Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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31745 Publications
Nanocomposite Au-SiO2 thin film deposition by co-sputtering: comparison of experiments with atomistic simulations
Khan, S.; Heinig, K.-H.; Avasthi, D.;
Fast atom beam co-sputtering has been found to be an excellent technique for producing metal nanoclusters in variety of matrices without the need of any post-deposition annealing. The films thus prepared show homogeneous distribution of nanoclusters having rather narrow size distributions. The average size of these embedded nanoclusters can be effectively controlled by varying the ratio of sputtered metal and matrix species. In this contribution, we present results from the computer simulation of the deposition process to investigate the structural evolution and growth of Au nanoclusters embedded in silica matrix during co-sputtering. A three dimensional kinetic Monte Carlo technique has been used here to study the growth kinetics of nanoparticles taking into consideration the effect of the energetic sputtered species reaching the surface of the film during deposition. Nucleation and subsequent growth of Au nanoclusters has been simulated under different deposition conditions. As a result, the simulation has been shown to be useful for deposition parameters optimization in the process of nanocomposite thin film growth by fast atom beam co-sputtering.
Keywords: layer deposition, co-sputtering, nanostructure, kinetic Monte Carlo
  • Poster
    16th International Conference on Ion Beam Modification of Materials (IBMM 08), 31.08.-05.09.2008, Dresden, Germany

Publ.-Id: 12189 - Permalink


Facetting Morphology of Crystallites under Ion Irradiation – a 3D Kinetic Lattice Monte Carlo Study
Heinig, K.-H.; Röntzsch, L.;
The orientation-dependent surface energies of crystal facets determine the shape of crystallites via Wulff’s theorem. Thus, in the framework of a nearest neighbor Ising model, the equilibrium shape of a fcc crystallite is a truncated octahedron. This crystallite shape is found frequently, e.g. for A-type CoSi2 crystallites embedded in silicon.
In this contribution we show that crystallites change their shape under intense ion irradiation. A first indication for a crystallite shape change under ion irradiation was reported several years ago [1]. In a Monte Carlo simulation the continuing vacancy production transformed the equilibrium fcc crystallite shape of a truncated octahedron into the steady-state shape of a cube. Here we present a systematic study of ion-irradiation-induced crystallite shape changes for different crystal structures and different irradiation intensities and temperatures. For the first time, an explanation of the shape changes based on the surface defect kinetics will be given: Whereas in thermodynamics the equilibrium concentration of surface defects is determined by energetics (“detailed balance”), under ion irradiation its steady-state value is controlled by the geometry of atomic displacements. Consequently, facets with a high atomic area density become unstable. It will be shown that this facet instability might be the reason for temperature dependent pattern formation on metal surfaces under ion erosion [2].
[1] P. Bellon, Phys. Rev. Letters 81, 4176 (1998).
[2] U. Valbusa et al., J. Phys.: Condens. Matter 14, 8153 (2002).
Keywords: ion irradiation, surface energy, crystal shape, kinetic Monte Carlo
  • Poster
    16th International Conference on Ion Beam Modification of Materials (IBMM 08), 31.08.-05.09.2008, Dresden, Germany

Publ.-Id: 12188 - Permalink


Mapping of 2 + 1 dimensional KPZ growth onto driven lattice gas model of dimers
Odor, G.; Liedke, B.; Heinig, K.-H.;
We show that a 2+1 dimensional discrete surface growth model exhibiting KPZ class scaling can be mapped onto a two dimensional conserved lattice gas model of directed dimers. In case of KPZ height anisotropy the dimers follow driven diffusive motion. We confirm by numerical simulations that the scaling exponents of the dimer model are in agreement with those of the 2+1 dimensional KPZ class. This opens up the possibility of analyzing growth models via reaction-diffusion models, which allow much more efficient computer simulations.
Keywords: crystal growth, KPZ equation, Edward-Wilkinson equation, scaling behavior, Monte-Carlo simulation

Publ.-Id: 12187 - Permalink


Ion mass dependence of irradiation-induced local creation of ferromagnetism in Fe60Al40 alloys
Fassbender, J.ORC; Liedke, M. O.; Strache, T.; Moeller, W.; Menendez, E.; Sort, J.; Rao, K. V.; Deevi, S. C.; Nogues, J.
Ion irradiation of Fe60Al40 alloys results in the phase transformation from the paramagnetic, chemically ordered B2 phase to the ferromagnetic, chemically disordered A2 phase. The magnetic phase transformation is related to the number of displacements per atom (dpa) during the irradiation. For heavy ions (Ar+, Kr+, and Xe+), a universal curve is observed with a steep increase in the fraction of the ferromagnetic phase that reaches saturation, i.e., a complete phase transformation, at about 0.5 dpa. This proves the purely ballistic nature of the disordering process. If light ions are used (He+ and Ne+), a pronounced deviation from the universal curve is observed. This is attributed to bulk vacancy diffusion from the dilute collision cascades, which leads to a partial recovery of the thermodynamically favored B2 phase. Comparing different noble gas ion irradiation experiments allows us to assess the corresponding counteracting contributions. In addition, the potential to create local ferromagnetic areas embedded in a paramagnetic matrix is demonstrated.
  • Physical Review B 77(2008), 174430

