of two novel [90Y]-DOTA-based maleimide reagents, [90Y]2 and [90Y]3, suitable for the mild radiolabeling of thiol-bearing peptides or thiol-modified L-RNAs. Application and reactivity of both maleimide reagents were evaluated by the labeling of glutathione (GSH) and a thiol-modified 12mer L-RNA as model substances.
Methods: L‑RNA [sequence: 5’‑(1-hydroxy-7,8-dithia-tetradecyl) UGACUGACUGAC‑3’, MW 4124] was synthesized at NOXXON Pharma AG (Germany). (S)‑p‑NH2‑Bn‑DOTA was purchased from Macrocyclics (USA). 90Y was purchased as [90Y]YCl3 from QSA Global GmbH (Germany). Measurements of 90Y were done in the 90Y channel of a dose calibrator ISOMED 2000 (Nuklear-Medizintechnik Dresden, Germany) by measuring the bremsstrahlung. The compounds were characterized by HPLC, gel electrophoresis and mass spectrometry.
Results: A straightforward method to synthesize [90Y]‑MAD [90Y]2 and [90Y]‑MABD [90Y]3 is to initially complex [90Y]Y3+ with (S)‑p‑NH2‑Bn‑DOTA and to subsequently transform the purified complex [90Y((S)‑p‑NH2‑Bn‑DOTA)]- into the corresponding maleimides by using activating agents. The scheme illustrates the subsequent preparation of [90Y]‑MAD‑GSH and [90Y]‑MABD‑GSH and the 90Y-labeling of an L‑RNA via the pre- and postlabeling approach. In comparison to the N‑aryl maleimide [90Y]‑MAD, N‑alkyl maleimide [90Y]-MABD showed an increased hydrolytic stability at pH ≥ 7. A slightly higher reactivity was found for [90Y]‑MAD by prelabeling of 0.1 and 1 μg glutathione, respectively in phosphate buffer (pH 7.2) at room temperature. In terms of high radiochemical yields, the direct radiolabeling of DOTA-L-RNA with [90Y]YCl3 proved to be more suitable than the prelabeling of the thiol-modified 12mer L-RNA derivative with [90Y]‑MABD.
Conclusions: We could demonstrate the applicability of maleimide reagents [90Y]‑MAD and [90Y]-MABD for the prelabeling approach. Both reagents showed a high potential for that purpose. Concerning high radiochemical yields, the direct labeling of DOTA‑l‑RNA with [90Y]YCl3 proved to be more efficient than the prelabeling of the thiol-modified 12mer l‑RNA with [90Y]‑MABD at low activity levels. With regard to 90Y‑labeling of thermally sensitive molecules prelabeling could have more advantages than the direct radiolabeling, due to the milder labeling conditions.
  • Poster
    18th International Symposium on Radiopharmaceutical Sciences, 12.-17.07.2009, Edmonton, Canada
  • Abstract in refereed journal
    Journal of Labelled Compounds and Radiopharmaceuticals 52(2009)Suppl 1, S491

Publ.-Id: 13105 - Permalink

Imaging of the cell cycle: Synthesis and radiopharmacological evaluation of 124I-labeled CDK4 inhibitors
Köhler, L.; Graf, F.; Bergmann, R.; Steinbach, J.; Pietzsch, J.; Wüst, F.;
Objectives: Tumor cells are characterized by their loss of growth control resulting from alterations in regulating pathways of the cell cycle, e.g., a deregulated cyclin dependent kinase (Cdk) activity and/or expression. In 80% of tumors the cell cycle relevant Cdk4-cyclin D1/retinoblastoma (pRb) cascade is altered. Hence, appropriately radiolabeled Cdk4 inhibitors are discussed as promising molecular probes for imaging cell proliferation processes and tumor visualization by PET. This work describes the synthesis and radiopharmacological evaluation of two 124I-labeled Cdk4 inhibitors as potential radiotracers for imaging of Cdk4 in vivo.
Methods: Reference substances and labeling precursors 1 and 2 were prepared with minor modifications according to literature procedures. Radioiodination was performed through regioselective destannylation reaction under mild conditions using [124I]NaI and Iodogen® as the oxidizing agents (Fig. 1). 124I-labeled radiotracers [124I]CKIA and [124I]CKIB were used in cell uptake studies. Biodistribution and small animal PET studies were carried out.
Results: Treatment of a solution containing labeling precursors 1 or 2 (5 mg/ml) with [124I]NaI (29.0 to 275.0 MBq) in Iodogen® precoated tubes gave radiolabeled Cdk4 inhibitors [124I]CKIA and [124I]CKIB in radiochemical yields of up to 35% after removal of Boc protecting group and final HPLC purification. Both compounds were isolated in high radiochemical purity exceeding 95%. The specific radioactivity (As) was 25-35 GBq/μmol at the end of synthesis. The lipophilicity (logP) was determined to be 2.77±0.13 for [124I]CKIA and 1.99±0.03 for [124I]CKIB, respectively. Both compounds remained stable in buffer (PBS, pH 7.4) and ethanol after 24 h at 37°C. In vitro radiotracer uptake studies in human tumor cells using [124I]CKIA showed substantial uptake in adenocarcinoma HT-29 (1264±84 %ID/mg protein) and squamous cell carcinoma FaDu cells (1429±229 %ID/mg protein) after 2 h at 37°C (As:25 GBq/μmol). A significantly lower uptake was detected at 4°C (HT-29: 383±38 %ID/mg protein, FaDu: 437±25 %ID/mg protein). Biodistribution studies of [124I]CKIA and [124I]CKIB showed rapid blood clearance in rats. [124I]CKIA and [124I]CKIB were mainly accumulated and metabolized by liver. Both radiotracers were administered intravenously to mouse FaDu xenograft tumor model and imaging studies were performed on a small-animal PET scanner confirming a high radioactivity concentration in the liver and intestine for both compounds. No radioactivity was found in the brain. PET showed only little uptake of both radiotracers in the tumor.
Conclusions: The radiosynthesis of two 124I-labeled Cdk4 inhibitors has been developed. Both radiotracers were obtained in reproducible radiochemical yields and purity enabling detailed radiopharmacological characterization. Small-animal PET and autoradiography studies showed only low tumor uptake. Further studies are needed to search for more suitable derivatives of these substances as radiotracers for imaging Cdk4 by means of PET.
  • Poster
    18th International Symposium on Radiopharmaceutical Sciences, 12.-17.07.2009, Edmonton, Canada
  • Abstract in refereed journal
    Journal of Labelled Compounds and Radiopharmaceuticals 52(2009)Suppl 1, S406

Publ.-Id: 13104 - Permalink

Pre-clean-up of reaction mixtures in radiopharmaceutical manufacturing by on-line solid phase extraction using HPLC
Füchtner, F.; Mäding, P.; Preusche, S.; Zessin, J.; Steinbach, J.;
Objectives: Radiopharmaceuticals are usually synthesised by reaction of simple radiolabeled compounds with a non-radioactive precursor. Afterwards the labeled precursor compound undergoes frequently a deprotection reaction. The resulting reaction mixture is often quite complex and needs HPLC purification to isolate the labeled target compound in high chemical and radiochemical purity. In some cases the composition of the reaction mixture is such complex, that an off-line solid phase extraction (SPE) step is carried out before HPLC purification to separate matrix components and/or interfering solvents. This SPE prepurification of the reaction mixture is difficult to automate and needs special hardware and solvents for rinsing and eluting the SPE cartridge. Additionally, remote controlled synthesis modules become more complex.The general aim of the present work is to develop a process, which allows the pre-cleaning of reaction mixtures from disturbing matrix components by online SPE using HPLC. In detail it results from the need to improve the radiochemical purity of [18F]FDOPA and to reduce the solvent content of dimethylformamide (DMF) during manufacturing of the serotonin transporter radioligand [18F]FMeMcN 5652.
The figure shows the scheme of the HPLC hardware, whereas a pre- or guard-column is used as pre-clean-up-column (X) instead of an injection loop. The selectivity of the packing material of both columns (III & X) can be selected in accordance with the separation requirements.The process includes following steps:1. Injection valve (I) in “load position”, The reaction mixture is transferred from the reaction vessel (IX) onto the pre-clean-up-column. The diameter of the packing material of the pre-clean-up-column is in the range, which allows the feeding by gas overpressure. The disturbing matrix components are passed to waste and the target compound is retained.2. The rinsing liquid is filled into the reaction vessel and rinse out the dead volume of the pre-clean-up-column. The target compound is cleaned-up and concentrated.3. Injection valve in “inject position”, The target compound is back flushed out of the pre-clean-up-column onto the separation column (III) by the HPLC mobile phase. The finely purification takes place on the separation column. The eluate is fractionated and the target compound is collected in the common way.For the purification of [18F]FDOPA from the critical radiochemical impurity [18F]fluoride a pre-clean-up-column filled with polymer-based reversed phase (RP) material is used. The finely separation was performed on a silica-based RP column.In case of [18F]FMeMcN 5652 production the clean-up from the solvent, needed for the radiolabeling, and the finely separation is carried out on columns filled with silica-based RP materials.
HPLC purification method
...........................................................................[18F]Fluoride [%].....................DMF [mg/ml]
Injection loop.........................................................7.7 (n=93)..............................1.4 (n=5)
Pre-clean-up-column............................................1.4 (n=25)..............................< 0.001 (n=4)

Conclusions: Using the interlinked on-line SPE / HPLC system, reaction mixtures of radiopharmaceutical synthesis can be cleaned up and disturbing matrix components can be separated from the target compound more efficiently.
  • Poster
    18th International Symposium on Radiopharmaceutical Sciences, 12.-17.07.2009, Edmonton, Canada
  • Abstract in refereed journal
    Journal of Labelled Compounds and Radiopharmaceuticals 52(2009)Suppl 1, S306

Publ.-Id: 13103 - Permalink

Direct labeling of peptides with [18F]FDG
Hultsch, C.; Bergmann, R.; Berndt, M.; Wüst, F.;
Objectives: The routine 18F labeling of biomacromolecules like peptides and proteins mainly exploits the use of bifunctional labeling precursors, also referred to as prosthetic groups. 2-[18F]Fluoro-2-deoxy-D-glucose ([18F]FDG) is the most important clinical PET radiotracer, but only very few examples using readily available [18F]FDG as a building block for the radiosynthesis of 18F-labeled compounds. The present study describes the use of [18F]FDG as a 18F building block for the direct labeling of various aminooxy-functionalized peptides via chemoselective oxime formation. The potential of this novel peptide labeling reaction was expemplified by means of various neurotensin NT(8-13) derivatives.
Methods: The labeling reaction was performed using a 0.9% NaCl solution of [18F]FDG and aminooxy-functionalized peptide at different concentrations in a mixture of MeOH/H2O at 80 °C for 30 min. The reaction mixture was analyzed by radio-HPLC to determine the radiochemical yield of the conjugation reaction (Fig. 1).
Results: Direct labeling of aminooxy-functionalized peptides with [18F]FDG was strongly dependent on the amount of used peptide. Monomeric NT(8-13) derivative gave best radiochemical yields of up to 80% based upon [18F]FDG. More complex dimeric and tetrameric neurotensin derivatives gave lower radiochemical yields at comparable peptide concentrations. Increase of [18F]FDG activity also lowered radiochemical yield due to an increasing competitive reaction with glucose originating from the [18F]FDG solution. Depending on the size of the used peptide, separation of [18F]FDG-labeled peptide from glucose-labeled peptide is possible by semi-preparative HPLC. The formation of isomers during the aminooxy-aldehyde conjugation reaction between [18F]FDG and aminooxy-functionalized peptides in aqueous media leads to the formation of isomers according to literature reports.
Conclusions: For the first time, readily available PET radiotracer [18F]FDG was shown to be a suitable prosthetic group for direct labeling of aminooxy-functionalized peptides with fluorine-18 under mild conditions. The reaction is especially suitable for small peptides. However, application of larger peptides seems to be limited by increasing separation difficulties of the corresponding glucose-peptide conjugate.
  • Poster
    18th International Symposium on Radiopharmaceutical Sciences, 12.-17.07.2009, Edmonton, Canada
  • Abstract in refereed journal
    Journal of Labelled Compounds and Radiopharmaceuticals 52(2009)Suppl 1, S145

Publ.-Id: 13102 - Permalink

Fluorine-18 Labeling of Phosphorpeptides: A convenient Approach for the Evaluation of Phosphorpeptide Metabolism in vivo
Richter, S.; Bergmann, R.; Steinbach, J.; Pietzsch, J.; Wüst, F.;
Objectives: Phosphopeptides are very useful reagents to study signal transduction pathways related with cellular protein phosphorylation/dephosphorylation. Phosphopeptides also have been identified as important drug candidates to both inhibit and stimulate intracellular signaling mechanisms through targeting phosphotyrosine, phosphoserine or phosphothreonine residue-binding protein domains. In this work we describe a convenient method for the mild and sufficient radiolabeling of phosphopeptides with the short-lived positron emitter fluorine-18 to allow radiopharmacological studies on phosphopeptide metabolism in vivo by means of positron emission tomography (PET).
Methods: Peptide syntheses were performed on peptide synthesizer (Syro I, MultiSynTech, Germany) using standard Fmoc chemistry. Radiolabeling was accomplished via conjugation of the N-terminus of Polo-box domain (PBD)-binding phosphopeptide H-Met-Gln-Ser-pThr-Pro-Leu-OH 1 and its unphosphorylated analog 2 with the bifunctional labeling agent N-succinimidyl-p-[18F]fluorobenzoate ([18F]SFB) (Fig. 1).
The radiolabeled phosphopeptide [18F]FB-Met-Gln-Ser-pThr-Pro-Leu-OH [18F]-1 and its unphosphorylated analog [18F]FB-Met-Gln-Ser-Thr-Pro-Leu-OH [18F]-2 were subjected to radiopharmacological evaluation involving investigation of metabolic stability in vitro and in vivo, cell uptake studies in human adenocarcinoma (HT-29) and squamous cell carcinoma (FaDu) cell lines, and small-animal PET studies in Wistar rats and NMRI nu/nu HT-29 tumor-bearing mice.
Results: Radiolabeling was achieved via 18F-fluorobenzoylation using the Bolton-Hunter-type reagent N-succinimidyl-p-[18F]fluorobenzoate ([18F]SFB). The optimized radiosynthesis was conducted in a 0.05 M Na2HPO4 buffer solution (pH 9.0) at 40°C within 30 min using low amounts of peptide precursor (0.5 mg) to afford reproducible radiochemical yields (25-29%) and high radiochemical purity (>98%) within 95-109 min including HPLC purification. Cell uptake studies in HT-29 and FaDu tumor cells revealed only very little radiotracer uptake (less than 0.6% ID/mg protein). Radiolabeled phosphopeptide [18F]-1 showed remarkable high metabolic stability in vivo (65% intact peptide after 20 min) compared to the corresponding unphosphorylated peptide [18F]-2 (<5% intact peptide after 20 min). A detailed discussion on the radiopharmacological profile in vitro and in vivo of peptides [18F]-1 and [18F]-2 will be presented.
Conclusions: We developed a reproducible synthesis for 18F-labeled phosphopeptides, and the presented method is a promising approach for studying phosphopeptide metabolism and kinetics in vivo. Furthermore, cell penetrating peptides (CPP) are currently under investigation as potential mediators to enhance cell uptake of the desired 18F-labeled phosphopeptides.
  • Poster
    18th International Symposium on Radiopharmaceutical Sciences, 12.-17.07.2009, Edmonton, Canada
  • Abstract in refereed journal
    Journal of Labelled Compounds and Radiopharmaceuticals 52(2009)Suppl 1, S144

