Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

The plasma-enhanced chemical vapour deposition (PECVD) of amorphous hydrogenated carbon films from pulsed discharges with frequencies in the range from 50 kHz to 250 kHz was investigated. Five different hydrocarbons (acetylene C2H2, isobutene C4H8, cyclopentene C5H8, toluene C7H8 and cycloheptatriene C7H8) were probed as film growth precursors. In addition, two types of pulse-generators with somewhat different waveforms were used to power the discharges in the so called mid-frequency range. The a-C:H films deposited in a parallel-plate reactor were characterised for their thickness/deposition rate, hardness and hydrogen content. The hydrogen concentration in the films varied between 19 at.-% and 37 at.-%. With the substrate temperature held constant, it is roughly in inverse proportion to the hardness. The film with the highest hardness of 25 GPa was formed at a deposition rate of 0.8 μm/h in the C2H2 discharge at the lowest investigated pressure of 2 Pa. With increasing molecular mass of the precursor mostly weaker films were deposited. Relatively high values of both deposition rate and hardness were achieved using the precursor isobutene: a hardness of 21 GPa combined with a deposition rate of 4.1 μm/h. From the probed precursors, isobutene is also most advantageous for a-C:H deposition at higher pressures (up to 50 Pa investigated). But, as an over-all trend, the a-C:H hardness decreases with increasing deposition rate.

Die quantitative Elementanalytik von Schichten und Schichtabfolgen im Dickenbereich weniger Nanometer ist in den letzten Jahren von steigender technologischer Relevanz geworden und somit im Fokus der aktuellen Forschung. Im Mittelpunkt dieser materialwissenschaftlichen Fragestellungen steht die Bestimmung von Tiefenverteilungen von Elementen in dünnen Schichten, die durch sequentielle Abscheideverfahren oder nachfolgende Prozessschritte wie Temperung erzielt werden, aber auch der Nachweis unbeabsichtigter Kontamination. Daraus können Informationen im Hinblick auf gezielte Materialentwicklung gewonnen werden und die Qualität bestehender Prozessführungen lässt sich bewerten.
Die meisten konventionellen Analyseverfahren wie z. B. Sekundärionenmassen-spektrometrie (SIMS) sind zur Quantifizierung ihrer Ergebnisse in der Regel auf Referenzmaterialien (gleicher Matrix) angewiesen. Im Gegensatz dazu kann die Ionenstrahlanalyse (ion beam analysis, IBA) standardfrei betrieben werden. Der physikalische Prozess, auf der fast alle Methoden der IBA beruhen, ist die binäre Wechselwirkung von MeV-Ionen mit den Atomkernen in den Schichten. Diese Wechselwirkung, elastische Streuung oder Kernreaktion, ist einfach und genau beschreibbar; kollektive Matrixeffekte treten dabei nicht auf.
Am Ionenstrahlzentrum des FZD kommen hauptsächlich drei Analysemethoden zur Anwendung:
• Kernreaktionsanalyse (Nuclear Reaction Analysis, NRA) zum tiefenabhängigen Nachweis von Wasserstoff über die resonante Kernreaktion 1H(15N,αγ)12C
• Rutherford-Rückstreuspektrometrie (Rutherford Backscattering Spectrometry, RBS) insbesondere zur Detektion von Elementen mit Ordnungszahlen Z > 14
• Elastische Rückstreuanalyse (Elastic Recoil Detection, ERD) zum Nachweis leichter Elemente mit Z = 2-14 (He-Si)
Die zur Messung ultradünner Schichten mit RBS und ERD erforderliche Tiefenauflösung (< 1 nm) kann mit Teilchenspektrometern mit höchster Energieauflösung erreicht werden.

The coordination chemistry of uranium in different oxidation states has recently generated much attention due to several reasons. The most important reason is the separation of U(VI) present in radioactive waste, but also the effects of U(VI) on our environment are of great interest.[1] The extraction and separation of U(VI) and other actinides, especially the separation from lanthanides, is most difficult due to their similar chemical behavior.[2] However, the introduction of soft heteroatoms, as imine nitrogen, in the ligand systems could be used as a tool for more selective and effective binding and extraction. We have synthesized and characterized some novel U(VI) complexes using multidentate Schiff base ligands. Structures of these complexes were characterized by X-ray crystallography and DFT calculations. It is the intention of this work to determine not only the structure of these complexes but also the extraction ability of the ligands towards U(VI) and Eu(III).

Historical mining dumps are useful archives for the investigation of weathering processes. The objective of this study was to investigate the weathering behavior of waste-rock material derived from the 800 years old silver ore mining in Freiberg, Germany. For identify time-dependent weathering indices, dumped material of four dumps of different ages and corresponding rock was examined regarding the geochemical composition. The dumped material is characterized by high contents of heavy metal containing sulfidic ores, such as pyrite, arsenopyrite, sphalerite and galena. Acid mine drainage (AMD) is produced by the oxidative weathering of the sulfide minerals and causes the increased dissolving of soluble metals with increasing age of dumps. As a result of these weathering processes, a clear depletion of chalcophile elements in the older dump material (800 years) compared to the youngest dump (100 years) was observed. In the soil horizons downstream the dumps, high quantities of heavy metals (e.g., up to 12000 ppm As, 3300 ppm Pb, 640 ppm Zn), mainly adsorbed on organic matter, were determined and indicate a time-dependent element transfer from the dumps into their surrounding soils.

This paper presents a systematic investigation of an ultrashort pulse laser acceleration of protons that yields unprecedented maximum proton energies of 17MeV at a table-top Ti:sapphire laser power level of 100TW. For plain fewmicron- thick foil targets, a linear scaling of the maximum proton energy with laser power is observed and this is attributed to the short acceleration period close to the target rear surface. Although excellent laser pulse contrast was available, slight deformations of the target rear were found to lead to a predictable shift of the direction of the energetic proton emission away from the target normal that could be used for better discrimination of the low-energy part of the spectrum.

We report on the layer-resolved imaging of the magnetization dynamics of vortices in different coupling states. The study is performed using time-resolved magnetic soft x-ray microscopy. Magnetic vortices confined into micron-sized trilayer stacks offer a unique opportunity to study the coupling of magnetic moments on the nanoscopic scale. Antiferromagnetically (AFM) coupled vortices can be created within cobalt-IL-permalloy stacks, if the material of the nonmagnetic interlayer (IL) is chosen properly, with the thickness corresponding to the first antiferromagnetic maximum of the interlayer-exchange-coupling (IEC). It is known that the strength, as well as the orientation of the IEC can be modified by noble gas ion irradiation. A controlled neon irradiation of such structures leads to a successive reorientation of the IEC and eventually AFM coupled vortices can be transformed into ferromagnetically (FM) coupled ones. The response of a vortex to an alternating magnetic field depends crucially on the specific orientation of its in-plane magnetization curling (circulation) and the direction of the out-of- plane vortex core (polarization). This holds true especially for the gyrotropic mode, which corresponds to an orbiting of the core around its equilibrium position. The cores in the individual layers of a strictly FM coupled vortex pair show an in-phase motion that is similar to that of a single layer vortex. However, in the case of a vortex pair with AFM coupled in-plane magnetization an inverse sense of gyration can be detected, with highly elliptical trajectories of the individual cores. Furthermore, independent vortex core switching processes were observed in the individual layers of a vortex pair with FM coupled circulation.

The Landweber iteration approach is used to construct the radial pair distribution function (RPDF) from an X-ray absorption (EXAFS) spectrum. The physical motivation for the presented investigation is the possibility to also reconstruct asymmetric RPDFs from the EXAFS spectra. From the methodical point of view the shell fit analysis in the case of complicated spectra would be much more eased if the RPDF for the first shell(s) are computed precisely and independently. The RPDF, as a solution of the fundamental EXAFS integral equation, is examined for theoretical examples, and a detailed noise analysis is performed. As a real example the EXAFS spectrum of curium(III) hydrate is evaluated in a stable way without supplementary conditions by the proposed iteration, i.e. by a recursive application of the EXAFS kernel.

Obsidian is a natural volcanic glass, which was one of the most appreciated materials of ancient man for cutting tools and has been found in many locations far away from any natural source. Reliable provenancing can provide evidence of contacts over certain distances and information about exchange patterns and mobility of prehistoric people.
The application of analytical methods can assist to solve the problem of obsidian provenancing by means of its highly specific chemical composition, the “chemical fingerprint”. Ion Beam Analysis (IBA) measurements, combining Particle Induced X-ray Emission (PIXE), Particle Induced Gamma-ray Emission (PIGE) and Rutherford Backscattering Spectrometry (RBS), are frequently used because of their high sensitivity and the non-destructive external beam mode [1-5]. Our studies have been carried out using the 4 MeV proton beam in-air of the 5 MV Tandem accelerator of the FZD. For comparative reasons and in order to obtain additional information, all obsidian samples were analysed by Neutron Activation Analysis (NAA) at the Atominstitut in Vienna, where previous investigations of volcanic rocks and glasses have been performed successfully [6-8].
Obsidian is generally described as a relatively homogeneous material [9]. Therefore, samples from the obsidian source Demenegakion (Milos, Greece) have been analysed in order to check the actual variation range of their chemical compositions. Special attention was paid to banded obsidians to clarify, if these bands show differences in the chemical composition or if these changes in the optical properties are related to inclusions of gas bubbles, microphenocrysts or similar features without significant compositional influence. Furthermore, both the influence of the surface quality and alteration by weathering has been studied.
This study is part of a joint project to apply selected analytical methods, in particular IBA, NAA and Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry (LA-ICP-MS), to reveal a maximum of compositional differences between (geological) samples of obsidian sources available in Europe. This knowledge is essential to decide, which least invasive analytical method should be chosen for the analysis of a specific archaeological artefact, on a case by case basis.

References: [1] Bugoi R. and Neelmeijer C. NIMB 226 (2004) 136-146. [2] Mäder M. et al. NIMB 239 (2005) 107-113. [3] Mäder M. and Neelmeijer C. NIMB 226 (2204) 110-118. [4] Jembrih D. et al. NIMB 181 (2001) 698-702. [5] Mäder M. et al. NIMB 136-138 (1998) 863-868. [6] Steinhauser G. et al. Appl. Geochem. 21 (2006) 1362-1375. [7] Steinhauser G. et al. Appl. Radiat. Isot. 65 (2007) 488-503. [8] Saminger S. et al. J. Radioanal. Nucl. Chem. 245 (2000) 375-383. [9] Pollard A.M. and Heron C. (2008) Archaeological chemistry Royal Society of Chemistry, Cambridge 80–81 [2nd edition].

