Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf
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Fundamentals and Modelling of Reactive Magnetron Sputtering
Moeller, W.
kein Abstract vorhanden
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Invited lecture (Conferences)
Tutorial "Fundamentals and Trends of Plasma Surface Processing", 14.09.2008, Garmisch-Partenkirchen, Germany
Permalink: https://www.hzdr.de/publications/Publ-12173
Reactive Magnetron Sputtering of Nitrides and Oxides: Understanding the Process and Optimizing the Film Quality
Moeller, W.
kein Abstract vorhanden
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Invited lecture (Conferences)
Plasmas, Surfaces, and Thin Films, 11.06.2008, London, United Kingdom
Permalink: https://www.hzdr.de/publications/Publ-12172
Nanostructures by Ion-Driven Self-Organisation: Can Ions Induce Order?
Moeller, W.
kein Abstract vorhanden
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Lecture (others)
VERA-Seminar, 05.06.2008, Wien, Austria
Permalink: https://www.hzdr.de/publications/Publ-12171
Nanostructures by Ion-Driven Self-Organisation
Moeller, W.
kein Abstract vorhanden
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Lecture (others)
Kolloquium des Max-Planck-Institutes für Plasmaphysik, 18.04.2008, Garching/ Muenchen, Germany
Permalink: https://www.hzdr.de/publications/Publ-12170
Forschung und Entwicklung für die Verfahrenstechnik
Kryk, H.
In einem Übersichtsvortrag werden die Aktivitäten des Institutes für Sicherheitsforschung auf den Gebieten der Verfahrens-, Prozess- und Messtechnik vorgestellt. Dies umfasst sowohl die Arbeiten zur Prozessaufklärung und Reaktionskalorimetrie zur Erhöhung der Sicherheit und Effektivität chemischer Prozesse als auch die Entwicklung und Anwendung von Spezialmesstechnik zur Untersuchung von Mehrphasenströmungen in verfahrenstechnischen Apparaten und Anlagen einschließlich der Modellierung und Simulation unter Nutzung von CFD-Methoden.
Einen Schwerpunkt der Präsentation bilden die Möglichkeiten und Perspektiven des Einsatzes von Praktikanten, Diplomanden und Doktoranden chemisch-technischer Studienrichtungen am Institut für Sicherheitsforschung des FZD.
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Lecture (others)
Hochschul-Informationstag, 10.01.2008, Freiberg, Deutschland
Permalink: https://www.hzdr.de/publications/Publ-12169
A rotating cell for in situ Raman spectroelectrochemical studies of photosensitive redox systems
Kavan, L.; Janda, P.; Krause, M.; Ziegs, F.; Dunsch, L.
A recently developed rotating spectroelectrochemical cell for in situ Raman spectroscopic studies of photoreactive compounds without marked decomposition of the sample is presented. Photochemically unstable compounds like fullerenes are difficult to be studied under stationary conditions by in situ spectroelectrochemistry using laser excitation as in Raman spectroscopy. Therefore, a rotating spectroelectrochemical was developed to avoid these difficulties. The cell can be used for any type of a planar electrode and of electrode materials in contact with aqueous or non-aqueous solutions as well as ionic liquids under appropriate laser power and accumulation times. The innovative advantage consists in the precession movement of the spectroelectrochemical cell with an eccentric drive. This precession movement allows a fixed electrical connection to be applied for interfacing the electrochemical cell to a potentiostat. Hence, any electrical imperfections and noise, which would be produced by sliding contacts, are removed. Further advantage of the rotating cell is a dramatic decrease of the thermal load of the electrochemical system. The size of the spectroelectrochemical cell is variable and dependent on the thickness of the cuvettes used ranging up to ca. 10 mm. The larger measuring area causes a higher sensitivity in the spectroscopic studies using this cell. The as constructed spectroelectrochemical cell is easy to be handled. The application of the cell is demonstrated for ordered fullerene C60 layers and the spectroelectrochemical behavior of nanostructured fullerenes. Here the charge transfer at highly ordered fullerene C60 films was studied by in situ Raman spectroelectrochemistry under appropriate laser power and accumulation time without marked photodecomposition of the sample.
Keywords: spectroelectrochemistry; Raman spectroelectrochemical cell; in situ measurements; fullerenes; fullerene layers
- Analytical Chemistry 81(2009), 2017-2021
Permalink: https://www.hzdr.de/publications/Publ-12168
An anisotropic Heisenberg model on the trigonal lattice for multiferroic oxides
Kunze, T.; Gemming, S.; Olbrich, C.; Chaplygin, I.; Schmidt, P.; Schreiber, M.
Hexagonal manganites are oxides, in which structural, electronic, and magnetic degrees of freedom are coupled in a complex manner. Therefore, such materials have the potential for novel, nanoscale sensing and switching applications. Manganites are composed of dense-packed hexagonal manganese oxide layers with strong in-plane and weak interlayer coupling, thus the possible spin configurations may be studied with the help of a two-dimensional model Hamiltonian. For this purpose a two-dimensionally periodic trigonal spin system is qualitatively studied with the help of an extended multiparameter Heisenberg model. The temperature dependence of the magnetisation is investigated with the help of a Metropolis-Monte-Carlo algorithm as a function of the anisotropy term and of an external magnetic field. Thermodynamic quantities such as the total energy, the heat capacity and the magnetization are determined by statistical evaluation.
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Poster
DPG Frühjahrstagung, 25.-29.02.2008, Berlin, Deutschland
Permalink: https://www.hzdr.de/publications/Publ-12167
Nanoschreiben mit fokussierten Ionen
Bischoff, L.
Fokussierte Ionenstrahlsysteme (FIB) sind ein modernes Werkzeug für die Strukturerzeugung sowie deren Analyse im µm bis in den nm- Bereich hinein. Ein Ionenstrahl, der aus einer Flüssigmetall-Ionenquelle (Liquid Metal Ion Source - LMIS) kommt wird mittels einer Ionenpotik beschleunigt und in einen Spot von bis zu wenigen nm fokussiert und dann Computergesteuert über die Probe geführt. Eine Auflösung von kleiner 10 nm bei Stromdichten von mehr als 10 Acm-2 können erreicht werden.
Der Einsatz von FIB Systemen ist spezialisiert auf die Präparation von Proben in der Analytik der Halbleiterindustrie sowie der nm - Strukturerzeugung in der Forschung. Die pixelweise Abarbeitung des Ionenstrahlschreibens ist für eine Massenproduktion nicht geeignet aber umso mehr für die Erzeugung von Prototypen neuer Bauelemente. Besonders effektiv ist die Kopplung des FIB mit einem Rasterelektronenmikroskop zu einem Zweistrahlsystem. Die Erweiterung auf neue Ionenarten durch den Einsatz spezieller Legierungen in der Ionenquelle eröffnet ein breites Spektrum neuer Anwendungsfelder.
Ausgewählte Applikationen aus dem FZD werden demonstriert und erläutert.
Keywords: Fokussierte Ionenstrahlsysteme; Strukturerzeugung; Analyse; nm- Bereich; Anwendungen
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Lecture (others)
Lange Nacht der Wissenschaften Dresden, 04.07.2008, Dresden, Germany
Permalink: https://www.hzdr.de/publications/Publ-12166
Application of mass-separated focused ion beams
Bischoff, L.; Akhmadaliev, C.; Pilz, W.; Schmidt, B.
During the last decades, focused ion beams (FIB) became a very useful and versatile tool in microelectronics industry, as well as in the field of basic and applied research and derived an exceedingly importance within the nanotechnology. For special purposes like ion milling, ion beam writing for doping or patterning from the µm- to the nm-range without any lithographic steps using Gallium and also other ion species which are of increasing interest. An introduction in design and operation of mass separated FIB systems, equipped with alloy liquid metal ion sources and the development and characterization of suited alloy liquid metal ion sources is given and their preparation and characterisation is discussed.
Keywords: focused ion beams; alloy liquid metal ion source; preparation; characterisation
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Lecture (others)
Seminar at Carl Zeiss NTS, 07.05.2008, Oberkochen, Germany
Permalink: https://www.hzdr.de/publications/Publ-12165
Application of Focused Ion Beams
Bischoff, L.
During the last decades, focused ion beams (FIB) became a very useful and versatile tool in microelectronics industry, as well as in the field of basic and applied research and derived an exceedingly importance within the nanotechnology. For special purposes like ion milling, ion beam writing for doping or patterning from the µm- to the nm-range without any lithographic steps using Gallium and also other ion species which are of increasing interest. An introduction in design and operation of mass separated FIB systems, equipped with alloy liquid metal ion sources and the development and characterization of suited ion sources is given.
Examples, like ion beam synthesis of CoSi2 nano-structures, sputtering investigations and applications, the formation of ripples under FIB irradiation or the fabrication of NEMS structures on SOI substrates should demonstrate the manifold utilization of the microbeam technology.
Finally an outlook to prospective work with FIB in FZD is presented.
Keywords: focused ion beam; nanotechnology; liquid metal ion source
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Lecture (others)
Seminar Materials Science at FZD, 28.10.2008, Dresden, Germany
Permalink: https://www.hzdr.de/publications/Publ-12164
Si+ implantation induced photoluminescence enhancement in PMMA
Tsvetkova, T.; Balabanov, S.; Avramov, L.; Borisova, E.; Bischoff, L.
Si+ ion implantation effects on the photoluminescence (PL) properties of polymethyl-methacrylate (PMMA) have been studied. Low-energy ion implantation (E=30÷50 keV) was carried out over a range of different ion doses (D=1013÷1017 cm-2). The observed effect of PL enhancement (PLE) is essentially dependent on the ion dose. For certain doses, the overall amplitude of the PL emission has a several times (~ 5 times) increase. Electron microscopy results and surface elemental analysis reveal implanted Si atoms clustering which could be related to the observed PLE effects.
Keywords: ion implanted polymers; polymethyl-methacrylate; photoluminescence
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Przeglad elektrotechniczny 84(2008)3, 72-74
ISSN: 0033-2097
Permalink: https://www.hzdr.de/publications/Publ-12162
Ultrasound Doppler array used for vortex investigations in liquid metals
Franke, S.; Büttner, L.; Czarske, J.; Räbiger, D.; Eckert, S.
An Ultrasound Doppler system for measuring the flow velocity field of magnetically-driven metal is introduced: Two orthogonally arranged sensor line arrays facilitate a two-dimensional measurement of two velocity components (2d/2c) in an area of 70 x 70 mm2. First measurement results of liquid metal flows driven by a rotating magnetic field are presented.
Keywords: Ultrasound Doppler method; sensor array; liquid metal; rotating magnetic field
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Lecture (Conference)
Sensor 2009, 26.-28.05.2009, Nürnberg, Germany
Permalink: https://www.hzdr.de/publications/Publ-12161
NEMS structures on SOI by writing FIB implantation and subsequent anisotropic wet chemical etching
Bischoff, L.; Schmidt, B.; Lange, H.
The further miniaturization of silicon nanomechanical structures in combination with the highly developed microelectronic technology at the micro- and nanometer level will lead to a new generation of nano-electro-mechanical systems (NEMS). A modern technique to fabricate such three-dimensional structures is the combination of high-concentration p-type doping of silicon by high resolution writing implantation using a focused ion beam (FIB) and subsequent anisotropic and selective wet chemical etching. FIB-patterned and chemically etched 3D Si structures with nanoscale thickness and width have been fabricated using 30 keV Ga+ ion implantation and subsequent anisotropic etching in KOH/H2O solution on Silicon-On-Insulator (SOI) substrates. Design and fabrication considerations to achieve freestanding Si structures, like nanowires and -bridges are discussed and some typical structures are shown. Electrical measurements are demonstrated which reveal a broad spectrum in the field of sensor applications.
Keywords: nano-electro-mechanical systems; focused ion beam; anisotropic etching; sensor applications
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Lecture (Conference)
Ionenstrahlphysik und Nanotechnologie, 11.-12.04.2008, Darmstadt, Germany
Permalink: https://www.hzdr.de/publications/Publ-12160
Comparative study of gas-oil and gas-water two-phase flow in a vertical pipe
Szalinski, L.; Da Silva, M. J.; Thiele, S.; Beyer, M.; Lucas, D.; Hampel, U.; Hernandez Perez, V.; Abdulkareem, L. A.; Azzopardi, B. J.
A wire-mesh sensor has been employed in a vertical pipe of 67 mm diameter and 6 m length to investigate two-phase flows of two different two-phase mixtures. Conductivity-based measuring electronics was used to measure water-air flow and permittivity-based one for silicone oil-air flow. This experimental setup enables a direct comparison of both two-phase flow systems. Thus, wire-mesh sensor data of both gas-liquid systems were analysed with regard to radial gas volume fraction profiles and bubble size distributions. Furthermore wire-mesh sensor images were evaluated to determine the occurring flow pattern. A flow pattern map was created which contains all experimental measurement points denoted with observed flow pattern.
Keywords: gas-liquid flow; flow visualization; wire-mesh sensor; capacitance; permittivity; conductivity
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Contribution to proceedings
3rd International Workshop on Process Tomography, 17.-19.04.2009, Tokyo, Japan
Proceedings of 3rd International Workshop on Process Tomography -
Lecture (Conference)
3rd International Workshop on Process Tomography (IWPT-3), 17.-19.04.2009, Tokyo, Japan -
Chemical Engineering Science 65(2010)12, 3836-3848
DOI: 10.1016/j.ces.2010.03.024
Cited 94 times in Scopus
Permalink: https://www.hzdr.de/publications/Publ-12159
Nano-Structures made by Swift Heavy Ions
Bolse, W.; Paulus, H.; Bolse, T.; Bischoff, L.
Recently we have discovered that the irradiation of thin oxide films with swift heavy ions (SHI) at small incident angles results in an instability of the film against periodic cracking and subsequent reorganisation on a sub-micron level due to ion hammering. Varying the conditions during irradiation (ion species, rotating the target) we were able to generate a wide range of nano-structures and patterns, the most interesting of which was an array of NiO-nanopillars with a diameter of the order of 100 nm and a height of about 2000 nm. Unfortunately, the arrangement of these nanotowers was not regular. [1] To overcome this problem, we have prestructured the films by means of a focused ion beam with an array of perpendicular cuts of about 100 nm width and 1000 nm distance. In fact, the subsequent irradiation with SHI under grazing incidence and permanent target rotation results in an ordered array of the NiO nanotowers. To our surprise, the same treatment of TiO-films lead to an ordered pattern of holes.
[1] W. Bolse, T. Bolse, C. Dais, D. Etissa-Debissa, A. Elsanousi, A. Feyh, M. Kalafat, H. Paulus, Surf. Coat. Technol. 200 (2005) 1430
Keywords: swift heavy ions; nano-structures; prestructured; focused ion beam; TiO-film
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Lecture (Conference)
72. Jahrestagung der DPG und DPG Frühjahrstagung des Arbeitskreises Festkörperphysik, 25.-29.02.2008, Berlin, Germany
Permalink: https://www.hzdr.de/publications/Publ-12158
Spin-state transition and spin-polaron physics in cobalt oxide perovskites: ab initio approach based on quantum chemical methods
Hozoi, L.; Birkenheuer, U.; Stoll, H.; Fulde, P.
A fully ab initio scheme based on quantum chemical wavefunction methods is used to investigate the correlated multiorbital electronic structure of a 3d-metal compound, LaCoO3. The strong short-range electron correlations, involving both Co and O orbitals, are treated by multireference techniques. The use of effective parameters like the Hubbard U and interorbital U′, J terms and the problems associated with their explicit calculation are avoided with this approach. We provide new insight into the spin-state transition at about 90 K and the nature of charge carriers in the doped material. Our results indicate the formation of a t2g
4eg
2 high-spin state in LaCoO3 for T > 90K. Additionally, we explain the paramagnetic phase in the low-temperature lightly doped compound through the formation of Zhang-Rice-like O hole states and ferromagnetic clusters.
Keywords: heavy fermions; electron correlation; local correlation methods; high-Tc superconductors
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New Journal of Physics 11(2009), 023023
DOI: 10.1088/1367-2630/11/2/023023
Cited 31 times in Scopus
Downloads
Permalink: https://www.hzdr.de/publications/Publ-12157
Ultrasound Doppler array system for flow field investigations in liquid metals
Franke, S.; Büttner, L.; Czarske, J.; Räbiger, D.; Eckert, S.
An Ultrasound Doppler system for measuring the flow velocity field of magnetically-driven metal is introduced: Two orthogonally arranged sensor line arrays facilitate a two-dimensional measurement of two velocity components (2d/2c) in an area of 70 x 70 mm2. First measurement results of liquid metal flows driven by a rotating magnetic field are presented.
Keywords: Ultrasound Doppler method; sensor array; liquid metal; rotating magnetic field
- Flow Measurement and Instrumentation 21(2010)3, 402-409
Permalink: https://www.hzdr.de/publications/Publ-12156
Application of rate theory modeling to cluster evolution in binary Fe-Cu alloys
Birkenheuer, U.; Bergner, F.; Ulbricht, A.; Gokhman, A.; Almazouzi, A.
