Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

In this contribution we concentrate on two selected oxides, MgO and BeO, and examine theoretically their basic positron characteristics. In particular, we calculate the bulk positron lifetime and affinity and determine the positron distribution in defect free systems. Both self-consistent and non-self-consistent computational methods are used in calculations. Obtained characteristics are then discussed in terms of the structure and bonding properties of oxides and are compared to experimental data available. The issue of electron-positron correlations in insulating materials is also mentioned.

The nature of the interface of the Si (001) surface with grown, native oxide is examined by a slow-positron beam equipped with coincidence Doppler broadening (DB). Measurements are combined with theoretical calculations of high-momentum DB profiles of Si, divacancy in Si, Brazilian quartz and the interface itself. From this comparison, the conclusion is drawn that an ordered structure exists at the interface. This structure resembles low quartz or a SiO2 structure with a lower density than low quartz.

Slow Positron Implantation Spectroscopy (SPIS), based on the generation, implantation and subsequent annihilation of mono-energetic positrons in a sample, has been used to study depth dependent vacancy-type damage in three ZnO films grown by pulsed laser deposition on c-plane sapphire. Doping was achieved by implantation of 250 keV Mn+ ions at 300 ◦C with three different fluences—1016, 3 × 1016, and 6 × 1016 cm−2, and subsequent thermal annealing in air. Evolution of the open volume damage, its depth distribution, and the magnetic behavior was investigated by
SPIS and Magnetic Force Microscopy. No indication of magnetic domain formation was found in any of the three films after implantation and the first annealing at 500 ◦C, whereas after the second annealing at 750 ◦C the two samples having the higher fluence showed stripe-like magnetic domains.

Thin niobium (Nb) films (thickness 350–400 nm) were prepared on (1 0 0)Si substrate in a UHV chamber using the cathode beam sputtering. The sputtering temperature Ts was varied from 40 up to 500 8C and the influence of the sputtering temperature on the microstructure of thin Nb films was investigated. Defect studies of the thin Nb films sputtered at various temperatures were performed by slow positron implantation spectroscopy (SPIS) with measurement of the Doppler broadening of the annihilation line. SPIS was combined with transmission electron microscopy (TEM) and X-ray diffraction (XRD). We have found that the films sputtered at Ts = 40 8C exhibit elongated, column-like nanocrystalline grains. No significant increase of grain size with Ts (up to 500 8C) was observed by TEM. The thin Nb films sputtered at Ts = 40 8C contain a high density of defects. It is demonstrated by shortened positron diffusion length and a high value of the S parameter for Nb layer compared to the well-annealed (defect-free) bulk Nb reference sample. A drastic decrease of defect density was found in the films sputtered at Ts ≥ 300 8C. It is reflected by a significant increase of the positron diffusion length and a decrease of the S parameter for the Nb layer. The defect density in the Nb layer is, however, still substantially higher than in the well-annealed reference bulk Nb sample. Moreover, there is a layer at the interface between the Nb film and the substrate with very high density of defects comparable to that in the films sputtered at Ts < 300 8C. All the Nb films studied exhibit a strong (1 1 0) texture. The films sputtered at Ts < 300 8C are characterized by a compressive macroscopic in-plane stress due to lattice mismatch between the film and the substrate. Relaxation of the in-plane stress was observed in the films sputtered at Ts ≥ 300 °C. The width of the XRD profiles of the films sputtered at Ts ≥ 300 °C is significantly smaller compared to the films sputtered at lower temperatures. This is most probably due to a lower defect density which results in reduced microstrains in the films sputtered at higher temperatures.

Hydrogen interaction with defects in thin niobium (Nb) films was investigated using slow positron implantation spectroscopy (SPIS) combined with X-ray diffraction (XRD) and transmission electron microscopy (TEM). Thin Nb films on Si substrates were prepared using cathode beam sputtering at room temperature. Initially, the microstructure of the virgin (hydrogen-free) films was characterized. Subsequently, the films were step-by-step electrochemically charged with hydrogen and the evolution of the microstructure with increasing hydrogen concentration was monitored. Hydrogen loading leads to a significant lattice expansion which was measured by XRD. Contrary to free-standing bulk metals, thin films are highly anisotropic. The in-plane expansion is prevented because the films are clamped on the elastically hard substrate. On the other hand, the out-of-plane
expansion is substantially higher than in the bulk samples. Moreover, an enhanced hydrogen solubility in the a-phase was found in nanocrystalline Nb films. It was found that most of positrons in the films are trapped at open-volume defects at grain boundaries (GBs). These defects represent trapping sites also for hydrogen atoms. Hydrogen trapping at vacancy-like defects like GBs leads to a local increase of the electron density and is reflected by a pronounced decrease of the S parameter in the hydrogen-loaded samples. In addition, it was found that new defects are introduced at higher concentrations of hydrogen due to the formation of NbH (b-phase) particles.

EPOS, the acronym of ELBE Positron Source, describes a running project to build an intense pulsed beam of mono-energetic positrons (0.2-40 keV) for materials research. Positrons will be created via pair production at a tungsten target using the pulsed 40 MeV electron beam of the superconducting electron linac with high brilliance and low emittance (ELBE) at Forschungszentrum Rossendorf (near Dresden, Germany). The chosen design of the system under construction is described and results of calculations simulating the interaction of the electron beam with the target are presented, and positron beam formations and transportation are also discussed.

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In spite of previous extensive studies, the helium behavior in metals still remains an issue in microelectronics as well as in nuclear technology. A gold–silver solid solution (Au60Ag40: synthetic gold-rich electrum) was chosen as a relevant model to study helium irradiation of heavy metals. After helium-3 ion implantation at an energy ranging from 4.2 to 5.6 MeV, nuclear reaction analysis (NRA) based on the 3He(d,p)4He reaction, was performed in order to study the thermal diffusion of helium atoms. At room temperature, NRA data reveal that a single Gaussian can fit the He-distribution, which remains unchanged after annealing at temperatures below 0.45 of the melting point. Slow positron implantation spectroscopy, used to monitor the fluence dependence of induced defects unveils a positron saturation trapping, which occurs for He contents of the order of 50–100 appm, whereas concentrations larger than 500 appm seem to favor an increase in the S-parameter of Doppler broadening. Moreover, at high temperature, NRA results clearly show that helium long range diffusion occurs, though, without following a simple Fick law.

The compound formation in the ternary system Pr-Si-O initiated by ion beam synthesis inside bulk-Si material was studied by transmission electron microscopy and x-ray diffraction. The oxygen content was varied by additional O ion implantation and by oxidation or implantation into SiO2. For annealing temperatures of 1100°C Pr silicate grains were observed consisting of Pr9.33Si6O26 or Pr2Si2O7. Pr silicide was found in minor fraction also in samples with enhanced oxygen content and for lower annealing temperatures such as 900°C. Pr oxide, the promising high-k material, was not definitely verified. The obtained results can be explained by the simple consideration that the energy should be minimized related with reordering inside the Si material during compound formation.

Silver nanoparticles are formed in a polystyrene film by temperature induced dissociation of an organometallic precursor dispersed in the polymer. Further heating of the sample above the polymer boiling point allows control over the fill content of the silver particles. The process is recorded in real time by spectroscopic ellipsometry. The ellipsometric data is modeled using the Maxwell-Garnett effective medium approximation. Modeling the silver component using a Drude term with a modified electronic relaxation frequency allows the particle size to be inferred by scaling the relaxation frequency with microstructural observations of the particle dimensions. The particle size can subsequently be determined during the growth process from the final radius of 7.4 nm back to 2.3 nm, at which point quantum size effects limit the effectiveness of the model.