Publ.-Id: 12186 - Permalink


Application of self-actuated 32 cantilever array in atomic force surface measurements
Gotszalk, T.; Zawierucha, P.; Woszczyna, M.; Zielony, M.; Ivanov, T.; Ivanova, K.; Volland, B. E.; Sarov, Y.; Persaud, A.; Dontzov, D.; Schmidt, B.; Nikolov, N.; Kostic, I.; Engl, W.; Sulzbach, T.; Mielczarski, J.; Kolb, S.; Pedreau, R.; Huq, S. E.; Edinger, K.; Fortagne, O.; Blom, H. O.; Rangelow, I. W.;
Main industry requirement for applying scanning probe microscopy in surface measurements is the high
scan speed, which allow the microelectronics producers to obtain the information about the technological
process quality in-situ on the semiconductor wafer. Common single topography measurement consume few
minutes for scanning area about 100 μm2 because of limited cantilever dynamic properties. To overcome
this problem one may utilize the cantilever with resonance frequency above 1 MHz but in this case,
cantilever suffer from wear and it requires complicated, large bandwidth measurement system. Different
approach to high speed topography measurement is to apply massive array of cantilevers, where the
surface topography image is taken simultaneously from every probe.
In the contribution present the application of the one dimensional VLSI NEMS-chip (Very Large Scale
Integrated Nano Electro Mechanical System) incorporating 32 proximal probes for high speed atomic force
microscopy measurements will be presented. Each array cantilever integrates a thermal deflection actuator, a
piezoresistor acting as a deflection detector and a microtip with radius of 10 nm.
Keywords: NEMS, proximal AFM probe array, piezoresistive deflection sensing, thermal deflection actuation
  • Poster
    34th Micro and Nano Engineering Conference MNE08, 15.-18.09.2008, Athens, Greece

Publ.-Id: 12183 - Permalink


Acceleration of irradiation hardening of low-copper reactor pressure vessel steel observed by means of SANS and tensile testing
Bergner, F.; Ulbricht, A.; Viehrig, H.-W.;
Neutron irradiation of low-copper reactor pressure vessel steels containing manganese and nickel gives rise to microstructural changes and a deterioration of mechanical properties apparently progressing slower than in steels containing more than or about 0.1 wt% Cu. An acceleration of this process after accumulation of a threshold fluence caused by so-called late blooming phases is a matter of debate. We report results of small angle neutron scattering (SANS) experiments and tensile tests for two low-Cu model RPV steels irradiated at 255°C. Motivation for the use of the integrated magnetic scattering as a microstructural parameter combining the volume fraction and magnetic contrast of nanometre-sized irradiation-induced features is given. The results indicate one of the rare cases of acceleration of both the change of a microstructural parameter and the yield stress increase. The issues of the nature of the irradiation-induced features, the role of phosphorus, and the observed strong correlation of integrated magnetic scattering and yield stress increase are addressed.
Keywords: neutron irradiation; SANS; tensile testing; pressure vessel steel

Publ.-Id: 12182 - Permalink


Investgation of crosstalk in cantilever arrays
Frank, A.; Zöllner, J.-P.; Sarov, Y.; Ivanov, T.; Klett, S.; Gotszalk, T.; Zielony, M.; Zawierucha, P.; Schmidt, B.; Zier, M.; Nikolov, N.; Engl, W.; Sulzbach, T.; Langlotz, E.; Dontsov, D.; Schott, W.; Rangelow, I. W.;
In this paper a macro model of a cantilever for mixed domain simulation only with SPICE is presented. Based on lumped elements of equivalent circuits a model is developed, which realizes a coupled electro-thermal-mechanical simulation including crosstalk effects. Capacitive crosstalk through the substrate are evaluated and modelled with SPICE. This is verified with measurement and helps to solve the crosstalk effect.
Keywords: Cantilever array, SPICE simulation, MEMS modeling
  • Lecture (Conference)
    EUROSENSORS XXII, 07.-10.09.2008, Dresden, Deutschland