A rate theory model for the simulation of the irradiation-induced time-evolution of Cu-rich precipitates in Fe-Cu model alloys is presented which takes into account that precipitate clusters are mixed Cu-vacancy aggregates by explicitly allowing the defect clusters to absorb vacancies. The resulting Vacancy-Coupled Copper Clustering (V3C) model is calibrated on a series of SANS experiments on two different Fe-Cu model alloys neutron-irradiated at four different doses. Quantitative agreement with the SANS experiments could be achieved by introducing a dependence of the Fe-Cu interface energy on the amount of vacancies in the mixed precipitate clusters. This energy is a function of the weight-percentage of Cu in the iron matrix. An analytic expression for this dependence is suggested.
Keywords: rate theory; percipitation; Fe-Cu model alloys; SANS experiments; neutron irradiation; irradiation damage; ageing of steels
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Contribution to HZDR-Annual report
Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; FZD-501 Dezember 2008, 70-76
ISSN: 1437-322X
Downloads
Permalink: https://www.hzdr.de/publications/Publ-12155
Fabrication of light-emitting Si quantum dots by pulsed annealing of Si-rich SiO2 layers
Kachurin, G. A.; Yankov, R. A.; Cherkova, S. G.; Marin, D. V.
Thin Si-rich SiO2 layers have been prepared by implantation of 100 to 190 keV Si ions in thermally grown oxide films. The ion doses provided the excess Si concentration of about 10-15%. KrF excimer laser pulses, flash lamp annealing and rapid thermal annealing were used for the post-implantation heat treatments to form light-emitting Si quantum dots. The pulse durations were 20 ns, 20 ms and 1 s, respectively. Studies were carried out using a spectroscopy of PL excited at room temperature by a nitrogen laser (λ = 337 nm). The excess Si atoms in SiO2 are not free to migrate, but are rather incorporated into the oxide network. The fabrication of Si-ncs necessitates segregation of the Si atoms, availability of sinks to which these atoms may diffuse, availability of Si-phase nucleation centers, growth of the incipient nanoprecipitates, their crystallization, and, finally, the Ostwald ripening Due to the high temperatures resulting from intense light pulses, the different stages in the formation of light-emitting Si quantum dots may occur quite rapidly. Treatment for times as short as 20 ns is already sufficient for the segregation of the excess Si in the SiO2 atomic network and the formation of quantum dots that luminesce in the visible portion of the spectrum (400-600 nm). For laser pulse duration of 20 ns no formation of nanocrystals occurs, which is evidently associated with the insufficient growth time. However, if one creates in advance amorphous Si precipitates of the right size, it is possible to form quantum-size Si nanocrystals by pulsed laser processing. This process occurs most likely via melting rather than in a solid phase, favored by the release of latent heat and the reduction in temperature of melting of the nanoparticles. Photoluminescence band near 800 nm, typical to quantum-size Si nanocrystals, was found after laser annealing. Formation of the luminesing Si nanocrystals in Si-rich SiO2 layers is feasible under the influence of intense light pulses of 20 ms and 1 s duration. In this case the SiO2 layer has not been heated above the Si melting point. Comparison of the nanocrystals formation rate and the estimates of the diffusion-limited growth yields diffusivity of the excess Si in SiO2 that are substantially larger than the values obtained in experiments using stationary annealing. The discrepancies may be explained by the existence of a transient mechanism of rapid growth at the very beginning of the pulsed annealing.
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Poster
15th International Conference on Semiconductor Dots, 11.-16.05.2008, Gyeongju, Korea
Permalink: https://www.hzdr.de/publications/Publ-12153
Pulsed annealing creation of light-emitting Si nanostructures in SiO2 layers implanted with Si ions
Kachurin, G. A.; Cherkova, S. G.; Yankov, R. A.; Marin, D. V.
Implantation of 100-190 keV Si ions in thin SiO2 layers followed by intense light pulse annealing was used to form Si quantum dots. The ion doses provided the excess Si concentrations of ~10-15%. KrF excimer laser pulses, flash lamp annealing and rapid thermal annealing were used for the post-implantation anneals. The pulse durations were 20ns, 20ms and 1s, respectively. Studies were carried out using photoluminescence excited at 20 oC by a N2 laser. Treatments for 20ns are already sufficient for the segregation of Si and formation of low-dimensional clusters, emitting light in the visible range (400-600 nm). For 20ns pulses no formation of Si-ncs occurs, which is associated with the lack of annealing time. However, if one creates in advance amorphous Si nanoprecipitates, it is possible to form Si-ncs by laser pulses. The crystallization occurs most likely via melting. Formation of the Si-ncs is feasible under the 20ms and 1s light pulses. In this case the temperatures never exceeded Si melting point. Comparison of the Si-ncs formation rate and the estimates of the expected diffusion-limited grain growth yields diffusivity of Si in SiO2 that is much higher, than the values obtained for stationary annealing. Possible mechanism of Si-ncs formation is discussed.
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Lecture (Conference)
9th International Conference on Applications of Nuclear Techniques, 08.-14.06.2008, Crete, Greece
Permalink: https://www.hzdr.de/publications/Publ-12152
Luminescing quantum-size Si nanostructures formed in Si rich SiO2 by intense light pulses
Kachurin, G. A.; Cherkova, S. G.; Yankov, R. A.; Marin, D. V.
Implantation of Si ions in thin thermally grown SiO2 layers followed by intense light pulse annealing was used to form light-emitting Si nanostructures. The ion doses provided the excess Si concentration of about 10-15%. KrF excimer laser pulses, flash lamp annealing and rapid thermal annealing were used for the post-implantation heat treatments. The pulse durations were 20 ns, 20 ms and 1 s, respectively. Studies were carried out using a spectroscopy of PL excited at room temperature by a nitrogen laser (λ = 337 nm). Due to the high temperatures resulting from intense light pulses, the different stages in the formation of light-emitting Si nanostructures may occur quite rapidly. Treatment for times as short as 20 ns is already sufficient for the segregation of the excess Si in the SiO2 atomic network and the formation of clusters that luminesce in the visible portion of the spectrum (400-600 nm). For laser pulse duration of 20 ns no formation of nanocrystals occurs, which is evidently associated with the insufficient growth time. However, if one creates in advance amorphous Si precipitates of the right size, it is possible to form quantum-size Si nanocrystals by pulsed laser processing. This process occurs most likely via melting rather than in a solid phase, favored by the release of latent heat and the reduction in temperature of melting of the nanoparticles. Photoluminescence band near 800 nm, typical to quantum-size Si nanocrystals, was found after laser annealing. Formation of the luminesing Si nanocrystals in Si-rich SiO2 layers is feasible under the influence of intense light pulses of 20 ms and 1 s duration. In this case the SiO2 layer has not been heated above the Si melting point. Comparison of the nanocrystals formation rate and the estimates of the diffusion-limited growth yields diffusivity of the excess Si in SiO2 that are substantially larger than the values obtained in experiments using stationary annealing. The discrepancies may be explained by the existence of a transient mechanism of rapid growth at the very beginning of the pulsed annealing.
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Poster
The 15th International Conference on Luminescence and Optical Spectroscopy of Condensed Matter (ICL'08), 07.-11.07.2008, Lyon, France
Permalink: https://www.hzdr.de/publications/Publ-12151
Light-emitting Si nanostructures formed in Si-rich SiO2 by pulsed annealing
Kachurin, G. A.; Cherkova, S. G.; Yankov, R. A.; Marin, D. V.
Formation of Si-nanocrystals hase been achieved under the influence of intense light pulses of 20 ms and 1 s duration. In this case the Si surface has not been observed to melt, and therefore the SiO2 layer has not been heated above 1400 °C. Comparison of the Si-nc formation rate and the estimates of the diffusion-limited growth yields diffusivity of the excess Si in SiO2 that are substantially larger than the values obtained in experiments using stationary annealing. The discrepancies have been explained by the occurrence of a transient mechanism of rapid growth at the start of the pulsed annealing.
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Poster
16th Annual International Conference on Composites/Nano Engineering (ICCE-16), 20.-26.06.2008, Kunming (City of Eternal Spring), China
Permalink: https://www.hzdr.de/publications/Publ-12150
Light-emitting Si nanostructures formed in Si implanted SiO2 layers by pulsed anneals
Kachurin, G. A.; Cherkova, S. G.; Marin, D. V.; Yankov, R. A.
Thin thermally grown SiO2 layers were implanted with 100 to 190 keV Si ions. The ion doses provided the excess Si concentration of about 10-15%. KrF excimer laser pulses, flash lamp annealing and rapid thermal annealing were used for the post-implantation heat treatments to analyze their possibilities to synthesize the light-emitting Si nanocrystals (Si-ncs) and therewith the mechanism of Si-ncs formation . The pulse durations were 20 ns, 20 ms and 1 s, respectively. Studies were carried out using the photoluminescence spectroscopy, excited at 20 oC by a nitrogen laser (λ = 337 nm). The formation of Si-ncs necessitates segregation of the Si atoms from the oxide network, availability of sinks to which these atoms may diffuse, availability of Si-phase nucleation centers, growth of the incipient nanoprecipitates, and, finally, their crystallization. Treatment for times as short as 20 ns is already sufficient for the segregation of the excess Si and for formation of nanostructures that luminesce in the visible range (400-600 nm). For laser pulse duration of 20 ns no formation of Si-ncs occurs. However, if one creates in advance amorphous Si nanoprecipitates, it is possible to form the luminescing Si-ncs by the 20-ns pulses. This process occurs most likely via melting, favored by the release of the latent heat. Formation of the luminescing Si-ncs is feasible under the 20-ms and 1-s light pulses. In these cases the SiO2 layer has not been heated above the Si melting point. Comparison of the Si-ncs formation rate with their conjectural diffusion-limited growth suggests the existence of a transient non-diffusional mechanism at the beginning of the pulsed annealing.
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Poster
16th International Conference on Ion Beam Modification of Materials, 31.08.-05.09.2008, Dresden, Germany
Permalink: https://www.hzdr.de/publications/Publ-12149
Light-emitting Si quantum dots formed by pulsed annealing
Kachurin, G. A.; Cherkova, S. G.; Yankov, R. A.; Marin, D. V.
Pulsed anneals are of high practical importance as they enable one to perform heat treatment locally while affecting insignificantly the adjacent regions. This is particularly advantageous for the processing of low dimensional devices. The ongoing drive for smaller devices coupled with the discovery of strong luminescence from quantum-sized Si nanocrystals (Si-ncs) has spurred extensive research into the processes of their fabrication. Nowadays a decomposition of supersaturated solid solution of Si in SiO2 layers is mostly employed for this purpose. The fabrication of Si-ncs necessitates segregation of the Si atoms, availability of sinks to which these atoms may diffuse, availability of Si-phase nucleation centers, growth of the incipient clusters, and subsequent crystallization. Our work is an attempt to address the dependence of the light-emitting Si nanostructure formation on the length of the annealing light pulses. Implantation of Si ions in thin thermally grown SiO2 layers followed by intense light pulse annealing was used to form Si quantum dots. The ion doses provided the excess Si concentrations of about 10-15%. KrF excimer laser pulses, flash lamp annealing and rapid thermal annealing were used for the post-implantation heat treatments. The pulse durations were 20 ns, 20 ms and 1 s, respectively. Studies were carried out using photoluminescence excited at 20 °C by a N2 laser (λ = 337 nm). Due to the high temperatures resulting from intense light pulses, the different stages in the formation of light-emitting Si nanostructures may occur quite rapidly. Treatment for times as short as 20 ns is already sufficient for the segregation of the excess Si and the formation of low dimensional clusters that emit light in the visible range (400-600 nm). For 20 ns laser pulses of no formation of Si-ncs occurs, which is evidently associated with the insufficient growth time. However, if one creates in advance amorphous Si nanoprecipitates, it is possible to form Si-ncs by pulsed laser processing. The crystallization occurs most likely via melting rather than in a solid phase, favored by the release of latent heat and the reduction in temperature of melting of the low dimensional particles. Formation of the luminescing Si-ncs is feasible under the 20 ms and 1 s intense light pulses. In this case the temperatures never exceeded Si melting point. Comparison of the Si-ncs formation rate and the estimates of the expected diffusion-limited grain growth yields diffusivity of the excess Si in SiO2 that are several orders larger, than the values obtained in experiments using stationary annealing. Possible mechanism of Si-ncs formation is discussed.
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Poster
Workshop on Recent Advances of Low Dimensional Structures and Devices (WRA-LDSD), 07.-09.04.2008, Nottingham, UK
Permalink: https://www.hzdr.de/publications/Publ-12148
Radiosynthesis and radiopharmacological evaluation of [N-methyl-11C]Org 34850 as a glucocorticoid receptor (GR)-binding radiotracer
Wüst, F.; Knieß, T.; Henry, B.; Peeters, B. W. M. M.; Wiegerinck, P. H. G.; Pietzsch, J.; Bergmann, R.
The radiosynthesis of [N-methyl-11C]Org 34850 as a potential brain glucocorticoid receptor (GR)-binding radiotracer is described. The radiosynthesis was accomplished via N-methylation of the corresponding desmethyl precursor with [11C]methyl triflate in a remotely controlled synthesis module to give the desired compound in a radiochemical yield of 23+/-5% (decay-corrected, based upon [11C]CO2) at a specific activity of 47+/-12 GBq/mmol (n ¼ 15) at the end-of-synthesis (EOS). The radiochemical purity after semi-preparative HPLC purification exceeded 95%. The total synthesis time was 3540 min after end-of-bombardment (EOB).
The radiotracer is rapidly metabolized in rat plasma leading to the formation of two more hydrophilic metabolites as the major metabolites. Radiopharmacological evaluation involving biodistribution and small animal PET imaging in normal Wistar rats showed that the compound [N-methyl-11C]Org 34850 is not able to sufficiently penetrate the bloodbrain barrier. Therefore, compound [N-methyl-11C]Org 34850 seems not to be a suitable PET radiotracer for imaging rat brain GRs. However, involvement of Pgp or species differences requires further clarification to establish whether the radiotracer [N-methyl-11C]Org 34850 may still represent a suitable candidate for imaging GRs in humans.
Keywords: [N-methyl-11C]Org 34850; Glucocorticoid receptor; Positron emission tomography (PET)
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Applied Radiation and Isotopes 67(2009), 308-312
DOI: 10.1016/j.apradiso.2008.10.014
Cited 6 times in Scopus
Permalink: https://www.hzdr.de/publications/Publ-12146
Messtechnik für Mehrphasenströmungen - Sensoren, Systeme und Anwendungen
Schleicher, E.; Da Silva, M. J.; Fischer, F.; Bieberle, A.; Bieberle, M.; Hampel, U.
Die Untersuchung von Mehrphasenströmungen ist für viele Forschungs- und Industriebereiche von großer Bedeutung. Im Bereich der Verfahrenstechnik und Kernenergietechnik bestimmen beispielsweise das Verhalten und die Struktur von Gasblasen maßgeblich Effizienz und Sicherheit von Prozessen in Rohrsystemen, Behälter oder Reaktoren. Angesichts dieses breiten Anwendungsspektrums sind in der Vergangenheit verschiedene Messmethoden und Systeme entwickelt worden, um die Untersuchung von Mehrphasenströmungen zu ermöglichen, bestimmte Phänomene sichtbar zu machen und um numerische Strömungsmodelle s. g. CFD-Codes (computational fluid dynamics) zu validieren. Am Institut für Sicherheitsforschung des Forschungszentrums Dresden-Rossendorf wurden beispielsweise auf elektrischer Leifähigkeit sowie Kapazität basierende Systeme wie Nadelsonden und Gittersensoren entwickelt, die in Zweiphasenströmungen den Gasgehalt und die Phasenverteilung mit sehr hohen räumlichen und zeitlichen Auflösungen erfassen können. Darüber hinaus werden verstärkt auch nicht-invasive tomographische Verfahren wie die Gamma-CT und die ultraschnelle Röntgen-CT beforscht. Letztere ist in der Lage bis zu 7000 tomographische Schnittbilder pro Sekunde mit einer Ortsauflösung von bis zu 1 mm zu erzeugen.
Keywords: flow measurement; two-phase flow; Ultra fast X-ray CT; multi phase flow measurement; flow visualization; capacitance measurement; high resolution gamma ray tomography; void fraction determination; wire mesh sensor
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Invited lecture (Conferences)
Institutskolloquium, 25.11.2008, Dresden, Deutschland
Permalink: https://www.hzdr.de/publications/Publ-12145
The Naimark dilated PT-symmetric brachistochrone
Günther, U.; Samsonov, B.
