Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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32228 Publications
Crossover in the surface anisotropy contributions of ferromagnetic films on rippled Si surfaces
Liedke, M. O.; Körner, M.; Lenz, K.; Fritzsche, M.; Ranjan, M.; Keller, A.; Cizmár, E.; Zvyagin, S.; Facsko, S.; Potzger, K.; Lindner, J.; Fassbender, J.ORC
We investigate the influence of a nanoscale periodic ripple morphology on the structure and magneto-crystalline anisotropy of thin ferromagnetic (FM) NiFe, Co, and Fe films. The ripples are created by ion beam erosion of the Si substrate. The periodic ripple structures induce a uniaxial magnetic anisotropy (UMA) in the FM films as confirmed by ferromagnetic resonance and magnetooptical Kerr effect measurements. The thickness dependence of the UMA reveals an abrupt transition. For a thin film regime there is a corrugated alignment of the magnetic moments and above a critical thickness one has dipolar interactions due to the sinusoidal surface modulations.
Keywords: ripples, magnetic anisotropy, uniaxial anisotropy, NiFe, Co, Fe, polycrystalline films, thin films, ion irradiation, MOKE, FMR, LLG

Publ.-Id: 17353 - Permalink


Electromagnetic excitation of a backward facing step flow
Weier, T.; Albrecht, T.; Wittwer, S.; Metzkes, H.; Stiller, J.; Gerbeth, G.;
We consider the flow over a backward facing step under time periodic electromagnetic forcing. Velocity fields have been obtained by time resolved Particle Image Velocimetry in an electrolyte channel at a step height Reynolds number of 1875.
Growth rates of the shear layer instability fit reasonably well to the classical values of Michalke (1965). As expected, excitation with the most amplified frequency results in a minimal reattachment length xr. For moderate excitation amplitudes (characterized here by the interaction parameter N, i.e. the ratio of electromagnetic to inertial forces), forcing with frequencies outside the range of amplified disturbances has no influence on the reattachment length. This behavior is essential in explaining our findings for non sinusoidal excitation. In that case and for a fixed excitation frequency, neither the rms nor the peak value of N is able to collapse recirculation length reductions for different wave forms. However, using only the amplitude of the fundamental sine wave of the applied wave form in N rearranges the data in such a way that they follow a single line in fair approximation. The harmonics of all investigated wave forms have frequencies at least three times higher than the fundamental one and are beyond the range of amplification. In contrast, for separation control on an airfoil (Weier and Gerbeth, 2004) and larger interaction parameters, the peak value of N was found to determine control efficacy, regardless of the wave form.
Proper orthogonal decomposition of the flow fields shows dominant shear layer modes in case of the unforced flow. Under forcing, the time coefficients of the most energetic modes seem to be related to the flapping frequency of the reattachment region.
Keywords: backward facing step, Lorentz force, flow control
  • Lecture (Conference)
    9th European Fluid Mechanics Conference (EFMC9), 09.-13.09.2012, Rom, Italien

Publ.-Id: 17352 - Permalink


DFT investigation of the heterostructure GaP (001) on Si (001)
Steinbach, G.; Schreiber, M.; Gemming, S.;
Semiconductor multilayers are a versatile tool in optoelectronics. The III-V/IV heterostructure GaP(001) on Si(001) provides a viable and almost lattice-matched stack making it suitable for device applications such as multi-junction solar cells. One of the main challenges still arises from the efficiency limitation due to symmetry breaking and imperfections at the buried GaP on Si interface. Here, we present a density-functional investigation of the interface using both the pseudopotential plane-wave code ABINIT and the all-electron augmented plane-wave code Wien2K. The study distinguishes between the Ga-rich and the P-rich interface termination of GaP in the (001) plane. Overall insight into the interface characteristics is gained from structural and electronic quantities. At the perfectly flat interface, the P-rich variant is found to exhibit higher stability. This is supported by the investigation of the atom distances and the local electronic system. Further, it could be shown that the impact of the interface is very local and does not reach far into the layers. Depending on the interface termination, the electronic system shows distinct behavior.
Keywords: gallium phosphide, silicon, heterostructure, photovoltaic, density-functional, DFT, interface

Publ.-Id: 17351 - Permalink


Electric Formation of Metal/SrTiO3 Junctions and its Correlation to Multi-Dimensional Defects
Meyer, D. C.; Stöcker, H.; Hanzig, J.; Hanzig, F.; Zschornak, M.; Abendroth, B.; Gemming, S.;
Regarding the successful use of strontium titanate with different doping within resistive switching memory cells, the presence of crystallographic defects seems to be an important prerequisite. Standard explanations for resistive switching rely on the redistribution of oxygen vacancies, however, this motion can be enhanced or prevented by higher-dimensional defects. Intrinsic defects in crystalline SrTiO3 include point defects such as oxygen or strontium vacancies, line defects, stacking faults like Ruddlesden-Popper phases and precipitates (TiO2, SrO etc.). Electric formation of the metal/oxide/metal cells is widely used as an initial step to enable resistive switching, but the interaction of the multi-dimensional defects during this treatment remains questionable. This talk will present several measurements that were performed in situ, i.e. during the application of an electric field, to investigate the effects of the electric formation on the real structure.
Keywords: multiferroic, memristive, ferroelectric, oxide, perovskite, titanate, Ruddlesden-Popper, DFT, density-functional, X-Ray, XRD, defect
  • Invited lecture (Conferences)
    DPG-Frühjahrstagung 2012, 26.-30.03.2012, Berlin, Deutschland

Publ.-Id: 17350 - Permalink


Gallium Phosphide - Silicon Interface: Structure and Anisotropy Investigations
Steinbach, G.; Gemming, S.; Döscher, H.; Hannappel, T.; Schreiber, M.;
Gallium phosphide thin films on cheap silicon substrates are a promising III-V/IV heterostructure to be used in optoelectronic devices. As an almost lattice matched system with a band gap difference of 1.14 eV it includes applicability for multi-junction solar cells. The present study concerns discontinuities emerging at the boundaries of a GaP thin layer on a silicon substrate. The optical anisotropy of the (001) interface has been determined by an optical model applied to reflectance anisotropy spectroscopy measurements of the GaP/Si heterostructure. Density-functional calculations of the interface have been performed with both, the pseudopotential plane wave code ABINIT [1] and the all-electron augmented plane wave code Wien2K [2]. The study distinguishes between the Ga-rich and the P-rich interface termination. At the perfectly flat interface, the latter exhibits higher stability as indicated by the work of separation. More complex interface models also consider defects. The calculated density of states projected onto in-plane directions gives an indication for anisotropy. It aims at distinguishing interface termination and defects as origin of the experimentally observed reflectance anisotropy. [1] www.abinit.org [2] www.wien2k.at
Keywords: gallium phosphide, silicon, photovoltaics, interface, density-functional
  • Poster
    DPG-Frühjahrstagung 2012, 26.-30.03.2012, Berlin, Deutschland

Publ.-Id: 17349 - Permalink


Conducting Molecules
Wieser, M.; Berger, S.; Kunze, S.; Gemming, S.; Grebing, J.; Erbe, A.; Morawetz, K.; Huhn, K.; Wolf, J.;
no abstract available
Keywords: molecular electronics, nanoelectronics, Green's functions, conductance, single-molecule, organic FET, DFT, self-assembly
  • Lecture (others)
    Topical Problems in Theoretical Physics, 09.05.2012, Chemnitz, Deutschland

Publ.-Id: 17348 - Permalink


Virtual Institute MEMRIOX - Memory Effects in Resistive Ion-beam Modified Oxides
Gemming, S.; Dittmann, R.; Meyer, D. C.; Mikolajick, T.; Ronning, C.; Schmidt, H.; Waser, R.; Spaldin, N. A.; Basov, D.;
The Virtual Institute (VI) „Memriox“ establishes a joint research initiative in the field of ion-tailored oxide-based memristive materials, to be pursued within a novel and unique combination of core competences from the Helmholtz centers Dresden-Rossendorf and Jülich and their university partners in Aachen, Dresden, Freiberg, and Jena. A nanoscale memristive switch may prove the ultimate future non-volatile memory and logic cell with a resistance set directly by electric currents. Thus, the nanoscale memristor has matured to a key player in strategies combining the virtues of the “More Moore” and “More than Moore“ concepts to drive the development of both miniature and functionalized electronic components for a resource-efficient “green“ computing.
Scientifically, the VI aims at stepping beyond the established layer-by-layer control of intrinsic defects during the synthesis of memristive homojunctions. For that purpose, the VI will employ the broad range of ion-beam techniques (HZDR and FSU Jena competence) to induce functionalized one- and two-dimensionally extended memristive nanoregions with high spatial precision. Nano-scale electronic and optical properties and functiona¬lities will be investigated at the partner institutions at the FZJ and the universities in Aachen, Freiberg, and Jena. Applica-bility will be assessed at the NaMlab facility of the TU Dresden. Associated partners at the U.C. San Diego (U.S.A.) and the ETH Zürich (Switzerland) extend the expertise on spectroscopy and simulation.
This combination of the VI partners’ profound, long-term expertise in complementary high-level synthesis, characterization and analysis techniques is unique in the German research area. It provides the ideal framework to explore the spatial limits of memristive elements and their environment hence the VI faces the challenges of the ‘More Moore’ concept, which is still less prominent in basic memristor research. The VI will thus make a significant, qualitatively and quantitatively distinct contribution to cutting-edge science, which aims at quantifying defect-related effects on memristive behavior according to the ‚More Than Moore‘ concept.
Keywords: memristor, memristive, oxide, titanate, ferrite, multiferroic
  • Lecture (others)
    HGF In-House Workshop PNI, 11.-12.06.2012, Freising, Deutschland

Publ.-Id: 17347 - Permalink


Thermodynamic treatment of morphogenesis of brine channels in sea ice
Thoms, S.; Kutschan, B.; Morawetz, K.; Gemming, S.;
Sea ice is a very variable biotope with respect to extension,thickness, porosity or texture. Therefore the basic understanding of brine channel formation in sea ice is important for the interplay between the microbial colonization and their natural habitat. The early phase of brine channel formation in sea ice is considered. The first structures emerging during sea-ice formation are determined by the phase instability of the ice-water system in the presence of salt. We apply a Ginzburg-Landau type approach to describe the phase separation in the two-component system (ice, salt). The free energy density involves two order parameters: one for the hexagonal ice phase with low salinity, and one for the liquid water with high salinity. A gradient dynamics minimizes the free energy with respect to the conservation of the salinity. The resulting model equations are solved numerically in one and two dimensions. The numerical solution shows a short-time behavior of structure formation where the freezing is assumed and a large-time broadening of the structure. A stability analysis provides the phase diagram where brine channels can be formed. In thermodynamics the parameters determine the supercooling or superheating region and the specific heat respectively. The size of the brine channels depends on the salinity and the temperature. With the help of realistic parameters the brine channel distribution is calculated and found in agreement with the measured samples.
Keywords: sea ice, brine, phase-field, modelling, binary system, nanostructure formation, reaction-diffusion equations
  • Contribution to proceedings
    EGU General Assembly 2012, 22.-27.04.2012, Wien, Österreich
    EGU General Assembly Conference Abstracts, Vol. 14, 6239

Publ.-Id: 17346 - Permalink


Band gap tuning of carbon nanotubes for sensor and interconnect applications — A quantum simulation study
Zienert, A.; Gemming, S.; Schuster, J.; Schulz, S. E.; Gessner, T.;
Carbon nanotubes (CNTs) are a promising material for novel sensor and interconnect applications. In both cases, the device performance depends strongly on the electronic properties of the tubes. Methods for tuning the electronic structure and especially the band gap are highly desirable. A computational study of cobalt decorated CNTs, by means of density functional theory, reveals that very few cobalt atoms can have a significant impact on the electronic structure, turning semiconducting CNTs into the metallic state. This is further verified by quantum transport simulations. The influence of different amounts of cobalt is also investigated.
Keywords: CNT, nanotube, density-functional, transport, nanoelectronic
  • Contribution to proceedings
    9th International Multi-Conference on Systems, Signals and Devices (SSD), 20.-23.03.2012, Chemnitz, Deutschland
    Systems, Signals and Devices: IEEE, 978-1-4673-1590-6

Publ.-Id: 17345 - Permalink


Multifunctional oxides - influence of defects on the ferroic properties
Gemming, S.; Weissbach, T.; Zschornak, M.; Stöcker, H.; Meyer, D. C.; Leisegang, T.; Ronneberger, I.; Potzger, K.;
Transition metal oxides exhibit many physical phenomena, among them ferroic properties such as ferroelasticity, ferroelectricity and ferromagnetism, or their combination in multiferroics. The stoichiometry of transition metal oxides depends on the oxygen partial pressure and changes conductivity and ferroic properties. Ternary/quaternary oxides are discussed, which correlate local defect-induced structure changes with changes of the elastic, polarization and magnetic properties. The microscopic interactions are determined by density functional theory as basis for more large-scale simulations with effective Hamiltonians. Oxygen vacancies in SrTiO3 accumulate in an external electric field and reduce the hardness. For Sr/O excess SrO(SrTiO3)n phases with additional SrO planes occur, which change the X-Ray reflectivity. Ion-irradiation triggers additional point defects which can form stable aggregates. In YMn2O5 several antiferromagnetic phases coexist with ferroelectricity; YFeMnO5 exhibits only one commensurable ferrimagnetic phase. Based on spin-polarized DFT calculations a Heisenberg model yields the coupling constants of the two compounds and relates them to crystal-field interactions.
Keywords: multiferroic, DFT, density-functional, oxide, titanate, ferrite, manganite
  • Poster
    DPG Frühjahrstagung 2012, 26.-30.03.2012, Berlin, Deutschland

Publ.-Id: 17344 - Permalink


Ion beam assisted deposition of nano-structured C:Ni films
Abrasonis, G.; Krause, M.; Mücklich, A.; Heller, R.; Heinig, K.-H.; Gemming, S.; Möller, W.;
Nanostructures influence material properties dramatically due to size, shape and interface effects. Thus the control of the structure at the nanoscale is a key issue in nanomaterials science. The interaction of hyperthermal ions with solids is confined to the nanometer scale. Thus, it can be used to control the morphology evolution during multiphase film deposition. Ion-induced displacements occur in a thin surface layer of the growing film where they increase the atomic mobility for the phase separation. Here the growth-structure relationship of C:Ni (~15 at.%) nanocomposite films grown by oblique incidence (~45) ion beam assisted deposition is reported. The influences of the flux of an assisting Ar+ ion beam (0-140 eV) as well as of an elevated substrate temperature have been studied. The formation of elongated nickel nanoparticles is strongly promoted by the ion beam assistance. Moreover, the metal nanocolumns no longer align with the advancing surface, but with the incoming ions. A window of conditions is established within which the ion assistance leads to the formation of regular composition modulations with a well defined periodicity and tilt. As the dominating driving force for the pattern formation is of physical origin, this approach might be applicable to other immiscible systems.
Keywords: ion-assisted growth, structure formation ECEMP, CNT, nickel, IBAD
  • Poster
    DPG Frühjahrstagung 2012, 26.-30.03.2012, Berlin, Deutschland

Publ.-Id: 17343 - Permalink


Multifunctional Oxides – Modifying the Ferroic Properties by Defects due to Irradiation, Doping and Annealing
Gemming, S.; Weissbach, T.; Zschornak, M.; Stöcker, H.; Meyer, D. C.; Leisegang, T.; Ronneberger, I.; Potzger, K.;
Transition metal oxides exhibit a wealth of physical phenomena, among them ferroic properties such as ferroelasticity, ferroelectricity and ferromagnetism, or their combination in multiferroics. In addition, transition metal oxides are sensitive to the chemical environment via the oxygen partial pressure or ion irradiation; changes induce stoichiometry deviations, which cause conductivity changes and modify the ferroic characteristics. Ternary and quaternary compounds from the perovskite family will be discussed as examples, which correlate local changes due to point and planar defects with changes of the elastic, polarization and magnetic properties. The microscopic interactions are determined by density functional calculations, which yield the basis for more large-scale simulations with effective Hamiltonian approaches. Under oxygen-poor conditions, oxygen vacancies in SrTiO3 accumulate in an external electric field and reduce the hardness. In an Sr/O-rich environment the phases SrO(SrTiO3)n are formed, which yield a distinct change of the X-ray reflectivity due to the regular arrangement of extrinsic SrO(001) stacking faults. YMn2O5 has a series of complex antiferromagnetic phases in coexistence with ferroelectricity. In YFeMnO5, only one commensurable ferrimagnetic phase was found and ferroelectricity is absent. Based on spin-polarized DFT calculations a Heisenberg model yields the coupling constants of the Fe-substituted and the mangenese-only compounds and relates them to crystal-field interactions. Finally, BiFeO3 will be addressed, which is a rhombohedral multiferroic with several domain wall configurations, which exhibit specific magnetic and conductance properties.
Keywords: oxide, DFT, density-functional, multiferroic, bismuth ferrite, manganite, titanate
  • Invited lecture (Conferences)
    MRS Spring Meeting, 09.-13.04.2012, San Francisco, U.S.A.

