Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

The 14N(p,gamma)15O reaction is the bottleneck of the hydrogen burning CNO cycle. Recent studies of this reaction at E < 500 keV have led to a revision of the S-factor value. However, also data at higher energy are necessary to predict the extrapolated S-factor at energies of astrophysical interest. Here we report on a new study of the E = 0.987MeV (Ex = 8.284MeV) resonance carried out at the high-current FZD Tandetron in Dresden. Solid TiN targets and four escape-suppressed HPGe detectors have been used.

The elastic properties of Mo₂BC were studied using ab initio calculations. The calculated bulk modulus of 324 GPa is by 45% larger than that of Ti_0.25Al_0.75N and 14% smaller than that of c-BN indicating a highly stiff material. The bulk modulus (B) to shear modulus (G) ratio is with 1.72 at the transition from brittle to ductile behavior. This, in combination with a positive Cauchy pressure (c12-c44), suggests moderate ductility. When compared to a typical hard protective coating such as Ti_0.25Al_0.75N (B = 178 GPa; B/G = 1.44; negative Cauchy pressure) Mo₂BC displays great potential as protective coating for metal cutting applications. In order to test this proposal, Mo₂BC thin films were synthesized using DC magnetron sputtering from three plasma sources on Al₂O₃(0001) at a substrate temperature of ~900°C. The calculated lattice parameters are in good agreement with values determined from xray diffraction. Measured Young’s modulus values of ~460±21 GPa are in excellent agreement with the 470 GPa value obtained by calculations. Scanning probe microscopy imaging of the residual indent revealed no evidence for crack formation as well as significant pile-up, which is consistent with the moderate plasticity predicted. The apparent contradiction between moderate ductility on one hand and indentation hardness values of 29 GPa can be understood by considering the electronic structure particularly the extreme anisotropy. The presence of stiff Mo-C and Mo-B layers with metallic interlayer bonding enables this intriguing and unexpected property combination.

The atomic layer deposition growth of BaB₂O₄ thin films was investigated using Ba(Tp^Et2)₂ and water as precursors between 240 and 400 °C. The process provided uniform films and exhibited a large ALD window between 250 and 375 °C, in which a constant growth rate of 0.23 Å/cycle was observed.

Since 2007, the Dresden High Magnetic Field Laboratory (Hochfeld-Magnetlabor Dresden, HLD) operates as a user facility, providing unique experimental possibilities in pulsed fields. The HLD offers various measurement techniques, such as electrical transport, magnetization, magnetostriction, ultrasound, and magnetic resonance. A particular feature of the laboratory is the next-door free-electron-laser installation used for high-field infrared spectroscopy cyclotron resonance, as well as electron spin resonance (ESR) in pulsed fields. Additionally nuclear magnetic resonance (NMR) and specific-heat measurement techniques are being developed in pulsed magnetic field. As the only laboratory in Europe, the HLD has reached magnetic fields of about 87 T. This field range is accessible now for experiments in modern materials research. Several 60 T and 70 T magnets are regularly used by in-house and external users as well. A two-coil 100 T prototype and a long-pulse (1000ms) 60 T magnet are ready for their first tests. Some recent scientific results on strongly correlated electron systems, nanostructures, low dimensional spin system, and high-Tc superconductors will be highlighted. Novel experimental techniques such as pulsed NMR in pulsed magnetic fields and technical applications for pulsed magnets will be demonstrated.

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Multiferroic rare-earth manganites have attracted much attention because of the coexistence of ferroelectric and magnetic orders. Geometrical frustrations appear to be one of the most important factors contributing to the multiferroicity. Combining conventional far-infrared Fourier-transform and multi-frequency electron spin resonance (ESR) spectroscopy techniques, magnetic excitations in hexagonal multiferroic YMnO₃ in the antiferromagnetically (AFM) ordered phase have been studied. The gap in the excitation spectrum, about 42 cm^-1, has been observed directly. A fine structure of AFM resonance absorption was revealed by means of ESR, which can be explained taking into account a finite interaction between the neighboring Mn³⁺ layers. Our observations has allowed us to refine spin-Hamiltonian parameters, emphasizing the role of interlayer interactions in this frustrated compound.

The successful use of picosecond-pulse free-electron-laser (FEL) radiation for the continuous-wave THz-range electron spin resonance (ESR) spectroscopy has been demonstrated. The unique combination of two linac-based FELs [1] (covering the wavelength range of 4 - 250 μm) with high magnetic fields at the Research Center Dresden-Rossendorf (FZD) allows for tunable-frequency ESR spectroscopy in a frequency range of 1.2 - 75 THz in magnetic fields up to ~ 70 T with a spectral resolution better than 1% [2]. The new approach is of particular importance for studying magnetic excitations in spin systems with a large zero-field splitting and materials exhibiting field-induced phenomena. The performance of the spectrometer is illustrated with ESR spectra obtained in the low-dimensional organic material (C6H9N2)CuCl3 and the multiferroic compound YMnO3††.

Multiferroic rare-earth manganites have attracted much attention because of the coexistence of ferroelectric and magnetic orders. Among hexagonal manganites, the largest magnetoelectric effect was found in HoMnO3, which is ferroelectric below Tc = 875 K and antiferromagnetically ordered below TNMn = 75 K (Mn subsystem). In addition, at TNHo ~ 5 K the Ho subsystem undergoes a transition into an antiferromagnetically ordered state. The coupling between the ferroelectric and antiferromagnetic order parameters in HoMnO3 has not been yet unambiguously explained, revealing the importance of geometrical frustrations and a complex interplay between Ho and Mn magnetic subsystems [1, 2]. Here, the magnetic excitation spectrum in high-quality single-crystalline samples of HoMnO3 was probed by means of X-band (9.3 GHz) electron spin resonance spectroscopy. A relatively strong absorption was found below 5 K, which corresponds to the temperature of the magnetic ordering of the Ho subsystem. The observed mode exhibits a very pronounced anisotropic behavior and can be interpreted as excitations within the antiferromagnetically ordered Ho subsystem.

In this study we used scanning force microscopy in order to determine size and density of Ge nanocrystals embedded in a 100 nm SiO2 layer. Wet chemical etching was utilized in order to uncover the clusters. Sample preparation was accomplished by Ge+ implantation with 70 keV with doses of 1e16cm-2 and 3e16cm-2. Annealing was performed in N2 ambient at 1050°C for 30 or 120 s, respectively. The elemental distribution before and after the annealing was examined by Rutherford backscattering spectrometry. For the surface analysis AFM images in scanning areas of 1x1 μm² and 500x500 nm² were recorded with a DI Nanoscope III. Through a variation of the etching time a tomographic information about the nanocrystal properties was obtained. The density of the nanoparticles exhibits a maximum of 1e11cm-2 for the highly implanted samples, and of 4e10cm-2 for the samples with lower implantation dose. The samples were also analyzed by transmission electron microscopy (TEM). Results and the unequal preparative effort were compared and discussed.

The electronic transport of electrons and holes through stacks of dicyano-dibutyl- quaterthiophene (DCNDBQT) as part of a novel organic ferroic field-effect transistor (OFFET) is investigated. The novel application of a ferroelectric instead of a dielectric substrate provides the possibility to switch bit-wise the ferroelectric domains and to employ the polarization of these domains as a gate field in an organic semiconductor. A device containing very thin DCNDBQT films of around 20 nm thickness is intended to be suitable for logical as well as optical applications. We investigate the device properties with the help of a phenomenological model called multilayer organic light-emitting diodes (MOLED), which was extended to transverse fields. The results showed, that space charge and image charge effects play a crucial role in these organic devices.

PET is a modern technique for imaging of pathological processes in vivo and a powerful tool in radiopharmaceutical research. The chemistry of the short lived radiotracers ¹⁸F-fluorine and ¹¹C-carbon requires special labelling practices and instruments, as well as new approaches of radiolabelling. The lecture presents recent results in the development of PET radiotracers in Rossendorf for research and gives a short glance on the routine production of PET-radiopharmaceuticals for the clinic.

We report upper critical field Bc2(T) data for LaO0.9F0.1FeAs1- δ in a wide temperature and field range up to 60 T. The large slope of Bc2≈- 5.4 to -6.6 T K-1 near an improved Tc≈28.5 K of the in-plane Bc2(T) contrasts with a flattening starting near 23 K above 30 T we regard as the onset of Pauli-limited behaviour (PLB) with Bc2(0)≈63–68 T. We interpret a similar hitherto unexplained flattening of the Bc2(T) curves reported for at least three other disordered closely related systems, Co-doped BaFe2As2, (Ba,K) Fe2As2 and NdO0.7F0.3FeAs (all single crystals), for applied fields Hpar(a,b), also as a manifestation of PLB. Their Maki parameters have been estimated by analysing their Bc2(T) data within the Werthamer–Helfand–Hohenberg approach. The pronounced PLB of (Ba, K)Fe2As2 single crystals obtained from an Sn flux is attributed also to a significant As deficiency detected by wavelength dispersive x-ray spectroscopy as reported by Ni et al (2008 Phys. Rev. B 78 014507). Consequences of our results are discussed in terms of disorder effects within conventional superconductivity (CSC) and unconventional superconductivity (USC). USC scenarios with nodes on individual Fermi surface sheets (FSS), e.g. p- and d-wave SC, can be discarded for our samples. The increase of dBc2/dT|Tc by sizeable disorder provides evidence for an important intraband (intra-FSS) contribution to the orbital upper critical field. We suggest that it can be ascribed either to an impurity-driven transition from s± USC to CSC of an extended s++-wave state or to a stabilized s±-state provided As-vacancies cause predominantly strong intraband scattering in the unitary limit. We compare our results with Bc2 data from the literature, which often show no PLB for fields below 60–70 T probed so far. A novel disorder-related scenario of a complex interplay of SC with two different competing magnetic instabilities is suggested.