We have investigated strain compensated Si/Si0.2Ge0.8 multilayers, which were grown pseudomorphically on relaxed Si0.5Ge0.5 pseudosubstrates by molecular beam epitaxy. The stability of these highly strained Si/SiGe structures upon in situ annealing has been measured by means of x-ray reflectivity (XRR) up to 830°C. The temporal evolution of XRR reciprocal space maps was recorded, and a gradual disappearance of the multilayer structure was detected after annealing for 7 h at a temperature of 790°C. From the temporal evolution of the optical constants of the layers, deduced from the simulations and fits of the specular reflectivity, we obtained an interdiffusion coefficient D = (1.01 ± 0.03) × 10^-21 m² s^-1 at 790°C.

Measurement with local needle probes is a well-established method for the investigation of multiphase flows. Different measuring techniques have been employed for the needle probes in the past. The most known techniques are based on: conductivity, capacitance, optical and/or temperature measurements [1-3]. Based on the detection of single phases, these probes can provide information about void fraction, bubble size, frequency, and velocity, among others. The existing needle probe systems have limitations regarding the range of substances they are able to measure, the environmental conditions they can be applied to as well as their time resolution. In this paper we describe two new developed needle probe sensors, which will enhance their application field. On one hand we present the further development of ultra-fast thermo needle probes for the phase-resolved temperature measurement aiming the investigation of interfacial areas in the multiphase flow. On the other hand we introduce a new complex admittance needle probe, which is able to measure either conducting or non-conducting fluids, thus enabling the investigation of multiphase flow problems (e.g. three-phase flow of oil, water and gas in the oil extraction).

Local void fractions measurements in two-phase flow phenomena are commonly carried out by the use of needle probes. The measuring principle of these probes is based on conductivity or optical measurements. In the past advanced needle probes with integrated micro-thermocouples have been introduced by Prasser et al., making possible to measure local temperatures at the same position where the void fractions are determined because the sheath of the micro-thermocouple serves as the measuring electrode for the conductivity measurement. Thereby - in principle - the temperatures of the two different phases (e. g. steam and water) can be distinguished. The big disadvantage of this technique is the relative long time constant (~20 ms) of mineral-insulated sheathed thermocouples. The usage of this type of thermocouples was necessary because the electronic was not able to separate the two signals (temperature and conductivity) from each other. Measuring of high-transient two phase flows were impossible due to the slow time response. Additionally the two signals had to be sampled sequentially because of influence of the rectangular excitation signal into the small temperature voltage. Investigations of temperature changing in the interfacial area between gas and liquid were therefore very difficult. To solve this problem we have developed a new combined temperature and conductivity needle probe measuring system, which is able to handle grounded or direct sheathed thermocouples (where the thermocouple wires are electrically-joined to the protective sheath) as well as open thermocouples (exposed junction).

In situ real-time spectroscopic ellipsometry is used to monitor the growth of magnetron sputtered silver nanoparticles on SiO2 substrates, through the percolation threshold and into the bulk film regime. The plasmon polariton resonances in the nanoparticulate regime are effectively modelled by a Lorentz oscillator. The resonance energy of the oscillator is observed to reduce to zero shortly after the percolation threshold, whereby the oscillation is described by Drude free electron theory. From the Drude theory, the electronic mean free path is observed to increase dramatically at the percolation threshold, to a value of 16 nm in the bulk regime, in good agreement with x-ray diffraction and transmission electron microscope measurements of the crystallite size in the films. Shortly before the percolation threshold the data is better modelled by two Lorentz oscillators, attributed to coupling between the plasmon polaritons. The onset of the coupling is determined to occur at a surface area coverage of 52%.

The Keggin type polyoxotungstate [Ti2W10PO40]7- forms stable associates with the biopolymer chitosan in the nanometer size range. The cluster compound crystallizes from aqueous solution as K4H3[Ti2W10PO40]×15H2O having a tetragonal structure. Both, the cluster compound and the chitosan/[Ti2W10PO40] associates show a high hydrolytic stability at pH 7.4. The associates formed of the cluster anion [Ti2W10PO40]7- with the polyaminosaccharide chitosan have been characterised by photon correlation spectroscopy, scanning electron microscopy, filtration, centrifugation and zeta potential measurements. The size of the associates formed is in the range of about 5 ∙ 10E+1 to 5 ∙ 10E+2 nm. These particles have a defined stoichiometry with 5-6 cluster anions bound per molecule chitosan. The isoelectric point determined by zeta potential measurements was found at a cluster anion to chitosan molar ratio of 5.5 indicating the charge neutralization between protonated chitosan and [Ti2W10PO40]7- anions. Cellular uptake studies with [Ti2W10PO40]7- using tumor cell lines FaDu (human squamous carcinoma) and HT-29 (human adenocarcinoma) showed that the tungsten amount inside the cells is remarkably enhanced in the presence of chitosan.

The aim of the present experiment was to analyse the structural evolution during annealing of Nickel-Titanium (Ni-Ti) SMA subjected to different thermomechanical treatments. As structural evolutions are accompanied by the changes in preferential orientations, pole figures were employed to study the in-situ conditions.

Recently it has been shown that lateral carrier confinement in an InGaAs quantum well (QW) embedded in GaAs can be achieved by using a laterally patterned InGaP stressor layer on top of the heterostructure. To exploit this effect in a device the structure has to be planarized by a second epitaxial step. It has been shown that the lateral strain modulation almost vanishes after overgrowth with GaAs, whereas overgrowth with a single ternary layer of opposite strain compared to the stressor layer suffers from strain induced decomposition. Here we show that the lateral carrier confinement of the initially free standing nanostructure can almost be maintained using a two step process for overgrowth, where a strained thin ternary layer is grown first followed by GaAs up to complete planarization of the patterned structure. Thickness and composition of the ternary layer are adjusted on the basis of finite element calculations of the strain distribution (FEM). The strain field achieved after overgrowth is probed by X-ray grazing-incidence diffraction (GID).

Thin films of indium tin oxide (ITO) are widely used in optoelectronic devices due to the materials transparency in the visible range of the spectrum and its low electrical resistivity. The ITO film formation and evolution at elevated temperatures is not properly addressed because the phase diagram of this material is not known. The amorphous-to-crystalline transition is often assumed as the reason for decrease of ITO resistivity at enhanced temperatures due to a Sn donor activation, but the physical mechanisms behind the experimental observations are not clear.
This study is focused on in situ spectroscopic ellipsometry (SE) monitoring of the film properties during growth at elevated temperatures (Ts=RT-500 °C) as well as during postdeposition annealing (Ta=200-300 °C). In addition, during annealing, the SE results are contrasted with data of in situ four point probe resistivity measurement technique, the in situ X-ray diffraction (XRD) and elastic recoil detection analysis (ERDA). The atomic force microscopy and cross-sectional transmission electron microscopy were used to study the film morphology ex situ.
The free electron parameters were determined from parameterization of the film optical constants in Drude-Lorentz approach. The applicability of spectroscopic ellipsometry as a non-contact and in situ tool for monitoring of the film resistivity is shown. However, quantitative characterization of the resistivity by SE requires further improvement of the optical model for the growing film. The existence of the resistivity grading through the film thickness was indicated by this method for the growth without heating. ITO film resistivity rapidly deteriorates at thickness below 40 nm if the substrate temperature is less or equal 270 °C due to decrease of the free electron density and mobility. It can be explained by formation of an amorphous layer or layer with chaotically oriented crystallites on initial stages of the film growth, depending on the film temperature. There is no such layer observed at deposition temperatures higher than 400°C that denotes change in the film growth mode.
Spectroscopic ellipsometry provides valuable information both on the properties and the morphology modification during isothermal annealing of ITO films. Isothermal heating modifies the film properties in two stages which are attributed to: (i) relaxation of In-O bonds in the amorphous phase, (ii) Sn-donor activation by removal of interstitial oxygen. Different crystallization modes at 210 and 240 °C are suggested both by the real-time roughness behavior from SE and in situ XRD analysis.