Publ.-Id: 13101 - Permalink

Radiofluorination via Staudinger Ligation
Mamat, C.; Pretze, M.; Steinbach, J.; Wüst, F.;
Objectives: The chemical labeling of biomolecules continues to be an important tool for the study of the cellular fate.[1] In particular the introduction of 18F into higher molecular weight compounds like peptides, proteins, oligonucleotides or antibodies represents a special challenge. Usually they can not be labelled with 18F at high specific activity directly due to the rough reaction conditions. To circumvent this problem prostetic groups were used for 18F labeling of peptides and proteins. Therefore 18F labeled small organic molecules were synthesised capable of being linked to peptides, proteins or antibodies under mild conditions. Only a handful of reactions are known for the selective introduction of these labeling agents.
Methods: Although several bioconjugation techniques are available for preparation of bioconjugates substituted with a limited number of functional groups, truly chemoselective ligation reactions are rather limited. Most ligation reactions rely on the reaction of an electrophile with a nucleophile. As biological systems are rich in diverse electrophilic and nucleophilic sites, only a few functional groups are available that exhibit orthogonal reactivity to the functional groups present. Bioorthogonal reactions like the [3+2] Huisgen cycloaddition[3] were applicated for the selective radiolabeling[4] of biomolecules. The Staudinger Ligation introduced by Saxon and Bertozzi[5] exploits the smooth reaction between an azide and a phosphane to form an amide bridge between the labeling agent and the respective biomolecule.
Results: Substituted phosphanes were used as synthons for the Staudinger Ligation. The preparation of these compounds succeeds via Pd-catalyzed P-C cross coupling of iodophenyl benzoates with HPPh2. No extensive protection group chemistry is needed for this coupling reaction.[2] The radiofluorination proceeds under standard conditions and the subsequent ligation reaction occurs under mild conditions (20 min, 50 watt microwave) that affords the respective Staudinger products in high yields.
Conclusions: Our first promising results show the potential of this labeling method for the radiofluorination of various organic model compounds and biomolecules. The experimental details will be presented.

References: [1] J. A. Prescher, C. R. Bertozzi, Nature Chem. Biol. 2005, 1, 13-21. [2] C. Mamat, A. Flemming, M. Kckerling, J. Steinbach, F. R. Wuest, Eur. J. Org. Chem. 2009, submitted. [3] C. Mamat, T. Ramenda, F. R. Wuest, Mini-Rev. Org. Chem. 2009, 6, 21-34. [4] T. Ramenda, R. Bergmann, F. Wuest, Lett. Drug Design Disc. 2007, 4, 279-285. [5] K. L. Kiick, E. Saxon, D. A. Tirrell, C. R. Bertozzi, Proc. Natl. Acad. Sci. U.S.A. 2002, 99, 19-24.
  • Poster
    18th International Symposium of Radiopharmaceutical Sciences, 12.-17.07.2009, Edmonton, Canada
  • Abstract in refereed journal
    Journal of Labelled Compounds and Radiopharmaceuticals 52(2009)Suppl 1, S142

Publ.-Id: 13100 - Permalink

Synthesis and Radiopharmacological Evaluation of 18F-labeled Bombesin Analog [18F]BX-00374436 for Imaging of GRP Receptor-Expression Prostate Cancer
Ramenda, T.; Bergmann, R.; Friebe, M.; Borkowski, S.; Srinivasan, A.; Dinkelborg, L.; Pietzsch, J.; Steinbach, J.; Wüst, F.;
Objectives: Over the last two decades, radiolabeled peptides have been widely used as promising radiotracers for tumor targeting. In recent years, bombesin and bombesin analogs have attracted much attention as high affinity and selectivity ligands for the gastrin-releasing peptide (GRP) receptor. The GRP receptor was found to be overexpressed and implicated in a variety of human tumors. Radiolabeled bombesin and bombesin analogs represent an interesting class of diagnostic probes for molecular imaging of GRP receptor-expressing prostate cancer. This work is aimed at the development of an 18F-labeled bombesin analog for molecular imaging GRP receptors in prostate cancer xenografts.
Methods: Aminopentanoic acid-modified bombesin analog BX-06053011 was conjugated with the bifunctional labeling agent N-succinimidyl-4-[18F]fluorobenzoate ([18F]SFB) in borate buffer (pH = 8.2) for 30 min at 50 °C to give the desired 18F-labeled bombesin analog [18F]BX-00374436 (Fig. 1). Tumor-targeting of radiolabeled bombesin analog [18F]BX-00374436 was evaluated in male nude mice bearing human prostate cancer (PC3) by means of biodistribution and dynamic small animal PET studies.
Results: 18F-labeled bombesin analog [18F]BX-00374436 was prepared in 30% radiochemical yield (based upon [18F]SFB) within 80 min including HPLC purification, evaporation of HPLC eluent and formulation in 0.9% saline. The radiochemical purity exceeded 95%, and the specific activity was 20 GBq/μmol. The binding affinity (KD) of fluorobenzoylated bombesin BX-00374436 was determined to be 0.7 nM. Radiotracer [18F]BX-00374436 showed reasonable metabolic stability in mouse blood, being 65% of intact radiolabeled peptide after 60 min. Tumor uptake of [18F]BX-00374436 in PC3 tumor bearing nude mice was 2.75 %ID/g after 5 min p.i., and 2.45 %ID/g after 60 min p.i. The receptor specificity of radiotracer [18F]BX-00374436 could be demonstrated by effective blocking of tumor uptake in the presence of non-radioactive BX-00374436. Dynamic small animal PET imaging confirmed specific radiotracer uptake in the PC3 tumor.
Conclusions: The present study showed that 18F-labeled bombesin analog [18F]BX-00374436 is a suitable radiotracer for molecular imaging of GRP receptor-positive prostate cancer by means of PET.
  • Lecture (Conference)
    18th International Symposium on Radiopharmaceutical Sciences, 12.-17.07.2009, Edmonton, Canada
  • Abstract in refereed journal
    Journal of Labelled Compounds and Radiopharmaceuticals 52(2009)Suppl 1, S29

Publ.-Id: 13099 - Permalink

Labelling of Proteins with Fluorine-18 via Click Chemistry
Ramenda, T.; Knieß, T.; Steinbach, J.; Wüst, F.;
Objectives: The radiolabeling of peptides and proteins with the short-lived positron emitter 18F requires rapid and mild reaction conditions compatible with the structural and functional integrity of these biomolecules. Over the last two years several approaches have been published focusing on the application of copper(I)-mediated 1,3-dipolar [3+2]cycloaddition of azides and alkynes for labeling peptides with 18F. However, to date no 18F labeling of proteins via click chemistry has been reported. In this work we describe for the first time the application of click chemistry for 18F labeling of proteins as exemplified with azide-functionalized human serum albumin (HSA). Click chemistry was accomplished through 4-[18F]fluoro-N-methyl-N-(prop-2-ynyl)benzenesulfonamide (p[18F]F-SA) as novel alkine-containing 18F-labeled click chemistry building block.
Methods: The novel click chemistry building block p[18F]F-SA was prepared in a single step reaction in a remotely controlled synthesis module starting from readily available labeling precursor (Fig. 1).
HSA was modified with azide residues through conjugation of the lysine residues in HSA with an azide-functionalized active ester. Azide-modified HSA was subjected to digest with three different endoproteinases and subsequent MALDI-TOF MS analysis to assess the number of introduced azide residues. Radiolabeling of modified HSA was accomplished with p[18F]F-SA in the presense of Cu(I)Br and the Cu(I) chelating ligand tris[(1-benzyl-1H-1,2,3-triazol-4-yl)methyl]amine (TBTA). Radiolabeled HSA was purified with size-exclusion chromatography and analyzed with SDS-PAGE.
Results: Radiolabeled sulfonamide p[18F]F-SA could be obtained in an automated synthesis unit in radiochemical yields of 21-35% (decay-corrected) within 75 min after HPLC purification. The radiochemical purity was >99%, and the specific activity was in the range of 71-128 GBq/μmol. Sulfonamide p[18F]F-SA showed favorable lipophilicity (logP = 1.6) allowing application in aqueous reaction media. Tryptic digest and subsequent MALDI-TOF MS analysis of modified HSA revealed the introduction of an average of 28 azide residues into HSA. Click chemistry of azide-functionalized HSA (0.5 mg) with CuBr (0.2 mg) and TBTA in phosphate buffer (pH 7.4) gave 31% of 18F-labeled HSA after size-exclusion chromatography.
Conclusions: The convenient radiosynthesis of p[18F]F-SA as a novel 18F-labeled sulfonamide-based click chemistry building block in an automated synthesis unit allows its wide application for a broad range of click chemistry reactions. For the first time, click chemistry could successfully be applied to the 18F labeling of proteins, which further expands the scope of click chemistry as versatile tool for radiolabeling reactions.
  • Lecture (Conference)
    18th International Symposium on Radiopharmaceutical Scieneces, 12.-17.07.2009, Edmonton, Canada
  • Abstract in refereed journal
    Journal of Labelled Compounds and Radiopharmaceuticals 52(2009)Suppl 1, S25

Publ.-Id: 13098 - Permalink

Synthesis of a potential tyrosine kinase inhibitor by knoevenagel condensation of oxindole with 4-[18F]Fluorbenzaldehyde
Knieß, T.; Kuchar, M.; Steinbach, J.; Wüst, F.;
Objectives: Receptor tyrosine kinases (RTKs) play an important role in tumour angiogenesis through their involvement in proliferation, migration and differentiation between tumour and endothelial cells. Recently, small molecule tyrosine kinase inhibitors like Imatinib mesylate (Gleevec®), Gefitinib (Iressa®) and SU11248 (Sutent®) have been radiolabelled to study tumour angiogenesis in vivo1,2,3. The aim of the present work is the development of an sufficient radiosynthesis of 3-(4’-[18F]fluoro-benzylidenyl]-indolin-2-one 2 as derivative of potent RTK inhibitor Semaxinib® based on Knoevenagel condensation of 4-[18F]fluorobenzaldehyde with oxindole.
Methods: Synthesis of 4-[18F]fluorobenzaldehyde was performed by reacting [18F]fluoride with 4-trimethylammoniumbenzaldehyde triflate in an automated synthesis module (Nuclear Interface). Briefly, 15 mg of precursor dissolved in acetonitrile (1 ml) was heated with dried [18F]KF at 90 °C for 10 min. After addition of water (11 ml), 4-[18F]fluorobenzaldehyde was purified via solid-phase extraction on a HLB-plus cartridge (250 mg, Waters). Purified 4-[18F]fluorobenzaldehyde was eluted from the cartridge with ethanol (3 ml) and transferred into a separate reaction vial containing oxindole 1 (10 mg) and a base. Knoevenagel condensation occurred at 90 °C for 20 min (Fig. 1). The radiochemical yield of product 2 was determined by radio-HPLC.

Results: Knoevenagel condensation of oxindole 1 with 4-[18F]fluorobenzaldehyde was optimised by screening the influence of different bases on the radiochemical yield (RCY) of the carbonyl olefination reaction. The results are summarised in Table 1. Knoevenagel condensation strongly depends on the used base. Best results could be obtained by using amine bases piperidine (18% to 29%) or diethylamine (48%). Application of stronger amine bases (DABCO, diisopropyl-ethyl amine) or weaker bases (ammonium acetate, 2,6-di-tert.-butyl pyridine) resulted in lower or no product formation. Phosphazane as a very strong base yielded 26% of desired product 2 along with formation of large amounts of non-identified side products.

Table 1. Knoevenagel condensation between 4-[18F]fluorobenzaldehyde and oxindole

Conclusions: Knoevenagel condensation of 4-[18F]Fluorobenzaldehyde with oxindole is a suitable labelling technique for the synthesis of radiotracer 2. Within a series of different bases, diethylamine provides highest radiochemical yields of up to 48%. The Knoevenagel condensation reaction optimised under the object of radiolabeling involving readily available 4-[18F]Fluorobenzaldehyde should be applicable for the convenient radiosynthesis of other compounds containing a benzylidene motif.

