Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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31629 Publications
A high-resolution time-of-flight mass spectrometer for the detection of ultracold molecules
Kraft, S. D.; Mikosch, J.; Staanum, P.; Deiglmayr, J.; Lange, J.; Fioretti, A.; Wester, R.; Weidemüller, M.;
We have realized a high-resolution time-of-flight mass spectrometer combined with a magneto-optical trap. The spectrometer enables excellent optical access to the trapped atomic cloud using specifically devised acceleration and deflection electrodes. The ions are extracted along a laser beam axis and deflected onto an off-axis detector. The setup is applied to detect atoms and molecules photoassociated from ultracold atoms. The detection is based on resonance-enhanced multiphoton ionization. Mass resolution up to m/Delta m = 1000 at the mass of 133^Cs is achieved. The performance of this spectrometer is demonstrated in the detection of photoassociated ultracold 7^Li133^Cs molecules near a large signal of 133^Cs ions.
  • Applied Physics B 89(2007), 453

Publ.-Id: 10788 - Permalink

Numerical Simulations of the onset of dynamo action with a hybrid finite volume/ boundary element method (FV-BEM)
Giesecke, A.; Stefani, F.;
The experimental realization of dynamo excitation as well as theoretical and numerical examinations of the induction equation have shown the relevance of boundary conditions and material properties for a self-sustaining dynamo. Generally, in non-spherical geometry typical insulating boundary conditions are described by elaborated schemes (e.g. solving of the Laplace equation in an extended domain) or by simplifying approximations (pseudo vacuum). A different approach is provided by a modified integral equation procedure, commonly known as the boundary element method (BEM). Integrating the Laplace equation on the boundaries allows to overcome the difficulties of the non-local character of insulating boundary conditions and the direct computation of the magnetic field next to an insulator becomes possible. However, within the interior of a field producing domain geometric constraints or varying material properties (e.g. electrical conductivity of the container walls or localized high-permeability material) might also play a role. For this problem, a more flexible approach utilizing a local discretization like the constraint transport (CT) method as a well known realization of a finite volume scheme is recommendable. The CT-scheme ensures a fast, robust and accurate solution of the kinematic dynamo problem and intrinsically maintains the solenoidal character of the magnetic field. Combining both methods in a hybrid FV-BEM scheme offers the flexibility of a local discretization with a stringent treatment of insulating magnetic boundary conditions in arbitrary geometries. Preliminary simulations of an alpha^2-Dynamo in a cartesian box and/or the decay of an initial magnetic field demonstrate the applicability of the approach.
Further examinations are intended to understand the behavior of the VKS-dynamo experiment where the field producing flow is driven by ferrous propellers and the dynamo mechanism probably is dominated by this high permeability material.
Other applications of the hybrid scheme may also be important for the evaluation of forthcoming dynamo experiments
for which a precise knowledge of the critical magnetic Reynolds number is essential.
  • Lecture (Conference)
    10th MHD Days, 26.-29.11.2007, Garching, Germany

Publ.-Id: 10787 - Permalink

Role of Four-Quark Condensates in QCD Sum Rules
Thomas, R.; Hilger, T.; Kämpfer, B.;
The QCD sum rule approach to the in-medium behavior of hadrons is discussed for omega meson, nucleon and D meson.
Emphasis is devoted to the impact of four-quark condensates and to order parameters of spontaneous symmetry breaking.

Publ.-Id: 10786 - Permalink

Characterization of hybrid amorphous-partially crystalline thin films
Martin, N.; Hamann, C.; McCord, J.; Fassbender, J.ORC; Quandt, E.; Gerber, A.; Bigall, N.; Eychmüller, A.; Schultz, L.
Amorphous FeCoBSi thin films with uniaxial anisotropy have been laterally structured by Co ion implantation into stripe arrays. The resulting multiphase samples were investigated regarding the magnetic properties. Hysteresis measurements revealed a large increase in coercivity of the implanted areas. By means of TEM investigations this could be attributed to formed crystallites in the amorphous matrix. Magneto-optical imaging was used to correlate the domain structure to the magnetic hysteresis. It is demonstrated that stripe orientation with respect to the magnetic easy axis governs the coupling between implanted and non implanted areas.
Keywords: magnetism, ion implantation, hybrid materials, crystalization, magnetic microscopy
  • Poster
    72. Jahrestagung der DPG und DPG Frühjahrstagung des Arbeitskreises Festkörperphysik, 25.-29.02.2008, Berlin, Germany

Publ.-Id: 10785 - Permalink

The influence of non centric holes on the magnetization dynamics of Landau structures
Wintz, S.; Kuepper, K.; Buess, M.; Raabe, J.; Quitman, C.; Fassbender, J.ORC
Magnetic vortex cores are attracted and can be trapped by artificial defects. If more than one of such defects are created a switching between different vortex core trapped states, which might serve as discrete levels in a multivalent memory device, can be achieved. Up to now a number of studies of circular vortex structures comprising holes has been reported, e. g. [1,2,3]. We report the imaging of the magnetic excitation spectrum in presence of holes, fabricated by focussed ion beam milling, in the magnetic domains and domain walls of Landau structures by means of x-ray magnetic circular dichroism photoemission electron microscopy (XMCD-PEEM). Due to the very high lateral and temporal resolution the magnetization dynamics and the corresponding Eigen modes, which are characteristic for the vortexhole interaction, are investigated in detail. The experimental results are compared to micromagnetic simulations.

[1] M. Rahm et al., Appl. Phys. Lett. 85, 1553 (2004).
[2] T. Uhlig et al., Phys. Rev. Lett. 95, 237205 (2005).
[3] F. Hoffmann et al., Phys. Rev. B 76, 014416 (2007).
Keywords: magnetism, magnetization dynamics, vortex, Landau structure, holes, defects
  • Lecture (Conference)
    72. Jahrestagung der DPG und DPG Frühjahrstagung des Arbeitskreises Festkörperphysik, 25.-29.02.2008, Berlin, Germany

Publ.-Id: 10784 - Permalink

Inclusive di-electron production in C+C collisions with HADES
Dohrmann, F.; Agakishiev, G.; Agodi, C.; Balanda, A.; Bellia, G.; Belver, D.; Belyaev, A.; Blanco, A.; Boehmer, M.; Boyard, J. L.; Braun-Munzinger, P.; Cabanelas, P.; Castro, E.; Chernenko, S.; Christ, T.; Destefanis, M.; Diaz, J.; Dohrmann, F.; Dybczak, A.; Eberl, T.; Fabbietti, L.; Fateev, O.; Finocchiaro, P.; Fonte, P.; Friese, J.; Froehlich, I.; Galatyuk, T.; Garzon, J. A.; Gernhaeuser, R.; Gilardi, C.; Golubeva, M.; Gonzalez-Diaz, D.; Grosse, E.; Guber, F.; Heilmann, M.; Hennino, T.; Holzmann, R.; Ierusalimov, A.; Iori, I.; Ivashkin, A.; Jurkovic, M.; Kaempfer, B.; Kanaki, K.; Karavicheva, T.; Kirschner, D.; Koenig, I.; Koenig, W.; Kolb, B. W.; Kotte, R.; Kozuch, A.; Krizek, F.; Kruecken, R.; Kuehn, W.; Kugler, A.; Kurepin, A.; Lamas-Valverde, J.; Lang, S.; Lange, J. S.; Lopes, L.; Maier, L.; Mangiarotti, A.; Marin, J.; Markert, J.; Metag, V.; Michalska, B.; Mishra, D.; Moriniere, E.; Mousa, J.; Muentz, C.; Naumann, L.; Novotny, R.; Otwinowski, J.; Pachmayer, Y. C.; Palk! A, M.; Pechenov, V.; Pechenova, O.; Cavalcanti, T. P.; Pietraszko, J.; Przygoda, W.; Ramstein, B.; Reshetin, A.; Roy-Stephan, M.; Rustamov, A.; Sadovsky, A.; Sailer, B.; Salabura, P.; Schmah, A.; Simon, R.; Spataro, S.; Spruck, B.; Stroebele, H.; Stroth, J.; Sturm, C.; Sudol, M.; Tarantola, A.; Teilab, K.; Tlusty, P.; Traxler, M.; Trebacz, R.; Tsertos, H.; Veretenkin, I.; Wagner, V.; Wen, H.; Wisniowski, M.; Wojcik, T.; Wuestenfeld, J.; Yurevich, S.; Zanevsky, Y.; Zumbruch, P.;
Inclusive di-electron production in C+C collisions at 1 and 2 AGeV has recently been measured by the HADES collaboration at GSI. Results are compared to a di-electron cocktail calculated from free hadron pi0, eta, omega decays after freeze-out. For the low invariant masses, M(e+e-) < 0.15 GeV/c2, the measured distributions are largely explained by the pi0 --> e+e- gamma Dalitz decay but for higher masses experimental yields significantly exceed expectations.
Keywords: In-medium properties of hadrons, heavy-ion collisions
  • Contribution to proceedings
    MENU2007 11th International Conference on Meson-Nucleon Physics and the Structure of the Nucleon, 10.-14.09.2007, Jülich, Germany
    Proceedings of the 11th International Conference on Meson-Nucleon Physics and the Structure of the Nucleon, SLAC, 67


Publ.-Id: 10783 - Permalink

Modification of magnetic order in Mn5Si3 and Mn5Ge3 by C ion implantation
Sürgers, C.; Joshi, N.; Montbrun, R.; von Löhneysen, H.; Potzger, K.; Möller, W.;
Antiferromagnetically ordered Mn5Si3 can be driven ferromagnetic by incorporation of carbon into the voids of Mn octahedra of the hexagonal structure. While for Mn5Si3Cx polycrystals the Curie temperature saturates for x > 0.22 at TC = 152 K [1], sputtered Mn5Si3C0.8 films exhibit a TC above room temperature [2]. An enhancement of TC is also found after C doping of the isostructural compound Mn5Ge3 which is currently in the focus of possible spintronic applications. In an alternative approach, Mn5Si3Cx and Mn5Ge3Cx films were prepared by implantation of 45 - 195 keV C+ ions into Mn5Si3 or Mn5Ge3 films at elevated temperatures. The carbon-implanted samples exhibit magnetic properties very similar to their respective magnetron-sputtered counterparts as inferred from magnetization and resistivity measurements.
Keywords: Magnetic semiconductors, Implantation, Mn5Ge3
  • Lecture (Conference)
    72. Jahrestagung der DPG und DPG Frühjahrstagung des Arbeitskreises Festkörperphysik, 25.-29.2.2008, Berlin, Germany

Publ.-Id: 10782 - Permalink

Magnetic anisotropies in ferromagnetic and exchange-coupled systems on rippled surfaces
Liedke, M. O.; Liedke, B.; Marko, D.; Keller, A.; Muecklich, A.; Facsko, S.; Fassbender, J.ORC; Cizmar, E.; Zvyagin, S.; Wosnitza, J.
The influence of a surface and interface modulation on the magnetic properties of ferromagnetic materials (Py, Fe and Co) and an exchange bias system (Py/FeMn) is studied. A periodic surface modulation (the so-called ripples) is achieved by low energy ion erosion. Subsequently the magnetic stack is deposited. Due to the film morphology a strong uniaxial anisotropy is induced in the ferromagnetic layers, which is fixed in its orientation along ripples elongation. In the case of the exchange bias system the direction of the induced unidirectional anisotropy can be varied by means of different field annealing cycles. For all mutual orientations both anisotropy contributions are superimposed independently. The angular dependence of the magnetization reversal behavior can be described perfectly by a coherent rotation model [1]. In addition, the magnitude of the uniaxial and the unidirectional anisotropy scales with the step density or wave length of the rippled substrate, which is in full agreement with theoretical predictions.

[1] M. O. Liedke et al., Phys. Rev. B 75, 220407(R) (2007)
Keywords: exchange bias, ripples, ion erosion, exchange coupling, Py, FeMn, Co, Fe, magnetic anisotropy
  • Lecture (Conference)
    72. Jahrestagung der DPG und DPG Frühjahrstagung des Arbeitskreises Festkörperphysik, 25.02.2008, Berlin, Germany

Publ.-Id: 10781 - Permalink

Magnetic microstructures produced by local ion irradiation induced interfacial mixing
Strache, T.; Grenzer, J.; Fassbender, J.ORC; Möller, W.; Kaltofen, R.; Mönch, I.
Ion irradiation of Ni80Fe20/Ta multilayers induces an interfacial mixing of these two materials, which subsequently leads to a suppression of the ferromagnetic properties. In order to quantify the structural change grazing incidence x-ray reflectometry has been used. The ion irradiation induced intermixing has been studied by means of TRIDYN simulations. The broadening of the interfaces due to intermixing causes an enrichment of Ta in Ni80Fe20 and finally an amorphization of Ni80Fe20 above a Ta concentration of 10 to 20 percent [1]. Consequently the ferromagnetic properties are altered or even suppressed completely for high enough ion fluences. It is observed that the critical ion fluence for a complete suppression of the ferromagnetism depends sensitively on the number of interfaces. It is demonstrated that pure magnetic microstructures can be easily fabricated by local ion irradiation without changing the substrate topography.