The quantum mechanical brachistochrone system with PT-symmetric Hamiltonian is Naimark dilated and reinterpreted as subsystem of a Hermitian system in a higher-dimensional Hilbert space. This opens a way to a direct experimental implementation of the recently hypothesized PT-symmetric ultra-fast (wormhole-like) brachistochrone regime of [C. M. Bender et al, Phys. Rev. Lett. 98, 040403 (2007)] in an entangled two-spin system. The talk is mainly based on Phys. Rev. Lett. 101, 230404 (2008).
Keywords: quantum brachistochrone; quantum computing; PT quantum mechanics; strongly non-Hermitian regime; exceptional point; Anandan-Aharonov lower bound; ultra-fast evolution; POVM; Naimark dilation; Naimark extension; entangled state; two-qubit system; wormhole
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Lecture (Conference)
QTRF5 - Quantum Theory: Reconsideration of Foundations, 5, 14.-19.06.2009, Vaxjo, Sweden
Permalink: https://www.hzdr.de/publications/Publ-12144
Photochemical reduction of UO22+ in the presence of alcohol studied by DFT calculations
Tsushima, S.
A well-known photochemical process of UVIO2
2+ reduction to UVO2
+ in the presence of alcohols was studied by density functional theory (DFT) calculations. It was found that the first process which takes place is a photoexcitation of the ground-state UO2
2+ to the triplet excited state (*UO2
2+) followed by a significant shortening of the *UO2
2+-to-alcohol Oax-H distance. A charge transfer from *UO2
2+ to alcohol and hydrogen abstraction takes place in the following step. Consequently, UVIO2
2+ gets reduced to UVO(OH)2+. The photochemical byproduct RC·HOH acts further as a reducing agent toward UO2
2+ to yield UO2
+ and RCHO (aldehyde). Only a combination of these two reactions can explain a high quantum yield of this reaction. In the absence of alcohol, the lowest-lying triplet state exhibits a different character, and photoreduction is unlikely to take place via the same mechanism. The present results agree well with recent experimental finding [J. Am. Chem. Soc. 2006, 128, 14024] and supports the idea that the Oax-H linkage between UO2
2+ and the solvent molecule is the key to the photochemical reduction process.
- Inorganic Chemistry 48(2009)11, 4856-4862
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Lecture (Conference)
ROBL-Radiochemie Workshop, 18.12.2008, Dresden, Germany
Permalink: https://www.hzdr.de/publications/Publ-12143
Anisotropic scaling of ripple morphologies on high-fluence sputtered silicon
Keller, A.; Cuerno, R.; Facsko, S.; Möller, W.
The evolution of Si(100) surfaces has been studied during oblique high-fluence ion sputtering by means of atomic force microscopy. The observed surface morphology is dominated by nanoscale ripples and kinetic roughening at small and large lateral scales, respectively. The large-scale morphology exhibits anisotropic scaling at high fluences with different roughness exponents an = 0.76 ± 0.04 and ap = 0.41 ± 0.04 in the directions normal and parallel to the incident ion beam, respectively. Comparison with the predictions of single field and two-field ("hydrodynamic") models of ion erosion suggests the relevance of nonlinearities that are not considered in the simpler anisotropic Kuramoto-Sivashinsky equation.
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Physical Review B 79(2009)11, 115437
DOI: 10.1103/PhysRevB.79.115437
Cited 45 times in Scopus
Permalink: https://www.hzdr.de/publications/Publ-12142
Sorption databases for increasing confidence in performance assessment
Richter, A.; Brendler, V.; Nebelung, C.; Payne, T.; Brasser, T.
World-wide activities focus on the remediation of radioactively contaminated sites. One common aim is to deliver a more profound chemical base for risk assessment, namely all those physico-chemical phenomena governing the contamination plume development in time and space. Coupled transport codes able to tackle this challenge have to simplify the resulting very complex reaction pattern. To do so in an adequate way requires extending the knowledge about retardation and mobilisation phenomena and the underlying basic processes and interactions (e.g. physisorption, chemisorption, surface precipitation).
Interactions at the solid-liquid interface can be described by two complementary approaches, the empirical Kd concept and the mechanistic Surface Complexation Models (SCM).
Kds are used by most reactive transport and risk assessment codes due to the straightforward numerics involved. In addition, the Kd concept is often the only feasible option for complex solid phases. However, the Kd concept is a rather simplistic approach. Many very different basic physico-chemical phenomena are contained in just one conditional parameter. Therefore, extrapolating Kd values may yield very large uncertainties.
SCM allows for the partitioning of retardation into the most important underlying physico-chemical processes. Parameters are site-independent and applicable despite large variations in geochemical conditions. This presents a high potential to increase confidence in safety analysis and risk assessment studies (performance assessment). The mechanistic description of sorption processes with SCM allows a thermodynamically consistent calculation of the species distribution between liquid and solid phase combined with more reliable inter- and extrapolations. However, this requires that all mineral constituents of the solid phase are characterized. Another issue is the large number of required parameters combined with time-consuming iterations.
Addressing both approaches, we present two sorption databases, developed mainly by or under participation of the Forschungszentrum Dresden-Rossendorf (FZD). Both databases are implemented as relational databases, assist identification of critical data gaps and the evaluation of existing parameter sets, provide web based data search and analyses and permit the comparison of SCM predictions with Kd values.
RES³T (Rossendorf Expert System for Surface and Sorption Thermodynamics) is a digitized thermodynamic sorption database (see www.fzd.de/db/RES3T.login) and free of charge. It is mineral-specific and can therefore also be used for additive models of more complex solid phases.
ISDA (Integrated Sorption Database System) connects SCM with the Kd concept but focuses on conventional Kd. The integrated datasets are accessible through a unified user interface.
An application case, Kd values in Performance Assessment, is given.
Keywords: RES3T; ISDA; database; sorption; surface complexation; KD; prediction
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Lecture (Conference)
ICEM'09 - 12th International Conference on Environmental Remediation and Radioactive Waste Management, 11.-15.10.2009, Liverpool, United Kingdom -
Contribution to proceedings
ICEM 2009, 11.-15.10.2009, Liverpool, United Kingdom
Proceedings of the 2009 12th International Conference on Environmental Remediation and Radioactive Waste Management, ICEM2009-16053
Permalink: https://www.hzdr.de/publications/Publ-12141
Sizing of safety valves using ANSYS CFX-Flo
Moncalvo, L.; Friedel, B.; Jörgensen, T.; Höhne, T.
This work discusses the effect of the degree of fineness of the flow volume discretization and that of the turbulence model on the accuracy of reproduction of air mass flow rates in two safety valves using the CFD software ANSYS Flo. Calculations show that the degree of fineness of the discretization is the decisive factor
affecting the exactness of the calculations and that the best reproduction is achieved with grids where at least two cells are built on the smallest edge. The selection of the turbulence model has by far in comparison a lower impact; however, the best accuracy is obtained using the standard k-x model and the SST modification of Menter.
Keywords: CFD; Safety valves
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Chemical Engineering & Technology 32(2009)2, 1-6
DOI: 10.1002/ceat.200800530
Cited 23 times in Scopus
Permalink: https://www.hzdr.de/publications/Publ-12140
Site-selective determination of coordination symmetries by anisotropic anomalous X-ray scattering
Zschornak, M.; Leisegang, T.; Stöcker, H.; Weißbach, T.; Gemming, S.; Meyer, D. C.
Based on an experiment of Kirfel and Petcov on rutile (136) P42/mnm, which verified anisotropic anomalous scattering (AAS) by measuring Forbidden Reflection near Edge Diffraction (FRED), we aimed to extend the results with allowed reflections to extract more tensor symmetries of the Ti scattering factor tensor f ij by fitting the model of AAS to the experimental data. Results from DFT calculations will also be presented. Furthermore we intended to study possible restrictions for atomic site occupation of unknown structures in an identified space group due to these local symmetry relations exemplary for this model structure.
Experiments were carried out at DESY/HASYLAB BL C using a Si (111) double crystal monochromator tuned to an energy of 4985eV. An automated optimization and Y-scan routine for a sample setup with rotating degree of freedom assured AAS measurements at the reflection maxima. The rutile samples investigated were 10x10x1mm3 wafers in (001), (110) and (111) orientation and Y-scans were measured for the reflections 001, 220, 110 and 111.
Ti occupies Wyckoff site 2a, its tensor symmetry must follow the local symmetry m.mm leaving 3 complex elements f 11, f 12, f 33. Simulations showed dependencies: 001 to f 12, 220 to f 11- f 33, 110 to f 11- f 33, 111 to f 12. For the 001 reflection intensity real and imaginary part correlate, but the 111 intensity displays asymmetric influence so the ambiguity is separable.
The measured data show clear evidence of AAS and the 001 FRED and 111 intensities could be fitted:
f Ti d 12 = -5.44 * 0.5(8)
f Ti d 12 = 3.98 * 1.4(2)
Since f 13 and f 23 were refined to zero, the positioning of Ti in the unit cell would by inverse symmetry arguments only be consistent with respect to site symmetry on Wyckoff sites a, b, e, f, g (out of k ).
Keywords: Anisotropic Anomalous X-Ray Scattering; Resonant X-Ray Scattering; Forbidden Reflection near Edge Diffraction
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Poster
XXI Congress and General Assembly of the International Union of Crystallography, 23.-31.08.2008, Osaka, Japan
Permalink: https://www.hzdr.de/publications/Publ-12139
Anisotropic Anomalous Scattering in Rutile TiO2
Zschornak, M.; Leisegang, T.; Gutmann, E.; Stöcker, H.; Meyer, D. C.
Based on an experiment of A. Kirfel and A. Petcov on rutile TiO2, space group (136) P42 mnm in 1989 [1], which verified the anisotropic anomalous scattering (AAS) in rutile through measuring Forbidden Reflection near Edge Diffraction (FRED) intensity at the 100 and 001 forbidden reflections just above the Ti-K absorption edge, we aimed to extend the results by measuring AAS not only for forbidden but also for allowed reflections, to find effects of anisotropy also in this case and to fit the model of anisotropic scattering [2] to the experimental data.
Experiments were carried out at DESY/HASYLAB beamline C1 (CEMO) using a (111) double crystal monochromator at the Ti resonance energy E = 4985 eV. An automated optimization and Y-scan routine called Peak-Optimized-Psi-Scan (POPS) which we programmed with LabView for a sample setup with rotating degree of freedom was tested for the first time for synchrotron conditions.
The rutile samples investigated were three 10 x 10 x 1 mm3 wafers synthesized by Crystec GmbH in (001), (110) and (111) orientation and Y-scans were measured for the reflections 001, 220, 110 and 111, respectively. Since the Ti in rutile occupies Wyckoff site 2a, its tensor symmetry must follow the local symmetry m.mm leaving 3 independent complex elements for the symmetric scattering tensor, f 11, f 12 and f 33. Calculations and simulations with the developed TensorScattering code (Fig. 1) showed following dependencies: 001 to f 12, 220 to f 11- f 33, 110 to f 11- f 33 and 111 to f 12. For the 001 reflection intensity the real and imaginary parts correlate, but the 111 intensity shows asymmetric influence so that the ambiguity should be separable.
The measured data show clear evidence of AAS and the 001 FRED and 111 reflection intensities could be fitted quite reasonably within the model. They were fitted simultaneously because both only depend on f 12, since the 111 is also forbidden within the Ti partial structure and the isotropic flat contribution is caused only by the oxygen partial structure. Within the fit the isotropic part of the 111 reflection intensity locks the constant and the asymmetry detangles f 12 and f 12. They were evaluated due to refinement as:
f 12 = f Ti(E=4985eV) * d 12 = -5.44 el * 0.58(2)
f 12 = f Ti(E=4985eV) * d 12 = 3.98 el * 1.42(0)
References
[1] A. Kirfel, A. Petcov, Anisotropy of anomalous dispersion. II. FRED (Forbidden Reflection near Edge Diffraction) in Rutile, TiO2, HASYLAB/DESY Jahresbericht (1989) 385-386.
[2] A. Kirfel, W. Morgenroth, Anisotropy of anomalous scattering in X-ray diffraction. III. `Forbidden' axial reflections in space groups up to orthorhombic symmetry, Acta Crystallogr. A 49 (1993) 35-45.
Keywords: Anisotropic Resonant X-Ray Scattering; Anisotropic Anomalous X-Ray Scattering; Forbidden Reflection near Edge Diffraction
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Poster
16. Jahrestagung der Deutschen Gesellschaft für Kristallographie, 03.-06.03.2008, Erlangen, Deutschland
Permalink: https://www.hzdr.de/publications/Publ-12138
Study of omega-meson production in pp collisions at ANKE
Barsov, S.; Buscher, M.; Hartmann, M.; Hejny, V.; Kacharava, A.; Keshelashvili, I.; Khoukaz, A.; Koptev, V.; Kulessa, P.; Kulikov, A.; Lehmann, I.; Leontyev, V.; Macharashvili, G.; Maeda, Y.; Mersmann, T.; Merzliakov, S.; Mikirtytchyants, S.; Mussgiller, A.; Oellers, D.; Ohm, H.; Rathmann, F.; Schleichert, R.; Seyfarth, H.; Stroher, H.; Trusov, S.; Valdau, Y.; Wustner, P.; Yaschenko, S.; Wilkin, C.
The production of omega-mesons in the pp --> pp omega reaction has been investigated with the COSY-ANKE spectrometer for excess energies of 60 and 92 MeV by detecting the two final protons and reconstructing their missing mass. The large physical background was subtracted using an event-by-event transformation of the proton momenta between the two energies. Differential distributions and total cross-sections were obtained after careful studies of possible systematic uncertainties in the overall ANKE acceptance. The results are compared with the predictions of theoretical models. Combined with data on the phi-meson, a more refined estimate is made of the Okubo-Zweig-Iizuka rule violation in the phi/omega production ratio.
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European Physical Journal A 31(2007), 95
DOI: 10.1140/epja/i2006-10161-2
ISSN: 1434-6001
Cited 22 times in Scopus
Permalink: https://www.hzdr.de/publications/Publ-12137
Prediabetic and diabetic in vivo modification of circulating low density lipoprotein attenuates its stimulatory effect on adrenal mineralocorticoid secretion
Kopprasch, S.; Pietzsch, J.; Ansurudeen, I.; Graessler, J.; Krug, A. W.; Erhart-Bornstein, M.; Bornstein, S. R.
Modification of low-density lipoprotein (LDL) and abnormal aldosterone and cortisol metabolism have been implicated in the pathogenesis of type 2 diabetes (DM2) and diabetic vascular disease. Since LDL serves as a major cholesterol source for adrenal steroidogenesis, we investigated whether LDL modification in prediabetic and diabetic subjects influences adrenocortical aldosterone and cortisol release. LDL was isolated from 30 subjects with normal glucose tolerance (NGT-LDL), 30 subjects with impaired glucose tolerance (IGT-LDL), and 26 patients with DM2 (DM2-LDL). Oxidation and glycoxidation characteristics of LDL apolipoprotein B100 of each individual was assessed by gas chromatography-mass spectrometry analysis. Human adrenocortical cells (NCI-H295R) were incubated for 24 h with 100 microg/ml LDL and after removal of supernatants stimulated for a further 24 h with angiotensin II (AngII). In supernatants, aldosterone and cortisol secretion was measured. IGT-LDL and DM2-LDL were substantially more modified than NGT-LDL. Each of the five measured oxidation/glycoxidation markers was significantly positively associated with glycemic control, measured as HbA(1c). LDL from all subjects stimulated both the basal and AngII-induced aldosterone and cortisol release from adrenocortical cells. However, hormone secretion was significantly inversely related to the degree of LDL oxidation/glycoxidation. We conclude that LDL modifications in IGT and DM2 subjects may have significant clinical benefits by counteracting prediabetic and diabetic overactivity of the renin-angiotensin-aldosterone system and enhanced cortisol generation.
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Journal of Endocrinology 200(2009), 45-52
DOI: 10.1677/JOE-08-0293
Cited 11 times in Scopus
Permalink: https://www.hzdr.de/publications/Publ-12136
Resonant two-photon transitions, quadratic detection, and photocurrent autocorrelation using multiple quantum wells
Schneider, H.; Liu, H. C.; Winnerl, S.; Drachenko, O.; Helm, M.; Walther, M.; Faist, J.
We report on two-photon detection based on quantum well intersubband nonlinear absorption. Three equidistant subbands, two of which are bound in the quantum well, and the third one in the continuum, result in a resonantly enhanced optical nonlinearity, which is by six orders of magnitude stronger than in usual semiconductors [1]. This device is very promising for quadratic autocorrelation measurements of pulsed mid-infrared sources, including modelocked quantum cascade lasers, radiation obtained by nonlinear optical frequency conversion, and free-electron lasers (FEL). Using these detectors as a quadratic autocorrelator for mid-infrared pulses, temporal resolution is only limited by the sub-ps intrinsic time constants of the intersubband transitions, namely the intersubband relaxation time and the phase relaxation time. We have investigated the performance of devices operating at various wavelengths from the mid-infrared to the Terahertz regimes using ps optical pulses from the FEL at the Forschungszentrum Dresden Rossendorf. In particular, device operation at shorter wavelengths around 5.5 µm is still possible at room temperature, which is crucial for applications in practical systems.