Publ.-Id: 17342 - Permalink


Techniques for image based in-vivo dosimetry: from particle therapy PET to in-beam prompt gamma imaging
Fiedler, F.;
no abstract available
  • Invited lecture (Conferences)
    OncoRay Retreat, 07.-08.03.2012, Dresden, Germany

Publ.-Id: 17341 - Permalink


Hydrodynamic characterization of an inclined rotating fixed bed reactor using tomographic imaging
Härting, H.-U.; Bieberle, A.; Schubert, M.;
Trickle bed reactors with liquid and gas phase flowing cocurrently downwards at moderate superficial velocities are widely used, e. g. for selective hydrogenation, processing of volatile organic compounds or wastewater treatment [Duduković et. al., 2010]. This reactor type, however, has inherent disadvantages like liquid maldistribution and hence, imperfect wetting of the packing. Furthermore, mass transfer limitations of the gas phase to the active sites of the catalyst through liquid films at the packing surface are another shortcome.

As a new process intensification concept, an inclined fixed bed reactor with superimposed rotation that allows a spatial periodic operation at constant gas and liquid flow rates is proposed. The packing is periodically immersed into the liquid phase that accumulates mainly in the lower part of the reactor cross-section. Inclination angle and rotational speed provide additional degrees of freedom to adjust liquid residence time and periodicity of wetting and draining, respectively.

The present work aims to study the hydrodynamics, i. e. dynamic liquid holdup and pressure drop, in the new reactor concept. These studies comprise variations of reactor inclination (α = 15° - 90°), rotational speed (up to 60 rpm) as well as gas (vG = 0.025 m/s - 0.05 m/s) and liquid (vL = 0.01m/s - 0.05 m/s) superficial velocities. Additional variations, e.g. of packing and packing particle size, liquid viscosity and liquid (water, silicone oil, cumene) will be reported.
The experimental setup consists of a tubular reactor (ID = 0.1 m, L = 1.2 m) with rotary unions. The whole reactor is supported by rollers, driven by a hollow shaft rotary actuator and mounted in an inclinable frame. The gas-liquid distribution patterns are visualized by means of a noninvasive compact γ-ray computer tomography system (CompaCT), which is mounted in the same frame on a rotary stage. The spatial in-plane resolution of the measurement system is 2 mm. The applicability of γ-ray CT for hydrodynamic investigations in packed bed reactors has been demonstrated recently [Bieberle et. al., 2010].

References
1. Bieberle, A., M. Schubert, M. J. da Silva, and U. Hampel, Ind. Eng. Chem. Res., 49, 9445-9453 (2010).
2. Duduković, M. P., F. Larachi, and P. L. Mills, Catal. Rev., 44, 123-246 (2002).
Keywords: Fixed bed reactor, Inclination, Rotation, Liquid holdup, Phase distribution, Gamma-ray tomography
  • Lecture (Conference)
    The 11th International Conference on Gas-Liquid & Gas-Liquid-Solid Reactor Engineering in conjunction with The 9th World Congress of Chemical Engineering, 18.-23.08.2013, Seoul, Republik Korea

Publ.-Id: 17340 - Permalink


Hydrodynamische Charakterisierung eines gas/flüssig-durchströmten geneigten Festbettdrehrohrreaktors
Härting, H.-U.; Schubert, M.;
Rieselbettreaktoren unterliegen Limitierungen bei Gaslöslichkeit und Gasphasenstofftransport an den Katalysator, die z.B. durch adiabatischen Betrieb bei hohen Drücken und Temperaturen kompensiert werden. Außerdem führen inhomogene Phasenverteilungen und Benetzungszustände zu verminderter Katalysatorausnutzung sowie zur Ausbildung von Hotspots. Zur Prozessintensivierung wurde u.a. die dynamische Betriebsweise vorgeschlagen, bei der dem Reaktor ein periodisch variierter Flüssigkeitsstrom zugeführt wird. Dadurch können Filmdicke und Benetzungsgrad periodisch variiert und der Zugang der Gasphase an den Katalysator verbessert werden. In Reaktoren im industriellen Maßstab sind jedoch nur geringer Effekte zu erwarten, da die aufgeprägte Periodizität mit der Reaktorlänge abnimmt. Außerdem erfordert die Betriebsweise zusätzliche Aufwendungen für MSR-Technik, Lastwechselkompensation und Schnittstellenmanagement im Anlagenverbund.

Beim neuen Reaktorkonzept führt die Neigung zu einer Phasensegregation und damit jeweils zu einem direkten Zugang beider fluiden Phasen an den Katalysator. Die zusätzlich aufgeprägte Rotation bewirkt eine periodischen Be- und Entnetzung der Katalysatorschüttung. Von Vorteil ist, dass neben der Periodizität auch die Verweilzeit eingestellt werden kann.

Zur Bewertung des neuen Reaktorkonzepts wurden hydrodynamische Untersuchungen bei unterschiedlichen Neigungswinkeln und Reaktordrehzahlen sowie bei verschiedenen Flüssigkeiten und Durchsätzen durchgeführt. Mittels kompakter Gamma-Tomographie sowie Gittersenortechnologie wurden die Zweiphasenströmung hinsichtlich Phasenverteilungen, Strömungsform und Verweilzeitverhalten charakterisiert. Neben dem neuen Reaktorkonzept werden im Beitrag die eingesetzte bildgebende Messtechnik sowie die hydrodynamischen Charakterisierungsmethoden vorgestellt sowie die Ergebnisse zusammengefasst.
Keywords: Fixed bed reactor, Inclination, Rotation, Phase distribution, Gamma-ray tomography, Wire-mesh sensor
  • Poster
    ProcessNet-Jahrestagung und 30. DECHEMA-Jahrestagung der Biotechnologen 2012, 10.-13.09.2012, Karlsruhe, Deutschland
  • Open Access LogoAbstract in refereed journal
    Chemie Ingenieur Technik 84(2012)8, 1250
    DOI: 10.1002/cite.201250162

Publ.-Id: 17339 - Permalink


Gas-liquid mass transfer in inclined rotating fixed bed reactors
Härting, H.-U.; Wiezorek, M.; Schubert, M.;
Periodic operation of trickle bed reactors (TBR) as a promising process intensification approach has been examined in many studies since more than 2 decades. It has been demonstrated to reduce known limitations and disadvantages of the conventional operation mode of such reactors, i. e. avoiding the formation of hot spots, enhancing liquid maldistribution and boosting poor mass transfer rates. Though widely examined in the academic field, an industrial implementation of periodically operated TBRs is not expected, mostly because of the higher requirements on the upstream peripheral devices in an industrial environment. Additionally, modelling and prediction of the transient behaviour of such reactors remain challenging tasks due to the complex hydrodynamics and related mass and heat transfer resulting from the dynamic mode of operation. As a consequence, alternative reactor concepts with enhanced performance which do not require flow modulation but potentially provide benefits over established configurations need to be studied.

To avoid the problem of shorter residence times arising from the pulse flow regime while maintaining a periodic wetting and draining of the packed bed, a superimposed rotation of the inclined TBR is proposed. This new concept allows process intensification via a spatial periodic mode of operation while feeding with invariant gas and liquid flow rates. Inclination angle and reactor rotational speed provide additional degrees of freedom to adjust liquid residence time and period length (periodicity), respectively.

The objective of this study is the systematic investigation of the influence of inclination and rotation on the gas-liquid mass transfer for selected gas and liquid flow rates. Therefore, oxygen desorption in a reactor (1.6 m length, 0.1 m diameter) with particle packing (4 mm diameter) will be studied and mass transfer coefficients determined. The mass transfer results will also be discussed with respect to flow patterns obtained from tomographic imaging. Furthermore, the results will be compared with experimental data of the conventional TBR configuration as well as with established correlations.
Keywords: Fixed bed reactor, Inclination, Rotation, Mass transfer, Phase distribution, Gamma-ray tomography
  • Lecture (Conference)
    20th International Congress of Chemical and Process Engineering CHISA 2012, 25.-29.08.2012, Praha, Česká republika

Publ.-Id: 17338 - Permalink


Ceramics Resistive Plate Chambers for High Rate Environment
Laso Garcia, A.; Kaspar, M.; Kämpfer, B.; Kotte, R.; Naumann, L.; Peschke, R.; Stach, D.; Wendisch, C.; Wüstenfeld, J.;
Multi-gap resistive plate chambers (RPCs) are proposed to build the Time-of-Flight wall of the Compressed Baryonic Matter experiment with a time resolution better than 80 ps. The high fluxes expected at the innermost part of the detector, ~20x103 cm2s-1, require the development of new materials capable of withstanding such fluxes. At Helmholtz-Zentrum Dresden-Rossendorf, several RPC prototypes of 10x10 cm2 and 20x20 cm2 have been built with ceramic plates with bulk resistivities in the range of 109-1010 Ω cm [1]. They have been tested at the superconducting electron accelerator facility ELBE with 30 MeV electrons. We present the characteristics of the ceramic electrodes and the latest results concerning the performance of these prototypes in electron and protons beams up to fluxes of 106 cm-2 s-1.
  • Open Access LogoProceedings of Science (2012), PoS(RPC2012)066

Publ.-Id: 17337 - Permalink


Plasma and Ion-Beam Assisted Materials Processing Introduction
Endrino, J. L.; Anders, A.; Andersson, J.; Horwat, D.; Vinnichenko, M.;
No abstract provided.

Publ.-Id: 17336 - Permalink


Electrical characterization of single molecules in liquid environments
Wieser, M.; Sendler, T.; Liu, S.-P.; Weisbrod, S.; Tang, Z.; Marx, A.; Wolf, J.; Scheer, E.; Moresco, F.; Grebing, J.; Erbe, A.;
We have developed the mechanical controllable break junction technique for the use in liquid environments in order to characterize the electrical properties of single molecules in their solvents. The metallic electrodes, which form the contacts for the molecular structures, are produced on an insulating substrate in order to reduce all spurious effects coming from parallel conduction through the liquid. We present first electrical characterization of such junctions in dry and in liquid environments. The solvents range from aqueous buffer, which will be used for measurements of DNA fragments, to toluene and THF, which are typical solvents for short, conjugated organic molecules.
Keywords: mechanical controllable break junction, MCBJ, molecules
  • Poster
    DPG-Frühjahrstagung 2012, Berlin, 26.03.2012, Berlin, Deutschland

Publ.-Id: 17335 - Permalink


Femtosecond laser micromachining of Nd:GdCOB ridge waveguides for second harmonic generation
Jia, Y.; Chen, F.; de Aldana, J.; Akhmadaliev, S.; Zhou, S.;
We report on the fabrication of Nd:GdCOB ridge waveguides by using femtosecond laser micromachining of planar waveguides that were produced by carbon ion irradiation. The guiding properties of the Nd:GdCOB ridge waveguides are investigated. The second harmonic generation (SHG) at 532 nm green laser from ridges in a series of transverse widths is realized. The results show that the optical conversion efficiencies of SHG in the fabricated ridge waveguides are considerably enhanced with respect to the planar waveguide, and the maximum value reaches 11.4% under a pulsed 1064 nm laser pump.
Keywords: Optical waveguides; Nd:GdCOB laser crystal; Femtosecond laser micromachining; Second harmonic generation

Publ.-Id: 17334 - Permalink


Thermoelectric properties of porous silicon
de Boor, J.; Kim, D. S.; Ao, X.; Becker, M.; Hinsche, N. F.; Mertig, I.; Zahn, P.; Schmidt, V.;
We have studied the thermoelectric properties of porous silicon, a nanostructured, yet single-crystalline form of silicon. Using electrochemical etching, liquid-phase doping, and high-temperature passivation, we show that porous Si can be fabricated such that it has thermoelectric properties superior to bulk Si, for both n- and p-type doping. Hall measurements reveal that the charge carrier mobility is reduced compared to the bulk material which presently limits the increase in thermoelectric efficiency.

Publ.-Id: 17333 - Permalink


Analyse und Optimierung einer Positronenreichweitenkorrektur innerhalb der iterativen Rekonstruktion für die Kleintierbildgebung
Sauerzapf, S.; Zakhnini, A.; Weber, W.; Pietrzyk, U.; Mix, M.;
Einleitung:
Hochenergetische Positronenstrahler, wie beispielsweise die Isotope I-124 oder Ga-68, besitzen aufgrund ihrer maximalen Zerfallsenergie von 2,1 bzw. 1,9 MeV eine mittlere Reichweite von ~3 mm in Wasser. Bei der Kleintierbildgebung mit hohen räumlichen Auflösungen von 1-2 mm, sind daher der resultierende Ortsauflösungsverlust und die Bildverschmierung besonders dominant. Die direkte Einarbeitung der Positronenreichweite in den Rekonstruktionsalgorithmus kann durch die Faltung der geschätzten Aktivität mit einem Kernel vor der Vorwärtsprojektion erfolgen (Positronen Range - Maximum Likelihood Expectation Maximization, PR-MLEM- lgorithmus). Ziel dieser Arbeit war die Implementierung und Validierung eines solchen Algorithmus verbunden mit einer exakten Kernelbestimmung mittels GATE Monte-Carlo (MC) Simulationen [1]. Zur Vereinfachung des Verfahrens wurden ferner verschiedener Gausskernel verwendet.
Anhand ihrer auflösungsrückgewinnenden Charakteristik und der Generierung von Bildartefakten im Iterationsprozess wurde überprüft, ob und wie genau ein Reichweitenkernel bestimmt werden muss.

Material und Methoden:
Für die exakte Bestimmung des Reichweiten kernels wurden GATE 6.1 Monte-Carlo Simulationen für das Concorde MicroPET Focus 120 gerechnet. Der simulierte Kleintierscanner ist ein stationäres Blockdetektorsystem bestehend aus 12x12 LSOKristallmatrizen angeordnet in 48 axialen Kristallringen und 24 transaxialen Modulen. Die am Gerät gemessene und für die Simulationen verwendete durchschnittliche Energieauflösung beträgt etwa 20%. Das Standardakquisitionsfenster von 350- 650keV wurde beibehalten. Simulationen wurden für eine punktförmige F-18, Ga-68 und I-124 Quelle (d = 1 Pxl = 0,796 mm) in einem kugelförmigen Phantom (d = 146 mm) mit verschiedenen Materialien (Knochen, Lungengewebe, Muskel, PMMA und Wasser) durchgeführt. Über die Reichweitenhistogramme der beiden I-124 und F-18 Quellen innerhalb eines wasseräquivalenten Materials wurden zwei- und dreidimensionale Faltungskerne bestimmt. Die Reichweitenverteilung für I-124 konnte über ein Polynom 6. Grades angenähert werden (Korrelationskoeffizient R=0,9993). Der daraus berechnete Kernel wurde bis zu einer Perzentilen von 95% verwendet. Dies entspricht einer Länge von jeweils 21 Pixeln für jede Dimension. Neben dem exakten Reichweitenkernel wurde ein Gausskernel mit entsprechender Halbwertsbreite σ gebildet. Für diesen wurde σ sowohl unter- als auch überschätzt
(Abb. 1). Der umgesetzte PR-MLEM-Algorithmus verwendet die „Ray Tracing“ Projektoren aus der STIR Library [2]. Bis zur annähernden Konvergenz des Algorithmus werden mindestens 50 Iterationen benötigt. Ab 75 Iterationen erschlechtert sich das Bild aufgrund von Rauschen, weswegen alle Bildrekonstruktionen mit dieser Anzahl an
Iterationen durchgeführt wurde. Die auflösungsrückgewinnende Bildrekonstruktion wurde bei verschiedenen I-124
und F-18 Phantommessungen (Image Quality Phantom nach NEMA NU4-2008 und Schoeppy-Auflösungsphantom) und einer I-124 Mausstudie angewandt. Das Image Quality Phantom besteht, neben einem homogen gefüllten Bereich mit zwei kalten 2 zylindrischen Einschüben, aus fünf heißen Inserts, jeweils mit Durchmessern von 1 bis 5 mm. Das Schoeppy-Auflösungsphantom besitzt fünf Segmente deren mit Aktivität gefüllte Inserts Durchmesser von 1 bis 3 mm in 0,5 mm Schritten besitzen. Die Auflösungsbestimmung erfolgte über die Kantenverschmierung der radialsymmetrischen Zylinderinserts in Polarkoordinatendarstellung (Softwaretool Rover von ABX [3]).