[1] J. Fassbender et al., Nucl. Instr. and Meth. in Phys. Res. B 248, 343 (2006).
Keywords: magnetism, ion irradiation, amorphization, irradiation induced mixing, magnetic microstructures
  • Lecture (Conference)
    72. Jahrestagung der DPG und DPG Frühjahrstagung des Arbeitskreises Festkörperphysik, 25.-29.02.2008, Berlin, Germany

Publ.-Id: 10780 - Permalink

Facile synthesis of various nitro-substituted derivatives of semaxinib (SU 5416)
Knieß, T.; Kuchar, M.; Wüst, F.;
The synthesis of novel nitro-substituted derivatives of the tyrosine kinase inhibitor SEMAXINIB (SU 5416) is described. The reaction of various substituted oxindoles with 3,5-dimethylpyrrol-2-carbaldehyde derivatives under Knoevenagel conditions gave an array of nitro-substituted derivatives of Semaxinib (SU 5416) in high yields of 72-87%.
Keywords: Nitration, semaxinib, tyrosine kinase

Publ.-Id: 10779 - Permalink

Surface improvement and biocompatibility of TiAl24Nb10 intermetallic alloy using rf plasma nitriding
Abd El-Rahman, A. M.; Maitz, M. F.; Kassem, M. A.; El-Hossary, F.; Prokert, F.; Reuther, H.; Pham, M. T.; Richter, E.;
The present work describes the surface improvement and biocompatibility of TiAl24Nb10 intermetallic alloy using rf plasma nitriding. The nitriding process was carried out at different plasma power from 400 W to 650 W where the other plasma conditions were fixed. Grazing incidence X-ray diffractometry (GIXRD), Auger electron spectroscopy (AES), tribometer and a nanohardness tester were employed to characterize the nitrided layer. Further potentiodynamic polarization method was used to describe the corrosion behavior of the un-nitrided and nitrided alloy. It has been found that the Vickers hardness (HV) and corrosion resistance values of the nitrided layers increase with increasing plasma power while the wear rates of the nitrided layers reduce by two orders of magnitude as compared to those of the un-nitrided layer. This improvement in surface properties of the intermetallic alloy is due to formation of a thin modified layer which is composed of titanium nitride in the alloy surface. Moreover, all modified layers were tested for their sustainability as a biocompatible material. Concerning the application area of biocompatibility, the present treated alloy show good surface properties especially for the nitrided alloy at low plasma power of 400 W.
  • Applied Surface Science 253(2007), 9067-9072

Publ.-Id: 10778 - Permalink

Radiolabeled glucocorticoids as molecular probes for imaging brain glucocorticoid receptors by means of positron-emission-tomography (PET)
Steiniger, B.; Knieß, T.; Bergmann, R.; Pietzsch, J.; Wüst, F.;
Over the last two decades, numerous attempts have been made to develop
11C- and 18F-labeled radiotracers in order to study glucocorticoid receptor (GR)-mediated abnormalities of the hypothalamus-pituitary-adrenocortical (HPA) axis function and regulation in vivo by means of positron emission tomography (PET). The present review wants to address the research efforts dealing with the design, radio-synthesis and radiopharmacological evaluation of PET radiotracers for brain GR im-aging. The underlying problems such as metabolic instability, insufficient blood-brain-barrier penetration and/or high non-specific binding will be discussed.
  • Mini-Reviews in Medicinal Chemistry 8(2008)7, 728-739

Publ.-Id: 10777 - Permalink

Ion irradiation induced local creation of ferromagnetism in Fe60Al40 alloys
Strache, T.; Liedke, M. O.; Fassbender, J.ORC; Möller, W.; Menendez, E.; Sort, J.; Gemming, T.; Weber, A.; Heyderman, L. J.; Rao, K. V.; Deevi, S. C.; Nogues, J.
Ion irradiation of Fe60Al40 alloys results in the phase transformation from the paramagnetic, chemically
ordered B2-phase to the ferromagnetic, chemically disordered A2-phase. The magnetic phase transformation is related to the number of displacements per atom (dpa) during the irradiation. For heavy ions (Ar+, Kr+, Xe+) a universal curve is observed with a steep increase in the fraction of ferromagnetic phase reaching saturation, i. e., a complete phase transformation, at about 0.5 dpa. This proves the purely ballistic nature of the disordering process. If light ions are used (He+, Ne+) a pronounced deviation from the universal curve is observed. This is attributed to bulk vacancy diffusion from dilute collision cascades, which leads to a partial recovery of the thermodynamically favored B2-phase. Comparing different noble gas ion irradiation experiments allows to asses the corresponding counteracting contributions. In addition, the potential to create local ferromagnetic areas embedded in a paramagnetic matrix is demonstrated.
Keywords: magnetism, ion irradiation, binary alloys, intermetallic, FIB, patterning
  • Lecture (Conference)
    72. Jahrestagung der DPG und DPG Frühjahrstagung des Arbeitskreises Festkörperphysik, 25.-29.02.2008, Berlin, Germany

Publ.-Id: 10776 - Permalink

Self-organized surface ripples as a source of magnetic anisotropies
Fassbender, J.ORC; Liedke, M. O.; Keller, A.; Facsko, S.; Marko, D.; Hanisch, A.; Grenzer, J.; Cizmar, E.; Zvyagin, S.
In thin film magnetism surface and interfacemorphologies are important sources of magnetic anisotropy. This can be either due to the reduced coordination of step edge atoms (intrinsic contribution) or due to magnetic stray fields emanating from the film corrugation (extrinsic contribution). Low energy ion erosion is perfectly suited to create a periodic surface modulation (so-called ripples) on the nanoscale. By changing the primary energy of the ions the ripple periodicities can be varied from 20 to 150 nm. Subsequently, thin magnetic films are deposited on these template systems in order to investigate the influence of the surface morphology on the induced magnetic anisotropies. For small ripple periodicities a strong uniaxial magnetic anisotropy is found which rapidly decrease for larger ripple periodicities. In the case of Permalloy (Ni81Fe19) the induced anisotropy can be more than a factor of 20 larger compared to the intrinsic anisotropy of flat Permalloy. The microscopic origin of this effect will be discussed.
Keywords: magnetism, ion erosion, self-organization, magnetic anisotropies, ferromagnetic resonance
  • Lecture (Conference)
    72. Jahrestagung der DPG und DPG Frühjahrstagung des Arbeitskreises Festkörperphysik, 25.-29.02.2008, Berlin, Germany

Publ.-Id: 10775 - Permalink

Magnetic thin film materials tailored by ion irradiation
Fassbender, J.ORC
In recent years the tailoring of magnetic properties by means of ion irradiation techniques has become fashionable.
Since the magnetic properties of multilayers depend sensitively on the mutual interfaces a modification of these interfaces by ion irradiation leads to a local modification of the magnetic anisotropy, the exchange bias or the interlayer exchange coupling [1,2]. Also structural phase transitions can be induced by ion irradiation. If these are accompanied by magnetic phase transformations ferromagnetic regions can immediately be written with a focused ion beam. In addition to pure radiation effects also doping effects can be exploited to achieve a pure magnetic patterning. Finally ion erosion of semiconductor substrates can be used as periodically modulated substrates which modify the magnetic anisotropies of subsequently deposited magnetic films.
Examples of all different approaches will be presented in order to demonstrate the large viability of ion beam technology to tailor magnetic materials.
Refs.: [1] J. Fassbender, D. Ravelosona,Y. Samson, J. Phys. D 37, R179 (2004). [2] J. Fassbender, J. McCord, J. Magn. Magn. Mater. 320, 579 (2008).
Keywords: magnetism, ion irradiation, FIB, self-organization, ripples
  • Invited lecture (Conferences)
    72. Jahrestagung der DPG und DPG Frühjahrstagung des Arbeitskreises Festkörperphysik, 25.-29.02.2008, Berlin, Germany

Publ.-Id: 10774 - Permalink

Absence of superconductivity in boron-implanted diamond
Heera, V.; Höhne, R.; Ignatchik, O.; Reuther, H.; Esquinazi, P.;
Recently, superconductivity has been found in heavily boron doped diamond prepared by high temperature/ high pressure synthesis or chemical vapour deposition. An alternative doping method of technological relevance is ion implantation. It is an open question whether superconductivity can also be obtained in boron implanted diamond. Here we report on the transport and magnetic properties of high-dose (2.3x1016-1.7x1017 cm-2) boron-implanted natural IIa diamond samples doped at elevated temperature of 900°C and subsequently annealed at 1500°C and 1700°C. For comparison implantation at room temperature was also carried out. The samples were further characterized by Raman and infrared spectroscopy. No superconductivity could be detected in the samples at temperatures down to 40 mK. We discuss the possible origin for the absence of superconductivity.
Keywords: diamond, boron implantation, implantation damage, graphitization, resistance, superconductivity, magnetic and electrical properties

Publ.-Id: 10773 - Permalink

Combining theoretical chemistry and XANES multi-edge experiments to probe actinide valence states
Fillaux, C.; Berthet, J.-C.; Conradson, S. D.; Guilbaud, P.; Guillaumont, D.; Hennig, C.; Moisy, P.; Roques, J.; Simoni, E.; Shuh, D. K.; Tyliszczak, T.; Castro-Rodriguez, I.; Den Auwer, C.;
Both structural and electronic properties of the actinide cations are of fundamental interest in order to describe the intramolecular interactions. The 5f and 6d orbitals are the first partially or totally vacant states of these elements and their properties reflect the nature of the actinideeligand bond. Because of its chemical and orbital selectivities, XANES spectroscopy is useful to probe the actinides’ frontier orbitals and then understand the cation reactivity toward chelating ligands. The actinide L3 edge contains structural information on the coordination polyhedron because of important scattering features. But very little electronic information can be extracted, due to the short core-hole lifetime, broadening the edge signal. On the other hand, the actinide M4,5 edges provide a better resolution and allow one to achieve electronic and structural information. Furthermore, coupling simulations of the experimental spectra and quantum chemical calculations lead to quantitative information such as the determination of the actinide coordination sphere and its effective charge. To cite this article: C. Fillaux et al., C. R. Chimie 10 (2007). 2007 Acade´mie des sciences. Published by Elsevier Masson SAS. All rights reserved.

Publ.-Id: 10772 - Permalink

RPV Material Investigation of the Former VVER-440 Greifswald NPP
Rindelhardt, U.; Viehrig, H.-W.; Konheiser, J.; Noack, K.; Schuhknecht, J.; Gleisberg, B.;
The real toughness response of RPV material can only be determined after the final shut down of the NPP. Such a chance is given now by investigating material from the former Greifswald NPP (VVER-440/230).
In the first part the paper deals with fast neutron fluence calculations and retrospective dosimetry based on Niobium. Unfortunately, a second neutron reaction besides 93Nb(n,n’) leading to 93mNb-activity is the reaction 92Mo(n,γ)93Mo. Based on the found Nb and Mo contents in the RPV material, it turns out that the 93mNb generation on the Mo path mostly dominates over the fast neutron induced generation from Nb.
The comparison between the calculated and the measured 93mNb activities typically resulted in deviations of 50%. Possible reasons for the observed differences are discussed.
In the second part first results of fracture mechanic investigations are reported. SE(B) specimens from three thickness positions were tested and evaluated according to the test standard ASTM E1921-05. Cleavage fracture toughness values, KJc, were determined and Master Curve based reference temperatures (T0) were evaluated. The T0 measured on the surface of this RPV does not show the highest value and, thus, reflect the conservative condition. The T0 of disc 1-1.3 located between the surface and ¼ thickness is about 40K higher compared with the surface.
The KJc values adjusted to a specimen thickness of 1T are enveloped by the WWER specific lower bound fracture toughness curve suggested in the VERLIFE procedure.
The measured KJc values are not enveloped by the 5% fractile indexed with T0 according to the Master Curve concept. However, the 5% fractile indexed with the VERLIFE reference temperature RTTo that includes an additional margin envelops the measured KJc values. Therefore the VERLIFE lower bound curve conservatively describes the fracture toughness of the investigated weld metal.
Keywords: VVER reactor, neutron fluence, Monte-Carlo calculation, retrospective dosimetry, neutron embrittlement, RPV material, Master Curve application.

Publ.-Id: 10771 - Permalink

P-Implantation in voramorphisiertes Ge und anschließende Temperung: Festphasen-Epitaxie, P-Diffusion und -Aktivierung
Posselt, M.; Schmidt, B.; Anwand, W.; Grötzschel, R.; Heera, V.; Wündisch, C.; Skorupa, W.; Hortenbach, H.; Gennaro, S.; Bersani, M.; Giubertoni, D.; Möller, A.; Bracht, H.;
For details please contact the first author
Keywords: germanium, ion implantation, annealing, phosphorus, diffusion, activation
  • Lecture (Conference)
    38. Treffen der Nutzergruppe Ionenimplantation, 09.11.2007, Dresden, Germany

Publ.-Id: 10770 - Permalink

The truth about ferromagnetic ZnO
Potzger, K.; Zhou, S.; Talut, G.; Kuepper, K.; Reuther, H.; Mücklich, A.; Grenzer, J.; Helm, M.; Fassbender, J.ORC; Schmidt, H.; Xu, Q.; Lorenz, M.
The combination of magnetic and semiconducting properties in oxides is currently one of most popular fields in materials research. Besides the expected gain of knowledge about basic physics, such materials have a large application potential in spin electronics. We present a summary of our results on transition metal doping of ZnO single crystals and thin films by means of ion implantation. We found that none of the samples investigated represents a diluted magnetic semiconductor as predicted by theory [1]. Nevertheless, transition metal ions can be dispersed within the ZnO matrix residing on different sites within the lattice depending on initial preparation conditions. The observed ferromagnetism mainly originates from secondary phase formation (metals or inverted spinels). We discuss the potential of those granular structures in spin-electronics. Moreover, we highlight the suppression of secondary phase formation by means of deliberately lowering the crystalline quality prior to the doping. In that case, purely defect induced ferromagnetic properties are observed. The effect of spin doping of such a defect induced ferromagnet is discussed.
[1] K. Sato and H. Katayama-Yoshida, Physica E 10, 251 (2001).
Keywords: Diluted magnetic semiconductors, ZnO, functional oxides
  • Invited lecture (Conferences)
    72. Jahrestagung der DPG und DPG Frühjahrstagung des Arbeitskreises Festkörperphysik, 25.-29.2.2008, Berlin, Germany

Publ.-Id: 10769 - Permalink

Fifty Years of radiopharmacy at Rossendorf
Spies, H.; Steinbach, J.;
The Central Institute of Nuclear Research was founded in Rossendorf near Dresden in 1956 and the production of radioactive materials and radiopharmaceuticals was started in 1958. The basis for the production was the irradiation of targets in the Rossendorf research reactor and, to a lower extent, at the Rossendorf cyclotron U-120.