The spectrum of the spherically symmetric α²-dynamo is studied in the case of idealized boundary conditions. Starting from the exact analytical solutions of models with constant α-profiles a perturbation theory and a Galerkin technique are developed in a Krein-space approach. With the help of these tools a very pronounced α-resonance pattern is found in the deformations of the spectral mesh as well as in the unfolding of the diabolical points located at the nodes of this mesh. Non-oscillatory as well as oscillatory dynamo regimes are obtained. Finally, Fréchet derivative (gradient) based methods are developed, suitable for further numerical investigations of Krein-space related setups like MHD α²-dynamos or models of PT-symmetric quantum mechanics.

No abstract available!

Halbleitermaterialien, insbesondere Silizium, erfordern nach bestimmten Prozessschritten wie der strahlenschädigenden Ionenimplantations-Dotierung eine Temperbehandlung, deren Zeitdauer im Verlauf der letzten Jahre im Extremfall nur noch ca. 1 sec betrug. Solche kurzen Temperzeiten erfordern Anlagen, bei denen die Oberflächen durch Lichteinstrahlung bewirkt werden kann, um schnelle Zykluszeiten und eine geringe Aufheizung der Probenumgebung zu gewährleisten. Kürzlich wurden diese Anforderungen noch verschärft, indem die Forderung nach Temperzeiten im msec-Bereich erhoben wurde. Während Temperzeiten bis hinab zu einer Sekunde noch mit relativ langsam reagierenden Halogenlampen gewährleistet werden können, sind kürzere Temperzeiten nur noch mit schnell schaltbaren Xenon-Blitzlampen oder gerasterten Laserstrahlen realisierbar. Der Vorteil solch einer extrem kurzen Oberflächen-Wärmebehandlung liegt vor allem darin, dass das Volumen der Probe nicht mehr unbedingt durchgeheizt wird, andererseits aber auch ein gezieltes Anschmelzen von Oberflächen möglich wird. Ebenso sind mit solchen Techniken extrem kurze Zykluszeiten in Produktionsabläufen realisierbar. Im Vortrag werden Fragen der Anlagentechnik sowie Anwendungsbeispiele aus der fortgeschrittenen Halbleitertechnologie behandelt: a) Unterdrückung der beschleunigten Diffusion von Bor-Implantaten, sowie b) Unterstützung der Heteroepitaxie von Siliziumkarbid auf Silizium durch nanoskalige Phasenverflüssigung an der Grenzfläche. Es wird ein kurzer Ausblick zu Anwendungen ausserhalb der Welt der Halbleiter gegeben.

No abstract available!

No abstract available!

NO abstract available!

Some of the references were numbered incorrectly. The correct reference list is as follows...

An approach for the defect density reduction in 3C-SiC epitaxially grown on Si is to improve the quality of the carbonized layer during the early stage of growth. For this reason the conventional carbonization process was replaced by a slower and nearer equilibrium carbonization method. Carbon is introduced by implantation into oxide of an ocidized Si substrate, near the SiO2/Si interface, and then it is transferred to the Si surface by annealing. Good quality 3C-SiC grains are formed embedded into the Si substrate, which are absolutely flat at the SiO2/Si interface. Another advantage of the new carbonization process is the elimination of the cavities due to the suppression of Si out-diffusion.

We studied the effect of electric field generated on photoluminescence (PL) of silicon nanocrystals embedded in SiO2 films. We show that the application of electric field generated by means of surface acoustic waves (SAW) results in an increase of the PL intensity of nanocrystal photoluminescence by as much as 10% at a field amplitude of 12 kV/cm at temperatures below 15 K. At temperatures above 20 K the PL intensity decreases as the electric field is applied. The results are discussed within the frame of the self-trapped exciton model.

This paper gives an insight into the thermal modeling of the i-FLASiC process, which is the flash lamp annealing of a 3C-SiC and silicon multilayer system. The model uses a standard heat flow model combined with an advanced multilayer optical model. Results from the model are consistent with experimentally observed phenomenon and have been used to explain diffusion mechanisms for the LPE of SiC.

Thin poly-crystalline silicon films are attractive for the fabrication of active matrix liquid crystal displays. We propose the use of flash lamp annealing to recrystallize amorphous silicon layers on glass substrates as a low cost manufacturing route. In this process amorphous silicon can be crystallized both by solid phase crystallization (SPC) and in the super lateral growth (SLG) regime. We present a thermal model which incorporates the phase transitions during annealing and we have shown that predictions from the model are in good agreement with experimental observations. In addition, the model is a valuable aid to optimizing the process conditions.

Using ion implantation different rare earth luminescent centers (Gd3+, Tb3+, Eu3+, Ce3+, Tm3+, Er3+) were formed in the silicon dioxide layer of a purpose-designed Metal Oxide Silicon (MOS) capacitor with advanced electrical performance, further called a MOS-light emitting device (MOSLED). Efficient electroluminescence was obtained for the wavelength range from UV to infrared with a transparent top electrode made of indium-tin oxide. Top values of the efficiency of 0.3 % corresponding to external quantum efficiencies distinctly above the percent range were reached. The electrical properties of these devices such as current-voltage and charge trapping characteristics, were also evaluated. Finally, application aspects to the field of biosensing will be shown.

The paper gives an overview of our recent work in the field of thermal processing of advanced semiconductor structures by millisecond flash lamp annealing (FLA). Topics covered include ultra-shallow junction (USJ) formation and heteroepitaxial growth of improved quality thin films of cubic silicon carbide (3C-SiC). The latter is a new development, which opens up promising 3C-SiC growth possibilities and may lead to wider application of FLA. The so-called FLASiC process (Flash LAmp Supported Deposition of SiC) is based on a new type of nanoscale liquid-phase epitaxy at the SiC/Si interface resulting in the formation of a thin, low defect density seed layer of SiC onto which thicker epitaxial SiC layers can be grown.

Recently a new interest evolved in short time annealing far below 1 sec, i.e. the lower limit of Rapid Thermal Processing (RTP). This was driven by the need of suppressing the so-called Transient Enhanced Diffusion in advanced boron-implanted shallow pn-junctions. After a short common overview about the new opportunities in materials processing, in this talk two examples will serve for the demonstration of the new interest in flash lamp annealing (time duration < 20 msec) within the framework of semiconductor materials processing: (i) For ultra-shallow junction formation in silicon Flash Lamp Processing (FLP) has become one of the challenging methods to meet the requirements for the next technology nodes defined by the ITRS roadmap. Low energy boron implants have been heat-treated in this way using peak temperatures in the range of 1100o to 1300oC and effective anneal times of 20 msec and 3 msec. Optimum processing conditions using a pulse time of 3 msec have been identified, under which one can obtain combinations of junction depth and sheet resistance values that meet even the 45 nm technology node requirements (ITRS 2001). (ii) The production of cubic SiC (3C-SiC) layers in device quality through the epitaxial growth on (100) Si wafers has remained a challenging task yet to overcome for selected applications the need in high cost bulk SiC wafers. It will be demonstrated that the use of Flash Lamp Processing (FLP) shows a new and promising way to the production of high quality 3C-layers. The FLASiC process bases on a new type of nanoscale liquid epitaxy at the interface SiC/Silicon leading to the formation of SiC seed layers with low defect density on which thicker SiC layers were epigrown.

Using ion implantation different rare earth luminescent centers (Gd3+, Tb3+, Eu3+, Ce3+, Tm3+, Er3+) were incorporated into the silicon dioxide layer of a purpose-designed Metal Oxide Silicon (MOS) capacitor with advanced electrical performance, further called a MOS-light emitting device (MOSLED). The silicon dioxide layer did not contain silicon nanoclusters. Efficient electroluminescence was obtained from UV to infrared with a transparent top electrode made of indium-tin oxide. The electroluminescence properties were studied with respect to the luminescence spectra, decay time, impact excitation, cross relaxation (Tb3+), and power efficiency. Top values of the efficiency of 0.3 % corresponding to external quantum efficiencies well above the percent range were reached. The electrical properties of these devices such as current-voltage and charge trapping characteristics, were also evaluated. Moreover, we demonstrate photo- and electroluminescence in correlation to charge trapping characteristics for Er-rich MOSLEDs with a varying silicon cluster content. Finally, application aspects to the field of biosensing will be discussed.