Ergebnisse:
Bei der Verwendung des PR-MLEM-Algorithmus treten im Laufe der Iterationen deutliche Bildartefakte auf. Als Artefakt wird hier eine asymmetrische Verschiebung der Aktivitätsverteilung bezeichnet. Äußere Bereiche im Objekt werden gegenüber innenliegenden überkorrigiert (beispielsweise die Randüberhöhung bei homogen gefüllten Bereichen). Daher können die Korrekturen nicht während des gesamten Iterationsprozesses, sondern nur am Ende angewandt werden. Die Bestimmung der notwendigen Anzahl an Faltungsiterationen erfolgte anhand des Gradienten der Log-
Likelihood Funktion. Ist der unkorrigierte MLEM bereits konvergiert (> 50 Iterationen), so reichen 4-5 Iterationen mit Korrektur um wieder in einen konvergierten Zustand zu gelangen. I-124 Phantommessungen: Bei der Verwendung des exakten I-124 Reichweiten und des äquivalenten Gausskernels mit einer Halbwertsbreite von σ = 3,2 mm entstehen Veränderungen in der Aktivitätsverteilung bereits ab der dritten Faltungsiteration. Bei einem Kernel mit 50% der exakten Halbwertsbreite (Full Width at Half Maximum FWHM) erhöht sich die Iterationsanzahl vor dem Auftreten von
Artefakten auf neun. Bei 25% FWHM (σ = 0,8 mm) können alle 75 Iterationen artefaktfrei gefaltet werden. Wird der Gausskernel überschätzt und σ z.B. auf 6,4 mm verdoppelt, können nur ein bis zwei Faltungsiterationen artefaktfrei durchgeführt werden.
Die höchste Auflösung wird für beide Phantomgeometrien mit der Faltung der letzten neun Iterationen mit einem Kernel von σ = 1,6 mm erreicht, der die tatsächliche FWHM um 50% unterschätzt (Tab. 1). Für das Image Quality Phantom ergibt sich somit am Ø 5 mm Insert eine Auflösungsverbessung von 2,70 mm FWHM gegenüber der unkorrigierten Rekonstruktion von 4,06 mm FWHM. Am Ø 3 mm Insert des Auflösungsphantoms ergibt sich noch eine Verbesserung von ca. 19% (4,11 mm FWHM vor gegenüber 3,34 mm FWHM nach der Korrektur). Dennoch verändert sich hierbei die Aktivitätsverteilung in den äußeren Inserts (Abb. 2 b). Ohne 3 Artefakte kann somit die Auflösung von F-18 nicht erreicht werden, die 2,18 mm FWHM am Ø 3 mm Insert des Auflösungsphantoms beträgt.
Bei einer zu großen Anzahl an Faltungsiterationen (Gausskernels (σ = 3,2 mm) auf alle 75 Iterationen) verschwindet im Auflösungsphantom die Darstellung des Segmentes mit dem geringsten Durchmesser (1 mm) nahezu komplett (Abb. 2 c). Demgegenüber können alle 75 Iterationen artefaktfrei mit einem Gausskernel gefaltet werden, dessen albwertsbreite lediglich 25% der tatsächlichen beträgt (σ = 0,8 mm).
F-18 Phantommessungen: Wird für F-18 der reichweitenäquivalente Gausskernel mit σ = 0,4 mm verwendet, ergibt sich keine Auflösungsverbesserung. Durch die Verdopplung der Halbwertsbreite wird der 1 mm Insert des Image Quality Phantoms deutlicher sichtbar, wobei in der Folge Ringartefakte in der transversalen Ansicht auftreten (Abb. 3).
I-124 Mausstudie: Ohne Korrektur können die beiden Schilddrüsenlappen einer mit I-124 injizierten Maus nicht separiert dargestellt werden (Abb. 4). Wenn hingegen für alle Iterationen ein Gausskernel mit geringer FWHM (σ = 0,8 mm) verwendet wird, ist eine Differenzierung beider Lappen zulasten eines erhöhten Rauschanteils möglich.
Dieser Rauschanteil wird bei Verwendung eines Gausskernels mit doppelter FWHM und bei der Faltung mit dem exakten Kernel aus GATE reduziert und es ergibt sich ein erhöhter Kontrast der Schilddrüse. Dennoch ist keine signifikante Verbesserung der Auflösung erkennbar, so dass die beiden Schilddrüsenlappen nach wie vor nicht
differenziert werden können (Abb. 4 e). Die Verwendung eines 3D Kernels ergibt für den Gauss mit σ = 1,6 mm (50% der tatsächlichen FWHM) leichte Veränderungen der Aktivitätsverteilung im Magen im Vergleich zum 2D Faltungskern (Abb. 5 a-b).
Der exakte 3D Reichweitenkernel aus GATE verstärkt diese Effekte weiter, wodurch die Aktivitätsverteilung im Magen überproportional erhöht wird (Abb. 5 c-d).

Diskussion:
Der exakte I-124 Reichweitenkernel aus GATE und der entsprechende Gausskernel mit σ = 3,2 mm liefern bzgl. der Auflösung und der rekonstruierten Bilder vergleichbare Ergebnisse. Daher ist die genaue Kenntnis der Form des Kernels nicht relevant. Ausschlaggebend ist vielmehr die verwendete Halbwertsbreite. Wird diese
überschätzt, treten bereits nach nur wenigen Faltungsiterationen Artefakte auf. Eine Unterschätzung um 50% (σ = 1,6mm) lieferte für beide Phantomgeometrien die höchste Auflösung ohne deutliche Randüberhöhungen. Bei einer FWHM von nur 25% (σ = 0,8mm) können alle Iterationen ohne Artefakte gefaltet werden und die Definition des Abbruchkriteriums hierfür entfällt. Bei der Anwendung im Rahmen einer I-124 Mausstudie konnte mit diesem Kernel die Auflösung soweit erhöht werden, dass beide Schilddrüsenlappen nun differenzierbar sind.
Aufgrund der geringen Reichweite der F-18 Positronen beträgt die Halbwertsbreite des äquivalenten Gausskernels nur 0,4 mm (entspricht 0,5 Pixel) und kann somit die Auflösung nicht signifikant erhöhen. Der Kontrast und die Auflösung können mit der beschriebenen Entfaltungsmethode für I-124 erhöht werden. Ein Kernel mit nur 25 bzw. 50% FWHM eignet sich hierfür besser als die Verwendung der exakten Reichweite. Dennoch ist aufgrund der Abhängigkeit der Faltung von der örtlich variierenden Aktivitätsverteilung eine absolute Quantifizierung erschwert, da die ktivitätskonzentrationen lokal überschätzt werden.

Literatur:
[1] S. Jan et al.: GATE V6: A major enhancement of the GATE simulation platform
enabling modelling of CT and radiotherapy. Phys. Med. Biol. (56) (2011) 881-901
[2] K. Thielemans et al.: STIR: software for tomographic image reconstruction release
2. Phys. Med. Biol. (57) (2012) 867-883
[3] Rover ROI Visualization, Evaluation and Image Registration. ABX Radeberg:
http://www.abx.de/rover/ 2012
  • Lecture (Conference)
    43. Jahrestagung der Deutschen Gesellschaft für Medizinische Physik, 26.-29.09.2012, Jena, Deutschland

Publ.-Id: 17332 - Permalink


GATE-Based Simulation in GeoSciences
Zakhnini, A.; Kulenkampff, J.; Lippmann-Pipke, J.; Pietrzyk, U.;
Es ist kein Abstract vorhanden.
  • Lecture (Conference)
    OpenGATE collaboration meeting, 03.-04.05.2012, Athen, Griechenland

Publ.-Id: 17331 - Permalink


Flash-lamp annealing of ternary rare earth oxides for use as alternative high-k materials
Lehmann, J.; von Borany, J.; Skorupa, W.; Schäfer, A.; Schubert, J.; Mantl, S.;
Motivated by the fact, that millisecond annealing methods are going to play an important role in an advanced CMOS technology, this investigation of the effects of flash-lamp annealing (FLA) on actual and possible future high-k materials was performed [1]. Employed high-k materials were HfO2, LaYbO3, LaScO3 or LaLuO3.
HfO2 is already used in the industry while LaYbO3, LaScO3 and LaLuO3 are interesting as possible replacements, because of their thermally stable (>800°C) amorphous states with k-values above 20 as well as large bandgaps > 5 eV [2, 3, 4].
The high-k materials were deposited on p-Si by atomic-layer, molecular beam or pulsed laser deposition. Afterwards, FLA was used as a post-deposition annealing technique in which the pulse durations and peak temperatures were varied from 1 to 20 ms and 1000 to 1300°C, respectively. Pt-top and Al-back contacts were created for electrical measurements.
The microstructure of the samples was investigated by electron microscopy, XRD and nuclear methods (RBS, ERD), while the electrical properties were derived from current-voltage and capacitance-voltage measurements. It was found that for example metal-oxide semiconductor capacitors (MOSCAP) containing LaLuO3 can profit from FLA because this oxide remains amorphous and the capacitance is increased. On the other hand, the picture is not so clear for HfO2-MOSCAPs, because their capacitance is reduced and the oxide crystallizes while the leakage current is decreased.

References:

[1] J. C. Gelpey, S. McCoy, D. Camm and W. Lerch, Mater. Sci. Forum 573-574, 257 (2008)
[2] W. Su, L. Yang, B. Li, Appl. Surf. Sci. 257, 2526 (2011)
[3] V. V. Afanas’ev, A. Stesmans, C. Zhao, M. Caymax, T. Heeg, J. Schubert, Y. Jia, D. G. Schlom, and G. Lucovsky, Appl. Phys. Lett. 85, 5917 (2004)
[4] J. Lehmann, N. Shevchenko, A. Mücklich, J.v. Borany, W. Skorupa, J. Schubert, J.M.J. Lopez, S. Mantl, Microelectron. Eng. 88, 1346 (2011)
Keywords: high-k, ternary rare earth oxides, flash-lamp annealing
  • Poster
    19th International Conferenz on Ion Implantation Technology, 25.-29.06.2012, Valladolid, Spanien

Publ.-Id: 17330 - Permalink


Post-deposition flash-lamp annealing of high-k materials
Lehmann, J.; Mücklich, A.; von Borany, J.; Skorupa, W.; Schäfer, A.; Schubert, J.; Mantl, S.;
In an advanced CMOS technology millisecond annealing methods such as flash lamp annealing (FLA) may play an important role [1]. For this reason, we did study the effects of FLA on actual and possible future high-k materials such as HfO2 or LaLuO3. HfO2 is already used in the industry while LaLuO3 is interesting as a possible replacement, because of its thermally stable (~1000°C) amorphous state with a k-value of 32 as well as its large bandgap of 5.2 eV and symmetrical band offsets of 2.1 eV [2].
TiN-capped and uncapped samples were annealed under different conditions with pulse durations ranging from 1 to 20 ms and peak temperatures up to 1300°C. The microstructure was investigated by electron microscopy, XRD and nuclear methods (RBS, ERD) Current-voltage and capacitance-voltage measurements helped to characterize the electrical properties. It was found that metal-oxide semiconductor capacitors containing LaLuO3 can profit from FLA because the oxide remains amorphous and the capacitance is increased. In case of HfO2 the capacitance is decreased and the oxide crystallizes.

References:

[1] J. C. Gelpey, S. McCoy, D. Camm and W. Lerch, Mater. Sci. Forum 573-574, 257 (2008)
[2] J. Lehmann, N. Shevchenko, A. Mücklich, J.v. Borany, W. Skorupa, J. Schubert, J.M.J. Lopez, S. Mantl, Microelectron. Eng. 88, 1346 (2011)
Keywords: high-k, ternary rare earth oxides, flash-lamp annealing
  • Lecture (Conference)
    E-MRS 2012 SPRING MEETING, 14.-18.05.2012, Strassbourg, Frankreich

Publ.-Id: 17329 - Permalink


Selective pump-probe measurements in Landau quantized graphene
Mittendorff, M.; Winnerl, S.; Schneider, H.; Helm, M.; Orlita, M.; Potemski, M.; Wendler, F.; Malic, E.; Knorr, A.; Sprinkle, M.; Berger, C.; de Heer, W. A.;
In two dimensional electron gases with parabolic band structure, the Landau level (LL) system is equidistant, hence bleaching of the absorption is strongly suppressed. In contrast to quantum wells in conventional semiconductors the dispersion in graphene is linear for low energies. Due to this linearity the Landau levels are not equidistant and pump-probe measurements are feasible. Additionally a Landau level at zero energy appears. We performed pump-probe measurements on quasi-neutral sheets of rotated multilayer epitaxial graphene in magnetic fields. The free-electron laser FELBE at Dresden-Rossendorf served as radiation source at a constant wavelength of 16.5 µm (photon energy of ~75 meV). The magnetic field was applied perpendicularly to the graphene sheets by a magneto-optical superconducting magnet system, which is able to generate a magnetic field of up to 7T. This combination of photon energy and variable magnetic field allowed us to perform resonant pump-probe measurements at three different Landau level transitions (see inset of Fig: 1): For the transitions LL-1(-2) -> LL2(1) and LL-2(-3) -> LL3(2) we could observe a slight increase of the pump-probe signal while the relaxation time stayed constant. For the transition LL-1(0) -> LL0(1) the amplitude of the pump-probe signal increased by a factor of 2.5, the relaxation time decreased from 20 ps to 5 ps. In fig.1 the signal amplitude is plotted as a function of the square root of the magnetic field. The faster relaxation was contrary to our expectations: Due to the reduced phase space we expected the relaxation time to increase. For further insights into the carrier dynamics we performed measurements with circularly polarized radiation. Therewith it was possible to distinguish between the transitions LL-1->LL0 and LL0->LL1. These measurements revealed complex dynamics involving positive and negative signals with a very fast component and a slow component with an increased relaxation time. We present a model that takes into account Auger-type processes as well as carrier cooling. The model explains the main signatures of the measured signals.
Keywords: Landau quantization relaxation dynamics pump-probe magnetic field graphene
  • Lecture (Conference)
    International Conference on Superlattices, Nanostructures, and Nanodevices, 22.-27.07.2012, Dresden, Deutschland

Publ.-Id: 17328 - Permalink


Combined PET/MR systems: an overview and comparison of currently available options
Herzog, H.; van den Hoff, J.;
The integration of positron emission tomography (PET) and magnetic resonance imaging (MRI) in a combined PET/MR scanner is attracting much interest. With this new bimodal approach novel functional-anatomical and multiparametric applications become feasible, which can be expected to deliver information beyond that accessible by separately applied modalities. Although the two technologies where initially regarded as inherently incompatible, different solutions have been developed and implemented to realise PET/MR instruments for both small animal and human bimodal imaging. The present review first summarizes the basic options for possible PET/MR designs. A chronological outline describes the evolution from the first ideas, how PET and MR imaging might be combined, over different experimental solutions to the systems recently realized by industry. The BrainPET/MR and the mMR developed by Siemens and the Philips Ingenuity TF PET/MR are characterised and application examples are provided illustrating the features of these instruments. Based on own experiences and those reported in different publications a number of open issues are discussed. Finally a short comparative analysis on the status and perspectives of human PET/MR imaging is given.
Keywords: Positron emission tomography; Magnetic resonance imaging; Diagnostic imaging
  • Quarterly Journal of Nuclear Medicine and Molecular Imaging 56(2012), 247-267

Publ.-Id: 17327 - Permalink


The HADES-at-FAIR Project
Lapidus, K.; Agakishiev, G.; Balanda, A.; Bassini, R.; Behnke, C.; Belyaev, A.; Blanco, A.; Böhmer, M.; Cabanelas, P.; Carolino, N.; Chen, J. C.; Chernenko, S.; Diaz, J.; Dybczak, A.; Epple, E.; Fabbietti, L.; Fateev, O.; Finocchiaro, P.; Fonte, P.; Friese, J.; Fröhlich, I.; Galatyuk, T.; Garzon, J. A.; Gernhäuser, R.; Gil, A.; Göbel, K.; Golubeva, M.; Gonzalez-Diaz, D.; Guber, F.; Gumberidze, M.; Harabasz, S.; Heidel, K.; Heinz, T.; Hennino, T.; Holzmann, R.; Huck, P.; Hutsch, J.; Ierusalimov, A.; Iori, I.; Ivashkin, A.; Jurkovic, M.; Kämpfer, B.; Kajetanowicz, M.; Karavicheva, T.; Koenig, I.; Koenig, W.; Kolb, B. W.; Korcyl, G.; Kornakov, G.; Kotte, R.; Kozuch, A.; Krebs, E.; Krücken, R.; Kuc, H.; Kühn, W.; Kugler, A.; Kurepin, A.; Kurilkin, A.; Kurilkin, P.; Ladygin, V.; Lalik, R.; Lange, J. S.; Liu, M.; Liu, T.; Lopes, L.; Lorenz, M.; Lykasov, G.; Maier, L.; Malakhov, A.; Mangiarotti, A.; Markert, J.; Metag, V.; Michalska, B.; Michel, J.; Müntz, C.; Münzer, R.; Naumann, L.; Palka, M.; Parpottas, Y.; Pechenov, V.; Pechenova, O.; Pereira, A.; Pietraszko, J.; Przygoda, W.; Ramstein, B.; Rehnisch, C.; Reshetin, A.; Rosier, P.; Rustamov, A.; Sadovsky, A.; Salabura, P.; Scheib, T.; Schmah, A.; Schuldes, H.; Schwab, E.; Siebenson, J.; Smolyankin, V.; Sobiella, M.; Sobolev, Y. G.; Spataro, S.; Spruck, B.; Ströbele, H.; Stroth, J.; Sturm, C.; Tarantola, A.; Teilab, K.; Tiflov, V.; Tlusty, P.; Traxler, M.; Trebacz, R.; Troyan, A.; Tsertos, H.; Usenko, E.; Vasiliev, T.; Visotski, S.; Wagner, V.; Weber, M.; Wendisch, C.; Wüstenfeld, J.; Yurevich, S.; Zanevsky, Y.;
After the completion of the experimental program at SIS18 the HADES setup will migrate to FAIR, where it will deliver high-quality data for heavy-ion collisions in an unexplored energy range of up to 8 A GeV. In this contribution, we briefly present the physics case, relevant detector characteristics and discuss the recently completed upgrade of HADES.