This experimental work is concerned with optimisation of the Czochralski crystal growth process. With respect to the shape of the solidication front and the related mono-crystalline growth, the ratio of the horizontal and the vertical temperature gradient at the triple point liquid-solid atmosphere is thought of being a crucial magnitude, which desirably should be in the order of unity. A liquid metal model experiment was therefore build that allows studying this ratio under the influence of magnetic elds applied to the melt.

Kunstwerke sind Unikate, unwiederbringliche Zeugen vergangener Zeit. Ähnlich wie Patienten können sie erkranken, unterliegen der Alterung und bedürfen der Pflege. Das Material, woraus sie bestehen und das Klima, in dem sie aufbewahrt werden, bestimmen ihr Wohlbefinden. Die Oberfläche von Kunstwerken aus Glas, zum Beispiel, kann „rosten“ wie Metall. Wenn das Glasobjekt matt und rissig erscheint, kommt Abhilfe schon sehr spät. Präventive Konservierung heißt das Zauberwort, Vorsorge also. Entscheidend dafür ist die Früherkennung von Veränderungen besser noch die Einschätzung möglicher Schädigungen. Dazu dient die zerstörungsfreie Materialanalyse. Das kann der Protonenstrahl an Luft im Zusammenspiel mit empfindlicher Messtechnik. Am Beispiel Glas, aber auch an Gemälden, Zeichnungen, Tinten auf Urkunden gibt die Präsentation Antworten auf die typischen Fragen von Restauratoren und Kunstwissenschaftlern: Wie gefährdet ist das Kunstwerk, welche Technologien hat der Künstler verwandt um bestimmte ästhetische Eindrücke zu erlangen, gibt es Anzeichen für eine Kopie anstelle des Originals?

Weltrekord in Protonenbeschleunigung mit Licht: Schnelle Protonen sind zum Beispiel für die Krebstherapie notwendig. Nicht immer kann man dabei an große Beschleunigeranlagen gehen. Forschern gelingt nun neue Bestmarke bei der Laser-Beschleunigung dieser Teilchen.

In der Bestrahlungstherapie von Tumoren spielen schnelle Teilchen eine wichtige Rolle. So können Strahlen schneller Protonen genutzt werden um Augenkrebs zu bekämpfen. Die Erzeugung solcher hochenergetischer Partikelstrahlen ist jedoch nicht nur in großen Beschleunigeranlagen möglich.

Man kann auch Laserlicht nutzen um Protonen und andere geladene Teilchen extrem zu beschleunigen. Dazu wird die Wechselwirkung des Lasers mit einem Materietarget, also einem materiellen Zielobjekt, genutzt. Dabei werden mikroskopischen Längenskalen sehr große Feldstärken erzeugt.

In einem kürzlich vorgestellten Versuch wurde ein neuer Rekordwert für diese Art von Teilchenbeschleunigung erzielt. Einem Forscherteam, an dem mehrere US-amerikanische Universitäten und Forschungseinrichtungen und das Forschungszentrum Dresden-Rossendorf (FZD) beteiligt sind, gelang es, einen Protonenstrahl mit einer Energie von 67 MeV (Megaelektronvolt) zu erzeugen.

Das entspricht der Energie, die ein Elektron oder ein Proton aufnähme, würde es mit einer Spannung von 67 Millionen Volt beschleunigt. Zum Vergleich: An Synchrotron-Beschleunigern wie etwa dam BESSY in Berlin oder PETRA III in Hamburg werden Energien erreicht, die etwa hundert bis tausend mal so groß sind.

Möglich wird die Teilchenbeschleunigung mit Licht durch die hohe Energiedichte moderner Hochleistungs-Kurzpuls-Laser. Trifft ein Puls aus einer solchen Quelle auf Materie, werden die Elektronen derartig stark beschleunigt, dass sie sich von ihren Atomrümpfen lösen.

Ein Plasma entsteht. Die endliche Ausdehnung des Lichtpulses sorgt nun dafür, dass die Elektronen nicht nur quer zur Ausbreitungsrichtung des Lasers beschleunigt werden, wie man das auch bei weniger intensivem Licht beobachtet.

Statt dessen tritt, nach dem der Puls durch die Materie gewandert ist, eine Plasmawelle aus zurückschwingenden Elektronen auf, die auch eine Komponente in Laserausbreitungsrichtung enthält.

Podcast zum Rekord für laser-beschleunigte Protonen von Kegeltargets.

An international group of physicists working at the Los Alamos Laboratory in the US has used a laser to generate 67.5 MeV protons – the highest-energy protons yet produced in this way. Their work points the way to new laser-based devices for proton therapy, which would be far smaller and cheaper than existing particle-accelerator sources.

High-Energy, short-pulse lasers can be used to accelerate ion beams. Laser-driven acceleration promises to provide very compact ion sources suitable for a variety of applications such as ion beam tumor therapy.
Up until recently, however, the ion energies observed in experiments were too low to be useful for treating tumors.
Using a novel target design, we have broken a long-lasting record for maximum proton energy measured in a laser acceleration experiment, reaching for the first time proton energies suitable for radiation therapy of intraocular tumors.
We present realistic particle-in-cell simulations of the laser interacting with the target that can explain the increase in energy seen in our experiment. The results from these simulations will help to improve the target design, paving the way towards even higher proton energies.

We present the setup for a new beam time on laser cooling of relativistic C3+ ion beams at the Experimental Storage Ring at GSI.
With laser cooling it becomes possible to reach very small relative momentum spread down to dp/p=10^-7 even at high-energy storage rings.
With new laser sources and new optical diagnostics it will become possible to detect the onset of beam ordering expected for ultra-cold ion beams.

We present the particle-in-cell code PIConGPU. This fully-relativistic plasma code utilizes the computational power of graphic processing units.
We show that it scales well even on a cluster of GPU-enhanced nodes, by interleaving the communication between the GPU and CPU and the inter-node communication with the local computation steps.

Mit der Erfindung wird eine Klasse von Bauelementen beschrieben, die es erlauben, beliebige Moden (definiert als räumliche Verteilung der elektrischen Feldstärke der Strahlung) von Terahertz-Wellen elementar zu erzeugen und in optimaler Weise, d. h. unter bestmöglicher Anpassung der Detektorgeometrie an die Mode, zu detektieren. Diese Freiheit bei der Erzeugung von Moden ist von grundlegendem Interesse für neue Anwendungen auf dem Gebiet der Terahertz-Strahlung und bringt große Vorteile bei Systemen, die Terahertz-Wellenleiter nutzen. Diese Terahertz-Emitter und -Detektoren zeichnen sich durch ihre Skalierbarkeit aus, so dass in den Emittern hohe Beschleunigungsfelder bei geringer Beschleunigungsspannung über große Flächen realisiert werden können. Damit wird der Betrieb vereinfacht und die Effizienz erhöht.

Die Erfindung beschreibt einen Si-basierten Lichtemitter, der aus einem frontseitigen Metallkontakt, einer dielektrischen Schutzschicht sowie einer Lumineszenzzentren enthaltenden SiO2-Schicht auf Silizium besteht, und derart auf SOI prozessiert wurde, dass er vorwiegend seitlich abstrahlt und sein Licht in eine Wellenleiterstruktur eingekoppelt werden kann.

This paper reports the investigation of different variables viz. specimen size, specimen geometry, crack to length ratio a/W and the sharpness of the initial crack on the Master Curve reference temperature T0. The investigations were performed on 1T-C(T) and SE(B) specimens with different thicknesses. The specimens were machined from a sections of a RPV forged ring of steel 22 NiMoCr 3 7 of the not commissioned German pressurized water reactor Biblis C.
It was found that SE(B) specimens with different sizes (specimen thickness B=0.4T, 0.8T, 1.6T, 3.2T, fatigue pre-cracked to a/W=0.5 and 20% side-grooved) have comparable T0, but with a trend to lower T0 as the size decreases. T0 is dependent on specimen type. T0 of 0.4T-SE(B) specimens is 86.1°C, 15 K below the T0 = 70.1°C of 1T-C(T) specimens. Specimens with a/W=0.3 and a/W=0.5 crack length ratios yield comparable T0. The T0 of EDM notched specimens lies 41 to 54 K below the T0 of fatigue pre-cracked specimens. This effect is observed for different specimen sizes (0.4T and 0.8T), in both SE(B) and C(T) specimen types and with different crack length ratios (a/W=0.5 and 0.3). The paper presents a first evaluation of data obtained within a larger research project. A more detailed scientific analysis of the data will follow.

Instability of magnetically driven flow in a vertical cylinder is considered in presence of a stable thermal stratification. The magnetic body force is induced by either a travelling or a rotating magnetic field. The problem models vertical gradient freeze semiconductor crystal growth of medium or large size.

The action of a two-phase inductor on the melt in a cylindrical cavity is investigated by corresponding velocity measurements in a GaInSn melt using ultrasonic Doppler velocimetry as well as local potential probes. The transition from a typical double vortex to a single toroidal vortex is shown depending on the phase shift between the two inductors.

Direct numerical simulation of turbulent flow in a straight square duct was performed in the spanwise magnetic field. Without magnetic field the turbulence can be maintained for values of the bulk Reynolds number above approximately Re = 1077 [1]. In the magnetohydrodynamic case that minimal value of the bulk Reynolds number increases with the Hartmann number. For example the flow is laminar at Re = 3000 when the Hartmann number is larger than approximately Ha = 12.3 and the flow is turbulent when the Hartmann number is equal all smaller than Ha = 12.15. The secondary mean flow structure is analyzed.

The radio frequency floating-zone growth of massive intermetallic single crystals very often fails due to an unfavourable solid-liquid interface geometry enclosing concave fringes. This interface depends on the flow in the molten zone. A tailored magnetic two-phase stirrer system has been developed enabling to control the melt flow ranging from intense inwards to outwards flows. Depending on the phase shift between the two induction coils, a transition from a double vortex structure to a single vortex structure is created at a preferable phase shift of 90°. This change in the flow field has a significant influence on the shape of the solid-liquid interface. The magnetic system was applied to the crystal growth of TiAl alloys. The segregation behaviour was studied and the experimental results were compared to samples grown with the common optical floating-zone technique.

Detailed knowledge of the flow fields in continuous casting moulds is of major importance, e.g., for the steel and the copper industry. Because there are only limited possibilities for measurements at real plant mould flows, model experiments and numerical simulations have been extensively used in the past for the inspection of mould flows. However, most data which are available in the literature are obtained at water model experiments, and most validation studies are based on those data sets. Recently, a new liquid-metal model of a continuous casting mould has been installed at the Forschungszentrum Dresden-Rossendorf. The facility allows for the first time flow measurements in liquid metal mould flows. The paper presents a first comparison of the experimental data with results from a numerical model of the mould flow. The numerical grid includes the submerged entry nozzle (SEN) and the mould. Simulations are performed with boundary conditions which fit to the operating parameters of the experiment. The Reynolds number based on the mean velocity and the hydraulic diameter of the SEN ports is about 4 x 10⁴, the Reynolds number based on the mean velocity and the hydraulic diameter of the mould cross section area is about 3 x 10³. The numerical model is based on the Reynolds-averaged Navier-Stokes (RANS) equations.