Publ.-Id: 12181 - Permalink


Fabrication of ultra-shallow p-n junctions by ion beam processing
Zier, M.;
Ultra-shallow p-n junctions in silicon play an important role in semiconductor industry, for example as source-drain extensions in highly integrated MOSFETs. The present talk shows their application as piezo-resistive bending sensors in massively parallel AFM arrays.
Difficulties in fabrication of ultra-shallow p-n junctions will be discussed and potential solutions will be given. To obtain ultra-shallow junctions several methods can be employed: pre-amorphisation, low energy ion implantation or the formation of a region with an enhanced vacancy concentration near the sample surface by high energy Si implantation. The activation of the dopant can be accomplished either by rapid thermal annealing or flash lamp annealing. Finally, the characterisation of the ultra-shallow doped layers using electrical and SIMS measurements will be shown.
Keywords: ion beam modification ion implantation ultra-shallow junction
  • Lecture (others)
    Materials Science Seminar, 29.04.2008, Dresden, Deutschland

Publ.-Id: 12180 - Permalink


Fabrication of ultra-shallow p-n junctions in Si using fast and ultra-fast annealing
Zier, M.; Schmidt, B.;
Ultra-shallow p-n junctions in silicon play an important role in the semiconductor industry, for example as source-drain extensions in highly integrated MOSFETs or in this case as piezo-resistive bending sensors for application in massively parallel AFM arrays.
To obtain ultra-shallow junctions several methods of fabrication have been employed: low energy ion implantation and vacancy enhancement near the sample surface by using high energy Si+ implantation followed by in-diffusion of boron from a solid source. The activation of the dopant was accomplished either by rapid thermal annealing or flash lamp annealing.
I-V measurements of the diode formed by the p-n junction show excellent diode behaviour of the p-doped layers, indicating that all employed fabrication methods result in real p-n junctions. The concentration depth profile of boron in the samples have been measured by SIMS, using O2- ions of 1500 and 500eV to minimise distortion of the depth profile due to the ion bombardment. Finally, measured sheet resistances of the p-doped layers obtained from dedicated test structures are compared against each other.
Keywords: ion implantation ultra-shallow junction RTA FLA
  • Poster
    16th International Conference on Ion Beam Modification of Materials 2008, 31.08.-05.09.2008, Dresden, Deutschland

Publ.-Id: 12179 - Permalink


[18F]FETA PET - A new method for hot spot imaging of the ischemic penumbra in acute stroke
Barthel, H.; Großmann, U.; Zeisig, V.; Patt, M.; Wagner, D.; Patt, J.; Kluge, M.; Franke, H.; Sorger, D.; Luthardt, J.; Nitzsche, B.; Dreyer, A.; Brust, P.; Steinbach, J.; Boltze, J.; Emmrich, F.; Sabri, O.;
Objectives:
In acute ischemic stroke, an imaging method to directly visualize the ischemic penumbra - the salvageable part of the affected brain - in positive image contrast would potentially improve therapy stratification and monitoring. This study aimed to test [18F] fluoroetanidazole ([18F]FETA), a second-generation radiolabeled 2-nitroimidazole, for the first time with respect to its suitability to image brain hypoxia with positron emission tomography (PET).

Methods:
Primary embryonal corticoencephalic cells (Wistar rats) and necortical brain slices (Sprague Dawley rats) were ex vivo exposed to nitrogen or air. The cells and brain slices were incubated with 5MBq [18F]FETA up to 120min, respectively. The activities of three nitroreductases - enzymes which mediate the intracellular [18F]FETA accumulation - were determined in the corticoencephalic cells. Further, organ distribution was determined in Sprague
Dawley rats up to 2h after i.v. injection of 20MBq [18F]FETA, and ex vivo brain autoradiography was performed up to 24h after permanent middle cerebral artery occlusion (pMCAO). Target-to background image contrast of [18F]FETA autoradiograms at 3h after pMCAO was compared with that of corresponding [18F]fluoromisonidazole ([18F]FMISO) autoradiograms. At 24h after pMCAO, animals were additionally i.v. injected with 1MBq [14C]iodoantipyrine to determine the local cerebral blood flow (lCBF). Nissl staining of brain slices as well as stroke-specific MRI were carried out at 24h after pMCAO to confirm the existence and localization of ischemic brain tissue damage.

Results:
In vitro, the oxygen concentration in the cell suspension was < 1 mm Hg and ~70 mm Hg under nitrogen and air, respectively. The normoxic [18F]FETA uptake by the cells and the brain slices was low and constant over time (0.3±0.08 %ID.mio cells-1 and 0.04±0.01 %ID.g tissue-1). In contrast, under hypoxia a time-dependent linear increase of the [18F]FETA uptake was found which was 2.0- and 2.5-fold by the cells and 2.0- and 2.4-fold by the brain slices at 60min and 120min (p< 0.05), respectively. The analyses of nitroreductases activities showed that cell oxygenation does not affect the enzyme activities. The biodistribution studies revealed fast blood clearance, a rapid urinary excretion and a constantly low uptake in unaffected brain tissue (0.1±0.02 %ID.g-1). Ex vivo brain autoradiography in the pMCAO rats showed a relevant time-dependent [18F]FETA uptake in ipsilateral brain regions which reached maximum target-to background ratios of 3.3±0.2 at 3h. The corresponding [18F]FMISO uptake ratios were only 1.5±0.3 (p< 0.05). Furthermore, at 24h after pMCAO the lCBF was reduced in the infarction core (as determined by Nissl staining and MRI) and surrounding brain areas by 25% and 10%, respectively.