This paper gives an account of the accomplishments of Rossendorf in the field of radiopharmacy from the early fifties, in the former department of 'Radioactive Isotopes', till to date. The production of radiopharmaceuticals is reviewed in brief. Investigations in technetium chemistry and pharmacology are discussed in more details, and efforts to set up positron emission tomography (PET) in Rossendorf, as the first PET centre in the former Eastern Block, are described. Nowadays, the research in radiopharmacy is carried out within the well-equipped Institute of Radiopharmacy, established in 1992.
  • Journal of Labelled Compounds and Radiopharmaceuticals 50(2007), 895-902
    DOI: 10.1002/jlcr.1431

Publ.-Id: 10768 - Permalink

Simultaneous determination of beta nuclides by liquid scintillation spectrometry
Nebelung, C.; Jähnigen, P.; Bernhard, G.;
The determination of radionuclides in environmental samples is of importance, because a large amount of hazardous radionuclides have been released into the biosphere and spread over large areas by weapon tests, releases from nuclear power plants or nuclear fuel reprocessing facilities. Many nuclides are radiotoxic even in small concentrations. Therefore, it is necessary to determine these nuclides at low levels. The usual way to analyze samples of several nuclides involves time-consuming chemical separations followed by activity measurement of the isolated nuclides. An alternative method is the simultaneous measurement of the nuclides by recording and analyzing the liquid scintillation spectra.
The nuclides 3H, 14C, 55Fe, 60Co, 90Sr, 99Tc, 137Cs were measured in various combinations of mixtures as well as with the TRICARB 3000 and Wallac1414a/b (both devices from PerkinElmer).
The TRICARB 3000 was used to measure up to three nuclides in one sample with the assay type dpm (triple) with a good accuracy even for large activity differences and beta energies close together. It is necessary to generate quench curves for each nuclide.
The multi nuclide spectra measured in the cpm mode in the Wallac1414 were deconvoluted with the knowledge of the shape of the single nuclide spectra [1]. In this case has to be considered the difference between the measured and fitted counts (cpm) and the real activity (dpm) subsequentlyThe spectra deconvolution allows to determine more than three nuclides in one sample but with a lower accuracy.
[1] C. Nebelung et al. 2007 Appl. Radiat. Isot. 65, 209-217
Keywords: liquid scintillation, beta-nuclide, beta-spectrum, deconvolution
  • Lecture (Conference)
    LSC 2008, Advances in Liquid Scintillation Spectrometry, 25.-30.05.2008, Davos, Switzerland
  • Contribution to proceedings
    LSC 2008, International Conference on Advances in Liquid Scintillation Spectrometry, 25.-30.05.2008, Davos, Switzerland
    Book of Abstracts, Villigen Schweiz: PSI Paul Scherrer Institut
  • Contribution to proceedings
    LSC 2008, International Conference on Advances in Liquid Scintillation Spectrometry, 25.-30.05.2008, Davos, Switzerland
    Radiocarbon 2009, Tucson, USA: University of Arizona, 978-0-9638314-6-0, 193-201

Publ.-Id: 10767 - Permalink

Das Hochfeld-Magnetlabor in Dresden – 100 Tesla für die Forschung
Herrmannsdörfer, T.; Wosnitza, J.;
  • Physik in unserer Zeit 38(2007), 242-248

Publ.-Id: 10766 - Permalink

Quasiparticle Model of Quark-Gluon Plasma at Imaginary Chemical Potential
Bluhm, M.; Kämpfer, B.;
A quasiparticle model of the quark-gluon plasma is compared with lattice QCD data for purely imaginary chemical potential. Net quark number density, susceptibility as well as the deconfinement border line in the phase diagram of strongly interacting matter are investigated. In addition, the impact of baryo-chemical potential dependent quasiparticle masses is discussed. This accomplishes a direct test of the model for non-zero baryon density. The found results are compared with lattice QCD data for real chemical potential by means of analytic continuation and with a different (independent) set of lattice QCD data at zero chemical potential.
Keywords: quasiparticle model, imaginary chemical potential
  • Physical Review D 77(2008), 034004

Publ.-Id: 10765 - Permalink

Photoactivation of 92Mo and investigation of the short-lived isomer in 91Mo with the new pneumatic delivery system at ELBE
Erhard, M.; Bemmerer, D.; Beyer, R.; Crespo, P.; Fauth, M.; Grosse, E.; Junghans, A. R.; Klug, J.; Kosev, K.; Rusev, G.; Schilling, K. D.; Schwengner, R.; Wagner, A.;
The photodisintegration cross section of the nucleus 92Mo is important for p-process nucleosynthesis. The superconducting electron accelerator ELBE at Forschungszentrum Dresden-Rossendorf provides the possibility to investigate photodisintegration with bremsstrahlung using the photoactivation technique. The reaction 92Mo(gamma,p)91Nb was studied using the decay of 91mNb with a 60.9 d half-life at ELBE [1]. Now the reaction 92Mo(gamma,n)91Mo has been probed using the new pneumatic delivery system to determine the activity of 91mMo (half-life: 65 s). Since the isomer 91mMo decays also into 91mNb it was necessary to measure this process to separate the (gamma,n) from (gamma,p) contributions.
[1] M. Erhard, C. Nair et al., PoS (NIC-IX) 056 (2006)
Keywords: photodisintegration, p-process, nucleosynthesis, bremsstrahlung, photoactivation, pneumatic delivery
  • Lecture (Conference)
    Frühjahrstagung der DPG, 2007, 13.03.2007, Gießen, Germany

Publ.-Id: 10764 - Permalink

Experimente mit reellen Photonen für die nukleare Astrophysik
Wagner, A.;
Experimente am ELBE Bescheuniger zur Photonenstreuung, Photoaktivierung wurden vorgestellt
  • Invited lecture (Conferences)
    Vortrag vor dem Fachbereich Physik der Technischen Universität Darmstadt, 31.10.2007, Darmstadt, Germany

Publ.-Id: 10763 - Permalink

Kerne und Sterne
Wagner, A.;
Vortrag vor der Astronomischen Arbeitsgemeinschaft Nürnberg e.V.
  • Lecture (others)
    Besuch der Nürnberger Astronomischen Arbeitsgemeinschaft, 02.11.2007, Dresden, Germany

Publ.-Id: 10762 - Permalink

Jahrestagung Kerntechnik - Sektionsbericht Sektion: Thermo- und Fluiddynamik
Stieglitz, R.; Kliem, S.;
Der Beitrag gibt einen Überblick über die in den Sitzungen der Sektion Thermo- und Fluiddynamik gehaltenen Vorträge.
  • atw - International Journal for Nuclear Power 52(2007)10, 652-654

Publ.-Id: 10761 - Permalink

Investigation of antimagnetic rotation in light Cadmium nuclei: Cd-106,Cd-108
Simons, A.; Wadsworth, R.; Jenkins, D.; Clark, R.; Cromaz, M.; Deleplanque, M.; Diamond, R.; Fallon, P.; Lane, G.; Lee, I.; Macchiavelli, A.; Stephens, F.; Svensson, C.; Vetter, K.; Ward, D.; Frauendorf, S.; Gu, Y.;
The lifetimes of excited states belonging to the lowest lying positive-parity bands in Cd-106,Cd-108 have been measured using the Doppler-shift attenuation method. The resulting B(E2) transition rates show a significant decrease with increasing spin in Cd-106, whereas in Cd-108 there is tentative evidence for a similar effect. The results are compared with cranking and semiclassical model calculations, which indicate that the structures have the properties expected from an "antimagnetic" rotational band resulting from the coupling of g(9/2) proton holes to aligned pairs of h(11/2) and g(7/2) neutron particles.
  • Physical Review C 72(2005), 024318

Publ.-Id: 10760 - Permalink

Evidence for Zn vacancy – hydrogen complexes in ZnO single crystals
Brauer, G.; Anwand, W.; Grambole, D.; Grenzer, J.; Skorupa, W.; Cizek, J.; Kuriplach, J.; Prochazka, I.; Ling, C. C.; So, C. K.; Schulz, D.; Klimm, D.;
A systematic study of various, nominally undoped ZnO single crystals, either hydrothermally grown (HTG) or melt grown (MG), has been performed. The crystal quality has been assessed by x-ray diffraction, and a comprehensive estimation of the detailed impurity and hydrogen contents by inductively coupled plasma mass spectrometry and nuclear reaction analysis, respectively, has been made also. High precision positron lifetime experiments show that a single positron lifetime is observed in all crystals investigated, which clusters at 180–182 ps and 165–167 ps for HTG and MG crystals, respectively. Furthermore, hydrogen is detected in all crystals in a bound state with a high concentration (at least 0.3 at. %), whereas the concentrations of other impurities are very small. From ab initio calculations it is suggested that the existence of Zn-vacancy–hydrogen complexes is the most natural explanation for the given experimental facts at present. Furthermore, the distribution of H at a metal/ZnO interface of a MG crystal, and the H content of a HTG crystal upon annealing and time afterward has been monitored, as this is most probably related to the properties of electrical contacts made at ZnO and the instability in p-type conductivity observed at ZnO nanorods in literature. All experimental findings and presented theoretical considerations support the conclusion that various types of Zn-vacancy–hydrogen complexes exist in ZnO and need to be taken into account in future studies, especially for HTG materials.
Keywords: zinc oxide, single crystal, positron lifetime, nuclear reaction analysis, X-ray diffraction, Inductively Coupled Plasma Mass Spectrometry, hydrogen, open volume defects, zinc vacancy-hydrogen complexes, ab initio calculations
  • Physical Review B 79(2009), 115212

Publ.-Id: 10759 - Permalink

Quantification of DNA double strand breaks
Beyreuther, E.;
Introduction and explanation of the quantification of DNA double strand breaks. First results measured for the time, dose and energy dependence for the induction of double strand breaks in cell line 184A1 are shown. Future plans are given.
  • Lecture (others)
    Seminar AG Mikrobiologie, 01.11.2007, Freiberg, Germany

Publ.-Id: 10758 - Permalink

Radiosynthesis of n.c.a. sodium [18F]fluoroacetate and radiopharmacological characterization in rats and tumour-xenografted mice
Richter, S.; Bergmann, R.; Pietzsch, J.; Beuthien-Baumann, B.; Wüst, F.;
A convenient remotely-controlled synthesis of no-carrier-added sodium [18F]fluoroacetate is described. Three ethyl esters 1a-1c and three tert.-butyl esters 3a-3c containing either a methanesulfonyloxy- (OMs), p-toluenesulfonyloxy- (OTs) or p-nitrobenzenesulfonyloxy (ONs) leaving group were investigated as labelling precursors. The optimized radiosynthesis of n.c.a. sodium [18F]fluoroacetate was performed in two steps: (1) Incorporation of fluorine into (methanesulfonyloxy)-acetic acid tert.-butyl ester 3a as the superior labelling precursor in acetonitrile at 100°C for 5 min followed by (2) acidic hydrolysis of the resulting [18F]fluoroacetic acid tert.-butyl ester at 100°C for 10 min to afford [18F]fluoroacetic acid. Several consecutive purification steps using anion exchange cartridges (Alltech Maxi-Clean SAX) and Sep-Pak neutral alumina cartridges gave sodium [18F]fluoroacetate in reproducible radiochemical yields of 20-25% (decay-corrected, n=20) in high radiochemical purity (>99%) within 50 min. Radiopharmacological characterization of sodium [18F]fluoroacetate was studied in Wistar rats and HT-29 tumour-bearing mice in comparison with [11C]acetate.
  • Current Radiopharmaceuticals 1(2008)2, 103-109

Publ.-Id: 10757 - Permalink

Characterization of sputtered Shape Memory Alloy Ni-Ti films by cross-sectional TEM and SEM
Martins, R. M. S.; Mücklich, A.; Schell, N.; Silva, R. J. C.; Mahesh, K. K.; Braz Fernandes, F. M.;
Characterization of sputtered Shape Memory Alloy Ni-Ti films by cross-sectional TEM and SEM
Keywords: shape memory alloy, Ni-Ti films TEM, SEM
  • Poster
    INCOMAM’07 - International Conference on Microscopy and Microanalysis - XLII Congress of the Portuguese Microscopy Society, 06.-07.12.2007, Coimbra, Portugal
  • Microscopy and Microanalysis 14(2008)supp 3, 85-86
    DOI: 10.1017/S1431927608089460

Publ.-Id: 10756 - Permalink

Spektroskopische Untersuchung der Uran(IV)- und Uran(VI)-Komplexierung mit organischen Modellliganden
Schmeide, K.; Joseph, C.; Raditzky, B.;
Spektroskopische Bestimmung von Stabilitätskonstanten für die U(VI)/U(IV)-Komplexierung durch Modellliganden
Keywords: Uran, hexavalent, tetravalent, Citronensäure, Benzolsulfonsäure, 4-Phenolsulfonsäure
  • Lecture (others)
    Workshop zum Forschungsvorhaben "Wechselwirkung und Transport von Actiniden im natürlichen Tongestein unter Berücksichtigung von Huminstoffen und Tonorganika", 11.-12.10.2007, Saarbrücken, Germany

Publ.-Id: 10755 - Permalink

Untersuchungen zur Isomerie des Komplexes [86Y((S) p NH2 bz DOTA)]-
Schlesinger, J.; Tamburini, S.; Bolzati, C.; Tisato, F.; Noll, B.; Bergmann, R.; Pietzsch, H.-J.;
Radioisotope des Yttriums und der Lanthaniden werden zu einer immer wichtigeren Komponente in medizinischen Applikationen, z. B. für die nicht-invasive in vivo-Bildgebung oder die Endoradionuklidtherapie von Tumorerkrankungen. Die Konjugation dieser dreiwertigen Metallionen an biologisch aktive Moleküle erfolgt in der Regel über bifunktionelle Chelatoren, z.B. 1,4,7,10-Tetraazacyclododecan-N,N’,N’’,N’’’-tetraessigsäure (DOTA). Die entsprechenden Metall-DOTA-Komplexe zeichnen sich durch eine hohe thermodynamische und kinetische in vivo Stabilität aus. Lanthaniden- und Yttrium-Komplexe optisch aktiver DOTA-Chelatoren treten jedoch als Konformationsisomere auf, über deren in vivo Verhalten, insbesondere über ihren Einfluss auf die markierten Moleküle nur wenig bekannt ist.