Publ.-Id: 17326 - Permalink


Subsecond thermal processing for advanced electronics and photovoltaics
Skorupa, W.;
This talk reviews the advances that subsecond thermal processing using flash lamps and lasers brings to the processing of the most advanced semiconductor materials, thus enabling the fabrication of novel electronic structures and materials. It will be demonstrated how such developments can translate into important practical applications leading to a wide range of technological benefits. Recently we could demonstrate that germanium and silicon exhibit superconductivity at ambient pressure. Techniques of the state-of-the-art semiconductor processing as ion implantation and FLA were used to fabricate such material based on a highly doped Ga-rich layer at the surface. Moreover we demonstrated that carrier-mediated ferromagnetism can be reached in manganese-implanted and Laser-annealed Ge. Regarding photovoltaic applications, we dealt with two aspects: (i) the thermal processing of so-called dirty silicon demonstrating a distinct improvement of the metal diffusion suppression compared to RTP and furnace treatments, and (ii), for the annealing of CIGS layers millisecond annealing leads to better optical output and lower degradation Whereas all these examples base on solid phase processing the more sophisticated approach of subsecond thermal processing regards on working with the liquid phase at the surface of solid substrates. A very recent example is the controlled formation of III-V nanocrystals (InAs, GaAs) in silicon after ion beam synthesis (Nano Lett. 11 (2011) 2814).
  • Invited lecture (Conferences)
    E-MRS 2012 SPRING MEETING, Symposium A: Advanced Silicon Materials Research for Electronic and Photovoltaic Applications III, 14.-18.05.2012, Strasbourg, France
  • Lecture (others)
    Eingeladener Seminarvortrag an CEMES, Toulouse, 12.07.2012, Toulouse, France

Publ.-Id: 17325 - Permalink


In-situ real-time observation of the self-assembled growth of ordered germanium nanocrystals embedded within a dielectric matrix
Grenzer, J.; Buljan, M.; Holý, V.; Baehtz, C.; Horák, L.; Bernstorff, S.; Radić, N.;
We report on an in-situ and ex-situ X-ray investigations of a self-assembled growth of Ge nanocrystals embedded in a dielectric matrix forming BCC- or FCC-like superstructures. Germanium quantum dots (QD’s) embedded in dielectric matrices like SiO2 [1] or Al2O3 [2] have numerous interesting properties e.g. a strong quantum confinement. They could be used in optoelectronic devices and memory systems. Such a material can be a key element for the development of a new generation of solar cells extending the spectral range for electrical energy generation, either for an up and/or down conversion of the incident photons or simply as one part of a multilayer stack arrangement.
Keywords: in-situ x-ray scattering & diffraction, Synchrotron based experiments
  • Lecture (Conference)
    The 11th Biennial Conference on High Resolution X-Ray Diffraction and Imaging, 15.-20.09.2012, Saint-Petersburg, Russia

Publ.-Id: 17323 - Permalink


Thin silicon films - texture and grain size improvement
Endler, R.; Voelskow, M.; Mücklich, A.; Schumann, T.; Skorupa, W.;
The structural optimization of polycrystalline silicon films is important to improve the electronic properties of microelectronic devices and photovoltaic solar cells, based on thin film silicon. The enlargement of the grain size is of big interest since the fabrication of silicon based thin film devices started. In this work we present results on the lateral dendritic growth in 100nm thin silicon layers which leads to lateral grain sizes in the range of 100µm. The second topic in this field is the manipulation of the grain lattice orientation within the layer which can lead to a uniformly oriented polycrystalline material.
  • Lecture (Conference)
    31. Deutsches Nutzertreffen RTP und Heißprozesse, 21.03.2012, Erlangen, Deutschland

Publ.-Id: 17322 - Permalink


Focused ion beam induced structural modifications in thin magnetic films.
Roshchupkina, O. D.; Grenzer, J.; Strache, T.; McCord, J.; Fritzsche, M.; Mücklich, A.; Baehtz, C.; Fassbender, J.ORC
Focused ion beam techniques are one way to modify locally the properties of magnetic thin films. We report on structural investigations of 50 nm thick non-ordered nano-crystalline Permalloy (Ni81Fe19) films modified by 30 keV Ga+ focused ion beam (FIB) irradiation. From the X-ray diffraction (XRD) measurements a considerable crystallite growth and a material texturing towards (111)-direction with a linearly increasing lattice constant was observed. In addition cross-sectional transmission electron microscope (XTEM) images show that crystallites are growing through the entire film at high irradiation fluences.
Extended X-ray absorption fine structure (EXAFS) analysis shows a perfect near-order coordination corresponding to a face-centered (fcc) unit cell for both FeNi and Ga atom surrounding. The structural changes are accompanied by a decrease of saturation polarization with increasing ion fluence. Such behavior is attributed to a simple incorporation of non-magnetic Ga atoms in the Permalloy film.

Publ.-Id: 17321 - Permalink


Iron assisted ion beam patterning of Si(001) in the crystalline regime
Macko, S.; Grenzer, J.; Frost, F.; Engler, M.; Hirsch, D.; Fritzsche, M.; Mücklich, A.; Michely, T.;
We present ion beam erosion experiments on Si(001) with simultaneous sputter co-deposition of steel at 660 K. At this temperature the sample remains remains within the crystalline regime during ion exposure and pattern formation takes place by phase separation of Si and iron-silicide. After an ion fluence of F ≈ 5.9 × 1021 ions m−2 investigations by atomic force microscopy and scanning electron microscopy identify sponge, segmented wall and pillar patterns with high aspect ratios and heights of up to 200 nm. Grazing incidence X-ray diffraction and transmission electron microscopy reveal the structures to be composed of polycrystalline iron-silicide. The observed pattern formation is compared to the one in the range from 140 K to 440 K under otherwise identical conditions, where a thin amorphous layer forms due to the ion bombardment.

Publ.-Id: 17320 - Permalink


Das Hochfeld-Magnetlabor Dresden: Rossendorfer Rekorde
Uhlarz, M.;
es hat kein Abstract vorgelegen.
  • Lecture (others)
    Berufsschulzentrum Radebeul, 20.06.2012, Radebeul, Deutschland

Publ.-Id: 17319 - Permalink


Investigation of metal binding by cell wall components of Gram-positive bacteria studied by QCM-D
Suhr, M.; Fischer, S.; Günther, T.; Raff, J.; Pollmann, K.;
Investigation of the interaction of metals with the biosphere is important not only from an ecological point of view but also from an application oriented one. Biosorption of metals by bacteria was intensively studied. Furthermore, bacterial cell wall components itself e.g. surface layer (S-layer) proteins, lipids and peptidoglycan were intensively studied. Nevertheless, the investigation of their interaction with metals both as molecules and as intact layers on a molecular level remains challenging.
Parts of our investigations concentrated on S-layers. These are the outermost cell envelope of many eubacteria and archaea, forming highly ordered paracrystalline lattices not only on the cell, but also after isolation on various technical surfaces by self-assembling processes. These proteins show remarkable high metal binding capacities.
In our work we used the quartz crystal microbalance with dissipation monitoring (QCM-D) in order to study the layer formation of single cell wall compounds and interaction processes on the nano scale range. This method gives a detailed understanding of biological structure formation and the amount of metal deposition. Within the experiments the influence of surface modification with adhesive promoters e.g. polyelectrolytes was studied in order to make exact statements regarding coating kinetics, layer stability and metal interaction. Subsequent atomic force microscopy (AFM) studies enable the imaging of bio nanostructures and reveal complex information of structural properties.
Aim of these investigations is the assembly of a simplified biological cell wall based on Gram-positive bacteria in order to clarify sorption processes in a complex system.
Keywords: biotechnology, S-layer, lipids, QCM-D, AFM, biosorption, proteins, layer formation, metal deposit, polyelectrolytes
  • Poster
    5th International Symposium on Biosorption and Bioremediation, 24.-28.06.2012, Prag, Tschechische Republik

Publ.-Id: 17318 - Permalink


Ge quantum dot lattices in Al2O3: a material with excellent mechanical and size-tuneable optical properties
Buljan, M.; Radić, N.; Ivanda, M.; Bogdanović-Radović, I.; Karlušić, M.; Grenzer, J.; Prucnal, S.; Dražić, G.; Pletikapić, G.; Svetličić, V.; Jerčinović, M.; Bernstorff, S.; Holy, V.;
In this article we show how to produce materials consisting of regularly ordered Ge quantum dots in amorphous alumina matrix with the controllable Ge quantum dot size, shape, spacing, crystalline structure and degree of regularity in the Ge quantum dot ordering. The production of such materials is achievable already at room temperature by magnetron sputtering deposition of a (Ge+Al2O3)/Al2O3 multilayer. The materials show large, size-dependent blueshift of the photoluminescence peak and enhancement in the oscillator strength caused by confinement effects. The materials also show advanced mechanical properties due to alumina matrix, and their internal structure is shown to be highly resistive to irradiation with energetic particles for a large range of the irradiation parameters. The reported materials have excellent potential for application in demanding environments for light harvesting.
Keywords: nano cluster, GISAXS

Publ.-Id: 17317 - Permalink


Ga(1−x)Mn(x)N epitaxial films with high magnetization
Kunert, G.; Dobkowska, S.; Li, T.; Reuther, H.; Kruse, C.; Figge, S.; Jakiela, R.; Bonanni, A.; Grenzer, J.; von Borany, J.; Stefanowicz, W.; Sawicki, M.; Dietel, T.; Hommel, D.;
We report on the fabrication of pseudomorphic wurtzite Gax Mnx N grown on GaN with Mn concentrations up to 10 % using molecular beam epitaxy. According to Rutherford backscattering the Mn ions are mainly at the Ga-substitutional positions, and they are homogeneously distributed according to depth-resolved Auger-electron spectroscopy and secondary-ion mass-spectroscopy measurements. A random Mn distribution is indicated by transmission electron microscopy, no Mn-rich clusters are present for optimized growth conditions. A linear increase of the c-lattice parameter with increasing Mn concentration is found using x-ray diffraction. The ferromagnetic behavior is confirmed by superconducting quantum-interference measurements showing saturation magnetizations of up to 150 emu/cm3 .
Keywords: GaN, GaMnN, DMS

Publ.-Id: 17316 - Permalink


TCOs auf Basis Tantal-dotierter TiO2 Schichten
Neubert, M.; Vinnichenko, M.; Cornelius, S.; Kolitsch, A.;
Die vielfältigen Anwendungen transparenter leitfähiger Oxide (TCO), wie zum Beispiel in Flachbildschirmen, Solarzellen und der Beleuchtungstechnik erfordern die Entwicklung neuartiger TCO-Materialien. Darüber hinaus ist der Einsatz der etablierten TCOs, wie Indiumzinnoxid (ITO) oder Fluor dotiertes Zinnoxid (FTO) zukünftig nur bedingt fortzuführen. Die Verwendung von ITO ist aufgrund des kontinuierlich steigenden Indiumpreises sehr kostenintensiv, während der Einsatz von FTO-Dünnschichten aufgrund des hochgradig toxischen Herstellungsprozesses weltweit umstritten ist. Es konnte gezeigt werden, dass Titandioxid dotiert mit Tantal (TTO) vergleichbare elektrische und optische Eigenschaften, verglichen mit den etablierten TCOs aufweist. Eine wesentliche Herausforderung besteht allerdings darin, TTO-Dünnschichten mittels eines industrienahen kostengünstigen Prozess abzuscheiden. Diese Problemstellung wurde gelöst, indem TTO-Schichten mittels eines 2-stufigen Prozesses bestehend aus Sputtern und anschließender thermischer Nachbehandlung abgeschieden wurden. Die dabei erreichten spezifischen Widerstände im Bereich von 0,001 Ohmcm sind für zahlreiche Anwendung ausreichend. Darüber hinaus wurde gezeigt, dass die Kurzzeittemperprozesse eine mögliche Alternative zur konventionellen Nachtemperung sind.
Keywords: transparent conductive oxide,TCO, TiO2, Ta, tantalum, thin film
  • Lecture (Conference)
    Workshop „Transparente leitfähige Oxide - Festkörperphysikalische Grundlagen und Technologie", 21.-22.05.2012, Dresden, Deutschland

Publ.-Id: 17315 - Permalink


CNT growth from C:Ni nanocomposites
Krause, M.; Haluska, M.; Wenisch, R.; Kunze, T.; Abrasonis, G.; Gemming, S.;
Precise control of single walled carbon nanotube (SWCNT) diameter, chirality, alignment, and intertube arrangement are still remaining challenges in the catalytic chemical vapour deposition (CCVD) synthesis. In this context it has still to be clarified whether a predefined size and shape of the nanoparticles can be stabilized by a suitable matrix material while preserving the catalytic activity of the metal.
For this study Ni nanoparticles were encapsulated in an amorphous carbon matrix by physical vapour deposition. As prepared Ni catalysts were used for CNT fabrication by laser assisted CVD applying either no external carbon source or C2H4 gas, and by low pressure CVD applying C2H2 or CH4 as carbon source. The broad range of CNT synthesis conditions indicates the robustness of the embedded Ni particles as a catalyst for carbon nanotube formation. SEM and laser wavelength dependent Raman spectroscopy were used for CNT characterisation. The nickel-SWCNT-interaction was modelled by density functional calculations with the projector augmented plane wave method, utilizing the generalized gradient approximation for the exchange-correlation functional.
Keywords: Nanocomposites, Carbon Nanotubes, Synthesis
  • Poster
    International winterschool on electronic properties of novel materials, 03.-10.03.2012, Kirchberg, Österreich

Publ.-Id: 17314 - Permalink


Fabrication of Si(1-x)Ge(x) Alloy on Silicon by Ge-ion-implantation and Short-Time-Annealing
Gao, K.; Prucnal, S.; Mücklich, A.; Skorupa, W.; Zhou, S.;
Silicon-Germanium is commonly used as a semiconductor material in integrated circuits (ICs) for heterojunction bipolar transistors or as a strain-inducing layer for CMOS transistors. Normally epitaxial methods (e.g., CVD, MBE) are applied to the synthesis of Si1-xGex alloys.
In our contribution we present the fabrication of Si1-xGex alloy by ion-implantation and short-time-annealing. The Ge ions in the fluence range of 3×1016 - 10×1016 cm2 were implanted into monocrystalline (100)-oriented Si wafers covered by 50 nm thermal oxide at an energy of 100 keV. As the consequence, the 50 nm amorphous Ge rich Si layers were obtained. The recrystallization of the implanted layers and the Si1-xGex alloying were carried out by flash lamp annealing or scanning continuous laser annealing in the time scale of 20 ms or 1 s, respectively. Both flash lamp treatment and laser annealing at high energy densities lead to local melting of the germanium rich silicon layer. The recrystallization of the Si1-xGex layer takes place due to millisecond range liquid phase epitaxy. Formation of the high quality monocrystalline Si1-xGex layer was confirmed by μ-Raman spectroscopy, RBS channeling and cross-section TEM investigation. The μ-Raman spectra reveal tree phonon modes located at around 293, 404 and 432 cm-1 corresponding to the Ge-Ge, Si-Ge and Si-Si in the Si1-xGex alloy vibrational modes, respectively. Due to much higher carrier mobility in SiGe layer than in silicon such system can be used for the fabrication of advanced devices.
Keywords: Silicon Germanium, ion-implantation, flash lamp annealing, continuous laser annealing
  • Lecture (Conference)
    IX-th International Conference Ion Implantation and other Applications of Ions and Electrons, 25.-28.06.2012, Kazimierz Dolny, Poland

Publ.-Id: 17312 - Permalink


Ressourcenanalytik - Spuren finden mit (Sp-)Ionen
Merchel, S.; Renno, A. D.; Rugel, G.;
Die Ionenstrahlanalytik nutzt hochenergetische Ionen zur Material-, Struktur- und Radionuklidanalyse. Sie wird im Rahmen der Ressourcenanalytik eingesetzt, um neue Technologien zur Erkundung, Gewinnung, Nutzung und Recycling von Rohstoffen entlang der Wertschöpfungskette zu entwickeln. Die Projektgruppe Ionenstrahlanalytik am Helmholtz-Institut Freiberg für Ressourcentechnologie (HIF) ist stark methodisch orientiert und entwickelt in interdisziplinären Forschungsprojekten nahezu unikale Analysemethoden unter Einsatz bzw. Eigenbau neuester Technologien. Diese Methoden eröffnen neue und interessante Möglichkeiten der (Ultra-)Spurenelementanalyse. Das HIF ist eine gemeinsame Einrichtung des Helmholtz-Zentrums Dresden-Rossendorf und der TU Bergakademie Freiberg.
Keywords: accelerator mass spectrometry, resource analytics, ion beam analysis, Super-SIMS
  • Lecture (others)
    Dresdner Seniorenakademie, TU Dresden, WS 2012/2013, 30.01.2013, Dresden, Deutschland

Publ.-Id: 17311 - Permalink


ADRIANA Project: identification of research infrastructures for the SFR, within the frame of European Industrial for substainable Nuclear Fission
Latge, O.; Gastaldi, O.; Vala, L.; Gerbeth, G.; Homann, C.; Benoir, P.; Papin, J.; Girault, N.; Roelofs, F.; Buceniecks, I.; Paffumi, E.; Ciampichetti, A.;
Fast neutron reactors have a large potential as sustainable energy source. In particular, Sodium Fast Reactors (SFR) with al closed fuel cycle and potential for minor actinide burning may allow minimization of volume and heat load of high level waste and provide improved use of natural resources (as compared to only 1 % energy recovery in the current once-through fuel cycle, with Thermal Reactors, such as EPR).
Keywords: SFR, sodium, experimental facilities, ADRIANA
  • Contribution to proceedings
    2012 International Congress on the Advances in Nuclear Power Plants (ICAPP'12), 24.-28.06.2012, Chicago, USA
  • Lecture (Conference)
    2012 International Congress on the Advances in Nuclear Power Plants (ICAPP'12), 24.-28.06.2012, Chicago, USA