In nanostructured materials spatial confinement effects lead to structure-dependent modifications of the bulk transport properties. In part, such modifications can be accounted for by a classical master equation approach for the transport of the different charge carrier species. The rather large quantity of parameters, which enter such an approach, can more or less easily be adjusted to the dimensional characteristics and the electronic settings of the system as well as to temperature effects. On the other hand, a microscopically more detailed and mostly parameter-free picture is obtained from a quantum-mechanical treatment on the basis of the density-functional theory. An extension by a Green's function formalism allows the determination and analysis of electronic transport through contacted nanostructures. Examples will be given to demonstrate the applicability of the different approaches for dissipative and hopping transport through a regular array of nanostructures, for a mechanically triggered metal-insulator transition in nanowires, and for the enhanced conductivity at multiferroic domain walls.

Modeling the changes in materials during everyday use requires a thorough understanding of processes on length and time scales which span several orders of magnitude. Standard simulation techniques are commonly restricted to much smaller ranges in length and time, thus a method hierarchy is desirable to join the virtues of approaches at different scales and employ this synergy for a scale-adapted description of modifications which materials undergo during processing and use. Electronic interactions including optical, magnetic and transport phenomena range at the shortest, the nanoscopic time and length scales. Their proper description provides the basis for more average meso- and macro-scale quantities, thus a precise nano-scale modelling provides the basis for a detailed and quantitative understanding of the macroscopic material piece. Density-functional theory is a computationally efficient numerical tool which provides fast access to the ground-state electronic properties and perturbation expansions yield also observables for more complex physical interactions. Determination of relevant processes at the atomistic scale and suitable averaging then yields input parameters for more meso-/macro-scale particel-based or continuum approaches.

The separated flow around an inclined flat plate at a Reynolds number 10↑4 has been computed using Direct Numerical and Large Eddy Simulation. A Lorentz force oscillates near the leading edge to reduce the separated flow region and increase the lift coefficient. Since no theory on relevant spanwise length scales of this flow is known to the authors, different mesh sizes have been investigated. Lift and drag coefficients seem to converge for ratio of spanwise length to chord ≥ 0.3. Although a comparison with PIV measurements is already quite satisfactory, simulation time should be extended to allow for more reliable statistics.

Abstract too long (9790) - is not allowed from system

100J-class diode-pumped lasers (HEC-DPSSLs)
Laser materials
Spectroscopic & thermo-mech. properties
Optical Quality
PW-Laser development @ FZD
Applications
Laser electron acceleration
Laser ion acceleration

wird nachgereicht

Huminsäuren (HS), ubiquitär vorkommende organische Makromoleküle, spielen eine wichtige Rolle in geochemischen Wechselwirkungsprozessen von Metallionen. HS sind löslich im pH-Bereich natürlicher Wässer und zeigen die Fähigkeit Metallionen zu komplexieren und Kolloide zu bilden. Außerdem sind HS durch ein ausgeprägtes Redoxverhalten charakterisiert. Aufgrund dieser Eigenschaften können HS die Speziation und somit auch den Transport von Metallionen, z. B. Actinidionen, in der Umwelt beeinflussen. Detaillierte Kenntnisse der geochemischen Wechselwirkungsprozesse von HS mit Actiniden sind z. B. für Langzeitsicherheitsanalysen für zukünftige Endlager hochradioaktiver Abfälle sowie zur Sanierung kontaminierter Flächen und Einrichtungen des ehemaligen Uranbergbaus erforderlich.
Im Vortrag werden am Beispiel von Uran detaillierte Untersuchungen zur Komplexierung von Actiniden mit HS vorgestellt. Der Einfluss der Uran-HS-Komplexierung auf die Uranspeziation wird anhand von Speziationsdiagrammen diskutiert. Weiterhin wird anhand von Ergebnissen aus Sorptions- und Transportuntersuchungen der mögliche Einfluss von HS auf Immobilisierung und Migration von Uran im Tongestein diskutiert und mit anderen Actiniden verglichen.

We experimentally and numerically characterize multiple filamentation of laser pulses with incident intensities of a few TW/cm². Propagating 100 TW laser pulses over 42 m in air, we observe a new propagation regime where the filament density saturates. As also evidenced by numerical simulations in the same intensity range, the total number of filaments is governed by geometric constraints and mutual interactions among filaments rather than by the available power in the beam.

Tetravalent actinides show a strong tendency towards hydrolysis followed by the formation of oligomers and colloids. This formation process was investigated on Th(IV), U(IV) and Np(IV) species with EXAFS, LIBD, XPS, HEXS, UV-Vis, NMR and XRD. We investigated the involved chemical bonds, the local structure and structure development as well as the formation mechanism.
We observed that the oligomerization of tetravalent actinides was limited by the presence of chelating ligands. The presence of carboxylic acids, for example, resulted in hexanuclear complexes [1]. Such polynuclear species consist of a framework made of oxo and hydroxo bonds which is terminated by chelating carboxylic acids. In absence of such terminating ligands, the polymerization often continues until stable colloids are formed [2]. This formation process is kinetically hindered due to several reasons related with (a) the limited number of OH groups in the An(OH)n4-n precursor and (b) terminating water molecules. The polymerization comprises of olation and oxolation processes. At a later stage, the initially amorphous structure of the colloides undergoes an ordering process during which hydroxo groups are systematically replaced by oxo groups. Zeta potential measurements indicated that the colloidal particles carry positive charge at acidic pH and negative charge at alkaline pH. We found that silicate is able to stabilize such colloids at near-neutral pH through modification of the inner structure and by influencing the electrostatic repulsion caused by an enhanced negative surface charge.
UV/Vis, EXAFS spectroscopy and light scattering proved to be sensitive tools to differentiate between hydolysis species, oligomers and colloids.

[1] Takao et al. (2009) Eur. J. Inorg. Chem. 32, 4771-4775.
[2] Ikeda-Ohno et al. (2009) Inorg. Chem. 48, 7201-7210.

Obsidian is a natural volcanic glass which was one of the most appreciated materials by of ancient man for cutting tools and has been found by researchers in many locations, far away from any natural source. Reliable provenancing can provide evidence of contacts over a certain distance and information about exchange patterns and mobility of prehistoric people.
The application of analytical methods can solve the problem of obsidian provenancing by means of its highly specific chemical composition, the “chemical fingerprint”. Combined external Ion Beam Analysis (IBA) measurements, consisting of Proton Induced X-ray Emission (PIXE), Proton Induced Gamma-ray Emission (PIGE) and Rutherford Backscattering Spectrometry (RBS), are frequently used due to the high sensitivity and the non-destructive beam mode. Our study has been carried out at the 5 MV Tandem accelerator of the Ion Beam Centre of FZD, where a number of quantitative glass analyses has been performed simultaneously with all three external ion beam techniques [1-5].
Obsidian usually exhibits a very uniform appear-ance and is generally described as a relatively homogeneous material. Banded obsidians can be observed also, and the question was raised, if these bands are caused by differences in the chemical composition or if these changes in the optical properties are related to inclusions of clouds of gas bubbles, microphenocrysts or similar features without significant compositional influence. Therefore, a systematic investigation of a banded obsidian sample from Demengakion (Milos, Greece) has been carried out in order to check the actual variation range of the chemical composition. (Fig. 1).
To investigate the influence of different preparation techniques on the analytical results, we produced an obsidian in-house reference sample (Fig. 2). This specimen originates from the highly homogeneous obsidian source Hrafntinnuhryggur (Iceland) and features three different surfaces: natural fracture, ground finish (1200 diamond lap) and polished [6].
This study is part of a project which aim is to apply selected analytical methods, in particular IBA, Neutron Activation Analysis (NAA) and Inductively Coupled Plasma-Mass Spectrometry (ICP-MS), to detect a maximum of compositional differences between easily available samples of the natural obsidian sources in Europe. This knowledge should enable to decide, which least invasive analytical method should be chosen for the analysis of a specific archaeological artefact, on a case by case basis.
References: [1] Bugoi R. and Neelmeijer C. NIMB 226 (2004) 136–146. [2] Mäder M. et al. NIMB 239 (2005) 107-113. [3] Mäder M. and Neelmeijer C. NIMB 226 (2004) 110–118. [4] Jembrih D. et al. NIMB 181 (2001) 698–702. [5] Mäder M. et al. NIMB 136-138 (1998) 863–868. [6] Tuffen H. and Castro J. M. Journal of Volcanology and Geothermal Research 185 (2009) 352–366.

In coordination chemistry, an open question is if the structure of an aqueous metal complex is equal to the structure of its solid form. While the structure of the solid can usually be determined with great reliability and precision by XRD, determination of the structure in solution by EXAFS may be much more biased. An intrinsic problem of EXAFS shell fitting is that the radial pair distribution function (RPDF) is approximated by Gaussians functions imitating the coordination shells. Different combinations of shells can yield different structures with similar fit quality, thereby making the structural solution non-unique. Even the so-called F-test often does not allow obtaining a unique solution.
Therefore, we developed two methods which enable the direct calculation of the RPDF and the spatial structure of metal complexes in solution. Solely based on the FEFF scattering theory, the Landweber inverse method [1] yields the RPDF for the aqueous bi- and tri-nuclear U(VI)-tartaric acid complexes without predefined assumptions about the form of the RPDF. With this information and density functional theory (DFT) calculations, the spatial structures of the complexes are refined by Monte Carlo Target Transformation Factor Analysis [2], which also include the calculation of higher order scattering events. Using this combinatorial structural analysis, we were able to show that in the (UO2)3(H-1Tar)3(OH)25- complex a central equatorial oxygen atom at a radial U-O distance of 2.22 Å connects the three uranium atoms symmetrically. Consequently, the formula of the aqueous complex corresponds to its stoichiometric equivalent (UO2)3(mue3-O)(H-1Tar)35-.

[1] Rossberg & Funke (2010), J. Synchr. Rad. 17, 280-288.
[2] Rossberg et al. (2005), Anal. Bioanal. Chem. 383, 56-66.