In dieser Arbeit wird die Erzeugung permanenter Nanostrukturen durch den Beschuss mit langsamen (v < 5x105m/s) hochgeladenen (q < 40) Ionen auf den Oberflächen der Ionenkristalle CaF2 sowie KBr untersucht. Die systematische Analyse der Probenoberfläche mittels Raster-Kraft-Mikroskopie liefert detaillierte Informationen über den Einfluss von potentieller und kinetischer Projektilenergie auf den Prozess der Strukturerzeugung. Der individuelle Einfall hochgeladener Ionen auf der KBr(001)-Oberfläche kann die Erzeugung monoatomar tiefer, lochartiger Strukturen -Nanopits- mit einer lateralen Ausdehnung von wenigen 10nm initiieren. Das Volumen dieser Löcher und damit die Anzahl gesputterter Sekundärteilchen zeigt eine lineare Abhängigkeit von der potentiellen Energie der Projektile. Für das Einsetzen der Locherzeugung konnte ein von der Projektilgeschwindigkeit abhängiger Grenzwert der potentiellen Energie E_grenz^pot (Ekin) gefunden werden. Auf der Basis der defekt-induzierten Desorption durch Elektronen wurde unter Einbeziehung von Effekten der Defektagglomeration ein konsistentes mikroskopisches Modell für den Prozess der Locherzeugung konzipiert. Für die CaF2(111)-Oberfläche kann die aus jüngsten Studien bekannte, individuelle Erzeugung hügelartiger Nanostrukturen -Nanohillocks- durch hochgeladene Ionen in dieser Arbeit auch für kleinste kinetische Energien (E_kin < 150eVxq) verifiziert werden. Die potentielle Energie der einfallenden Ionen wird damit erstmalig zweifelsfrei als alleinige Ursache der Nanostrukturerzeugung identifiziert. Zudem zeigt sich bei geringer Projektilgeschwindigkeit eine Verschiebung der potentiellen Grenzenergie zur Hillock-Erzeugung. Im Rahmen einer Kooperation an der Technischen Universität Wien durchgeführte Simulationsrechnungen auf der Grundlage des inelastischen thermal spike-Modells zeigen, dass die individuelle Hillock-Erzeugung durch hochgeladene Ionen mit einer lokalen Schmelze des Ionenkristalls verknüpft werden kann. Dem essentiellen Einfluss der Elektronenemission während der Wechselwirkung des hochgeladenen Ions mit der Oberfläche auf den Prozess der Nanostrukturerzeugung wird in komplementären Untersuchungen zur Sekundärelektronenstatistik Rechnung getragen. Erstmalig werden dabei Gesamtelektronenausbeuten für Isolatoroberflächen bei kleinsten Projektilgeschwindigkeiten (v < 1x10^5 m/s) bestimmt. Für Geschwindigkeiten v < 5x10^4 m/s findet sich für die Isolatoroberfläche in starkem Kontrast zu Metallen ein signifikanter Abfall der Elektronenausbeute mit sinkender kinetischer Energie. Mögliche Ursachen dieses Effektes werden auf der Grundlage unterschiedlicher Modelle diskutiert.

Die Erhebung räumlich verteilter Prozessparameter in großtechnischen Behältern, wie Rührkesselreaktoren oder Schüttgutbehältern, ist für die Untersuchung und Optimierung von verfahrenstechnischen Anlagen und Prozessen von großer Bedeutung. Die Messung und die Überwachung solcher Prozesse werden jedoch durch den eingeschränkten Zugang zu den Behältern oft erschwert. Herkömmliche Messsonden werden üblicherweise nur lokal installiert und räumlich auflösende Apparate, wie Kameras oder Tomografen, sind oft nicht anwendbar oder zu teuer. Aus diesen Gründen gewinnen autonome Sensortechnologien zunehmend an Interesse.
Zur Erhebung von Prozessparametern in einem Biogasfermenter wurde das Konzept auftriebsneutraler autonomer Sensorpartikel entwickelt. Der vorhandene Prototyp besteht aus einer Elektronik zur Messung und Speicherung der Daten von drei miniaturisierten Messfühlern, welche zusammen in einer robusten Kapsel eingehaust sind (Abb. 1a). Bei der Auswahl der Sensoren wurden zunächst die grundlegenden Prozessparameter Temperatur, Druck und Beschleunigung berücksichtigt, um erste Rückschlüsse auf die Hydrodynamik und den Prozessverlauf im Fermentationsbehälter zu ziehen. Das System kann durch weitere Sensoren erweitert werden. Als Temperatursensor für den Bereich 10…70°C wird ein NTC-Thermistor verwendet. Die Druckmessung im Bereich 0…200 kPa erfolgt mit einem piezoresistiven Druckaufnehmer. Die Beschleunigung wird mittels eines linearen 3D-MEMS-Inertialsensors erfasst. Der Betrieb des autonomen Sensors wird von einem Mikrocontroller gesteuert, in dem ein Energiemanagement mit mehreren Betriebszuständen implementiert ist. Im autonomen Messregime erfasst der autonome Sensor einen Datensatz aller Messfühler in einem benutzerdefinierten Intervall zwischen 100 ms und 60 s, speichert die Daten im EEPROM-Speicher (4 x 1 Mbit) und wechselt dann automatisch in einen Schlafmodus zurück, wodurch eine längere Laufzeit erzielt wird. Die Versorgungsspannung (3,3 V) wird über eine NiMH-Akkuzelle (600 mAh, 1,2 V) und einen DC-DC-Wandler bereitgestellt. Bei einer Messfrequenz von 1 min-1 ist eine Laufzeit von ca. 100 Tagen realisierbar. Die Parametrierung des Sensors und das Auslesen der EEPROMs nach dem Ausscheiden aus dem Prozess erfolgt über ein Bluetooth-Funk-Modul. Die Auftriebsneutralität des autonomen Sensors kann bei Bedarf manuell eingestellt werden. Dabei wird eine isolierte und definierte Menge Metallgranulat im Gehäuse platziert, um das Sensorgewicht an die mittlere Dichte des Prozessmediums anzupassen. Diese Anpassung ist notwendig, damit sich der Sensor frei mit der strömenden Flüssigkeit im Prozess mitbewegen kann.
In einem ersten Experiment wurde die autarke Funktionsweise des Sensors getestet. Der beschwerte Sensor wurde in einem mit Wasser befüllten vertikalen Rohr (Höhe 1,4 m), in welchem eine Temperaturschichtung vorhanden war, manuell auf- und abbewegt. Mit zunehmender Eindringtiefe in die Flüssigkeit ist demnach eine Abnahme der Temperatur zu erwarten und umgekehrt. In Abb. 1b ist der gemessene Zeitverlauf der Temperatur und der aus dem hydrostatischen Druck ermittelten Eindringtiefe dargestellt. Wie in der Auf- und Abtauchphase deutlich zu erkennen ist, wurde der zu erwartende Verlauf beider Größen durch die Messung eindeutig abgebildet. In einem nächsten Schritt soll der Sensor in dem Modell eines Biogasfermenters mit Rührwerk getestet werden.

We implanted 57Fe with 5x1016 ions/cm² into SnO2 films containing 0.1% Sb and 3% Sb at the substrate temperature of 500°C in vacuum. As a result, four kinds of subspectra were observed in the DCEM spectra by using a back scattered type of gas counter. Two doublets are assigned to paramagnetic Fe3+ and Fe2+ species and two sextets are assigned to site A and site B of magnetite. Magnetite formation was found to prefer the top layer, whereas paramagnetic Fe2+ species were included in the deeper layer of the films. SnO2 (with 0.1% and 3% Sb) films doped with 5x1016 57Fe ions/cm² at 500°C and post-annealed at 400°C for 6 h showed bulk ferromagnetism at room temperature although the 57Fe implanted SnO2 (3% Sb) film showed smaller Kerr effect than the 57Fe implanted SnO2 (0.1% Sb) film. This phenomenon was attributed mainly to the amount of magnetite in the as prepared samples and to the maghemite in the post-annealed samples, respectively, in addition to magnetic defects.

Large research facilities, such as the Forschungszentrum Dresden-Rossendorf, provide a scientific work environment for employees, guests and students from all over the world. All these users require access to local and remote facilities, to the scientific equipment and the communication, information and collaboration infrastructure. Nearly all projects currently running are using state of the art web and GRID technologies crossing borders and continents with people joining in and leaving. Managing a dynamic environment like this is a challenging task. This paper describes the concepts and implementation aspects of an Identity Management System (IDM) for a large scale research facility.

Uranium (U) is a widespread occurring radioactive toxic heavy metal. It could be accumulated in plant roots and to a lesser extent in leaves. Hence, it is mandatory for plants to develop sophisticated tolerance strategies against this heavy metal.
Glutathion is one of the key players in this network, because of its ability to complex heavy metals, its redox-capacity, and/or as precursor in the biosynthesis of heavy metal-binding peptides, e.g. phytochelatines. The cytoplasmic glutathione content (reduced glutathione, GSH) dropped on the half in cell suspensions of canola (Brassica napus) within the first 30 minutes after U contact. However, the GSH recovery to the normal level was reached after 60 minutes. Various U concentrations (1 – 50 µM) caused different GSH kinetics indicating several defence reactions.
Artificial depletion of cytoplasmic GSH with 1-chloro-2,4-dinitrobenzene (CDNB) enhances the U toxicity in cells determined by a metabolic test.
Because of a clear excess of GSH against the slowly accumulating U in the cytoplasm, the massive GSH decrease could not exclusively be dedicated to a complex formation between GSH and U. Additionally, a reduction of U(VI) to U(IV) can be ruled out because of a lack of U(IV) in cytoplasm revealed by photoacoustic measurements. However, the rapid GSH drop could be caused by its oxidation to GSSG (oxidized GSH). One possibility is the involvement of GSH in detoxification mechanisms against oxidative burst, e.g. reactive oxygen species (ROS), induced by U. Another could be the GSH dependent recovery of redox equivalents or other metabolites. Consequently, this GSH based detoxification processes will, at least transiently, generate a redox signal and therefore impact on cellular redox poise.
It has to figure out weather the direct complexation of U with GSH (see abstract Geipel et al.) or the conjugation via glutathione S-transferase and the subsequent transport to the vacuole takes place. However, the formation of phytochelatines cannot be excluded because of cytoplasmic U bounded proteins being smaller than 14 KDa revealed by SDS gel electrophoresis and subsequent fluorescence measurements.
Further investigations should provide more detailed insights in the intracellular network of GSH functions in U detoxification as a redox buffer and as a detoxification reagent.

Glutathione is a ubiquitous compound in living systems. It is a tripeptide containing besides two carboxylic groups also a thiol group as well as amino groups. Glutathione has antioxidant properties and therefore it helps to protect cells against reactive oxygen species. In plant cells glutathione is essential for the stress management. Due to its carboxyl groups and the thiol group the peptide may contribute to the metal complexation.
We have studied the complex behavior towards uranium(VI) exploiting several spectroscopic techniques, like UV-Vis and fluorescence measurements /1/. Direct UV-Vis measurements of the absorption spectra of the uranylspecies lead to a stability constant of log β121 = 38.70 ± 0.15. The glutathione itself does not absorb any light in the spectral range from 350 nm to 500 nm. Additionally the glutathione can be modified by fluoropyrovate in order to generate a species absorbing light in the wavelength range around 300 nm. The pyruvate group substitutes the proton of the thiol group. From these measurements a stability constant for the uranyl-glutathione complex was assigned to be log β121 = 38.85 ± 0.08.
Secondly we exploited the fluorescence properties of the uranyl ion. At a pH of 7.4 the main uranium species in carbonate free solutions are the hydroxospecies (UO2)3(OH)5+ and (UO2)4(OH)7+. By increasing the concentration of glutathione the fluorescence of these species disappears as consequence of the formation of a uranyl-glutathione complex. The stability constant using the Stern-Volmer equation was derived to be log β121 = 38.65 ± 0.02.
Glutathione itself doesn’t show any florescence properties. However, it is known, that the derivatisation of the thiol group by monobrombimane leads to a fluorescent glutathione species. In analogy to the measurements of the fluorescence of the uranylspecies the fluorescence of this conjugate also disappears upon complex formation with heavy metal ions. The resulting stability constant for the uranyl complex was derived to be log β121 = 38.96 ± 0.02 neglecting that the thiol group was modified.
Summarizing all studies the stability constant for formation of a 1:1 uranyl-glutathione complex can be assigned to be log β121 = 38.79 ± 0.15.
As the stability constants the measurements of the pure and the modified glutathione agree very well, we can conclude that the thiol group is not involved in the complex formation. Additionally it could be shown that glutathione does not reduce the uranium(VI) under the experimental conditions.
Comparing these data with stability constants for several flavonoids, showing also very high complex stability constants towards uranium, we conclude that glutathione in plant cells is much more involved in heavy metal stress reactions than flavonoids.