[1] H. Schneider, T. Maier, H. C. Liu, M. Walther, and P. Koidl, Optics Lett. 30, 287 (2005).
Keywords: intersubband transition; two-photon absorption; quantum well infrared photodetector; autocorrelation; free-electron laser
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Invited lecture (Conferences)
SPIE Photonics West, 24.-29.01.2009, San Jose, CA, USA
Permalink: https://www.hzdr.de/publications/Publ-12135
Two-photon photocurrent spectroscopy of quantum well intersubband relaxation and dephasing
Schneider, H.; Liu, H. C.; Maier, T.; Walther, M.
We have studied electron intersubband relaxation and dephasing in n-type InGaAs/AlGaAs quantum wells by femtosecond two-photon photocurrent spectroscopy using mid-infrared pulses of 165 fs duration. The approach enables us to determine systematically the dependence of these time constants on structural parameters, including carrier density and modulation/well doping, and to discriminate between different scattering processes [1]. By varying the excitation energy, we also tuned the two-photon transition from resonant, yielding optimum resonant enhancement with a real intermediate state, to nearly-resonant, with a virtual but resonantly enhanced intermediate state [2]. For autocorrelation purposes, the latter configuration improves time resolution whilst partially retaining a resonant enhancement of the two-photon transition strength.
[1] H. Schneider, T. Maier, M. Walther, H. C. Liu, Appl. Phys. Lett. 91, 191116 (2007).
[2] H. Schneider, T. Maier, H. C. Liu, M. Walther, Opt. Express 16, 1523 (2008).
Keywords: intersubband transition; two-photon absorption; quantum well infrared photodetector; phase relaxation; autocorrelation
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Invited lecture (Conferences)
SPIE Photonics West, 24.-29.01.2009, San Jose, CA, USA
Permalink: https://www.hzdr.de/publications/Publ-12134
Quadratic detection with two-photon quantum well infrared photodetectors
Schneider, H.; Liu, H. C.; Winnerl, S.; Drachenko, O.; Helm, M.; Walther, M.; Faist, J.
Two-photon quantum well infrared photodetectors (QWIPs) are based on three equidistant subbands, two of which are bound in the quantum well, and the third one in the continuum. This configuration leads to a resonantly enhanced optical nonlinearity, which is by six orders of magnitude stronger than in bulk semiconductors [1]. This device is useful for quadratic autocorrelation measurements of pulsed mid-infrared sources, including modelocked quantum cascade lasers, radiation obtained by nonlinear optical frequency conversion, and free-electron lasers (FEL). In quadratic autocorrelation experiments, temporal resolution of two-photon QWIPs is only limited by the sub-ps intrinsic time constants of the intersubband transitions, namely the intersubband relaxation time and the phase relaxation time.
We will report on autocorrelation measurements at various wavelengths from the mid-infrared to the Terahertz regimes using ps optical pulses from the FEL at the Forschungszentrum Dresden Rossendorf. In particular, quadratic detection at wavelengths around 5.5 µm is still possible at room temperature [2], which is crucial for applications in practical systems. Two-photon detection beyond the Reststrahlen band will also be addressed.
[1] H. Schneider, T. Maier, H. C. Liu, M. Walther, and P. Koidl, Optics Lett. 30, 287 (2005).
[2] H. Schneider, H. C. Liu, S. Winnerl, O. Drachenko, M. Helm, J. Faist, App. Phys. Lett. 93, 101114 (2008).
Keywords: intersubband transition; two-photon absorption; quantum well infrared photodetector; autocorrelation
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Lecture (Conference)
Quantum Structure Infrared Photodetector (QSIP) 2009 International Conference, 18.-23.01.2009, Yosemite, USA -
Infrared Physics and Technology 52(2009), 419
DOI: 10.1016/j.infrared.2009.05.036
Cited 8 times in Scopus
Permalink: https://www.hzdr.de/publications/Publ-12133
A field-focusing imaging sensor for fast visualization of multiphase flows
Da Silva, M. J.; Hampel, U.
A novel imaging sensor based on multichannel capacitance measurement is introduced in this article. The field-focusing sensor uses a multitude of strip electrodes located at two opposing and parallel walls of a vessel, whereby the opposing electrodes run perpendicular to each other. By the use of a special multiplexed excitation-sensing scheme a focusing of the electrical field to well-defined regions within the sensor is achieved which allows the sensor to individually interrogate each one of those regions and thus to two-dimensionally map the flow constituents contained by the sensor. Associated electronics can generate up to 625 frames per second. The sensor can be considered as a high-speed capacitance camera for a channel flow. Electrical field simulations with finite element method confirm the focusing effect explored by the sensor. The imaging capability is shown by the visualization of a stratified air-water mixture. Furthermore, the sensor was used to monitor the transient behaviour of the mixing of two substances with different densities.
Keywords: electrical capacitance; sensor; flow visualization; multiphase flow; electrical field simulation; finite element method
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Measurement Science and Technology 20(2009)10, 104009
DOI: 10.1088/0957-0233/20/10/104009
Cited 21 times in Scopus
Downloads
Permalink: https://www.hzdr.de/publications/Publ-12132
Photosensitive defects in silica layers implanted with germanium ions
Zatsepin, A. F.; Fitting, H.-J.; Kortov, V. S.; Pustovarov, V. A.; Schmidt, B.; Buntov, E. A.
Ge-implanted silica layers have been investigated by high-power pulsed synchrotron-photoluminescence (PL), photoluminescence excitation spectroscopy (PLE), and optically stimulated electron emission (OSEE) with respect to association of excitation and absorption bands to respective emission bands and lifetimes of excited defect states. In this way singletsinglet (4.35 eV) and tripletsinglet (3.18 eV) radiative transitions from excited states of oxygen-deficient centers (ODC) in Ge-doped silica glass are characterized by their absorption and emission bands as well as their lifetimes. The main channel for non-radiative relaxation of photoexcitation is electron emission by the OSEE effect. The OSEE shows non-radiative transitions of surface E's and bulk E'-centers found with concentrations of (2.73.4)x1012 cm-2 and (24)x1016 cm-3, respectively.
Keywords: Synchrotron radiation; Radiation effects; Defects; Optical properties; Absorption Luminescence; Optical spectroscopy; Photoinduced effects; Time resolved measurements; Oxide glasses; Silica; Structure defects; Short-range order
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Journal of Non-Crystalline Solids 355(2009), 61-67
DOI: 10.1016/j.jnoncrysol.2008.08.025
Cited 16 times in Scopus
Permalink: https://www.hzdr.de/publications/Publ-12131
QCD equation of state: Physical quark masses and asymptotic temperatures
Bluhm, M.; Kämpfer, B.; Schulze, R.; Seipt, D.
Within a phenomenological quasiparticle model, the quark mass and temperature dependence of the QCD equation of state is discussed and compared with lattice QCD results. Different approximations for the quasiparticle dispersion relations are employed, scaling properties of the equation of state with quark mass and deconfinement temperature are investigated and a continuation to asymptotically large temperatures is presented.
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Contribution to proceedings
International School of Nuclear Physics - 30th Course: Heavy-Ion Collisions from the Coulomb Barrier to the Quark-Gluon Plasma, 16.-24.09.2008, Erice, Sicilia, Italia
QCD equation of state: Physical quark masses and asymptotic temperatures -
Progress in Particle and Nuclear Physics 62(2009), 512-517
DOI: 10.1016/j.ppnp.2008.12.041
Cited 1 times in Scopus
Permalink: https://www.hzdr.de/publications/Publ-12130
Sintes prekursora alumooxidnoj keramiki, uprotschnennoj dioxidom zirkonija, is neorganitscheskich sojedinenii v prisutstvii motschevini
Scharnylskaja, A. L.; Wolchin, W. W.; Schtscherban, M. G.; Reuther, H.
Sintes prekursora alumooxidnoj keramiki, uprotschnennoj dioxidom zirkonija, is neorganitscheskich sojedinenii v prisutstvii motschevini
- Zurnal prikladnoj chimii 81(2008), 1069-1074
Permalink: https://www.hzdr.de/publications/Publ-12129
Surface nanostructuring of TiO2 thin films by ion beam irradiation
Romero-Gomez, P.; Palmero, A.; Yubero, F.; Vinnichenko, M.; Kolitsch, A.; Gonzalez-Elipe, A. R.
This work reports a procedure to modify the surface nanostructure of TiO2 anatase thin films through ion beam irradiation with energies in the keV range. Irradiation with N+ ions leads to the formation of a layer with voids at a depth similar to the ion-projected range. By setting the ion-projected range a few tens of nanometers below the surface of the film, well-ordered nanorods appear aligned with the angle of incidence of the ion beam. Slightly different results were obtained by using heavier (S+) and lighter (B+) ions under similar conditions.
Keywords: ion beam irradiation; titanium dioxide; anatase
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Scripta Materialia 60(2009), 574-577
DOI: 10.1016/j.scriptamat.2008.12.014
Cited 23 times in Scopus
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Permalink: https://www.hzdr.de/publications/Publ-12128
Surface Doping of VT6 Alloy with Zirconium by Pulsed Electron-Beam Mixing of Predeposited Multilayer Zr/Ti Film
Rotshtein, V. P.; Markov, A. B.; Shevchenko, N.; Reuther, H.; Oskomov, K. V.; Shulov, V. A.
We have studied characteristics of the surface doping of VT6 alloy (Ti-6Al-4V) with zirconium, which was effected in order to reduce the concentrations of Al and V at the surface. The doping was performed by liquid-phase mixing of a Zr(20 nm)/Ti(20 nm). It is established that the pulsed beam-induced melting leads to the homogeneous mixing of all Ti/Zr nanolayers and the diffusion of Zr into substrate to a depth of similar to 0.5 µm. As a result, the surface layer with a thickness of similar to 0.5 µm is free of Al and V atoms and has a single-phase submicrocrystalline structure of alpha-Ti70Zr30 solid solution. Subsequent vacuum annealing leads to a decrease in the average grain size in the nearsurface layer to 90 nm and to an increase in the nanohardness of the doped layer.
Keywords: Ti alloy; multilayer; electron beam; surface treatment; nanohardness
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Technical Physics Letters 34(2008)10, 891-894
ISSN: 1063-7850
Permalink: https://www.hzdr.de/publications/Publ-12127
In situ study of the effect of Sn doping on the electrical properties of indium oxide
Rogozin, A.; Vinnichenko, M.; Shevchenko, N.; Kreissig, U.; Kolitsch, A.; Möller, W.
Indium oxide (In2O3) and ITO (In2O3 :Sn) amorphous films grown by pulsed reactive magnetron sputtering have been annealed in vacuum. The film structure and properties have been studied during annealing using in-situ diagnostics. The evolution of the film structure has been continuously monitored by synchrotron X-ray diffraction at the European Synchrotron Radiation Facility in Grenoble, France. Four point probe measurements, spectroscopic ellipsometry, and elastic recoil detection analysis have been undertaken to determine and correlate with the structure in real time the evolution of the film resistivity (ρ), the free electron density (Ne), and the film stoichiometry. At the start of annealing both the In2O3 and the ITO films show a fast decrease in ρ and an increase in Ne, which is explained by the formation of oxygen vacancies and reordering of the amorphous phase. Subsequent film crystallization does not influence the In2O3 film electrical properties, but causes a further decrease in ITO resistivity due to the Sn donor activation. The estimated efficiency of the Sn donor activation is 40%. All the films show during annealing a resistivity decrease which is caused not only by an increase in the free carrier density, but also by a rise in the electron mobility.
Keywords: Indium oxide; ITO; annealing; in-situ; electrical properties; Sn donor
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Lecture (Conference)
14th International Conference on Thin Films & Reactive Sputter Deposition 2008, 17.-20.11.2008, Ghent, Belgium
Permalink: https://www.hzdr.de/publications/Publ-12126
Equation of state for strongly interacting matter within a HTL quasiparticle model
Schulze, R.
Equation of state for strongly interacting matter within a HTL quasiparticle model
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Lecture (Conference)
International School of Nuclear Physics, 22.09.2008, Erice, Italy
Permalink: https://www.hzdr.de/publications/Publ-12125
Estrogen detection in drinking water by Silicon based light emitters
Cherkouk, C.; Rebohle, L.; Skorupa, W.; Helm, M.
The immediate and accurate monitoring of chemical and biological substances is essential in environmental analysis for minimizing the health risk for citizens and their exposure to pollutants. Recently, considerable attention has been focused on endocrine-disrupting compounds EDCs, such as estrogens, which constitute a wide group of environmental pollutants, especially in drinking water.
A new concept for measuring the concentration of such organic compounds by using Si-based integrated light sources for fluorescence analysis is presented. In that concept the analyte, estrogen in this example, is labelled with a Fluorescence marker and is immobilized at the passivated surface of the light emitter by receptor molecules. This kind of labelling opens a way to extremely small device dimensions and is of great interest for point-of-care measurements.
The current system has been characterized by FTIR, Raman and electroluminescence measurements.
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Lecture (Conference)
E-MRS 2008 Spring Meeting, 26.-30.05.2008, Straßburg, France
Permalink: https://www.hzdr.de/publications/Publ-12124
The effect of ITO film thickness on the microstructure evolution and crystallization kinetics during annealing
Shevchenko, N.; Rogozin, A.; Vinnichenko, M.; Kolitsch, A.; Moeller, W.
Amorphous indium tin oxide (ITO) films have been grown by reactive pulsed medium-frequency dual magnetron sputtering on Si substrates covered with SiO2. The real-time evolution of the ITO film structure during annealing has been investigated by synchrotron X-ray diffraction at ROssendorf Beam Line (ROBL) located at the European Synchrotron Radiation Facility in Grenoble, France. The annealing experiments have been carried out in a UHV annealing chamber equipped with a beryllium dome at a constant temperature of 310 C. The XRD experiment has been performed in BraggBrentano geometry over a range of scattering angles of 27° to 37°. The incident X-ray beam has been monochromatized to 8.048 keV (λ=0.154 nm). An in situ four-point probe technique has been used to characterize the film resistivity. The microstructure of the annealed films has been examined by transmission electron microscopy (TEM).
This work is focused on the effect of ITO film thickness on the crystallization kinetics during annealing. Three series of samples with thicknesses of ~50, 170 180, and 310-320 nm have been investigated. The evolution of the (222) and (400) peaks of the In2O3 phase has been monitored. The time dependence of the integral intensity of these peaks exhibits an s-like shape, which is typical of a crystallization process. The XRD data have been analyzed in the frame of the Kolmogorov Johnson Mehl Avrami (KJMA) model. The activation energy and the kinetic parameters of the crystallization process have been determined. The value of the KJMA exponent of about 2 obtained for all ITO films points toward two-dimensional grain growth in the site saturated mode. However, detailed TEM studies of partly crystallized ITO samples display two-dimensional grain growth only during the crystallization of the 50 nm ITO films. In contrast, the thicker films show two stages of crystallization. During the first stage, the single grains grow from the film surface to the interface, after which lateral growth of the grain has been observed to occur. The KJMA model is unable to predict the difference in the crystallization kinetics for films of different thicknesses. The specific film anisotropy and the limited thickness are discussed as the main reasons for the change in the crystallization kinetics. The film resistivity decrease correlating with the film crystallization depends non-linearly on the degree of crystallization.
Keywords: ITO; in-situ; synchrotron X-ray diffraction; microstructure; annealing; crystallization kinetics
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Poster
14th International Conference on Thin Films & Reactive Sputter Deposition 2008, 17.-20.11.2008, Ghent, Belgium
Permalink: https://www.hzdr.de/publications/Publ-12122
Porous metal surfaces produced by ion implantation
Shevchenko, N.; Kolitsch, A.
Development of novel materials and structures for drug delivery systems is currently a very active field of research. Plasma immersion ion implantation (PIII) using helium or argon plasmas has been employed for porous layers creation on metal surfaces. These void structures may show unique characteristics which offer potential for medical applications such as metal-based drug-eluting stents. The paper addresses the influence of implantation parameters on surface morphology, cavity characteristics and mechanical properties of stainless steel stents. Argon and/or helium PIII processing of stainless steel samples has been performed at ion energies ranging from 5 to 35 keV, ion fluence of more than 1e17 cm-2, and substrate temperature in the range 50 400 C. Scanning electron microscopy, grazing incidence X-ray diffraction analysis, X-ray photoelectron spectroscopy, and elastic recoil detection analysis have been employed for sample characterization. Argon PIII treatment at elevated temperatures of 200 350 C leads to spongy structure formation of a size of 1-2 micron. Helium implantation results in a surface roughening and creation of voids in high concentration with size in the range 300 500 nm as well as nano-scale cavities (5-50 nm). So, varying the ion species (helium or argon), ion energy and fluence, and substrate temperature has been found to produce either void or sponge like structures at the nano- (~10 nm) to micro-scale (~1 micron). The best mechanical properties have been obtained in the stainless steel samples implanted at elevated temperature (higher than 250 C). Surface flaking and cracks formation have been greatly reduced by subsequent post-implantation annealing at temperatures of 600 800 C.