There are many applications for which it is important to know the composition of surface layers and even to know the composition as a function of depth. Such information is needed for (ultra) shallow implantation profiles and the damage caused by implantation, diffusion barriers for IC technology, interface mixing in IBAD processing, multilayers for X-ray mirrors, magnetic multilayer structures, etc.
Ion Beam Analysis (IBA) can provide answers through a variety of methods for the compositional analysis of surface layers. In this presentation, the principles of (IBA) are presented with the emphasis on those methods useful for materials science like Rutherford Backscattering Spectrometry (RBS) and Elastic Recoil Detection Analysis (ERDA). The possibilities of analysis with our equipment is shown by means of examples of applications.

We developed a neutrally buoyant self-powered sensor particle for the measurement of spatially distributed process parameters in large vessels. One intended application is the measurement of flow parameters in stirred fermentation biogas reactors. The prototype sensor particle is a robust and neutrally buoyant capsule with integrated measurement electronics which performs logging of temperature, absolute pressure (immersion depth) and 3D-acceleration data. In an initial flow experiment the autonomous operation of the developed prototype was successfully proven, showing feasibility for future application in fermentation reactors and other industrial processes.

Plutonium is the major transuranium actinide in nuclear waste and a highly toxic environmental contaminant. As iron(II) minerals are ubiquitous and known to reduce a range of metal(loid)s, including As, Cr, Se, Pu and Np, through surface-mediated redox reactions, we investigated here the reactivity of magnetite (Fe3O4) and mackinawite (FeS) towards Pu(III) and (V) using XAFS to analyse the oxidation state and molecular structure of the reaction products.
Experimental Conditions
Mineral syntheses and reactions were carried out under anoxic conditions in N2 or Ar glove-boxes. Fe3O4 and FeS were reacted for 40 days in 0.1 M NaCl with Pu (1x10-5M) at approx. pH 8. 242Pu was added as electrolytically prepared Pu(V) to Fe3O4 and FeS, and as Pu(III) to Fe3O4.
Results and Discussion
The spectra obtained from tri- and pentavalent Pu reacted with magnetite are nearly identical; shell fitting yielded a Pu-O distance of 2.50 Å, indicative of Pu(III). Using Monte Carlo modeling of the EXAFS spectra (MC) [1], we were able to unequivocally identify a distinct Pu(III) surface complex wherein Pu(III) is connected via three oxygen atoms to three edge-sharing FeO6-octahedra of the Fe3O4 {111} face. This result is in disagreement with [2], where in the absence of spectroscopic methods Pu(IV) had been determined as the oxidation state resulting from reduction of Pu(V) by magnetite under anoxic conditions. After reaction of Pu(V) with mackinawite, Pu(IV) was identified as the prevalent Pu oxidation state by both XANES and EXAFS shell fitting. The EXAFS spectrum closely ressembles that of PuO2 solids and colloids. Our study demonstrates that under reducing conditions in geological environments both Pu(IV) and Pu(III) species may be relevant and migration as eigen-colloids or adsorbed species may play an important role in controlling Pu mobility.

Hydrogen is ubiquitous and it is often difficult to remove hydrogen from synthesis of nano-materials. Therefore, studying interaction of hydrogen with metals and semiconductors is of immense interest owing to the development of efficient materials for the storage of hydrogen and gas-sensing devices.

Photon Counting System for Time-resolved Experiments in Multibunch Mode

Das Institut für Radiochemie des Forschungszentrums Dresden-Rossendorf e.V. beschäftigt sich mit der Aufklärung des Schicksals von radioaktiven Schwermetallen in der Umwelt. Hierzu werden u. a. sowohl die Bindung an natürlich vorkommende Liganden untersucht, als auch die komplexeren Wechselwirkungen in Pflanzen- und Bakterienzellen oder in Biofluiden. Die vorgestellte Promotionsarbeit befasst sich dabei mit der spektroskopischen Aufklärung der Bindungsform von Curium(III) und Europium(III) in natürlichem, menschlichem Urin.
Curium und Europium sind zwei f-Elemente, deren Metabolismus im Biosystem bis heute nicht vollständig geklärt ist. Da Curium innerhalb des Kernbrennstoffzyklus gebildet wird und nur radioaktive Isotope aufweist, stellt es im Falle einer Kontamination oder unfallbedingter Freisetzung in die Umwelt eine ernste Gefahr für die Gesundheit dar. Um mögliche Dekontaminationsmittel zu erforschen, müssen daher sein Metabolismus und die Bindungsform in Biofluiden bekannt sein. Im Gegensatz dazu ist Europium nicht radioaktiv und gewinnt in der Medizin immer mehr an Bedeutung als Bestandteil von Kontrastmitteln in der bildgebenden Diagnostik. Trotz seiner wachsenden Applikation ist auch der Metabolismus dieses Metalls bisher unbekannt. Beide Elemente weisen ähnliche Eigenschaften auf, da sie in Form ihrer dreiwertigen Ionen vergleichbare Elektronenkonfigurationen besitzen. Aufgrund seiner besseren Handhabbarkeit wird Europium daher oft als Analogon für Curium verwendet. Darüber hinaus zeigen beide Elemente einzigartige Fluoreszenzeigenschaften. Dies erlaubt Untersuchungen mittels (zeitaufgelöster) laserinduzierter Fluoreszenzspektroskopie im Spurenkonzentrationsbereich.
Urin ist das Hauptausscheidungsmedium im menschlichen Körper und besteht zu über 90 % aus Harnstoff. Mögliche Reaktionen mit dieser Matrixkomponente wurden daher zuerst untersucht. Weitere biologisch relevante, organische Liganden, deren Komplexbildungsvermögen gegenüber Curium(III) und Europium(III) ebenfalls untersucht wurde, sind Citronensäure und Aminosäuren. Die Ergebnisse zeigen, dass die Komplexirung mit Harnstoff vernachlässigbar gering ist und Aminosäuren bei physiologisch relevanten pH-Werten ebenfalls nur schwache Komplexe bilden. Demgegenüber bildet Citronensäure starke Komplexe mit beiden Metallen.
Erste Aufnahmen von Lumineszenzspektren natürlicher, menschlicher Urinproben, die in vitro mit einem der beiden Elemente versetzt wurden, zeigen, dass bei niedrigeren pH-Werten Komplexe mit Citronensäure dominieren. Im Gegensatz dazu scheinen bei höheren pH-Werten Komplexe mit anorganischen Liganden, vorzuherrschen.

We describe experiments and microscopic modelling based on density matrix theory to study the relaxation dynamics in graphene. Experiments using the free-electron laser at FZD include also experiments in magnetic fields which will show how Landau quantization can quench relaxation channels.

We present FELBE, the free-electron laser at FZD and discuss time-resloved experiemnts using its radiation. Furthermore we discuss tabletop terahertz sources based on surface emitters and scalable photoconductive emitters.

We present a novel approach to overcome efficiency limitations of nanosecond lasers based on Yb-doped materials. Furthermore, we introduce a combination of bulk and thin-disk design for power scaling of diode-pumped lasers.

Humic acid (HA) model substances with pronounced redox functionality were synthesized by oxidation of hydroquinone or catechol in the presence of glycine or glutamic acid and characterized concerning their elemental, structural and functional properties. In order to characterize the redox properties of the synthetic products, formal redox potentials and Fe(III) reducing capacities were determined and compared to purified Aldrich HA (AHA). Furthermore, the reduction of U(VI) in the presence of HA was studied.
The synthetic products show elemental, functional and structural properties comparable to natural HA, however, they are characterized by high amounts of phenolic/acidic OH groups. Furthermore, the synthetic HA show significantly higher reducing capacities for Fe3+ and [Fe(CN)6]3- at pH 3.0 and at pH 9.2, respectively, than AHA. The highest reducing capacities were obtained for HA Cat-Gly, an oxidation product from catechol and glycine, which is characterized by the lowest formal redox potential of all studied HA. Indications for a slight reduction of U(VI) in the presence of HA were observed, whereby, HA Cat-Gly exhibits again the highest reducing capacity. Using modified HA with blocked phenolic/acidic OH groups the importance of these functional groups for the redox behavior of HA was confirmed.
Synthetic HA with pronounced redox functionality can be used to study the redox behavior of HA and the redox stability of metal ions in the presence of HA and furthermore, to stabilize redox-sensitive metal ions against oxidation in complexation and transport studies with HA. This contributes to a better understanding of interaction processes of metal ions with humic substances in soils, sediments and waters.

Germanium is currently considered as a potential replacement for silicon devices [1]. The formation of heavily doped, shallow junctions in Ge by ion im-plantation and appropriate annealing techniques is under investigation [2, 3]. In contrast to Si the Ge surface is severely affected by irradiation damage. Im-plantation into the uncovered Ge surface leads to sur-face roughening and even porous layers [3]. Therefore, the Ge surface must be protected by a thin cover layer, which is commonly a sputtered SiO2-layer between 10 and 30 nm. This cover layer remains on the Ge sample also during annealing. For light dopants like B or P this oxide layer remains stable and smooth. However, with increasing ion mass and fluence surface erosion and oxide degradation can occur. A relatively heavy ion of interest is Ga [3]. It is a shallow acceptor with a high solid solubility in Ge. We studied the effect of Ga im-plantation through a SiO2 cover layer.

High-spin states in 73Kr were studied at the XTU tandem accelerator of the Laboratori Nazionali di Legnaro using the reaction 40Ca(40 Ca,2pn) at a beam energy of 185 MeV. Gamma rays were detected with the EUROBALL spectrometer. Particle detection enabled us to identify the reaction channel leading to 73Kr. The yrast bands of positive and negative parity were established up to probable spins of 61/2+ and 63/2- , respectively. The energies of the two identified bands agree well with the predictions of the configuration-dependent Cranked Nilsson-Strutinsky approximation and indicate that the nucleus remains collective up to the maximum spins of the respective high-spin configurations. The positive-parity band represents one of the rare cases where band non-termination at the highest spin of the configuration could be established experimentally.

The last ten years witnessed a strong research activity into so called PT Quantum Mechanics (PTQM) --- a Quantum Mechanics whose Hamiltonians are allowed to be non-Hermitian but PT-symmetric. In general, PTQM has sectors of exact PT-symmetry with purely real energy spectrum as well as sectors of spontaneously broken PT-symmetry with pairwise complex conjugate energy branches. Sectors of exact PT-symmetry can be isomorphically mapped into models of conventional (von Neumann) Quantum Mechanics (possibly of highly nonlocal type). Sectors of spontaneously broken PT-symmetry might have realizations as certain effective quantum systems. Varying the coupling parameters of PTQM models the corresponding quantum system can undergo phase transitions from exact PT symmetry to spontaneously broken PT-symmetry. Such PT phase transitions are associated with branch points (exceptional points) of the energy spectrum --- so called spectral singularities.

In the talk two PTQM models and their behavior in the vicinity of spectral singularities will be discussed.