Publ.-Id: 17310 - Permalink


Positron emission tomography in pebble beds. Part 1: Liquid particle deposition
Barth, T.; Ludwig, M.; Kulenkampff, J.; Gründig, M.; Franke, K.; Lippmann-Pipke, J.; Hampel, U.;
Accidental scenarios such as the depressurisation of the primary circuit of high temperature gas cooled pebble bed reactors may lead to the release of fission products via the discharge of radioactive graphite dust. For a detailed source term assessment in such accident scenarios knowledge of the flow mechanics of dust transport in complex coolant circuit components, like pebble beds, recuperator structures and pipe systems is necessary. In this article an experimental study of aerosol deposition in a pebble bed is described. We investigated the deposition of radiolabelled liquid aerosol particles in a scaled pebble bed in an air-driven small-scale aerosol flow test facility under isothermal ambient conditions. The aerosol particles were generated by means of a condensational aerosol generator with potassium-fluoride (KF) condensation nuclei. Particle concentration measurements upstream and downstream of the pebble bed were performed by isokinetic sampling and particle counting. The results agree with typical deposition curves for turbulent and inertia driven particle deposition. Furthermore, positron emission tomography (PET) was performed to visualize and measure particle deposition distributions in the pebble bed. Results of a selected deposition experiment with moderately large particles (daero = 3.5 μm, Re′pb=2200) show that the deposited particles are located in the vicinity of the upstream stagnation points of the pebbles. These findings support the thesis that inertia driven particle deposition is predominating.
Keywords: Aerosol deposition, Positron emission tomography, High Temperature Reactor

Publ.-Id: 17309 - Permalink


Experimental setup for in vivo irradiation with laser accelerated electrons
Schürer, M.; Brüchner, K.; Karsch, L.; Nicolai, M.; Oppelt, M.; Pawelke, J.;
  • Poster
    Oncoray Retreat, 07.-08.03.2012, Dresden, Deutschland

Publ.-Id: 17308 - Permalink


First in vivo experiments with laser accelerated electrons
Oppelt, M.; Laschinsky, L.; Beyreuther, E.; Brüchner, K.; Kaluza, M.; Karsch, L.; Krause, M.; Leßmann, E.; Nicolai, M.; Reuter, M.; Säbert, A.; Schnell, M.; Schürer, M.; Pawelke, J.;
  • Poster
    OncoRay Retreat, 07.-08.03.2012, Dresden, Deutschland

Publ.-Id: 17307 - Permalink


Dosimetry for in vivo experiments with laser accelerated electrons
Karsch, L.; Schürer, M.; Woithe, J.; Pawelke, J.;
  • Poster
    OncoRay Retreat, 07.-08.03.2012, Dresden, Deutschland

Publ.-Id: 17306 - Permalink


Establishment of a tumor model on the ear of mice
Brüchner, K.; Oppelt, M.; Pfitzmann, D.; Krause, M.; Pawelke, J.; Baumann, M.;
  • Poster
    OncoRay Retreat, 07.-08.03.2012, Dresden, Deutschland

Publ.-Id: 17305 - Permalink


First Approximation Concept Design for Achromatic Particle Beamline for Laser Accelerated Protons
Masood, U.; Bussmann, M.; Enghardt, W.; Karsch, L.; Pawelke, J.;
  • Poster
    OncoRay Retreat, 07.-08.03.2012, Dresden, Deutschland

Publ.-Id: 17304 - Permalink


Radiobiological consequences of ultra-short electron pulses
Beyreuther, E.; Karsch, L.; Kroll, F.; Laschinsky, L.; Leßmann, E.; Oppelt, M.; Richter, C.; Schürer, M.; Woithe, J.; Pawelke, J.;
  • Poster
    OncoRay Retreat, 07.-08.03.2012, Dresden, Deutschland

Publ.-Id: 17303 - Permalink


Towards the medical application of laser driven particle beams: In vitro dose response studies as the first translational step
Beyreuther, E.; Baumann, M.; Burris-Mog, T.; Enghardt, W.; Kaluza, M.; Karsch, L.; Kraft, S.; Laschinsky, L.; Leßmann, E.; Metzkes, J.; Nicolai, M.; Oppelt, M.; Richter, C.; Schlenvoigt, H.-P.; Schramm, U.; Schürer, M.; Zeil, K.; Pawelke, J.;
  • Poster
    2012 Conference of the Association of Radiation Research, 25.-27.06.2012, London, Great Britain

Publ.-Id: 17302 - Permalink


Laserbeschleunigte Ionen für die Strahlentherapie
Pawelke, J.;
  • Invited lecture (Conferences)
    18. Jahreskongress der Deutschen Gesellschaft für Radioonkologie, 07.-10.06.2012, Wiesbaden, Deutschland

Publ.-Id: 17301 - Permalink


Eigenschaften eines schnellen, szintillatorbasierten 3D-Dosimeters
Karsch, L.; Kroll, F.; Pawelke, J.;
  • Abstract in refereed journal
    Strahlentherapie und Onkologie 188(2012)Suppl. 1, 13
  • Lecture (Conference)
    18. Jahreskongress der Deutschen Gesellschaft für Radioonkologie, 07.-10.06.2012, Wiesbaden, Deutschland

Publ.-Id: 17300 - Permalink


Towards laser driven proton therapy: results of the first translational step
Laschinsky, L.; Baumann, M.; Beyreuther, E.; Burris-Mog, T.; Cowan, T.; Enghardt, W.; Kaluza, M.; Karsch, L.; Kraft, S.; Leßmann, E.; Metzkes, J.; Nicolai, M.; Oppelt, M.; Richter, C.; Schlenvoigt, H.-P.; Schramm, U.; Schürer, M.; Zeil, K.; Pawelke, J.;
  • Abstract in refereed journal
    Radiotherapy and Oncology 102(2012)Suppl. 1, S76
  • Lecture (Conference)
    International Conference on Translational Research in Radiation Oncology / Physics for Health in Europe, 27.02.-02.03.2012, Geneva, Switzerland

Publ.-Id: 17299 - Permalink


Biologische Wirksamkeit laserbeschleunigter Protonen im Vergleich zu konventionell beschleunigten Protonen
Oppelt, M.; Baumann, M.; Beyreuther, E.; Burris-Mog, T.; Dammene, Y.; Enghardt, W.; Karsch, L.; Kraft, S.; Laschinsky, L.; Leßmann, E.; Metzkes, J.; Naumburger, D.; Richter, C.; Schramm, U.; Schürer, M.; Woithe, J.; Zeil, K.; Pawelke, J.;
  • Contribution to proceedings
    20. Symposium Experimentelle Strahlentherapie und Klinische Strahlenbiologie, 10.-12.02.2011, Dresden, Deutschland
    Experimentelle Strahlentherapie und Klinische Strahlenbiologie 20, 73-77
  • Lecture (Conference)
    20. Symposium Experimentelle Strahlentherapie und Klinische Strahlenbiologie, 10.-12.02.2011, Dresden, Deutschland

Publ.-Id: 17298 - Permalink


Influence of pulse length and high pulse dose on saturation correction of ionization chamber
Karsch, L.; Richter, C.; Pawelke, J.;
  • Contribution to proceedings
    International Symposium on Standards, Applications and Quality Assurance in Medical Radiation Dosimetry (IDOS), 09.-12.11.2010, Wien, Austria
    Book of Extended Synopsis International Atomic Energy Agency IAEA-CN-182 (2010), 273-274
  • Poster
    International Symposium on Standards, Applications and Quality Assurance in Medical Radiation Dosimetry (IDOS), 09.-12.11.2010, Wien, Austria

Publ.-Id: 17297 - Permalink


Towards laser-plasma ion accelerators for cancer therapy
Pawelke, J.;
  • Invited lecture (Conferences)
    13th Workshop on Ion Beams in Biology and Medicine (IBIBAM), 26.-29.10.2010, Berkeley/CA, USA

Publ.-Id: 17296 - Permalink


Biologische Wirksamkeit von laserbeschleunigten Elektronen im Vergleich zu konventionell beschleunigten Elektronen
Laschinsky, L.; Beyreuther, E.; Enghardt, W.; Kaluza, M.; Karsch, L.; Leßmann, E.; Naumburger, D.; Nicolai, M.; Pawelke, J.; Richter, C.; Sauerbrey, R.; Schlenvoigt, H.-P.; Baumann, M.;
  • Contribution to proceedings
    19. Symposium Experimentelle Strahlentherapie und Klinische Strahlenbiologie, 04.-06.03.2010, Dresden, Germany
    Experimentelle Strahlentherapie und klinische Strahlenbiologie 19, 109-111
  • Poster
    19. Symposium Experimentelle Strahlentherapie und Klinische Strahlenbiologie, 04.-06.03.2010, Dresden, Deutschland

Publ.-Id: 17295 - Permalink


The project onCOOPtics: High-intensity lasers for radiooncology
Enghardt, W.; Baumann, M.; Cowan, T.; Kaluza, M.; Pawelke, J.; Sauerbrey, R.; Schramm, U.; Tünnermann, A.;
Background: The present technology for proton and ion therapy requires large devices for accelerating and delivering the beams with accordingly high investment costs. Therefore, the potential of several technologies for developing compact and cost effective sources of therapeutic proton or ion beams is intensively studied. One feasible solution may be the interaction of ultra-short, high-intensity laser pulses with matter.

Material and methods: Combining their competences in laser physics and technology as well as in radiation physics and biology the centers ultra optics in Jena and OncoRay in Dresden, respectively, initiated in 2007 the research project onCOOPtics being focused on the long-term goal of developing laser driven particle irradiation devices. The work in Jena is concentrated onto the physics of laser-matter-interaction, the technology of high-power lasers and the development of optimal radiator targets. The research in Dresden comprises the real-time physical characterization of laser driven particle pulses, the investigation of the biological efficiency of this new radiation modality and the development of dedicated therapeutic irradiation equipment. For experiments three high-intensity laser systems are available: JeTi (pulse power: 15 TW, pulse duration: 80 fs) and POLARIS (150 TW, 170 fs) in Jena as well as DRACO (150 TW, 25 fs) in Dresden all equipped with real-time dosimetry and setups for in-vitro cell radiobiology.

Results: The main scientific results of onCOOPtics are (i) the optimization of laser based ion beam generation, in particular the development of novel and highly reliable techniques for direct manipulation of the ion energy spectrum and spatial distribution; (ii) the development of devices for a real-time physical characterization of laser accelerated charged particle pulses; (iii) the first systematic in-vitro studies of the RBE of laser driven electron beams, (iv) the production of proton beams with energies up to 12 MeV; (v) the prediction of an enhancement of proton energies by targets consisting of stacked ultrathin (~100 nm) foils.

Conclusions: If a clinical laser based accelerator for protons or ions will be feasible at all, the development of this technology is expected to require intensive research in the upcoming 10 years. Among other groups worldwide the the partners in the onCOOPtics project have taken the first successful steps on this risky way.
  • Lecture (Conference)
    48th Particle Therapy Cooperative Group (PTCOG) Meeting, 28.09.-03.10.2009, Heidelberg, Germany
  • Contribution to proceedings
    48th Particle Therapy Cooperative Group (PTCOG) Meeting, 28.09.-03.10.2009, Heidelberg, Germany
    Abstract Book (2009) 49 DOI: 10.3205/09ptcog162

Publ.-Id: 17294 - Permalink


Radiobiology with laser accelerated particle pulses
Pawelke, J.;
  • Invited lecture (Conferences)
    440th Heraeus Seminar on Laser Driven Particle and X-ray Sources for Medical Applications, 13.-17.09.2009, Frauenwörth, Germany

Publ.-Id: 17293 - Permalink


Laser-Teilchen Beschleuniger für die Strahlentherapie: Zellexperimente mit Laser beschleunigten Elektronen
Pawelke, J.;
  • Lecture (others)
    Fortbildungsvortrag, 23.03.2009, Dresden, Deutschland

Publ.-Id: 17292 - Permalink


Dosis-Effekt-Kurven für in vitro Zellbestrahlungen mit laserbeschleunigten Elektronen
Laschinsky, L.; Beyreuther, E.; Enghardt, W.; Kaluza, M.; Karsch, L.; Leßmann, E.; Naumburger, D.; Nicolai, M.; Pawelke, J.; Richter, C.; Sauerbrey, R.; Schlenvoigt, H.-P.; Baumann, M.;
  • Lecture (Conference)
    18. Symposium für Experimentelle Strahlentherapie und Klinische Strahlenbiologie, 13.-14.02.2009, Dresden, Germany
  • Contribution to proceedings
    18. Symposium Experimentelle Strahlentherapie und Klinische Strahlenbiologie, 13.-14.02.2009, Dresden, Germany
    Experimentelle Strahlentherapie und klinische Strahlenbiologie, Vol. 18, Dresden, 139

Publ.-Id: 17291 - Permalink


Laser particle accelerators for radiotherapy: cell response to laser-accelerated electron beams
Pawelke, J.;
  • Lecture (Conference)
    2nd Symposium on Laser-Driven Relativistic Plasmas Applied to Science, Industry and Medicine, 19.-23.01.2009, Kizugawa/Kyoto, Japan

Publ.-Id: 17290 - Permalink


Methods and equipment for in vitro cell experiments at laser particle accelerators
Leßmann, E.; Beyreuther, E.; Laschinsky, L.; Naumburger, D.; Pawelke, J.;
  • Poster
    OncoRay Retreat, 14.-15.01.2009, Bautzen, Germany

Publ.-Id: 17289 - Permalink


Biological effectiveness of laser-accelerated electron beams: in vitro cell studies
Laschinsky, L.; Beyreuther, E.; Enghardt, W.; Karsch, L.; Leßmann, E.; Naumburger, D.; Nicolai, M.; Pawelke, J.; Richter, C.; Sauerbrey, R.; Schlenvoigt, H.-P.; Baumann, M.;
  • Poster
    OncoRay Retreat, 14.-15.01.2009, Bautzen, Germany

Publ.-Id: 17288 - Permalink


Dosimetric characterization of a laser-accelerated electron beam for precise cell irradiation experiments.
Karsch, L.; Beyreuther, E.; Enghardt, W.; Laschinsky, L.; Leßmann, E.; Nicolai, M.; Pawelke, J.; Richter, C.; Sauerbrey, R.; Schlenvoigt, H.-P.; Woithe, J.; Baumann, M.;
No abstract.
Dosimetric characterization of a laser-accelerated electron beam for precise cell irradiation experiments
  • Poster
    OncoRay Retreat, 14.-15.01.2009, Bautzen, Germany

Publ.-Id: 17287 - Permalink


Intersubband dynamics in two-photon quantum well infrared photodetectors
Franke, C.; Schneider, H.; Faist, J.; Liu, H. C.;
Two-photon quantum well infrared photodetectors (QWIPs) are interesting nonlinear devices for autocorrelation measurements in the mid-infrared and THz-regime. Here we investigate two-photon QWIPs in the mid-infrared with absorption wavelengths at around six microns, based on the material systems InGaAs/AlGaAs on GaAs and GaInAs/AlInAs on InP. We study the intersubband relaxation dynamics by interferometric autocorrelation. To create the necessary mid infrared sub-picosecond pulses, we use a regenerative amplifier system with subsequent wavelength conversion by optical parametric amplification and difference frequency generation. With this we can create mid-infrared laser pulses shorter than 200 fs tunable from 3 to 10 µm. For the intersubband relaxation time we determined values between 590 and 730 fs.
Keywords: QWIP, Interferometric Autocorrelation
  • Poster
    DPG-Frühjahrstagung 2012, 25.-30.03.2012, Berlin, Deutschland
  • Poster
    ICSNN 2012, 22.-27.07.2012, Dresden, Deutschland

Publ.-Id: 17286 - Permalink


Sensitization of the blue-green electroluminescence by gadolinium coupled to Si nanocluster embedded in a SiO2 matrix
Prucnal, S.; Rebohle, L.; Sun, J. M.; Skorupa, W.; Drozdziel, A.; Pyszniak, K.; Turek, M.; Zuk, J.;
In this work an enhancement of the blue and green electroluminescence (EL) related to silicon inclusions into SiO2 layer by gadolinium co-doping was investigated. The blue (460 nm) and green (550 nm) EL corresponds to the oxygen-deficient-centres (ODC) and Si nanoclusters with average diameter below 1 nm, respectively. After gadolinium co-doping a fourfold increase of the total EL intensity was observed. It was found that the increase of the blue and green EL is due to the energy transfer from Gd3+ ions to the ODC defects and amorphous silicon nanoclusters. Moreover, the gadolinium co-doping increases the concentration of the small silicon nanoclusters.
Keywords: electroluminescence, Gd, Si-nc, MOSLED, energy transfer
  • Poster
    RADIATION INTERACTION WITH MATERIAL AND ITS USE IN TECHNOLOGIES 2012, 14.-17.05.2012, Kaunas, Lithuania
  • Open Access LogoMaterials Science - Medziagotyra 19(2013)2, 125-128
    DOI: 10.5755/j01.ms.19.2.1789

Publ.-Id: 17285 - Permalink


Conductivity type and crystal orientation of GaAs nanocrystals in silicon
Prucnal, S.; Voelskow, M.; Mücklich, A.; Liedke, M. O.; Pyszniak, K.; Drozdziel, A.; Turek, M.; Zuk, J.; Skorupa, W.;
Semiconductors quantum dots of the size in the range of the exciton Bohr radius or smaller are very attractive objects, both for research and application, due to their special optical and electrical properties. In this paper we present investigations of microstructural, electrical and optical properties of GaAs quantum dots (QDs) formed in silicon. The GaAs QDs were obtained by means of sequential ion implantation and flash lamp annealing (FLA). It is shown that the crystallographic orientation of nanocrystals (NCs) and their size can be controlled by varying the annealing parameters. Besides the crystallographic orientation the conductivity type of the GaAs NCs can be controlled as well. The influence of the post implantation millisecond-range annealing on the evolution of the nanoparticles size, shape, crystallographic orientation and doping type of GaAs QDs is discussed.
Keywords: GaAs, ion implantation, flash lamp annealing, silicon, quantum dots
  • Poster
    RADIATION INTERACTION WITH MATERIAL AND ITS USE IN TECHNOLOGIES 2012, 14.-17.05.2012, Kaunas, Lithuania