Conclusions:
These results demonstrate that [18F]FETA has a better potential than [18F]FMIS to serve as a brain hypoxia marker. Further testing of this promising new stroke PET marker is warranted. First results employing a new sheep stroke model developed recently by our group [1] are encouraging.

References:
[1] Boltze et al., J Cereb Blood F Metab 2008

First and second author contributed equally to this study

This research was supported by the Translational Centre for Regenerative Medicine Leipzig/BMBF (PtJ-Bio 0313909)
  • Lecture (Conference)
    XXIVth International Symposium on Cerebral Blood Flow, Metabolism and Function and the IXth International Conference on Quantification of Brain Function with PET, 29.06.-03.07.2009, Chicago, USA
  • Abstract in refereed journal
    Journal of Cerebral Blood Flow and Metabolism 29(2009)Suppl. 1, S42-S43

Publ.-Id: 12178 - Permalink


Scanning proximal probes for parallel imaging and lithography
Ivanova, K.; Sarov, Y.; Ivanov, T.; Frank, A.; Zöllner, J.; Bitterlich, C.; Wenzel, U.; Volland, B. E.; Klett, S.; Rangelowa, I. W.; Zawierucha, P.; Zielony, M.; Gotszalk, T.; Dontzov, D.; Schott, W.; Nikolov, N.; Zier, M.; Schmidt, B.; Engl, W.; Sulzbach, T.; Kostic, I.;
Scanning proximity probes are uniquely powerful tools for analysis, manipulation, and bottom-up synthesis. A massively parallel cantilever-probe platform is demonstrated. 128 self-sensing and self-actuated proximal probes are discussed. Readout based on piezoresistive sensors and bending control based on bimorph dc/ac actuations are described in detail.
Keywords: Scanning proximity probes, piezoresistive sensing, bimorph actuations, parallel cantilever-probe platform
  • Journal of Vacuum Science & Technology B 26(2008)6, 2367-2373
    DOI: 10.1116/1.2990789

Publ.-Id: 12177 - Permalink


Shaping of nanospheres into disks and rods with swift heavy ions
Schmidt, B.; Heinig, K.-H.; Mücklich, A.; Akhmadaliev, C.;
The swift heavy ion induced deformation of SiO2 and metal nanoparticles were studied intensively in the last years. Recently, we reported on ion beam shaping of Ge nanospheres. Surprisingly, Ge nanospheres in silica form oblate ellipsoids, what is opposite to prolate ellipsoids found for metal spheres.
This presentation reports on the experimental features of the shaping of Ge nanospheres and our theoretical search for the shaping mechanism(s). A stack of alternating Ge and SiO2 layers was sputtered on an oxidized Si wafer. The Ge layer thickness varied from 2.5 to 7.5 nm with 100 nm SiO2 in-between. Heating this layer stack to 950 °C for 300 s transformed each Ge layer into a layer of Ge nanospheres. With growing Ge layer thickness the mean diameter increases from 10 to 40 nm. After irradiation with (1-10)x1014 I7+cm-2 at 38 MeV, cross-section TEM images of as-prepared and irradiated samples showed that the largest Ge nanospheres kept spherical, whereas medium-size Ge spheres became oblates, and smaller ones shaped diamond-like. The different shaping of metal and semiconducting spheres is explained by their differences in thermodynamic properties.
Keywords: Ge nanoparticles, ion beam shaping
  • Lecture (Conference)
    Workshop "Ionenstrahlphysik und Nanotechnologie", 11.-12.04.2008, Darmstadt-Wixhausen, Germany