Keywords: Plasma immersion ion implantation; surface morphology; porous; stainless steel; stent; annealing
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Lecture (Conference)
9th International Conference on Modification of Materials with Particle Beams and Plasma Flows, 21.-26.09.2008, Tomsk, Russia
Permalink: https://www.hzdr.de/publications/Publ-12121
Real-time monitoring of ITO film structure during annealing: effect of film thickness
Shevchenko, N.; Rogozin, A.; Vinnichenko, M.; Kolitsch, A.; Moeller, W.
The amorphous indium tin oxide (ITO) films were grown by reactive pulsed middle frequency dual magnetron sputtering on the Si substrates covered with SiO2. The real-time evolution of the ITO film structure during annealing was continuously investigated by synchrotron X-ray diffraction at ROssendorf Beam Line (ROBL), which is located at the European Synchrotron Radiation Facility in Grenoble, France. The annealing experiments were carried out in UHV annealing chamber equipped with beryllium dome at constant temperature of 310 C. In situ four-point probe technique was applied to characterize film resistivity. Three series of samples with thicknesses of ~50, 170 180, and 310-320 nm have been investigated.
The time dependence of the integral intensity exhibits an s-like shape, which is typical of the crystallization process. The XRD data were analyzed in a frame of the Kolmogorov Johnson Mehl Avrami (KJMA) model. The kinetic parameters of crystallization process were determined. The range of KJMA exponent of approximately 2 obtained for all ITO films points to two-dimensional grain growth in the site saturated mode. However, detailed TEM studies of partly crystallized ITO samples display two-dimensional grain growth only during crystallization of 50 nm ITO films. In contrast, the thicker films show two stages of crystallization process. During the first stage, the single grains grew from a film surface to interface, after that, lateral growth of the grain was observed. The KJMA model can not predict the difference in the crystallization kinetics for the films with diverse thicknesses. The essential anisotropy and limited thickness of the films are discussed as the main reasons for the change of the crystallization kinetics.
Keywords: ITO; annealing; structure; grain growth; synchrotron X-ray diffraction; crystallization
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Poster
9th International Conference on Modification of Materials with Particle Beams and Plasma Flows, 21.-26.09.2008, Tomsk, Russia
Permalink: https://www.hzdr.de/publications/Publ-12120
Surface Alloying of Ti6Al4V with Zirconium by Pulsed Electron-beam Melting of Zr/Ti Multilayers
Rotshtein, V. P.; Markov, A. B.; Shevchenko, N.; Reuther, H.; Oskomov, K. V.; Shulov, V. A.
Surface alloying of Ti6Al4V with Zr aiming at depletion of Al and V was realized by liquid-phase intermixing of multi-layer film [Zr(20 nm)/Ti(20 nm)]12 of total thickness of 480 nm with substrate (Ti6Al4V) using a low energy (~20 keV), high-current electron beam (2.5 μs, 3.5 J/cm2). Scanning electron microscopy and energy dispersive X-ray spectroscopy, Auger electron spectroscopy, X-ray diffraction, and atomic force microscopy were used to study the surface morphology, microstructure, elemental and phase compositions of the alloyed layer. It was found that a homogeneous intermixing of all Zr/Ti nanolayers and diffusion of Zr into the substrate up to a depth of ≈1 μm take place after a singleshot pulsed melting. The surface layer of depth ≈ 0.5 μm is free of Al and V and contain ≈ 30 at % Zr. The near-surface layer, due to quenching from the melt, has a sub-microcrystalline grain structure with an average grain size of 112 nm. The post-irradiation vacuum annealing (500 °С, 2 h) leads to enrichment of alloyed layer with O and С impurities, and decrease of grain size up to 90 nm. As a result, the nanohardness of the alloyed layer was increased in comparison with the substrate.
Keywords: Ti alloy; Zr/Ti multilayers; electron beam; nanohardness; microstructure
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Poster
9th International Conference on Modification of Materials with Particle Beams and Plasma Flows, 21.-26.09.2008, Tomsk, Russia -
Contribution to proceedings
9th International Conference on Modification of Materials with Particle Beams and Plasma Flows, 21.-26.09.2008, Tomsk, Russia, 327-330
Permalink: https://www.hzdr.de/publications/Publ-12119
Nanoporous stainless steel surfaces produced by plasma immersion ion implantation
Shevchenko, N.; Kolitsch, A.
Plasma immersion ion implantation (PIII) using helium or argon plasmas has been employed for porous layers creation on metal surfaces. These void structures may show unique characteristics which offer potential for medical applications such as metal-based drug-eluting stents. The paper addresses the influence of implantation parameters on surface morphology, cavity characteristics and mechanical properties of stainless steel stents. Argon and/or helium PIII processing of stainless steel samples has been performed at ion energies ranging from 5 to 35 keV, ion fluence of more than 1e17 cm-2, and substrate temperature in the range 50 400 ° C. Scanning electron microscopy, grazing incidence X-ray diffraction analysis, X-ray photoelectron spectroscopy, and elastic recoil detection analysis have been employed for sample characterization. Argon PIII treatment at elevated temperatures of 200 350 °C leads to spongy structure formation of a size of 1-2 µm. Helium implantation results in a surface roughening and creation of voids in high concentration with size in the range 300 500 nm as well as nano-scale cavities (5-50 nm). So, varying the ion species (helium or argon), ion energy and fluence, and substrate temperature has been found to produce either void or sponge like structures at the nano- (~10 nm) to micro-scale (~1 µm). The best mechanical properties have been obtained in the stainless steel samples implanted at elevated temperature (higher than 250 °C). Surface flaking and cracks formation have been greatly reduced by subsequent post-implantation annealing at temperatures of 600 800 °C.
Keywords: ion implantation; PIII; nanoporous; surface morphology; stainless steel stents
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Poster
16th International Conference on Ion Beam Modification of Materials, 31.08.-05.09.2008, Dresden, Germany
Permalink: https://www.hzdr.de/publications/Publ-12118
Bacterial biomineralization: New insights from Myxococcus induced mineral precipitation
González-Muñoz, M. T.; Rodriguez-Navarro, C.; Martínez-Ruiz, F.; Maria Arias, J.; Merroun, M.; Rodriguez-Gallego, M.
There is growing evidence showing that bacteria have contributed to the formation of minerals since the advent of life on Earth. Bacterial biomineralization thus appears to be crucial for the complex interactions of biological, chemical, and physical processes which drive modern and ancient biogeochemical cycles. On the other hand, the technological and environmental applications of bacterial mineralization are now being demonstrated to be far reaching. Despite the numerous efforts to better understand how bacteria induce/mediate or control mineralization, our current knowledge is far from complete. Considering that the number of recent publications on bacterial biomineralization has been overwhelming, here we attempt to show the importance of bacteria-mineral interactions by focusing in a single bacterial genus, Myxococcus, which displays an unusual capacity of producing mineral precipitates of varying compositions and morphologies. The first part of this review presents an overview of the recent history of bacterial mineralization, and briefly describes the most common bacteriogenic minerals as well as current models on bacterial biomineralization. The second part presents a description of myxobacteria. Myxococcus induced precipitation of a number of phosphates, carbonates, sulphates, chlorides, oxalates, and silicates is described and discussed in lieu of the information presented in the first part. Finally, implications of bacterial mineralization and perspectives for future research are outlined. This review strives to show that the mechanisms which control bacterial biomineralization are not mineral- or bacterial-specific. On the contrary, they appear to be universal and depend on the environment in which bacteria dwell.
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Contribution to external collection
in: Tufas and Speleothems: Unravelling the Microbial and Physical Controls 336, London: Geological Society of London, 2009, 31-50
Permalink: https://www.hzdr.de/publications/Publ-12117
Surface structure of Sn-doped In2O3 (111) thin films by STM
Morales, E. H.; He, Y.; Vinnichenko, M.; Delley, B.; Diebold, U.
High-quality Sn-doped In2O3 (ITO) films were grown epitaxially on yttria stabilized zirconia (111) with oxygen-plasma assisted molecular beam epitaxy (MBE). The 12 nm thick films, containing 26% Sn, are fully oxidized. Angle-resolved x-ray photoelectron spectroscopy (ARXPS) confirms that the Sn dopant substitutes In atoms in the bixbyite lattice. From XPS peak shape analysis and spectroscopic ellipsometry measurements it is estimated that, in a film with 6 at.% Sn, ~1/3 of the Sn atoms are electrically active. Reflection high energy electron diffraction (RHEED) shows a flat surface morphology and scanning tunneling microscopy (STM) shows terraces several hundred nanometers in width. The terraces consist of 10 nm wide orientational domains, which are attributed to the initial nucleation of the film. Low energy electron diffraction (LEED) and STM results show a bulk-terminated (1×1) surface, which is supported by first-principles density functional theory (DFT) calculations. Atomically resolved STM images are consistent with TersoffHamann calculations that show that surface In atoms are imaged bright or dark, depending on the configuration of their O neighbors. The coordination of surface atoms on the In2O3(111)1×1 surface is analyzed in terms of their possible role in surface chemical reactions.
Keywords: transparent conductive oxides; tin-doped indium oxide; molecular beam epitaxy; scanning tunneling microscopy; spectroscopic ellipsometry; free electron density
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New Journal of Physics 10(2008), 125030
DOI: 10.1088/1367-2630/10/12/125030
Cited 63 times in Scopus
Permalink: https://www.hzdr.de/publications/Publ-12116
Die Mobilisierung von Actiniden durch mikrobiell produzierte Liganden unter Berücksichtigung der Endlagerung von radioaktivem Abfall
Moll, H.; Bernhard, G.
- wird nachgereicht
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Lecture (others)
8. Projektstatusgespräch zur Forschungsförderung zur Entsorgung gefährlicher Abfälle in tiefen geologischen Formationen, 06.-07.05.2008, Karlsruhe, Deutschland
Permalink: https://www.hzdr.de/publications/Publ-12115
Controlled Assembly and Nanoscale Doping of Epitaxial Si(Ge) Quantum Dot Nanostructures
Graham, J. F.; Kell, C. D.; Gray, J. L.; Wolf, S. A.; Floro, J. A.; Bischoff, L.; Hull, R.
Self-assembled Si(Ge) quantum dots (QDs) may prove useful in future nanoelectronic device architectures. For this, they must be spatially arranged in specific patterns and possess the electronic or magnetic properties required for device operation. Previous work demonstrated Ga+ focused ion beam (FIB) templating of Si surfaces prior to epitaxial growth for fabricating patterned QDs with any desired complexity.1, 2
Our current research employs a mass-selecting FIB to template QD structures and to individually dope them. Ion species can be selected according to isotope mass and charge state using a Wien filter. Working with suitable liquid metal alloy ion sources (LMISs) provides the means to template with electrically non-invasive ions (e.g. Si+ from AuSi), then implant dopant ions for electronic or magnetic activation (e.g. with B+ from AsPdB or Mn+ from GeMn), with resolution of tens of nm and doses down to a few ions per dot.
Keywords: quantum dots; focused ion beam; liquid metal alloy ion sources
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Poster
2008 MRS Fall Meating, 01.-05.12.2008, Boston, USA
Permalink: https://www.hzdr.de/publications/Publ-12114
In-situ grazing incidence scattering investigations during magnetron sputtering deposition of FePt/Ag thin films
Cantelli, V.; von Borany, J.; Jeutter, N.; Grenzer, J.
Using synchrotron in-situ X-ray diffraction and grazing incidence small angle scattering, we studied the growth of FePt islands incorporated into a Ag matrix. The deposition, by dual DC magnetron sputtering on amorphous Si/SiO2 substrate, was carried out at 400°C to support the formation of the hard ferromagnetic L10-FePt phase during growth. Thin Ag interspacing layers provide a granular FePt film but, by depositing 6 nm Ag layer directly on the SiO2 substrate, we obtained well defined FePt clusters. FePt nanoislands have been achieved without degradation of the magnetic properties. We obtained a magnetic asymmetry with magnetic moments preferentially oriented parallel to the layer surface.
Keywords: FePt; nanoclusters; GISAXS
- Advanced Engineering Materials 11(2009)6, 478-482
Permalink: https://www.hzdr.de/publications/Publ-12113
Direct spectroscopic characterization of aqueous actinyl(VI) species: A Comparative Study of Np and U
Müller, K.; Foerstendorf, H.; Tsushima, S.; Brendler, V.; Bernhard, G.
For the first time the hydrolysis reactions of submillimoar aqueous Np(VI) and U(VI) solutions was investigated comparatively, applying Attenuated Total Reflection Fourier-transform Infrared (ATR FT-IR) and NIR absorption spectroscopy. Actinyl(VI) concentration was set to 500 µM in a pH range from 2 to 5.3 under ambient conditions. Both spectroscopic methods give evidence that three different Np(VI) species contribute to the speciation. Using the structural information obtained from the FT-IR spectra these species are the fully hydrated NpO2
2+ ion at pH ≤ 3, a monomeric complex probably formed by hydrolysis reactions at pH 3 − 5 and a carbonate containing complex at pH ≥ 5. A comparison of the obtained results to the updated NEA thermodynamic data confirms the presence of the free neptunyl(VI) ion and neptunyl(VI) carbonate complexation within the investigated pH range. The monomeric hydrolysis complex is not predicted to be relevant by the current thermodynamic data. In comparison to U(VI) forms structural similar species at pH ≤ 4, namely the fully hydrated AnO2
2+ and monomeric hydroxo species. In contrast to Np(VI), the infrared spectroscopic data of U(VI) does not evidence carbonate complexation at higher pH.
Keywords: neptunyl(VI); uranyl(VI); ATR FT-IR spectroscopy; NIR spectroscopy; hydrolysis
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Journal of Physical Chemistry A 113(2009)24, 6626-6632
DOI: 10.1021/jp9008948
Cited 36 times in Scopus
Permalink: https://www.hzdr.de/publications/Publ-12112
Residence time measurements in pilot-scale electrolytic cells Application of laser induced fluorescence
Schubert, M.; Kryk, H.; Hessel, G.; Friedrich, H.-J.
The flow distribution in the rectangular channel of a pilot-scale electrolytic cell was observed using an imperfect tracer-pulse injection technique in order to study residence time distribution (RTD), back-mixing effects and velocity profiles of the electrolyte liquids within the cathode compartment. The electrolytic cell was operated under cold flow and at process conditions. While residence time studies performed in a vast number of applications are mainly based on classical conductometric measurements, alternative measurement methods have to be applied in electrochemical systems. Hence, the paper deals with the investigation of the residence time distribution (RTD) using laser induced fluorescence (LIF) visualization. Back-mixing effects of the electrolyte are quantified using the axial dispersion flow model. RTD studies for the overall cell as well as velocity profile analysis for selected individual regions are conducted. Additionally, the effects of the non-stabilized membrane and of the membrane stabilizing spacer grid are investigated.
Keywords: electrolytic cell; laser induced fluorescence; axial dispersion; imperfect pulse; hydrodynamics method
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Chemical Engineering Communications 197(2010), 1172-1186
DOI: 10.1080/00986440903574800
Cited 4 times in Scopus
Permalink: https://www.hzdr.de/publications/Publ-12111
Ultra-sensitive in-beam gamma-ray spectroscopy for nuclear astrophysics at LUNA
Caciolli, A.; Agostino, L.; Bemmerer, D.; Bonetti, R.; Broggini, C.; Confortola, F.; Corvisiero, P.; Costantini, H.; Elekes, Z.; Formicola, A.; Fülöp, Z.; Gervino, G.; Guglielmetti, A.; Gustavino, C.; Gyurky, G.; Imbriani, G.; Junker, M.; Laubenstein, M.; Lemut, A.; Limata, B.; Marta, M.; Mazzocchi, C.; Menegazzo, R.; Prati, P.; Roca, V.; Rolfs, C.; Rossi Alvarez, C.; Somorjai, E.; Straniero, O.; Strieder, F.; Terrasi, F.; Trautvetter, H. P.
Ultra-sensitive in-beam gamma-ray spectroscopy studies for nuclear astrophysics are performed at the LUNA (Laboratory for Underground Nuclear Astrophysics) 400 kV accelerator, deep underground in Italy's Gran Sasso laboratory. By virtue of a specially constructed passive shield, the laboratory gamma-ray background for E_\gamma < 3 MeV at LUNA has been reduced to levels comparable to those experienced in dedicated offline underground gamma-counting setups. The gamma-ray background induced by an incident alpha-beam has been studied. The data are used to evaluate the feasibility of sensitive in-beam experiments at LUNA and, by extension, at similar proposed facilities.