Zur Untersuchung der Isomerie des radioaktiven Komplexes [86Y((S) p NH2 bz DOTA)]- wurde der nicht-radioaktive, strukturell analoge Komplex [Y((S) p NH2 bz DOTA)]- synthetisiert und charakterisiert. Zwei Isomere des [Y((S) p NH2 bz DOTA)]- Komplexes wurden über die HPLC getrennt und mittels NMR- und CD-Messungen als Konformationsisomere identifiziert. Die Isomere liegen in einer quadratisch antiprismatischen (SAP) und einer verdrillt quadratisch antiprismatischen (TSAP) Geometrie vor.

Untersuchungen zur Bioverteilung der [86Y((S) p NH2 bz DOTA)]- Isomere in Wistar Ratten zeigten bereits nach 5 min unterschiedliche SUV-Werte (standardized uptake value) für beide Isomere in der Leber ((TSAP) 1,65 ± 0,45; (SAP) 0,50 ± 0,04). Der Vergleich der experimentell bestimmten logD7,0 Werte beider Isomere weist auf eine höhere Lipophilie des TSAP-Isomeren hin (logD7,0: (TSAP) -2,0 ± 0,029; (SAP) -2,3 ± 0,032). Bei der thermischen Behandlung der Isomere bei 90°C konnte auch nach 168 h keine gegenseitige Umwandlung beobachtet werden.

Die unterschiedlichen physikalischen Eigenschaften der [86Y((S) p NH2 bz DOTA)]- Konformationsisomere und deren unterschiedliche Bioverteilung zeigen, dass es unbedingt notwendig ist, den Einfluss der Chelateinheit auf das biologische Verhalten von Metallopharmaka zu berücksichtigen.
  • Poster
    Wissenschaftsforum Chemie 2007, GDCh-Jahrestagung, 16.-19.09.2007, Ulm, Germany

Publ.-Id: 10754 - Permalink

Growth and optical characterization of dielectric/metal nanocomposites
Baumgart, C.; Abendroth, B.; Abrasonis, G.; Kolitsch, A.; Möller, W.;
Thin films of Ag nanoclusters embedded in dielectric aC and SiO2 media have been prepared by pulsed cathodic arc and dual magnetron sputtering. The optical properties of the composite layers have been investigated by spectroscopic ellipsometry. The results show the dependence of the plasmon resonance band of the Ag particles from temperature and Ag concentration.
  • Lecture (Conference)
    VEIT 2007 - Fifttienth International Summer School on Vacuum, Electron and Ion Technologies, 17.-21.09.2007, Sozopol, Bulgaria

Publ.-Id: 10753 - Permalink

Quasifree Lambda, Sigma0, and Sigma- electroproduction from 1,2H, 3,4 He, and Carbon
Dohrmann, F.; Ahmidouch, A.; Armstrong, C. S.; Arrington, J.; Asaturyan, R.; Avery, S.; Bailey, K.; Baker, O. K.; Bitao, H.; Breuer, H.; Brown, D. S.; Carlini, R.; Cha, J.; Chant, N.; Christy, E.; Cochran, A.; Cole, L.; Crowder, J.; Danagoulian, S.; Elaasar, M.; Ent, R.; Fenker, H.; Fujii, Y.; Gan, L.; Garrow, K.; Geesaman, D. F.; Gueye, P.; Hafidi, K.; Hinton, W.; Juengst, H.; Keppel, C.; Liang, Y.; Liu, J. H.; Lung, A.; Mack, D.; Markowitz, P.; Mitchell, J.; Miyoshi, T.; Mkrtchyan, H.; Mtingwa, S. K.; Mueller, B.; Niculescu, G.; Niculescu, I.; Potterveld, D. H.; Raue, B. A.; Reimer, P. E.; Reinhold, J.; Roche, J.; Sarsour, M.; Sato, Y.; Segel, R. E.; Semenov, A. Y.; Stepanyan, S.; Tadevosian, V.; Tajima, S.; Tang, L.; Uzzle, A.; Wood, S.; Yamaguchi, H.; Yan, C.; Yuan, L.; Zeier, M.; Zeidman, B.; Zihlmann, B.;
Kaon electroproduction from light nuclei and hydrogen, using 1H, 2H, 3He, 4He, and carbon targets has been measured at Jefferson Laboratory. The quasifree angular distributions of Lambda and Sigma hyperons were determined at Q^2= 0.35 (GeV/c)^2 and W= 1.91 GeV. Electroproduction on hydrogen was measured at the same kinematics for reference.
Keywords: Electroproduction of Strangeness, Hyperons, Hypernuclear Physics

Publ.-Id: 10751 - Permalink

MOS light emitting devices based on rare-earth ion implantation
Rebohle, L.; Skorupa, W.;
In this article we will give an overview of our work to Si-based light emission which was done in the last years. Si-based light emitters were fabricated by ion implantation of rare earth elements into the oxide layer of a conventional MOS structure. Efficient electroluminescence was obtained for the wavelength range from UV to the visible by using a transparent top electrode made of indium-tin oxide. In the case of Tb-implantation the best devices reach an external quantum efficiency of 16 % which corresponds to a power efficiency in the order of 0.3 %. The properties of the microstructure, the IV characteristics and the electroluminescence spectra were evaluated. The electroluminescence was found to be caused by hot electron impact excitation of rare earth ions, and the electric phenomena of charge transport, luminescence centre excitation, quenching and degradation are explained in detail.
Keywords: Electroluminescence, Silicon-based light emission, Rare earth ion implantation
  • Contribution to external collection
    in: Advances in Light Emitting Materials, Stafa-Zurich: Trans Tech Publications Ltd, 2008, 117-138

Publ.-Id: 10749 - Permalink

The Influence of Natural and Manufactured Nanoparticles on Heavy Metal Behavior in Natural Waters
Zänker, H.; Schierz, A.;
A rapid development of the application of manufactured nanoparticles in science, technology, medicine and every day life is anticipated. Currently, there is still little knowledge about the behavior of manufactured nanoparticles in natural waters, their influences on the transport of organic pollutants, their effect on the behavior of toxic and radiotoxic heavy metals etc. Manufactured NPs are not yet present in the nature in significant amounts, i.e. “field studies” are not yet possible. However, conclusions by analogy based on the behavior of natural nanoparticles (natural colloids) can already be drawn. First, a very short introduction into the field of the detection of natural nanoparticles is given. The transport-impeding and the transport-facilitating effects of natural nanoparticles on heavy metal transport are analyzed. Examples are the immobilization of uranium by ferrihydrite nanoparticles in near-neutral mine waters during the flooding of an abandoned uranium mine and the mobilization of lead and arsenic by schwertmannite/H-jarosite nanoparticles in acid mine water from an abandoned Zn-Pb-Ag mine. The use of manufactured nanoparticles for the immobilization of heavy metals in natural waters is discussed. The adsorption of Pb2+, Cd2+, Cu2+ and UO22+ onto modified carbon nanotubes, synthetic ferrihydrite nanoparticles and titanium dioxide nanoparticles are considered with the focus on the carbon nanotubes. It is shown that all the nanoparticles considered have a potential for removing the above-mentioned heavy metal ions. A different point might be the challenge of gaining regulatory and public acceptance for using nanomaterials in water purification because of their still unknown or little known toxicity and environmental impact. The questions of the mobility of manufactured nanoparticles in natural waters and of potential transport-facilitating effects of artificial nanoparticles on heavy metals in case of accidental nanomaterial release are also addressed.
Keywords: Nanoparticles, carbon nanotubes, natural waters, contaminants, heavy metals, water purification
  • Lecture (Conference)
    Aquatic Nanoscience & Nanotechnology - bridging environmental nanosciences and nanotoxicology - 1st International workshop, 09.-11.12.2007, Wien, Austria

Publ.-Id: 10748 - Permalink

Generation of pulsed magnetic fields for synchrotron radiation experiments using a mobile pulsed-power supply
Herrmannsdörfer, T.;
no abstract available
Keywords: Pulsed magnetic fields, X-ray magnetic scattering
  • Invited lecture (Conferences)
    PETRA III Workshop: HighRes and RSD Beamlines, 27.-28.09.2007, DESY Hamburg, Germany

Publ.-Id: 10747 - Permalink

Switchable multi-color light emitter based on Eu implanted SiO2 layers confined in a MOS structure
Rebohle, L.; Prucnal, S.; Sun, J. M.; Helm, M.; Skorupa, W.;
Recent results regarding the electroluminescence properties of Si-based light emitters made by ion implantation are presented. The focus is on MOS structures either implanted with Eu or with Gd co-implanted with K or F.
  • Invited lecture (Conferences)
    Silicon to Light & Light to Silicon - Materials, Characterisation and Applications, 09.-10.07.2007, Halle, Deutschland

Publ.-Id: 10746 - Permalink

Switchable multi-color light emitter based on Eu-implanted SiO2 layers confined in a MOS structure
Rebohle, L.; Prucnal, S.; Sun, J. M.; Helm, M.; Skorupa, W.;
Si based light emitter become more and more important for the integration of optical and electrical function in one and the same chip. Among the various approaches rare earth (RE) implanted SiO2 layers confined in a MOS structure are especially promising due to the well-known optical properties of RE ions, the excellent material properties of the hosting SiO2 matrix and the full compatibility with current Si technology.
Here we report on the switchable multi-color electroluminescence (EL) from a MOS capacity doped with Eu. Depending on the electrical excitation conditions either the red narrow EL originating from a 4f inner shell transition of the Eu3+ ion or the blue broad emission from Eu2+ assigned to a 5d-4f electronic transition is dominant. The behavior of the EL spectrum as a function of the excitation and fabrication conditions is investigated, and the mechanisms behind will be discussed. The Si-based multi-color emitter introduces a new functionality into photonics and shows great potential for future micro-photonic applications.
  • Lecture (Conference)
    SEMINANO'07: 3rd International Workshop on Semiconductor Nanostructures, 13.-16.06.2007, Bad Honnef, Germany

Publ.-Id: 10745 - Permalink

Equation of State of Strongly Interacting Matter
Bluhm, M.;
Equation of State of Strongly Interacting Matter
  • Lecture (Conference)
    XXXVIII. Arbeitstreffen "Kernphysik", 22.02.-01.03.2007, Schleching, Germany

Publ.-Id: 10744 - Permalink

Complexation of uranium(VI) with aromatic acids in aqueous solution – A combined computational and experimental study
Wiebke, J.; Moritz, A.; Glorius, M.; Moll, H.; Bernhard, G.; Dolg, M.;
The complexes of uranium(VI) with salicylhydroxamate, benzohydroxamate, and benzoate have been investigated in a combined computational and experimental study using density functional theory methods and extended X-ray absorption fine structure spectroscopy, respectively. The calculated molecular structures, relative stabilities, as well as excitation spectra from time-dependent density functional theory calculations are in good agreement with experimental data. Furthermore, these calculations allow to identify the coordinating atoms in the uranium(VI)-salicylhydroxamate complex, i.e. salicylhydroxamate binds to the uranyl ion via the hydroxamic acid oxygen atoms and not via the phenolic oxygen and the nitrogen atom. Carefully addressing solvation effects has been found to be necessary to bring in line computational and experimental structures and excitation spectra.
Keywords: Uranyl - hydroxamic acid - density functional theory - EXAFS - spectroscopy
  • Inorganic Chemistry 47(2008)8, 3150-3157

Publ.-Id: 10743 - Permalink

QCD Equation of State - Impact on elliptic flow and transverse momentum spectra
Bluhm, M.;
QCD Equation of State - Impact on elliptic flow and transverse momentum spectra
  • Lecture (Conference)
    Heavy Ion Collisions at the LHC - Last Call for Predictions, 14.05.-08.06.2007, Genf, Switzerland

Publ.-Id: 10742 - Permalink

Dual-magnetron sputtering deposition of ferromagnetic FePt layers: in-situ x-ray investigations
Cantelli, V.; Grenzer, J.; von Borany, J.;
In this contribution it is discussed the use of the order parameter S as factor to judge the order degree of a L10 FePt layer grown at 350°C on a-SiO2. Because of the peculiar set-up of the deposition chamber, the FePt plasma is not thermalized, and energetic Ar ions allowed reducing the transition temperature, from the disorder to the order phase, to 350°C, for homogeneous 70 nm thick layers. The S parameter could be easily calculated by XRD measurements; therefore in-situ XRD could be applied to calculate the activation energy of the disorder order transformation. But, in the case of FePt layers deposited at low temperature, the evaluation of the degree of order (S parameter) in thin FePt layers is faulty and could cause to misleading data interpretations. Inconsistency was found between the high S values and the experimental FePt lattice parameters, which were showing a weaker deformation from the cubic to the tetragonal phase in respect to the theoretical values. This is explained in terms of low crystallinity degree and small grains size that are characteristic of the layer.
Keywords: Dual Magnetron sputtering, FePt, in-situ XRD
  • Lecture (others)
    Neue Entwicklungen in Röntgendiffraktometrie und -topographie, 24.04.2007, Frankfurt (Oder), Germany

Publ.-Id: 10741 - Permalink

Gluon Radiation of Heavy Quarks passing Deconfined Matter
Schade, H.;
Gluon Radiation of Heavy Quarks passing Deconfined Matter
  • Lecture (others)
    ITP, TU - Dresden, 23.06.2006, Dresden, Germany

Publ.-Id: 10740 - Permalink

Energy Loss of Charm Quarks Passing Hot Deconfined Matter
Schade, H.;
Energy Loss of Charm Quarks Passing Hot Deconfined Matter
  • Lecture (Conference)
    DPG Frühjahrstagung 2007, 13.03.2007, Gießen, Germany