/1/ Diploma thesis L. Frost, TU Dresden, 2009

A still intriguing issue in the field of molecular electronics is the dependence of the transport properties of a molecule or cluster on the exact geometric realization of the contact at the atomic scale. Here, Si4 clusters come in handy as they have a very well known rhombohedral geometry [1] as well as a limited yet diverse number of possibilities of being contacted: A contact may be formed along the long or the short axis, along the median of an edge, or along the surface normal of the rhombohedron.

After soft-landing from the gas phase, using a mechanically controllable breakjunction technique, possibly single or few Si4 clusters were contacted with atomically sharp tips and transport characteristics were measured. In addition to conductance histograms, current-voltage (IV) curves with and without clusters in the junction have been recorded. By comparison with the outcome of DFT calculations, the presence of the clusters in three of the four aforementioned contact geometries could be identified in the histograms.

By fitting a resonant tunneling model to the IV curves, the coupling between the clusters and the leads as well as the energy difference of the molecular orbital contributing to the transport and the Fermi energy in the leads could be determined. The highly non-linear IV curves obtained in the scope of these measurements contradict the theoretical predictions previously performed by C. Roland et al. who suggested a linear IV characteristic in the range of experimentally accessible bias voltages [2].

We thank F. Pauly for providing the DFT code and for introducing us to it’s use, A. Erbe and J. C. Cuevas for the introduction to the resonant tunneling model and valuable discussions.

[1] e.g., E. C. Honea et al., nature 366 (6450), 42 (1993)
[2] C. Roland et al., Phys. Rev. B 66 (3), 035332 (2002)

A phenomenological quasiparticle model, featuring dynamically generated self-energies of excitation modes, successfully describes lattice QCD results relevant for the QCD equation of state and related quantities both at zero and non-zero net baryon density. Here, this model is extended to study bulk and shear viscosities of the gluon-plasma within an effective kinetic theory approach. In this way, the compatibility of the employed quasiparticle ansatz with the apparent low viscosities of the strongly coupled deconfined gluonic medium is shown.

We analyze mu⁺mu^- pair production generated by high-energy electrons emerging from a laser-wakefield accelerator. The mu⁺mu^- pairs are created in a solid thick high-Z target, following the electron accelerating plasma region. Numerical estimates are presented for electron beams obtained presently in the LBL TW laser experiment \cite{C2} and possible future developments. Reactions induced by the secondary bremsstrahlung photons dominate the dimuon production. According to our estimates, a 20 pC electron bunch with energy of 1 (10) GeV may create about 200 (6000) muon pairs. The produced mu(+/-) can be used in studying various aspects of muon-related physics in table top installations. This may be considered as an important step towards the investigation of more complicated elementary processes induced by laser driven electrons.

Self-ion irradiation in combination with nanoindentation offers the possibility to characterize irradiation damage in a broad range of irradiation temperature and fluence. Nanoindentation results are reported for Fe-2.5at%Cr, Fe-9at%Cr and Fe-12.5at%Cr irradiated at room temperature, 300°C and 500°C. Special features of this work are roughly rectangular damage profiles and exploitation of the full load dependence of hardness. The effects of Cr content, fluence and irradiation temperature are discussed. Cases of both broad consistence with and deviations from reported trends are found. Hardening features were characterized by means of TEM also taking into account SANS data reported for neutron-irradiated conditions of the same alloys. A tentative two-feature hardening model was applied.

Due to the high sensitivity of Ni–Ti films to environmental changes, e.g. thermal, and/or to stress, they are ideal materials for applications on micro-sensors. It was aimed to obtain Ni–Ti films exhibiting the beginning of the B25R-phase transformation between room temperature (RT) and 0°C. Thus, films with a slightly Ni-rich composition were prepared by sputtering, without intentional heating of the substrate. The Ni–Ti films were deposited on an Si₃N₄ intermediate layer previously deposited on naturally oxidized Si(100). The crystallization behaviour of the samples (at a constant temperature of 430°C) was studied by X-ray diffraction in grazing incidence geometry off-plane (GIXD) at a synchrotron-radiation beamline. The GIXD patterns obtained during the annealing process of the Ni–Ti polycrystalline films revealed mainly an austenitic structure (B2 phase) and the precipitation of Ni₄Ti₃. The results have also shown that the presence of an intermediate layer of Si₃N₄ enhances the crystallization process of the Ni–Ti sputtered films when compared to the films deposited directly on single-crystal Si (with native oxide).
The phase transformation behaviour of the Ni–Ti film on Si₃N₄ was evaluated by XRD in off-plane Bragg–Brentano geometry during cooling (RT-> -40°C) and heating (-40°C ->RT). It has been observed that a high fraction of the Ni–Ti film is already transformed to R-phase at 9°C (austenitic at RT), as well as a very small temperature hysteresis for the B25R-phase transformation.
After the characterization described above, the film was removed from the substrate. The free-standing film showed a pronounced ‘‘two-way’’ shape memory effect (SME). In the austenitic state the film presents a flat shape. During cooling, by reducing its distance from ice cubes (i.e., decreasing the surrounding temperature), the film starts bending exhibiting a final curled shape (yet without touching the ice). On heating it recovers its flat shape. The authors attribute the nature of this ‘‘two-way’’ SME to the Ni₄Ti₃ precipitates that formed during the heat treatment.

Nominally undoped, hydrothermally grown ZnO single crystals have been investigated after doping in remote H plasma. Characterizations have been made by positron annihilation (slow positron implantation spectroscopy, lifetime, coincidence Doppler broadening), temperature-dependent Hall and photoluminescence measurements. The H content before and after the doping has been determined using nuclear reaction analysis. In addition, changes of the polished surface of the crystals have been monitored by atomic force microscopy.
H plasma doping produced a metallic conducting near-surface layer. It is discussed if this is due to an increased H and zinc incorporation into pre-existing zinc vacancy – H complexes, as this also could explain the occurrence of a second positron lifetime component in the volume of the crystals, from which a bulk positron lifetime of (153 +/- 2) ps for ZnO is derived in very good agreement with previous experiments and theoretical calculations.

We have investigated the magnetic properties of pure ZnO thin films grown under N2 pressure on a-, c- and r-plane Al2O3 substrates by pulsed laser deposition. The substrate temperature and the N2 pressure were varied from room temperature to 570 °C and from 0.007 mbar to 1.0 mbar, respectively. The magnetic properties of bare substrates and ZnO films were investigated by SQUID magnetometry. ZnO films grown on c- and a-plane Al2O3 substrates did not show significant ferromagnetism. However, ZnO films grown on r-plane Al2O3 showed reproducible ferromagnetism at 300 K when grown at 300¡400 °C and 0.1-1.0 mbar N2 pressure. Positron annihilation spectroscopy measurements as well as density functional theory calculations suggest that the ferromagnetism in ZnO films is related to Zn vacancies.

We investigate theoretically the electron dynamics in a single-channel mesoscopic ring with a localized impurity subjected to picosecond linearly polarized asymmetric electromagnetic pulses. A nonequilibrium coherent population of electronic states that possesses a time-dependent polarization is induced. The associated radiation emission decays on a time scale determined by the system relaxation and hence lasts long, after the pulses have perished. We derive analytically and confirm numerically that the presence of an impurity influences strongly the time-dependent charge polarization and allows the generation of higher harmonics in the terahertz range.

To activate silica optically our investigations are extended to ion implantation, mainly to overstoichiometric injection or isoelectronic substitution of the both constituents silicon or oxygen, i.e. by ions of the group IV (C, Si, Ge, Sn, Pb) or the group VI (O, S, Se). Such implantation produce new luminescence bands in silica layers, partially with optical electronic–vibronic transitions and respective multimodal spectra. In this context, special interest should be directed to low-dimension nanocluster formation in silica layers. Cathodoluminescence, high resolution transmission (HR-TEM) and scanning transmission electron microscopy (STEM), and energy dispersive X-ray analysis (EDX) have been used to investigate Si and Ge cluster formation in amorphous silicon dioxide layers and their respective luminescence behavior.

This paper describes the home-made MULTIpurpose MAGnetic field system MULTIMAG, a facility composed of compact coil systems carrying high currents. Prominent features of MULTIMAG are (i) The large bore of 400 mm in height and 365 mm in diameter, which supports, in conjunction with the high current densities, the attainability of similarity criteria in the industrial range. (ii) Because the use of ferromagnetic material was strictly avoided in the construction, the rotating, travelling, pulsating, and DC in either homogeneous or cusp configuration magnetic fields may be superimposed linearly. (iii) In order to have as flexible as possible spatio-temporal distributions of the magnetic fields, the power supplies are realised as amplifiers. Each of the seven phases, three for the rotating and the travelling field, respectively, and one for the pulsating field, comprises a pulse width modulated power amplifier controlled by its own freely programmable frequency synthesizer.

The verification of design improvements of a fuel assembly of a nuclear reactor core and their influence on the critical heat flux require expensive experiments. Therefore the supplementation or even the replacements of experiments by numerical analyses are of relevant interest in fuel assembly design. The CFD modeling has the potential of simulation independent on the certain geometry.
The presentation describes the actual state of CFX modeling of subcooled boiling and their possible contribution for rod bundle design. The comparative investigation of different designs is possible at least qualitatively. For more quantitatively reliable results the models have to be improved. In the presentation the demands on the accuracy of measured values are established. The usage of model fluids enables the enlargement of the investigated geometry. The most promising results are expected by tomographic methods like gamma tomography or especially by fast X-ray tomography.

The verification of design improvements of a fuel assembly of a nuclear reactor core and their influence on the critical heat flux require expensive experiments. Therefore the supplementation or even the replacements of experiments by numerical analyses are of relevant interest in fuel assembly design. The CFD modeling has the potential of simulation independent on the certain geometry.
The presentation describes the actual state of CFX modeling of subcooled boiling and their possible contribution for rod bundle design. The comparative investigation of different designs is possible at least qualitatively. For more quantitatively reliable results the models have to be improved. In the presentation the demands on the accuracy of measured values are established. The usage of model fluids enables the enlargement of the investigated geometry. The most promising results are expected by tomographic methods like gamma tomography or especially by fast X-ray tomography.