References: [1] Kil KE et al. Nucl Med Biol, 2007, 34, 153. [2] Wang JQ et al. Bioorg Med Chem Lett, 2006, 16, 4102. [3] Wang JQ et al. Bioorg Med Chem Lett, 2005, 15, 4380.
Keywords: 4-[18F]fluorobenzaldehyde, tyrosine kinase inhibitor, Knoevenagel condensation
  • Poster
    18th International Symposium on Radiopharmaceutical Sciences, 12.-17.07.2009, Edmonton, Canada
  • Abstract in refereed journal
    Journal of Labelled Compounds and Radiopharmaceuticals 52(2009)Suppl 1, S.182

Publ.-Id: 13097 - Permalink

MnSi1.7 nanoparticles embedded in Si: Superparamagnetism with collective behavior
Zhou, S.; Shalimov, A.; Potzger, K.; Helm, M.; Fassbender, J.ORC; Schmidt, H.
The doping of Mn in Si is attracting research attentions due to the possibility to fabricate Si-based diluted magnetic semiconductors. However, the low solubility of Mn in Si favors the precipitation of Mn ions even at nonequilibrium growth conditions. MnSi1.7 nanoparticles are the common precipitates, which show exotic magnetic properties in comparison with the MnSi1.7 bulk phase. In this paper we present the static and dynamic magnetic properties of MnSi1.7 nanoparticles. Using the Preisach model, we derive the magnetic parameters, such as the magnetization of individual particles, the distribution of coercive fields and the interparticle interaction field. Time-dependent magnetization measurements reveal aging and memory effects, qualitatively similar to those seen in spin glasses.
Keywords: ageing, coercive force, elemental semiconductors, magnetic anisotropy, magnetic particles

Publ.-Id: 13096 - Permalink

The effects of surface tension on flooding in counter-current two-phase flow in an inclined tube
Deendarlianto; Ousaka, A.; Indarto; Kariyasaki, A.; Lucas, D.; Vierow, K.; Vallee, C.; Hogan, K.;
The purpose of the present study is to investigate the effects of surface tension on flooding phenomena in counter-current two-phase flow in an inclined tube. Previous studies by other researchers have shown that surface tension has a stabilizing effect on the falling liquid film under certain conditions and a destabilizing or unclear trend under other conditions. Experimental results are reported herein for air-water systems in which a surfactant has been added to vary the liquid surface tension without altering other liquid properties. The flooding section is a tube of 16 mm in inner diameter and 1.1 m length, inclined at 30 to 60 degree from horizontal. The flooding mechanisms were observed by using two high-speed video cameras and by measuring the time variation of liquid hold-up along the test tube. The results show that effects of surface tension are significant. The gas velocity needed to induce flooding is lower for a lower surface tension. There was no upward motion of the wave upon flooding occurrence, even for lower a surface tension. Observations on the liquid film behavior after flooding occurred suggest that the entrainment of liquid droplets plays an important role in the upward transport of liquid. Finally, an empirical correlation is proposed that includes functional dependencies on surface tension and tube inclination.
Keywords: Counter-current two-phase flow, Flooding, Inclined tube, Surface tension, Flooding mechanisms


Publ.-Id: 13095 - Permalink

Nanopatterning of Si surfaces by normal incident ion erosion: Influence of iron incorporation on surface morphology evolution
Zhou, J.; Facsko, S.; Lu, M.; Möller, W.;
The surface morphology of Si(100) induced by 1200 eV Ar+ ion bombardment at normal incidence with and without Fe incorporation is presented. The formation of nanodot patterns is observed only when the stationary Fe areal density in the surface is above a threshold value of 8×1014 cm-2 . This result is interpreted in terms of an additional surface instability due to locally nonuniform sputtering in connection with the presence of a Fe rich amorphous phase at the peak of the nanodots. At Fe concentrations below the threshold, smoothing dominates and pattern formation is inhibited. The transition from a k-2 to a k-4 behavior in the asymptotic power spectral density function supports the conclusion that under these conditions ballistic smoothing and ion-enhanced viscous flow are the two dominant mechanisms of surface relaxation.
Keywords: dot patterns, ion sputtering, silicon, metal incorporation

Publ.-Id: 13094 - Permalink

Superconductivity of Mg-B layers prepared by a multi-energy implantation of boron into magnesium and magnesium into boron bulk substrates followed by the furnace and pulsed plasma annealing
Piekoszewski, J.; Kempinski, W.; Barlak, M.; Werner, Z.; Los, S.; Andrzejewski, B.; Stankowski, J.; Piekara-Sady, L.; Skladnik-Sadowska, E.; Szymczyk, W.; Kolitsch, A.; Groetzschel, R.; Starosta, W.; Sartowska, B.;
B ions into Mg and Mg ions into B substrates were implanted in triple mode, i.e. each sample was sequentially implanted at three different energies starting from the highest one (80-150 keV range) to the lowest one (40-70 keV range). The energies and fluencies in each particular batch were simulated to yield a possibly large region in which the Mg:B ratio corresponds to stoichiometric MgB2 compound. These structures were next annealed using high intensity hydrogen plasma pulses of energy densities between 1.5 and 4.0 J/cm(2), or furnace annealed at 350-600 degrees C in a stream of flowing Ar-4%H-2 mixture. The simulated profiles were in fair agreement with those derived from the RBS measurements. Magnetically modulated microwave absorption (MMMA), magnetization and resistance measurements showed that the superconducting transition onset temperature T-c(onset) shifted from about 13 K in the best magnesium sample implanted with single-energy B ions, to 22-28 K for multi-energy!
implantation treatments. Respective shift in Mg-implanted boron samples was from about 33.3 K to 36.5 K. However, broadening of the transition to the superconducting state is observed for the multi-energy treatment in both cases. Possible reasons for these effects and proposed means to improve the method are discussed. (C) 2009 Elsevier B.V. All rights
  • Surface & Coatings Technology 203(2009)17-18, 2694-2699

Publ.-Id: 13093 - Permalink

Wettability improvement of carbon ceramic materials by mono and multi energy plasma pulses
Barlak, M.; Piekoszewski, J.; Werner, Z.; Stanislawski, J.; Skladnik-Sadowska, E.; Borkowska, K.; Miskiewicz, M.; Kolitsch, A.; Groetzschel, R.; Starosta, W.; Sartowska, B.; Kierzek, J.;
joining of carbon type ceramics with other materials presents an important challenge, especially in view of ITER technology. The crucial problem in joining is wettability of such ceramics with copper. In our previous works we succeeded in improving wettability using two-steps procedure, i.e.: pre-treatment of the ceramics surface with Ti ions implantation and/or deposition of metallic Ti using high intensity pulse plasma treatment followed in both cases by the deposition of additional, thicker Ti layers using the Arc PVD technique. In the present work we performed successful experiments in which two-steps procedure is reduced to the one step using exclusively the pulse plasma pre-treatment in various combinations of the number of pulses and their energy density. (C) 2009 Elsevier B.V. All rights reserved.
  • Surface & Coatings Technology 203(2009)17-18, 2536-2540

Publ.-Id: 13092 - Permalink

Plasma-Immersion-Ion-Implantation of Fluorine to Protect TiAl-Components against High-Temperature Oxidation
Donchev, A.; Kolitsch, A.; Schuetze, M.; Yankov, R.;
Titanium aluminides are promising light weight materials for several high-temperature applications, e.g., in aero engines but due to their insufficient oxidation resistance at temperatures above roughly 800 degrees C they cannot be used yet despite of their good mechanical high-temperature properties. The oxidation behavior of TiAl-alloys can be improved significantly by adding small amounts of fluorine into the subsurface zone of the components (microalloying). One possibility to apply fluorine to the surface of complex TiAl-components is the PI3-technique (plasma-immersion-ion-implantation). The use of an Ar/CH2F2-plasma for the F-PI3 into small coupons led to a positive effect which was as good as the beamline implantation of elemental fluorine gas into samples of the same geometry. Turbine blades, as examples for real TiAl-components, were implanted with an optimum set of parameters. Post-exposure investigations like scanning electron microscopy revealed a thin protectiv!
e alumina scale on the surface of the implanted samples in contrast to a thick mixed oxide scale (TiO2/Al2O3) growing on untreated samples during high-temperature oxidation in air. The high-temperature oxidation resistance of several TiAl-alloys was improved by plasma-immersion-ion-implantation of fluorine. Small coupons showed a much lesser oxidation during high-temperature exposure after fluorine treatment than untreated samples. The performance of turbine blades for the low pressure compressor of a new generation of jet engines was also improved. Fluorine treated samples are covered with a thin, protective alumina scale after high-temperature exposure in air instead of a fast growing, nonprotective mixed oxide (TiO2/Al2O3) scale which is found on untreated samples.
  • Plasma Processes and Polymers 6(2009)6, 434-439

Publ.-Id: 13091 - Permalink

Quantitative dopant profiling in semiconductors: A Kelvin probe force microscopy model
Baumgart, C.; Helm, M.; Schmidt, H.;
Kelvin probe force microscopy (KPFM) is used to investigate the electrostatic force between a conductive probe and nanostructured Si with shallow or buried selectively doped regions under ambient conditions. A unique KPFM model correlates the measured Kelvin bias with the calculated Fermi energy, and thus allows quantitative dopant profiling. We show that due to an asymmetric electric-dipole formation at the semiconductor surface the measured Kelvin bias is related with the difference between Fermi energy and respective band edge, and independent of the probe potential.

Publ.-Id: 13090 - Permalink

Einführung eines Dokumentenmanagementsystems für die Unterstützung des Beschaffungsprozesses des Forschungszentrum Dresden-Rossendorf
Zander, R.;
In dieser Arbeit wird ein Lösungsvorschlag für die Einbindung eines Dokumentenmanagementsystems in den Beschaffungsprozess des Forschungszentrum Dresden-Rossendorf vorgestellt. Nach einer eingehenden Analyse der Prozessabläufe bei der Beschaffung und der am Standort vorhandenen IT-Landschaft wurde in Zusammenarbeit mit den zukünftigen Anwendern und einer beratenden externen Firma ein Konzept erarbeitet, durch dessen Umsetzung das Forschungszentrum Dresden-Rossendorf in der Lage ist, seinen Beschaffungsprozess zu optimieren.
Keywords: Dokumentenmanagementsystem, DMS, Beschaffungsprozess
  • Article, self-published (no contribution to HZDR-Annual report)
    Forschungszentrum Rossendorf 2009
    64 Seiten


Publ.-Id: 13089 - Permalink

Qualitative und quantitative Analysen dünner Funktionsschichten für das Kleben durch XPS-, AES-, REM- und TEM-Untersuchungen
Lebelt, P.; Gehrke, J.; Hallmeier, K.-H.; Reuther, H.; Dörfel, I.;
Die Schwachstelle aller Klebverbindungen ist die Grenzschicht zwischen Klebstoff und Substrat. Aus diesem Grund ist eine Optimierung hinsichtlich Klebstoffauswahl und Oberflächenvorbereitung/-vorbehandlung des Substrats unerlässlich, um definiert und sicher zu kleben.
  • Galvanotechnik 100(2009)4, 930-937

Publ.-Id: 13088 - Permalink

Spin-dependent transport in nanocomposite C:Co films
Zhou, S.; Berndt, M.; Bürger, D.; Heera, V.; Potzger, K.; Abrasonis, G.; Radnóczi, G.; Kovács, G. J.; Kolitsch, A.; Helm, M.; Fassbender, J.ORC; Möller, W.; Schmidt, H.
The magneto-transport properties of nanocomposite C:Co (15 and 40 at.% Co) thin films are investigated. The films were grown by ion beam co-sputtering on thermally oxidized silicon substrates in the temperature range from 200 to 500 °C. Two major effects are reported: (i) a large anomalous Hall effect amounting to 2 μΩ cm, and (ii) a negative magnetoresistance. Both the field-dependent resistivity and Hall resistivity curves coincide with the rescaled magnetization curves, a finding that is consistent with spin-dependent transport. These findings suggest that C:Co nanocomposites are promising candidates for carbon-based Hall sensors and spintronic devices.
Keywords: Carbon:cobalt nanocomposite; TEM; Magneto-transport; Anomalous hall effect; Magnetic nanoparticles

Publ.-Id: 13087 - Permalink

Wire-mesh sensors for high-resolution gas-liquid multiphase flow visualization
Da Silva, M. J.; Thiele, S.; Schleicher, E.; Hampel, U.;
Wire-mesh sensors are flow imaging devices and allow the investigation of multiphase flows with high spatial and temporal resolution. This type of sensor was introduced about ten years ago at Research Center Dresden-Rossendorf, Germany and since then it has been successfully employed to investigate several single phase and two-phase flow phenomena. The sensor can be seen as a hybrid solution in between intrusive local measurement of phase fraction and tomographic cross-sectional imaging. It comprises of two set of wires stretched over the cross-section of a vessel or pipe. The planes of wires are perpendicular to each other with a small axial separation between them, thus forming a grid of electrodes. The associated electronics measures an electrical property of the flowing media at each crossing point in a very fast and multiplexed manner. The wire mesh subdivides the flow channel cross section into a number of independent sub-regions, whereas each crossing point represents one sub-region. Each of the measured signals reflects the constitution of the flow within its associated sub-region, i.e. each crossing point acts as local phase indicator. Hence, the set of data obtained from the sensor directly represents the phase distribution over the cross-section and no reconstruction procedure, e.g. by solving an inverse problem as usual in tomography, is needed in order to determine cross-sectional phase distributions. The first generation of wire-mesh sensors is based on conductivity measurements, thus being able to investigate electrically conducting fluids only. Typically air-water and steam-water flows have been investigated. Recently, the capacitance wire-mesh sensor has been developed and tested, which allow the investigation of non-conducting fluids such as oil or organic liquids. The newest systems are able to produce up to 10,000 images per second. Sensors can be constructed to operate under temperatures up to 286 °C and pressures up to 7 MPa. First this article reviews the measuring principle of wire-mesh sensors. In addition, measurement results of the application of a new-developed capacitance wire-mesh sensor to investigate two-phase gas-oil flow are presented. Furthermore, the use of a wire-mesh sensor for the investigation of a simulated three-phase flow in a laboratory setup is described and discussed. Thus, the wire-mesh sensor can considered as a simpler and inexpensive alternative to investigate either two-phase gas-liquid or three-phase gas-liquid-liquid flows. The good accuracy achieved in the permittivity measurement allows the wire-mesh system to securely distinguish even each of the three phases of a gas-oil-water flow.
Keywords: multiphase flow, flow visualization, phase fraction, wire-mesh sensor, imaging system
  • Contribution to proceedings
    20th International Congress of Mechanical Engineering, 15.-20.11.2009, Gramado, Brazil
    Proceedings of COBEM 2009, Paper No. COB09-2457, 2176-5480
  • Lecture (Conference)
    20th International Congress of Mechanical Engineering, 15.-20.11.2009, Gramado, Brazil

Publ.-Id: 13086 - Permalink

Investigation on drag reduction phenomenon in oil-water dispersed pipe flow via wire-mesh sensor
Rodriguez, I. H.; Yamaguti, H. K. B.; de Castro, M. S.; Da Silva, M. J.; Rodriguez, O. M. H.;
Liquid-liquid flows are present in a wide range of industrial processes; however they have not been studied as intensively as gas-liquid flows. The interest in two-phase liquid-liquid flows have increased recently mainly due to the petroleum industry where oil and water are often produced and transported together for long distances. Nevertheless, the frictional pressure gradient in oil-water pipe flow not rare cannot be predicted by correlations developed for gas-liquid flow. The dispersed flow pattern is common in crude oil transmission pipelines and offshore pipelines, with either oil or water as the dominant phase. An interesting feature of dispersed flow is that it can behave as a non-Newtonian fluid. There are several works on drag reduction in single and gas-liquid two-phase flows, but only few on liquid-liquid flow. Drag reduction phenomenon in oil-water flows without the addition of any drag reduction agent has been detected in previous works, but the physics behind the phenomenon is yet not well understood. This work’s main goal is the experimental study of the drag reduction phenomenon in dispersed oil-water flow. Pressure gradients were measured during the flow of oil (860 kg/m3 density and 100 mPa.s viscosity) and water. The experimental work was performed in a 12-m-long 2.62-cm-i.d. horizontal glass pipe. A new wire-mesh sensor based on capacitance (permittivity) has been employed in this study. The sensor consists of two layers made of 8 steel wires each separated 1 mm from each other. It is able to discriminate fluids having different relative permittivity values in a multiphase flow and was used to measure local, transient and time-and-space averaged phase fraction distributions in the flow cross-section. A high-speed video camera and the Quick Closing Valves technique were used to compare and validate the signals of the wire-mesh sensor.
Keywords: liquid-liquid flow, drag reduction, dispersed flow, pressure gradient, wire-mesh sensor, liquid holdup
  • Contribution to proceedings
    20th International Congress of Mechanical Engineering, 15.-20.11.2009, Gramado, Brazil
    Proceedings of COBEM 2009, Paper No. COB09-0476
  • Lecture (Conference)
    20th International Congress of Mechanical Engineering, 15.-20.11.2009, Gramado, Brazil