Publ.-Id: 10739 - Permalink

Elemental analysis through X-ray techniques applied in archeological gold authentication — the case of Transylvanian gold and of the Dacian bracelets
Constantinescu, B.; Bugoi, R.; Cojocaru, V.; Simon, R.; Grambole, D.; Munnik, F.; Oberländer-Târnoveanu, E.;
To identify the provenance of gold archeological metallic artifacts, trace elements are more significant than the main components. The most promising elements are Platinum Group Elements (PGE), Sn, Sb, Hg, Pb, Te, and Cu. Several minute fragments of natural Transylvanian gold – placers and primary – were studied by micro Particle Induced X-ray Emission (micro-PIXE) at Forschungszentrum Dresden-Rossendorf, Germany and micro Synchrotron Radiation X-Ray Fluorescence (micro SR-XRF) at ANKA Synchrotron Radiation Facility of the Forschungszentrum Karlsruhe, Germany. The goal of the study was to identify the trace elements characterizing Transylvanian gold, especially Sn, Sb, Pb and Te. A spectacular application of these measurements to the authentication of nine Dacian gold bracelets is presented.
Keywords: micro-PIXE, micro SR-XRF, ED-XRF, archeological gold, Dacian bracelets, Transylvania
  • Poster
    ICXOM 2007, 19th International Congress on X-Ray Optics and Microanalysis, 16.-21.09.2007, Kyoto, Japan
  • Spectrochimica Acta Part B 64(2009), 1198-1203
    DOI: 10.1016/j.sab.2009.08.007

Publ.-Id: 10738 - Permalink

Quark mass dependence of 1-loop and HTL self-energies
Seipt, D.;
Quark mass dependence of 1-loop and HTL self-energies
  • Lecture (Conference)
    DPG Frühjahrstagung 2007, 13.03.2007, Gießen, Germany

Publ.-Id: 10737 - Permalink

Towards an EOS for the cold and dense QGP: plasmons, plasminos and Landau damping
Schulze, R.;
Towards an EOS for the cold and dense QGP: plasmons, plasminos and Landau damping
  • Lecture (Conference)
    Zimanyi 75 Memorial Workshop, 04.07.2007, Budapest, Hungary

Publ.-Id: 10736 - Permalink

QCD quasi-particle model with widths and Landau damping
Schulze, R.;
QCD quasi-particle model with widths and Landau damping
  • Lecture (Conference)
    DPG Frühjahrstagung 2007, 13.03.2007, Gießen, Germany

Publ.-Id: 10735 - Permalink

Density dependence of four-quark condensates: Impact on in-medium spectral properties
Kämpfer, B.;
Density dependence of four-quark condensates: Impact on in-medium spectral properties
  • Lecture (Conference)
    Quarks in Hadrons and Nuclei, 17.-23.09.2007, Erice, Italy

Publ.-Id: 10733 - Permalink

Non-perturbative aspects of QCD condensates
Hilger, T.;
Non-perturbative aspects of QCD condensates
  • Invited lecture (Conferences)
    Physics of Compressed Baryonic Matter - 10th CBM Collaboration Meeting, 25.-28.09.2007, Dresden, Germany

Publ.-Id: 10732 - Permalink

In-medium studies of omega, nucleon and open charm with QCD sum rules
Thomas, R.;
In-medium studies of omega, nucleon and open charm with QCD sum rules
  • Invited lecture (Conferences)
    Physics of Compressed Baryonic Matter - 10th CBM Collaboration Meeting, 25.-28.09.2007, Dresden, Germany

Publ.-Id: 10731 - Permalink

Nucleon and omega-Meson at Finite Density: The Role of Four-Quark Condensates in QCD Sum Rules
Thomas, R.;
Nucleon and omega-Meson at Finite Density: The Role of Four-Quark Condensates in QCD Sum Rules
  • Lecture (Conference)
    DPG Frühjahrstagung 2007, 13.03.2007, Gießen, Germany

Publ.-Id: 10730 - Permalink

Self-assembly FePt nanoislands: surface studies and magnetic properties
Cantelli, V.; von Borany, J.; Grenzer, J.;
L10 ordered, c-axis oriented FePt thin films belong to the most promising ferromagnetic materials for future magnetic storage media; but the coercive filed could be significantly improved if changing from homogeneous to granular films or even to FePt nanoislands arrays . This contribution describes the formation of self-assembled FePt nanoislands on amorphous SiO2/Si substrates by conventional DC magnetron sputtering. Ag is well known to follow the Volmer-Weber growth on SiO2: the as-deposited Ag islands are exploited as substrate for the FePt granular layer. If a characteristic ratio between Ag and FePt amonut is respected, no nano-islands agglomeration was observed after annealing at 450°C for 30 minutes. This effect is here explained in terms of thermal buget given to the system during deposition and the demand of a unimodal size distribution of the Ag nanoislands. From synchrotron x-ray GISAS investigations, the FePt islands have a pallet like shape with a 30 nm average diameter and 18 nm average height. SEM and AFM analysis didn't prove any order in the pallets placement over the SiO2. After annealing, the strong ferromagnetic L10 phase was detected by XRD. But, either SQUID or MFM measurements evidence no difference between a granular FePt layer without Ag and with Ag pallets as buffer, and an enhanced coercivity of FePt thin granular films has been confirmed, in comparison to thick homogeneous FePt layers.
Keywords: FePt, DC magnetron sputtering, Ag, nanoislands
  • Lecture (Conference)
    7th Autumn School on X-ray scattering from surfaces and thin layers, 04.-06.10.2007, Smolenice, Slovakia

Publ.-Id: 10729 - Permalink

Implantation of halogens to improve TiAl-components for high temperature applications,
Donchev, A.; Kolitsch, A.; Möller, W.; Schütze, M.; Yankov, R.;
No abstract available.
Keywords: TiAl alloys, halogen effect, oxidation resistance
  • Lecture (others)
    2nd Meeting of the International Advisory Committee of the Ion Beam Centre at FZD, 01.10.2007, Dresden, Germany

Publ.-Id: 10728 - Permalink

Fluorine surface treatment of TiAl alloys for aerospace applications
Donchev, A.; Kolitsch, A.; Schütze, M.; Yankov, R.;
No abstract available.
Keywords: TiAl alloys, halogen effect, oxidation resistance
  • Poster
    Euromat 2007 - European Congress on Advanced Materials and Processes, 10.-13.09.2007, Nürnberg, Germany

Publ.-Id: 10727 - Permalink

Oxidation-resistant TiAl alloys produced by plasma immersion ion implantation of fluorine
Yankov, R. A.; Kolitsch, A.; Steinert, M.; Donchev, A.; Schütze, M.;
Gamma-TiAl alloys (γ-TiAl) are a class of light-weight materials that hold great promise for advanced automobile, aerospace and power generation applications. Their use, however, has currently been limited to below 700°C because of inadequate resistance to oxidation at higher temperatures. Recent research work has established that dramatic enhancement in the high-temperature oxidation resistance of these alloys can be achieved by ion implanting halogens, notably fluorine. In the present study, samples of technical γ-TiAl alloys have been surface-modified by plasma immersion ion implantation (PIII) of fluorine using suitable F-containing precursor gases. Rutherford Backscattering Spectrometry, Elastic Recoil Detection Analysis and Auger Electron Spectrometry have been employed for sample characterization. The degree of oxidation protection has been assessed by testing F-implanted samples under conditions of isothermal oxidation in air at temperatures up to 1050°C. Optimum process parameters have been identified under which the modified alloys acquire a stable, adherent and highly protective alumina scale against high-temperature environmental oxidation.
Keywords: TiAl alloys, plasma immersion ion implantation, fluorine
  • Lecture (Conference)
    9th International Workshop on Plasma-Based Ion Implantation & Deposition, 02.-06.09.2007, Leipzig, Germany

Publ.-Id: 10726 - Permalink

Oxidation-resistant γ-TiAl alloys produced by ion implantation of fluorine
Yankov, R. A.; Kolitsch, A.; Rogozin, A.; Steinert, M.; Donchev, A.; Schütze, M.;
Gamma-TiAl alloys (γ-TiAl) are of great interest for advanced automobile, aerospace and power generation applications due to their light weight and high strength. However, destructive oxidation occurring in these materials at temperatures above 700°C has to date restricted their widespread use. It has recently been established that the high-temperature oxidation resistance of γ-TiAl alloys can be enhanced significantly by ion implanting halogens, notably fluorine. In this study, samples of technical γ-TiAl alloys have been surface-modified by either standard beamline ion implantation of fluorine or plasma immersion ion implantation using suitable fluorine-containing precursor gases. The degree of oxidation protection has been evaluated by testing ion implanted samples under conditions of both isothermal and thermal cyclic oxidation in air. Optimized ion implantation treatment produces marked improvement in the oxidation behavior of γ-TiAl. The alloys modified in this way acquire a stable, adherent and highly protective alumina scale against environmental oxidation while retaining the bulk mechanical properties of the starting material. Further improvements have been made in the oxidation resistance by co-implanting two additive elements, namely fluorine and silicon. Some of the most important process parameters that enable the formation of an efficient protective scale are considered and assessed.
Keywords: TiAl alloys, ion implantation, oxidation resistance, halogen effect
  • Poster
    E-MRS Spring Meeting, 28.05.-01.06.2007, Strasbourg, France

Publ.-Id: 10725 - Permalink

Improvement of the Oxidation Resistance of TiAl-Alloys with Fluorine
Donchev, A.; Richter, E.; Schütze, M.; Yankov, R.;
The technical TiAl-alloy γ-MET (Ti–46.5Al–4(Cr, Nb, Ta, B)) was oxidised thermocyclically (24 h-cycle-test) at 900 °C in wet and dry air. In this paper results of untreated and fluorine treated TiAl-samples are presented. Their oxidation behaviour will be shown. Several methods were used to apply the halogens to the surface, e.g. beamline ion implantation, spraying of or dipping into a halogen containing liquid. A pure protective alumina scale was found, e.g. after treatment with a fluorine containing polymer and thermocyclic oxidation up to 1 year at 900 °C in laboratory air. On the other side thick fast growing and non-protective mixed oxide scales were found on the untreated samples.
Keywords: Intermetallics; Oxidation; Metallography; Halogen effect; Titanium aluminides

Publ.-Id: 10724 - Permalink

Formation of a resonant microcavity in hydrogen ion-implanted silicon-on-insulator structures
Tyschenko, I. E.; Talochkin, A. B.; Bagaev, E. M.; Cherkov, A. G.; Popov, V. P.; Misiuk, A.; Yankov, R. A.;
Studies have been carried out on silicon-on-insulator (SOI) structures after the implantation of 24 keV, 3×10^17 cm−2 hydrogen ions, and annealing at temperatures of 200−1000 °C in an argon ambient at either atmospheric pressure or under conditions of hydrostatic compression at 6 and 12 kbar. Photoluminescence (PL), Raman spectroscopy, secondary ion mass spectrometry, and high-resolution electron microscopy have been used to characterize the optical and structural properties of the resulting SOI structures. It has been found that annealing at a pressure above 6 kbar leads to a wavelength-selective increase (up to 37×) in the intensity of the PL from hydrogen implanted SOI samples. The appearance of fine structure in the PL spectrum correlates with the impeded outdiffusion of hydrogen from the implanted top Si layer as well as with the suppressed process of hydrogen microbubble formation in the near-surface region as a result of the annealing at a pressure P>6 kbar. These processes enable one to fabricate an optical resonant microcavity with mirrors formed by the air/silicon and the top Si layer/SiO2 interfaces, and the optically active layer resulting from the implantation of hydrogen and the subsequent annealing. Theoretical calculations of the PL spectra in the resonator help explain some of the specific spectral features. The mechanism of the observed photoluminescence has been discussed in terms of recombination processes occurring in nanometer-sized amorphous silicon regions saturated with hydrogen.
Keywords: silicon-on-insulator, photoluminescence, optical resonant microcavity, hydrogen implantation
  • Journal of Applied Physics 102(2007), 074312

Publ.-Id: 10723 - Permalink

Slow-positron implantation spectroscopy in nanoscience
Prochazka, I.; Cizek, J.; Brauer, G.; Anwand, W.;
  • Lecture (Conference)
    NANO'07 - Nanostructured Materials for Functional, Structural and Bio-applications, 08.-10.10.2007, Brno, Czech Republic

Publ.-Id: 10722 - Permalink

Scouting the feasibility of Monte Carlo reactor dynamics simulations
Legrady, D.; Hoogenboom, J. E.;
Usual space dependent reactor dynamics simulations still rely on heavily simplified transport modelling, often restricted to two energy groups prepared with considerably debatable presumptions. The radical increase in computing power availability of recent times allows for more detailed modelling, more energy groups, better physics treatment or for choosing Monte Carlo (MC) methods. Developing MC methods for reactor dynamics are not supported up to now due to the lack of confidence of feasibility for realistic cases fearing unpractical computing times, but the capability of easy parallelization of the MC computing flow may offer hope of real applications. Our investigations here treat the options for performing and optimizing dynamic MC calculations including thermal feedback with the aim of determining the necessary computer resources for realistic simulations. We focus here on methodological questions as previous papers on the subject did not elaborate on such details.
Keywords: Monte Carlo, Reactor Dynamics, keff, variance reduction, Reactor Kinetics, feedback
  • Contribution to proceedings
    International Conference on the Physics of Nuclear Reactors, "Nuclear Power:a Sustainable Source", 14.-19.09.2008, Interlaken, Switzerland
    Proceedings of the International Conference on the Physics of Nuclear Reactors

Publ.-Id: 10721 - Permalink

Application of Wavelet Transform to Extended X-ray Absorption Spectroscopy
Funke, H.; Chukalina, M.; Scheinost, A.;
- wird nachgereicht
  • Contribution to external collection
    Dondon P., Mladenov V., Impedovo S., Cepisca S.: Mathematical Methods and Computational Techniques in Research and Education, ka: WSEAS Press, 2007, 978-960-6766-08-4, 117-121
  • Lecture (Conference)
    7th WSEAS International Conference on Wavelet Analysis & Multirate Systems (WAMUS07), 13.-15.10.2007, Arcachon, France