The investigation of insulation debris generation, transport and sedimentation becomes important with regard to reactor safety research for PWR and BWR, when considering the long-term behaviour of emergency core cooling systems during all types of loss of coolant accidents (LOCA). A joint research project on such questions is being performed in cooperation between the University of Applied Sciences Zittau/Görlitz and the Forschungszentrum Dresden-Rossendorf. The project deals with the experimental investigation of particle transport phenomena in coolant flow and the development of CFD models for its description. While the experiments are performed at the University at Zittau/Görlitz, the theoretical modelling efforts are concentrated at Forschungszentrum Dresden-Rossendorf.
In the current paper the basic concepts for CFD modelling are described and feasibility studies are presented.

The investigation of insulation debris generation, transport and sedimentation becomes important with regard to reactor safety research for PWR and BWR, when considering the long-term behavior of emergency core cooling systems during all types of loss of coolant accidents (LOCA). The insulation debris released near the break during a LOCA incident consists of a mixture of disparate particle population that varies with size, shape, consistency and other properties. Some fractions of the released insulation debris can be transported into the reactor sump, where it may perturb/impinge on the emergency core cooling systems.
Open questions of generic interest are the sedimentation of the insulation debris in a water pool, its possible re-suspension and transport in the sump water flow and the particle load on strainers and corresponding pressure drop. A joint research project on such questions is being performed in cooperation between the University of Applied Sciences Zittau/Görlitz and the Forschungszentrum Dresden-Rossendorf. The project deals with the experimental investigation of particle transport phenomena in coolant flow and the development of CFD models for its description. While the experiments are performed at the University at Zittau/Görlitz, the theoretical modeling efforts are concentrated at Forschungszentrum Dresden-Rossendorf.
In the current paper the basic concepts for CFD modeling are described and feasibility studies including the conceptual design of the experiments are presented.

This experimental work is concerned with optimisation of the Czochralski crystal growth process. With respect to the shape of the solidification front and the related mono-crystalline growth, the ratio of the horizontal and the vertical temperature gradient r* = DTh /DTv 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 built that allows studying this ratio under the influence of magnetic fields applied to the melt. The cylindrical liquid metal column was homogeneously heated from below, whereas on top the heat was extracted in a concentrical region covering only about one third of the surface in order to simulate the growing crystal. It was shown that the native, i. e. without flow control, r* ≈ 3 is far removed from unity. In a first series of measurements, it was then possible to reach the target value r* = 1 for any temperature difference between the bottom and the top at a moderate field strength while applying a rotating magnetic field.

The solubility limit of Cr in Fe (a-Fe-Cr) at lower temperatures is a matter of debate. We report a direct estimation of the solubility limit at 300°C from SANS data obtained for neutron-irradiated Fe-Cr alloys. The SANS results indicate that the equilibrium concentration of a’ was reached via irradiation-enhanced diffusion. The solubility limit was estimated using an iterative approach based on the SANS invariant and the lever rule of phase equilibrium

Defects in zinc-implanted and thermally annealed ZnO thin films were investigated by means of capacitance-voltage spectroscopy (C-V), thermal admittance spectroscopy (TAS), deep level transient spectroscopy (DLTS), and photoluminescence (PL) spectroscopy. The authors report on the formation of two donor states approximately 35 and 190 meV below the conduction band edge, observed by TAS and DLTS, respectively. In the PL spectra of a reference sample a peak at 3.366 eV was present, which diminished after the implantation, while a new peak at 3.364 eV was observed only in the spectrum of the implanted sample. Since only intrinsic ions were implanted, the authors consider the defects formed by the zinc implantation and annealing to be intrinsic.

Dendritic microstructure is one of the major microstructural constituents of peritectic alloys. In the present work, the effect of melt convection on the secondary dendritic arm spacing (SDAS) and volume fraction of properitectic alpha-Fe was investigated during solidification of stoichiometric Nd-Fe-B alloys under forced crucible rotation technique. The resulting microstructure of the alloy in consideration of melt convection has been investigated using scanning electron microscopy and optical microscopy. The average SDAS was determined for each sample from the whole cross-section of the cylindrical test samples using image analyzing software LEICA QWIN. A detailed statistical analysis of the spacing distribution was performed on the basis of the variation of SDAS values averaged from about 80 to 120 dendrites in different zones. The a-Fe volume fraction measured by vibrating sample magnetometer (VSM) reduces with increasing crucible rotation frequency. Similarly, the SDAS values decrease with increasing rotation frequency. These results are explained from the viewpoint of a reduced melt convection state under steady forced crucible rotation leading to a reduced effective mass transfer coefficient.

AlYB₁₄ (Imma) thin films were synthesized by magnetron sputtering. Based on X-ray diffraction, no phases other than crystalline AlYB₁₄ could be identified. According to electron probe microanalysis, energy dispersive X-ray analysis and elastic recoil detection analysis, the Al and Y occupancy varies in the range of 0.73 to 1.0 and 0.29 to 0.45, respectively. Density functional theory based calculations were carried out to investigate the effect of occupancy on the stability of Al_xY_yB₁₄ (x, y = 0.25, 0.75, 1). The mean effective charge per icosahedron and the bulk moduli were also calculated. It is shown that the most stable configuration is Al_0.5YB₁₄, corresponding to a charge transfer of 2 electrons to the boron icosahedra. Furthermore, it is found that the stability of a configuration is increased if the charge is homogeneously distributed within the icosahedra. The bulk moduli for all investigated configurations are in the range between 196 and 220 GPa, rather close to known hard phases such as α-Al₂O₃.

We have measured the temperature and frequency-dependant transmission and phase shift through LuNi₂B₂C thin films on MgO substrates at terahertz frequencies. From the measured data, we could accurately determine the complex dielectric constant, epsilon, the complex optical conductivity, sigma, and the penetration depth, gamma. Comparing our measured results with theory, we find strong deviations from the standard one-band BCS predictions. These deviations can be attributed to the multiband nature of the superconducting state in LuNi₂B₂C.

Impact of a highly charged ion upon a solid surface can induce dramatic changes in the morphology only by the release of its potential energy. Hillocks and mono-atomic deep pits have been observed on the surfaces of CaF2 and KBr, respectively. For both processes a threshold in the potential energy exists for the creation of these nanostructures. Above this threshold the structure size increases linearly with potential energy. The mechanisms for the formation of hillocks and pits are discussed and a rst attempt to present a unied microscopic picture is made.

In diesem Vortrag wird Beschleunigermassenspektrometrie am FZD vorgestellt.

Outline
Ion – Solid interaction
Experimental
RBS + high resolution
ERDA + high resolution
H analysis
Summary

Abstract is not available

Abstract is not available

not available. will be published later

The novel technology of particle acceleration based on high intensity laser systems promises accelerators of compact size and reasonable costs and may significantly contribute to a widespread use of high precision hadron radiotherapy. Although some basic properties of laser acceleration are reasonably well known from theory, simulations and fundamental physical experiments, several further requests have to be fulfilled for its medical application such as supply of a stable and reliable particle beam with reproducible properties and precise delivery of dose in an appropriate irradiation time with required exposure of a desired irradiation field. Moreover, the ultra-short pulsed (in the region of 100 fs) particle beams with resulting high pulse dose-rate (in the order of 1012 Gy/min) have to be characterized with regard to their radiobiological properties.
First in-vitro cell irradiations with laser accelerated electrons have been performed at the Jena Titanium:Sapphire (JeTi) 10 terawatt laser system and dose-effect-curves were obtained for four cell lines and two endpoints. Laser pulses (80 fs duration, 2.5 Hz repetition rate) were focused into a helium gas jet, accelerating electrons to energies of up to 20 MeV. Before irradiation, the JeTi system was optimized for cell experiments: the electron spectrum was limited to a minimum energy of 3 MeV, the beam spot size was adjusted and the dose rate and homogeneity were improved. Each cell sample was equipped with two Gafchromic EBT radiochromic films, one in front and one behind the cell monolayer, used for retrospective precise dose determination. A Roos ionization chamber and a Faraday Cup monitored the beam providing on-line dose information necessary for irradiation control. Moreover the energy spectrum was measured both with an electromagnetic spectrometer and by analyzing film stack measurements. Following to the irradiation the cell survival fraction was determined using clonogenic survival assay. In addition, DNA double strand breaks present in cell 24 h after irradiation were analyzed.
Normally used for physical single-shot experiments, the JeTi was customized for a long-time cell irradiation. 163 Samples were irradiated at 13 experiment days over a period of 10 weeks with doses between 0.3 and 10 Gy. A reasonably stable and reproducible beam was achieved. Dose homogeneity was examined for all samples within the target area and the inhomogeneity obtained was less than 10 % for all days and all applied doses. Although still preliminary, the dose-effect-curves obtained show in general a lower biological effectiveness for the laser accelerated electron beams in comparison with conventional x-rays.

A concentrated vortex with properties similar to a tornado may be created by magnetic body forces. We study this phenomenon experimentally by applying combined travelling and rotating magnetic fields to a liquid metal cylinder. The bulk velocity is measured by ultrasound Doppler velocimetry and the surface velocity is reconstructed by particle image velocimetry. The travelling magnetic field (TMF) creates an axial body force with a parabolic radial profile. The induced meridional flow follows the field at the rim and returns through the central part. Thus an intense converging flow is created at one end of the cylinder. The additionally superimposed rotating magnetic field (RMF) with a substantially different frequency sets the flow into rotation. The angular momentum conservation forces the rotation to intensify towards the centre of the converging flow. The swirl intensification is limited by the centrifugal force which stops the radial inflow at some equilibrium radius. The resulting concentrated vortex is unstable but persistent. We determine conditions of its formation in terms of the ratio of the two magnetic body forces. It turns out that the maximum strength of the vortex is determined by the TMF but its structure is governed by a much weaker RMF. The maximum time-averaged swirl is observed at a force ratio of about 100. A pronounced two-cell vortex with a reversed meridional circulation in the inner core is observed at a force ratio of about 50. The inner core is encircled then by a number of smaller vortices resembling a large wedge-shaped tornado or eye of a tropical cyclone. As the force ratio is further increased the inner core expands until it occupies the entire cylinder. The flow is then essentially controlled by the RMF despite the TMF might be still much stronger. The phenomenon may be useful to stir floating particles into the melt. A related sink-vortex may occur over a drain-hole in various technological processes. Magnetic body forces can be used to alter or eliminate it.

This paper describes laboratory experiments for investigations of flow structures in liquid metal bubbly flows under the influence of a travelling magnetic field (TMF). The melt flow is driven by central gas injection into a cylindrical container filled with the low melting point alloy GaInSn. Velocity fields of the liquid were measured non-intrusively using the ultrasound Doppler method. Depending on the travelling direction of the magnetic field, the TMF mainly imposes either a co-current or counter flow with respect to the original bubble-driven circulation. The application of a downward TMF significantly increases the liquid velocity all over the fluid volume. An upward TMF gives rise to more complex structures of the velocity field resulting in alternately arranged up- and downstream regions. Both the upward and downward TMF promote the occurrence of non-steady motions with distinct velocity fluctuations leading to an intensification of related transport processes in the melt and providing the perspective of enhanced mixing efficiencies.