Publ.-Id: 13085 - Permalink

Kapazitäts-Gittersensor: Prinzip und Anwendung
Da Silva, M. J.; Hampel, U.;
Gittersensoren ermöglichen räumlich und zeitlich hochaufgelöste Untersuchungen von Mehrphasenströmungen. Solche Sensoren können damit für viele strö-mungsdiagnostische Probleme in der Forschung und Industrie eingesetzt werden. Dieser Beitrag beschreibt den neu entwickelten Kapazitäts-Gittersensor, welcher auf der Messung der elektrischen Permittivität (Kapazität) basiert. Neben der Beschreibung des Messprinzips und der dazugehörigen Messelektronik wird auch ein ausgewähltes Anwendungsbeispiel der Visualisierung einer Gas-Öl-Zweiphasenströmung präsentiert.
Keywords: wire-mesh sensor, multiphase flow, flow visualization, void fraction, electrical capacitance
  • Contribution to proceedings
    XXIII. Messtechnisches Symposium des Arbeitskreises der Hochschullehrer für Messtechnik e.V., 17.-19.09.2009, Bremen, Deutschland
    Tagungsband XXIII. Messtechnisches Symposium des AHMT, Gert Goch (Hrsg.), Aachen: Shaker Verlag, 978-3-8322-8491-6, 139-148
  • Lecture (Conference)
    XXIII. Messtechnisches Symposium des Arbeitskreises der Hochschullehrer für Messtechnik e.V., 17.-19.09.2009, Bremen, Deutschland
  • Technisches Messen 77(2010), 209-214
    DOI: 10.1524/teme.2010.0055

Publ.-Id: 13084 - Permalink

Thermoelectric currents in laser induced melts pools
Lange, A.; Cramer, A.; Beyer, E.;
Applying an external static magnetic field to laser beam welding may lead to a change in geometry of the weld seam. Since the most common influence of a magnetic field acting on an electrically high conducting fluid is the generation of a Lorentz force, the outcome of such experiments is a strong indication of the presence of electric current in the melt pool. Owing to the static nature of the magnetic field, induction is restricted to the movement of the liquid metal and therefore negligible, leaving thermoelectricity as the sole potential source of current. The present work discloses analytically that the current may indeed originate from a gradient of thermoelectric power. Based on the examples iron and aluminum, key features of the current distribution are determined numerically together with an investigation of the dependence of the distribution on material properties. By carrying out welding experiments in the heat conduction mode, validation is achieved of the thermoelectric source of the current and of basic properties of its contribution.
Keywords: thermoelectric current, laser welding, geometry of weld seam
  • Journal of Laser Applications 21(2009)2, 82-87

Publ.-Id: 13083 - Permalink

Voigt effect measurement on PLD grown NiO thin films
Scarlat, C.; Mok, K. M.; Zhou, S.; Vinnichenko, M.; Lorenz, M.; Grundmann, M.; Helm, M.; Schubert, M.; Schmidt, H.;
NiO has great potential applications in spin valves, magnetooptical sensors, optical fibers, solar thermal absorbers, and in nonvolatile resistive random access memory devices. In our study NiMnO and NiMnLiO films have been grown on double-side polished r-plane sapphire substrates by pulsed laser deposition (PLD). We measured the complex Voigt angle using the polarized light from a HeCd laser, a Glan Taylor polarizer, a Hinds PEM-100 [1] and two Lock-Ins. The Voigt effect is a second order magnetooptic effect [2]. The polarization state of light after transmission through a sample consisting of ca. 1 μm thick, weak ferromagnetic NiO thin on purely diamagnetic r-plane sapphire substrates has been modelled using the 4x4 matrix formalism [3] in dependence of an external magnetic field applied in-plane, i.e. in Voigt configuration. The modelling results revealed that for the diamagnetic sapphire substrate the Voigt angle depends parabolically on the external magnetic field and that the weak ferromagnetic NiO thin films change 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.

[2] R. Carey and B.W.J. Thomas, J. Phys. D: Appl. Phys. 7,
2362-2368 (1974).
[3] M. Schubert, Phys. Rev. B 53, 4265 (1996).
Keywords: Magnetooptical effects, Magnetic semiconductors
  • Contribution to proceedings
    12th International Conference on the Formation of Semiconductor Interfaces (ICFSI-12), 05.-10.07.2009, Weimar, Germany
  • Physica Status Solidi (C) 7(2010)2, 334-337

Publ.-Id: 13082 - Permalink

Paramagnetic Mn-implanted amorphous Si
Xu, Q.; Zhou, S.; Schmidt, B.; Mücklich, A.; Schmidt, H.;
Different fluences of Mn ions have been implanted into 200 nm thick, n-type conducting amorphous Si films on a cold stage cooled by liquid N2 with a Mn concentration in MnxSi1-x ranging from x=0.0006 to 0.088. Magnetic measurements reveal paramagnetism in all the films at temperatures down to 2 K. The field dependent magnetization curves were well fitted by Brillouin functions, indicating that the magnetically active Mn ions are on MnI2+ interstitial sites with J=5/2. Only a small percentage of the implanted Mn ions contribute to the magnetization, indicating that the magnetic moments are quenched for most of the Mn ions, which was attributed to the nonuniform distribution of Mn ions in amorphous Si. Positive magnetoresistance due to ordinary magnetoresistance was observed at 5 K in the highest fluence Mn implanted amorphous Si film, indicating the lack of magnetic scattering of the conducting electrons by the implanted Mn2+ ions.
Keywords: diluted magnetic semiconductor, implantation, paramagnetism, magnetoresistance

Publ.-Id: 13081 - Permalink

Micro-Hall effect probes for applications at pulsed magnetic fields above 75 T
Mironov, O. A.; Palewski, T.; Zherlitsyn, S.; Uhlarz, M.; Skourski, Y.; Wosnitza, J.;
Microminiature Hall probes (MHP) may be used as magnetic field transducers, with virtually no change of sensitivity with temperature, for applications at room and cryogenic temperatures. The probes have a nominal active sensing area of 90x90 µm and are based on Sn-doped n-InSb/i-GaAs MBE-grown heterostructures. Previously MHPs were intensively tested [1] and shown to be appropriate for various applications in the temperature range 50 mK- 300 K and in pulsed magnetic fields up to 52 T (of 120 ms pulse duration). The latest probes, with overall dimensions of 150x750 µm, are the smallest encapsulated Hall probes currently available and can be placed in areas not previously accessible to commercial packaged sensors. The new MHP modification has recently been tested in pulsed magnetic fields above 75 T using a new 9 MJ dual-coil magnet designed and fabricated at the Dresden High Magnetic Field Laboratory. The inner coil, having a bore of 20 mm, produced a 10 ms pulse on top of the 30 T background field from the outer coil of 100 ms duration. Tests over the range 300 K to 78 K yielded a remarkably linear Hall voltage up to 76.7 T, with a temperature independent sensitivity of 2.3 µV/mT (at an input current of 5 mA). The Hall-device input resistance was less than 0.4 ohms and < 1.5 ohms including the 80 mm long MHP copper wires.
  • Poster
    RHMF 09 (Research in High Magnetic Fields 2009), 22.-25.07.2009, Dresden, Deutschland

Publ.-Id: 13080 - Permalink

Optimization of large multiple coil systems for pulsed magnets
Perenboom, J. A. A. J.; Frings, P.; Béard, J.; Bansal, B.; Herlach, F.; Peng, T.; Zherlitsyn, S.;
The generation of pulsed magnetic fields is limited by the Lorentz force on the conductor and by ohmic heating. A large coil can give higher field (and/or longer pulse duration), but for a single coil this may require high power that cannot be supplied by a feasible source. Power can be kept within acceptable limits by using a system of multiple coils. Pulsed field coils can be energized either by a pulsed power supply or a pulsed energy source. The energy or power supplies tend to be the most expensive part of the installation and a combination of high power and high energy is extremely expensive. In a multi-coil system , the increased design freedom allows to optimize the strength, pulse duration and heating of the coil, and to optimize the selection of materials and power supplies; one can so also minimize damage in case of coil failure. Because of the increased number of parameters, systematic insight into their mutual dependence is helpful in order to converge to an optimized design. Since the local optima are relatively weak, for the final design any standard method of pulsed coil design can be used. In this paper we will discuss strategies to determine the optimum choice for the design of inner- and outer-coil and how to optimize their design in relation to the supply type used. In particular, we will consider energy-limited capacitor banks and power-limited supplies. The approach will use scaling arguments and modeling tools as the PMDS package originally developed in Leuven. Optimization of coil systems is demonstrated with practical examples, such as the successful 87 T pulsed dual coil system in Dresden, and the design of the future ‘ARMS’ successor in Toulouse
  • Poster
    RHMF 09 (Research in High Magnetic Fields 2009), 22.-25.07.2009, Dresden, Deutschland

Publ.-Id: 13079 - Permalink

Temperatur Dependence of the Upper Critical Field of Superconducting Eu0.5K0.5Fe2As2
Weickert, F.; Hirale, J. S.; Gegenwart, P.;
The discovery of superconductivity (SC) in FeAs-layered systems has triggered enormous activities on this field of solid state physics. Up to now a variety of compounds based on the two families RFeOAs (R = rare-earth element) and AFe2As2 (A = Ba, Sr, ...) were found with transition temperatures up to 57 K. A main feature of these compounds is, that SC occurs in close proximity to magnetic order, which suggests, that magnetic fluctuations play a crucial role in the formation of the superconducting ground state. In the system EuFe2As2 even two different types of magnetic order have been found. At 190 K a Fe spin density wave (SDW) forms, which is accompanied by a structural phase-transition. Below 19 K a second magnetic phase transition is observed, where Eu2+-irons order antiferromagnetically. Band structure calculation suggest, that both magnetic lattices are predominantly decoupled. A detailed study of Eu1-xKxFe2As2 indicates the complete suppression of the SDW order for x = 0.5 and the simultaneous development of SC below 32 K. In the contribution, we present magnetoresistance measurements carried out at the Hochfeldmagnetlabor Dresden on polycrystalline samples of Eu0.5K0.5Fe2As2 in pulsed magnetic fields up to 60 T. We could determine the complete temperature dependence of the upper critical field Hc2(T), at temperatures down to 1.5 K. The initial slope µ0dHc2/dT in the proximity of Tc(H = 0) varies between -1.60 T/K (0.1 Rn) and -1.75 T/K (0.9 Rn), dependent on the used criterion, and is rather small compared to other pnictides of the same family. A comparison of our results with the Werthamer-Helfand-Hohenberg (WHH) model indicates that the upper critical field in Eu0.5K0.5Fe2As2 is not Pauli limited. Moreover, the experimentally estimated critical field µ0Hc2(T → 0) of 45 T is significant higher than the value of 38 T expected for orbital limiting in the WHH model.
  • Poster
    RHMF 09 (Research in High Magnetic Fields 2009), 22.-25.07.2009, Dresden, Deutschland

Publ.-Id: 13078 - Permalink

Probing magneto-transport properties of carbon nanostructures in pulsed magnetic fields
Jhang, S.; Marganska, M.; Schmidmeier, S.; Skourski, Y.; Preusche, D.; Eroms, J.; Grifoni, M.; Strunk, C.;
We present the magnetoconductance of carbon nanostructures (including carbon nanotubes, graphene and graphene nanoribbons) in pulsed magnetic fields up to 60 Tesla. Applying a magnetic field to such systems provides an efficient tool to investigate the band structure near the charge neutrality point. From the study of magnetoconductance in carbon nanotubes, we show how axial magnetic field as well as curvature, spin-orbint coupling, and Zeeman splitting modify the bandstructure of carbon nanotubes. Preliminary results on graphene and graphene nanoribbons are also reported, and technical issues to measure magnetoconductance of nanostructures in pulsed magnet facility are discussed.
  • Poster
    RHMF 09 (Research in High Magnetic Fields 2009), 22.-25.07.2009, Dresden, Deutschland

Publ.-Id: 13077 - Permalink

Evidence for a metamagnetic transition in the heavy fermion system CeTiGe
Deppe, M.; Skourski, Y.; Caroca-Canales, N.; Geibel, C.; Sereni, J. G.;
Systems located close to a quantum critical point are of high interest, because low lying quantum fluctuations (QF’s) can lead to new physical phenomena. The compound CeTiGe crystallizes in the CeFeSi structure type, which presents some (2D) character enhancing QF’s. Our first detailed investigations of Cp(T), Chi(T), and rho(T) at low temperatures for CeTiGe indicate that it is a new paramagnetic heavy fermion system with an enhanced Sommerfeld - coefficient gamma0 ≈ 0.3 J/(K2mol). Further analyses using the Coqblin-Schrieffer (CS) model showed that the whole J = 5/2 multiplet is involved in the formation of the ground state. The CS - model predicts a broad s-shaped magnetization at high fields and to study this we extended our investigation to measurements under high magnetic field. Here we present the results of magnetization measurements M vs. B in fields up to 14 T performed in a commercial Physical Property Measurement System (PPMS®) and additional data obtained in pulsed high fields up to 60 T performed at the Dresden high magnetic field laboratory (HLD). Instead of the expected behavior these measurements revealed a steplike metamagnetic transition (MMT) at a critical field of μ0Hc ≈ 12.5 T of the size ΔM ~ 0.74 μB/Ce for T = 1.4 K. Thus CeTiGe is the second paramagnetic Ce - based Kondo lattice besides CeRu2Si2 showing a clear MMT below 20 T. In contrast to CeRu2Si2, CeTiGe shows a hysteresis at the MMT. We shall further present the effect of substitution La for Ce on this metamagnetic transition.
  • Poster
    RHMF 09 (Research in High Magnetic Fields 2009), 22.-25.07.2009, Dresden, Deutschland

Publ.-Id: 13076 - Permalink

Nitrocarburizing of AISI-304 stainless steel using high-voltage plasma immersion ion implantation
Abd El-Rahman, A. M.; Mohamed, S. H.; Ahmed, M. R.; Richter, E.; Prokert, F.;
AISI-304 austenitic stainless steel has been nitrocarburized in N-2 and C2H2 ambient using high-voltage plasma immersion ion implantation (PIII) technology. The use of different PIII treatment times revealed important hints with respect to the microstructural, mechanical and corrosion properties of the nitrocarburized layer. Grazing incidence X-ray diffraction (GIXRD) shows the presence of nitride (gamma(N) and CrN) and carbide (gamma(c) and Fe3C) phases. Glow discharge optical spectroscopy (GDOS) has been used to characterize the elemental depth profiles in which the thickness of the modified layers is derived. Dynamic microindentation method is used for the study of mechanical performance of the nitrocarburized layer as well as the untreated material. The microhardness has been increased to a maximum value of more than nine times compared to that of the untreated one. The corrosion performance is characterized by potentiodynamic polarization technique and was found to be t! reatment time dependent.