We have demonstrated intense violet electroluminescence (EL) from thermally-grown SiO2 films containing Ge nanocrystals produced by ion beam synthesis. An outline is given of the electrical and optical characteristics of ITO/SiO2/Al light-emitting devices incorporating Ge nanocluster-rich oxide films. Optimization schemes based on the use of local oxidation of Si (LOCOS) have been developed and tested successfully. Arrays of 4 × 6 light-emitting devices with a diameter of 300 μm and spacing of 500 μm between the adjacent devices have been formed using standard lithography patterning. Bioanalyses have been carried out following fluorescent-based detection procedures. As distinct from the standard case of diagnostics in which the light source is typically a laser and the necessary spatial resolution is provided by a CCD camera, our light sources are small enough to immediately ensure high resolution while permitting their light emission to be detected by single inexpensive Si diodes. The relevance of the all-Si light sources to microarray, miniaturized sensor and lab-on-a-chip systems for point-of-care diagnostics is discussed. Finally, first EL spectra of Si-based light sources containing Tb are shown.

The influence of the different additions to the melt on the nucleation behavior during short time flash lamp processing was investigated. It was observed that germanium and carbon additions to the silicone melt led to an increase of the mass transport to the growing surface and to an increase of the nuclei size. In the case of germanium additions to the silicon melt an incorporation of germanium in the silicon substrate was observed.

We have studied the effect of plasma treatment on both the electroluminescent (EL) properties of Ge-implanted light-emitting metal-oxide–silicon (MOS) devices and the charge trapping processes occurring therein. Under optimum conditions of plasma treatment, an appreciable increase in the device lifetime has been observed while maintaining unchanged the intensity of the light emission in the violet portion of the spectrum. These phenomena are believed to be associated with recovery of the oxide network resulting from a relief of internal mechanical stresses, and bond rearrangement that leads to a decrease in generation efficiency of electron traps, which are responsible for the device degradation.

Metal-oxide-silicon (MOS) structures containing different rare earth and germanium ions exhibit strong luminescence from 300 to 1540 nm.
It is very interesting from the viewpoint of the formation of silicon-based light-emitting devices. The different behaviour of charge trapping in Ge, Tb, Gd and Eu enriched SiO2 layer was studied under constant current regime. High-frequency (100 kHz) capacitors-voltage (C-V) characteristics exhibit a strong dependence of the charge trapping on the type of elements implanted into the SiO2 layer. The increase of the Eu concentration up to 3 percent leads to a shift of the C-V characteristics towards negative voltage in comparison with fresh samples, which reveals positive charge trapping. The capture cross section and the concentration of the different type of charge traps can also be strongly influenced by changing the annealing temperature and annealing time.

Metal-oxide-silicon (MOS) structures containing different rare earth and germanium ions exhibit strong luminescence from 300-1540 nm. This emission is very interesting from the viewpoint of the silicon-based light-emitting devices formation. Charge trapping behaviour in Ge and rare earth (Ce, Eu, Gd, Tb, Er and Tm) enriched SiO2 during high field electron injection corresponding to operation of the light-emission devices has been studied. Employing of constant current injection regime and high frequency C-V characteristics it was shown that embedment of rare earth impurities into dioxide matrix results in formation of similar system of charge traps with following capture cross section 2..3e-15 cm2 for electron and >1e-14 cm2 for holes. In various rare earths doping the amphoteric charge traps with distributed capture cross section in range from 1e-15 to 1e-17 cm2 is observed. Observed system of the traps is considerable different from one in the Ge implanted structures. For distributed traps an increase of injected current into the dielectric results in increase to positive charge trapping. Model of charge trapping in the defect shell located around rare earth inclusions inside of dioxide matrix is discussed.

The recent progress in the fabrication of silicon-based light sources with a view to their application in miniaturized sensor and Lab-on-a-Chip systems is described. The core of an all-Si light emitting device is a SiO2 film containing ion-beam-synthesized nanoclusters. A brief account is given of the structural, electrical and optical properties of such nanocluster-rich oxide films. A notable feature of the devices so produced is their ability to exhibit intense UV, violet-to-blue or green electroluminescence depending on the ion-implanted species (rare earth elements or group-IV elements like Ge, Sn and Si). The fabrication of the devices is carried out in standard CMOS technology.
The relevance of the all-Si light sources to microarray and miniaturized sensor systems for point-of-care diagnostics and analysis is outlined.

Photoluminescence (PL) properties of 500 nm thick SiO2 films on Si substrate subjected to combined Ge–Si implantations have been studied: Sequentially 400 keV Ge+ and 200 keV Si+ ions were implanted into SiO2 to concentrations of 3% and 1–10%, respectively. As calculated using the SRIM 2000 code, under these conditions depth profiles of implanted species should be contained in the region 100–400 nm below the oxide surface. After the implantation, samples were annealed at temperatures ranging from 700 to 1100 °C, in order to obtain Si and Ge nanoclusters. A weak near UV luminescence peak at a wavelength of about 315 nm, a strong blue band at 400 nm and a near-infrared 780 nm band were observed for thus prepared samples. The optical emission was stable and reproducible. Diffusion of germanium towards the Si/SiO2 interface during the annealing process is suppressed by silicon ions additionally introduced into SiO2.

In the so called FLASiC process, due to the transparency of the 3C-SiC, the irradiated energy is selectively absorbed at the SiC/Si interface where the most defected part of the 3C-SiC film exists. The Si at the interface melts up to a depth depending on the energy density of the flash pulse. Thus the lower part of the SiC film is dissolved into the melted Si substrate, then during the solidification phase separation occurs and the SiC is recrystallized forming high quality 3C-SiC trapezoidal pyramids (TPs) on the backside of the non-dissolved SiC film. 1. However due to significant Si mass transport the Si-surface is seriously undulated. Also the SiC film is mainly improved from the backside, which cannot be used for further epitaxial growth. For these reasons an improved method was developed with the aim, to (i) minimize the undulations of the Si substrate, and to (ii) improve the quality of the SiC film at the front interface. This method involves the deposition of a silicon overlayer (SOL) onto the SiC, followed by an additional SiC layer on the SOL. The new method is called i-FLASiC where the “i” stands for “inverse”.

Er-doped SiO2 layers containing silicon nanoclusters were obtained by dual ion implantation and subsequent annealing. All the double beam implantations of Er and Si ion were sequentially and simultaneously performed at 900 and 200 keV to doses of 1.2×1015 and 8×1016/cm2, respectively. After these implantations, the samples were annealed at a temperature range of 800–1100 °C for 60 min to form Si nanoclusters in SiO2 layers. Er concentration and distribution in the matrix was confirmed by Rutherford backscattering spectrometry. Point defects induced by ion implantation were reduced and finally removed during increasing annealing temperature. Moreover, the simultaneous implantation creates more defects in the matrix than the sequential implantation. Interestingly, a photoluminescence of Er3+ ions excitation with a typical band at around 1.54 μm could be efficiently enhanced once Si nanoclusters form in SiO2 layers, which suggests an evident energy transfer process from Si nanoclusters to Er3+ ions.

Time periodic Lorentz forces have been used to influence the separated flow on an inclined flat plate in deep stall at a Reynolds number of 10000. The influence of the control parameters effective momentum coefficient and excitation frequency as well as excitation wave form is discussed based on phase averaged PIV measurements. As expected, control authority depends strongly on momentum input and excitation frequency, but effects of the excitation wave form can be shown as well.