Radiotherapy is a mainstay of cancer treatment. More than 50 % of tumour patients in developed countries receive radiotherapy, either as the only method of treatment or as a crucial component in combination with surgery and/or systemic treatment. However, in many cases, especially for compact, deep-seated, radiation-resistant tumours growing in close vicinity to organs at risk, state-of-the-art radiotherapy which is based on photon or electron beams delivered by compact electron linear accelerators comes to its limits. Considerably improved conformance of radiation dose to the tumour volume with simultaneous preservation of surrounding healthy tissue will derive from utilization of ions whose favourable physical and radiobiological properties have already been demonstrated in clinical application [1, 2]. However, only a few ion therapy facilities are running worldwide, due to their complexity, large scale and high investment cost linked to present radiofrequency accelerator technology. Laser-based particle acceleration is a rapidly evolving new technology [3-9]. It promises the development of compact ion accelerators with reasonable costs, which may be integrated into existing hospitals since they are based on compact table-top multi-terawatt laser systems and the acceleration process takes place within micrometer distances. This novel technology appears to be a key that many more patients could benefit from ion radiotherapy and its favourable properties.

The MLLTRAP at the Maier-Leibnitz-Laboratory (Garching) is a new Penning trap facility designed to combine several novel technologies to decelerate, charge breed, cool, bunch and purify the reaction products and perform high-accuracy nuclear and atomic mass measurements. It is now in the commissioning phase, achieving a mass-resolving power of about 105 in the purification trap for stable ions.

Was sind Magnetfelder? Wo findet man sie? Wie erzeugt man sie und zu was sind sie nutze? Antworten auf diese Fragen sollen in dem Vortrag durch Vorstellung der weltweiten Bestrebungen, immer höhere Magnetfelder zu erreichen, gegeben werden. Ähnlich wie z. B. Druck und Temperatur haben magnetische Felder einen tief greifenden Einfluss auf den Zustand und Zustandsänderungen der Materie. Untersuchungen von Materialien in hohen Magnetfeldern sind daher mittlerweile Standard und eine Vielzahl von Anwendungen in unserem täglichen Leben sind ohne Magnetfeldeffekte undenkbar. In der Forschung wird der stetig wachsende Bedarf an möglichst großen Magnetfeldstärken durch Hochfeldlaboratorien abge-deckt. In dem neu aufgebauten Hochfeld-Magnetlabor Dresden sollen demnächst gepulste Magnetfelder bis zu 100 Tesla erzeugt werden. Erste Hochfeldmagnete sind in Betrieb und seit 2007 hat neben der Eigenforschung der Nutzerbetrieb begonnen. Der momentane Status des Labors, die Schwierigkeiten, die zur Erzeugung so hoher Magnetfelder überwunden werden müssen, und exemplarische wissenschaftliche Ergebnisse aus Hochfeldstudien sollen vorgestellt werden.

One of the most powerful methods to determine important bulk band-structure parameters in metals is the measurement of magnetic quantum oscillations. By applying high magnetic fields, this can be done e.g. by detecting the oscillations in the field-dependent magnetization, called de Haas-van Alphen (dHvA) effect, or by resolving Shubnikov-de Haas (SdH) oscilla-tions in the field-dependent resistivity. The combination of such kind of experimental data with sophisticated band-structure calculations often is a necessary prerequisite to gain a deeper understanding of the electronic properties of metals. One example for such a joint ef-fort of experimental and theoretical work is the finding and explanation of the field-induced band-structure change in CeBiPt [1]. In this material, a drastic change of the electronic band structure, as seen in the SdH and Hall signals, is found above about 25 T. This field-induced Lifshitz transition can be understood by the splitting of the Ce-5d bands close to the Fermi energy due to the exchange interaction with the polarized Ce-4f states. Another example where dHvA measurements were successfully combined with highly precise full-potential local-orbital calculations is the borocarbide superconductor LuNi₂B₂C [2]. By carefully com-paring the experimentally extracted effective masses with the calculated bare masses the many-body mass enhancements could be determined independently for several bands and for different directions.

The temperature dependences of the electric-transport properties of the two-dimensional organic conductors β"--(BEDT-TTF)₂SF₅CH₂CF₂SO₃, β"-(d₈-BEDT-TTF)₂SF₅CH₂CF₂SO₃, and β"-(d₈-BEDTTTF)₂SF₅CH₂CF₂SO₃ are measured by dc methods in and perpendicular to the highly conducting plane. Microwave measurements are performed at 24 and 33.5GHz to probe the high-frequency behavior from room temperature down to 2 K. Superconductivity is observed in β"-(BEDT-TTF)₂SF₅CH₂CF₂SO₃ and its deuterated analogue. Although all the compounds remain metallic down to low-temperatures, they are close to a charge-order transition. This leads to deviations from a simple Drude behavior of the optical conductivity which become obvious already in the microwave range. In β"-(BEDT-TTF)₂SF₅CH₂CF₂SO₃, for instance, charge fluctuations cause an increase in microwave resistivity for T < 20K which is not detected in dc measurements. β"-(BEDT-TTF)₂SF₅CHFSO₃ exhibits a simple metallic behavior at all frequencies. In the dc transport, however, we observe indications of localization in the perpendicular direction.

We report on precise low-temperature specific-heat measurements, C(T), of YbRh₂Si₂ in the vicinity of the antiferromagnetic phase transition on a single crystal of superior quality (residual resistivity ratio of ~150).We observe a very sharp peak at TN = 72 mK with absolute values as high as C/T = 8 J/molK². A detailed analysis of the critical exponent α around T_N reveals α ≤ 0.38 which differs significantly from those of the conventional universality classes in the Ginzburg-Landau theory, where α ≤ 0.11. Thermal-expansion measurements corroborate this large positive critical exponent. These results provide insight into the nature of the critical magnetic fluctuations at a temperature-driven phase transition close to a quantum critical point.

We demonstrate that the third elemental group-IV semiconductor, germanium, exhibits superconductivity at ambient pressure. Using advanced doping and annealing techniques of state-of-the-art semiconductor processing, we have fabricated a highly Ga-doped Ge (Ge:Ga) layer in near-intrinsic Ge. Depending on the detailed annealing conditions, we demonstrate that superconductivity can be generated and tailored in the doped semiconducting Ge host at temperatures as high as 0.5 K. Critical-field measurements reveal the quasi-two-dimensional character of superconductivity in the ~60 nm thick Ge:Ga layer. The Cooper-pair density in Ge:Ga appears to be exceptionally low.

Large-scale ab initio molecular dynamics simulations of ion-solid interactions in SiC reveal that significant charge transfer occurs between atoms, and defects can enhance charge transfer to surrounding atoms. The results demonstrate that charge transfer to and from recoiling atoms can alter the energy barriers and dynamics for stable defect formation. The present simulations illustrate in detail the dynamic processes for charged defect formation. The averaged values of displacement threshold energies along four main crystallographic directions are smaller than those determined by empirical potentials due to charge-transfer effects on recoil atoms.

Understanding the dynamics of metals and radionuclides in soil environments is necessary for evaluating risks to pristine sites. An iron-rich creek soil of a former uranium-mining district (Ronneburg, Germany) showed high porewater concentrations of heavy metals and radionuclides. Thus, this study aims i) to evaluate metal dynamics during terminal electron accepting processes (TEAPs) and ii) to characterize the active microbial populations in biostimulated soil microcosms using a stable isotope probing (SIP) approach. In biostimulated soil slurries, concentrations of soluble Co, Ni, Zn, As, and unexpectedly U increased during Fe(III)-reduction. This suggests that there was a direct reduction of As and a release of sorbed metals during reductive dissolution of Fe(III)-oxides. Subsequent sulfate-reduction was concurrent with a decrease of U, Co, Ni, and Zn concentrations. The relative contribution of U(IV) in the solid phase changed from 18.5 to 88.7% after incubation. The active Fe(III)-reducing population was dominated by δ-Proteobacteria (Geobacter) in 13C-ethanol amended microcosms. A more diverse community was present in 13C lactate amended microcosms including taxa related to Acidobacteria, Firmicutes, δ- Proteobacteria, and β-Proteobacteria. Our results suggested that biostimulated Fe(III)-reducing communities facilitated the release of metals including U to groundwater which is in contrast to other studies.

The successful use of picosecond-pulse free-electron-laser (FEL) radiation for the continuous-wave terahertz-range electron spin resonance (ESR) spectroscopy has been demonstrated. The combination of two linac-based FELs (covering the wavelength range of 4–250 µm) with pulsed magnetic fields up to 70 T allows for multifrequency ESR spectroscopy in a frequency range of 1.2–75 THz with a spectral resolution better than 1%. The performance of the spectrometer is illustrated with ESR spectra obtained in the 2,2-diphenyl-1-picrylhydrazyl and the low-dimensional organic material (C₆H₉N₂)CuCl₃

The stopping of high-energy light ions in a host solid is characterised by a very high ratio of electronic to nuclear stopping powers. Consequently, alpha particles (⁴He cores whose energies range between 3.9 and 8.8 MeV) penetrating into a host mineral cause tremendous amounts of lattice ionisation, whereas they are rather marginally efficient in generating atomic displacements. Radiohaloes in rock-forming minerals are therefore mostly characterised by relatively low levels of structural radiation damage [1,2]. It is well known, however, that ion-beam irradiation may not only create defects, but it may also cause structural reconstitution [3-5]. It has been suspected that the electronic excitation by the alpha particles may result in radiation-enhanced annealing of pre-existing radiation damage, as for instance the bulk metamictization or fission tracks [6] in minerals.
The present study aimed at checking the principal effect of alpha particles on the self-irradiation damage (i.e., predominantly alpha-recoil damage) in U- and Th-bearing accessory minerals. Three hypothetical possibilities had to be considered, namely, (i) the creation of additional damage, (ii) structural reconstitution of the pre-existing damage, or (iii) insignificant effects on the structural state. For this, a suite of well-characterised zircon and monazite samples, covering the entire range from well-crystallised to fully metamict, were irradiated with 8.8 MeV ⁴He²⁺ ions (which are the analogue of alpha particles generated in the ²¹²Po ---> ²⁰⁸Pb decay in the Th chain). Fluences were varied in the range 10¹² - 10¹⁷ He ions/cm². In the case of He-irradiated metamict (i.e., amorphous) samples, no indication of recrystallisation or nucleation was found. For all non-amorphous starting materials, we found that the degree of structural damage has always notably increased after the He irradiation. Consequently, alpha particles do create structural damage not only in well-crystallised but also in mildly to highly radiation-damaged zircon and monazite. In contrast, the hypothetical ability of alpha particles to assist damage annealing is not supported.
Our observations do not seem to confirm results of dual-beam ion irradiation experiments (i.e., the simultaneous irradiation of a solid with a heavy ion beam with relatively high nuclear excitation, and a second beam with high electronic excitation, such as high-energy light ions or electrons). Such experiments suggested that the simultaneous, intense electronic excitation may retard or prevent amorphisation by heavy ions [7]. The apparent contrast to our results may perhaps be explained by the consideration that self-irradiating minerals do virtually never experience genuine dual irradiation. Due to their generally low irradiation rates (averaging a few events per minute and mm³), alpha recoils and alpha particle irradiation in the very same volume area do not occur simultaneously but successively.