Publ.-Id: 13075 - Permalink

Stoichiometric MgB2 layers produced by multi-energy implantation of boron into magnesium
Werner, Z.; Szymczyk, W.; Piekoszewski, J.; Seah, M. P.; Ratajczak, R.; Nowicki, L.; Barlak, M.; Richter, E.;
Ion implantation manufacture of superconducting magnesium diboride films of the MgB2 stoichiometry (B: Mg = 2:1 composition) by boron implantation in Mg wafers requires a precise knowledge of the implantation process properties, in particular of the partial sputtering yields of Mg atoms by B ions. To verify these yields experimentally we deposited thin Mg films on glassy carbon platelets and implanted them with high fluences of 40, 60, and 80 keV B+ ions. He-backscattering (RBS) spectrometry was used to determine before- and after-implantation depth profiles of Mg and B. The sputtering yields turned out to be small enough (<0.1 atoms per ion) to neglect sputtering in simulations of the implanted profiles. The results of the simulations have been compared to RBS spectra recorded on samples treated with 3 energies/fluencies optimised for a wide plateau of the B:Mg = 2:1 stoichiometric composition.

Publ.-Id: 13074 - Permalink

Upper critical field measurements up to 60 T in arsenic-deficient LaO0.9F0.1 Fe As: Pauli limiting at high fields vs. improved superconductivity at low fields
Fuchs, G.; Drechsler, S.-L.; Kozlova, N.; Bartkowiak, M.; Wosnitza, J.; Behr, G.; Nenkov, K.; Klaus, H.-H.; Büchner, B.; Schultz, L.;
We report resistivity, Hall and upper critical field Bc2(T) data for arsenic deficient LaO0.9F0.1 FeAs1-δ in a wide temperature and high field range up to 60 T. These disordered samples exhibit a slightly enhanced transition temperature of Tc = 29.0 K and a significantly enlarge slope dBc2/dT = –5.4 T/K near Tc. The high-field Bc2(T) data obtained from resistance measurements in pulsed magnetic fields follow up to about 30 T the WHH (Werthamer-Helfand-Hohenberg) curve for the orbital limited upper critical field, but show a clear flattening above 30 T. This flattening is interpreted as the onset of Pauli-limited behavior with Bc2(0) ~ 63 to 68 T. We compare our results with Bc2(T) data reported in the literature for clean and disordered samples. Whereas clean samples show no Pauli-limiting behavior for fields below 60 to 70 T as measured so far, the hitherto unexplained flattening of Bc2(T) for applied fields H||ab observed for several disordered closely related systems as Co-doped BaFe2As2 or (Ba,K)Fe2As2 (obtained from a Sn-flux) is interpreted as a manifestation of Pauli-limiting behavior. The corresponding enhanced Maki parameters point to significant paramagnetic effects in these disordered FeAs-based superconductors. Consequences of our results are discussed in terms of disorder effects within the frame of conventional and unconventional superconductivity. The enhancement of the upper critical field slope near Tc by strong disorder provides evidence for an important attractive intraband contribution to s-wave pairing of Cooper pairs in disordered Fe pnictides at relatively high transition temperatures.
  • Poster
    RHMF 09 (Research on High Magnetic Fields 2009), 22.-25.07.2009, Dresden, Deutschland

Publ.-Id: 13073 - Permalink

Magnetic properties of ZnO nanopowders
Xu, Q.; Zhou, S.; Schmidt, H.;
We report the magnetic characterization of ZnO nanopowders with an average grain size of about 50 nm prepared by sol-gel method. At room temperature, ZnO nanopowders exhibit diamagnetism like bulk ZnO. However, strong paramagnetism was observed at 4 K. With increasing temperature, ferromagnetic to paramagnetic transition happens at around 90 K. Paramagnetism changes to diamagnetism at around 100 K, which is due to the competition between the paramagnetism from defects and diamagnetism from the bulk ZnO. Our work clearly demonstrates that the interaction betweeen the defects is short-range. Thus the interaction between the defects is weak due to low defect concentration. It is suggested that a high defect concentration is needed for room temperature ferromagnetism.
Keywords: Diluted magnetic semiconductor; ZnO; Magnetism; Defect

Publ.-Id: 13072 - Permalink

Charge Transport and Magnetotransport Properties of Polyimide Irradiated by 80 keV Co Ions
Chen, T.; Yao, S.; Hua, W.; Fa, T.; Li, L.; Zhou, S.;
Charge transport properties of polyimide films implanted with 80 keV Co ions at two different fluences (series I: 1.25 x 10(17) ions/cm(2), series II: 1.75 x 10(17) ions/cm(2)) are studied in detail. For series I, the temperature dependence of surface resistivity fits Mott's equation very well. It is on the insulating side of the insulator-metal transition (IMT). However, for series II, the temperature dependence of surface resistivity is not in agreement with Mott's equation. It is on the metallic side of IMT. The magnetotransport properties of these two series are also studied. No significant magnetoresistive effect is observed for series I at both 5K and 300 K. For series II, an obvious magnetoresistive effect is observed at 5K, while there is no magnetoresistive effect at 300 K. Rutherford backscattering spectrometry (RBS) is applied to confirm the actual fluence for these two series.
  • Chinese Physics Letters 26(2009), 087201

Publ.-Id: 13071 - Permalink

Modification of the electrical properties of polyimide by irradiation with 80 keV Xe ions
Chen, T.; Yao, S.; Wang, K.; Wang, H.; Zhou, S.;
We modify the electrical properties of polyimide (PI) films by irradiation with 80 keV Xe ions. The surface resistivity of irradiated PI film at room temperature decreases remarkably from 1.2 x 10(14) Omega/square for virgin PI film to 3.15 x 10(6) Omega/square for PI film irradiated by 5.0 x 10(16) ions/cm(2), and the temperature dependence of the resistivity of the treated films is well-fit using Mott's Equation. The irradiated PI film structure is studied using Raman spectroscopy, X-ray diffraction, and Rutherford Backscattering Spectrometry. The concentration of O in the irradiated layer decreases with increasing fluence, while the variation of N concentration is negligible. Graphite-like carbon-rich phases are created in the irradiated layers, leading to the modification of the electrical properties. (C) 2009 Elsevier B.V. All rights reserved.
Keywords: Ion implantation; Polyimide; Electrical properties

Publ.-Id: 13070 - Permalink

Dose effect curve for in vitro cell irradiations with laser accelerated electrons
Karsch, L.; Beyreuther, E.; Enghardt, W.; Kaluza, M.; Laschinsky, L.; Lessmann, E.; Naumburger, D.; Nicolai, M.; Pawelke, J.; Richter, C.; Sauerbrey, R.; Schlenvoigt, H.; Baumann, M.;
Fragestellungen: Die neue Technologie der Laserteilchenbeschleunigung verspricht die Realisierung von kompakten und ökonomisch effektiven Therapieanlagen. Die dabei zur Anwendung kommenden Hochintensitätslaser führen, verglichen mit den heute in der Strahlentherapie eingesetzten Beschleunigern, zu viel kürzeren Teilchenpulsen mit geringerer Wiederholfrequenz, aber viel größerer Pulsdosisleistung. Vor einem klinischen Einsatz der Laserteilchenbeschleunigung müssen deshalb die Konsequenzen bezüglich dosimetrischer Erfassung und Strahlenwirkung auf menschliches Gewebe untersucht werden. Im Beitrag werden die weltweit ersten systematischen Zellbestrahlungen mit Laser beschleunigten Elektronen vorgestellt und die Ergebnisse diskutiert.
Methodik: Die Experimente wurden am Lasersystem JETI in Jena durchgeführt.
Das Lasersystem, bisher nur für physikalische Einzelschussexperimente benutzt, wurde für die Durchführung von Routine-Zellbestrahlungen angepasst und ein geeignetes Dosimetriesystem für die ultrakurz gepulsten Elektronen mit einer Energie bis zu 20 MeV entwickelt. Über einen Zeitraum von mehreren Monaten wurden Zellen von je zwei humanen Normal- und Tumorgeweben bestrahlt. Zur Erfassung der Strahlenwirkung wurden die residuellen Doppelstrangbrüche (24 h nach Bestrahlung) und der Anteil des klonogenen Zellüberlebens bestimmt. Der Effekt jeder applizierten Dosis wurde zunächst durch Bestrahlung mehrerer Zellproben an einem Tag doppelt bestimmt und jede Dosis-Effekt-Kurve an zwei weiteren Tagen wiederholt. Parallel dazu wurden Referenzbestrahlungen mit kontinuierlicher 200 kV Röntgenstrahlung durchgeführt.
Ergebnisse: Auf dem Weg zur klinischen Anwendung der Laserteilchenbeschleunigung sind die erfolgreichen systematischen in vitro Zellbestrahlungen ein erster wichtiger Schritt. Obwohl die hohen Anforderungen für Patientenbestrahlung noch nicht vollständig erfüllt sind, wurde über mehrere Wochen ein für Zellbestrahlungen ausreichend stabiler, reproduzierbarer Elektronenstrahl erzeugt. Die dosimetrische Überwachung erlaubte eine kontrollierte Bestrahlung der Zellen mit einer vorgegebenen Dosis. Für alle vier Zelllinien wird eine deutlich niedrigere biologische Wirksamkeit der ultrakurz gepulsten, Laser beschleunigten Elektronenstrahlen nachgewiesen. Die Ergebnisse der beiden biologischen Endpunkte sind dabei konsistent.
Schlussfolgerungen: Gegenwärtige Experimente untersuchen die Ursache der reduzierten Strahlenwirkung für Laser beschleunigte Elektronen. Erste Ergebnisse zum Einfluss der Pulsdosisleistung, der mittleren Dosisleistung und dem Energiespektrum werden vorgestellt.
Die Arbeit wird gefördert durch das BMBF 03ZIK445.
  • Strahlentherapie und Onkologie 185(2009)(Suppl. 1), 158
  • Poster
    DEGRO 2009 15. Jahreskongress der Deutschen Gesellschaft für Radioonkologie, 11.-14.06.2009, Bremen, Deutschland

Publ.-Id: 13069 - Permalink

Magnetic-field dependence of the T*-anomaly in quasi-2D organic superconductors
Brandenburg, J.; Müller, J.; Das, P.; Lang, M.; Weickert, F.; Bartkowiak, M.; Wosnitza, J.;
The family of quasi-2D superconductors kappa–(BEDT–TTF)2X are model systems for strongly correlated low–dimensional metals. Recently, the unusual normal–conducting state — characterized by a line of anomalies T* (in the order of 40 K) — has attracted considerable attention: a ”pseudo-gap”behavior in analogy to the high-Tc cuprates, a crossover from an incoherent ”bad” metal to a coherent Fermi–liquid regime, and a density–wave–type phase transition have been suggested as possible scenarios. To investigate the possibility of a magnetic origin we carried out detailed transport measurements in pulsed magnetic fields up to 60 T. For two different compounds, X = Cu[N(CN)2 ]Br and Cu(NCS)2 , we observed a maximum in the relative magnetoresistance change right around T* . This indicates the significance of magnetic degrees of freedom which are coupled to the transport properties. Also, for the first time we were able to determine the magnetic–field dependence of T* showing a small negative shift with increasing field. We discuss the implications of our experimental data for possible models explaining the anomalous normal–conducting state.
  • Poster
    RHMF 09 (Research on High Magnetic Fields 2009), 22.-25.07.2009, Dresden, Deutschland

Publ.-Id: 13068 - Permalink

Theory of Unusual Superconducting Phase Transitions in Heavy Fermion Metals at High Magnetic Fields
Maniv, T.; Zhuravlev, V.; Wosnitza, J.;
The large effective masses characterizing heavy-fermion metals enable, at sufficiently high magnetic fields and low temperatures, paramagnetically-driven first-order superconducting (SC) phase transitions, as well as phase transitions to non-uniform SC states with spatially modulated order parameters along the field direction. Here, we present a non-perturbative theory of these phase transitions, which reliably determines the stable SC phases, treats properly the corresponding finite jumps of the order parameter, and can account for various unusual features reported recently for some heavy-fermion superconductors. It is found that for quasi-2D heavy-fermion metals, such as CeCoIn5, at high magnetic fields oriented perpendicular to the highly conducting planes, the compensation effect of the Fulde-Ferrel (FF) modulation is too weak to prevent a first-order phase transition from the normal to the uniform SC state. No modulated FF phase can be therefore stabilized at fields below Hc2 in this material. The calculated thermodynamic properties are in good quantitative agreement with the experimentally derived phase diagram [1] and the sharp additional damping of the de Haas-van Alphen (dHvA) oscillations observed at Hc2 in CeCoIn5 [2]. For 3D heavy-fermion metals, such as URu2Si2, the FF modulation stabilizes, under a decreasing magnetic field, a non-uniform SC state via a second-order phase transition from the normal state. However, at a slightly lower field the modulated phase becomes unstable, transforming to a uniform SC state via a first-order transition. The sharp onset of the SC order parameter calculated for this double-stage scenario of the SC transition, including fluctuation effect, is found to be in good agreement with dHvA results in the SC state of URu2Si2 [3].
  • Lecture (Conference)
    RHMF 09 (Research on High Magnetic Fields 2009), 22.-25.07.2009, Dresden, Deutschland

Publ.-Id: 13067 - Permalink

Violation of critical universality at the antiferromagnetic phase transition of YbRh2Si2
Krellner, C.; Hartman, S.; Pikul, A. P.; Oeschler, N.; Klingner, C.; Donath, J. G.; Geibel, C.; Steglich, F.; Wosnitza, J.;
In recent years,....
  • Poster
    Quantum Critically & Novel Phases 2009, 02.-05.08.2009, Dresden, Deutschland