Publ.-Id: 17284 - Permalink


Flash lamp processing of III/V nanostructures in silicon
Turek, M.; Prucnal, S.; Voelskow, M.; Mücklich, A.; Liedke, M. O.; Pyszniak, K.; Drozdziel, A.; Zuk, J.; Skorupa, W.;
Conventionally, the integration of III-V semiconductors with silicon is based on heteroepitaxial growth of multi-layered structures on silicon. But up to now the modification of the optoelectronic properties of silicon in the microelectronic industry is based on the ion implantation method and subsequent thermal annealing. An alternative technique to the epitaxial growth of III-V nanostructures is the high fluence ion implantation followed by milliseconds range annealing. Potentially, with this method any kind of compound semiconductors can be formed in any solid substrate. InP and GaAs with a bulk band gap of 1.34 and 1.42 eV at room temperature, respectively, are most suitable for near infrared light emitters, and InAs (0.35 eV) with an extremely high electron mobility (up to 40000 cm2/Vs) seems to be the most suitable candidate for better electronic devices performance. In this paper formation of the InAs, GaAs and InP nanocrystals in silicon are presented. The optoelectronic and microstructural properties of the compound semiconductors nanostructures were investigated by means of -Raman and temperature dependent photoluminescence spectroscopy, X-ray diffraction, high-resolution transmission electron microscopy (HRTEM) and energy-dispersive X-ray spectroscopy (EDS). It is show that conductivity type, size and crystallographic orientation of the III-V nanostructures can be fully controlled by varying implantation and annealing parameters. Finally the heterojunction devices consisting of III-V NCs on a silicon finger realized by selective etching of silicon will be presented.
Keywords: III-V quantum dots, ion implantation, flash lamp annealing, silicon
  • Poster
    RADIATION INTERACTION WITH MATERIAL AND ITS USE IN TECHNOLOGIES 2012, 14.-17.05.2012, Kaunas, Lithuania

Publ.-Id: 17283 - Permalink


Flash Lamp Processing of III/V compound semiconductors on silicon and SOI wafers for functional photronic devices
Prucnal, S.; Zuk, J.; Pyszniak, K.; Drozdziel, A.; Facsko, S.; Mücklich, A.; Zhou, S. Q.; Ou, X.; Liedke, M. O.; Liedke, B.; Turek, M.; Skorupa, W.;
One of the solutions enabling performance progress, which can overcome the downsizing limit in silicon technology, is the integration of different functional optoelectronic devices within a single chip. Silicon with its indirect band gap has poor optical properties, which is its main drawback. Therefore, a different material has to be used for the on-chip optical interconnections, e.g. a direct band gap III-V compound semiconductor material. Recently we demonstrated a compact, CMOS compatible and fully integrated solution for the integration of III-V semiconductor nanocrystals with silicon technology for optoelectronic applications. They are synthesized in silicon using combined ion beam implantation and millisecond flash lamp annealing (FLA) techniques [NanoLett. 11, 2814 (2011)]. FLA appears to be the most suitable technique for this purpose. The energy budget introduced to the sample during FLA is sufficient to recrystallize silicon amorphized during the ion implantation and to form III-V nanocrystals (NCs) via the liquid phase. In this talk we will present results of the microstructural, optical and electrical properties of III-V quantum dots (InAs, GaAs and InP) formed in silicon or SOI wafers. An evolution of the III-V nanocrystals growth during FLA and the influence of the annealing parameters on the crystallographic orientation, shape and size will be explored. Moreover, the self-organization of the III-V nano-objects on the SOI wafers after flashing will be presented. A unique nano-swelling effect appearing during ion implantation of the SOI wafers combined with milliseconds range liquid phase epitaxy for the self-organization is responsible. Conventional selective etching was used to form the n-III-V/p-Si heterojunction. Current-voltage measurements confirm the heterojunction diode formation between n-type III-V quantum dots and p-type Si substrate. The main advantage of our method is its integration with large-scale silicon technology, which also allows applying it for Si-based photronic devices.
Keywords: III-V QDs, silicon, ion implantation, SOI, flash lamp annealing, heterojunction
  • Invited lecture (Conferences)
    9th International Conference Ion implantation and other applications of ions and electrons, ION 2012, 25.-28.06.2012, Kazimierz Dolny, Poland

Publ.-Id: 17282 - Permalink


Superconducting layers by Ga implantation and short-term annealing in Si
Fiedler, J.; Heera, V.; Skrotzki, R.; Herrmannsdörfer, T.; Voelskow, M.; Mücklich, A.; Schmidt, B.; Skorupa, W.; Gobsch, G.; Helm, M.;
Superconductivity in elemental group-IV semiconductors is of great interest because of both, the high potential for new microelectronic applications and its underlying physics.
To observe superconductivity at ambient pressure conditions high doping levels are needed. Sufficient doping concentrations of few at.% were achieved first for boron doped diamond [1]. Suprisingly also silicon, the basic material of todays microelectronic indurstry becomes superconducting below 0.6 K when heavily doped with boron [2]. In our previous work we used ion implantation and short-term annealing to fabricate superconducting Ga doped Ge layers with critical temperatures below 1 K [3]. The solid solubility is exceeded by far and therefore the presence of Ga clusters has to be excluded [4].
However the question arises, how superconducting precipitates influence the low- temperature transport properties. We demonstrate the possibility of embedding extrinsic superconducting nanolayers in commercial microelectronic Si wafers. Ga implantation (4x1016cm-2) through a 30 nm SiO2 cover layer is used because Ga itself is a superconducting element. Sturctural investigations by means of RBS/C and TEM reveal the stabilization of a Ga-rich layer at the SiO2/Si interfae after rapid thermal annealing (RTA). At defined RTA temperatures of 600 – 700°C this interface layer becomes superconducting [5,6]. Amorphous Ga has a critical temperature of 7 K which is comparable to the value of our Ga-rich interface layers. High critical magnetic fields up to 14 T and critical current densities as high as 50 kA/cm2 make the Si:Ga layers interesting for applications.
These results in combination with investigations on similar prepared Ga-rich layers at SiO2/Ge interfaces imply that superconductivity driven by Ga clusters occurs at temperatures of 6 – 7K [7]. If in Ge the onset of superconductivity is below 1 K, it can clearly be attributed to a doping effect.

Financial support by DFG (HE 2604/7-1) is gratefully acknowledged.
[1] E. A. Ekimov et al., Nature 2004;428:542.
[2] E. Bustarret et al., Nature 2006;444:465.
[3] T. Herrmannsdörfer et al., Phys, Rev. Lett. 2009;102:217003.
[4] V. Heera et al., J. Appl. Phys. 2010;107:053508.
[5] R. Skrotzki et al., Appl. Phys. Lett. 2010;97:192505.
[6] J. Fiedler et al., Phys. Rev. B 2011;83:214504.
[7] J. Fiedler et al., Phys. Rev. B 2012;85:134530.
  • Lecture (Conference)
    IX-th International Conference ION IMPLANTATION AND OTHER APPLICATIONS OF IONS AND ELECTRONS - ION 2012 (Ausgezeichnet mit dem 1. Preis für den besten Vortrag im "Young Scientist Contest".), 25.-28.06.2012, Kazimierz Dolny, Polen

Publ.-Id: 17281 - Permalink


Plasma Immersion Ion Implantation for the doping and texturization of silicon based solar cells
Prucnal, S.; Abendroth, B.; Krockert, K.; König, K.; Kolitsch, A.; Steinert, M.; Möller, H. J.; Skorupa, W.;
Cost reduction is the overall goal in the further development of solar cell technologies. In case of low quality mc-Si containing a relatively high concentration of metal impurities a low temperature process is desirable for solar cell fabrication. In order to avoid diffusion of metal impurities into the space charge region of the p-n junction the temperature of the mc-Si substrate should not exceed 400 oC. Although ion implantation doping got very recently distinct consideration for doping of monocrystalline solar material, efficient doping of multicrystalline solar material remains the main challenge to reduce costs. The influence of different annealing and implantation techniques on the optical and electrical properties of mc-Si solar cells was investigated. Flash Lamp Annealing in the ms-range combined with plasma immersion ion implantation (PIII) is demonstrated here as a very promising techniques for the emitter formation at an overally low thermal budget.
The flat silicon surface has a natural reflectivity in the range of 40 % with a strong spectral dependence. The minimization of the reflection loss is very important for high efficiency solar cells fabrication. In order to reduce the surface reflectivity wet chemical etching is the most widely used method in photovoltaic fabrication. Here we present a novel environment friendly method for silicon texturisation. As the reactive gases the mixture of SF6 and O2 with the ratio of 3:2 was used. After 10 min etching the black needle-like surface was obtained. The black silicon fabricated by PIII etching shows the average reflectance below 2% measured over the range from 200 nm to 1100 nm. Presented technology shows great promise to replace the conventional POCl3 –doping and wet chemical etching texturization for efficient silicon based solar cells fabrication.
Keywords: mc-Si, black silicon, flash lamp annealing, PIII, solar cells
  • Poster
    9th International Conference Ion implantation and other applications of ions and electrons, ION 2012, 25.-28.06.2012, Kazimierz Dolny, Poland

Publ.-Id: 17280 - Permalink


III-V compound semiconductors integrated with silicon for functional photronic devices
Prucnal, S.; Facsko, S.; Mücklich, A.; Zhou, S. Q.; Ou, X.; Liedke, M. O.; Turek, M.; Zuk, J.; Skorupa, W.;
The further downsizing of CMOS devices below 16 nm will need to solve some of the practical limits caused by one of the integration issues, such as chip performance, cost of development and production, power dissipation, reliability, etc. One solution for such a performance progress is the integration of different functional optoelectronic elements within one chip.
Recently we demonstrated a compact, CMOS compatible and fully integrated solution for the integration of III-V semiconductor nanocrystals with silicon technology for optoelectronic applications. They are synthesized in silicon using combined ion beam implantation and millisecond flash lamp annealing (FLA) techniques [NanoLett. 11, 2814 (2011)]. FLA appears to be the most suitable technique for this purpose. The energy budget introduced to the sample during FLA is sufficient to recrystallize silicon amorphized during the ion implantation and to form III-V nanocrystals (NCs) via the liquid phase. In this talk we will present results of the microstructural, optical and electrical properties of III-V quantum dots (InAs, GaAs and InP) formed in silicon. Conventional selective etching was used to form the n-III-V/p-Si heterojunction. Current-voltage measurements confirm the heterojunction diode formation between n-type III-V quantum dots and p-type Si. The main advantage of our method is its integration with large-scale silicon technology, which also allows applying it for Si-based photronic devices.
Keywords: III-V semiconductors, silicon, ion implantation, flash lamp annealing
  • Invited lecture (Conferences)
    E-MRS 2012 SPRING MEETING, 14.-18.05.2012, Strasbourg, France

Publ.-Id: 17279 - Permalink


Improvement of CIGS layer quality by Flash Lamp Annealing
Prucnal, S.; Jiao, F.; Zhao, K.; Skorupa, W.; Helm, M.; Zhou, S.;
Copper Indium Gallium diselenide (CIGS) become more significant for solar cell applications as an alternative to silicon. The quality of the layer has a critical impact on the final efficiency of the solar cell. An influence of the post-deposition millisecond range flash lamp annealing (FLA) on the optical and microstructural properties of the CIGS films was investigated. Based on the Raman and photoluminescence spectroscopy, it is shown that FLA reduces the defect concentration and leads to an increase of the photoluminescence intensity by a factor of six compared to the not annealed sample. Moreover, after FLA the degradation of the photoluminescence is significantly suppressed.
Keywords: CIGS, flash lamp annealing, photoluminescence, solar cells
  • Poster
    E-MRS 2012 SPRING MEETING, 14.-18.05.2012, Strasbourg, France

Publ.-Id: 17278 - Permalink


Gettereing of metal impurities by flash lamp annealing in dirty-silicon solar cells
Prucnal, S.; Abendroth, B.; Krockert, K.; König, K.; Henke, D.; Kolitsch, A.; Möller, H. J.; Skorupa, W.;
Multicrystalline silicon has attracted considerable attention because of its high stability against light soaking. In case of Solar Grade (SoG) mc-Si the rigorous control of metal impurities is desirable for solar cell fabrication. Although ion implantation doping got very recently distinct consideration for doping of monocrystalline solar material, efficient doping of multicrystalline solar material remains the main challenge to reduce costs. To extend the application of the ion implantation technique to SoG mc-Si the diffusion of metal impurities during electrical activation of phosphorous and recrystallization of silicon has to be suppressed. Here an advanced annealing technique will be presented and explored, which allows the electrical activation of implanted elements by short time light pulse annealing. Flash Lamp Annealing in the ms-range is demonstrated here as a very promising technique for the emitter formation at an overally low thermal budget. It could be presented that FLA at 1000oC for 3 ms even without preheating is sufficient to recrystallize implanted silicon. The sheet resistance (SR) of FLA samples shows values of about 50 Ohm/sq. Especially, the minority carrier diffusion length for the FLA samples is in the range of 80 um without surface passivation. This is up to one order of magnitude higher than that observed from RTA or FA samples. This technology shows great promise to replace the conventional POCl3 –doping.
Keywords: solar cells, mc-Si, Flash Lamp Annealing, ion implantation
  • Poster
    E-MRS 2012 SPRING MEETING, 14.-18.05.2012, Strasbourg, France

Publ.-Id: 17277 - Permalink


Superconducting layers by gallium implantation and short-term annealing in semiconductors
Fiedler, J.; Heera, V.; Voelskow, M.; Mücklich, A.; Reuther, H.; Skorupa, W.; Gobsch, G.; Helm, M.;
Superconducting layers in silicon and germanium are fabricated via gallium implantation through a thin SiO2 cover layer and subsequent rapid thermal annealing. Gallium accumulation at the SiO2/Si and SiO2/Ge interfaces is observed but no pure gallium phases were found. In both cases superconducting transition occurs around 6 – 7 K which can be attributed to the metallic conduct-ing, gallium rich interface layer. However, the superconducting as well as the normal-state transport properties in gallium overdoped silicon or germanium are different.

Publ.-Id: 17276 - Permalink


Free radical kinetics in a plasma immersion ion implanted polystyrene: Theory and experiment
Kosobrodova, E. A.; Kondyurin, A. V.; Fisher, K.; Moeller, W.; Mckenzie, D. R.; Bilek, M.;
The kinetics of free radicals in polystyrene (PS) treated by plasma immersion ion implantation (PIII) in nitrogen plasma are investigated by means of electron paramagnetic resonance (EPR). EPR spectra are recorded for PS samples with various PIII treatment times ranging from 40 to 1600 s (corresponding to ion fluences of 5 x 10(14)-2 x 10(16) ions/cm(2)) after storage times ranging from 45 min to 3 weeks (room temperature). An unexpected, non-linear behaviour at short treatment times is observed. As treatment time increased, the EPR signal first remains constant then shows a sharp increase and a subsequent saturation at long treatment times. An analytical model for the processes of formation and decay of free radicals in PIII treated polymers is proposed. The model describes the kinetics of short-lived and long-lived radicals using a system of linear differential equations. The model is in good agreement with experimental data.
Keywords: Ion implantation; Polystyrene; Radical kinetics

Publ.-Id: 17275 - Permalink


Enhanced Subthreshold e+e- Production in Short Laser Pulses
Titov, A. I.; Takabe, H.; Kämpfer, B.; Hosaka, A.;
The emission of e+e- pairs off a probe photon propagating through a polarized short-pulsed electromagnetic (e.g., laser) wave field is analyzed. A significant increase of the total cross section of pair production in the subthreshold region is found for decreasing laser pulse duration even in the case of moderate laser pulse intensities.