Imatinib is a tyrosine kinase inhibitor with activity in gastrointestinal stromal tumor and a variety of other solid and hematological malignancies. Studies in vitro and in a mouse model suggested that the imatinib might also be active in malignant Leydig cell tumor. We report on the—to our knowledge—first treatment experiment with imatinib in a patient with metastatic Leydig cell tumor. Unfortunately, the tumor progressed during treatment.

The simultaneous dual ipn implantation was recently shown to be an effective method to achieve better results from ion beam synthesis of SiC. The "in situ" generation of vacancies during implantation accomodates volume expansion due to phase formation and in this way increases the amount of synthesized material.
In this study different methods of introduction of vacancies are compared for the ion beam synthesis of a buried layer of SiO2 in Si (SOI structure).

The motivation of this study was to investigate the binding structure of uranium attached to mine water colloids and sediments gained from an abandoned uranium mine currently being flooded. U LIII-edge EXAFS spectroscopy was applied to identify the oxidation state and the atomic coordination sphere of bound uranium. First results from shell fitting showed that U(VI) was coordinated by a mononuclear, inner-sphere complex to the edge of an Fe(O,OH)6 octahedron originating from 2-line ferrihydrite (Fh) which predominated the bulk solid phase. This is in accordance with [1].
However, a small spectral contribution at R+Δ ~2.4 Å in the Fourier transform (FT) of the EXAFS could not be explained. Therefore, synthetic U(VI)-Fh coprecipitates were prepared under varied chemical conditions in order to step by step rule out possible contributions of other constituents in the samples such as sulfur, silicon, and carbon. Interestingly, the FT peak was independent of the preparation conditions, i.e. it also appeared under CO2-free atmosphere and in absence of other ligands. Hence Monte Carlo Target Transformation Factor Analysis (MCTFA) [2] was employed to find a structural model consistent with both spectroscopic and experimental data. It was found that the FT peak originates from a third O-atom of the Fe octahedron at a radial distance of 2.84 Å which consistently explains the other atomic distances of the sorption complex calculated from the experimental data. This 3D topology is presented and discussed in comparison with the complex structure of U(VI) sorbed onto aluminum hydroxide gel.
By another set of sorption experiments the influence of carbonate was examined at different pH conditions under ambient air (pCO2 = 35.5 Pa) and increased CO2 atmosphere (pCO2 = 1014 Pa). It was shown by iterative factor analysis that two eigenvectors are sufficient to fully reproduce the measured spectra. One is given by the aforementioned binary complex structure, the other is represented by the UO2(CO3)34- aqueous complex suggesting accessory outer-sphere complexation of uranylcarbonate ions on ferrihydrite at elevated carbonate concentrations. Further research is needed to understand the complex topology in detail and to explain the role of steric influences by neighboring Fe octahedra of the adsorbent.

References
[1] Waite, T.D. et al. (1994) Geochim. Cosmochim. Acta 58, 5465-5478.
[2] Rossberg, A. et al. (2005) Anal. and Bioanal. Chem. 383, 56-66.

Experimental results on ion implantation into SiGe show a very high content of residual vacancy defects after annealing. On the other hand theory predicts a decreasing excess vacancy production in SiGe with increasing Ge content. The contribution adresses this problem.

Magnetron sputtered film stacks of 5nm Ta/50(15)nm NiMn/20nm Fe19Ni81 /5nm Ta deposited at Si/SiO2 substrates were subsequently irradiated with He+ ions (30 keV, 1e15 - 3e16 cm-2). Using synchrotron X-ray diffraction and reflectivity, the transition from the paramagnetic NiMn phase to the chemically ordered, antiferromagnetic L10 phase during annealing was studied. The transformation to a dominating L10 ordered NiMn film takes place between 300-400°C irrespective of the irradiation. Ion irradiation at low fluences offers beneficial effects with respect to a reduction of the mosaicity for both, the NiMn and the permalloy film, and a smoothening of internal interfaces.

Die Kombination PIXE-RBS am externen Protonenstrahl wurde genutzt, um die Ursache einer ungeklärten Schichtbildung auf der Oberfläche eines Kirchenfensters von St. Marien in Rostock zu klären. Die zerstörungsfreien Analysen gaben den Hinweis, dass der gesuchte Effekt durch Wettersteinbildung erklärt werden kann, die infolge Abschattung durch Fassung des Glases in Bleiruten verzögert ablgelaufen ist.

The Master Curve (MC) approach used to measure the transition temperature, T0, was standardized first-time in the ASTM Standard Test Method E1921 in 1997. The basic MC approach for analysis of fracture test results is intended for macroscopically homogeneous steels with a body centred cubic (ferritic) structure only. In reality, due to the manufacturing process, the steels in question are seldom fully macroscopically homogeneous.
Charpy size SE(B) specimens of base and weld metal from the WWER-440 Greifswald Unit 8 RPV were tested according to the ASTM test standard E1921-05. The measured fracture toughness values at brittle failure (KJc) of the specimen show a large scatter. In general the KJc values of the RPV weld and base metal follow the trend of the MC. For two base metals more than 5% of the KJc values lie below the 5% fracture probability line. It is therefore suspected that the investigated WWER-440 RPV base material is macroscopically inhomogeneous. In this paper, two recent extensions of the MC for inhomogeneous material are applied on these fracture toughness data and the nature of inhomogeneity was investigated.

The coherent interaction of femtosecond laser pulses in the pump–probe regime has been experimentally studied in the time domain by monitoring light reflection from a tellurium single crystal. The optical response of the probed medium exhibits periodic variations at a frequency equal to that of the exciting laser radiation. Experimental dependences of the observed "coherent artifact" on the pump/probe intensity ratio, the number of accumulated pulses, and the mutual orientation of the polarization vectors of electromagnetic fields and the crystallographic axes are well described by the proposed phenomenological model.

In this paper we present a compact terahertz cyclotron resonance (CR) spectrometer based on a GaAs/AlGaAs quantum cascade laser. We demonstrate high reproducibility as well as high precision in order of ~1% in the position of CR absorption and ~10% in amplitude. The spectrometer is, finally, used for measurements of InAsxSb1-x alloys with As concentration ranged between 0 and 6%.

Nanowires (NWs) and chains of nanocrystals (NCs) embedded in dielectrics or semiconductors are intensively studied for applications in photonics and nanoelectronics. CoSi2 NWs and NC chains are of particular interest for photonic functionalities of system-on-a-chip architectures because of their full CMOS compatibility, the low damping of surface plasmons at the CoSi2-Si interface, and the transparency of Si at the plasmon frequency. Here, we present predictions of atomistic computer simulations which describe the ion beam synthesis of CoSi2 NWs in Si and their thermally activated decay into chains of CoSi2 NCs. The simulations on focused ion beam (FIB) Co implantation is based on the binary collision codes TRIDYN and TRIM incorporating a convolution over the few tens of nanometer beam profile. The resulting 3D implantation profile serves as input for kinetic lattice Monte-Carlo simulations by means of which nucleation and growth of CoSi2 precipitates and their coalescence into a CoSi2 NW are predicted. From an evolutionary viewpoint, NW synthesis proceeds on a shorter time scale than its decay. The NW decay into a NC chain (“Rayleigh instability”) is driven by the minimization of interfacial free energy. Moreover, we demonstrate that the orientation of the Co implantation profile to the single crystalline Si matrix strongly influences the stability of the synthesized CoSi2 NW. Since the system energetically favors the coherent CoSi2(111)/Si(111) interface, driving faceting forces may occur which accelerate the NW decay into a NC chain for FIB implantation not aligned with the Si-[110] orientation. Thus, intentional misalignment between the focused Co ion beam and the Si substrate is suggested as way to a controlled decay of the ion beam synthesized CoSi2 NW into a chain of monodisperse and equidistant CoSi2 NCs.