In the first part of the talk, I will report on the quantum brachistochrone problem for PTQM, i.e. the problem of finding a PT-symmetric Hamiltonian which minimizes the time needed for evolving a given initial state into a predefined final state (e.g. for a spin-flip). This problem was solved by Bender, Brody, Jones and Meister in 2007. It turned out that in PTQM the evolution time for a spin flip can be tended toward zero so that the Aharonov-Anandan lower bound on the evolution time for Hermitian systems would be violated --- a kind of "quantum wormhole" effect. In 2007 we showed that this effect occurs in the vicinity of a PT phase transition (a spectral singularity). A still open problem at that time was a possible scheme for an experimental realization, because one somehow would have to switch between PTQM and experimental setups based on conventional QM. In [Phys. Rev. Lett. 101, 230404, 2008] we solved this switching problem by embedding the PTQM brachistochrone into a higher dimensional Hilbert space. In this way we found a realization of the PTQM brachistochrone evolution as a special kind of tuned unitary evolution in a highly asymmetrically entangled two-qubit setup --- which in principle might be realized experimentally in the nearest future.

The second part of the talk will be devoted to a non-Hermitian PT-symmetric two-mode Bose Hubbard model which might describe e.g. a BEC in a double-well potential with additional well-balanced gain-loss couplings. The main focus is laid on the unfolding of the higher-order spectral singularities typical for this kind of models. A perturbative Newton polygon technique allows us to qualitatively explain the numerically obtained branching behavior of the energy spectrum. It turns out that the Hessenberg type of the effective coupling matrix is responsible for the special Galois structure of the occurring eigenvalue rings in the complex energy plane.

Sb exists in nature in a wide range of oxidation states and can be a potential hazardous contaminant depending on its speciation and reactivity. In this study we employed cryogenic-XPS and XAS techniques in order to understand the reduction of SbV at the surface of mackinawite (FeS) as a function of pH and surface loading.
Experimental Conditions
Nanoparticulate, Mackinawite samples were prepared and stored as suspensions under strictly anoxic conditions (~ 1 ppmv O2) in a Jacomex glovebox. Sorption experiments at pH 5 and pH 8 with increasing Sb concentrations (0.1, 0.3, 0.6, 0.8 mM) were also conducted in the same glovebox under anoxic conditions [1, 2]. X-ray Photoelectron Spectroscopy (XPS) and X-ray Absorption Spectroscopy (XAS) measurements were conducted on frozen wet pastes of reacted mackinawite samples.
Results and Discussion
Sb3d XPS spectra of reacted sample series at pH 5 revealed presence of increasing amounts of SbIII at the surface suggesting that the rate of reduction of SbV was directly proportional to surface loading. Corresponding Fe 2p ans S 2p spectra of the same samples showed significant increase in the proportion of FeIII species and presence of S0 at the surface. However, the proportion of S0 remained constant suggesting that Fe is the dominant redox partner in this sytem. At pH 8, presence of SbIII was only observed at higher surface loadings indicating that adsorption and redox processes both occur at much slower rate compared to that at pH 5. In addition, increased contribution of surface monosulfide group at pH 5 suggest that Sb is most likely bound to S atoms at the surface, which was confirmed by Sb K-edge EXAFS spectra. In contrast, at pH 8, such increase in surface monosulfide contributions are absent, suggesting Sb is most likely bound to O atoms at the surface.

Active polymer substrates have found their way in the semiconductor industry as a base layer for flexible electronics, as well as in sensor and actuator applications. The optimum performance of these systems may be affected by dirt adsorbed on its surface, which can also originate mechanisms for the degradation of the polymer. Titanium dioxide (titania) semiconductor photocatalytic thin films have been deposited by unbalanced reactive magnetron sputtering on one of the most applied and investigated electroactive polymer: poly(vinilidene fluoride), PVDF In order to increase the photocatalytic efficiency of the titania coatings, a reduction of the semiconductor band-gap has been attempted by using a nitrogen doping. Rutherford Backscattering Spectroscopy was used in order to assess the composition of the titania thin films, whereas Heavy Ion Elastic Recoil Detection Analysis provided the evaluation of the doping level of nitrogen. X-ray Photoelectron Spectroscopy provided valu!
able information about the cation-anion binding within the semiconductor lattice. The photocatalytic performance of the titania films have been characterized by decomposing an organic dye illuminated with combined UV/visible light.

Die Plasma-Immersion-Ionen-Implantation (Pl3) von Fluor, das aus z. B. einem CH2F2-Plasma generiert wurde, in die Oberfläche von TiAl-Bauteilen kann deren Oxidationsbeständigkeit im Temperaturbereich von 700 bis 1100°C an trockener und feuchter Luft oder anderen oxidierenden Atmosphären auch unter Temperaturwechselbeanspruchung gegenüber unbehandelten TiAl-Legierungen deutlich erhöhen. Entgegen dem bisherigen Kenntnisstand, wo nur die reinen Halogene verwendet wurden, lässt sich durch Verwendung von z. B. Difluormethan oder Tetrafluorkohlenstoff ein deutlich vereinfachter Ionen-Implantationsprozess durchführen als bei reiner Fluorimplantation, ohne eine Beeinträchtigung des positiven Fluoreffekts zu erzielen. Das Fluor wird in kontrollierbaren Mengen in die Oberflächenrandzone von TiAl-Bauteilen implantiert, wo es seinen positiven Effekt auf den Oxidationswiderstand entfaltet.

Die Erfindung betrifft eine Vorrichtung zur Auswertung einer in einem bewegten Zielobjekt auftretenden Aktivitätsverteilung, welche durch einen mit einer Bestrahlungseinrichtung erzeugten Strahl erzeugbar ist, aufweisend:

• einen Positronen-Emissions-Tomographen, welcher ausgebildet ist zum Aufzeichnen von durch den Strahl im Zielobjekt erzeugten Photonen und zur Erzeugung von Messdaten, welche Entstehungsorte der Photonen repräsentieren,
• eine Bewegungserfassungseinrichtung, welche ausgebildet ist, ein Bewegungssignal zu erzeugen, das die Bewegung des Zielobjekts repräsentiert,
• eine Auswertungseinheit, welche ausgebildet ist, die Entstehungsorte der gemessenen Photonen zu Positionen im Zielobjekt unter Verwendung des Bewegungssignals zuzuordnen, wodurch eine räumliche Charakteristik der tatsächlich im Zielobjekt erzeugten Aktivitätsverteilung über die durch den Strahl erzeugten Photonen auswertbar ist, sowie eine Bestrahlungsanlage und ein Verfahren, in welchen eine derartige Vorrichtung eingesetzt wird.

In many areas of material sciences hydrogen analysis is of particular importance. For example, hydrogen is most abundant as impurity in thin-film materials - depending on the deposition process - and has great influence on the chemical, physical and electrical properties of many materials. Therefore, it is necessary to monitor the H-concentration by depth profiling. Best-suited methods for depth-resolved hydrogen analysis are ion beam techniques such as elastic recoil detection analysis (ERDA) and nuclear reaction analysis (NRA). In principle, both methods can be performed as primary - reference material free - methods.
The most common method, NRA, makes use of the 6385 keV resonance of the 1H(15N,αγ)12C nuclear reaction. The correct quantification of the depth scale in the measured hydrogen profiles essentially relies on accurate stopping power values, i.e. any imperfection in the stopping power values is influencing all H-values provided by NRA. For the determination of the accurate stopping power of ~6.4 MeV 15N ions in hydrogen-containing amorphous Si-layers (a-Si:H), we have, therefore, combined NRA with X-ray reflectometry (XRR), also a primary method.
The samples are prepared by magnetron sputtering of a-Si in an Ar/H2-atmosphere on a Cr-layer, which is needed as contrast material for XRR. The energy loss in the layers is measured by NRA at FZD. The layer thickness, density and roughness are determined by XRR using synchrotron radiation. XRR measurements were performed at the electron storage ring BESSY at the hard X-ray beamline BAMline. The beam was monochromatised to 10 keV using a Si [111]-double-crystal monochromator. The reflected photons of the θ-2θ-scans from the 6-circle goniometer are counted by a scintillation detector and a photodiode, respectively. Data analysis is performed by the IMD 4.1 software package.
The unique combination of results from NRA and XRR allows the accurate calculation of the mass stopping power independent of the density of the material. Our preliminary results show significant discrepancies in the order of 15-20% to the commonly used stopping powers calculated by the well accepted SRIM program (version 2006). These discrepancies have to be considered, if transforming the energy loss scale to a depth scale in hydrogen profiles. Thus, further work for confirmation is absolutely needed.
Acknowledgments: The help of D. Grambole and S. Merchel (FZD) is greatly appreciated.

Der Arbeitskreis „Analytik mit Radionukliden und Hochleistungsstrahlenquellen“ (ARH) wird gemeinsam von den GDCh-Fachgruppen „Nuklearchemie”, „Analytische Chemie”, „Makromolekulare Chemie“, „Festkörperchemie und Materialforschung“ und der „Wöhler-Vereinigung für Anorganische Chemie“ getragen. Der ARH Vorstand setzt sich aus Synchrotron-, Neutronen- und Ionen-Experten zusammen und steht hiermit in direktem Bezug zum SNI2010. Der Arbeitskreis setzt sich die Förderung und den Einsatz von Radionukliden zur Qualitätssicherung von Analysenverfahren und die Analytik mit Großgeräten zum Ziel. Zurzeit strebt der ARH-Vorstand insbesondere eine Vertiefung von Kontakten zu anderen wissenschaftlichen Vereinigungen wie dem „Komitee für Synchrotronstrahlung“ (KFS) und dem Komitee Forschung mit nuklearen Sonden und Ionenstrahlen (KFSI) an. Ein weiterer Schwerpunkt ist die (Fort-)Bildung sowie der Wissenstransfer und der Erfahrungsaustausch in Form von wissenschaftlichen Tagungen und Seminaren. Zum Beispiel finden das 23. SAAGAS („Seminar Aktivierungsanalyse und Gammaspektroskopie“) im September 2009 und der Workshop „Ionenstrahlphysik“ im März 2010 in Dresden statt. In dieser Posterpräsentation werden der Arbeitskreis ARH, seine Arbeitsschwerpunkte und Ziele sowie zukünftige
Aktivitäten dargestellt.

Das Forschungszentrum Dresden-Rossendorf (FZD) erweitert diesen Sommer sein Portfolio um eine weitere hochsensitive analytische Methode: die Beschleunigermassenspektrometrie (accelerator mass spectrometry, AMS). Die AMS ermöglicht insbesondere die Bestimmung langlebiger Radionuklide mit Halbwertszeiten im Bereich von ka bis Ma.