Publ.-Id: 13066 - Permalink

Stand der experimentellen Arbeiten im Rahmen des TOPFLOW-PTS Projektes
Beyer, M.; Schleicher, E.; Pietruske, H.; Hampel, U.; Weiß, F.-P.;
Ausgehend von einer Beschreibung der Aufgabenstellung und eines kompakten Überblicks über die TOPFLOW Versuchsanlage wird im Vortrag auf die in den Jahren 2006 bis 2009 realisierten Arbeitsschwerpunkte eingegangen. Detailliert werden die notwendigen anlagentechnischen Erweiterungen im Bereich des TOPFLOW Drucktankes sowie die Konstruktion und der Aufbau der Testsektion beschrieben. Des Weiteren enthält der Vortrag ausführliche Informationen zur Spezialmesstechnik und zur Versuchsmatrix. Eine Zusammenfassung der gegenwärtigen Arbeitsaufgaben und ein Ausblick schließen den Vortrag ab.
Keywords: PTS, pressurized thermal shock, TOPFLOW facility, pressure equilibrium, wire mesh sensor, heat flux prob
  • Lecture (others)
    Steering Committee Meeting on R&D Cooperation between FZD and AREVA NP GmbH, 07.09.2009, Dresden, Deutschland

Publ.-Id: 13065 - Permalink

Stand der experimentellen Arbeiten im Rahmen des TOPFLOW-II Projektes
Beyer, M.; Fischer, F.; Danciu, D. V.; Seidel, T.; Schütz, P.; Pietruske, H.; Lucas, D.; Weiß, F.-P.;
Ausgehend von einer Darstellung der versuchstechnischen Aufgaben und einem kurzen Überblick über die TOPFLOW Anlage wird der aktuelle Stand der Arbeiten zum Projekt erläutert. Insbesondere in den Bereichen Kondensations- und Verdampfungsexperimente sowie zur schnellen Röntgentomographie werden die 2008 und 2009 durchgeführten Arbeiten detailliert beschrieben. Zu den Experimenten mit Phasenübergang an freien Oberflächen wird auf die Designphase des Testbassins und die in den vergangenen Jahren durchgeführten kleinskaligen Versuche zum impinging jet eingegangen. Eine Zusammenfassung und ein Ausblick auf die zukünftigen Arbeitsaufgaben schließen den Vortrag ab.
Keywords: condensation, evaporation, vertical tube, condensation on free surfaces, impinging jet, bubble entrainment, wire mesh sensor, CFD validation, TOPFLOW facility
  • Lecture (others)
    CFD im Containment / CFD für Zweiphasenströmungen (Meilstein-Workshop Sommer 2009), 29.07.2009, Dresden, Deutschland

Publ.-Id: 13064 - Permalink

Spraying spin coating silanization at room temperature of a SiO2 surface for silicon-based integrated light emitters
Cherkouk, C.; Rebohle, L.; Skorupa, W.; Strache, T.; Reuther, H.; Helm, M.;
A new silanization method for SiO2 surfaces has been developed for Si-based light emitters which are intended to serve as light sources in smart biosensors relying on fluorescence analysis. This method uses a special silanization chamber and is based on spraying and spin coating (SSC) in nitrogen atmosphere at room temperature for 10 min. It avoids processes like sonication and the use of certain chemicals being harmful to integrated light emitters. The surface of a SiO2 layer serving as a passivation layer for the light emitters was hydrolyzed to silanols using an in situ-hybridization chamber and catalyzed with MES (2-(N-morpholino)ethanesulfone acid hydrate) buffer solution. Subsequently, the substrates were silanized with the SSC method using two coupling agents as (3-Aminopropyl)trimethoxysilane (APMS), and N0-(3-(trimethoxysilyl)-propyl)-diethylenetriamine (triamino-APMS). The structure of the SiO2 surface, the APMS and the triamino-APMS layers was controlled and characterized
by Infrared spectroscopy, Raman spectroscopy and X-ray photoelectron spectroscopy. The results show a covalent binding of the silane coupling agents on the surface. Atomic force microscopy was used to investigate the roughness of the surface. The silanized samples exhibit smooth and densely covered surfaces. Finally, the suitability of the SSC method was verified on real light emitters.
Keywords: Si-based light emission Estrogen Biosensors X-ray photoelectron spectroscopy Atomic force microscopy APMS Silanol Silanization

Publ.-Id: 13063 - Permalink

Physical limitations of the electroluminescence mechanism in Terbium-based light emitters: Matrix and layer thickness dependence
Rebohle, L.; Lehmann, J.; Prucnal, S.; Sunb, J. M.; Helm, M.; Skorupa, W.;
The physical limits of downscaling the SiO2 thickness of rare earth implanted metal-oxynitride-oxide-semiconductor based light-emitters are explored by investigating the drop down of the electroluminescence power efficiency with decreasing SiO2 thickness of Tb-implanted devices. It will be experimentally shown that there is a dark zone with an extension of about 20 nm behind the injecting interface in which the hot electrons have not yet gained enough kinetic energy in order to excite the Tb3+ luminescence centers. In addition, replacing the host matrix SiO2 by SiON results in a decrease of power efficiency by two orders of magnitude which is consistent with experimental data about the hot energy distribution in these media.
Keywords: electroluminescence, rare earth, SiO2, MOS, Terbium
  • Applied Physics B 98(2010)2, 439

Publ.-Id: 13061 - Permalink

In situ Spectroelectrochemical Investigation of Pt(II/IV) Oxidation in Aqueous Solution Using X-ray Absorption Spectroscopy
Takao, K.; Takao, S.; Scheinost, A. C.; Bernhard, G.; Hennig, C.;
The oxidation from PtIICl42− to PtIVCl62− in HCl aq. was studied in situ by combining electrochemistry with XAFS spectroscopy. During the oxidation of PtIICl42−, isosbestic points were observed in Pt LIII and LII XANES spectra as a function of time, indicating that the Pt(II/IV) redox equilibrium is the only reaction in the system. The Pt LIII and LII X-ray absorption edge energies of the initial PtIICl42− are 11562.9 and 13271.8 eV, respectively, while those of the electrolyzed species are 11564.6 and 13273.7 eV which are identical with those of a PtIVCl62– reference sample. The coordination of the electrolyzed species was characterized by structural parameters derived from the EXAFS curve fit, and identified to PtIVCl62–.
Keywords: XAFS, Spectroelectrochemistry, Platinum(II/IV), Redox, Molecular Structure

Publ.-Id: 13060 - Permalink

Vanadium:Silicon - an ion-beam generated diluted magnetic semiconductor? Vanadium diffusion and concentration predictions in Silicon
Thieme, M. B.; Gemming, S.; Potzger, K.;
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 semiconductor device is challenging, we have concentrated on the binary and fully integrable system Vanadium:Silicon. Vanadium form several binary compounds in Silicon at higher doping concentrations; 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 crystal matrix as well as its diffusion. Spin dependent density functional band-structure calculations with the Projector Augmented Wave (PAW)-method (with Abinit, VASP) in LDA and GGA have been carried out to investigate magnetism for all configurations. For special structures also the all-electron full-potential local-orbitals (FPLO)-method (with FPLO) have been used, to confirm the magnetic properties. At the same time first experiments (RBS, XRD, SQUID) have been arranged to support the simulations.
  • Lecture (Conference)
    23rd Nordic Semiconductor meeting, 14.-17.06.2009, Reykjavik, Iceland

Publ.-Id: 13059 - Permalink

Magnetostriction and Thermal Expansion on the quantum spin system Azurite
Wolff-Fabris, F.; Francoual, S.; Zapf, V.; Jaime, M.; Lacerda, A.;
Azurite is a natural mineral with a chemical structure Cu3(OH)2(CO3)2. This compound has been proposed as a model substance for the 1D distorted diamond chain where a frustrated triangular quantum magnet consisting of Cu S=1/2 atoms arranged alternately to form infinite chains along the b axis. The magnetic behavior of this compound reflects the existence of both monomers and dimers made of S = 1/2 Cu. A magnetization plateau at 1/3 of the saturization magnetization is observed in M vs H measurements between 11 and 30 T due to saturization of the monomers. For fields above the plateau, the magnetic field energy exceeds the dimer bonding and thus the dimers cant and then align with the field. The magnetic structure and the detailed phase diagram in temperature and field are largely unknown or controversial. A recent report [1] in the specific heat behavior suggests a more complicated structure than previously thought. In addition, recent ultrasound measurements [2] indicate significant magnetoelastic coupling must be taken into account. We have acquired interesting results on magnetic torque, magnetostriction and thermal expansion. We have demonstrated that significant, anisotropic magnetostriction is evidenced in azurite, giving us an indication of the magnetically induced structural distortions.
  • Poster
    RHMF09 (Research on High Magnetic Fields 2009), 22.-25.07.2009, Dresden, Deutschland
  • Poster
    Perspectives in Highly Frustrated Magnetism (PHMF10), 19.-23.04.2010, Dresden, Deutschland

Publ.-Id: 13058 - Permalink

Spin Dynamics in the Model Spin-ladder Compound (C5H12N)2CuBr4 Probed with ESR
Zvyagin, S.;
In first part of my presentation I will talk about recent development of the high-fi eld electron spin resonance (ESR) facility at the Dresden High Magnetic Field Laboratory. The unique feature of the facility is a combination of the free electron laser (1.2 – 75 THz) and pulsed (up to 65 T) magnetic fields. In the low-frequency range the FEL facility is complemented by conventional radiation sources allowing for ESR experiments down to 30 GHz. In second part of my talk I will present results of ESR studies of the spin-ladder compound (C5H12N)2CuBr4 (known as BPCB). Angular, temperature dependences, as well as the frequency-fi eld diagram of magnetic excitations have been studied in detail. The energy gap in center of the Brillouin zone (16.46 K), was observed directly, confirming the presence of the Dzyaloshinskii-Moriya interaction. A small (~140 mK) splitting between the gapped modes can be accounted by a weak interladder coupling. In addition, the temperature evolution of the ESR excitation spectrum revealed a highly unusual behavior, whose peculiarities are discussed.
  • Invited lecture (Conferences)
    RHMF09 (Research on High Magnetic Fields 2009), 22.-25.07.2009, Dresden, Deutschland

Publ.-Id: 13057 - Permalink

High-field magnetization of Er2(Co0.4Fe0.6)17
Skourski, Y.; Andreev, A. V.; Kuz´Min, M. D.; Wosnitza, J.;
The quasibinary intermetallic compound Er2(Co0.4Fe0.6)17 (hexagonal Th2Ni17-type structure) is a ferrimagnet with TC = 1170 K and Ms = 21 μB/f.u. The magnetic anisotropy is of easy-axis type at low temperatures, changing to an easy-plane anisotropy near room temperature. In the present work, the magnetization was measured in fields up to 60 T along the easy c axis. A first-order transition was observed at 47 T with a magnetization jump of 9 μB/f.u. Er2(Co0.4Fe0.6)17 is an ideal model system for high-field experiments since the observed transition admits an unambiguous quantitative interpretation. This is because the compound also undergoes a first-order magnetization process at 1.5 T enabling an independent direct determination of the anisotropy constants. A further advantage is the smallness of the 3d contribution to the anisotropy, which can be neglected altogether. With these parameters the observed high-field magnetization curve was successfully modeled.
  • Poster
    ICM09 (International Conference on Magnetism 2009), 26.-31.07.2009, Karlsruhe, Deutschland

Publ.-Id: 13056 - Permalink

Ultrasonic investigation of the quasi-2D quantum antiferromagnet Cs2CuCl4
Zherlitsyn, S.; Sytcheva, A.; Wosnitza, J.; Zvyagin, A. A.; Chiatti, O.; Coldea, R.;
We report results of sound-velocity and sound-attenuation measurements in the triangularlattice quasi-two-dimensional spin-1/2 antiferromagnet (AFM) Cs2CuCl4 (TN = 0.6 K) in magnetic fields up to 18 T applied along the a axis. The possibility for a Bose-Einstein condensation of magnons in the AFM phase and a proximity to the spin liquid state at low temperatures beyond the AFM phase has been suggested for this compound. The longitudinal acoustic c11 mode shows pronounced anomalies in sound velocity and sound attenuation at low temperatures and in applied magnetic field. Below 1.5 K, this mode demonstrates a softening with increasing field, followed by an increase of the sound velocity close to the saturation field, Bs approx 8.5 T. The ultrasonic results are analyzed with a theory based on exchange-striction coupling. There is good qualitative agreement between theoretical results and experiment.
  • Poster
    ICM 09 (International Conference on Magnetism), 26.-31.07.2009, Karlsruhe, Deutschland

Publ.-Id: 13055 - Permalink

Multiband superconductivity in YNi2B2C single crystals studied by use of specific-heat measurements
Bekkali, A.; Wosnitza, J.; Uhlarz, M.; Beyer, R.; Schneider, M.; Behr, G.; Drechsler, S.-L.; Fuchs, G.;
We present new specific-heat data for two different YNi2B2C single crystals grown by a zone-melting method. The two samples (Tc,A = 15.26(4)K, Tc,B = 15.6(1) K) were studied in magnetic fields up to B = 9 T in the temperature range from T = 0.35 . . . 20 K, using both a relaxation and a heat-pulse method. In the superconducting state (B = 0) we find an uncommon dependence of the electronic contribution to the specific heat, Cel(T), strengthening the assumption of a multiband nature of the superconducting state of YNi2B2C. A quantitative analysis of Cel(T) evidences multiple electronic contributions from electrons with very different electron-phonon coupling strengths, thus exhibiting several different superconducting energy gaps Δ(T,B = 0). This feature is in agreement with recent de Haas–van Alphen results [1] and point-contact spectroscopy data [2].
  • Poster
    RHMF 09 (Research on High Magnetic Fields 2009), 22.-25.07.2009, Dresden, Deutschland