References:

[1] Nasdala, L., Wildner, M., Wirth, R., Groschopf, N., Pal, D.C., Möller, A. (2006) Mineral. Petrol. 86, 1-27
[2] Krickl, R., Nasdala, L., Götze, J., Grambole, D., Wirth, R. (2008) Eur. J. Mineral. 20, 517-522
[3] Priolo, F., Spinella, C., Rimini, E. (1990) Phys. Rev. B 41, 5235-5242
[4] Heera, V., Kögler, R., Skorupa, W., Grötzschel, R. (1993) Nucl. Instr. Meth. Phys. Res. B80/81, 538-542
[5] Som, T., Ghatak, J., Sinha, O.P., Sivakumar, R., Kanjilal, D. (2008) J. Appl. Phys. 103, 123532
[6] Hendricks B.W.H., Redfield, T.F. (2005) Earth Plan. Sci. Lett. 236, 443-458
[7] Devanathan, R., Sickafus, K.E., Weber, W.J., Nastasi, M. (1998) J. Nucl. Mat. 253, 113-119

The underlying motivation of this work is the tailored growth of Ge nanocrystals (NC) for photovoltaic applications. The use of superlattices (SL) delivers a reliable method to control the Ge NC size after phase separation. In this contribution we report the deposition of (GeOx-SiO2) SL via reactive dc magnetron sputtering and the self-ordered Ge NC formation during subsequent annealing. Main attention is directed to define proper deposition conditions for tuning the GeOx composition between elemental Ge (x = 0) and GeO2 (x = 2) by the variation of the deposition temperature and the oxygen partial pressure. A convenient process window has been found which allows sequential GeOx-SiO2 deposition without changing the oxygen partial pressure during deposition. The phase separation and Ge NC formation after subsequent annealing were investigated with in−situ X-ray scattering, Raman spectroscopy and electron microscopy. By these methods the existence of 2-5 nm Ge NC at annealing temperatures of 600-750°C has been confirmed which is within the SL stability range. The used technique allows to produce SL stacks with very smooth interfaces (roughness <1 nm), thus the Ge NC layers could be separated by very thin SiO2 films (d > 3 nm) which offers interesting possibilities for charge transport via direct tunneling.

High quality Al_1-xIn_xN/GaN bilayers, grown by Metal Organic Chemical Vapour Deposition (MOCVD), were characterized using structural and optical techniques. Compositional analysis was performed using Rutherford Backscattering Spectrometry (RBS) and Elastic Recoil Detection Analysis (ERDA). The InN molar fraction x decreased approximately linearly with increasing growth temperature and ranged from x=0.13 to 0.24. Up to x=0.20 the layers grow pseudomorphically to GaN with good crystalline quality. These layers show a smooth surface with V-shaped pits. Two layers with InN contents around 24% showed partial strain relaxation. However, the mechanisms leading to relaxation of compressive strain are very different in the two samples grown both at low temperature but with different growth rate. One sample shows a decreased c/a ratio, as expected for relaxation of the compressive strain, while In was shown to be homogeneously distributed with depth. Another sample started to grow with x=0.24 but relaxed mainly by reduction of the incorporated InN content towards the lattice-match composition of x~0.17. Both samples have an increased surface roughness. All samples show strong Al_1-xIn_xN band edge luminescence with large bowing parameter and Stokes’ shifts.

A MoS₂ microtube synthesized by chemical transport reaction was studied by Raman line scan mapping. The Raman spectrum of the MoS₂ microtube closely resembles that of a MoS₂ single crystal. In both, first order A_1g and E_2g Raman lines are observed with equal wave numbers, while line widths are slightly larger in the microtube spectrum, which can be attributed to defects. In the line scan along the tube axis the wave numbers of first order peaks are constant, while a slight up-shift of the Raman lines is observed in a line scan perpendicular to the tube. Possible mechanisms are discussed and the heating effect is proposed. Line scan approach over the edge of an object thus enables accurate determination of positions of first order peaks in highly absorbing materials.

The effect of the tube diameter and of the surface layer on the Raman spectra of WS₂ nanotubes is investigated. With decreasing diameter, a disorder-induced line in the A_1g mode range, the D-A_1g line, is selectively enhanced. This enhancement is attributed to an increasing structural disorder in smaller nanotubes. On the other hand, no significant effect on the D-A_1g / A_1g intensity ratio is observed for a Raman scan perpendicular to a 290 nm diameter tube. Therefore the enhancement of the disorder induced line is an intrinsic property of WS₂ nanostructures and not a surface layer effect.

Two methods based on bremsstrahlung were applied to the stable even Mo isotopes for the experimental determination of the photon strength function covering the high excitation energy range above 4 MeV with its increasing level density. Photon scattering was used up to the neutron separation energies Sn and data up to the maximum of the isovector giant resonance(GDR) were obtained by photo-activation. After a proper correction for multi-step processes the observed quasi-continuous spectra of scattered photons show a remarkably good match to the photon strengths derived from nuclear photo effect data obtained previously by neutron detection and corrected in absolute scale using the new activation results. The combined data form an excellent basis to derive a shape dependence of the E1 strength in the even Mo isotopes with increasing deviation from the N = 50 neutron shell, i.e. with the impact of quadrupole deformation and triaxiality. The wide energy coverage of the data allows for a stringent assessment of the dipole sum-rule, and a test of a novel parameterization developed previously which is based upon. This parameterization for the electric dipole strength function in nuclei with A>80 deviates significantly from prescriptions generally used previously. In astrophysical network calculations it may help to quantify the role the p-process plays in the cosmic nucleosynthesis. It also has impact on the accurate analysis of neutron capture data of importance for future nuclear energy systems and waste transmutation.

Recent success in laser-driven particle acceleration has increased interest in laser-generated “accelerator-quality” beams, for example, protons and ions have been produced with up to several tens of MeV per nucleon, and with extremely low emittance (<0.01 mm mrad, normalized). Compact, high-gradient laser-accelerators are therefore now being discussed as a potentially viable technology for a host of particle-beam applications, including future compact medical accelerators for medical diagnostics and therapy. After commissioning of a 150 TW laser system at the FZD, a joint research center for radiation therapy with laser-accelerator ions is being established together with the OncoRay Center for Radiation Research in Oncology, and the University Clinic of the Technical University of Dresden. The present status and future plans of the center, and the results from first proton acceleration experiments at FZD will be presented.

Introduction to Ion Beam Materials Analysis (IBA)
Characterisation of thin films by Ion Beam Materials Analysis (IBA)
Research topics for Ion Beam Materials Analysis (IBA)

Polychromatic decorations of ancient Egyptians tombs and temples have a long tradition over three millennia but are hard to identify because many pigments have been subjected to severe chemical reactions, which have entirely changed their original colours. Optical microscopy, PIXE and microbeam-PIXE have been used for determination of the nature of pigments, their chronology, and identification of domestic and imported materials. Paint flakes from various archeological sites in Egypt were analyzed: we report the results of the analysis of samples which were collected at the Mortuary Temple of Ramesses III (Habu Town), and the tombs of Tuthmosis III (Valley of the Kings) and Sennefer (Valley of the Noblemen). The paint is composed of grains of sizes typically ranging from 50 μm to 300 μm embedded in binding material and has great non-uniformity of pigment depth and lateral distributions and discontinuity of the paint layers. Qualitative analysis using broad beam PIXE has been performed to allow determination of the average composition of both support and pigments. Microbeam-PIXE has been used for mapping of selected grains. Goethite FeO(OH) (yellow), orpiment As₂S₃ (green), and the two blues: Egyptian Blue CaCuSi₄O₁₀ and Green Frit CaCuSiO₃ (mixed with the red haematite Fe₂O₃) were identified, and interesting details of the painting technique of ancient masters, like blending of pigments and the use of multilayer structures, were revealed.

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Rossendorf als lebendiger und attraktiver Standort für Wissenschaft und Wirtschaft

Problem: The goal of this study is to prepare novel chelators suitable for conjugation to vector molecules which can be labeled by yttrium or copper in order to achieve high specific activities and to improve pharmacokinetics. In this context, new water soluble bifunctional DOTA- and bis (2-pyridylmethyl)triazacyclocyclononane (DMPTACN)-based chelators have been synthesized and conjugated to the monoclonal antibody Cetuximab which binds to HER2 of the epithelial growth factor receptor (EGFR) family which is over-expressed by various tumors.

Material and Method: Both chelators have been conjugated to Cetuximab via thiourea-bridging. Radiolabeling of DOTA derivatives has been performed in aqueous ammonium acetate solution at r.t. using ⁸⁶YCl₃ or ⁹⁰YCl₃. Radiolabeling of DMPTACN conjugates with ⁶⁴Cu was achieved in MES buffer solution at 50°C using ⁶⁴CuCl₂. The affinity of the bioconjugates towards EGFR was determined by ELISA.

Results: The ELISA test showed that the affinity of the bioconjugates has decreased compared to native Cetuximab. A chelator/antibody molar ratio of 4 was achieved as determined by MALDI-TOF-MS for the DOTA-Cetuximab conjugate. Radiolabeling of DOTA-conjugates with ⁸⁶Y and ⁹⁰Y at 37°C requires optimization to improve radiochemical yield. DMPTACN-Cetuximab conjugates can be rapidly labeled with 64Cu under mild conditions in almost quantitative yield.

Conclusions: DMPTACN- and DOTA-ligands are attractive bifunctional chelating agents which can be conjugated to vector molecules for PET-imaging and radiotherapy. In the near future, the work with the ligands investigated will be extended using the pre-labeling approach.

Thermoelectromagnetic convection in cubic containers was studied experimentally. Two opposing side walls were cooled and heated, respectively, to produce an uniform temperature gradient. Inhomogeneous magnetic field distributions were achieved either with a permanent magnet or with specifically shaped pole shoes of an electromagnetic system. Ultrasonic Doppler velocimetry demonstrated that even a moderate temperature gradient may drive distinct convection. Two different flow regimes were investigated with the permanent magnet. Located at an isothermal wall, it produced a single vortex spreading the whole container while the flow was relatively stable. Moving the magnet to the center altered the flow structure. Four vortices developed and the velocity fluctuations were intensified. The more generic case realised with the electromagnet provided a gradient of the magnetic field only in one direction. Since the field strength and the area of impact on the melt were larger, developed turbulent regimes were accomplished.