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Contribution to WWW
http://arxiv.org/abs/0812.3223v1 -
European Physical Journal A 39(2009), 179-186
DOI: 10.1140/epja/i2008-10706-3
Cited 78 times in Scopus -
Poster
Nuclear Physics in Astrophysics IV, 08.-12.06.2009, Frascati, Italien
Permalink: https://www.hzdr.de/publications/Publ-12110
Uporaba metode datiranja povrsinske izpostavljenosti na primeru podora Veliki vrh
Mrak, I.; Merchel, S.; Benedetti, L.; Braucher, R.; Bourlès, D. L.; Finkel, R. C.; Reitner, J. M.
O podoru v Velikem vrhu (Kouta, Karavanke) ni zanesljivih zgodovinskih zapisov, vendar pa le ti obstajajo o podoru na Dobraču (25.1.1348), ki je od Velikega vrha oddaljen 46 km. Podor je povzročil potres in naa hipoteza je bila, da je tudi podor v Velikem vrhu posledica istega dogodka. Tako smo s pomočjo metode datiranja povrinske izpostavljenosti analizirali vzorce matične kamnine v steni Velikega vrha ter vzorce s povrine podornih blokov. Ugotavljali smo vsebnost 36Cl, ki se je začel tvoriti po podoru. Na podlagi poznavanja tevila atomov 36Cl na gram Ca na leto izpostavljenosti, čas dogodka (podor) izračunamo iz koncentracij 36Cl izmerjenih s pomočjo pospeevalnika (AMS). Prvi rezultati kaejo, da sta se podora na Dobraču in Velikem vrhu posledica potresa v Furlaniji Julijski krajini. Starost podora v Velikem vrhu je (740 +- 71) a. Za bolj zanesljive rezultate bo potrebno izboljati sam model in upotevati več dejavnikov - predvsem nadmorsko viino in klimatske razmere.
There are no reliable historical data about the Veliki vrh rockfall (Kouta, Karavanke Mountains) but the records exist about the Dobrach rockfall (25th of January 1348) 46 km to the West of Veliki vrh. The rockfall was triggered by the earthquake and our hypothesis was that Veliki vrh rockfall was induced by the same event. Therefore we used the surface exposure dating method to analyze the bedrock samples in the Veliki vrh rock face as well as the samples of the boulder surface. The content of 36Cl, that started to produce after the earthquake, was measured. On the basis of the known number of 36Cl per gram Ca per year of exposure, the time of the rockfall can be calculated from the concentration of 36Cl measured by accelerator mass spectrometry (AMS). Preliminary results show the correlation of the two rockfalls (Dobrach and Veliki vrh) as the consequence of the earthquake in Friuli Venezia Julia. The age of Veliki vrh rockfall is (740 +- 71) a. For more reliable results further research should be conducted using also the data on altitude and climate.
Keywords: historic rockfall; cosmogenic nuclide exposure dating; Karavanke Mountains; Veliki vrh; terrestrial cosmogenic nuclides (TCN); accelerator mass spectrometry
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Contribution to proceedings
1. Trienalni Posvet, Naravne Nesrece v Sloveniji (NNS '08 - 1st seminar on natural hazards in Slovenia), 11.12.2008, Ljubljana, Slovenia
NARAVNE NESREČE 1 OD RAZUMEVANJA DO UPRAVLJANJA, 978-961-254-185-9, 105-111
Downloads
Permalink: https://www.hzdr.de/publications/Publ-12109
The chemical potential for the inhomogeneous electron liquid in terms of its kinetic and potential parts with special consideration of the surface potential step and BCS-BEC crossover
Morawetz, K.; March, N. H.; Squire, R. H.
The chemical potential μ of a many-body system is valuable since it carries fingerprints of phase changes. Here, we summarize results for μ
for a three-dimensional electron liquid in terms of average kinetic and potential energies per particle. The difference between μ and the energy
per particle is found to be exactly the electrostatic potential step at the surface. We also present calculations for an integrable one-dimensional
many-body system with delta function interactions, exhibiting a BCSBEC crossover. It is shown that in the BCS regime the chemical potential
can be expressed solely in terms of the ground-state energy per particle. A brief discussion is also included of the strong coupling BEC limit.
- Physics Letters A 372(2008), 1707-1711
Permalink: https://www.hzdr.de/publications/Publ-12108
Transport in OFETs by surface Green functions
Morawetz, K.
Theorieseminar TU Chemnitz
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Lecture (others)
Theorieseminar Professur Theorie ungeordneter Systeme, 17.12.2008, Chemnitz, Germany
Permalink: https://www.hzdr.de/publications/Publ-12106
Bose condensation for attractive interaction?
Maennel, M.; Lipavský, P.; Morawetz, K.; Schreiber, M.
We investigate an interacting Bose gas using a scheme to eliminate successive collisions. For attractive interaction we find a two-particle bound state. When the binding energy of this bound state becomes twice the chemical potential there is a second order phase transition and a gap appears in the dispersion relation. The gap decreases with increasing density. At the critical point the gap vanishes, the dispersion becomes linear for small momenta and a Bose condensate appears. We interpret the appearance of the gap as a sign of structure formation.
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Poster
International Workshop on Nonequilibrium Nanostructures, 01.-06.12.2008, Dresden, Germany
Permalink: https://www.hzdr.de/publications/Publ-12105
Phase diagram for interacting Bose systems
Maennel, M.; Morawetz, K.; Schreiber, M.
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Poster
72. Jahrestagung der DPG und DPG Frühjahrstagung des Arbeitskreises Festkörperphysik, 25.-29.03.2008, Berlin, Germany
Permalink: https://www.hzdr.de/publications/Publ-12104
Enhancement of Tc due to charge transfer
Morawetz, K.
International Workshop on Physics and Chemistry of FeAs-based Superconductors,
Dresden: Enhancement of Tc due to charge transfer
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Poster
International Workshop on Physics and Chemistry of FeAs-based Superconductors, Dresden, 27.-29.10.2008, Dresden, Germany
Permalink: https://www.hzdr.de/publications/Publ-12103
Quantum Kinetic Theory beyond Quasiparticle Picture - Bernoulli Potential in Superconductors
Morawetz, K.
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Lecture (others)
Interviewtalk for Professorship, 16.11.2008, Loughborogh, Great Britain
Permalink: https://www.hzdr.de/publications/Publ-12102
Quantum Kinetic Theory beyond Quasiparticle Picture - Bernoulli potential in Superconductors
Morawetz, K.
International Center for Condensed Matter Physics, Bras´ılia:
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Lecture (others)
International Center for Condensed Matter Physics, 29.09.2008, Brasilia, Brazil
Permalink: https://www.hzdr.de/publications/Publ-12101
Nonlocal kinetic theory
Morawetz, K.
Talk for Professorship at University College Dublin
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Lecture (others)
Colloquium talk, 14.08.2008, UCD, Ireland
Permalink: https://www.hzdr.de/publications/Publ-12100
Counter-current flow limitation experiments in a model of the hot leg of a pressurised water reactor - comparison between high pressure steam/water experiments and low pressure air/water experiments
Vallee, C.; Seidel, T.; Lucas, D.; Beyer, M.; Prasser, H.-M.; Pietruske, H.; Schütz, P.; Carl, H.
In order to investigate the two-phase flow behaviour in a complex reactor-typical geometry and to supply suitable data for CFD code validation, a model of the hot leg of a pressurised water reactor was built at Forschungszentrum Dresden-Rossendorf (FZD). The hot leg model is devoted to optical measurement techniques, therefore, a flat test section design was chosen and equipped with large windows. In order to enable the operation at high pressures, the test section is installed in the pressure chamber of the TOPFLOW test facility of FZD, which is used to perform the experiments under pressure equilibrium with the inside atmosphere. Counter-current flow limitation (CCFL) experiments were performed, simulating the refluxcondenser cooling mode appearing in small break LOCA scenarios. The fluids used were air and water at room temperature and pressures of up to 3.0 bar, as well as steam and water at pressures of up to 50 bar and the corresponding saturation temperature of 264°C. One selected 50 bar experiment is presented in detail: the observed behaviour is analysed and illustrated by typical high-speed camera images of the flow.
Furthermore, the flooding characteristic obtained from the different experimental runs are presented in terms of the Wallis parameter and Kutateladze number, which are commonly used in the literature. However, both parameters fail to properly correlate the data: a discrepancy is observed between the air/water and steam/water series. Therefore, a modified Wallis parameter is proposed, which takes into account the effect of the fluid viscosities on the CCFL. The new parameter is validated against comparable data found in the literature, even though no data was found with such a large range of viscosities. This analysis points out that the effect of the dynamic viscosity on flooding has already been observed, but not identified. Furthermore, it is shown that the proposed modification of the Wallis parameter allows a significant improvement for experimental series with variation of the viscosities.
Keywords: two-phase flow; flooding; counter-current flow limitation; hot leg; pressurised water reactor; Wallis parameter; viscosity
Involved research facilities
- TOPFLOW Facility
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Contribution to proceedings
13th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-13), 27.09.-02.10.2009, Kanazawa, Japan, N13P1107 -
Lecture (Conference)
13th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-13), 27.09.-02.10.2009, Kanazawa, Japan
Permalink: https://www.hzdr.de/publications/Publ-12099
Borverdünnungsanalysen beim Start der ersten HKP - Ergänzende Nachweise
Kliem, S.
In diesem Bericht werden die offenen Punkte OP1 bis OP3 aus der TÜV-Stellungnahme A-Nr.: 5576 vom 24.09.2008 durch ergänzende Nachweise zur von uns vorgelegten Borverdünnungsanalyse abgearbeitet.
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Article, self-published (no contribution to HZDR-Annual report)
Forschungszentrum Rossendorf 2008
FZD\FWS\2008\12
12 Seiten
ISSN: 1437-322X
Permalink: https://www.hzdr.de/publications/Publ-12098
Evaluation Scheme for a Positron Emission Tomography System Used in Monitoring of Radiation Therapy
Shakirin, G.; Fiedler, F.; Enghardt, W.
Positron emission tomography (PET) is used for independent monitoring of dose delivery in ion therapy. An in-beam PET scanner registers the annihilation γ-rays following the decay of β+-radioactive nuclei produced via nuclear reactions between the ions of the therapeutic beam and the irradiated tissue. From a comparison of the reconstructed activity distributions with those predicted from the treatment plan, deviations between the prescribed and the applied dose can be detected. In-beam PET, therefore, allows to verify the physical beam model of the treatment planning, to detect patient dislocations and density changes in the irradiated tissue. Issues related to the image quality and evaluation of a whole PET imaging system are discussed in this paper.
Keywords: in-beam PET; radiation therapy; image quality
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Contribution to proceedings
Workshop Bildverarbeitung für die Medizin - Algorithmen, Systeme, Anwendungen (BVM), 22.-25.03.2009, Heidelberg, Germany
Evaluation Scheme for a Positron Emission Tomography System Used in Monitoring of Radiation Therapy: Springer-Verlag -
Lecture (Conference)
Workshop Bildverarbeitung für die Medizin, 22.-25.03.2009, Heidelberg, Germany
Permalink: https://www.hzdr.de/publications/Publ-12097
Study of the ELBE RF-couplers with a new 1.3 GHz RF- coupler test bench driven by a resonant ring
Büttig, H.; Arnold, A.; Büchner, A.; Freitag, M.; Krätzig, M.; Lehnert, U.; Michel, P.; Schurig, R.; Staats, G.; Teichert, J.; Voigtländer, J.; Winter, A.
To study the performance of the ELBE RF-couplers until their limits a 1.3 GHz resonant ring driven by a 10 kW CW klystron (VKL7811St, CPI) has been built to operate a RF-coupler and RF-window test bench. The ring allows tests with RF power up to 100 kW in continuous wave (CW) mode and 200 kW in pulsed mode.
Details of the resonant ring, the test bench design and results of the ELBE RF-coupler tests will be presented.
Keywords: RF power couplers; Superconducting CW RF; Resonant Ring; Travelling wave resonator; Waveguide window; RF test bench; Linac RF-system
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Nuclear Instruments and Methods in Physics Research A A 612(2010), 427-437
DOI: 10.1016/j.nima.2009.10.148
Cited 9 times in Scopus
Permalink: https://www.hzdr.de/publications/Publ-12096
Optimierung optischer und mechnischer Eigenschaften magnetrongesputterter Niobpentoxidschichten
Vinnichenko, M.; Rogozin, A.; Kolitsch, A.; Grambole, D.; Möller, W.; Stenzel, O.; Wilbrandt, S.; Chuvilin, A.; Kaiser, U.
Using high plasma ion density influence during the reactive pulsed magnetron sputtering allowed formation of the dense amorphous Nb2O5 layers with controlled nano-porosity for optical applications. The films possess unique combination of high refractive index (n> 2.5 at wavelength 400 nm), low optical extinction (k<5x10^-4 at 400 nm), low mechanical stress and negligible thermal shift.
Keywords: optical coatings; Nb2O5; nano-sized porosity; optical properties; reactive pulsed magnetron sputtering
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Lecture (Conference)
OptoNet Workshop: Funktionale Oberflächen für optische Anwendungen, 12.11.2008, Jena, Germany
Permalink: https://www.hzdr.de/publications/Publ-12095
Effect of elevated temperature on electrical properties and structure of ZnO:Al films with different dopant concentrations
Vinnichenko, M.; Rogozin, A.; Cornelius, S.; Shevchenko, N.; Gago, R.; Jimenez, I.; Kolitsch, A.; Möller, W.
Al-doped ZnO (ZnO:Al) is a cost-effective alternative to the Sn-doped indium oxide which is widely used as a material for transparent electrodes. To further reduce the production costs, it would be preferable to sputter reactively from a metal alloy target at sufficiently high partial pressure of oxygen. However, under this condition, a sufficiently low resistivity of the films can not readily be obtained, so that a deposition on heated substrates is necessary. The mechanisms of incorporation and electrical activation of the Al doping impurity into ZnO at elevated temperatures are not well understood that makes difficult improvement of reproducibility and long-term stability of the film electrical properties.
In order to have a deeper insight into these processes, polycrystalline ZnO and ZnO:Al films were grown by reactive pulsed magnetron sputtering of Zn and Zn:Al (4.7 and 8.7 at. % of Al) targets, respectively. The O2 partial pressure in Ar-O2 sputtering gas mixture was precisely monitored during deposition using a capacitance gauge. The substrate temperatures (Ts) were spanning in the 40-580 °C range. The films were characterized by Hall effect measurements, spectroscopic ellipsometry (SE), X-ray diffraction (XRD) and X-ray absorption near edge spectroscopy (XANES). At fixed oxygen partial pressure, the electrical resistivity of ZnO:Al films shows a clear minimum at Ts=300 and 350 °C for the films grown using magnetron targets with 8.7 and 4.7 at. % of Al, respectively. The lower resistivity is due to the increased density and mobility of free electrons according to the Hall effect measurements. A maximum of the film crystallinity (grain size) is observed at temperatures of 250 and 300 °C for higher and lower Al concentration, respectively. At Ts>350 °C, the ZnO:Al film crystallinity significantly deteriorates with even stronger temperature effect at higher Al content, leading to formation of nanocrystalline ZnO:Al films at Ts>400 °C in the latter case. It is in contrast to undoped ZnO films grown at identical conditions whose crystallinity always improves by increasing Ts. XANES results show that the poorer film crystallinity and higher resistivity at high Ts can be related to a new homologous phase (ZnO)3(Al2O3) . Further, the electrical properties correlate with changes in the O(1s) absorption edge, whereas the Zn(2p) edge shows no modification with respect to undoped ZnO films.
The authors gratefully acknowledge the financial support of SMWA/SAB under the Project #11815/1854.
Keywords: transparent conducitve oxides; Al-doped ZnO; free electron mobility; reactive pulsed magnetron sputtering
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Lecture (Conference)
2nd International Symposium on Transparent Conductive Oxides, 22.-26.10.2008, Hersonissos, Crete, Greece
Permalink: https://www.hzdr.de/publications/Publ-12094
Formation of light-emitting Si nanostructures in SiO2 by pulsed anneals
Kachurin, G. A.; Cherkova, S. G.; Marin, D. V.; Yankov, R. A.; Deutschmann, M.
Intense excimer laser pulses, flash lamp annealing and rapid thermal annealing were used to form Si nanocrystals in thin SiO2 layers implanted with high doses of Si ions. The pulse durations were 20 ns, 20 ms and 1 s, respectively. Laser annealing produced light sources luminescing in the wavelength range of 400-600 nm. They were attributed to the Si clusters formed as a result of the fast segregation of Si atoms from the SiO2 network. There were no indications of nanocrystal formation in the as-implanted layers after 20 ns laser pulses; however, nanocrystals formed when, before the laser annealing, the amorphous Si nanoprecipitates were prepared in the oxide layers. Evaluations show that the crystallization may proceed via melting. A photoluminescence band near 800 nm, typical of Si nanocrystals, was found after 20 ms and 1 s anneals. Calculations revealed that the annealing times in both cases were too short to provide the diffusion-limited crystal growth if one uses the values of stationary Si diffusivity in SiO2. This points toward the existence of a transient rapid growth process at the very beginning of the anneals.