Publ.-Id: 13054 - Permalink

High-field properties of spin-1/2 frustrated square lattice compounds
Tsirlin, A.; Schmidt, B.; Skourski, Y.; Nath, R.; Weickert, F.; Geibel, C.; Rosner, H.;
Quantum spin systems present a broad range of exotic phenomena upon the application of external magnetic field. High-field properties of numerous low-dimensional Heisenberg models are actively studied theoretically, but still poorly understood experimentally due to the lack of proper materials with feasible saturation fields. Recently, we proposed a bundle of vanadium compounds that show the physics of spin-1/2 frustrated square lattice model at the energy scale of 5–10 K. In this contribution, we present experimental results for high-field properties of these materials.
Magnetization curves of five frustrated square lattice compounds were recorded in either static or pulsed magnetic fields. Most of the compounds show the saturation at 15–25 T and present the ideal energy scale for high-field studies. The values of the saturation fields are in remarkable agreement with the previous estimates of individual exchange couplings, based on thermodynamic measurements in low fields. The consistency of the low-field and high-field results confirms the interpretation of the materials within the frustrated square lattice model, despite the actual crystal symmetry is low, and numerous non-equivalent exchange couplings are possible. The change of the frustration ratio within the same compound family enables to study the change of the magnetization curve as the frustration is enhanced. We show that the increase of the frustration ratio leads to the enhanced bending of the magnetization curve. This result agrees with the recent theoretical study of the model [1] and is further supported by the direct comparison of the experimental magnetization curves and simulations for finite-size clusters.
  • Poster
    RHMF 09 (Research on Hihg Magnetic Fields 2009), 22.-25.07.2009, Dresden, Deutschland

Publ.-Id: 13053 - Permalink

Deviations from the conventional BCS behavior in the penetration depth of LuNi2B2C films at terahertz frequencies
Fischer, T.; Pronin, A. V.; Wosnitza, J.; Lobo, R. P. S. M.; Niemeyer, T.; Holzapfel, B.;
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.
  • Poster
    RHMF 09 (Research on High Magnetic Fields 2009), 22.-25.07.2009, Dresden, Deutschland

Publ.-Id: 13052 - Permalink

NMR in pulsed magnetic fields
Meier, B.; Haase, J.; Braun, M.; Bartkowiak, M.; Herrmannsdörfer, T.; Wosnitza, J.;
The first observation of NMR in the pulsed high magnetic field at the Hochfeld-Magnetlabor Dresden (HLD), Forschungszentrum Dresden-Rossendorf (FZD) is reported. The new spectrometer that operates at up to 3:0 GHz is described, as well as its implementation in the pulsed field facility. Free induction decays and spin echo experiments on 1H and 63,65Cu will be described and discussed in terms of sensitivity and resolution.
  • Poster
    RHMF 09 (Research in High Magnetic Fields), 22.-25.07.2009, Dresden, Deutschland

Publ.-Id: 13051 - Permalink

Field induced phases in UPtSi2
Schulze Grachtrup, D.; Süllow, S.; Bleckmann, M.; Willenberg, B.; Mydosh, J.; Skourski, Y.; Rakoto, H.; Bartkowiak, M.; Sheikin, I.;
Tetragonal UPtSi2 has recently been characterized as moderately mass enhanced antiferromagnetic compound, which in various physical properties and in low magnetic fields reveals a resemblance to URuSi2 [1-3]. In contrast to URuSi2 with the order parameter still unknown, UPtSi2 was shown to order antiferromagnetically below TN = 32 K in zero magnetic field [1]. Here, we present an extensive study of the behaviour of UPtSi2 in high magnetic fields. We have examined single crystalline UPtSi2 with resistivity and magnetization measurements in pulsed and static magnetic fields up to 50 T. Initially, and as it is typical for antiferromagnets, in these measurements we find the antiferromagnetic phase transition at TN = 32 K in zero field to shift downwards with increasing field for both crystallographic axes. However, below ~15 K and for magnetic fields B parallel to the a axis we see this transition to split up, forming a new and distinct high field phase between ~38 T and 45 T. Similarly, with the magnetic field applied parallel to the c axis we also find a splitting resulting in a new high field phase between 24 T and 31 T. Moreover, below 5 K our measurements along c axis show even more structure, indicating the presence of at least one more high field phase between 29 T and 33 T. Altogether, our data reveal a rich high field magnetic phase diagram, which closely resembles the observations made for URuSi2 [4]
  • Poster
    RHMF 09 (Research in High Magnetic Fields 2009), 22.-25.07.2009, Dresden, Deutschland

Publ.-Id: 13050 - Permalink

Porous steel surfaces produced by plasma immersion ion implantation
Shevchenko, N.; Kolitsch, A.;
Plasma immersion ion implantation (PIII) using helium or argon plasmas has been employed for porous layers creation on metal surfaces. These void structures may show unique characteristics which offer potential for medical applications such as metal-based drug-eluting stents. The paper addresses the influence of implantation parameters on surface morphology, cavity characteristics and mechanical properties of stainless steel stents. Argon and/or helium PIII processing of stainless steel samples has been performed at ion energies ranging from 5 to 35 keV, ion fluence of more than 1e17 cm-2, and substrate temperature in the range 50 – 400°C. Scanning electron microscopy, grazing incidence X-ray diffraction analysis, X-ray photoelectron spectroscopy, and elastic recoil detection analysis have been employed for sample characterization. Argon PIII treatment at elevated temperatures of 200 – 350°C leads to spongy structure formation of a size of 1-2 micron. Helium implantation results in a surface roughening and creation of voids in high concentration with size in the range 300 – 500 nm as well as nano-scale cavities (5-50 nm). So, varying the ion species (helium or argon), ion energy and fluence, and substrate temperature has been found to produce either void or sponge like structures at the nano- (~10 nm) to micro-scale (~1 micron). The best mechanical properties have been obtained in the stainless steel samples implanted at elevated temperature (higher than 250°C). Surface flaking and cracks formation have been greatly reduced by subsequent post-implantation annealing at temperatures of 600 – 800°C.
Keywords: Plasma immersion ion implantation, porous layers, stainless steel, structure
  • Poster
    International Conference on Physical Mesomechanics and Computer-Aided Design and Development of Advanced Materials, 08.-11.09.2009, Tomsk, Russia

Publ.-Id: 13049 - Permalink

Aluminum incorporation in Ti1-xAlxN films studied by x-ray absorption near-edge structure
Gago, R.; Redondo-Cubero, A.; Endrino, J. L.; Jimenez, I.; Shevchenko, N.;
The local bonding structure of titanium aluminum nitride (Ti1-xAlxN) films grown by dc magnetron cosputtering with different AlN molar fractions (x) has been studied by x-ray absorption near-edge structure (XANES) recorded in total electron yield mode. Grazing incidence x-ray diffraction (GIXRD) shows the formation of a ternary solid solution with cubic structure (c-Ti1-xAlxN) that shrinks with the incorporation of Al and that, above a solubility limit of x similar to 0.7, segregation of w-AlN and c-Ti1-xAlxN phases occurs. The Al incorporation in the cubic structure and lattice shrinkage can also be observed using XANES spectral features. However, contrary to GIXRD, direct evidence of w-AlN formation is not observed, suggesting a dominance and surface enrichment of cubic environments. For x>0.7, XANES shows the formation of Ti-Al bonds, which could be related to the segregation of w-AlN. This study shows the relevance of local-order information to assess the atomic structure of Ti1-xAlxN solutions.
Keywords: local bonding structure, Ti1-xAlxN, XANES, GIXRD

Publ.-Id: 13048 - Permalink

[Ni(phen)(fum)]: an S = 1 two-dimensional quantum magnet
Orendacova, A.; Cizmar, E.; Pavlova, A.; Kajnakova, M.; Uhlarz, M.; Wosnitza, J.; Orendac, M.; Cernak, J.; Feher, A.;
[Ni(phen)(fum)] comprises of weakly bound covalent-layers containing Ni(II) ions forming a spatially anisotropic square lattice with pronounced intradimer exchange coupling. Susceptibility studies performed from 1.8 to 300 K revealed significant differences between field and zero-field cooling below 10 K suggesting the presence of easy-axis anisotropy. Specific heat, investigated in zero magnetic field from 0.3 to 20 K, did not reveal any lambda-like anomaly only a tiny hump was observed at about 1.2 K. The amount of magnetic entropy removed down to 1.2 K supports the notion of magnetic low dimensionality. The specific-heat data are dominated by a round anomaly at 4.2 K which was analyzed within limiting models of a paramagnet with E/D = 0.27 and D/kB = -13.4 K and antiferromagnetic S = 1 dimers with D/J = -0.8 and D/kB = -5.3 K. The analysis indicates the importance of introducing an interdimer coupling responsible for the formation of magnetic order on the square lattice.
  • Poster
    ICM 2009 (The International Conference on Magnetism), 26.-31.07.2009, Karlsruhe, Deutschland

Publ.-Id: 13047 - Permalink

Slow spin relaxation in the Heisenberg antiferromagnet Gd2(fum)3(H2O)4·3H2O induced by magnetic field
Sedlakova, L.; Orendac, M.; Cizmar, E.; Orendacova, A.; Zvyagin, S. A.; Wosnitza, J.; Gao, S.;
The spin relaxation of Gd2(fum)3(H2O)4·3H2O, an S = 7/2 Heisenberg antiferromagnet was investigated by ac-susceptibility measurements at temperatures from 2 to 30 K, frequencies from 100 Hz to 10 kHz, and magnetic fields up to 3 T. It was found, that the magnetic field induces thermally activated relaxation over an energy barrier EB/kB approx 55 K. Subsequent investigation of the specific heat, magnetic entropy, magnetization, and shape of the electron-spin-resonance line yielded consistent values of the g-factor g = 2.0, single-ion anisotropy D/kB approx 0.23 K, and exchange interaction J/kB approx 0.12 K. The knowledge of these characteristic parameters allows to discuss the origin of the observed relaxation behavior. In particular, resonance trapping of low-energy phonons, recently proposed in Ni10 magnetic molecules [1] will be considered.
  • Poster
    ICM 2009 (The International Conference on Magnetism), 26.-31.07.2009, Karlsruhe, Deutschland

Publ.-Id: 13046 - Permalink

ESR Study of the Spin-Ladder Compound (C5H12N)2CuBr4
Cizmar, E.; Ozerov, M.; Wosnitza, J.; Zvyagin, S. A.; Thielemann, B.; Rüegg, C.; Klanjsek, M.; Horvatic, M.; Berthier, C.;
A systematic multi-frequency electron spin resonance (ESR) study of the spin-ladder material (C5H12N)2CuBr4 (known as BPCB) and its deuterated analog have been performed at temperatures down to 1.3 K in magnetic fields up to 16 T. The energy gap in the magnetic excitation spectrum at k = 0, Delta/kB = 16.45 K, was observed directly, confirming the existence of Dzyaloshinskii-Moriya interaction in this compound. A small (» 140 mK) splitting between the levels of the excited spin-triplet confirmed the presence of a weak interladder coupling. The temperature evolution of the ESR excitation spectrum in BPCB revealed its very unusual behavior, whose origin is discussed.
  • Poster
    ICM 2009 (The International Conference on Magnetism), 26.-31.07.2009, Karlsruhe, Deutschland

Publ.-Id: 13045 - Permalink

The Dresden High Magnetic Field Laboratory (HLD), a User Facility for Advanced Pulsed-Field Experiments
Herrmannsdörfer, T.; Wosnitza, J.; Zherlitsyn, S.; Zvyagin, S.;
Since 2007, the Dresden High Magnetic Field Laboratory operates as a user facility, providing unique experimental capabilities in pulsed fields. The HLD offers a variety of measurement 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, cyclotron and electron spin resonance (ESR) in pulsed fields. Additionally, experimental techniques such as nuclear magnetic resonance (NMR) and calorimetry are being adapted for their use in pulsed magnetic fields. The HLD maintains design programs for pulsed-power supplies and pulsed magnets focusing on the development of benchmark equipment for scientific and industrial use as well. Recently, the HLD has reached magnetic fields of up to 87 T. This field range is accessible now for experiments in advanced materials research. Several 60 T and 70 T magnets are regularly used by in-house and external users as well. A two-coil 100 T prototype and a long-pulse (1000 ms) 60 T magnet are ready for their first tests. The HLD participates in the EuroMagNET II program, a coordinated research initiative which supports users of European high-magnetic field installations. The in-house research program of the FZD is dedicated to electronically correlated systems, comprising material classes such as heavy-fermion compounds, novel and high-Tc superconductors, confined metallic nanostructures and low-dimensional spin systems as well.
  • Poster
    RHMF 09 (Research in High Magnetic Fields 2009), 22.-25.07.2009, Dresden, Deutschland

Publ.-Id: 13044 - Permalink

Quantum oscillations in the superconducting state of LuNi2B2C
Bergk, B.; Ignatchik, O.; Maniv, T.; Zhuravlev, V.; Canfield, P.; Wosnitza, J.;
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 at high magnetic fields up to 15 T and at low temperatures down to 0.5 K. Starting in the normal state we were able to observe dHvA oscillations deep inside the superconducting state with only a minor additional damping of the oscillation amplitudes. Only close to the upper critical field we find a slightly stronger damping. However, in this region we also observe a strong peak effect which hampers the analysis and complicates the interpretation. We compare our results with recent theories and discuss the possibilities of determining the magnetic-field-dependent gap for different bands with this method. Nevertheless, the apparent correlation between the occurence of the peak effect and the extra damping might be attributet to suppression of vortex-lattice order associated with the enhanced flux-line pinning in this region.
  • Poster
    RHMF09 (Research in High Magnetic Fields), 22.-25.07.2009, Dresden, Deutschland

Publ.-Id: 13043 - Permalink

Sound-Wave Anomalies in UCuGe
Yasin, S.; Sytcheva, A.; Wosnitza, J.; Zherlitsyn, S.; Andreev, A.;
The hexagonal compound UCuGe is an antiferromagnet (AFM) with TN = 48 K. In this study we report on results of sound-velocity and sound-attenuation measurements performed on a single crystal of UCuGe at different frequencies, in the temperature range 1.3 K > T > 295 K, and in a magnetic fields up to 18 T applied along the c axis (hard axis). The temperature dependences of the sound velocity and attenuation display a pronounced anomaly at TN suggesting a large magnetoelastic coupling. A double-peak structure is observed in the sound velocity at TN which might be due to frustration. In the paramagnetic state (T > TN), both acoustic characteristics show large frequency-dependent changes revealing the presence of unusual relaxation processes. No hysteresis in the field dependence of the sound velocity in the AFM state is observed confirming that the compound UCuGe has a single-domain state.
  • Poster
    ICM 09 (International Conference On Magnetism 2009), 26.-31.07.2009, Karlsruhe, Deutschland

Publ.-Id: 13041 - Permalink

Infrared spectroscopy of La2-xEuxCuO4
Pronin, A. V.; Lobo, R. P. S. M.; Wosnitza, J.; Tsukada, A.; Naito, M.;
We report on measurements of the complex conductivity of LaEuCu-oxide super-conductors in a wide frequency range (10 - 50000 cm-1) and for temperatures 4 K < T < 300 K. High-quality films on transparent substrates have been used for the investigations. We discuss the temperature and frequency behavior of the complex conductivity for several samples with different Eu concentrations.
  • Poster
    ICM 09 (International Conference On Magnetism 2009), 26.-31.07.2009, Karlsruhe, Deutschland