Publ.-Id: 12176 - Permalink


Electroluminescence in silicon nanocrystals fabricated by ion beam mixing and annealing of gate oxide/silicon interfaces
Schmidt, B.; Heinig, K.-H.; Beyer, V.; Stegemann, K.-H.;
A light emitting field-effect transistor (LEFET) which is based on silicon nanocrystals in the gate oxide is demonstrated. The Si nanocrystals in the gate oxide were optimized for a multi-dot floating-gate nonvolatile memory operation [1]. For this aim, ion irradiation through the MOSFET stack of 50 nm poly-Si/15 nm SiO2/Si substrate was performed with 50 keV Si+ ions. The ion beam mixing of the upper poly-Si/SiO2 interface and the lower SiO2/(001)Si interface leads to Si excess in the gate oxide. Subsequent rapid thermal annealing reforms sharp interfaces and separates the excess Si from SiO2. Adjacent to the recovered interfaces, 3-4 nm thick SiO2 zones denuded completely of excess Si have been found, whereas the more distant tails of excess Si form well-aligned narrow layers of nanocrystals with 2-3 nm diameter. LEFETs with an active gate area of 20x20 µm2 were fabricated as nMOSFET devices in a standard 0.6 µm CMOS process line. An AC voltage was applied to the gate in order to inject charges of both polarities into the lower and upper Si nanocrystal layer from the channel and the poly-Si gate of the transistor, respectively. AC voltage and frequency dependent electroluminescence spectra were recorded in the wavelength region of 400-1000 nm as a function of the annealing conditions. The performance of the LEFETs and further possibilities of optimization of efficient light emission will be discussed.
[1] B. Schmidt, et al. Nucl. Instr. and Meth. B 242 (2006) 146.
Keywords: Silicon nanocrystals, electroluminescence, light emitting field-effect transistor
  • Lecture (Conference)
    E-MRS Spring Meeting, 26.-30.05.2008, Strasbourg, France

Publ.-Id: 12175 - Permalink


Nanomagnets - created and tailored by ions
Fassbender, J.ORC
Report on the activities in the field of ion beam modification of magnetic materials.
Keywords: magnetism, ion irradiation, focused ion beam, binary alloys, nanostructures
  • Invited lecture (Conferences)
    Physik von Nanostrukturen, 19.12.2008, Dresden, Deutschland
  • Lecture (Conference)
    International Seminar and Workshop on Magnonics: From Fundamentals to Applications, 02.-07.08.2009, Dresden, Deutschland
  • Lecture (others)
    Forschungsseminar, 13.05.2009, Berlin, Deutschland
  • Invited lecture (Conferences)
    Kolloquiumsvortrag Universität Paderborn, 02.07.2009, Paderborn, Deutschland
  • Lecture (others)
    SFB 668 - Kolloquium Magnetismus vom Einzelatom zur Nanostruktur, 16.06.2009, Hamburg, Deutschland
  • Invited lecture (Conferences)
    Nanoscale Modification of Surfaces and Thin Films, 30.08.-03.09.2009, Rathen, Deutschland
  • Invited lecture (Conferences)
    Kolloquium, Institute of Physics, 21.02.2014, Bhupaneshwar, Indien
  • Invited lecture (Conferences)
    Kolloquium, Universität Kiel, 27.01.2014, Kiel, Deutschland
  • Invited lecture (Conferences)
    Kolloquium Institute of Physics, Polish Academy of Sciences, 07.10.2014, Warschau, Polen
  • Invited lecture (Conferences)
    Eigth International Meeting on Recent Developments in the Study of Radiation Effects in Matter, 20.-23.09.2015, Kerteminde, Dänemark
  • Invited lecture (Conferences)
    Physikalisches Kolloquium, 13.10.2015, Leipzig, Deutschland
  • Invited lecture (Conferences)
    Colloquium, 17.05.2016, Krakow, Polen
  • Invited lecture (Conferences)
    Kolloquium, 07.07.2016, Leipzig, Deutschland

Publ.-Id: 12174 - Permalink


Fundamentals and Modelling of Reactive Magnetron Sputtering
Moeller, W.;
kein Abstract vorhanden
  • Invited lecture (Conferences)
    Tutorial "Fundamentals and Trends of Plasma Surface Processing", 14.09.2008, Garmisch-Partenkirchen, Germany

Publ.-Id: 12173 - Permalink


Reactive Magnetron Sputtering of Nitrides and Oxides: Understanding the Process and Optimizing the Film Quality
Moeller, W.;
kein Abstract vorhanden
  • Invited lecture (Conferences)
    Plasmas, Surfaces, and Thin Films, 11.06.2008, London, United Kingdom

Publ.-Id: 12172 - Permalink


Nanostructures by Ion-Driven Self-Organisation: Can Ions Induce Order?
Moeller, W.;
kein Abstract vorhanden
  • Lecture (others)
    VERA-Seminar, 05.06.2008, Wien, Austria

Publ.-Id: 12171 - Permalink


Nanostructures by Ion-Driven Self-Organisation
Moeller, W.;
kein Abstract vorhanden
  • Lecture (others)
    Kolloquium des Max-Planck-Institutes für Plasmaphysik, 18.04.2008, Garching/ Muenchen, Germany

Publ.-Id: 12170 - Permalink


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.
  • Lecture (others)
    Hochschul-Informationstag, 10.01.2008, Freiberg, Deutschland

Publ.-Id: 12169 - Permalink


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

Publ.-Id: 12168 - Permalink


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.
  • Poster
    DPG Frühjahrstagung, 25.-29.02.2008, Berlin, Deutschland

Publ.-Id: 12167 - Permalink


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
  • Lecture (others)
    Lange Nacht der Wissenschaften Dresden, 04.07.2008, Dresden, Germany