- Nanotechnology 19(2008)35, 355305
Permalink: https://www.hzdr.de/publications/Publ-12093
The Fluorine Effect for High Temperature Oxidation Protection of TiAl-Alloys for Automotive and Aero-Engine Applications
Donchev, A.; Kolitsch, A.; Möller, W.; Schütze, M.; Yankov, R. A.
The insufficient oxidation resistance of TiAl-alloys above roughly 800°C is a major disadvantage for their use in several high temperature applications. This problem can be overcome by small amounts of halogens in the surface zone of the TiAl-material. Especially fluorine has proven to be a beneficial doping element. The fluorine effect is stable at least for one year at temperatures up to 900°C under thermocyclic conditions. Results of fluorine treated and untreated TiAl-coupons, more complex samples and real components are shown in this paper. The specimens were exposed isothermally and thermocyclically in the temperature range from 700 1050°C in laboratory air or synthetic air. The specimens can be treated with fluorine in several ways e.g. spraying or ion implantation. Without any treatment some samples were heavily destroyed during high temperature oxidation but after fluorine treatment the components were still intact. Post oxidation investigations revealed the formation of a thin and protective Al2O3-scale confirming the fluorine effect.
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Lecture (Conference)
The Minerals, Metals & Materials Society Annual Meeting, 09.-13.03.2008, New Orleans, USA
Permalink: https://www.hzdr.de/publications/Publ-12092
Self- growing shark skin pattern on the surface of gamma-TiAl alloys
Pflumm, R.; Schütze, M.; Yankov, R.; Kolitsch, A.
This work deals with surface structuring of gamma-titanium aluminide engineering alloy samples by using the oxidation behaviour of the material between 800 and 1000°C. Previous experiments showed that if the pattern of the structures is similar to that of a shark skin, aerodynamical losses due to shear strain at the surface of a solid moving in a flow are decreased. Tiny riblets arranged parallel to the flow direction hamper the cross flow which causes the most of the wall shear stress. Such improvement in the flow conditions is foreseen to be applied to compressor and turbine blades of aero engines for example. These components operate at temperatures between 500 and 1000°C and in strong temperature gradients. Therefore the surface structuring process should not prevent the growth of a protective oxide layer, necessary to protect the material against high temperature corrosion. Several structuring methods leading to self-growing of a shark skin pattern via partial microalloying of halogens (e.g. Fluor) in the first 100 nm of the sample surface were investigated. On the halogen- rich domains a thin protective Al-oxide layer grows slowly at temperatures up to 1000°C (so called halogen effect). On the domains free of halogen a thick mixed Al- and Ti-oxide layer grows fastly and builds the riblets. The growth of the non- protective mixed oxide layer should be stopped by lateral diffusion of the halogen from the halogen-rich to the halogen-free domains in order to prevent the spallation of the riblets. The principle and results on the development of such structures including the nucleation process depending on the halogen distribution over the sample surface are shown and discussed for isothermal oxidation at temperatures between 800 and 1000°C.
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Lecture (Conference)
Materials Science and Engineering, 01.-04.09.2008, Nürnberg, Germany
Permalink: https://www.hzdr.de/publications/Publ-12091
High temperature oxidation resistance of fluorine-treated TiAl alloys: Chemical vs. ion beam fluorination techniques
Neve, S.; Masset, P. J.; Yankov, R. A.; Kolitsch, A.; Zschau, H.-E.; Schütze, M.
Surface modification of TiAl alloys by introducing fluorine is known to improve significantly their oxidation behaviour at high temperatures. The effect is based on the preferential reaction of the aluminium with the applied fluorine at the oxide/alloy interface, and is associated with the formation of an adherent and stable protective alumina layer.
Well-defined fluorine profiles beneath the surface of the material can be formed by either fluorine beam line ion implantation (BLI²) or plasma immersion ion implantation (PI3). As an alternative to the implantation-based approach, chemical fluorination techniques such as gas-phase treatment and dipping in F-based solutions have also been investigated in the present work. The fluorine depth profiles have been measured before and after oxidation at 900 °C using non-destructive ion beam analyses (Proton Induced Gamma-ray Emission, Rutherford Backscattering Spectroscopy and Elastic Recoil Detection Analysis). The results of this study enable one to optimize the fluorination conditions and to produce surface-modified technical TiAl alloys suitable for industrial applications.
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Poster
16th International Conference on Ion Beam Modification of Materials (IBMM08), 31.08.-05.09.2008, Dresden, Germany - Nuclear Instruments and Methods in Physics Research B 268(2010), 3381-3385
Permalink: https://www.hzdr.de/publications/Publ-12090
Plasma immersion ion implantation of fluorine for oxidation-resistant TiAl alloys
Yankov, R. A.; Kolitsch, A.; Munnik, F.; Donchev, A.; Schütze, M.
Titanium aluminides are being used in an expansive variety of advanced applications requiring lightness in weight and retention of strength at elevated temperatures. To date, the upper temperature limit has been at about 700°C because of the poor oxidation resistance of the TiAl alloys at higher temperatures. It has recently been established that the TiAl alloys can be rendered highly resistant to environmental degradation by ion implanting halogens, notably fluorine. In modifying the oxidation properties of the TiAl alloys, strong preference has been given to the technique of plasma immersion ion implantation (PIII) because of the possibility to shorten substantially the implant times as well as to avoid the line-of-sight limitation inherent to the standard beamline implantation process. In this work, various TiAl alloys in the form of either rectangular coupons or actual components have been treated by PIII of fluorine. A cheap, easy-to-handle and environmentally-friendly hydrofluorocarbon (difluoromethane) mixed with argon has been used as the precursor gas to implant fluorine into the TiAl alloys. Energy Dispersive X-ray Analysis, Scanning Electron Microscopy, Rutherford Backscattering Spectrometry and Elastic Recoil Detection Analysis have been undertaken for sample characterization. Optimum processing windows and conditions have been identified under which the modified TiAl alloys acquire a stable, adherent and highly protective alumina scale against high-temperature oxidation. The degree of oxidation protection has been evaluated by testing F-implanted samples under conditions of both isothermal oxidation and thermal cyclic oxidation in air at temperatures up to 1050°C and for times as long as 6000 hours.
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Poster
16th International Conference on Ion Beam Modification of Materials (IBMM08), 31.08.-05.09.2008, Dresden, Germany
Permalink: https://www.hzdr.de/publications/Publ-12089
Plasma immersion ion implantation of fluorine: an efficient technique for enhancing the oxidation resistance of TiAl alloys
Yankov, R.; Kolitsch, A.; Munnik, F.; Wolfhard, M.; Donchev, A.; Schütze, M.
Titanium aluminides are promising lightweight materials for novel aerospace, automobile and power generation applications. However, because of their insufficient oxidation resistance at temperatures above 700°C, they cannot yet find broader use. The oxidation behaviour of TiAl-alloys can be improved considerably by adding small amounts of fluorine into the subsurface zone of the components (microalloying). The use of TiAl-components after fluorine treatment is feasible up to 1050°C in oxidising environments. One possibility to introduce fluorine into the near-surface of complex TiAl-components is the plasma immersion ion implantation (PI³) technique. The use of an Ar/CH2F2-plasma for the F-PI³ processing leads to a positive halogen effect. The main characterization techniques used in this study have been ERDA and RBS. The oxidation behavior of TiAl samples treated by PI³ of F has been examined using thermogravimetric analysis, and oxidation kinetics curves have been derived. Post-oxidation analyses by SEM reveal a thin protective alumina scale at the surface of the implanted samples as opposed to the thick mixed oxide scale (TiO2/Al2O3) that unavoidably grows upon high temperature oxidation in air.
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Invited lecture (Conferences)
11th International Conference on Plasma Surface Engineering, 15.-19.09.2008, Garmisch-Partenkirchen, Germany
Permalink: https://www.hzdr.de/publications/Publ-12088
Ion implantation of fluorine: towards high-temperature oxidation-resistant TiAl alloys
Yankov, R. A.; Kolitsch, A.; Munnik, F.; Donchev, A.; Schütze, M.
Due to their light weight and high strength, TiAl alloys are of great interest for advanced automobile, aerospace and power generation applications. However, destructive oxidation occurring in these materials in air at temperatures above 700°C has to date hindered their widespread use. In the present study, the high-temperature oxidation behaviour of TiAl has been examined with consideration of the role of ion-implanted fluorine in providing practically useful oxidation protection. Samples of technical TiAl alloys have been treated by either beamline ion implantation of F or plasma immersion ion implantation (PIII) of F using various F-containing precursor gases. The degree of oxidation protection has been evaluated by testing ion implanted samples under conditions of isothermal and thermal cyclic oxidation at temperatures as high as 1050°C. Optimized ion implantation processing has been found to produce marked improvement in the oxidation behaviour of the TiAl alloys. After PIII of F at a bias voltage of 30 kV, broad fluorine implant profiles extending to depths well beyond those predicted by the theory have been identified by elastic recoil detection analysis (ERDA) in the as-implanted samples. The alloys modified in this way acquire a stable, adherent and highly protective alumina scale against environmental oxidation while retaining the bulk mechanical properties of the starting material. Some of the most important process parameters that enable the formation of an efficient protective scale are considered and assessed. PIII of F using suitable F-containing precursor gases has been successfully applied in protecting machine components made of gamma-TiAl and TNB such as turbine blades and turbochargers.
Keywords: Composition and Microstructure; Fluorine; TiAl alloys; Corrosion
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Lecture (Conference)
2008 MRS Fall Meeting, 01.-05.12.2008, Boston, USA
Permalink: https://www.hzdr.de/publications/Publ-12087
Laser-driven Electron Acceleration in Plasmas with Few-Cycle Pulses
Veisz, L.; Schmid, K.; Tavella, F.; Benavides, S.; Tautz, R.; Herrmann, D.; Buck, A.; Hidding, B.; Marcinkevicius, A.; Schramm, U.; Geissler, M.; Meyer-Ter-Vehn, J.; Habs, D.; Krausz, F.
We report on laser-driven electron acceleration with 8 fs -three optical cycle- long pulses and only 40 mJ energy. This situation constitutes an ideal parameter range for laser wake-¯eld acceleration as prophesied by theory and numerical simulations, which was experimentally not explored before. The produced electron spectra are monoenergetic with a peak in the tens-of-MeV range -up to 50 MeV- and free of low-energy electrons with thermal spectrum. The electron beam has a typical divergence of 5 - 10 mrad. The accelerator is routinely operated at 10 Hz and correspondingly it is a promising source for several applications.
Keywords: bubble regime; bubble; monoenergetic; electron acceleration; ultrashort; few-cycle; laser; laser plasma
- Comptes Rendus Physique 10(2009)2-3, 140-147
Permalink: https://www.hzdr.de/publications/Publ-12086
Penning Trap Progress in Munich
Szerypo, J.; Kolhinen, V. S.; Bussmann, M.; Habs, D.; Neumayr, J. B.; Schuermann, C.; Sewtz, M.; Thirolf, P. G.; Schramm, U.
The MLLTRAP, presently under construction at the Maier---Leibnitz Laboratory (Garching), is a Penning trap system designed to decelerate, purify, charge-breed and cool the radioactive ions with the aim to perform the high-accuracy nuclear mass measurements. It involves novel techniques, like sympathetic cooling of highly-charged ions of interest with laser-cooled Mg+ ions. The goal is to reach an accuracy of 10-10, which is required for high precision fundamental physics studies like the determination of fundamental constants and measurement of electron binding energies for QED at strong fields.
Keywords: Penning trap; sympathetic laser cooling; mass measurement
- Acta Physica Polonica B 39(2008), 471-476
Permalink: https://www.hzdr.de/publications/Publ-12085
X-ray investigations off nano structures manufactured by focused ion beam techniques
Grenzer, J.
Nanowires and chains of nanoparticles are of emerging interest in nanoelectronics, nanophotonics and plasmonics. One possible method is the use of a focused ion beam (FIB) that allows to write any pattern directly into the sample to create a particular nano structure. FIB implantation opens the way to manipulate the device structure locally on a length scale of a few 10 nm only and therefore as well as its electronic and optical properties. FIB combines implantation and lithography. The big advantage over other techniques is the reduction of technological steps necessary to make a particular device structure.
We report on strain and defect analysis of lateral nanostructures created in GaAs and Si substrates. The investigations were performed utilizing the method of high resolution X-ray diffraction using grazing incidence and micro focusing techniques at ESRF beamlines.
We have used two different ways to create lateral nanostructures in Si and GaAs, either by creating one or two dimensional patterns by FIB implantation using a liquid metal ion source of Ga or AuGeSi or by focused ion beam synthesis that allows the fabrication of epitaxial CoSi2 layers embedded in silicon. The spot size of the focused ion beam was in the order of 50nm; an ion beam energy in the order of 25keV was used. The whole implanted area had a size of less than 0.2 mm2.
Keywords: ion beam synthesis; X-ray diffraction; nano focussing
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Lecture (others)
Seminar on structure analysis, 06.01.2009, Prag, Tschechische Republik
Permalink: https://www.hzdr.de/publications/Publ-12084
Tuning exchange spring magnets by ion irradiation and annealing: X-ray investigations
Roshchupkina, O.; Grenzer, J.; Fassbender, J.; Choi, Y.; Jiang, J. S.; Bader, S. D.
The coupling effectiveness of the exchange spring effect can be influenced by the interface structure between hard and soft magnetic films. We have investigated the structural and magnetic properties of an Fe/Sm2Co7 exchange spring bilayer system after annealing and after low-energy ion irradiation. To study the interface properties X-ray reflectivity (XRR) measurements were carried out. From the XRR measurements it was shown that annealing influences the roughness of the layer surfaces causing an almost symmetrical broadening of the interfacial layers. Irradiation induces changes in the top three layers and the most pronounced effect upon irradiation is a change in electron density of the first two top layers and an interface broadening between Fe and Sm2Co7. In contrast annealing after irradiation triggers a material flow influencing the whole irradiated layers. The annealing afterwards therefore influences mainly the Fe layer by creating an Fe/Sm2Co7 intermixed region.
Keywords: X-ray reflectivity; magnetic nano structures
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Lecture (Conference)
DPG Frühjahrstagung, 22.-27.03.2009, Dresden, Germany
Permalink: https://www.hzdr.de/publications/Publ-12083
MLLTRAP: A Penning trap facility for high-accuracy mass measurements
Kolhinen, V.; Bussmann, M.; Habs, D.; Neumayr, J.; Schramm, U.; Schurmann, C.; Sewtz, M.; Szerypo, J.; Thirolf, P.
The MLLTRAP, presently under construction at the Maier-Leibnitz-Laboratory (Garching), is a Penning trap facility designed to
combine several novel techniques to decelerate, purify, charge breed and cool the reaction products and perform high-accuracy nuclear mass measurements of highly charged, laser-cooled ions.
Keywords: Gas cell; Ion cooling; Mass measurement; Penning trap; RFQ; Sympathetic laser-cooling
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Nuclear Instruments and Methods in Physics Research B 266(2008), 4547-4550
DOI: 10.1016/j.nimb.2008.05.100
Cited 17 times in Scopus
Permalink: https://www.hzdr.de/publications/Publ-12082
Xe+ ion beam induced rippled structures on Si miscut wafers
Hanisch, A.; Grenzer, J.; Biermanns, A.; Pietsch, U.
We report on the influence of the initial roughness and crystallography of the substrate on the formation of self-organized ripple structures on semiconductors surfaces by noble gas ion bombardment. The Bradley-Harper theory predicts that an initial roughness is most important for starting the sputtering process which in the ends leads to the evolution of regular patterns. We produced regular patterns with intermediate Xe+ ion energies (5-70 keV) at different incidence and azimuthal angles which lead to the assumption that also crystallography plays a role at the beginning of ripple evolution. Most of the previous investigations started from the original roughness of a polished silicon wafer. We used (001) silicon wafers with a miscut angle of 1°, 5° and 10° towards [110]. We studied the ripple formation keeping the ion beam parallel to the [111], [-1-11] or [-111] direction, i.e. parallel, antiparallel or prependicular to the miscut direction [110]. The parallel and antiparallel case implies a variation of the incidence angle with increased roughness over the surface step terraces. The perpendicular orientation means almost no roughness. The results were compared to normal Si(001) and Si(111) wafers.
Keywords: rippled structures nanostructures miscut self-organization
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Lecture (Conference)
DPG Frühjahrstagung der Sektion Kondensierte Materie (SKM) 2009, 22.-27.03.2009, Dresden, Germany
Permalink: https://www.hzdr.de/publications/Publ-12081
Transition from smoothing to roughening of ion-eroded GaSb surfaces
Keller, A.; Biermanns, A.; Carbone, G.; Grenzer, J.; Facsko, S.; Plantevin, O.; Gago, R.; Metzger, T. H.