Entgegen der sonst allgemein üblichen Zerfallszählung warten die „ungeduldigen AMS-Wissenschaftler“ dabei nicht auf den Zerfall des Radionuklids und die Detektion des durch den Zerfall emittierten Teilchens bzw. der Strahlung. Vielmehr werden die noch nicht zerfallenen Radionuklide wesentlich effizienter massenspektrometrisch bestimmt. Die AMS besitzt allerdings gegenüber der konventionellen Massenspektrometrie den Vorteil, dass sie Störsignale, hervorgerufen von Molekülionen oder Ionen ähnlicher Masse, insbesondere Isobare, effektiver unterdrücken kann. Die AMS liefert somit weitaus niedrigere Nachweisgrenzen als die konventionellen Methoden.

Im Gegensatz zu den in Deutschland und Europa gängigen niederenergetischen AMS-Anlagen, die sich hauptsächlich auf die Bestimmung des Radiokohlenstoffs (¹⁴C) spezialisiert haben, wird die AMS-Anlage des FZD - DREAMS (DREsden AMS) - als erste moderne Anlage in der EU mit einer Terminalspannung von 6 MV betrieben werden. Sie ist somit prädestiniert zur effizienten und hochempfindlichen Analyse der Radionuklide ¹⁰Be, ²⁶Al, ³⁶Cl, ⁴¹Ca und ¹²⁹I (t_1/2=0,1-15,7 Ma).

Die Einführung der AMS wird die interne Vernetzung der FZD-Forschungsaktivitäten im Bereich Materialforschung, Strahlenphysik, Radiochemie und Radiopharmazie vorantreiben. Darüber hinaus wird die AMS aber auch externen Nutzern zur Verfügung stehen. Die möglichen Arbeitsgebiete sind vielfach und multidisziplinär. So haben die instrumentellen Weiterentwicklungen auf dem Gebiet der AMS, die Anwendungsfelder der Methode stark ausgeweitet. Die anfänglich bevorzugt untersuchten Proben aus der Kosmochemie, Astrophysik und Kernreaktionsdaten, werden zunehmend von Proben aus den Bereichen Strahlenschutz, Nuklearsicherheit, Nuklearentsorgung, Radioökologie, Phytologie, Ernährungswissenschaften, Toxikologie und Pharmakologie verdrängt.

Zudem hat die AMS vor allem in den Geo- und Umweltwissenschaften in den letzten Jahren an Bedeutung gewonnen. Mittels kosmogener Radionuklide können relativ plötzlich aufgetretene prähistorische Ereignisse wie Vulkanausbrüche, Bergstürze, Tsunamis, Meteoriteneinschläge und Erdbeben datiert werden. Die Quantifizierung von geomorphologischen Vorgängen wie Erosion und Flusseinschnitte über lange Zeiträume, sowie hydrogeologische Studien sind ebenfalls möglich. Mittels der Datierung von Gletscher-bewegungen und Untersuchungen an Eisbohrkernen können zudem Klimaveränderungen rekonstruiert und Klimamodelle für die Zukunft validiert werden.

Nach dem Motto „Ready for dreams for DREAMS“ sehen wir gespannt den neuen AMS-Möglichkeiten am FZD und den damit verbundenen interdisziplinären Kooperationen, vor allen Dingen auch im Bereich der Helmholtz-Gemeinschaft, entgegen.

The stability of a thermally stratified liquid metal flow is considered numerically. The flow is driven by the rotating magnetic field in a cylinder heated from above and cooled from below. The stable thermal stratification turns out to destabilise the flow. This is explained by the fact that a stable stratification suppresses the secondary meridional flow, thus indirectly enhancing the primary rotation. The instability in the form of Taylor-Görtler rolls is consequently promoted. It is known from earlier studies that these rolls can be only excited by finite disturbances in the isothermal flow. A sufficiently strong thermal stratification transforms this non-linear bypass instability into a linear one reducing, thus, the critical value of the magnetic driving force. A weaker temperature gradient delays the linear instability but makes the bypass transition more likely. We quantify the non-normal and non-linear components of this transition by direct numerical simulation of the flow response to noise.
It is observed that the flow sensitivity to finite disturbances increases considerably under the action of a stable thermal stratification. The capabilities of the random forcing approach to identify disconnected coherent states in a general case are discussed.

The version of fusion driven system (FDS), a sub-critical fast fission assembly with a fusion plasma neutron source, theoretically investigated here is based on a stellarator with a small mirror part. In the magnetic well of the mirror part, fusion reactions occur from collision of an RF heated hot ion component (tritium), with high perpendicular energy with cold background plasma ions. The hot ions are assumed to be trapped in the magnetic mirror part. The stellarator part which connects to the mirror part provides confinement for the bulk (deuterium) plasma. Calculations based on a power balance analysis indicate the possibility to achieve a net electric power output with a compact FDS device. For representative thermal power output of a power plant (P (th) a parts per thousand P (fis) = 0.5-2 GW) the computed electric Q-factor is in the range Q (el) = 8-14, which indicates high efficiency of the FDS scheme.

Bacterial envelope proteins, so called surface layers (S-layer) are widely spread paracrystalline surface structures which coat the cells of lots of bacterial strains and as universal attribute of all archaea. They are mostly composed of protein monomers which form via self-assembling high regular two dimensional arrays on the cells as well as on surfaces and interfaces after their isolation. The S-layer proteins we investigate are from bacterial strains recovered from the uranium mining waste pile “Haberland” in Saxony, Germany. Their special S-layer proteins selectively bind uranium and protect the cells from its toxicity. These special S-layer characteristics make them interesting for many technological applications such as filter materials, biosensors, as functional surfaces, or for example as drug containers.
In order to produce surface layer proteins in a high efficient way a heterologous expression in Escherichia coli is essential. In our study, the S-layer-like protein SllB of Lysinibacillus sphaericus JG-A12 was expressed in E. coli Bl21 (DE3). Noteworthy, recombinant protein production resulted in a high stability of the cells against mechanical and chemical treatment. These unusual cells were analyzed by light microscopy, AFM and TEM.
All methods demonstrated a total changed cell morphology. The cells formed long filaments in the beginning of the exponential growth stage and started to form 5-200 µm long tube like transparent structures at the end of the exponential growth stage, which contained E. coli single cells. These tube-like structures were isolated and analyzed by SDS-PAGE, N-terminal sequencing and infra red spectroscopy. The analyses showed that the tube-like structures consist of outer membrane associated with recombinant surface layer proteins. These findings point to a disordered cell division. However, the underlying mechanisms of these morphological changes are not known and will be analyzed in future. Investigations of supernatant proteins and proteins of periplasmic space in combination with enzyme assays demonstrate a transport of recombinant proteins that is not caused by cell damage. The long filaments, in combination with high expression level, good growth and high stability make these unusual E. coli cells interesting for biotechnological applications. In addition, these results cast a new light on one of the best studied microorganisms.

Currently, the HADES spectrometer undergoes un upgrade program to be prepared for measurements at the upcoming SIS-100 synchrotron at FAIR. We describe the current status of the HADES di-electron measurments at the SIS-18 and our future plans for SIS-100.

Abstract-We apply scanning probe microscopy (SPM) to study the morphology and electrical properties of vertical zinc oxide nanorods grown by hydrothermal methods on silicon substrates. It is demonstrated that – against the intuition – SPM techniques can indeed be used to study such fragile high-aspect ratio semiconductor nanorods. Atomic-force microscopy (AFM) operating in tapping mode yields - via the analysis of the height histograms calculated from AFM images - easy access to the height fluctuations in the nanorod ensemble. High-resolution AFM images reveal the three-dimensional shape of the nanorods including transition facets between the (0001) top terrace and the {10-10} side facets. Further, we were able to acquire currentvoltage curves of individual nanorods by conductive atomic force microscopy (CAFM) operating in contact mode.

The main objective of the present paper is to communicate a study of defects behavior in zirconia-based nanomaterials—pressure-compacted yttria-stabilized zirconia (YSZ) nanopowders with different contents of Y2O3 and ceramics obtained by sintering the YZS nanopowders. In addition, YZS single crystals were also investigated. Positron annihilation techniques including positron lifetime and coincidence Doppler broadening with a conventional positron source and Doppler broadening experiments on a monoenergetic positron beam were involved in this study as the principal tools. These techniques were supplemented with transmission electron microscopy and x-ray diffraction observations. In order to get better support of the experimental data interpretation, the state-of-art theoretical calculations of positron parameters were performed for the perfect ZrO2 lattice and selected defect configurations in the YSZ. Theoretical calculations have indicated that neither the oxygen vacancies nor their neutral complexes with substitutional yttrium atoms are capable of positron trapping. On the other hand, the zirconium vacancies are deep positron traps and obviously are responsible for the saturated positron trapping observed in the YSZ single crystals. In the compacted YSZ nanopowders, a majority of positrons is trapped either in the vacancylike defects situated in the negative space-charge layers along grain boundaries (τ1≈185 ps) or in vacancy clusters at intersections of grain boundaries (τ2≈370 ps). The intensity ratio I2/I1 was found to be correlated with the mean grain size d as I2/I1∼d−2. A small fraction of positrons (≈10%) form positronium in large pores (τ3≈2 ns, τ4≈30 ns). A significant grain growth during sintering of the YSZ nanopowders above 1000 °C was observed.

We present a detailed study of the thermal evolution of H ion-induced vacancy related complexes and voids in bulk GaN implanted under ion-cut condition. By using transmission electron microscopy, we found that the damaged band in as-implanted GaN is decorated with a high density of nanobubbles of ~1-2 nm in diameter. Variable energy Doppler broadening spectroscopy showed that this band contains vacancy clusters and voids. In addition to vacancy clusters, the presence of VGa, VGa-H2, and VGaVN complexes was evidenced by pulsed low energy positron lifetime spectroscopy. Subtle changes upon annealing in these vacancy complexes were also investigated. As a general trend, a growth in open volume defects is detected in parallel to an increase in both size and density of nanobubbles. The observed vacancy complexes appear to be stable during annealing. However, for temperatures above 450ºC, unusually large lifetimes were measured. These lifetimes are attributed to the formation of positronium in GaN. Our finding contradicts the prevalent belief that the formation of postronium is not possible in a semiconductor. Based on the Tao-Eldrup model, the lattice opening during thermal annealing was quantified. We found that a wall spacing of 0.4 nm is induced by annealing at 600ºC. The role of these complexes in the sub-surface microcraking is discussed.

The contactless inductive flow tomography (CIFT) aims at reconstructing the velocity field in electrically conducting melts from externally measured induced magnetic fields. One of its possible applications is the velocity reconstruction in the continuous casting process. In this paper, we apply this method to the flow field in a small model (containing approximately 1.4 liters of the eutectic alloy GaInSn) of a mould for thin slab casting. It is shown that the flow structure in general, and the jet position and intensity in particular, can be reliably determined from magnetic field data using only a modest number (in the order of 5) of sensors.