Publ.-Id: 12166 - Permalink


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
  • Lecture (others)
    Seminar at Carl Zeiss NTS, 07.05.2008, Oberkochen, Germany

Publ.-Id: 12165 - Permalink


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
  • Lecture (others)
    Seminar Materials Science at FZD, 28.10.2008, Dresden, Germany

Publ.-Id: 12164 - Permalink


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
  • Przeglad elektrotechniczny 84(2008)3, 72-74

Publ.-Id: 12162 - Permalink


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
  • Lecture (Conference)
    Sensor 2009, 26.-28.05.2009, Nürnberg, Germany

Publ.-Id: 12161 - Permalink


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
  • Lecture (Conference)
    Ionenstrahlphysik und Nanotechnologie, 11.-12.04.2008, Darmstadt, Germany

Publ.-Id: 12160 - Permalink


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
  • 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

Publ.-Id: 12159 - Permalink


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
  • Lecture (Conference)
    72. Jahrestagung der DPG und DPG Frühjahrstagung des Arbeitskreises Festkörperphysik, 25.-29.02.2008, Berlin, Germany

Publ.-Id: 12158 - Permalink


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 t2g4eg2 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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Publ.-Id: 12157 - Permalink


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

Publ.-Id: 12156 - Permalink


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
  • Contribution to HZDR-Annual report
    Wissenschaftlich-Technische Berichte / Forschungszentrum Dresden-Rossendorf; FZD-501 Dezember 2008, 70-76

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Publ.-Id: 12155 - Permalink


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.
  • Poster
    15th International Conference on Semiconductor Dots, 11.-16.05.2008, Gyeongju, Korea

Publ.-Id: 12153 - Permalink


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.
  • Lecture (Conference)
    9th International Conference on Applications of Nuclear Techniques, 08.-14.06.2008, Crete, Greece

Publ.-Id: 12152 - Permalink


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.
  • Poster
    The 15th International Conference on Luminescence and Optical Spectroscopy of Condensed Matter (ICL'08), 07.-11.07.2008, Lyon, France

Publ.-Id: 12151 - Permalink


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.
  • Poster
    16th Annual International Conference on Composites/Nano Engineering (ICCE-16), 20.-26.06.2008, Kunming (City of Eternal Spring), China

Publ.-Id: 12150 - Permalink


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.
  • Poster
    16th International Conference on Ion Beam Modification of Materials, 31.08.-05.09.2008, Dresden, Germany

Publ.-Id: 12149 - Permalink


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.
  • Poster
    Workshop on Recent Advances of Low Dimensional Structures and Devices (WRA-LDSD), 07.-09.04.2008, Nottingham, UK

Publ.-Id: 12148 - Permalink


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 35–40 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 blood–brain 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)

Publ.-Id: 12146 - Permalink


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
  • Invited lecture (Conferences)
    Institutskolloquium, 25.11.2008, Dresden, Deutschland

Publ.-Id: 12145 - Permalink


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
  • Lecture (Conference)
    QTRF5 - Quantum Theory: Reconsideration of Foundations, 5, 14.-19.06.2009, Vaxjo, Sweden

Publ.-Id: 12144 - Permalink


Photochemical reduction of UO22+ in the presence of alcohol studied by DFT calculations
Tsushima, S.;
A well-known photochemical process of UVIO22+ 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 UO22+ to the triplet excited state (*UO22+) followed by a significant shortening of the *UO22+-to-alcohol Oax-H distance. A charge transfer from *UO22+ to alcohol and hydrogen abstraction takes place in the following step. Consequently, UVIO22+ gets reduced to UVO(OH)2+. The photochemical byproduct RC·HOH acts further as a reducing agent toward UO22+ 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 UO22+ and the solvent molecule is the key to the photochemical reduction process.
  • Inorganic Chemistry 48(2009)11, 4856-4862
  • Lecture (Conference)
    ROBL-Radiochemie Workshop, 18.12.2008, Dresden, Germany

Publ.-Id: 12143 - Permalink


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.

Publ.-Id: 12142 - Permalink


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).
Kd’s 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
  • 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

Publ.-Id: 12141 - Permalink


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

Publ.-Id: 12140 - Permalink


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
  • Poster
    XXI Congress and General Assembly of the International Union of Crystallography, 23.-31.08.2008, Osaka, Japan

Publ.-Id: 12139 - Permalink


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
  • Poster
    16. Jahrestagung der Deutschen Gesellschaft für Kristallographie, 03.-06.03.2008, Erlangen, Deutschland

Publ.-Id: 12138 - Permalink


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.

Publ.-Id: 12137 - Permalink


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.