Publ.-Id: 10720 - Permalink

Influence of Acid Treatment of Multiwall Carbon Nanotubes on the Sorption of U(VI) and on the Stability of Aqueous Suspensions
Schierz, A.; Zaenker, H.; Bernhard, G.;
The unique properties of CNTs are being exploited in a growing number of products and applications [1]. The oxidation process is of great importance for CNT application since it is necessary for CNT purification and functionalization [2]. Acid treatment was recommended as a method of purification [2]. Additionally, the oxidation causes chemical and/or structural changes on CNTs which modify their properties.
Due to their hollow and nanosized structure the use of CNTs as adsorbent for pollutants such as dioxins and heavy metals such as Cd2+, Pb2+, Am3+ [3, 4, 5] for environmental remediation purposes has been considered. Different authors reported that CNTs treated with acid show a higher adsorption capacity for heavy metal ions and dioxins compared with other adsorbents such as activated carbon. These studies suggested that CNTs may be a promising adsorbent for use in environmental protection. The high cost of CNTs still limits their practical use. As these materials make their way to industrial and consumer products, their unintended release in the environment can not be excluded. However, not much research has been conducted to study the characteristics, the fate and behaviour of CNTs in the environment.
The aim of this study is gaining information on both the properties of the CNTs as a potential adsorbent material in water purification and the behaviour of the CNTs as potential carriers of pollutants in the case of their accidental release to the environment.
  • Contribution to proceedings
    NanoECO: Nanoparticles in Environment-Implications and Applications, 02.-07.03.08, Monte Verita, Schwitzerland
    Book of Abstracts, 127

Publ.-Id: 10719 - Permalink

Geplante PLEPS-Messungen an ZnO-Dünnfilmen
Brauer, G.; Schmidt, M.; von Wenckstern, H.; Anwand, W.; Skorupa, W.; Helm, M.; Grundmann, M.;
  • Lecture (Conference)
    2nd User Meeting at NEPOMUC, 30.10.2007, Garching, Germany

Publ.-Id: 10718 - Permalink

Positron Annihilation Spectroscopy – Its Basics and Application to ZnO single crystals
Brauer, G.; Anwand, W.;
  • Lecture (others)
    Seminar am Institute of Physics, Opole University, 25.10.2007, Opole, Poland
  • Lecture (others)
    Seminar am Institute of Experimental Physics, Wroclaw University, 26.10.2007, Wroclaw, Poland

Publ.-Id: 10717 - Permalink

Correlation between magnetic properties and lattice site location of Fe implanted TiO2 at different temperetures
Talut, G.; Reuther, H.; Zhou, S.; Potzger, K.;
Diluted magnetic semiconductors are materials which exhibit ferromagnetic and semiconducting properties simultaneously and are of great interest for spin injection. An interesting candidate is the transition metal doped TiO2 which has been reported to be ferromagnetic above room temperature (RT). It was found that nanometer-sized precipitates substantially contribute to the ferromagnetic properties.
In this study, rutile TiO2(110) single crystals were implanted with 100 keV 57Fe ions at 623 K with fluences between 1x10^16 and 4x10^16 cm^-2 and subsequently annealed at temperatures up to 1073 K. The maximum Fe concentration at the projected range Rp = 50 nm is about 8 at.%.
Virgin, implanted and post-annealed samples were investigated using conversion electron Mößbauer spectroscopy, channeling Rutherford backscattering spectrometry, x-ray diffraction, and super-conducting quantum interference device magnetometry.
Crystalline, imperfect bcc-Fe and FeO-TiO2 composites were detected already in the as-implanted state in the sample implanted at 623 K with 4x10^16 cm^-2. Besides secondary phases a small fraction of Fe^2+ is observed both in the as-implanted and at 923 K annealed sample and can be ascribed to Fe substituting Ti sites.
During annealing at 923 K, both phases grow in grain size, while the amount of FeO-TiO2 is drastically increased. After annealing at 1073 K, FeO-TiO2 composites are the predominant precipitates at the cost of metallic Fe. Both, bcc-Fe and FeO-TiO2 composites are textured. According to the CEMS and SQUID measurements the origin of ferromagnetism is attributed to bcc Fe clusters. The oxidization of metallic Fe with increasing annealing temperature results in the decrease of the saturation moment.
In order to prevent the formation of clusters another set of samples was implanted at RT and 230 K with same fluences. No cluster formation but also no ferromagnetism was observed in both cases.
Keywords: rutile TiO2, Fe, DMS
  • Lecture (Conference)
    52nd Magnetism and Magnetic Materials Conference, 05.-09.11.2007, Tampa, Florida, USA

Publ.-Id: 10716 - Permalink

Probing in-medium vector meson decays by double-differential di-electron spectra in heavy-ion collisions at SIS energies
Wolf, G.; Kämpfer, B.; Pavlenko, O. P.;
Within a transport code simulation for heavy-ion collisions at bombarding energies around 1 AGeV we demonstrate that double-differential di-electron spectra with suitable kinematical cuts are useful to isolate (i) the ρ meson peak even in case of strong broadening, and (ii) the in-medium ω decay contribution. The expected in-medium modifications of the vector meson spectral densities can thus b probed in this energy range via the di-electron channel.
Keywords: heavy-ion collisions, di-electrons, in-medium modifications of vector mesons

Publ.-Id: 10715 - Permalink

Ab-initio calculation of exchange interactions in YMnO3
Novak, P.; Chaplygin, I.; Seifert, G.; Gemming, S.; Laskowski, R.;
The density functional based calculations of the electronic structure of YMnO3 are performed for selected spin configurations and from the differences of the total energies the exchange integrals are determined. To improve the description of strongly correlated 3d electrons of Mn the LDA+U method is employed. The strongest exchange interaction is found between the nearest neighbor Mn spins, the interaction between the next nearest neighbors being more than order of magnitude weaker.
Exchange integrals are inversely proportional to the parameter U, pointing to the dominance of the superexchange interaction. Due to the triangular arrangement of the nearest Mn the magnetism is geometrically frustrated so that biquadratic or/and anisotropic exchange may be important. The calculation of noncollinear spin structures indicates the presence of the biquadratic exchange interaction.
Keywords: Exchange interaction, ab-initio calculation, yttrium manganite

Publ.-Id: 10714 - Permalink

Targetry upgrade at the Rossendorf CYCLONE 18/9
Preusche, S.; Mehaudens, M.;
kein Abstract verfügbar
  • Lecture (others)
    6th Workshop, CYCLONE 18/9 and 10/5 User Community, 23.-26.09.2007, Sevilla, Spain

Publ.-Id: 10713 - Permalink

Evaluation of 18F- L-DOPA PET-CT for surgery in focal congenital hyperinsulinism
Barthlen, W.; Mau, H.; Koch, M.; Höhne, C.; Blankenstein, O.; Mohnike, W.; Eberhard, T.; Füchtner, F.; Lorenz-Depiereux, B.; Mohnike, K.;
Context: In congenital hyperinsulinism (CHI), the identification and precise localization of a focal lesion is essential for successful surgery.
Objective: Our objective was to evaluate the predictive value and accuracy of integrated [F-18] fluoro-L-DOPA ([F-18]FDOPA) positron emission tomography (PET)-computed tomography (CT) for the surgical therapy of CHI.
Design: This was an observational study.
Setting: The study was performed in the Department of Pediatric Surgery at a university hospital.
Patients: From February 2005 to September 2007, 10 children with the clinical signs of CHI and an increased radiotracer uptake in a circumscribed area of the pancreas in the [F-18]FDOPA PET-CT were evaluated.
Interventions: Guided by the [F-18]FDOPA PET-CT report, all children underwent partial pancreatic resection, in two cases twice.
Main Outcome Measures: Correlation of the anatomical findings at surgery with the report of the [F-18] FDOPA PET-CT, and the results of surgery and clinical outcome were determined.
Results: In nine children the intraoperative situation corresponded exactly to the description of the [F-18] FDOPA PET-CT. A limited resection of the pancreas was curative in eight cases at the first surgery, in one case at the second intervention. We observed no diabetes mellitus or exocrine insufficiency in the follow up so far. In one child, hypoglycemia persisted even after two partial resections of the pancreatic head. Histological analysis finally revealed an atypical intermediate form of CHI.
Conclusions: The integrated [F-18]FDOPA PET-CT is accurate to localize the lesion in focal CHI and is a valuable tool to guide the surgeon in limited pancreatic resection.
  • Journal of Clinical Endocrinology and Metabolism 93(2008)3, 869-875

Publ.-Id: 10712 - Permalink

18F-DOPA Positron Emission Tomography for Preoperative Localization in Congenital Hyperinsulinism
Mohnike, K.; Blankenstein, O.; Minn, H.; Mohnike, W.; Füchtner, F.; Otonovski, T.;
In recent years, considerable progress has been made in the biochemical, morphological and molecular genetic differentiation of congenital hyperinsulinism (CHI). Fluorine-18 L -3,4-dihydroxyphenylalanine positron emission tomography
( 18 F-DOPA-PET) has been introduced for differentiation between focal and diffuse CHI. The ability to take up L -DOPA and convert it into dopamine is correlated with the activity of the aromatic amino acid decarboxylase and increased in the hyperfunctional affected pancreatic area in comparison to normally functioning pancreas. The high sensitivity of this method allows the surgeon to perform a curative limited resection of a focus without the risk of long-term diabetes. The exact preoperative planning by 18 F-DOPA-PET/CT computer tomography allows laparoscopic operation in selected cases with the focus in the tail and limits necessity to open the pancreatic duct in cases with focus in the head. Patients with persistent CHI should be managed within a strong network of diagnostic, treatment, and research institutions.
Keywords: [ 18 F]-DOPA-PET/CT, L -DOPA, Congenital hyperinsulinism , Positron emission tomography , Computer tomography

Publ.-Id: 10711 - Permalink

Formation and morphology control of nanostructures produced by PIII
Shevchenko, N.; Weber, J.; Kolitsch, A.;
Development of novel materials and structures for drug delivery systems is currently a very active field of research. For bare metal stents the in-stent restenosis was a serious problem for about 25 - 35% of the patients and this spurred the medical device companies to come up with a solution. Recently the drug-eluting stents were designed to deliver a drug locally from a surface layer to reduce restenosis.
High-fluence ion implantation of noble gas ions into metals can be used to create porous layers on metal surface. These void structures may show unique characteristics which offer potential for drug-eluting stents application. This application requires interconnected pores with the dimension in the range on the nano- to microscale.
The aim of the present work is to study the formation of nanostructures on stainless steel surfaces by means of plasma immersion ion implantation (PIII) using different noble gases. Argon and/or helium ion implantation was performed at following parameters: ion energies ranging from 5 to 35 keV, ion fluence of more than 1e18 cm-2, substrate temperature in the range 50 – 400°C. The modified steel surfaces have been analyzed by scanning electron microscopy, grazing incidence X-ray diffraction analysis (GIXRD), X-ray photoelectron spectroscopy, and elastic recoil detection analysis.
Varying the ion energy, fluences, and substrate temperature has been found to produce either void or sponge like structures on the nano- (~10 nm) to micro-scale (~1 µm). Argon PIII treatment at elevated temperatures leads to spongy structure formation (Fig. 1). Helium implantation results in a surface roughening and creation of voids in high concentration with size in the range 100 – 200 nm as well as nano-scale cavities (5-20 nm) (Fig. 2). Apart from the austenite iron peaks, the GIXRD patterns of the implanted samples display weak peaks of ferrite (bcc iron) as well as oxide phases.
Keywords: plasma immersion ion implantation, noble gases, void structures, modified steel surfaces
  • Lecture (Conference)
    Workshop: Beschichtung für Biotechnologie und Medizintechnik, 16.-17.10.2007, Dresden, Germany

Publ.-Id: 10710 - Permalink

Nanoporous metal surfaces produced by plasma immersion ion implantation
Shevchenko, N.; Weber, J.; Kolitsch, A.;
Development of novel materials and structures for drug delivery systems is currently a very active field of research. For bare metal stents the in-stent restenosis was a serious problem for about 25 - 35% of the patients and this spurred the medical device companies to come up with a solution. Recently the drug-eluting stents were designed to deliver a drug locally from a surface layer to reduce restenosis.
High-fluence ion implantation of noble gas ions into metals can be used to create porous layers on metal surface. These void structures may show unique characteristics which offer potential for medical applications such as metal-based drug-eluting stents. This application requires interconnected pores with the dimension in the range on the nano- to microscale. Systematic investigations of the influence of implantation parameters on the surface morphology and cavity characteristics (e.g. size, distribution, and degree of interconnection) have to date been rather limited.
The aim of the present work is to study the formation of nanostructures on stainless steel surfaces by means of plasma immersion ion implantation (PIII) using different gases (helium or argon).
Argon and/or helium ion implantation was performed at following parameters: ion energies ranging from 5 to 35 keV, ion fluence of more than 10e18 cm -2, substrate temperature in the range 50 – 400°C. The surface topography of the modified steel has been analyzed by scanning electron microscopy and atomic force microscopy. Focused ion beam (FIB) tool was used to prepare sections perpendicular to implanted surface (i.e. transverse section). The phase and element compositions have been examined by grazing incidence X-ray diffraction analysis (GIXRD), X-ray photoelectron spectroscopy, and elastic recoil detection analysis.
Varying the ion energy, fluences, and substrate temperature has been found to produce either void or sponge like structures on the nano- (~10 nm) to micro-scale (~1 µm). Argon PIII treatment at elevated temperatures leads to spongy structure formation. 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). Apart from the austenite iron peaks, the GIXRD patterns of the implanted samples display weak peaks of ferrite (bcc iron) as well as oxide phases.
Keywords: drug-eluting stent, porous layer, stainless steel, PIII, argon, helium, nanostructure
  • Poster
    VEIT 2007 - 15th International Summer School on Vacuum, Electron and Ion Technologies, 17.-21.09.2007, Sozopol, Bulgaria

Publ.-Id: 10709 - Permalink

Realisation of a prototype superconducting CW cavity and cryomodule for energy recovery
Mcintosh, P. A.; Bate, R.; Beard, C. D.; Cordwell, M.; Dykes, D. M.; Pattalwar, S.; Strachan, J.; Wooldridge, E.; Belomestnykh, S.; Liepe, M.; Padamsee, H.; Buechner, A.; Gabriel, F.; Michel, P.; Kimura, T.; Smith, T. I.; Byrd, J.; Corlett, J. N.; Li, D.; Lidia, S.;
For Energy Recovery applications, the requirement for high-Q accelerating structures, operating in CW mode, at large beam currents, with precise phase & amplitude stability and modest accelerating gradients are all fundamental in achieving intense photon fluxes from the
synchronised FEL insertion devices. Both Daresbury Laboratory and Cornell University are developing designs for advanced Energy Recovery Linac (ERL) facilities which require accelerating Linacs which meet such demanding criteria. The specification for the main ERL accelerator for both facilities dictates a modest accelerating gradient of 20 MV/m, at a Qo of better than 10^10, with a Qext of up to 10^8. A collaborative R&D
program has been set-up to design and fabricate a ‘proofof-principle’ cryomodule (which is well underway) that can be tested on ERLP at Daresbury and also on the Cornell ERL injector. This paper details the new cryomodule design, provides an insight to the design solutions employed and reports on the present status of the project.
Keywords: Elbe; accelerator ; cryomodule; energy recovery; accelerator RF;
  • Contribution to proceedings
    13th International Workshop on RF Superconductivity, 14.-19.10.2007, Beijing, China