During ion sputtering of GaSb(100) surfaces a transient behavior from initial smoothing to roughening accompanied by self-organized pattern formation has been observed using in-situ x-ray reflectivity and grazing incidence small angle scattering. A characteristic hexagonal dot pattern with a spatial periodicity of 30 nm is observed and the correlation length increases with ion fluence. In the framework of the Bradley-Harper model, where the dot pattern formation results from an interplay of surface roughening due to sputtering and surface smoothing due to diffusion, the initial smoothing behavior results from the same diffusion processes as the pattern formation.
Keywords: ion beam erosion; X-ray scattering; nano strucutures
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Applied Physics Letters 94(2009)19, 193103
DOI: 10.1063/1.3136765
Cited 15 times in Scopus
Permalink: https://www.hzdr.de/publications/Publ-12080
Ripple structures on surfaces and underlying crystalline layers in ion beam irradiated Si wafers
Grenzer, J.; Biermanns, A.; Mücklich, A.; Grigorian, S. A.; Pietsch, U.
We report on the formation of ion beam induced ripples in Si(001) wafers when bombarded with Ar+ ions at an energy of 60keV. A set of samples varying incidence and azimuthal angles of the ion beam with respect to the crystalline surface orientation was studied by two complementary near surface sensitive techniques, namely atomic force microscopy and depth-resolved X-ray grazing incidence diffraction. Additionally cross-section TEM investigations were carried out. The ripple-like structures are formed at the sample surface as well as at the buried amorphous-crystalline interface. Best quality of the ripple pattern was found when the irradiating ion beam was aligned parallel to the <111> planes. The quality decreases rapidly if the direction of ion beam deviates from <111>.
Keywords: ion beam erosion; nano structures; X-ray diffraction; TEM; AFM
- Physica Status Solidi (A) 206(2009)8, 1731-1735
Permalink: https://www.hzdr.de/publications/Publ-12079
Submicron resolution X-ray diffraction from periodically patterned GaAs nanorods grown onto Ge[111]
Davydok, A.; Biermanns, A.; Pietsch, U.; Grenzer, J.; Paetzelt, H.; Gottschalch, V.; Bauer, J.
We present spatially resolved X-ray diffraction pattern of individual GaAs nanorods grown catalyst-free throughout a pre-patterned amorphous SiNx mask onto germanium [111] surfaces. The experiment has been performed using synchrotron radiation using a micro-sized beam prepared by compound refractive lenses. Due to the non-polar character of the substrate the shapes of NR´s appear not uniform and vary between deformed hexagonal and trigonal in symmetry. Because the average diameter of NR´s equals the experimental resolution certain cuts through slightly inclined edges or corners of individual nanorods with lateral size of about 225 nm could be selected using spatially resolved reciprocal space mapping.
Keywords: X-ray diffraction; nano structures
- Physica Status Solidi (A) 206(2009)8, 1704-1708
Permalink: https://www.hzdr.de/publications/Publ-12078
Polyedrisierung dreidimensionaler digitaler Objekte mit Mitteln der konvexen Hülle
Schulz, H.
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Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; FZD-506 2008
ISSN: 1437-322X
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Permalink: https://www.hzdr.de/publications/Publ-12077
Annual Report 2007 - Institute of Safety Research
Weiss, F.-P.; Rindelhardt, U.; (Editors)
The Institute of Safety Research (ISR) is one of the six Research Institutes of Forschungszentrum Dresden-Rossendorf e.V. (FZD e.V.), which is a member institution of the Wissenschaftsgemeinschaft Gottfried Wilhelm Leibniz (Leibniz Association). Together with the Institute of Radiochemistry, ISR implements the research programme Safety and Environment, which is one of the three scientific programmes of FZD. In the framework of this research programme, the institute is responsible for the programme areas Plant and Reactor Safety and Thermal Fluid Dynamics, respectively (see Table 1). By participating in the development and operation of a pulsed photo-neutron source at the radiation source ELBE (Electron linear accelerator for beams of high brilliance and low emittance), we also contribute to the project Neutron Induced Processes, which is part of the FZD programme dedicated to the structure of matter.
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Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; FZD-501 2008
ISSN: 1437-322X
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Permalink: https://www.hzdr.de/publications/Publ-12076
Large-area Terahertz Emitters based on GaInAsN
Peter, F.; Winnerl, S.; Schneider, H.; Helm, M.; Köhler, K.
The high price and the complexity of commonly used titanium-sapphire lasers hinder a more widespread use of pulsed THz systems. Er-doped fiber lasers can be a promising alternative. Since the band gap of GaAs is larger than the photon energy at 1.55 µm, this material while being the standard material for photoconductive THz antennas excited with titanium-sapphire lasers is not suitable for systems driven by fiber lasers. Dipole antennas have been successfully demonstrated on low-temperature grown InGaAs [1] and ion-irradiated InGaAs [2]. However, the resistivity of these small-gap materials is too low for microstructured large-area emitters. Such emitters consist of an interdigitated finger structure on the semiconductor substrate and a second metallization preventing destructive interference from THz wavelets excited in regions with opposite direction of the bias field [3]. Since these microstructured large-area emitters can withstand large excitation power and high bias fields, they show improved efficiency and higher THz power as compared to conventional antennas.
A 1000 nm thick Ga0.89In0.11As0.96N0.04 layer was grown lattice matched on semi-insolating GaAs by molecular beam epitaxy. On top, additional layers of 60 nm AlGaAs and 5 nm GaAs were grown, resulting in a higher resistivity of the substrate. A THz emitter with an active area of 1 mm 1 mm with a microstructure similar to the one described in ref. 3 was produced using standard optical lithography. The emitter was excited with radiation from an optical parametric oscillator (OPO; tuning range: 1.1 - 1.5 µm). The THz radiation was detected by electro-optic sampling in a ZnTe crystal gated with an 800 nm beam from a titanium sapphire laser. Strong THz emission is observed for excitation wavelength below 1.35 µm [4]. No saturation effects occur within the available range of average power (up to 50 mW) of the OPO. Furthermore the GaInAsN emitter was compared with an emitter based on semi-insolating GaAs at an excitation wavelength of 800 nm. The THz field amplitude of the GaAs emitter is eight times higher as compared to the GaInAsN emitter. Again, in the available excitation power range (up to 0.5 W), no saturation effects are observed.
In summary an efficient and easy-to-align microstructured THz emitters based on GaInAsN has been demonstrated. While further improvement of the material is necessary for excitation at 1.55 µm, the material studied here is suitable for fiber lasers operating at 1.1 µm.
References
[1] M. Suzuki and M. Tounouchi, Appl. Phys. Lett. 86, 163504, (2005).
[2] A. Takazato, et al., Appl. Phys. Lett. 91, 011102, (2007).
[3] A. Dreyhaupt, et al., Appl. Phys. Lett. 86, 121114 (2005).
[4] F. Peter et al., Appl. Phys. Lett. 93, 101102 (2008).
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Lecture (Conference)
SPIE Europe Michrotechnologies for the New Millenium, 04.-06.05.2009, Dresden, Deutschland -
Contribution to proceedings
SPIE Europe Michrotechnologies for the New Millenium, 04.-06.05.2009, Dresden, Deutschland, 04.-06.05.2009, Dresden, Deutschland
Proceedings of SPIE, 73661R-73661R-6
Permalink: https://www.hzdr.de/publications/Publ-12075
Terahertz Emitters and Detectors for Radially and Azimuthally Polarized Beams
Winnerl, S.; Zimmermann, B.; Peter, F.; Schneider, H.; Helm, M.
Typical pulsed terahertz (THz) systems operate with freely propagating THz waves of linear polarization and Gaussian beam profile. In the range of visible light and near-infrared radiation, Bessel-Gauss modes have stimulated great interest over last years. The lowest order Bessel-Gauss modes have a donut-like intensity distribution and are either radially or azimuthally polarized. Radially polarized beams have interesting fundamental properties such as smaller beam waists in the focus as compared to Gaussian modes and strong longitudinal field components in the focus. In the THz range, superior coupling properties for radially polarized light to plasmonic guided modes on wires, so called Sommerfeld modes are predicted. While there are many investigations on these guided THz modes, only little work is done on freely propagating modes of radial polarization [1] and no publications exist for azimuthally polarized THz beams. Here we present a concept that allows creating emitters and detectors for any desired mode. The principle is demonstrated by showing results on radially and azimuthally polarized THz beams.
The photoconductive emitter and detector structures are based on a microstructured electrode pattern on a semiconductor substrate. The electrode pattern is inverse to the desired polarization pattern, i.e. emitters for radially polarized modes consist of equidistant concentric ring electrodes, while emitters for azimuthally polarized modes are a circular structure of metallized sectors. To avoid electric fields pointing in the opposite direction, a second metallization layer is used in a similar way as previously described for emitter of linearly polarized radiation [2]. While the emitters were fabricated on semi-insulating GaAs, detectors were prepared on GaAs substrates implanted with N+. A titanium sapphire laser was used for excitation of the emitters and gating of the detectors. Beam profiles were measured for the divergent beam 25 mm behind the emitters, and for the refocused beam after a path of ~0.5 m. In this experiment the detector was sensitive for a linearly polarized component of the radiation. The observed beam profiles agree well with the ones expected for Bessel-Gauss beams. Furthermore radiation with radial polarization was detected with an antenna optimized for radial polarization and one for azimuthal polarization. With the detector for azimuthal polarization no signal is expected. However, due to imperfections of the beam profile of the near-infrared laser, a residual signal of about 10 % compared to the signal measured with the detector for radial polarization is observed. This experiment serves as a proof of principle that the emitter-detector combination well suited for studying changes of the mode structure.
References:
[1] G. Chang, Ch.J. Divin, C.-H. Liu, S.L. Williamson, A. Galvanauskas, and T.B. Norris, Opt. Lett. 32, 433 (2006).
[2] A. Dreyhaupt, S. Winnerl, T. Dekorsy, and M. Helm, Appl. Phys. Lett. 86, 121114 (2005).
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Lecture (Conference)
SPIE Europe Microtechnologies for the New Millenium, 04.-06.05.2009, Dresden, Deutschland -
Contribution to proceedings
SPIE Europe Microtechnologies for the New Millenium, 04.-06.05.2009, Dresden, Deutschland
Proceedings of SPIE, 73661N-73661N-7
Permalink: https://www.hzdr.de/publications/Publ-12074
Terahertz Vector Beams
Winnerl, S.; Zimmermann, B.; Peter, F.; Schneider, H.; Helm, M.
We present a concept for the design of photoconductive antennas which allows the generation and detection of terahertz radiation pulses of freely selectable modes. We demonstrate the principle by showing electric field distributions for vector beams, namely the lowest order Gaussian-Bessel beams. They have a donut-like intensity distribution and either radial or azimuthal polarization. For comparison, Gaussian beams are investigated.
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Poster
33rd International Conference on Infrared, Millimeter, and Terahertz Waves, 14.-19.09.2008, Pasadena, USA -
Contribution to proceedings
33rd International Conference on Infrared, Millimeter, and Terahertz Waves, 14.-19.09.2008, Pasadena, USA
Conference Digest of the 33rd International Conference on Infrared, Millimeter, and Terahertz Waves
Permalink: https://www.hzdr.de/publications/Publ-12073
Terahertz Bessel-Gauss beams of radial and azimuthal polarization from microstructured photoconductive antennas
Winnerl, S.; Zimmermann, B.; Peter, F.; Schneider, H.; Helm, M.
We report on emission and detection of pulsed terahertz radiation of radial and azimuthal polarization by microstructured photoconductive antennas. To this end the electrode geometry of the emitter is inverse to the desired THz field pattern and a second periodic structure prevents destructive interference effects. Beam profiles of freely propagating THz waves are studied for divergent and refocused beams. They can be well described as the lowest order Bessel-Gauss modes with a divergence comparable to linearly polarized Gaussian beams. Additionally, polarization sensitive detection is demonstrated for radially polarized radiation.
- Optics Express 17(2009), 1571-1576
Permalink: https://www.hzdr.de/publications/Publ-12072
Nanocrystals formation in a Si/SiO2 layer by ion mixing and plasma immersion ion implantation in different energy ranges
Mello, C. B.; Ueda, M.; Beloto, A. F.; Mücklich, A.; Reuther, H.
Nanocrystals formation in a Si/SiO2 layer by ion mixing and plasma immersion ion implantation in different energy ranges
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Poster
16th International Conference on Ion Beam Modification of Materials, 31.08.-05.09.2008, Dresden, Deutschland
Permalink: https://www.hzdr.de/publications/Publ-12071
Nitrogen PIII in SS304 stainless steel using different temperature time-histories
Ueda, M.; Diaz, C.; Lepienski, C. M.; Reuther, H.
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Poster
16th International Conference on Ion Beam Modification of Materials, 31.08.-05.09.2008, Dresden, Deutschland
Permalink: https://www.hzdr.de/publications/Publ-12070
Tribological Effects of Plasma Immersion Ion Implantation Heating Treatments on SS304 Stainless Steel
Mello, C. B.; Ueda, M.; Geraldo, A. S.; Nascimento, D. P.; Lepienski, C. M.; Reuther, H.
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Poster
VII Encontro da SBPMat, Symposium C Mechanical properties of surfaces, thin films and coatings, 28.09.-02.10.2008, Guarujá, Brasilien
Permalink: https://www.hzdr.de/publications/Publ-12069
Pages: [1.] [2.] [3.] [4.] [5.] [6.] [7.] [8.] [9.] [10.] [11.] [12.] [13.] [14.] [15.] [16.] [17.] [18.] [19.] [20.] [21.] [22.] [23.] [24.] [25.] [26.] [27.] [28.] [29.] [30.] [31.] [32.] [33.] [34.] [35.] [36.] [37.] [38.] [39.] [40.] [41.] [42.] [43.] [44.] [45.] [46.] [47.] [48.] [49.] [50.] [51.] [52.] [53.] [54.] [55.] [56.] [57.] [58.] [59.] [60.] [61.] [62.] [63.] [64.] [65.] [66.] [67.] [68.] [69.] [70.] [71.] [72.] [73.] [74.] [75.] [76.] [77.] [78.] [79.] [80.] [81.] [82.] [83.] [84.] [85.] [86.] [87.] [88.] [89.] [90.] [91.] [92.] [93.] [94.] [95.] [96.] [97.] [98.] [99.] [100.] [101.] [102.] [103.] [104.] [105.] [106.] [107.] [108.] [109.] [110.] [111.] [112.] [113.] [114.] [115.] [116.] [117.] [118.] [119.] [120.] [121.] [122.] [123.] [124.] [125.] [126.] [127.] [128.] [129.] [130.] [131.] [132.] [133.] [134.] [135.] [136.] [137.] [138.] [139.] [140.] [141.] [142.] [143.] [144.] [145.] [146.] [147.] [148.] [149.] [150.] [151.] [152.] [153.] [154.] [155.] [156.] [157.] [158.] [159.] [160.] [161.] [162.] [163.] [164.] [165.] [166.] [167.] [168.] [169.] [170.] [171.] [172.] [173.] [174.] [175.] [176.] [177.] [178.] [179.] [180.] [181.] [182.] [183.] [184.] [185.] [186.] [187.] [188.] [189.] [190.] [191.] [192.] [193.] [194.] [195.] [196.] [197.] [198.] [199.] [200.] [201.] [202.] [203.] [204.] [205.] [206.] [207.] [208.] [209.] [210.] [211.] [212.] [213.] [214.] [215.] [216.] [217.] [218.] [219.] [220.] [221.] [222.] [223.] [224.] [225.] [226.] [227.] [228.] [229.] [230.] [231.] [232.] [233.] [234.] [235.] [236.] [237.] [238.] [239.] [240.] [241.] [242.] [243.] [244.] [245.] [246.] [247.] [248.] [249.] [250.] [251.] [252.] [253.] [254.] [255.] [256.] [257.] [258.] [259.] [260.] [261.] [262.] [263.] [264.] [265.] [266.] [267.] [268.] [269.] [270.] [271.] [272.] [273.] [274.] [275.] [276.] [277.] [278.] [279.] [280.] [281.] [282.] [283.] [284.] [285.] [286.] [287.] [288.] [289.] [290.] [291.] [292.] [293.] [294.] [295.] [296.] [297.] [298.] [299.] [300.] [301.] [302.] [303.] [304.] [305.] [306.] [307.] [308.] [309.] [310.] [311.] [312.] [313.] [314.] [315.] [316.] [317.] [318.] [319.] [320.] [321.] [322.] [323.] [324.] [325.] [326.] [327.] [328.] [329.] [330.] [331.] [332.] [333.] [334.] [335.] [336.] [337.] [338.] [339.] [340.] [341.] [342.] [343.] [344.] [345.] [346.] [347.] [348.] [349.] [350.]