Publ.-Id: 12136 - Permalink


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
  • Invited lecture (Conferences)
    SPIE Photonics West, 24.-29.01.2009, San Jose, CA, USA

Publ.-Id: 12135 - Permalink


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
  • Invited lecture (Conferences)
    SPIE Photonics West, 24.-29.01.2009, San Jose, CA, USA

Publ.-Id: 12134 - Permalink


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
  • 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

Publ.-Id: 12133 - Permalink


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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Publ.-Id: 12132 - Permalink


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 singlet–singlet (4.35 eV) and triplet–singlet (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 (2.7–3.4)x1012 cm-2 and (2–4)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

Publ.-Id: 12131 - Permalink


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.
  • 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

Publ.-Id: 12130 - Permalink


Sintes prekursora alumooxidnoj keramiki, uprotschnennoj dioxidom zirkonija, is neorganitscheskich sojedinenii v prisutstvii motschevini
in Russian
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

Publ.-Id: 12129 - Permalink


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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Publ.-Id: 12128 - Permalink


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)](12) multilayer film with a total thickness of 480 nm and the substrate (VT6 alloy) under the action of low-energy (similar to 20 keV) pulsed high-current electron beam (2.5 µs, 3.5 J/cm2). 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
  • Technical Physics Letters 34(2008)10, 891-894

Publ.-Id: 12127 - Permalink


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
  • Lecture (Conference)
    14th International Conference on Thin Films & Reactive Sputter Deposition 2008, 17.-20.11.2008, Ghent, Belgium

Publ.-Id: 12126 - Permalink


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
  • Lecture (Conference)
    International School of Nuclear Physics, 22.09.2008, Erice, Italy

Publ.-Id: 12125 - Permalink


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.
  • Lecture (Conference)
    E-MRS 2008 Spring Meeting, 26.-30.05.2008, Straßburg, France

Publ.-Id: 12124 - Permalink


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 Bragg–Brentano 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
  • Poster
    14th International Conference on Thin Films & Reactive Sputter Deposition 2008, 17.-20.11.2008, Ghent, Belgium

Publ.-Id: 12122 - Permalink


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
  • Lecture (Conference)
    9th International Conference on Modification of Materials with Particle Beams and Plasma Flows, 21.-26.09.2008, Tomsk, Russia

Publ.-Id: 12121 - Permalink


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
  • Poster
    9th International Conference on Modification of Materials with Particle Beams and Plasma Flows, 21.-26.09.2008, Tomsk, Russia

Publ.-Id: 12120 - Permalink


Surface Alloying of Ti–6Al–4V 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 Ti–6Al–4V 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 (Ti–6Al–4V) 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
  • 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

Publ.-Id: 12119 - Permalink


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
  • Poster
    16th International Conference on Ion Beam Modification of Materials, 31.08.-05.09.2008, Dresden, Germany

Publ.-Id: 12118 - Permalink


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.
  • Contribution to external collection
    in: Tufas and Speleothems: Unravelling the Microbial and Physical Controls 336, London: Geological Society of London, 2009, 31-50

Publ.-Id: 12117 - Permalink


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 2–6% 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 Tersoff–Hamann 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

Publ.-Id: 12116 - Permalink


Die Mobilisierung von Actiniden durch mikrobiell produzierte Liganden unter Berücksichtigung der Endlagerung von radioaktivem Abfall
Moll, H.; Bernhard, G.;
- wird nachgereicht
  • Lecture (others)
    8. Projektstatusgespräch zur Forschungsförderung zur Entsorgung gefährlicher Abfälle in tiefen geologischen Formationen, 06.-07.05.2008, Karlsruhe, Deutschland

Publ.-Id: 12115 - Permalink


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
  • Poster
    2008 MRS Fall Meating, 01.-05.12.2008, Boston, USA

Publ.-Id: 12114 - Permalink


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

Publ.-Id: 12113 - Permalink


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 NpO22+ 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 AnO22+ 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

Publ.-Id: 12112 - Permalink


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

Publ.-Id: 12111 - Permalink


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.

Publ.-Id: 12110 - Permalink


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 (Košuta, 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 naša hipoteza je bila, da je tudi podor v Velikem vrhu posledica istega dogodka. Tako smo s pomočjo metode datiranja površinske izpostavljenosti analizirali vzorce matične kamnine v steni Velikega vrha ter vzorce s površine podornih blokov. Ugotavljali smo vsebnost 36Cl, ki se je začel tvoriti po podoru. Na podlagi poznavanja števila atomov 36Cl na gram Ca na leto izpostavljenosti, čas dogodka (podor) izračunamo iz koncentracij 36Cl izmerjenih s pomočjo pospeševalnika (AMS). Prvi rezultati kažejo, 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 izboljšati sam model in upoštevati več dejavnikov - predvsem nadmorsko višino in klimatske razmere.