Publ.-Id: 10708 - Permalink

Friction properties of implanted alumina for vacuum applications
Jagielski, J.; Piatkowska, A.; Merstallinger, A.; Librant, Z.; Aubert, P.; Groetzschel, R.; Suszko, T.;
The influence of ion irradiation on friction properties in vacuum of alumina ceramics was studied. The effects of irradiation fluence, ion energy, thickness of the modified layers and of the possible role of solid lubrication were analyzed. The tests performed under vacuum clearly show, that radiation damage-induced softening of the surface layer leads to significant, approximately two times, decrease of a friction coefficient. Further decrease of the friction force, down to about 1/3 of the initial value, was obtained when the implanted species revealed solid lubrication effect. The results obtained are discussed in the frames of theory of adhesive friction.
Keywords: Ion implantation; Ion irradiation; Friction properties; Alumina
  • Vacuum 81(2007)10, 1357-1362

Publ.-Id: 10707 - Permalink

Calorimetric Evidence for a Fulde–Ferrell–Larkin–Ovchinnikov Superconducting State in the Layered Organic Superconductor κ-(BEDT-TTF)2Cu(NCS)2
Lortz, R.; Wang, Y.; Demuer, A.; Böttger, P. H. M.; Bergk, B.; Zwicknagl, G.; Nakazawa, Y.; Wosnitza, J.;
The specific heat of the layered organic superconductor κ-(BEDT-TTF)2Cu(NCS)2, where BEDT-TTF is bisethylenedithio-tetrathiafulvalene, has been studied in magnetic fields up to 28 T applied perpendicular and parallel to the superconducting layers. In parallel fields above 21 T, the superconducting transition becomes first order, which signals that the Pauli-limiting field is reached. Instead of saturating at this field value, the upper critical field increases sharply and a second firstorder transition line appears within the superconducting phase. Our results give strong evidence that the phase, which separates the homogeneous superconducting state from the normal state is a realization of a Fulde-Ferrell-Larkin-Ovchinnikov state.
  • Physical Review Letters 99(2007), 187002

Publ.-Id: 10705 - Permalink

Interactions of U(VI) and Eu(III) with natural bacterial isolates
Merroun, M.; Geissler, A.; Nedelkova, M.; Selenska-Pobell, S.;
- wird nachgereicht
  • Poster
    Goldschmidt 2007, 19.-24.08.2007, Köln, Germany

Publ.-Id: 10704 - Permalink

Tolerancia y fijacion de uranio por Idiomarina Ioihiensis MAH1
Morcillo, F.; Merroun, M.; Bueno, J. D.; Gonzalez-Munoz, M. T.; Arias, J. M.;
- wird nachgereicht
  • Poster
    XXI Congresso Nacional de Microbiologia, 17.-20.09.2007, Sevilla, Espana

Publ.-Id: 10703 - Permalink

Recent developments at the Dresden High Magnetic Field Laboratory
Wosnitza, J.;
A high magnetic field laboratory for pulsed non-destructive fields up to 100 T has being final-ized at the Forschungszentrum Dresden-Rossendorf, situated at the outskirts of Dresden, Germany. Since the beginning of 2007 the Dresden High Magnetic Field Laboratory (Hochfeld-Magnetlabor Dresden), HLD, is accepting proposals for magnet time and has hosted the first users. The available coils at the HLD produce both high magnetic fields (above 70 T, with 150 ms pulse length) and smaller ones (60-65 T, with 25-50 ms pulse lengths). Besides the ultimate goal of a pulsed magnet reaching 100 T for a timescale of 10 ms in a bore of 20 mm, further large-scale magnets (e.g. 60 T, 0.5 s, 40 mm) are planned. The necessary energy for the pulsed coils is provided by a world-unique 50 MJ capacitor bank. A free-electron-laser facility next door allows high-brilliance radiation to be fed into the pulsed field cells of the HLD, thus making possible unique high-field magneto-optical ex-periments in the range 3-200 µm. Cryotechniques and different sample probes for a broad range of experimental techniques custom designed for the variety of pulsed magnets are read-ily available for users and own in-house research.
  • Lecture (Conference)
    VIII Latin American Workshop on Magnetism, Magnetic Materials and their Applications - LAW3M2007, 12.-16.08.2007, Rio de Janeiro, Brasil

Publ.-Id: 10701 - Permalink

Magnetic and superconducting properties of RuSr2GdCu2O8
Papageorgiou, T. P.; Casini, E.; Skourski, Y.; Herrmannsdoerfer, T.; Freudenberger, J.; Braun, H. F.; Wosnitza, J.;
Magnetization measurements of the magnetic (TM ≈ 138 K) superconductor (TS ≈ 42 K) RuSr2GdCu2O8 in pulsed magnetic fields up to 47 T reveal at 48 K and the highest available magnetic field a Ru contribution to the measured magnetic moment of about 2.2 µB/ formula unit. This value is indicative of a mixed-valence state of the Ru ions involving Ru5+(S = 3/2) and Ru4+(S = 1) ions. We propose that the mixed-valence state combined with charge transport in the RuO2 planes results in a competition between ferromagnetic double exchange involving Ru>sup>5+ and Ru4+ ions and antiferromagnetic superexchange involving Ru5+ ions. This causes magnetic-phase separation in ferromagnetic (non-superconducting) and antiferromagnetic (superconducting) domains. We conclude that the magnetic and superconducting properties of the ruthenocuprates critically depend on the Ru5+/Ru4+ ratio which can be affected by the preparation conditions.
  • Physica C 460-462(2007), 390-391

Publ.-Id: 10700 - Permalink

Driving Forces of Surface Patterning and Nanocluster Tailoring with Ion and Laser Beams
Heinig, K.-H.;
Surface ripple formation as well as modification of nanocluster shapes and size distributions have been observed after irradiation with ion or laser beams. Both phenomena occur during far-from-equilibrium processing. In many cases, these effects can be attributed to an either temperature dependent or effective negative surface (interface) tension. Thus, the ripples found after laser irradiation in a PMMA layer are due to the surface temperature undulation caused by spatial-dependent energy dissipation of standing surface plasmon waves in the underlying gold film (thermocapillarity, see [1]). Thermocapillarity has been idendified to be also the main mechanism of swift-heavy-ion-induced shaping of gold nanoparticles in silica into gold rods or even wires [2]. On the other hand, an effective negative surface tension can be found under low-energy ion irradiation of surfaces [3] and ion beam mixing of interfaces [4]. This negative surface tension tends to increase the surface by surface patterning or inverse Ostwald ripening [4]. Here, these and other driving forces will be discussed in a systematic manner.
[1] L. Röntzsch, K.-H. Heinig, J. Schuller, M. Brongersma, Appl. Phys. Lett. 90 (2007) 044105.
[2] K.-H. Heinig and A. Vredenberg, IBMM2006 conference and in preparation.
[3] R. M. Bradley and J. M. E. Harper, J. Vac. Sci. Technol. A 6, 2390 (1988).
[4] K.-H. Heinig et al., Appl. Phys. A 77, 17 (2003).
Keywords: ion irradiation, nanopattern, self-organization, theory, computer simulations
  • Invited lecture (Conferences)
    2007 MRS Fall Meeting, Symposium "Nanoscale Pattern Formation", 26.-29.11.2007, Boston, United States

Publ.-Id: 10699 - Permalink

Ab initio method for excited states in solids: correlation corrections to the band structure of oxides
Hozoi, L.; Birkenheuer, U.; Fulde, P.;
A new ab initio wave-function based method to study the electron correlation effects on band structures of oxide systems is presented here. It is based on the "simplified method" first introduced by Fulde and Stoll [Theor. Chem. Acc. 116 (2006) 398-403] and analyzed in more detail by Pahl and Birkenheuer [J. Chem. Phys. 124 (2006) 214101]. Bulk MgO is chosen as a prototype closed-shell ionic oxide, a realistic but at the same time still relatively simple insulating system, to prove the abilities of that new approach. We will identify the major correlation induced corrections to the valence and conduction bands of MgO and the closing of the Hartree-Fock band gap due to electron correlation.
Keywords: electronic structure, quantum chemistry, electron correlation, local correlation methods, frozen local hole approximation, ionic systems, MgO, band structure, quasi particle energies, band gap
  • Contribution to external collection
    J.-M. Rost, S. Flach, U. Gneise: MPI for the Physics of Complex Systems: Scientific Report 2005-2006, Dresden: MPI-PKS, 2007, 86-91

Publ.-Id: 10698 - Permalink

Driving forces of ion-beam-induced nanopatterning
Heinig, K.-H.; Röntzsch, L.;
The driving forces of ion-beam-induced nanopatterning will be reconsidered. The original model proposed by Bradley and Harper [1] is a continuum theory for the change of the surface height due to sputtering, based on a linear expansion of the Sigmund model of ion erosion [2], and surface diffusion in the form proposed by Herring and Mullins [3]. Another model, which might be relevant for amorphous surface layers and relatively high ion energies, assumes a smoothing mechanism by viscous relaxation [4]. Taking into consideration the “ion hammering effect” [5], viscous flow could be even responsible for ripple formation. For monocrystalline metallic systems, the step edge barrier for surface vacancy and adatom diffusion results in typical surface pattern under ion irradiation [6].
Besides these driving forces discussed in the literature so far, at least two additional mechanisms have to be considered. (i) After first indications seen by Bellon [7], we found by systematic studies that under ion irradiation the steady-state stability of crystal facets depends on ion flux and temperature [8]. We investigated this instability of crystal facets under ion irradiation by kinetic Monte-Carlo simulations and explained consistently the temperature dependent ripple rotation of Ag(110) surfaces under normal Ar ion impact [9]. (ii) Finally, a mechanism related to ion-irradiation-induced “inverse Oswald ripening” [10] can cause ripple formation: The Gibbs-Thomson relation, which describes the radius-dependent solute concentration around a precipitate, determines the curvature-dependent vacancy/adatom concentration on surfaces too (this is the driving force for ripple smoothing used by by Herring and Mullins [3]). Under high ion fluxes the capillary radius in the Gibbs-Thomson relation can become negative [10], i.e. vacancy/adatom diffusion leads no longer to smoothing but to growth of surface ripples.
Atomistic computer simulation studies of the mechanisms listed above will be presented and discussed in relation with experiments.

[ 1] R. M. Bradley and J. M. E. Harper, J. Vac. Sci. Technol. A 6, 2390 (1988).
[ 2] P. Sigmund, Phys. Rev. 184, 383 (1969).
[ 3] C. Herring, J. Appl. Phys. 21, 301 (1950); W. W. Mullins, J. Appl. Phys. 30, 77 (1959).
[ 4] C. C. Umbach, R. L. Headrick, and K. C. Chang, Phys. Rev. Lett. 87, 246104 (2001).
[ 5] see, e.g., T. van Dillen, A. Polman, P.R. Onck, and E. van der Giessen, Phys. Rev. B 71, 024103 (2005).
[ 6] see, e.g., T. Michely, M. Kalff, G. Comsa, M. Strobel, and K.-H. Heinig, Phys. Rev. Lett. 86, 2589 (2001).
[ 7] P. Bellon, Phys. Rev. Lett. 81, 4176 (1998).
[ 8] Lars Roentzsch, PhD Thesis 2007, K.-H. Heinig and L. Roentzsch, to be published.
[ 9] U. Valbusa, C. Boragno, and F. Buatier de Mongeot, J. Phys.: Condens. Matter 14, 8153 (2002).
[10] K.-H. Heinig, T. Mueller, B. Schmidt, M. Strobel, and W. Moeller, Appl. Phys. A 77, 17 (2003).
Keywords: nanopatterning, surfaces, ion erosion, theory, computer simulations
  • Lecture (Conference)
    Nanopatterning via Ions, Photon beam and Epitaxy, 23.-27.9.2007, Sestri Levante, Italy

Publ.-Id: 10697 - Permalink

Frozen local hole approximation
Pahl, E.; Birkenheuer, U.;
The frozen local hole approximation (FLHA) is an adiabatic approximation which is aimed to simplify the correlation calculations of valence and conduction bands of solids and polymers or, more generally, of the ionization potentials and electron affinities of any large system. In this work we address the question to which extent it is possible to simplify a correlation calculation on electron hole states by focusing on so-called "frozen" local hole configurations although, in reality, the electron hole is usually delocalized over the entire system.
Keywords: electronic structure, quantum chemistry, electron correlation, local correlation methods, frozen local hole approximation, Li and H2 chains
  • Contribution to external collection
    J.-M. Rost, S. Flach, U. Gneise: MPI for the Physics of Complex Systems: Scientific Report 2005-2006, Dresden: MPI-PKS, 2007, 81-86

Publ.-Id: 10696 - Permalink

Thin film patterning by surface-plasmon-induced thermocapillarity
Heinig, K.-H.; Röntzsch, L.; Schuller, J. A.; Brongersma, M. L.;
It will be reported that laser-induced standing surface-plasmon-polariton (SPP) waves can cause regular thickness undulations of thin polymethyl methacrylate (PMMA) films above a metallic substrate [1]. Ripples, rings, and hillock arrays with long-range order were found.Numerical simulations reveal that periodic in-plane temperature profiles are generated in the PMMA due to the non-radiative damping of SPP interference patterns. Calculations of the temperature-gradient-generated Laplace pressure and mass transport confirm
that thermocapillarity is the dominating mechanism of the observed surface patterning.
[1] L. Röntzsch, K.-H. Heinig, J.A. Schuller, M.L. Brongersma, Appl. Phys. Lett. 90 (2007) 044105
Keywords: nanopatterning, laser irradiation, surface plasmons, thermocapillatity, computer simulations
  • Lecture (Conference)
    Nanopatterning via Ions, Photon beam and Epitaxy, 23.-27.09.2007, Sestri Levante, Italy