Atomic layer deposition (ALD) of rhodium oxide thin films has been studied using Rh(acac)₃ (acac = acetylacetonato) and ozone as precursors. Amorphous Rh₂O₃ thin films were deposited between 160 and 180 °C. The sublimation temperature of Rh(acac)₃ set the low temperature limit for the oxide film deposition, while the high temperature limit was governed by the partial reduction of the film to metallic rhodium. The rhodium oxide films were successfully deposited on Al₂O₃ nucleation layers, soda lime glasses, and native oxide covered silicon substrates. The films demonstrated excellent conformality as characteristic for ALD. The films were not uniform across the substrate, which was most likely due to the catalyzing effect of Rh₂O₃ for ozone decomposition. The nonuniformity was repeatable and could be simply compensated in the cross-flow reactor. By splitting the deposition in two stages with 180° substrate rotation in between, good uniformity across the substrate was accomplished. The resistivities of about 80 nm thick Rh₂O₃ films were from 5 to 8 mΩcm.

Wurtzite GaN(001)-films were implanted with 195 keV 57Fe ions with a fluence Φ = 4*10^{16 cm-2} at room temperature. No secondary phase was detected in as implanted state. In order to reduce the implantation damage and to investigate the formation of secondary phases the implanted samples were annealed at 1073 K in a reduced N2-atmosphere (0.5 bar) for several cycles in a minute range. The formation of secondary phases in Fe implanted GaN upon annealing was detected by means of in-situ x-ray diffraction and conversion electron Mössbauer spectroscopy (CEMS). In contrast to our previous experiments with the annealing in a N2-flow at 1.1 bar pressure [3] no α-Fe cluster were found, but Fe3N. The repeatable phase change from Fe3N at room temperature and Fe3-xN at 1023 K was observed by means of in-situ x-ray diffraction. The diffusion of Fe during the annealing process limits the availability of secondary phase and hence the repeatability. The annealing process is accompanied by a strong diffusion of Fe and dissolution of GaN. Oxygen contamination promotes the dissolution of GaN and the formation of β-Ga2O3. The oxidation is confirmed by CEMS. The ferromagnetism in the samples is related to the presence of Fe3-xN. No DMS related phenomena have been observed. The results demonstrate that by variation of pressure phase compositions, other than α-Fe, are possible. It is expected that by the proper choice of annealing conditions specific secondary phases can be created, leading to different electronic, magnetic and other properties.

In this study, we report the unequivocal demonstration of midinfrared mode-locked pulses from quantum cascade lasers. The train of short pulses was generated by actively modulating the current and hence the gain of an edge-emitting quantum cascade laser (QCL). Pulses with duration of about 3 ps at full-width-at-half-maxima and energy of 0.5 pJ were characterized using a second-order interferometric autocorrelation technique based on a nonlinear quantum well infrared photodetector. The modelocking dynamics in the QCLs was modeled based on the Maxwell-Bloch equations in an open two-level system. Our model reproduces the overall shape of the measured autocorrelation traces and predicts that the short pulses are accompanied by substantial wings as a result of strong spatial hole burning. The range of parameters where short mode-locked pulses can be formed is found.

The neutron deficient p-nuclei are shielded from the s- or r-process by stable isotopes. P-nuclei are likely to be formed in high temperature cosmic scenarios like exploding supernovae by photodisintegration reactions on heavy r- or s- seed nuclei. The lack of experimental information on energy-dependent cross sections especially for (gamma,p) and (gamma,gamma) reactions reduces the applicability of nucleosynthesis models. Using intense bremsstrahlung produced at the superconducting electron linear accelereator ELBE at Forschungszentrum Dresden-Rossendorf we investigated (gamma,n), (gamma,p) and (gamma,alpha) reactions for the medium-mass p-nuclei 92Mo and 144Sm, as well as (gamma,n) reactions for 100Mo and 154Sm by photo-activation. The lowest photoactivation yields have been measured in an underground laboratory. The photodisintegration of 197Au serves as a benchmark and it is compared to data measured previously with the positron annihilation technique.

This talk summarizes our activities in nonlinear laser spectroscopy using the free-electron laser at FZD and tabletop lasers. Our research concentrates on III-V semiconductor quantum wells and superlattices. In particular, I will focus on pump-probe spectroscopy, two-photon absorption, and photocurrent autocorrelation involving intersubband transitions in quantum wells at mid-infrared wavelengths, and discuss a concept for scalable photoconductive Terahertz emitters.

Quantum well infrared photodetectors (QWIPs) provide unique opportunities for high-performance thermal imaging. Due to their narrow absorption bands with relative spectral widths of the order of 10%, QWIPs are particularly suitable for thermal imaging applications involving several atmospheric transmission bands or several colors within the same band. For dual-band/dual-color FPAs, QWIP technology has the unique property that the active region for the long-wavelength band is transparent for the short-wavelength band. Narrow intersubband transition linewidths also enable us to enhance resonantly the cross section for two-photon-absorption by several orders of magnitude. This approach results in particularly sensitive quadratic two-photon detectors, which are useful for pulse diagnostics and photon correlation measurements of mid-infrared laser sources. In the first part of this talk, I will report on QWIP structures optimized for thermal imaging applications and on the performance of QWIP thermal imagers which were jointly realized by the Fraunhofer-Institute for Applied Solid State Physics (Freiburg, Germany) and AIM Infrarot-Module GmbH (Heilbronn, Germany). In particular, a dual-band QWIP FPA with 384x288 pixels detecting simultaneously in the 8 – 12 µm long-wavelength infrared (LWIR) and 3 – 5 µm mid-wavelength infrared (MWIR) regimes was found to exhibit a noise-equivalent temperature difference as low as 20.6 mK in the LWIR and 26.7 mK in the MWIR spectral bands. The array, which is based on a photoconductive QWIP for the MWIR and a photovoltaic "low-noise" QWIP for the LWIR, allows for synchronous and pixel-registered image acquisition in both bands. This functionality yields several advantages, including better distinction between target and background clutter, operation in a much wider range of ambient conditions, and the ability of remote absolute temperature measurement. The second part of my talk will address quadratic detection involving two-photon transitions in specially designed QWIP structures. These two-photon QWIPs are exploited in autocorrelation measurements of pulsed infrared sources including the free-electron laser FELBE in Dresden.

The possibility of detecting ³⁶Cl for geological exposure dating has been explored for several years at VERA (the Vienna Environmental Research Accelerator). First results on real samples were obtained with an ionization chamber (developed at the ETH/PSI, Zürich, Switzerland) with two anodes. To improve the suppression of ³⁶S, we equipped the ionization chamber with an exit window and added a Time-of-Flight (TOF) system with a double-sided silicon strip detector (50x50 mm²) as stop detector. We optimized the TOF setup by using silicon nitride foils to reduce scattering tails in the energy spectra.
At 3 MV terminal voltage, corresponding to a particle energy of 24 MeV of ³⁶Cl⁷⁺, we achieved a ³⁶S7+-suppression of 21500 (50% ³⁶Cl-detector-efficiency).

The EC-funded project SPIRIT (Support of Public and Industrial Research using Ion beam Technology) [1] started in March 2009. It will provide free transnational access to European ion beam infrastructures for users from research and industry. Besides we will improve the methods and tools for ion-beam based analysis and processing of materials by helping European researchers to carry out state-of-the-art multidisciplinary scientific and technological research.
SPRIT partners are eleven leading ion beam facilities, i.e.
• FZD Dresden-Rossendorf (management), Germany*
• Centre d’Etudes Nucléaires de Bordeaux-Gradignan, France*
• Centre de Recherche sur les Ions, les Matériaux et la Photonique, Caen & Service de Recherche en Métallurgie Physique, Saclay, France*
• Instituto Tecnológico e Nuclear, Portugal
• Jožef Stefan Institute, Ljubljana, Slovenia*
• Katholieke Universitet Leuven, Belgium*
• Ruđer Bošković Institute, Zagreb, Croatia
• Surrey Ion Beam Centre, University of Surrey, Great Britain*
• Swiss Federal Institute of Technology, Zurich, Switzerland
• Universität der Bundeswehr, München, Germany*
• Université de Pierre et Marie Curie, Paris, France
Within the project the partners use and provide fast ions (10 keV-100 MeV) for the purpose of modification and analysis of surfaces, interfaces, thin films and nanostructured systems. The partners themselves and their external users focus on fundamental and applied research spanning from material sciences over life, environmental and Earth sciences to investigations of objects from art and cultural heritage.
For example, element distributions can be determined non-destructively and standard-free by mean of ion beam analysis (IBA) including Rutherford Backscattering Spectrometry (RBS), Nuclear Reaction Analysis (NRA), Elastic Recoil Detection Analysis (ERDA), Particle-Induced X-Ray (PIXE) and Gamma-Emission (PIGE) [2]. All natural-occurring elements are accessible; most elements with lateral, some in 3-D resolution (depth-range: nm-µm; depth-resolution: 0.5-30 nm). Typical detection limits are 10 µg/g (H), 500 µg/g - 1% (He-O), 1 µg/g (F), 10-100 µg/g (Na-U).
Seven SPIRIT partners – those marked above with a * – provide transnational access to researchers from the European Community. Help is provided to external users during planning, performance and evaluation of their research projects. Proposals [3] for running experiments in person (“hands-on”) or remote services are selected after a formal reviewing and ranking following scientific criteria as innovation/originality by an international expert panel. All costs including travel for external users are covered by the EC.
References: [1] www.spirit-ion.eu, contract number 227012. [2] C. Neelmeijer et al., this meeting. [3] http://www.spirit-ion.eu/Project/Transnational-Access/Application-Form.html.

no abstract available

Saturable absorption mode-locking based on intersubband transitions in quantum wells at 2 μm.

The formation of Fe-filled carbon nanotubes by thermal decomposition of ferrocene combined with a Fe-catalyst-nanostructuring on an oxidized Si substrate is investigated in the temperature range of 1015 – 1200 K. The optimal growth conditions for aligned and homogeneous carbon nanotubes are found at 1100 K. Mössbauer spectroscopy (both in transmission geometry and CEMS) was used to analyze and quantify the different formed Fe-phases. In general, a-Fe, g-Fe and Fe3C are found to form within the carbon nanotubes. Depending on the growth conditions their fractions vary strongly. Moreover, an alignment of the a-Fe in the tubes could be detected.

Kaons and Antikaons in Nuclear Matter: AA vs. pA Collisions

Transport model calculations for HADES

Transport Models for Heavy-Ion Collisions

The coordination of the limiting U(IV) carbonate species in aqueous solution was investigated by comparing its structure parameters with those of the complex preserved in a crystal structure. The solution species was obtained in a aqueous solution of 0.05 M U(IV) and 1 M NaHCO3. Single crystals of Na6[U(CO3)5]•12H2O were obtained directly from this mother solution. The U(IV) carbonate complex in the crystal structure was identified as [U(CO3)5]6 anionic complex. This monomeric complex forms a network with charge compensating Na+ cations and H2O ligands. The interatomic distances around the U(IV) coordination polyhedron show average distances of U-O = 2.461(8) Å, U-C = 2.912(4) Å and U-Odist = 4.164(6) Å. U L3edge EXAFS spectra were collected from the solid Na6[U(CO3)5]•12H2O and the corresponding solution. In both samples, the first shell of the Fourier transforms (FTs) revealed ten oxygen atoms at an average distance of 2.450.02 Å, the second shell originates from five carbon atoms with a U-C distance of 2.910.02 Å, and the third shell was fit with single and multiple scattering paths of the distal oxygen at 4.170.02 Å. These data indicate the identity of the [U(CO3)5]6 complex in solid and solution state. The high negative charge of the [U(CO3)5]6 anion is compensated by Na+ cations. In solid state the Na+ cations form a bridging network between the [U(CO3)5]6 units, while in liquid state they seem to be located closer at the anionic complex. The average metal-oxygen distances of the coordination polyhedron show a linear correlation to the radius contraction of the neighbour actinide(IV) ions and indicate the equivalence of the [An(CO3)5]6 coordination within the series of thorium, uranium, neptunium and plutonium.