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Using small animal PET with ⁶⁸Ga-radiolabeled human albumin microspheres (Ga-68-microspheres), we investigated the effect of posture on regional pulmonary blood flow (PBF) in normal rats. This in vivo method is noninvasive and quantitative, and it allows for repeated longitudinal measurements. The purpose of the experiment was to quantify spatial differences in PBF in small animals in different postures. Two studies were performed in anesthetized, spontaneously breathing Wistar rats. Study 1 was designed to determine PBF in the prone and supine positions. Ga-68-microspheres were given to five prone and eight supine animals. We found that PBF increased in dorsal regions of supine animals (0.75) more than in prone animals (0.70; P = 0.037), according to a steeper vertical gradient of flow in supine than in prone animals. No differences in spatial heterogeneity were detected. Study 2 was designed to determine the effects of tissue distribution on PBF measurements. Because microspheres remained fixed in the lung, PET was performed on animals in the position in which they received Ga-68-microsphere injections and thereafter in the opposite posture. The distribution of PBF showed a preference for dorsal regions in both positions, but the distribution was dependent on the position during administration of the microspheres. We conclude that PET using Ga-68-microspheres can detect and quantify regional PBF in animals as small as the rat. PBF distributions differed between the prone and supine postures and were influenced by the distribution of lung tissue within the thorax.

In our comment some essential issues concerning determination of arterial input function (AIF), cardiac and respiratory related motion artifacts, contrast agent application and compartmental model fitting done by Cao et al., 2009 are discussed.

The present study aimed to investigate cerebral activation following intranasal trigeminal chemosensory stimulation using O15-H2O-PET. A total of 12 healthy male participants underwent a PET scan presented with four scanning conditions; two left-sided intranasal CO2-stimuli and two matched baseline conditions consisting of odorless air. CO2 was used as it produces burning and stinging sensations. Stimulation started 20 s before intravenous injection of the isotope and lasted for the first 60 s of the 5 min scan time. A comparison between CO2 and baseline showed a pronounced activation of the trigeminal projection area at the base of the postcentral gyrus (primary and secondary somatosensory cortex) which was more intense for the right hemisphere, contralateral to the side of stimulation. In addition, activation was also found in the piriform cortex which is typically activated following odor presentation and thus thought of as primary olfactory cortex. In conclusion, and in line with previously published work, our data suggest that intranasal trigeminal stimulation not only activates somatosensory projection areas, but that it also leads to activation in cerebral areas associated with the processing of olfactory information. This may be interpreted in terms of the intimate relation between the intranasal chemosensory systems.

We studied quantitatively the effects of the discontinuity introduced in an otherwise homogeneous background by the cold walls of the standard spherical glass inserts commonly used in phantom measurements for calibration of
threshold-based approaches to volumetric evaluation of PET investigations. We concentrated especially on the question of threshold-based volume determination. We computed analytically the convolution of an isotropic Gaussian point-spread function with the insert geometry (hot sphere + cold wall + warm background) and derived the theoretical background dependence of the volume reproducing threshold. This analysis shows a clear wall-related reduction of the optimal threshold with increasing background. The predictions of our theoretical analysis were verified in phantom measurements at background fractions between 0 and 0.29. Defining the background-corrected relative threshold T = T_abs−B ./. A−B (T_abs: absolute volume reproducing threshold, A: measured activity at centre, B: background), we find that for a wall-less sphere T is independent of the background level. In the presence of cold walls, T drops (for not too small spheres, where recovery at the centre approaches 100%) from about 43% at B/A = 0 to about 25% at B/A = 0.5. Applying these thresholds towall-less spheres leads to sizeable overestimates of the true volumes (43% at B/A = 0.5 for a sphere of 6 ml volume). We conclude that phantom measurements with standard sphere inserts for calibration of optimal thresholding algorithms introduce a systematic bias if performed at finite background levels. The observed background dependence is an artefact of the measurement procedure and does not reflect the conditions present in actual patient investigations.

The dipole response of the doubly-magic 208Pb was studied in a photon-scattering experiment at the electron linear accelerator ELBE with bremsstrahlung produced at a kinetic electron energy of 14.0 MeV. The present (gamma,gamma') data combined with (gamma,n) data from literature are compared with results of calculations using a quasiparticle random-phase approximation and with results of shell-model calculations. It turns out that the shell model describes the experimental low-lying E1 strength as well as the giant dipole resonance well by applying a small spreading width only.

For increasing the predictability of equipment and improving efficiency of production, there is a high demand to develop a compact and efficient mathematical model capable of modelling the complex bubbly flow structures which frequently occur in large-scale industrial engineering systems. A generalized Average Bubble Number Density (ABND) transport equation model in conjunction with three forms of bubble coalescence and breakage kernels was implemented and incorporated into commercial software ANSYS CFX 11. The main focus of this paper is to assess the overall performance of the ABND model and the three different bubble mechanism kernels under a large-scale gas-liquid bubbly flow system. Based on the high-quality TOPFLOW database for airwater two-phase flows in a large vertical pipe with nominal diameter of 195.3mm, experimental data were strategically selected for model validation. To examine the relative merits and drawbacks of three forms of coalescence and breakage kernels, model predictions of
local radial distributions of bubble rise velocity, volume fraction and bubble size were compared against experimental results. The capabilities in predicting the “core peak” volume fraction profiles and evolution process of bubble rise of different kernels were discussed.

Bacterial surface layer protein polymers (S-layers) are excellently suited for the development of a wide range of novel nano-structured biocomposite materials. The presentation summarizes current developments at the Institute of Radiochemistry as starting point for an intensive discussion of their application potential, marketability and general market needs.

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Die Erfindung beschreibt ein Herstellungsverfahren von Halbleiterstrukturen auf Silizium-Germanium-Basis. Durch die Germanium-Ionenimplantation und die anschließende Bestrahlung mit einem Lichtimpuls können die Germanium legierten Gebiete kurzzeitig und lokal aufgeschmolzen werden und die entstandenen Schäden während der Implantation an den Profilkanten ausgeheilt werden. Dadurch wird eine erhöhte Effizienz und rationellere Produktion erreicht, die vor allem bei der Produktion von Solarzellen verwendet werden kann. Weiterhin können mit diesem Verfahren verspannte Silizium-Halbleiterstrukturen hergestellt werden.

Compared to conventional ion implantation, focused ion beam (FIB) implantation works with a current density which is up to five orders of magnitude higher. This has an effect on the accumulated radiation damage during the implantation process. The present work shows how the radiation damage is influenced by the dwell-time in the case of focused ion beam synthesis (IBS) of cobalt disilicide. If the accumulated damage during implantation is not too high the use of conventional ion implantation IBS results in single-crystalline CoSi2 layers

Computer simulation and RBS/C studies of high-dose N + and Al + co-implantation in 6H-SiC

A series of experimental and theoretical investigations has been initiated for 6H–SiC samples sequentially implanted with high doses of N⁺(65 keV) + N⁺(120 keV) + Al⁺(100 keV) + Al⁺(160 keV) ions at temperatures between 200 and 800 °C. Nitrogen and carbon distribution profiles are measured by ERD and structural defect distributions are measured by Rutherford backscattering with channeling. A comparison between the experimental data and the results of computer simulation yields a physical model to describe the relaxation processes of the implanted SiC structure, where the entire implanted volume is divided into regions of different depth, having different guiding kinetics mechanisms.

Thermal wave measurements on 6H-SiC with a particular emphasis on Al+ and Al+/N+ implanted 6H-SiC was carried out. The 6H-SiC wafers were implanted at different substrate temperatures. The photothermal measurements of the conversion coefficient K and the reflectivity R show a strong dependence on the implantation temperature. This result is discussed in relation to Rutherford backscattering spectrometry/ion channeling measurements. The behaviour of the reflectivity in dependence on the implantation conditions could be modelized by using a simple two layer optical model. The carried out investigations of the implanted SiC demonstrate, that photothermal methods are suitable for both research and on-line production use.

Im Rahmen eines Promotionsvorhabens wurde erstmalig ein hochpräziser und räumlich hochauflösender Computertomograph für industrielle Anwendungen entwickelt. Das Messsystem umfasst eine leistungsstarke Cs-137 Isotopenquelle, einen hochgenauen, driftfreien 320-kanaligen Gammastrahlendetektor sowie eine automatisierte rotatorisch-translatorische Stelleinheit. Der Computertomograph dient vorrangig der Untersuchung von Strömungsprozessen in technischen Anlagen und Strömungsmaschinen und kommt darüber hinaus auch in der zerstörungsfreien Prüfung schwerer Bauteile zur Anwendung. Der Schwerpunkt im Systemdesign wurde auf eine hohe Nachweiseffizienz des Strahlendetektors sowie Unempfindlichkeit gegenüber elektromagnetischen Feldern und Umgebungstemperaturänderungen gelegt.

The effects of high dose ion irradiation through an amorphous surface layer on single crystalline 6H–SiC at 500°C are studied in detail. Material swelling, subsequent densification, surface erosion and recrystallization are quantified. The results demonstrate that undisturbed epitaxial regrowth of an amorphous surface layer on (0001)-oriented 6H–SiC cannot be achieved at this temperature by ion irradiation. The shift of the amorphous/crystalline interface observed by RBS/C analysis is a consequence of columnar regrowth and surface erosion. The columnar growth starts inside the heavily damaged transition region between the amorphous surface layer and the single crystalline bulk material. It is stopped by random nucleation. Neither the interface roughness nor the kind of impurity atoms influence the thickness of the columnar layer.

In this paper we discuss ion-beam-assisted nanocrystal nucleation in amorphized silicon (a-Si) layers produced by high-dose implantation of Pb+ and Bi+. (100)-oriented Si wafers were implanted at room temperature (RT) with 50 keV Pb+ and Bi+ ions at doses ranging from 5E13 to 1E18 cm−2 and a constant ion current density of 10μAcm−2. The resulting structures were studied by conventional transmission electron microscopy (CTEM), high resolution transmission electron microscopy (HRTEM) and Rutherford backscattering spectroscopy (RBS) in combination with computer simulations. The dynamics of the ion-beam-induced crystallization of new phases and precipitates evolution in the implanted layer were studied as a function of implant dose. It is established that the front of the new phase crystallization (cubic Pb and hexagonal Bi nanocrystals) starts approximately at the peaks of the implanted species profiles; the crystallography of the nucleated nanocrystal is examined as a function of the dose.