We present results of atomistic computer simulations which predict the reaction pathways of the ion beam synthesis of single-crystalline nanowires embedded in a matrix and the disintegration of nanowires into a chain of nanoparticles which is driven by anisotropic surface energies.

The effect of target poisoning is commonly observed in reactive magnetron sputtering, where a metallic target is sputtered in reactive gas atmosphere. This phenomenon can be described quite well in terms of sputter rate, reactive gas pressure and pumping speed, however the details of the processes on the target are not yet understood. In this work, an experimental setup is presented that combines energy resolved mass spectroscopy with quantitative in situ nuclear reaction analysis (NRA) of the reactive species target coverage. By adjusting the position of the magnetron, locally resolved information is obtained across the target surface. Experiments have been performed for the reactive deposition of TiN in an Ar/N2 gas mixture at varying process parameters, with special emphasis on the transition from metallic to poisoned target mode.
In the centre of the race track the nitrogen coverage is significantly smaller than on the remaining part of the target surface. The maximum amount of retained nitrogen significantly exceeds one adsorbed monolayer, which is attributed to nitrogen ion implantation and recoil implantation of adsorbed nitrogen.
The energy distribution of the neutral species is clearly composed from particles originating from the gas atmosphere and sputtered particles from the magnetron target. Significant differences in the energy distribution of the sputtered atoms are observed between the centre and the erosion zone of the target. The ratio of sputtered N/Ti atoms reflects characteristically the metallic or compound mode of operation.

In recent years, immense effort has been devoted to the synthesis of Si nanocrystals (NCs) for multi-dot floating-gate MOSFETs. To assure optimum memory device characteristics, the Si NCs should be equal in size and equally distant from the transistor channel. This desired Si NCs structure can be fabricated in a two-step process of ion irradiation through a SiO2-Si interface and subsequent annealing [1,2]. Previously, the Si NCs could not directly been studied with XTEM because of the low mass contrast of Si NCs to SiO2 and their very small size of less than 3nm.
In this XTEM study we prove the validity of the Si NC formation process. For a mass contrast enhancement of the Si NCs we used Ge to decorate them: A thin Ge layer was embedded into the oxide. During annealing, diffusing Ge is captured by the Si NCs due to the favourable Si-Ge bond. Thereby, the Si NCs are alloyed resulting in Si1−xGex NCs which are equally aligned with the SiO2-Si interface in a tunnel distance of about 3nm. These structural results are in line with the eletronic device characteristics which are dicussed in the contributions of Heinig and Schmidt in this symposium.

Functionalisation of an L-RNA oligonucleotide with 1,4,7,10-tetraazacyclododecane-N,N',N'',N'''-tetraacetic acid (DOTA) was performed using the N-succinimide ester 2. The DOTA-functionalised L-RNA oligonucleotide 3 was radiolabelled with the positron-emitting radiometals ⁸⁶Y(III) and ⁶⁸Ga(III) in radiochemical yields of 76 % and 93 %, respectively. Compound 4a represents the first example of an oligonucleotide labelled with the positron emitter ⁸⁶Y. Biodistribution studies of the ⁸⁶Y-radiolabelled L-RNA oligonucleotide 4a were performed in Wistar rats showing higher levels of radioactivity in the adrenal glands and kidneys. The low bone uptake (0.19 %ID/g after 60 min) is indicative of the high kinetic stability of the ⁸⁶Y-DOTA chelate in vivo.

Reliably acting diffusion barrier films are basically for the functionality of the copper inter-connect technology. Tantalum (Ta) and Tantalum nitride (TaN) are established materials for diffusion barriers against copper diffusion. In this study, the characterization of TaN like films produced using N+ plasma immersion ion implantation (PIII) was performed using Auger electron spectroscopy (AES). Chemical information was extracted from the Auger data using linear least square fit (LLS). The capability of the method in order to detect very little changes in the film composition dependent on small process changes was demonstrated. The nitrogen incorporation by PIII into high aspect ratio contact holes was proven using analytical TEM.

Recent investigations of ultra fine-grained metals (Cu, Fe, Ni) performed within a Prague-Rossendorf-Ufa collaboration will be reviewed. The specimens were prepared by severe plastic deformation: the high-pressure torsion and equal channel angular pressing. Positron annihilation spectroscopy was used as the main method including (i) the conventional lifetime and the Doppler broadening measurements with 22Na and (ii) the slow-positron implantation spectroscopy with the Doppler broadening measurement. Other methods were also involved: transmission electron microscopy, X-ray diffraction, and microhardness. First, the mean grain size was determined and defects were identified in the as-deformed materials. Defects concentration and spatial distribution were studied in detail. Dislocations situated in distorted regions along grain boundaries, and a few-vacancy clusters distributed homogeneously inside dislocations-free grains, were observed in the ultra fine-grained Cu, Fe, and Ni. Subsequently, the thermal evolution of the ultra fine-grained structures during isochronal annealing was studied.

Since irradiation affects in-service properties of zirconia, we investigated the fluence dependence on production and thermal stability of defects induced by helium and oxygen-ion implantation in single crystals of yttria-fully-stabilized zirconia. In either case, depth profiling by slow positron implantation spectroscopy (SPIS) detects a distribution of vacancy-type defects peaking at 60% of the projected ion range Rp. Owing to the saturation of positron-trapping occurring for low fluences, which depends on the ion mass, we could estimate a critical size of clusters ranging from 0.4 to 1.6 nm. The lack of SPIS-evidence of an open-volume excess at Rp is explained by the presence of over-pressurized gas bubbles. This assumption is confirmed by Nuclear Reaction Analysis of 3He concentration profiles, which shows that helium remains partly trapped at Rp, even after annealing above 400 °C.

In the present work, positron annihilation spectroscopy (PAS) is employed for microstructure investigations of various ultra fine grained (UFG) metals (Cu, Ni, Fe) prepared by severe plastic deformation (SPD), namely high-pressure torsion (HPT) and equal channel angular pressing (ECAP): Generally, UFG metals prepared using both the techniques exhibit two kinds of defects introduced by SPD: dislocations and small microvoids. The size of the microvoids is determined from the PAS data. Significantly larger microvoids are found in HPT deformed Fe and Ni compared to HPT deformed Cu. The microstructure of UFG Cu prepared by HPT and ECAP is compared and the spatial distribution of defects in UFG Cu samples is characterized. In addition, the mircrostructure of a pure UFG Cu prepared by HPT and HPT deformed Cu+Al2O3 nanocomposite (GlidCop) is compared.

Introducing dopant atoms in quantum wells (QWs) and superlattices results in a random impurity potential in addition to the confinement in growth direction. As has recently been demonstrated, their hydrogenic levels form resonant states attached to each QW subband and finally develop into a novel type of impurity band in the case of superlattices [1].
Here we present detailed numerical studies of coupled double and quadruple QW structures with relatively low doping (few 10¹⁰cm⁻² per layer), which can be seen as precursors to superlattices. By treating impurity and QW potential in a unified framework we exactly diagonalize the fully three-dimensional Schrödinger equation and calculate the infrared absorption spectrum. We find that, by varying the lattice temperature, the absorption spectrum changes dramatically, not only in its energetic resonances but also in its electronic origin. Analyzing the 3D - wavefunctions of the electronic states contributing to the final absorption spectra shows that at room temperature mainly delocalized states (intersubband states) contribute to the spectra, whereas at low temperature they are dominated by strongly localized states (impurity states). Hitherto unexplained experimental data of a quadruple QWsample are nearly perfectly reproduced by our calculation.
[1] D. Stehr et al., Phys. Rev. Lett., in print (2005).