Publ.-Id: 13040 - Permalink

Fractional chain-end effects in quasi-one-dimensional S = 1 material NTNB: electron spin resonance studies
Ozerov, M.; Kamenskyi, D.; Cizmar, E.; Wosnitza, J.; Zvyagin, S. A.; Long, V. C.; Willet, R. D.;
We report on X-band electron spin resonance studies (ESR) of the quasi-one-dimensional anisotropic S = 1 Heisenberg antiferromagnet compound Ni(tn)2NO2BF4 (or NTNB for short). The presence of interacting S = 1/2 chain-end states is clearly observed in the ESR spectra even in nominally pure samples, visible as a g ~ 2 main peak with several satellites. The data are analyzed in the frame of the theory proposed by Batista et al. [Phys. Rev. B 60, R12533 (1999)]. The ESR angular dependence revealed a pronounced anisotropy, whose origin can be explained assuming the presence of the field-induced staggered magnetization.
  • Poster
    ICM 09 (International Conference on Magnetism 2009), 26.-31.07.2009, Karlsruhe, Deutschland

Publ.-Id: 13039 - Permalink

High-field ESR and magnetization study of [Cu(pyz)2(HF2)]PF6: an S = 1/2 quasi-two-dimensional Heisenberg magnet
Cizmar, E.; Ozerov, M.; Skourski, Y.; Beyer, R.; Uhlarz, M.; Zvyagin, S. A.; Schlueter, J. A.; Manson, J. L.; Wosnitza, J.;
Electron spin resonance and magnetization studies of the quasi-two-dimensional spin system [Cu(pyz)2(HF2)]PF6 have been performed in static and pulsed magnetic fields up to 50 T. It is argued that the magnetization is governed by the two-dimensional nature of spin correlations due to the large anisotropy of the exchange couplings (J_perp/J = 0.01, where J is the in-plane and J_perp is the interlayer exchange parameters). The magnetization saturates at the critical fields 37.1 T and 34.3 T for magnetic field applied perpendicular and parallel to the direction, respectively. The frequency-field diagram of the magnetic excitations changes dramatically below the Néel temperature (TN = 4.38 K). Our observation reveals an easy-plane type of the magnetic anisotropy. The exchange field (HE = 18.5 T) and out-of-plane anisotropy field (HA = 0.05 T) were calculated using a mean-field-theory approximation.
  • Poster
    RHMF09 (Research in High Magnetic Fields 2009), 22.-25.07.2009, Dresden, Deutschland

Publ.-Id: 13038 - Permalink

Superconducting Phase Diagram of Rh17S15
Uhlarz, M.; Ignatchik, O.; Wosnitza, J.; Naren, H. R.; Thamizhavel, A.; Ramakrishnan, S.;
Rh17S15 (Miasite) is a 4d-electron metal which displays superconductivity below Tc = 5.4 K at zero field, with an upper critical field value Bc2 = 19.2 T at T = 0.07 K. Above Tc, Rh17S15 is a paramagnet. The crystallographic structure (Pm3m) of Rh17S15 features a nearest-neighbor Rh-Rh distance even less than in elementary (fcc) Rh, resulting in a high density of 4d-electron states at the Fermi level [1]. In our contribution, we report on measurements of the specific-heat and resistivity in fields up to 14 T and of the magnetic susceptibility in fields up to 20 T of a polycrystalline sample of Rh17S15. Our data allow us to map out the complete superconducting phase diagram. The existence of narrow 4d band states (and thus of strong electronic correlations that seem not to provide magnetic correlations) is supported by the found moderately high electronic contribution to the specific-heat of about 100 mJ/molK2 and favors the existence of a strong superconducting interaction. Together with the remarkably high upper critical field (exceeding the Pauli limit by a factor of two), these facts make Rh17S15 a likely candidate for unconventional superconductivity.
  • Poster
    RHMF09 (Research in High Magnetic Fields 2009), 22.-25.07.2009, Dresden, Deutschland

Publ.-Id: 13037 - Permalink

Superconductivity in Ga-doped Germanium
Skrotzki, R.; Herrmannsdörfer, T.; Heera, V.; Ignatchik, O.; Uhlarz, M.; Mücklich, A.; Posselt, M.; Reuther, H.; Schmidt, B.; Heinig, K.-H.; Skorupa, W.; Voelskow, M.; Wündisch, C.; Helm, M.; Wosnitza, J.;
We report the first observation of superconductivity in heavily p-type doped germanium at ambient pressure conditions. Using Ga as dopant, we have produced a series of Ge:Ga samples by ion-beam implantation and subsequent short-term (msec) flash-lamp annealing. The combination of these techniques allows for Ga concentrations up to 6 %, i.e., a doping level which is clearly larger than the solubility limit and not accessible to any other method so far. Transport measurements reveal superconducting transitions with Tc up to 0.5 K. In more detail, we observe a strong dependence of the superconducting critical parameters on the annealing conditions. Further, we find a strong anisotropy of the superconducting critical field reflecting the two-dimensional character of the superconducting state in the ~ 60 nm thin Ge:Ga layer. We find critical magnetic in-plane fields following a linear temperature dependence up to a maximum field which is even larger than the Pauli-Clogston limit. Ge:Ga appears to be a superconductor in the extreme type-II limit with a very small Cooper-pair density. After its finding in Si [1] and diamond [2], our work reports another unexpected observation of superconductivity in doped elemental semiconductors.
  • Poster
    RHMF09 (Research in High Magnetic Fields 2009), 22.-25.07.2009, Dresden, Deutschland

Publ.-Id: 13036 - Permalink

de Haas-van Alphen study of the mixed-valence compound YbCoIn5
Polyakov, A.; Ignatchik, O.; Bianchi, A.; Prevost, B.; Seyfarth, G.; Fisk, Z.; Hurt, D.; Goodrich, R. G.; Wosnitza, J.;
The interplay between conduction and localized electrons in mixed-valence materials has received great attention and remain to be a hot topic. The de Haas-van Alphen (dHvA) technique in combination with band-structure calculations is one of the best methods to investigate the multiband Fermi surfaces inherently present in these compounds. Here, we present a dHvA study of the nonmagnetic mixed-valence compound YbCoIn5. This material has the same crystal structure as the heavy-fermion superconductors CeCoIn5 and CeIrIn5 [1,2]. Our dHvA measurements thus allow a comparative investigation of the electronic properties of these highly interesting isostructural compounds. The dHvA signal was measured by use of a capacitive torque cantilever in a He3 cryostat in fields up to 13 T as well as in a dilution refrigerator down to 20 mK and up to 18 T. A number of different dHvA branches could be resolved. Besides their angular dependence, we as well determined the effective masses of the different bands by following the temperature-dependent amplitude change of the dHvA oscillations. In contrast to the heavy fermions CeCoIn5 and CeIrIn5, the effective masses for YbCoIn5 are in the range from 0.7 to 2.0 m0.
  • Poster
    RHMF09 (Research in High Magnetic Fields 2009), 22.-25.07.2009, Dresden, Deutschland

Publ.-Id: 13035 - Permalink

Specific heat of the highly anisotropic antiferromagnet [Cu(pyz)2(HF2)]PF6
Beyer, R.; Uhlarz, M.; Schlueter, J. A.; Manson, J.; Wosnitza, J.;
The metal-organic compound [Cu(pyz)2(HF2)]X with X = PF6 exhibits a quasi-cubic lattice of copper ions (S = ½), but the magnetic properties show a predominantly two-dimensional (2D) nature due to a large anisotropy in the exchange couplings. The magnetic entropy and the antiferromagnetic ordering, eventually occurring at about 4 K, were investigated by specific-heat measurements. For this we established a continuous relaxation-time technique, using a single relaxation process to get specific-heat data over a wide temperature range. The calorimetric investigations, performed between 2 and 100 K and in magnetic fields up to 14 T, have revealed a non-monotonic field dependence of the ordering temperature. The results are as expected from the model for an S = ½ two-dimensional square-lattice quantum Heisenberg antiferromagnet with an additional weak interlayer exchange (via Cu-F-H-F-Cu bonds). In comparison to the X = BF4 compound, the antiferromagnetically ordered phase extends into much higher temperatures. In a more detailed analysis, we can extract all exchange interactions with an interlayer coupling ten times higher than in X = BF4. Thus, the 2D character is significantly reduced in X = PF6.
  • Poster
    RHMF09 (Research in High Magnetic Fields 2009), 22.-25.07.2009, Dresden, Deutschland

Publ.-Id: 13034 - Permalink

Upper critical fields and magnetic phase diagram of F-doped LaFeAsO
Jun Sung, K.; Kremer, R.; Bartkowiak, M.; Wosnitza, J.;
The high-Tc superconductivity in ReFeAsO1−xFx (Re=Rare earths) with a maximum Tc of about 55 K has attracted great interest. LaFeAsO1−xFx is the first-discovered superconducting compound in this class of materials, and has been intensively studied so far. We have performed resistivity measurements on polycrystalline samples of LaFeAsO1−xFx with different Tc’s and obtained the superconducting-to-normal state transition at various temperatures with 60 T pulsed magnetic fields. At the normal state, the under-doped samples show a positive magnetoresistivity ~ 30% at 60 T while for the optimally-doped sample, the magnetoresitivity effect is almost negligible. In the superconducting state, the magnetoresistance shows a broad transition, which is often observed in polycrystalline samples consisting of randomly oriented anisotropic grains. The temperature dependence of Hc2 (T) for all LaFeAsO1−xFx samples with different Tc’s do not follow the conventional Werthammer-Helfand-Hohenberg (WHH) behavior, and shows an almost linear temperature dependence down to ~ 0.1 Tc. A strong deviation of Hc2 (T) from the WHH prediction will be discussed in terms of a multiband effect and a Pauli paramagnetic limiting effect.
  • Poster
    RHMF09 (Research in High Magnetic Fields 2009), 22.-25.07.2009, Dresden, Deutschland

Publ.-Id: 13033 - Permalink

Untersuchungen zu Redoxprozessen von Uran in Mischkulturbiofilmen und spektroskopische Verifizierung von ultradünnen Mineralüberzügen auf „Depleted Uranium“ mit Laser- Fluoreszenz- Techniken
Arnold, T.; Großmann, K.; Baumann, N.;
Particles of U(V) and U(VI) were observed in vivo in a living multispecies biofilm by a combined laser-induced fluorescence spectroscopy (LIFS) and confocal laser scanning microscopy (CLSM) approach. The fluorescent uranium particles were located at the bottom and at the edges of biofilms colonies and ranged in size from up to 20 µm in length to 7 µm in width. Laser fluorescence spectroscopy was applied to identify these uranium particles. They showed either a characteristic fluorescence spectrum in the wavelength range of 415-475 nm, indicative for U(V), or in the range of 480-560 nm, which is typical for U(VI). The particles of U(V) as well as U(VI) were simultaneously observed in the biofilms. For U(VI) the particles were attributed to biologically mediated precipitation and for U(V) to redox processes taking place within the biofilm. The detection of U(V) in a living multispecies biofilm was interpreted as a short-lived intermediate of the U(VI) to U(IV) redox reaction. The presence of U(V) clearly shows that the U(VI) reduction is not a two electron step but that only one electron is involved.
LIFS was also applied to study the alteration of a depleted uranium (DU) disk in contact with synthetic pore water. The pore water used was a calcium phosphate solution (2.5 × 10-3 M Ca, 1 × 10-3 M P) and should mimic fertilized agricultural soil. The storage of the DU disk in calcium phosphate solution for 12 month led to the formation of a thin film of a secondary uranium mineral on the metallic DU. Time-resolved laser-induced fluorescence spectroscopy (TRLFS) was applied to spectroscopically characterise the reaction product. TRLFS provided its unequivocal identification as meta-autunite based on the positions of the fluorescence emission maxima at 487.8, 502.0, 523.6, 547.0, 572.1, and 600.6 nm and fluorescence lifetimes of 410 ± 15 and 3300 ± 310 ns. These results highlight the enhanced performance and sensitivity of the TRLFS technique for mineralogical characterization of thin surface films. Furthermore, they demonstrate that the dissolution of uranium from DU projectiles under the conditions described here is limited by the development and solubility of a meta-autunite secondary phase.
  • Invited lecture (Conferences)
    15. Tagung Festkoerperanalytik, 12.-16.07.09, Chemnitz, Deutschland

Publ.-Id: 13031 - Permalink

Wear-resistant Ti–B–N nanocomposite coatings synthesized by reactive cathodic arc evaporation
Neidhardt, J.; Czigány, Z.; Sartory, B.; Tessadri, R.; Mitterer, C.;
Wear-resistant Ti–B–N coatings have been deposited by reactive arc evaporation of Ti–TiB2 compound cathodes in a commercial Oerlikon Balzers Rapid Coating System. Owing to the strong non-equilibrium conditions of the deposition method, a TiN–TiBx phase mixture is observed at low N2 partial pressures, as determined by elastic recoil detection analysis, X-ray diffraction, X-ray spectroscopy, transmission electron microscopy and selected area electron diffraction. The indicated formation of a metastable solid solution of B in face-centered cubic TiN gives rise to a maximum in hardness (>40 GPa) and wear resistance on the expense of increased compressive stresses. A further saturation of the nitrogen content results in the formation of a TiN–BN nanocomposite, where the BN phase fraction was tailored by the target composition (Ti/B ratio of 5/3 and 5/1). However, the amorphous nature of the BN phase does not support self-lubricious properties, showing friction coefficients of 0.7 ± 0.1 against alumina. The effect of an increased bias voltage on structure and morphology was investigated from -20 to -140 V and the thermal stability assessed in Ar and air by simultaneous thermal analysis up to 1400 °C.

Publ.-Id: 13030 - Permalink

First Hexanuclear U(IV) and Th(IV) Formate Complexes - Structure and Stability Range in Aqueous Solution
Takao, S.; Takao, K.; Kraus, W.; Emmerling, F.; Scheinost, A. C.; Bernhard, G.; Hennig, C.;
The actinide(IV) hexanuclear M6(mu3-O(H))8(HCOO)12(LT)6 complexes were prepared (LT = H2O or CH3OH). HCOO- acts as a bridging ligand, which prevents formation of polynuclear hydrolysis species of U(IV) hydrous oxide colloids at least until pH 3.25, and stabilizes the nano-sized clusters in solution. The charge of the hexamer is balanced by the O/OH ratio of the mu3-bridges.
Keywords: actinides, polynuclear species, formic acid, solution, XAFS

Publ.-Id: 13029 - Permalink

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