(100) Si was implanted at 150 or 100 keV with fluences from 5 E 15 to 2 E16 cm^-2. The samples were processed by rapid thermal annealing at temperatures between 1000 and 1200°C and dwell times at T(max) from 1 to 30 s. As depth distributions were measured by RBS and SIMS. By comparison of experimental profiles with computer simulations based on the diffusion model proposed by Tsai et al. and including a time independent enhancement factor or a transient enhancement according to Fair a transient enhanced diffusion has been found. The influence of As clustering or precipitation on the diffusion behaviour of high concentrations is discussed. The comparison of samples implanted through 30 nm SiO2 or in bare Si shows an enhanced As concentration at the SiO2 interface and a decreased diffusivity for the former case. These effects are explained by an interaction of As with oxygen recoil atoms.

Amorphous silicon layers deposited by chemical vapour deposition on monocrystalline silicon substrates partly covered with silicon dioxide to produce SOl structures were epitaxially recrystallised by ion beam induced epitaxial crystallisation at 400 C after preamorphisation of the transition region layer/substrate. The implantation with a dose of 5E17 cm-2 into the wafers with SOl structure resulted in a 1.5 um wide overgrown crystalline layer.

Doping effects after carbon implantation at 0 .33 and 10 MeV were investigated at silicon wafers with different oxygen content. No distinct influence of the oxygen concentration on the carbon induced doping effect was found for rapid thermal annealing at 1250°C for 30 s whereas for furnace annealing at 1000°C the doping effect is higher for Czochralski-grown silicon wafers with their higher oxygen content. The gettering efficiency of a buried carbon implanted layer for additionally introduced iron atoms was investigated by deep level transient spectroscopy. Gettering sets in at a dose of 10E14 cm² and is completed for a carbon dose of 1E16 cm² for iron doses up to 1E13 cm². The microstructure of such a buried layer is characterised by a narrow band of dark contrast containing mainly stacking faults of the extrinsic type .

Thermoelectromagnetic convection in electrically conducting cubic containers was studied experimentally. Two opposing side walls were cooled and heated, respectively, to produce a uniform temperature gradient. Inhomogeneous magnetic field distributions were achieved either with a small permanent magnet located above the melt layer, or with specifically shaped pole shoes of the magnetic system. Ultrasonic Doppler velocimetry measurements demonstrated that even a moderate temperature gradient may drive a distinct convection. Two different flow regimes were investigated with the permanent magnet. When it was positioned in the vicinity of an isothermal wall, with its direction of magnetisation parallel to the temperature gradient, a single vortex spreading the whole container developed while the flow might be assessed as relatively stable. Moving the magnet to the centre led to a modified distribution of the magnetic field which, in turn, altered the flow structure. The convective pattern changed to four vortices and the velocity fluctuations were intensified. A more generic case was realised with the pole shoes providing a gradient of the magnetic field only in one direction. Since the strength of the field could be raised significantly above that provided by the small permanent magnet and the area of impact onto the melt was larger, developed turbulent regimes were accomplished. Numerical results obtained for the Lorentz force and the rotor thereof support the experimental findings.

Synthesis of a highly conductive surface layer on 6H-silicon carbide was achieved by high-dose, room temperature implantation of tungsten at 200 keV. Subsequently, the samples were annealed in two steps, namely at 500°C and 950°C. ‘I%e influence of both dose and annealing on the reaction of W with Sic was investigated. Rutherford Backscattering Spectrometry (RBS), X-Ray Diffraction (XRD) and Auger Electron Spectroscopy (AES) contributed to study the structure and composition of the layer as well as the chemical states of the elements. During implantation sputtering becomes significant for doses exceeding 1.0 X 10” cm- ‘. Formation of tungsten carbide and silicide is already observed in the as-implanted state. An annealing temperature of 950°C is necessary to crystallize tungsten carbide. However, tungsten silicide remains amorphous at this temperature. Therefore, a mixture of polycrystalline tungsten carbide and amorphous tungsten silicide develops under these conditions. The resistivity of such a layer implanted with 1.0 E17 W+ cm² and annealed at 950°C is 565 uohmcm.

The formation of a novel (SiC)1-x(AlN)x compound (x=0.2) at low temperatures within the miscibility gap of the SiC/AlN phase diagram by hot, high-dose co-implantation of N+ and Al+ ions into 6H±SiC substrates is investigated. The compound layers have been studied by Rutherford backscattering spectrometry/ion channelling (RBS/C), Auger electron spectroscopy (AES), polarized infrared re¯ection spectroscopy (PIRR) and cross sectional electron microscopy (XTEM) and the temperature dependence of their fabrication has been examined. An optimum temperature window has been established within which the structure of the synthesized material retains good crystallinity during implantation.

SiC(1-x)AlN(x) has been prepared by ion co-implantation of Nqand Alqinto a 6H-SiC n-type wafer. The substrate temperature during implantation was varied from 200°C to 800°C in order to reduce the damage created by ion implantation. The obtained structures have been investigated by Slow Positron Implantation Spectroscopy (SPIS). and Rutherford Backscattering and Ion Channeling (RBS). Both methods are sensitive to different kinds of defects and the results are complementary. The defect structures determined by SPIS and RBSrC are presented and the influence of the variation of the substrate temperature is discussed.

A theoretical model is developed which allows to describe the defect evolution in silicon carbide implanted with high doses of nitrogen and aluminium ions and subsequently annealed to form a solid solution. The diffusion of defects, the formation of complexes of defect clusters and the influence of the internal elastic stress fields produced by the implanted ions and the complexes formed are taken into account. Results from the simulations have been correlated with data obtained by Rutherford backscattering spectrometry/ion channelling (RBS/C).

Vortrag im Rahmen der Reihe Dresdner Vertriebsfrühstück

Several approaches to suppress a non-stationary melt flow and related fluctuations of the temperature and the dopant concentration in bulk crystal growth by means of external magnetic fields are presented. The paper includes results of model and growth experiments carried out in Bridgman- or Czochralski-like configurations under the influence of different fields (rotating, traveling, axial steady, cusp, combinations of which). It is shown that both time-dependent and steady fields can be used to stabilize a melt. The impact of a magnetic field on the melt flow, however, depends strongly on the configuration and thermal conditions of the growth. Therefore, type and parameters of the applied field have to be properly adjusted to the particular setup under consideration to achieve an optimal damping of fluctuations and to avoid unfavorable effects.

We consider three versions of recently developed contactless flowrate sensors: the well-known magnetic flywheel, a newly developed phase-sift sensor based on an applied alternating magnetic field, and a new force-free sensor based on a rotating single magnet. Comparative measurements were performed at a GaInSn-loop.

An Euler-Euler approach has been employed to investigate the effects of varying flow rate of argon gas and static magnetic field on the flow pattern in a slab mold. The mathematical model is based on the k − ǫ turbulence model and coupled with the MHD model in CFX. In this work, three dimensional localized DC magnetic fields were constructed and calculated by a finite element method and then imported into CFX. The results show that a static magnetic field does not always slow down the bulk flow, but occasionally gives rise to large eddies for increasing magnetic field strengths. In principle, the injection of Argon gas is able to suppress the fluctuation of the free surface and to reduce the penetration depth significantly. However, gas bubbles may produce a reversed flow surrounding the nozzle at the meniscus if large bubbles float up rapidly in the case the flow rate ratio of argon gas to molten steel reaches a certain value. The MUSIG (multiple size group) model considering coalescence and breakup of bubbles provides an effective tool to solve the multiphase flow and to get insight into the flow pattern in a continuous casting mold with argon gas injection.

In reflux cooling, steam generated in the reactor core and water condensed in a steam generator (SG) form a countercurrent flow in a hot leg, which consists of a horizontal pipe, an elbow and an inclined pipe. At Forschungszentrum Dresden-Rossendorf (FZD), both countercurrent air-water and steam-water tests were previously carried out using the 1/3rd scale rectangular channel simulating a PWR hot leg installed in the pressure chamber of the TOPFLOW facility. In this paper, in order to evaluate the effects of fluid properties, numerical calculations for the steam-water CCFL tests at FZD were conducted using the CFD code, FLUENT6.3.26. The numerical calculation region included the reactor vessel simulator, hot leg and SG inlet chamber, in order to avoid uncertainties of boundary conditions at both ends of the hot leg. The VOF (volume of fluid) model or two-fluid (2F) model was used. In the 2F model, we used the combination of three correlations on the interfacial friction coefficients as a function of void fractions, which had been validated for the 1/15th and 1/5th scale tests at Kobe University. The CCFL characteristics calculated by the 2F and VOF models agreed with the steam-water CCFL data at FZD and showed the same trends with the data for fluid properties.

Hexagonal barium ferrites were deposited onto sapphire substrates by radio frequency magnetron sputtering. The composition, microstructure, and magnetic properties of these isotropic thin films were investigated with Rutherford backscattering spectroscopy, X-ray diffraction, atomic force microscopy, magnetic force microscopy and SQUID magnetometry. The intrinsic coercivity of the films reaches about 11.5 kOe at room temperature. The mechanism of the coercivity is proposed to be nucleation in the decoupled single domain nanometer particles as shown by the characteristics of the magnetic domains and the virgin magnetization curves.

Air-water CCFL (countercurrent flow limitation) tests were previously carried out at Kobe University using the 1/5th scale rectangular channel and 1/15th scale circular tube simulating a PWR hot leg. Then numerical calculations for these tests and full-scale PWR conditions were made using the CFD code, FLUENT6.3.26. At Forschungszentrum Dresden-Rossendorf (FZD), similar tests were previously carried out for both air-water and steam-water flows using the 1/3rd scale rectangular channel simulating a PWR hot leg installed in the pressure chamber of the TOPFLOW facility.
In this paper, numerical simulations for the air-water CCFL tests of FZD using FLUENT6.3.26 are presented and compared with the experimental data obtained at Kobe University and FZD. In the calculations, the VOF (volume of fluid) model or two-fluid (2F) model was used. In the 2F model, we used the combination of three correlations on the interfacial friction coefficients as a function of void fractions, which had been validated for the 1/15th and 1/5th scale tests at Kobe University. Calculation parameters were the air flow rates and air inlet locations, which were at the top of the reactor vessel simulator simulating the FZD test facility (inlet 1) and the opposite side of the hot leg junction simulating the test loops at Kobe University (inlet 2). Conclusions were as follows : (1) the calculated CCFL characteristics using the 2F model for the FZD tests agreed well with the 1/15th scale circular tube data obtained at Kobe University and the calculated results for full-scale PWR conditions, which supported the validity of the 1/3rd scale rectangular channel to simulate CCFL in circular tubes; (2) there were no significant differences between the calculated CCFL characteristics with the air inlet 1 and inlet 2, which indicated that the air inlet location did not influence CCFL behavior in a hot leg; and (3) comparison with the FZD data showed that the calculations using the 2F and VOF models overestimated the water flow rates for deflooding.