Defects in He-implanted n-type 6H–SiC samples have been studied with deep-level transient spectroscopy. A deep-level defect was identified by an intensity with a logarithmical dependence on the filling pulse width, which is characteristic of dislocation defects. Combined with information extracted from positron-annihilation spectroscopic measurements, this defect was associated with the defect vacancy bound to a dislocation. Defect levels at 0.38/0.44 eV (E1/E2), 0.50, 0.53, and 0.64/0.75 eV (Z1/Z2) were also induced by He implantation. Annealing studies on these samples were also performed and the results were compared with those obtained from e–-irradiated (0.3 and 1.7 MeV) and neutron-irradiated n-type 6H–SiC samples. The E1/E2 and the Z1/Z2 signals found in the He-implanted sample are more thermally stable than those found in the electron-irradiated or the neutron-irradiated samples.

We have investigated the electrically active deep level defects in n-type 6H silicon carbide through the use of a series of complimentary spectroscopic techniques such as deep level transient spectroscopy, positron annihilation spectroscopy and photolumniescence. The deep level defects were created by neutron irrdiation, He implantation and electron irradiation with different energies. After analysis of the information gained from the different types of spectroscopy, as well as consideration of the defect creation and annealing behavior under different controlled environments, we provide experimental evidence for the microstructure of certain important deep level defects.

6H-SiC samples subjected to He-implantation and e–-irradiation (Ee=0.2MeV–1.7MeV) were investigated by deep level transient spectroscopy (DLTS). E1/E2 were identified in the He-implanted and the e–-irradiated samples with Ee0.3MeV. Considering the minimum e– energy required to displace the atoms in the lattice, the E1/E2 creation was related to the C-atom displacement. Similar to previous reports, the peak intensity and the capture cross sections of E1/E2 anomalously varies from samples to samples. It was shown that these anomalies were due to the presence of a DLTS peak overlapping with the E1/E2 signals.

Ion bombardment plays a special role in the deposition of cubic boron nitride (cBN) for hard coating applications. On one hand, low energy ion bombardment (100-500 eV) of the growing film surface is required to produce the hard cubic phase, on the other hand this implements extremely high compressive stresses (~10 Gpa) limiting film thickness and adhesion. Recently, high energy ion implantation (from keV to MeV range) has been successfully used to release the compressive stress in the films.
In this work the stress relaxation mechanism was investigated using the cantilever bending principle for in situ real time stress measurement during ion beam assisted deposition and Magnetron sputter deposition with simultaneous high energy ion bombardment. The amount of the relaxation is dependent on the product of the energy and the flux of the high energy ions. Using a variety of structural investigations, it can be shown that the relaxation takes place within the cBN grains, likely via the relaxation of interstitials. A relaxation due to the transformation of cBN to the more ductile hexagonal BN modification is less likely. This suggests a stress relaxation mechanism that is driven by a collisional relocation of strained film atoms due to high energy ion impact. A theoretical description of the stress relaxation based on TRIM simulation is presented and discussed. Assuming the stress in the layer to be proportional to the density of unrelaxed atoms, the calculation of the collisional relocation yield enables the calculation of a relative stress relaxation rate. The relocation yield is dependent on the incident ion energy and on the chosen relocation threshold energy. The experimental data are consistent with the model for different deposition parameters and processes for a relocation threshold energy of 5 eV.

We report about our study of the annealing effect on the resultant chemical composition of the APE (Annealed Proton Exchange) layers and their optical properties, with emphasis on their potential active function. The samples were annealed at various conditions and characterised by a number of nuclear analytic methods (NDP; ERDA; HIERDA) to investigate concentration profiles of the exchanged ions. The content of OH groups, which are undesirable in the active waveguiding layers owing to their effect of erbium excited state lifetimes shortening, was studied by IR absorption spectrometry. The waveguiding properties (number of guided modes, refractive index vs. depth profile) were measured by mode spectroscopy at 632.8 nm. We found out that hydrogen introduced to the surface layers of LiNbO3 by PE (Proton Exchange) moves deeper into the substrate during A (Annealing), lowering thus total refractive index increment. Consequently, the crystallographic phase of the exchanged layers changes towards the a-phase. The lowest amounts of OH groups were found when highest annealing temperatures were used; however, a limitation exists there as temperatures above 400°C cause degradation of the waveguiding properties.

We have studied the influence of synthesis temperature on chemical composition and mechanical properties of X-ray amorphous boron–oxygen–hydrogen (B–O–H) films. These B–O–H films have been synthesized by RF sputtering of a B-target in an Ar atmosphere. Upon increasing the synthesis temperature from room temperature to 550 °C, the O/B and H/B ratios decrease from 0.73 to 0.15 and 0.28 to 0.07, respectively, as determined by elastic recoil detection analysis. It is reasonable to assume that potential sources of O and H are residual gas and laboratory atmosphere. The elastic modulus, as measured by nanoindentation, increases from 93 to 214 GPa, as the O/B and H/B ratios decreases within the range probed. Hence, we have shown that the effect of impurity incorporation on the elastic properties is extensive and that the magnitude of the incorporation is a strong function of the substrate temperature.

Light emission from silicon has attracted considerable attention in the past few years due to the future potential in on-chip and inter-chip optical interconnects. This report reviews our current research work on efficient electroluminescence (EL) from silicon pn diodes and metal oxide semiconductor (MOS) devices. Efficient band edge EL with attractive power efficiencies up to 0.12 % has been observed in Si pn diodes prepared by boron implantation. We focus on the origin of the relatively high EL efficiency in Si pn diodes prepared by high-dose boron implantation, especially on the intriguing and anomalous increase of the EL for a temperature increase up to room temperature. EL from rare earth doped metal oxide semiconductor (MOS) devices was also studied using ion implantation of different rare earth luminescent centers (Gd3+, Tb3+, Eu3+, Ce3+, Tm3+, Er3+) into the silicon dioxide layers with a transparent top electrode made of indium-tin oxide. Strong EL was obtained from different rare earth centers in UV to infrared. The electroluminescence properties were studied with respect to the luminescence spectra, decay time, impact excitation, cross relaxation (Tb3+), and efficiency. Top external quantum efficiency above 15 % was obtained, which is comparable to the InGaN quantum well light emitting diodes

Field-induced quenching of the efficient photoluminescence at 1535 nm was observed from Si-rich SiO2:Er thin films prepared by Er and Si co-implantation. The quenching effect was strongly enhanced by increasing the density of silicon nanoclusters at an electric field above 5 MV/cm. A modulation ratio of 0.37 was obtained at an electric field of 9 MV/cm for a 200 nm Er-doped Si-rich layer containing 0.24 % of Er atoms and 10% excess Si nanoclusters. The mechanism of the field-induced quenching of the photoluminescence was studied by simultaneously measuring the light intensity from nanolusters and Er3+ ions, the injection current and the electric field. The quenching mechanism could be attributed to the field induced separation of the excitons created in silicon nanoclusters and tunneling of carriers between the Er ions and silicon nanoclusters. This strong field quenching effect will be useful for controlling the optical gain in a Si-rich SiO2:Er waveguide amplifiers, but also for the small size optical modulator in silicon photonics.

Strong green electroluminescence with brightness up to 2800 cd/m2 was obtained from indium-tin-oxide/SiO2:Tb/Si metal-oxide-semiconductor devices. The SiO2:Tb gate oxide was prepared by thermal oxidation followed by Tb+ implantation and annealing. Electroluminescence and photoluminescence properties were studied with variations of the Tb3+ ion concentration and annealing temperatures. The optimized device has a high external quantum efficiency of 16 % and a luminous efficiency of 2.1 lm/W. The excitation process of electroluminescence can be attributed to the impact excitation of the Tb3+ luminescent centers by hot electrons and the subsequent cross-relaxation from the 5D3 to 5D4 levels. Light emitting devices with micrometer size were demonstrated by the complementary metal-oxide-semiconductor technology.