Publ.-Id: 17274 - Permalink


Experimental realization of dynamo action: present status and prospects
Giesecke, A.; Stefani, F.; Gundrum, T.; Gerbeth, G.; Nore, C.; Leorat, J.;
Cosmic magnetic fields are an ubiquitous phenomenon arising in and around many astrophysical objects like planets, stars, or galaxies. There is a common consensus that these fields are generated by (mostly) turbulent flows of conducting liquids or plasmas. Whereas dynamo action in the astrophysical context seems to be quite simple, essentially because of the large scales of the involved flows, the experimental realization of dynamo action on typical laboratory scales is a demanding task. So far only three facilities have been able to demonstrate fluid flow driven self-generation of magnetic fields. The first dynamos in Riga and in Karlsruhe were characterized by non-axisymmetric geometries of the eigenfield which can be well explained utilizing a laminar flow structure or a mean-field model, respectively. More dynamical effects like bursts, oscillations or sudden field reversals have been observed in the von-Karman-Sodium (VKS) dynamo experiment conducted at Cadarache in France. In that experiment a flow of liquid sodium is driven by two opposing impellers located close to the lids of a cylindrical container. However, dynamo action is obtained only when at least one of the flow driving impellers is made of soft iron with a relative permeability around ~65. In contrast to the previous experiments the observed magnetic field geometry is dominated by an axisymmetric mode which is in contradiction with the expectations from simulations as well as with the restrictions from Cowling's anti-dynamo theorem. Our kinematic simulations of an axisymmetric model of the Cadarache dynamo show a close linkage between the exclusive occurrence of dynamo action in the presence of soft iron impellers and the axisymmetry of the magnetic field. We observe two distinct classes of axisymmetric eigenmodes, a purely toroidal mode that is amplified by paramagnetic pumping at the fluid-impeller interface, and a mixed mode consisting of a poloidal and a toroidal contribution that is rather insensitive to the impeller permeability. In the limit of large permeability, the purely toroidal mode is close to the onset of dynamo action with a slightly negative growth-rate that is rather independent of the flow field. However, since in our axisymmetric configuration the purely toroidal mode is decoupled from any poloidal field component no dynamo action can be expected from this mode alone. Thus, a satisfying explanation of the observed axisymmetric dynamo mode requires mean field effects like the alpha-effect. Since the flow is considerably turbulent such effects are undoubtedly operative, however, so far their properties (e.g. spatial distribution or amplitude) are only speculative. Further progress in the experimental examination of dynamo action is expected from the planned liquid sodium facility DRESDYN (DREsden Sodium facility for DYNamo and thermohydraulic studies). Within this framework, a homogeneous dynamo, driven exclusively by precession, will represent the most ambitious compound. We present recent results of preparatory water experiements and design studies, and delineate the scientific prospects for the final set-up.
Keywords: dynamo
  • Lecture (Conference)
    IAU 18 General Assembly, 20.-31.08.2012, Beijing, China
  • Contribution to proceedings
    IAU 18 General Assembly, 19.-31.08.2012, Beijing, China
    Proceedings of the International Astronomical Union Volume 8 - Symposium S294 (Solar and Astrophysical Dynamos and Magnetic Activity) Experimental realization of dynamo action: present status and prospects: Cambridge University Press, 411-416
    DOI: 10.1017/S1743921313002846

Publ.-Id: 17273 - Permalink


The ELBE 1.6-mA-upgrade and status of the new SRF gun
Teichert, J.; Arnold, A.; Büttig, H.; Lehnert, U.; Michel, P.; Murcek, P.; Staats, G.; Xiang, R.; Kamps, T.; Rudolph, J.; Will, I.; Kneisel, P.;
Kein Abstract vorhanden.
Keywords: superconducting radio-frequency, electron accelerator, solid state amplifier, electron source
  • Lecture (Conference)
    PITZ Collaboration Meeting, 12.-13.06.2012, Zeuthen, Germany

Publ.-Id: 17272 - Permalink


Unwanted beam observations at ELBE
Teichert, J.; Arnold, A.; Michel, P.; Murcek, P.; Xiang, R.; Barday, R.; Kamps, T.; Schubert, S.;
Unwanted beam can cause beam losses and may produce acute or chronic damages of the accelerator. Furthermore it can considerably disturb experiments or increase its back-ground. The operation of the superconducting RF photo gun at the ELBE accelerator has delivered the first experimental information on that topic. It was found, that dark current is an important issue, similar to normal conducting RF photo injectors.
Keywords: superconducting radio-frequency, electron source, photo-electron injector, electron accelerator, dark current, beam loss
  • Lecture (Conference)
    FLS 2012– ICFA Beam Dynamic Workshop, 05.-09.03.2012, Newport News, USA

Publ.-Id: 17270 - Permalink


Status and future plans for the SRF gun at ELBE
Teichert, J.; Arnold, A.; Lehnert, U.; Michel, P.; Murcek, P.; Xiang, R.; Kamps, T.; Rudolph, J.; Will, I.; Kneisel, P.;
At the ELBE radiation facility a superconducting RF photo injector has been developed and operated during the last years. The gun has a 3 ½ cell niobium cavity for 1.3 GHz and uses normal-conducting photo cathodes. Since 2010 the electron beam of the gun has been injected into the ELBE linac. In 2011 beam was delivered for the first sophisticated experiment producing x-rays by Compton backscattering of photons of the high-power laser DRACO. The successful operation of the SRF gun confirms the general design with an elliptical cavity, superconducting RF choke filter, and normal-conducting photocathodes as well as the proper design of most of the subsystems like couplers and tuners. At present, the main draw-back is the low acceleration gradient of the cavity. Therefore two new cavities have been designed, built and tested in collaboration with Jlab. This work is in its final stage now, and we expect assembly of the new cavity in an improved cryomodule and its installation at ELBE for 2012.
Keywords: superconducting radio-frequency, electron source, photo injector, niobium cavity, electron accelerator, electron beam, photocathode
  • Lecture (Conference)
    FLS 2012 – ICFA Beam Dynamic Workshop, 05.-09.03.2012, Newport News, USA

Publ.-Id: 17269 - Permalink


Research activities of photocathodes for HZDR SRF gun
Xiang, R.; Arnold, A.; Freitag, M.; Michel, P.; Murcek, P.; Teichert, J.;
Since 2005 the photocathode laboratory has been in operation at HZDR. The main goal is to prepare Cs2Te photocathodes for the SRF gun. A vacuum transport system with UHV is used to move the cathodes from preparation lab to accelerator hall. Up to now 34 Cs2Te photocathodes have been deposited and eight of them have been used in the SRF gun. Quantum efficiency (QE) of 1% and life time of months can be maintained during the gun operation. At the same time activities are directed towards new photocathode materials with high Q.E. for high current electron sources. Cs3Sb and GaN(Cs) photocathodes have been tested as new candidates, and the design of a preparation system for GaAs(Cs, O) is ongoing
Keywords: SRF-gun, Photocathode, Quantum efficiency
  • Open Access LogoContribution to proceedings
    International Particle Accelerator Conference 2012 (IPAC2012), 20.-25.05.2012, New Orleans, USA
    Proceedings of IPAC2012, 978-3-95450-115-1, 1524
  • Poster
    International Particle Accelerator Conference 2012 (IPAC2012), 20.-25.05.2012, New Orleans, USA

Publ.-Id: 17268 - Permalink


Coupling Schemes and Measurements for Multiple Eigenmode Application in Superconducting RF Guns
Arnold, A.; Murcek, P.; Teichert, J.; Xiang, R.;
Superconducting electron sources are a promising candidate to meet the challenges of future electron accelerator, such as high average beam current and high peak brilliance at the same time. Compared to their normal conducting rf equivalent and due to the Meissner-Ochsenfeld effect, the solenoid for emittance compensation has to be placed far in front of the cathode. To solve this problem the use of transverse electric (TE) modes in parallel to the accelerating mode was proposed*. This contribution presents two suitable coupling schemes and first rf measurements at the warm and cold HZDR SRF gun cavity.
* V. Volkov, D. Janssen, Phys. Rev. ST Accel. Beams 11, 061302 (2008)
Keywords: TE mode, emittance compensation, SRF gun, coupling scheme
  • Poster
    International Particle Accelerator Conference IPAC12, 20.-25.05.2012, New Orleans, LA, USA

Publ.-Id: 17267 - Permalink


Monopol HOM Analysis for the 3.5 Cell SRF Gun Cavity
Arnold, A.; Murcek, P.; Teichert, J.; Xiang, R.;
Superconducting radio frequency photoinjectors (SRF gun) seems to be a promising candidate to achieve the required brightness and the high average current for future light sources. In contrast to normal conducting DC and RF guns, higher order modes (HOM) and their influence on beam quality are of particular interest. For this reason, a method is presented that considers the accelerated motion of nonrelativistic electrons to calculate the longitudinal coupling impedances. The results are compared with first beam-based measurements and used to determine the required HOM damping. Additionally, a selective detuning of the eigenmode spectra is discussed.
Keywords: higher order mode, HOM, SRF gun
  • Invited lecture (Conferences)
    EuCARD SRF Annual Review, 29.-30.03.2012, Berlin, Deutschland

Publ.-Id: 17266 - Permalink


RF power upgrade at the superconducting 1.3 GHz CW LINAC “ELBE” with solid state amplifiers
Büttig, H.; Arnold, A.; Büchner, A.; Justus, M.; Kuntzsch, M.; Lehnert, U.; Michel, P.; Schurig, R.; Staats, G.; Teichert, J.;
The RF power for the superconducting CW LINAC has been doubled from 10 to 20 kW per cavity. In January 2012 the four 10 kW klystrons used to drive the four superconducting cavities of the LINAC have been replaced by a pair of 10 kW solid state power amplifiers. ELBE is now worldwide the first 1.3 GHz CW LINAC equipped with Solid State RF Power Amplifiers. This technical note details on this project.
Keywords: Solid state RF power amplifiers, Superconducting CW RF, 1.3 GHz Solid state RF-power amplifiers, ELBE-RF, Superconducting LINAC RF.

Publ.-Id: 17265 - Permalink


Core-core interaction in spin-torque double-vortex oscillators
Sluka, V.; Kákay, A.; Deac, A. M.; Bürgler, D. E.; Hertel, R.; Schneider, C. M.;
Owing to their ability of narrow bandwidth operation, magnetic vortex based spin-torque nano-oscillators (STNOs) are promising candidates for future on-chip microwave sources. Typically, these oscillators are nanopillars containing two stacked ferromagnetic disks, one in a vortex state, the other with quasi-homogeneous magnetization. Devices of that kind have been investigated extensively over the past years [1-3]. Only recently, a different type of vortex oscillators has attracted much interest. In these “double vortex oscillators”, both ferromagnetic disks are in a vortex state. Depending on the relative vorticity, the local alignment of the magnetic layers can be either parallel or antiparallel. Thus, the system constitutes an analogue to single domain spin valves, while also retaining the good oscillator properties of magnetic vortices, which makes this type of STNO particularly interesting for studying fundamental aspects of spin-transfer torque. However, only few studies of double-vortex oscillators exist to-date [5,6].
Here we present our results on Fe/Ag/Fe double vortex oscillators. Combining experimental and numerical methods, we address the yet open question of how the magnetostatic interaction of the vortices – their separation is typically in the order of a few nanometers –affects the spin-torque induced dynamics. Our samples are all-metallic nanopillars 150 nm in diameter, containing a Fe(30)/Ag(6)/Fe(15) pseudo spin valve (layer thicknesses given in nm). By applying d.c. currents perpendicular to the plane of the layers, we excite magnetization dynamics corresponding to gyrotropic vortex motion. The sample geometry stabilizes the magnetic vortex state in each Fe disk even if the strong Oersted fields and the vortex magnetization have opposite sense of rotations. This high degree of stability provides a yet unprecedented opportunity to investigate a more exotic class of double vortex states – those with opposed vorticities – under the high current densities necessary to enter the spin-torque precession regime.
Figure 1 displays a typical combined magnetoresistance and high frequency measurement. The magnetic field, which has an angle of 30° with the sample plane, is swept from positive values to negative saturation. For each field value, in addition to the d.c. voltage, a spectrum is also recorded. In a field interval about 100 mT wide, the sample is in a double vortex state where the vorticities of the top and bottom vortices are opposed to each other. According to the top panel of Fig. 1, this state exhibits magnetization dynamics. We vary our state preparation procedure in order to create the various vorticity and core polarity combinations. The obtained states are characterized with respect to their d.c. and high frequency behavior using the above described measuring technique where in all measurements, the electron flow is directed from the bottom to the top Fe disk. We obtain a fine structure in the modes, where the frequency splittings are in the order of hundreds of MHz.
The micromagnetic simulations are performed with our code TetraMag [7]. The simulations include the Oersted field corresponding to a sample current of 10 mA in magnitude. For a given vorticity and core polarity combination, we find the eigenmodes and frequencies of the system. Comparing the experimentally found set of frequencies to the simulated cases, we find that each measured peak matches the lowest mode of a corresponding computed spectrum in frequency. This suggests that the observed fine structure is caused by two effects. First, the Oersted field lifts the degeneracy of states with the top vortex vorticity parallel or antiparallel to the field’s sense of rotation. On top of this Zeemann-type frequency alteration, the resulting modes are split further depending on the relative alignment of the top and bottom vortex cores. This suggests that the second splitting is due to the magnetostatic interaction of the vortex cores. This remarkable result sheds light on the subtle interplay of forces governing the dynamics of double vortex oscillators, while on the other hand it allows measuring changes in relative core alignment.
References:
[1] V. S. Pribiag et al., Nature Phys. 3, 498 (2007).
[2] A. Dussaux et al., Nat. Commun. 1:8 DOI:10.1038 / ncomms1006 (2010).
[3] X. W. Yu et al., Phys. Rev. Lett. 106, 167202 (2011).
[5] A. V. Khvalkovskiy et al., Appl. Phys. Lett. 96, 212507 (2010).
[6] N. Locatelli et al., Appl. Phys. Lett. 98, 062501 (2011).
[7] A. Kákay, E. Westphal, R. Hertel, IEEE Trans. Magn. 46, 2303 (2010).
Keywords: magnetic vortex, magnetization dynamics, spin-transfer torque, spin-torque nano-oscillators
  • Lecture (Conference)
    Intermag 2012, 07.05.2012, Vancouver, Canada

Publ.-Id: 17264 - Permalink


Quenched Slonczewski-windmill in spin-torque vortex-oscillators
Sluka, V.; Kákay, A.; Deac, A. M.; Bürgler, D. E.; Hertel, R.; Schneider, C. M.;
Spin-torque nano-oscillators (STNOs) typically consist of two single domain ferromagnetic layers separated by a metallic spacer or a tunnel barrier, one with its magnetization fixed (polarizing layer), the other one susceptible to torques (free layer). An electric current traversing the system perpendicular to the layers becomes spin-polarized and exerts torques on the magnetic moments [1-3], thereby inducing switching or steady-state dynamics. The pinning of the polarizing layer can be achieved by exchange coupling to an antiferromagnet [4] or by extending its thickness and lateral dimension [5]. In the absence of pinning, both ferromagnetic layers can be excited. For increasingly symmetric STNOs, this can lead to a dynamic equilibrium state called the Slonczewski-windmill [1,6], with the magnetic moments of both layers rotating in the same direction with a constant relative angle, resulting in a vanishing magnetoresistance (MR) time-dependence.
Here we investigate STNOs containing two stacked magnetic vortices, i.e., a system consisting of two ferromagnetic disks, each in a vortex state and separated by a metallic, nonmagnetic spacer. Employing analytical and numerical methods, we study the coupled spin torque-driven motion of the magnetizations in the two disks, which are not pinned by any of the above mentioned mechanisms. The theoretical findings are supported by our experimental data obtained from double-vortex Fe/Ag/Fe STNOs.
The motion of the magnetic vortex in each of the disks is governed by the Thiele equation [7] with an additional force expression arising from the transfer of spin angular momentum from the polarised current to the vortex. Assuming that in the double vortex system, each vortex is free to move while at the same time it serves as a polarizing layer for the other, we solve the system of Thiele equations coupled by the spin-polarized current. We use parabolic approximations to the magnetostatic potentials for each vortex, which are chosen to represent our Fe/Ag/Fe nanopillars with ferromagnetic layers with a thickness ratio of 5/3; the uncoupled top and bottom vortices’ eigenfrequencies are set to 1.0 and 1.7 GHz, respectively.
The solutions are obtained numerically using Maple's rkf45 implementation. The results can be summarized as follows: While the spin torque induces large orbit vortex gyration in one of the layers, the vortex motion in the other disk is strongly reduced, resulting in a quenching of the Slonczewski-windmill mode. Which of the two layers contributes dominantly to the magnetization dynamics is determined by the direction of the applied current. This effect results from an adaption of the motion of the constricted vortex according to the dominant one. The former acquires a stable phase to the dominant vortex, while the latter determines the frequency and sense of gyration of the whole system: If its core polarity is positive (negative), the system gyrates in the counterclockwise (clockwise) direction. If the dominating vortex is in the top disk, the gyration frequency is 1.0 GHz while for large orbit gyration in the bottom disk, we obtain 1.7 GHz. Figure 1 displays the relations between the phase, frequency and gyration radius of the bottom vortex in the case, where the top vortex is dominant. For an experimental confirmation of the frequency and phase adaption mechanism and the related quenching of the windmill modes, we study the current-induced magnetization dynamics of a Fe/Ag/Fe nanopillar with a Fe layer thickness ratio of 5/3. We apply current densities of 6.1x107 A/cm2 and investigate the resulting double vortex dynamics depending on the current polarity. At low external field, the ratio between the obtained frequencies is close to the ratio of the disk aspect ratios, which strongly supports our numerical findings.