Publ.-Id: 10695 - Permalink

Exotisches Verhalten von Grenzflächen unter Ionenbestrahlung
Heinig, K.-H.;
Das Verhalten von Grenz- und Oberflächen unter Ionenbestrahlung wird mittels atomistischer Computersimulationen untersucht. Es wird gezeigt, dass es unter Ionenbestrahlung zu negativen effektiven Grenzflächenenergien, Kristallflächeninstabilitäten und zu Formänderungen von Nanoteilchen kommen kann.
Keywords: ion irradiation, computer simulation, surface energy
  • Lecture (Conference)
    Ionenstrahlphysik und Nanotechnologie, 10.-11.5.2007, Bochum, Deutschland

Publ.-Id: 10694 - Permalink

A simplified method for the computation of correlation effects on the band structure of semiconductors
Birkenheuer, U.; Fulde, P.; Stoll, H.;
We present a simplified computational scheme in order to calculate the effects of electron correlations on the energy bands of diamond and silicon. By adopting a quasiparticle picture we compute first the relaxation and polarization effects around an electron set into a conduction band Wannier orbital. This is done by allowing the valence orbitals to relax within a self-consistent field (SCF) calculation. The diagonal matrix element of the Hamiltonian leads to a shift of the center of gravity of the conduction band while the off-diagonal matrix elements result in a small reduction of the conduction-electron band width. This calculation is supplemented by the computation of the loss of ground state correlations due to the blocked Wannier orbital into which the added electron has been placed. The same procedure applies to the removal of an electron, i.e., to the valence bands. But the latter have been calculated previously in some detail and previous results are used to estimate the energy gap in the two materials. The numerical data reported here shows that the methods works, in principle, but that also some extension of the scheme is necessary to obtain fully satisfactory results.
Keywords: electronic structure, quantum chemistry, local correlation methods, frozen local hole approximation, silicon, band structure, quasi particle energies, band gap
  • Theoretical Chemistry Accounts 116(2006), 398-403

Publ.-Id: 10693 - Permalink

Ab initio wave function-based methods for excited states in solids: Correlation corrections to the band structure of ionic oxides
Hozoi, L.; Birkenheuer, U.; Fulde, P.; Mitrushchenkov, A.; Stoll, H.;
Ab initio wave function-based methods are applied to the study of electron correlation effects on the band structure of oxide systems. We choose MgO as a prototype closed-shell ionic oxide. Our analysis is based on a local Hamiltonian approach and performed on finite fragments cut from the infinite solid. Localized Wannier functions and embedding potentials are obtained from prior periodic Hartree-Fock (HF) calculations. We investigate the role of various electron correlation effects in reducing the HF band gap and modifying the bandwidths. On-site and nearest-neighbor charge relaxation as well as long-range polarization effects are calculated. Whereas correlation effects are essential for computing accurate band gaps, we found that they produce smaller changes on the HF bandwidths, at least for this material. Surprisingly, a broadening effect is obtained for the O 2p valence bands. The ab initio data are in good agreement with the energy gap and bandwidth derived from thermoreflectance and x-ray photoemission experiments. The results show that the wave function-based approach applied here allows for well controlled approximations and a transparent identification of the microscopic processes which determine the electronic band structure.
Keywords: electronic structure, quantum chemistry, electron correlation, local correlation methods, frozen local hole approximation, ionic systems, MgO, band structure, quasi particles, band gap

Publ.-Id: 10692 - Permalink

Intersubband relaxation dynamics in single and double quantum wells based on strained InGaAs/AlAs/AlAsSb
Villas-Boas Grimm, C.; Priegnitz, M.; Winnerl, S.; Schneider, H.; Helm, M.;
Intersubband relaxation dynamics in single and coupled double quantum well (QW) structures based on strained InGaAs/AlAs/AlAsSb are studied by femtosecond pump probe spectroscopy at wavelengths around 2 um. For single QWs the transient transmission was observed to decay exponentially with a time constant of 2 ps, showing that side valleys have negligible influence on the intersubband relaxation dynamics for strained InGaAs QWs. For double QWs, the pump-probe signal at the intersubband energy involving the two electronic levels located at the wider QW exhibits an induced absorption component attributed to the population of the second subband (associated with the narrow QW) by hot-electrons.
Keywords: Intersubband relaxation, InGaAs/AlAs/AlAsSb, single quatum well, double quatum well

Publ.-Id: 10691 - Permalink

Ion-induced ripple structures on silicon, x-ray measurements and TEM
Hanisch, A.; Grenzer, J.; Facsko, S.; Biermanns, A.; Pietsch, U.; Metzger, T. H.; Carbone, G.;
Ion-induced ripple structures on silicon, x-ray measurements and TEM The formation of periodic surface structures varying from several nanometers to a few micrometers caused by ion-beam sputter erosion processes on semiconductor surfaces has attracted significant interest for the fabrication of laterally structured materials on a nanoscale.
We started systematic investigations of the rippled surface produced by Xe irradiation applying AFM. The subsurface structure has been identified by both TEM and depth resolved X-ray scattering methods such as GID. Furthermore the crystal structure of semiconductor surfaces should also kept clearly in mind. There is a strong evidence that the formation of ripples via ion beam erosion depends on preferred crystallographic directions of the silicon lattice.
Keywords: ion beam errosion, X-ray measurements
  • Poster
    7th Autumn School on X-ray scattering from surfaces and thin layers, 04.-06.10.2007, Smolenice, Slovakia

Publ.-Id: 10690 - Permalink

Beam dynamics studies for a 3½ cell superconducting RF photo injector operating at low and high bunch charge
Staufenbiel, F.; Janssen, D.; Kamps, T.; Lehnert, U.; Lipka, D.; Michel, P.; Teichert, J.; Xiang, R.;
This paper presents the results of electron beam tracking simulations with the ASTRA code for the 3½ cell superconducting RF gun at the Forschungszentrum Dresden-Rossendorf. The SRF gun will improve the quality of the electron beam parameters for the ELBE superconducting electron linear accelerator. The ELBE electron accelerator is a general purpose facility for secondary radiation production. The facility produces x-rays, gamma-rays, neutrons, positrons and IR FEL radiation. The SRF gun will run in two operation modes with different repetition rates and bunch charges of the pulsed electron beam. The commonly used ELBE mode will operate with electron bunches with 13 MHz repetition rate and a bunch charge of about 77 pC with a maximal average current of 1 mA. The high charge mode with 500 kHz repetition rate and a bunch charge up to 1 nC will be used to generate neutrons by inducing nuclear reactions. For the future BESSY Soft X-ray FEL a bunch charge of about 2.5 nC is required. For these operation modes of the SRF gun preferential operation parameters are determined by the results of beam dynamics studies.

Publ.-Id: 10689 - Permalink

Nanostrukturen - Neue Konzepte und Verfahren für die Photovoltaik
von Borany, J.;
Der Beitrag gibt einen kurzen Überblick über neue technologische und konzeptionelle Entwicklungen auf dem Gebiet der Si-Photovoltaik.
Im Mittelpunkt stehen dabei Beiträge des FZD zur Entwicklung transparenter leitfähiger Oxide sowie Nanocluster-Strukturen (Halbleiter, Metalle), deren Quanteneffekte bzw. Lichtstreuung innovative Ansätze für Hocheffizienz-Solarzellen ermöglichen.
Keywords: photovoltaics, transperent conductive oxide, nanoclusters
  • Lecture (others)
    Gründerimpuls-Veranstaltung "Nanotechnologie", 10.10.2007, Dresden, Germany

Publ.-Id: 10688 - Permalink

Flux dependene of cluster formation in neutron irradiated weld material
Ulbricht, A.; Bergner, F.; Hein, H.; Kammel, M.;
A flux effect on the formation of irradiation-induced clusters in reactor presure vessel (RPV) steels and weld materials is usually assumed. However, it is not easy to quantify this effect because changes of neutron flux are frequently mixed with changes of fluence. This investigation is focused on the influence of neutron flux on the formation of irradiation-induced clusters at a fixed fluence. Small-angle neutron scattering experiments were performed for a neutron irradiated RPV weld material containing 0.22wt% Cu. Clearly distinguishable scattering curves were observed for the irradiated conditions. Data analysis shows that the peak radius of the cluster size distribution of the material irradiated at higher neutron flux of 2.1x10E12 cm^-2s^-1 (E > 1 MeV) is 0.85 nm and the peak radius for the material irradiated at a 35 times lower flux is 1.60 nm. The cluster volume fraction was found to be independent of flux. The effect of flux on the cluster size is surprisingly strong and indicates that cluster growth must have occurred during the low flux irradiation.
Keywords: SANS, RPV steel, weld, irradiation-induced clusters, flux effect
  • Poster
    4th European Conference on Neutron Scattering, 25.-29.06.2007, Lund, Sweden
  • Contribution to proceedings
    4th European Conference on Neutron Scattering, 25.-29.06.2007, Lund, Sweden
    Poster Presentations 4th European Conference on Neutron Scattering, Lund: Media-Tryck, 434-434
  • Contribution to external collection
    U. Stahnke, A. Brandt, H. A. Graf: BENSC Experimental Reports 2007, Berlin: Hahn-Meitner-Institut, HMI-B617, 2008, ISSN 0936-0891, 210-210

Publ.-Id: 10687 - Permalink

s-d exchange interaction induced magnetoresistance in magnetic ZnO
Xu, Q.; Hartmann, L.; Schmidt, H.; Hochmuth, H.; Lorenz, M.; Spemann, D.; Grundmann, M.;
The magnetoresistance (MR) effect in Co-doped ZnO films prepared by pulsed laser deposition on a-plane sapphire substrates with electron concentration at 5 K ranging from 8.3×10^(17) cm^(−3) to 9.9×10^(19) cm^(−3) has been studied experimentally and theoretically. A large positive MR of 124% has been observed in the film with the lowest electron concentration of 8.3×10^(17) cm^(−3), while only a negative MR of −1.9% was observed in the film with an electron concentration of 9.9×10^(19) cm^(−3) at 5 K. The positive MR is attributed to the quantum correction on the conductivity due to the s-d exchange interaction induced spin splitting of the conduction band. The negative MR is attributed to the magnetic field suppressed weak localization. The presented modeling of superimposed positive and negative MR well agrees with the experimentally observed MR and hints at the physical origin of MR in Co-doped ZnO.
Keywords: 75.50.Pp, 75.47.De, 75.30.Et, 73.20.Fz
  • Physical Review B 76(2007), 134417

Publ.-Id: 10686 - Permalink

HF-Modulationsspektroskopie zur Bestimmung optischer Parameter in trüben Medien
Schleicher, E.; Da Silva, M. J.; Paul, S.; Hampel, U.;
Die ortsaufgelöste HF-Modulationspektroskopie ist eine Methode zur Quantifizierung optischer Parameter wie Absorption und Streuung von trüben Medien. Sie findet sowohl in der medizinischen Diagnostik zur Bestimmung der Blutsauerstoffsättigung im Kapillarbett als auch in technischen Prozessen beispielsweise zur Trübungs- oder Fettgehaltsmessung Anwendung. Das in diesem Beitrag vorgestellte Messsystem arbeitet auf Basis der homodynen Demodulation und eröffnet auf Grund der faseroptischen Ankopplung ein breites Einsatzgebiet. Erste vielversprechende Ergebnisse werden vorgestellt.
Keywords: NIR-spectroscopy, laser diagnostics, optical properties, turbid media, RF-modulation spectroscopy
  • Contribution to proceedings
    8. Dresdner Sensor-Symposium, 10.-12.12.2007, Dresden, Germany
    Dresdner Beiträge zur Sensorik, Band 29, Dresden: TUDpress, Verlag der Wissenschaft GmbH, ISBN-13: 978-3-940046-45-1, 79-82
  • Lecture (Conference)
    8. Dresdner Sensor-Symposium, 11.12.2007, Dresden, Germany

Publ.-Id: 10685 - Permalink

Phase change in Fe implanted rutile TiO2 after thermal treatment
Talut, G.; Reuther, H.; Zhou, S.; Potzger, K.;
Diluted magnetic semiconductors (DMS) are materials which simultaneously exhibit ferromagnetic and semi-conducting properties by substitution of transition metal atoms onto cation sites. Recently, transition metal doped TiO2 has been reported to be ferromagnetic above room temperature. It was found that nanoscaled precipitates can substantially contribute to the ferromagnetic properties.
In this study, commercial rutile TiO2(110) single crystals were implanted with 180 keV 57Fe ions at 623 K with fluences between 1x10^16 and 4x10^16 cm^-2 and subsequently annealed at temperatures up to 1073 K. The maximum Fe concentration at projected range Rp = 89 nm was about 5 %.
Virgin, implanted and post-annealed samples were investigated using conversion electron Mößbauer spectroscopy, channeling Rutherford backscattering spectrometry (C-RBS), synchrotron-XRD, and super-conducting quantum interference device (SQUID) magnetometry.
Crystalline, imperfect bcc-Fe and FeO-TiO2 composites (or solid solution) were detected in the sample implanted with 4x10^16 cm^-2 already in the as-implanted state. Besides secondary phases a small fraction of Fe^2+ is observed in the as-implanted and at 923 K annealed sample and can be ascribed to Fe substituting Ti sites.
During annealing at 923 K, both phases grow in grain size, while the amount of FeO-TiO^2 is drastically increased, accompanied by a change of the Fe site location. After annealing at 1073 K, FeO-TiO2 composites are the predominated precipitates at the cost of metallic Fe. Both, bcc-Fe and FeO-TiO2 composites are textured.
According to the CEMS and SQUID measurements the origin of ferromagnetism is attributed to bcc-Fe-clusters. The oxidization of metallic Fe with increasing annealing temperature results in the decrease of the saturation moment .
Keywords: DMS, Fe, rutile
  • Poster
    International Conference on the Applications of the Mössbauer Effect, 14.-19.10.2007, Kanpur, India

Publ.-Id: 10678 - Permalink

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