There are no reliable historical data about the Veliki vrh rockfall (Košuta, 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, accelerator mass spectrometry, terrestrial cosmogenic nuclides (TCN); cosmogenic nuclide exposure dating, Veliki vrh, Karavanke Mountains
  • 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:

Publ.-Id: 12109 - Permalink


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 BCS–BEC 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

Publ.-Id: 12108 - Permalink


Transport in OFETs by surface Green functions
Morawetz, K.;
Theorieseminar TU Chemnitz
  • Lecture (others)
    Theorieseminar Professur Theorie ungeordneter Systeme, 17.12.2008, Chemnitz, Germany

Publ.-Id: 12106 - Permalink


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.
  • Poster
    International Workshop on Nonequilibrium Nanostructures, 01.-06.12.2008, Dresden, Germany

Publ.-Id: 12105 - Permalink


Phase diagram for interacting Bose systems
Maennel, M.; Morawetz, K.; Schreiber, M.;
  • Poster
    72. Jahrestagung der DPG und DPG Frühjahrstagung des Arbeitskreises Festkörperphysik, 25.-29.03.2008, Berlin, Germany

Publ.-Id: 12104 - Permalink


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
  • Poster
    International Workshop on Physics and Chemistry of FeAs-based Superconductors, Dresden, 27.-29.10.2008, Dresden, Germany

Publ.-Id: 12103 - Permalink


Quantum Kinetic Theory beyond Quasiparticle Picture - Bernoulli Potential in Superconductors
Morawetz, K.;
  • Lecture (others)
    Interviewtalk for Professorship, 16.11.2008, Loughborogh, Great Britain

Publ.-Id: 12102 - Permalink


Quantum Kinetic Theory beyond Quasiparticle Picture - Bernoulli potential in Superconductors
Morawetz, K.;
International Center for Condensed Matter Physics, Bras´ılia:
  • Lecture (others)
    International Center for Condensed Matter Physics, 29.09.2008, Brasilia, Brazil

Publ.-Id: 12101 - Permalink


Nonlocal kinetic theory
Morawetz, K.;
Talk for Professorship at University College Dublin
  • Lecture (others)
    Colloquium talk, 14.08.2008, UCD, Ireland

Publ.-Id: 12100 - Permalink


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
  • 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

Publ.-Id: 12099 - Permalink


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.
  • Article, self-published (no contribution to HZDR-Annual report)
    Forschungszentrum Rossendorf 2008
    FZD\FWS\2008\12
    12 Seiten

Publ.-Id: 12098 - Permalink


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
  • 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

Publ.-Id: 12097 - Permalink


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.

Publ.-Id: 12096 - Permalink


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
  • Lecture (Conference)
    OptoNet Workshop: Funktionale Oberflächen für optische Anwendungen, 12.11.2008, Jena, Germany

Publ.-Id: 12095 - Permalink


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
  • Lecture (Conference)
    2nd International Symposium on Transparent Conductive Oxides, 22.-26.10.2008, Hersonissos, Crete, Greece

Publ.-Id: 12094 - Permalink


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

Publ.-Id: 12093 - Permalink


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.
  • Lecture (Conference)
    The Minerals, Metals & Materials Society Annual Meeting, 09.-13.03.2008, New Orleans, USA

Publ.-Id: 12092 - Permalink


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.
  • Lecture (Conference)
    Materials Science and Engineering, 01.-04.09.2008, Nürnberg, Germany

Publ.-Id: 12091 - Permalink


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.
  • Poster
    16th International Conference on Ion Beam Modification of Materials (IBMM’08), 31.08.-05.09.2008, Dresden, Germany
  • Nuclear Instruments and Methods in Physics Research B 268(2010), 3381-3385

Publ.-Id: 12090 - Permalink


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.
  • Poster
    16th International Conference on Ion Beam Modification of Materials (IBMM’08), 31.08.-05.09.2008, Dresden, Germany

Publ.-Id: 12089 - Permalink


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.
  • Invited lecture (Conferences)
    11th International Conference on Plasma Surface Engineering, 15.-19.09.2008, Garmisch-Partenkirchen, Germany

Publ.-Id: 12088 - Permalink


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.
  • Lecture (Conference)
    2008 MRS Fall Meeting, 01.-05.12.2008, Boston, USA

Publ.-Id: 12087 - Permalink


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

Publ.-Id: 12086 - Permalink


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
  • Open Access LogoActa Physica Polonica B 39(2008), 471-476

Publ.-Id: 12085 - Permalink


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
  • Lecture (others)
    Seminar on structure analysis, 06.01.2009, Prag, Tschechische Republik

Publ.-Id: 12084 - Permalink


Tuning exchange spring magnets by ion irradiation and annealing: X-ray investigations
Roshchupkina, O.; Grenzer, J.; Fassbender, J.ORC; 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
  • Lecture (Conference)
    DPG Frühjahrstagung, 22.-27.03.2009, Dresden, Germany

Publ.-Id: 12083 - Permalink


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