References:
[1] J. C. Slonczewski, J. Magn. Magn. Mater. 159, L1 (1996).
[2] L. Berger, Phys. Rev. B 54, 9353 (1996).
[3] J. C. Slonczewski, J. Magn. Magn. Mater. 247, 324 (2002).
[4] I. N. Krivorotov et al., Science 307, 228 (2005).
[5] I. Kiselev et al., Nature 425, 380 (2003).
[6] Y. B. Bazaliy, D. Olaosebikan, and B. A. Jones, J. Nanosci. Nanotechnol. 8, 2891 (2008).
[7] A. A. Thiele, Phys. Rev. Lett. 30, 230 (1973).
Keywords: Spin-transfer torque, spin-torque nano-oscillators, magnetic vortex, magnetization dynamics
  • Poster
    Intermag 2012, 07.-11.05.2012, Vancouver, Canada

Publ.-Id: 17263 - Permalink


Use of cold liquid metal models for investigations of the fluid flow in the continuous casting process
Timmel, K.; Wondrak, T.; Röder, M.; Stefani, F.; Eckert, S.; Gerbeth, G.;
Model experiments with low melting point liquid metals are an important tool to investigate the flow structure and related transport processes in melt flows relevant for metallurgical applications. Water model experiments are of limited value, particularly in the cases of strong temperature gradients, two-phase flows or flows exposed to electromagnetic fields. We present the new experimental facility LIMMCAST for modelling the continuous casting process of steel using the alloy SnBi at temperatures of 200-400°C. The parameters of the facility and the dimensions of the test sections will be given, and the possibilities for flow investigations in tundish, submerged entry nozzle and mould will be discussed. In addition, the smaller set-up mini-LIMMCAST will be presented, which works with the room-temperature liquid alloy GaInSn. The main value of cold metal laboratory experiments consists in the capabilities to obtain quantitative flow measurements with a reasonable spatial and temporal resolution. New ultrasonic and electromagnetic techniques for measuring the velocity in liquid metal flows came up during the last decade allowing for a satisfying characterisation of flow quantities in the considered temperature range up to 400°C. A selection of results from LIMMCAST and mini-LIMMCAST will be presented in this paper covering various phenomena occurring in single-phase and two-phase flows.
Main emphasis of the experimental programme is put on the effect of diverse magnetic fields on the fluid flow in the mould. Although magnetic fields have already been adopted for industrial use since more than 20 years, the impact of electromagnetic brakes or stirrers on complex and highly turbulent flows appears to be very complex and has not been fully understood until now. The flow measurements performed at the liquid metal model experiments deliver a valuable experimental data base being suitable for validation of numerical simulations.
Keywords: continuous casting, liquid metal models, electromagnetic brake, ultrasonic flow measurement, contactless inductive flow tomography
  • Lecture (Conference)
    5th International Congress on the Science and Technology of Steelmaking, 01.-03.10.2012, Dresden, Deutschland
  • Contribution to proceedings
    5th International Congress on the Science and Technology of Steelmaking, 01.-03.10.2012, Dresden, Deutschland
  • Steel Research International 85(2014)8, 1283-1290
    DOI: 10.1002/srin.201300034

Publ.-Id: 17262 - Permalink


Ultrafast electron beam X-ray computed tomography for 2D and 3D two-phase flow imaging
Bieberle, M.; Barthel, F.; Hoppe, D.; Banowski, M.; Wagner, M.; Lucas, D.; Stürzel, T.; Hampel, U.;
Imaging of complex and dynamic processes such as two- or multiphase flows with high structural as well as temporal resolution has always been a challenging task. In recent years, the electron beam X-ray computed tomography technique has been developed towards a powerful imaging tool, which reaches frame rates of 8000 fps in 2D and 1000 fps in 3D. In this paper, the latest developments as well as selected applications of ultrafast electron beam X-ray CT are presented.
Keywords: X-ray; computed tomography; two-phase flow; measurement; electron beam
  • Lecture (Conference)
    2012 IEEE International Conference on Imaging Systems and Techniques, 16.-17.07.2012, Manchester, United Kingdom
  • Contribution to proceedings
    2012 IEEE International Conference on Imaging Systems and Techniques, 16.-17.07.2012, Manchester, United Kingdom
    Proceedings 2012 IEEE International Conference on Imaging Systems and Techniques: IEEE, 978-4577-1774-1, 1569596631

Publ.-Id: 17261 - Permalink


Grundlagen und Anwendungen der kontaktlosen induktiven Strömungstomographie
Stefani, F.; Gerbeth, G.; Gundrum, T.; Wondrak, T.;
The contactless inductive flow tomography (CIFT) aims at the determination of flow structures in metal and semiconductor melts. It relies on the induction of electric currents in moving conductors exposed to magnetic fields. The flow induced deformations of the magnetic fields can be measured in the exteriour of the melt and utilized for the reconstruction of the velocity field. After a presentation of the principles, first applications and possible extensions of the method are discussed.

Publ.-Id: 17260 - Permalink


Combining contactless inductive flow tomography and mutual inductance tomography for two-phase flow measurements at a continuous casting model
Stefani, F.; Eckert, S.; Gerbeth, G.; Klotsche, K.; Timmel, K.; Wondrak, T.; Peyton, A. J.; Terzija, N.; Yin, W.;
The flow structure in the mould of a continuous caster is of key importance for the quality of the final product. The use of most conventional flow measurement techniques is prevented by the high temperature of the liquid steel. For a downscaled physical model of the continuous casting process, we present combined measurements of the flow in the mould by Contactless Inductive Flow Tomography (CIFT), and of the conductivity distribution in the submerged entry nozzle by Mutual Inductance Tomography (MIT). In addition, we summarize an experiment with a magnetic stirrer around the submerged entry nozzle and its effects on the flow in the mould. Some new developments towards a robust implementation of CIFT at a real caster, including the use of pickup coils and gradiometric probes, are also discussed.
  • Lecture (Conference)
    7th International Conference on Electromagnetic Processing of Materials (EPM2012), 22.10.-26.12.2012, Bejing, China
  • Journal of Iron and Steel Research International 19(2012)Suppl. 1-1, 479-482

Publ.-Id: 17259 - Permalink


Temperature impact on the sorption of selenium(VI) onto anatase
Jordan, N.; Müller, K.; Franzen, C.; Brendler, V.;
The impact of temperature (298 K, 313 K and 333 K) on the sorption of selenium(VI) onto anatase was investigated for the first time. At a macroscopic level, batch experiments showed a decrease of selenium(VI) retention with both increasing pH (3.5-7.0) and temperature. The thermodynamic parameters of the sorption reaction, i.e. the enthalpy ΔRH, entropy ΔRS and the Gibbs free energy ΔRG were determined from the temperature dependence sorption data using the van´t Hoff equation. The sorption process was found to be exothermic. Neither significant phase transformation nor a significant increase of anatase solubility could be detected with increasing temperature by XRD and ICP-MS. However, electrophoretic mobility measurements showed that both the zeta potential as well as the isoelectric point (pHIEP) of anatase were shifted to lower values with increasing temperature, decreasing selenium(VI) sorption. At a microscopic level, the sorption mechanism of selenium(VI) onto anatase was elucidated at the three investigated temperatures by means of in situ Attenuated Total Reflection Fourier-Transform Infrared spectroscopy (ATR FT-IR). Results evidenced the formation of outer-sphere surface complexes, with no significant structural changes within the investigated temperature range.
Keywords: selenate, titanium dioxide, anatase, infrared spectroscopy, ATR FT-IR

Publ.-Id: 17258 - Permalink


Superconducting layers in semiconductors – Ready for the quantum interference?
Fiedler, J.; Heera, V.; Skrotzki, R.; Herrmannsdörfer, T.; Skorupa, W.; Gobsch, G.; Helm, M.;
Superconductivity is a fascinating ground state of matter and has been discovered one century ago. A new debate about the fundamental physical background and technological potential of superconducting group-IV semiconductors occurred, since superconductivity at ambient pressure conditions was shown for boron doped diamond [1] and silicon [2]. These unusual superconductors open the way towards new microelectronic devices and applications.
In our previous work, we used Ga-ion implantation and subsequent short-time annealing for creating highly Ga doped layers in Ge. [3] These layers show an intrinsic superconducting transition at temperatures below 1 K because of the high doping level. [4] In a next step we could show the feasibility to stabilize Ga-rich layers at SiO2/Si [5,6] and SiO2/Ge [7] interfaces by using a 30 nm SiO2 cover layer during implantation and annealing.
The presented structural investigations by means of Rutherford Backscattering Spectrometry (RBS) and cross-sectional Transmission Electron Microscopy (XTEM) reveal the presence of a 10 nm thin, superconducting layer at the interfaces containing Ga-rich precipitates. In both cases the critical temperature increases to 7 K which is comparable to amorphous Ga and therefore enables the detailed investigation of the influence of superconducting precipitates on the superconducting properties of doped semiconductor layers.
However, the previous investigations were done on 1 x 1 cm2 size samples. The possibility of fabricating superconducting microstructures in Si with standard microelectronic lithography will be shown. Theses microstructures still undergo a superconducting transition below 7 K. High critical magnetic fields in the range of 10 T and high critical current densities of 50 kA/cm2 were achieved. For applications in superconducting microelectronics a Josephson-Junction has to be implemented. [8] We plan to use a Focused Ion Beam (FIB) for this task. Details about the sample processing, layer microstructure and processing of superconducting microstructures will be presented.

[1] E. A. Ekimov et al., Nature (London) 428 (2004) 542.
[2] E. Bustarret et al., Nature 444 (2006) 465.
[3] V. Heera et al., J. Appl. Phys. 107 (2010) 053508.
[4] T. Herrmannsdörfer et al., Phys, Rev. Lett. 102 (2009) 217003.
[5] R. Skrotzki et al., Appl. Phys. Lett. 97 (2010) 192505.
[6] J. Fiedler et al., Phys. Rev. B 83 (2011) 214504.
[7] J. Fiedler et al., Phys. Rev. B 85 (2012) 134530.
[8] J. Q. You et al., Nature 474 (2011) 589.
  • Poster
    18th International Conference on Ion Beam Modifications of Materials (IBMM 2012) - Ausgezeichnet mit einem "Best Poster Award", 02.-07.09.2012, Qingdao, China

Publ.-Id: 17257 - Permalink


Superconductivity in Ga-implanted group-IV semiconductors
Fiedler, J.; Heera, V.; Skrotzki, R.; Herrmannsdörfer, T.; Voelskow, M.; Mücklich, A.; Facsko, S.; Reuther, H.; Perego, M.; Schmidt, B.; Skorupa, W.; Gobsch, G.; Helm, M.;
Beginning in 2004, the interest in superconductivity of elemental group-IV semiconductors has been renewed because Ekimov et al. [1] showed that boron doped diamond could become superconducting at ambient pressure conditions. Besides fundamental physical background of driving a semiconductor into a superconducting state, the high potential for applications in new microelectronic devices is in the main focus.
High doping levels are needed to observe superconductivity at ambient pressure conditions in elemental group-IV semiconductors. Gas immersion laser doping is used to fabricate superconducting boron doped silicon [2]. The possibility to use Ga-ion implantation and short-time annealing for creating superconducting Ga-doped Ge layers was shown in our previous work [3, 4]. These highly doped Ge-layers show an onset of superconductivity below 1 K. All doping techniques mentioned above exceed the equilibrium solid solubility limit by far and the question arises, whether the observed superconductivity is a doping effect or related to dopant clusters [5].
Especially if the doping element itself is a superconductor, like Ga in Ge, it was not clear how superconducting precipitates influence the low-temperature transport properties. To investigate these effects, we stabilized superconducting Ga-rich layers at SiO2/Si interfaces [6, 7]. Again, we have used ion implantation through a 30 nm thick SiO2 cover layer and rapid thermal annealing. The critical temperature of 7 K is comparable to the values obtained for amorphous Ga. Furthermore, high critical magnetic fields of 14 T and critical current densities of 50 kA/cm2 were achieved.
With the results of the investigations discussed above, we could go one step further and fabricate similar Ga-rich layers at SiO2/Ge interfaces. Now it is possible to investigate selectively the influence of superconducting Ga-rich areas on the normal- and superconducting properties of Ga-doped Ge. It will be shown that the critical temperature changes dramatically while the critical magnetic field stays rather constant. The results of detailed microstructural investigations by means of XTEM and time-of-flight SIMS will be correlated with electrical properties. Finally, the presented results indicate that superconductivity with critical temperatures around 1 K can clearly be attributed to a doping effect.

[1] E. A. Ekimov et al., Nature (London) 428 (2004) 542.
[2] E. Bustarret et al., Nature 444 (2006) 465.
[3] T. Herrmannsdörfer et al., Phys, Rev. Lett. 102 (2009) 217003.
[4] V. Heera et al., J. Appl. Phys. 107 (2010) 053508.
[5] N. Dubrovinskaia et al., PNAS 105 (2008) 11619.
[6] R. Skrotzki et al., Appl. Phys. Lett. 97 (2010) 192505.
[7] J. Fiedler et al., Phys. Rev. B 83 (2011) 214504.
  • Lecture (Conference)
    18th International Conference on Ion Beam Modifications of Materials (IBMM 2012), 02.-07.09.2012, Qingdao, China

Publ.-Id: 17256 - Permalink


Nanoteilchen in biologischen Systemen
Bergmann, R.;
kein Abstract verfügbar
  • Lecture (others)
    Akademisches Donnerstagkolloquium der Dresdner Seniorenakademie, 24.05.2012, Dresden, Deutschland

Publ.-Id: 17255 - Permalink


From sponge to dot arrays on (100) Ge by increasing the energy of ion impacts
Böttger, R.; Bischoff, L.; Heinig, K.-H.; Pilz, W.; Schmidt, B.;
Ge surfaces were subjected to normal incidence Bi+ irradiation with ion energies from 10 to 30 keV. The Ge substrate was irradiated with fluences up to 1 x10^17 / cm² and substrate temperatures up to 780 K. Surface modification was investigated using scanning electron microscopy. While at room temperature porous networks are obtained, increase of temperature during irradiation leads to formation of hexagonal dot arrays at the surface, which vanish at very high temperatures. Extensive experimental studies of energy and temperature ranges and limits for dot formation are presented. Formation of dot arrays is governed by the vacancy diffusion mechanism via different energy densities deposited in the cascade volume, as well as by substrate heating. An energy-temperature phase diagram of the obtained surface morphology is composed with respect to varying order of dot-like patterns.
Keywords: Ge, FIB, sponge, ordered dots, self-organization, vacancy, ion beam

Publ.-Id: 17254 - Permalink


Probing Graded Perpendicular Anisotropy with Polarized Neutron Reflectometry
Greene, P.; Gilbert, D.; Kirby, B.; Borchers, J.; Lau, J.; Shull, R.; Chih-Huang, L.; Osten, J.; Fassbender, J.ORC; Davies, J.; Fitzsimmons, M.; Zimanyi, G.; Liu, K.
Magnetic nanostructures with graded anisotropy offer a solution to both thermal stability and writability challenges in advanced magnetic recording media. The interlayer exchange coupling lowers the overall coercivity, facilitating the writing process, while the magnetically hard layer provides pinning for the media and ensures its thermal stability. However, it is challenging to probe and tune the depth-dependent anisotropy gradient, as conventional magnetometry approaches only give convoluted response from the entire layer. In this work, we have investigated magnetization reversal in Co/Pd and Co/Pt films and patterned structures with perpendicular anisotropy using polarized neutron reflectometry (PNR), along with magnetometry and structural characterizations. Perpendicular magnetic anisotropy is varied by changing the growth conditions during synthesis (Co layer thickness, sputtering pressure, or multilayer deposition order), or post-deposition ion irradiation. PNR directly reveals depth-dependent magnetization profiles along the in-plane magnetic hard axis, which reflect the magnetic anisotropy gradient as different amounts of magnetic moment come into alignment with the in-plane field. Effects of lateral patterning have also been investigated in patterned nanostructures (networks and nanodots). An increase in coercivity and a modified switching field distribution are observed in patterned structures. This is due to the reduced lateral dimensions which limit the domain nucleation and propagation commonly found in unpatterned films. These results demonstrate attractive features of nanostructures with graded anisotropy towards future magnetic recording applications.
Work supported by the US NSF (DMR-1008791 & ECCS-0925626).
  • Invited lecture (Conferences)
    ACNS American Conference on Neutron Scattering, 24.-28.06.2012, Washington, DC, USA

Publ.-Id: 17253 - Permalink


Tuning Perpendicular Anisotropy Gradients in Co/Pd Multilayers by Ar Ion Irradiation
Greene, P.; Osten, J.; Fassbender, J.ORC; Endo, T.; Iwata, N.; Liu, K.
Magnetic nanostructures with graded anisotropy offer a solution to both thermal stability and writability challenges in advanced magnetic recording media. The interlayer exchange coupling lowers the overall coercivity, facilitating the writing process, while the magnetically hard layer provides pinning for the media and ensures its thermal stability. Typically, the anisotropy gradient has been achieved by changing the sample growth conditions [3-5]. In this work we report an alternative approach of using Ar ion irradiation to create an anisotropy gradient in Co/Pd multilayer films.
  • Lecture (Conference)
    INTERMAG 2012, IEEE International Magnetics Conference, 07.-11.05.2012, Vancover, Kanada

Publ.-Id: 17252 - Permalink


Microscopic magnetic structuring of a spin-wave waveguide by ion implantation in a Ni81Fe19 layer
Obry, B.; Meyer, T.; Pirro, P.; Brächer, T.; Lägel, B.; Neb, R.; Osten, J.; Strache, T.; Fassbender, J.ORC; Hillebrands, B.
Ion implantation of ferromagnetic films has proven to be a promising tool for the fabrication of fully planar samples with a microscopic magnetic substructure. A waveguide-like propagation of spin waves in a Ni81Fe19 film which was locally patterned by ion implantation could be observed. The investigations have been performed using Brillouin light scattering microscopy on samples patterned with varying ion fluences. Further investigations on the coupling behavior of two parallel stripes in this fully planar structures have been performed. The presented fabrication technique of spin-wave waveguides provides much lower stray fields and better heat conduction. Especially the latter is a matter of interest when the objects are exposed to intense microwave fields (excitation of spin waves) or investigated by laser spectroscopy like Brillouin light scattering. Financial support by the DFG (GRK 792) is gratefully acknowledged.
  • Poster
    Frühjahrstagung der Sektion Kondensierte Materie (SKM), 25.-30.03.2012, Berlin, Deutschland
  • Poster
    INTERMAG 2012, 07.-11.05.2012, Vancover, Kanada
  • Applied Physics Letters 102(2013)2, 022409
    DOI: 10.1063/1.4775759

Publ.-Id: 17251 - Permalink


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