The L3-edge x-ray absorption spectrum of the aqua trivalent Cm ion in aqueous solution exhibits a double photoexcitation involving 2p and 4f electrons. The sharp resonance structure of the multielectron excitation reveals a shake-up process at 508.110 eV. The data indicate a monotonic increase of the [2p4f] excitation energy between elements of sixth period (Au, Hg, Pb, and Bi) and the early actinides (Th, Pa, U, Np, Pu, Am and Cm).

It is our pleasure to publish the Proceedings of the 16th International Conference on Ion Beam Modification of Materials (IBMM 2008), which was held at the Lecture Hall Centre of the Technische Universität at Dresden, Germany, from August 31 to September 5, 2008, under the common organization by the Forschungszentrum Dresden-Rossendorf, Dresden, Germany and the Leibniz-Institut für Oberflächenmodifizierung, Leipzig, Germany.
The biannual IBMM International Conference Series looks back on a 30-years history starting in 1978, being considered as the major international forum to present and discuss recent results in ion-related materials research and to point into the future of the field. It assembles physicists, chemists, material scientists and engineers from all over the world and along the whole chain from basic research to industrial production.

Microorganisms, microbial components, biopolymers and bioligands secreted by microbes have a great potential to influence the behavior of actinides in the environment. Functional groups provided by both lipopolysaccharide (LPS: main part of the cell wall of Gram-negative bacteria), and peptidoglycan (PG: main part of the cell wall of Gram-positive bacteria) are very effective in complexing uranium(VI) over a wide pH range (2.0 to 9.0) [1, 2]. The main functionalities for uranyl binding are phosphoryl and carboxyl groups of LPS and carboxyl groups of PG. The aerobic soil bacterium Pseudomonas fluorescens (CCUG 32456 A) isolated from the aquifers at the Äspö Hard Rock Laboratory, Sweden secretes pyoverdins. These unique bioligands have a high potential to bind uranium(VI) and curium(III) mainly due to their hydroxamate and catecholate functionalities [3, 4]. However, the interaction of neptunium(V) with both microbial cell wall components (LPS, PG) and secreted bioligands (PYO) are unknown. To address this lack, we thus present findings regarding the complexation of neptunium(V) with LPS, PG, and P. fluorescens (CCUG 32456) pyoverdins (PYO) obtained using near-infrared (NIR) absorption spectroscopy.
The spectrophotometric titrations of the Np(V)-LPS system showed a dominant neptunyl(V) coordination to phosphoryl groups between pH 4 and 8 followed by hydroxyl interactions in the alkaline pH range. A very low affinity of Np(V) to interact with the carboxyl groups of PG was measured. Strong Np(V)-pyoverdin species of the type MxLyHz could be identified from the spectrophotometric titrations. Remarkable was that the influence of Np(V)-pyoverdin species could already be detected under equimolar conditions.
Estimates are possible, on the basis of the determined stability constants, if neptunium(V) prefers to interact with the microbial cell wall (LPS), with biopolymers (PG) or with the secreted pyoverdin bioligands (PYO). The calculations were performed using nearly equimolar conditions of Np(V) and functional groups of the biosystems. More than 80% of all Np(V) is bound to pyoverdin species at pH 8 compared to ~37% bound to LPS and less than 1% bound to PG. This shows both the high affinity of neptunium(V) to bioligands containing hydroxamate and catecholate groups and the importance of indirect interaction processes between neptunium(V) and bioligands secreted by resident microbes.

[1] A. Barkleit, H. Moll, G. Bernhard, Dalton Trans. 2879-2886 (2008).
[2] A. Barkleit, H. Moll, G. Bernhard, Dalton Trans. published online: DOI 10.1039/b818702a (2009).
[3] H. Moll, M. Glorius, G. Bernhard, A. Johnsson, K. Pedersen, M. Schäfer, H. Budzikiewicz, Geomicrobiol. J. 25, 157-166 (2008).
[4] H. Moll, A. Johnsson, M. Schäfer, K. Pedersen, H. Budzikiewicz, G. Bernhard, Biometals 21, 219-228 (2008).

This work was funded by the BMWi under contract number: 02E9985.

Seit langem ist bekannt, dass die Magnetfelder von Planeten, Sternen und Galaxien durch den hydromagnetischen Dynamoeffekt erzeugt werden. Weniger bekannt ist die erstaunlich aktive Rolle, die Magnetfelder in der kosmischen Strukturbildung spielen. So sind die hohen Wachstumsraten von Sternen und Schwarzen Löchern nur erklärbar, wenn die Akkretionsscheiben, aus denen sie gefüttert werden, turbulent sind und damit Drehimpuls effektiv nach außen transportieren können. Die Ursache dieser Turbulenz liegt in der destabilisierenden Wirkung von Magnetfeldern auf rotierende Strömungen, die als Magnetorotationsinstabilität (MRI) bezeichnet wird. Der Vortrag gibt eine kurze Einführung in die Theorien zur Entstehung und Wirkung kosmischer Magnetfelder. Im Mittelpunkt stehen aber die Flüssigmetall-Experimente der letzten zehn Jahre, in denen Dynamoeffekt bzw. MRI untersucht worden sind, insbesondere das PROMISE-Experiment am Forschungszentrum Dresden-Rossendorf.

The charge retention characteristics of SONOS (silicon-oxide-nitride-oxide-silicon) nonvolatile memory cells at elevated temperatures were investigated. Assuming the thermal excitation model to be the dominant charge loss mechanism, the trap energy distribution in the nitride was determined. We present an improved model which includes the influence of subsequent tunneling of the charge carriers through the bottom oxide after being thermally emitted into the conduction band of the silicon nitride. The trap energy distribution was evaluated from samples with different bottom oxide thicknesses. Using this model it was found that the detected trap energy distribution is nearly identical despite the different tunneling probabilities from the various bottom oxide thicknesses.

The oxygen content of binary Ti₄₅Al₅₅ and ternary Ti₄₄Al₅₂Nb₄ single crystals and polycrystalline alloys
was quantified with secondary ion mass spectrometry (SIMS) using Cs⁺ primary ions. The SIMS measurements
were calibrated with respect to concentration and depth scale using oxygen implanted samples.
The measurements revealed considerably lower oxygen content in the ternary alloy indicating a protecting
impact of the Nb addition in grain boundaries against oxygen contamination. The relative strong
surface oxide layer thickness of the investigated samples was determined to about 1µm.

Electrostatic charging changes the critical temperature of superconducting thin layers. To understand the basic mechanism, it is possible to use the Ginzburg-Landau theory with the boundary condition derived by de Gennes from the BCS theory. Here we show that a similar boundary condition can be obtained from the principle of minimum free energy.
We compare the two boundary conditions and use the Budd-Vannimenus theorem as a test of approximations.

Magnetic characterization is shown to be a highly effective, nondestructive, and commonly available method to accurately assess dehydrogenation temperatures and further clarify the reaction mechanisms during dehydrogenation in systems with superconducting or ferromagnetic constituents. As examples, the dehydrogenation temperature of NaBH4 in a nanostructured NaBH4/MgH2 system and the dehydrogenation process of nanostructured Mg2CoH5, based on the superconducting and ferromagnetic properties of MO, and Co, respectively, are determined.

A selfconsistent T-matrix theory of many-Fermion systems is proposed. In the normal state the theory agrees with the Galitskii-Feynmann approximation, in the superconducting state it has the form of the renormalized Kadanoff-Martin approximation. The two-particle propagator satisfies the Baym-Kadanoff symmetry condition which guarantees that the theory conserves the number of particles, momentum and energy. The theory is developed for retarded interactions leading to the Eliashberg theory in the approximation of a single pairing channel.

Hydrogen (H) is continuously produced by the large dose fast neutron irradiation on fusion reactor material. The concentration, diffusion and evolution of H in the structure material may cause H-embrittlement. Ion beam analysis is one of the most useful methods for studying the micro-kinetics of H in solids. In this work, the H-distribution in titanium (Ti) has been studied by resonance nuclear reaction analysis (resonance-NRA) and micro-elastic recoil detection analysis (micro-ERDA). The evolution of H-depth-profile in titanium samples has been studied versus the change of normal stress. Evident H diffusion has been observed, while a normal stress is changed in the range of 107-963 MPa. The H diffusion is related to the concentration of H in samples.

It is well known that oblique low and medium energy (typically 0.1 – 100 keV) ion erosion of solid surfaces can lead to the formation of periodic ripple patterns with wavelengths ranging from 10 to 1000 nm. These ripple structures have been found on a large variety of materials, including semiconductors, metals, and insulators. The formation and early evolution of the ripple patterns can be described by a linear continuum equation derived by Bradley and Harper. At longer times, however, nonlinear terms have to be taken into account, leading to nonlinear models based on the Kuramoto-Sivashinsky equation.
This talk will provide an overview of ion-induced pattern formation and summarize the theoretical basics. Recent experimental results on the evolution of nanoscale ripple patterns on silicon surfaces during high-fluence ion sputtering will be presented and compared to the predictions of different continuum models. In addition, promising applications of nanorippled substrates as templates in thin film growth will be discussed.

Silicon ion implantation effects on the optical and photoluminescence (PL) properties of polymethylmethacrylate (PMMA) have been studied. Low-energy ion implantation (E = 30-50 keV) was carried out over a range of different ion fluences (D = 10(13)-10(17) cm(-2)). Visible PL and optical transmission spectra in the range (330-800 nm) have been measured. The existing visible range PL emission in the unimplanted PMMA samples is clearly affected by the Si+ ion implantation and the observed modification effect of photoluminescence enhancement (PLE) is essentially dependent on the implantation fluence. For certain fluences, dependent on the ion energy, the overall amplitude of the PL emission has a several times (similar to 5 times) increase. Optical absorption also gradually increases with the fluence.

We present extended experimental material about optical and mechanical properties of oxide optical coating materials, deposited by electron beam evaporation, ion and plasma ion assisted evaporation, sputtering and ion plating. A clear correlation between these experimental data is established and understood as being caused by the different degree of the porosity of the films. This assumption has been verified by investigation of the layer structure and accompanying simulations of the effect of porosity on refractive index, layer stress and thermal shift. As a practical conclusion, we find that a certain pore fraction in the films is essential in order to get a valuable balance between optical and mechanical coating properties.