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The effect of energy supplied to the growing alumina film on the composition and structure has been investigated by varying substrate temperature and substrate bias potential. The constitution and composition were studied by X-ray diffraction and elastic recoil detection analysis, respectively. Increasing the substrate bias potential from −50 to −100 V caused the amorphous or weakly crystalline films to evolve into stoichiometric, crystalline films with a mixture of the α- and γ-phase above 700 oC, and γ-phase dominated films at temperatures as low as 200 oC. All films had a grain size of <10 nm. The combined constitution and grain size data is consistent with previous work stating that γ-alumina is thermodynamically stable at grain sizes <12 nm [McHale et al., Science 277, 788 (1997)]. In order to correlate phase formation with synthesis conditions, the plasma chemistry and ion energy distributions were measured at synthesis conditions. These results indicate that for a substrate bias potential of −50 V, ion energies in excess of 100 eV are attained, both from a high energy tail and the accelerated ions with charge >1. These results are of importance for an increased understanding of the evolution of film composition and microstructure, also providing a pathway to γ-alumina growth at temperatures as low as 200 o C.

For the simulation of experiments investigating the behavior of the lower head of a nuclear power station in case of a core meltdown scenario like FOREVER (performed at the Royal Institute of Technology, Stockholm) it is necessary to model the melt pool convection and the temperature field within the vessel as well as creep and plasticity processes. Therefore a 2D Finite Element Model with 3 different physics environments is developed based on the code ANSYS® Multiphysics.
A thermal environment was build up including planar and contact elements for conductive heat transfer, additional surface elements to simulate convection and radiation from outer surface areas and a radiation matrix to account for internal radiative heat exchange. Normally a CFD-simulation would have been required for the natural convective heat transfer in the melt pool, but at very high internal Rayleigh numbers no turbulence model is capable for a correct simulation. Therefore an Effective Conductivity Convectivity Model (ECCM) was developed to simulate the heat transfer from the melt pool to its environment.
The resulting temperature field of the vessel wall is applied to the mechanical model. To describe the visco-plastic deformation a numerical creep data base (CDB) is developed where the creep strain rate is evaluated in dependence on the current total strain, temperature and equivalent stress. In this way the use of a single creep law, which employs constants derived from the data for a limited stress and temperature range, is avoided. For an evaluation of the failure times a damage model according to an approach of Lemaitre is applied.
The third physics environment is a kind of fictitious physics environment: it uses hyperelasticity and contact to move the melt pool along with the creeping vessel wall.
In this paper problems on the numerical side are explained and differences between the results of a simple coupled and a kinematically coupled FE-simulation are highlighted. The final comparison with the experiments shows that the kinematically coupled model is closer to reality than the single step model.

The presented core calculations are aimed at the demonstration of the feasibility of weapon-grade plutonium burning in VVER-1000 type reactors with emphasis on safety aspects of the problem. Particular objectives of weapon-grade Pu burning are the net burning of fissile Pu isotopes in general, but also the conversion of the Pu vector of the fuel from weapon-grade to reactor plutonium. Three different fuel-loading options have been considered - full UO2 loading, mixed UO2 and MOX loading and full MOX loading. All considered cases meet the requirements on nuclear safety and design limits related to both normal operation and accident conditions. Two reactivity initiated accidents have been analyzed, caused by the ejection of the operational control rod group during 0.1 s and unauthorized withdrawal of the same control rod group with operational speed. The analyses have been performed for the beginning and the end of the fuel cycle. The maximum reactor power peak of 1.79 of the nominal reactor power was observed for the 2nd fuel-loading option (mixed loading). However, it does not cause an overheating of fuel rods.
The performed simulations demonstrated that the code DYN3D can be used for analyses of reactivity-initiated accidents in VVER type reactors with various fuel designs.
Feasibility of the VVER-1000 type reactor for burning weapon-grade Pu and changing its isotopic composition has been demonstrated.

We introduce a novel optical wire-mesh tomograph for the investigation of multiphase flows. The sensor consists of an optical fibre matrix that covers the cross-section of a vessel or pipeline with fibres arranged in two distinct axial planes. Optical measurement is performed at the cross-points of the fibres where the cladding material is partially removed to enable light crossing from a fibre of the emitter plane to fibres of the receiver plane. A rapid optoelectronic processing unit enables the acquisition of cross-sectional images with frame rates above 10 kHz. We demonstrate the operation of the sensor for an oil-gas two-phase flow.

Considering the late in-vessel phase of an unlikely core melt down scenario in a light water reactor (LWR) with the formation of a corium pool in the lower head of the re-actor pressure vessel (RPV) the possible failure modes of the RPV and the time to failure have to be investigated to assess the possible loadings on the containment. In this work, an integral model was developed to describe the processes in the lower plenum of the RPV. Two principal model domains have to be distinguished: The temperature field within the melt and RPV is calculated with a thermodynamic model, while a mechanical model is used for the structural analysis of the vessel wall.
In the introducing chapters a description is given of the considered accident scenario and the relevant analytical, experimental, and numerical investigations are discussed which were performed worldwide during the last three decades. Following, the occur-ring physical phenomena are analysed and the scaling differences are evaluated between the FOREVER-experiments and a prototypical scenario.
The thermodynamic and the mechanical model can be coupled recursively to take into account the mutual influence. This approach not only allows to consider the tem-perature dependence of the material parameters and the thermally induced stress in the mechanical model, it also takes into account the response of the temperature field itself upon the changing vessel geometry.
New approaches are applied in this work for the simulation of creep and damage. Using a creep data base, the application of single creep laws could be avoided which is especially advantageous if large temperature, stress, and strain ranges have to be covered. Based on experimental investigations, the creep data base has been de-veloped for an RPV-steel and has been validated against creep tests with different scalings and geometries.
It can be stated, that the coupled model is able to exactly describe and predict the vessel deformation in the scaled integral FOREVER-tests. There are uncertainties concerning the time to failure which are related to inexactly known material parame-ters and boundary conditions.
The main results of this work can be summarised as follows: Due to the thermody-namic behaviour of the large melt pool with internal heat sources, the upper third of the lower RPV head is exposed to the highest thermo-mechanical loads. This region is called hot focus. Contrary to that, the pole part of the lower head has a higher strength and therefore relocates almost vertically downwards under the combined thermal, weight and internal pressure load of the RPV.
On the one hand, it will be possible by external flooding to retain the corium within the RPV even at increased pressures and even in reactors with high power (as e.g. KONVOI). On the other hand, there is no chance for melt retention in the considered scenario if neither internal nor external flooding of the RPV can be achieved.
Two patents have been derived from the gained insights. Both are related to pas-sively working devices for accident mitigation: The first one is a support of the RPV lower head pole part. It reduces the maximum mechanical load in the highly stressed area of the hot focus. In this way, it can prevent failure or at least extend the time to failure of the vessel. The second device implements a passive accident mitigation measure by making use of the downward movement of the lower head. Through this, a valve or a flap can be opened to flood the reactor pit with water from a storage res-ervoir located at a higher position in the reactor building.
With regard to future plant designs it can be stated - differing from former presump-tions - that an In-Vessel-Retention (IVR) of a molten core is possible within the reac-tor pressure vessel even for reactors with higher power.

The static and dynamic magnetic properties, especially the magnetic damping behavior, have been investigated as a function of saturation magnetization in thin Permalloy films. Ion implantation doping with Cr in the percentage regime has been used to effectively reduce the Curie temperature and thus the saturation magnetization at room temperature. In order to understand the magnetic modifications the changes in stoichiometry but also the ion induced structural changes have been addressed. As a function of fluence first an improvement of the (111) fiber texture, then a lattice expansion and finally a partial amorphization of the interface near region of the Permalloy layer is found. The region of amorphization can be understood quantitatively by the concentration profiles as a function of depth in combination with irradiation induced damage formation. The magnetic properties change correspondingly. For increasing Cr doping a drop in saturation magnetization and a decrease of the uniaxial magnetic anisotropy is observed. For a fluence of 0.8 x 10^16 Cr/cm^2 (4 at.%) the magnetic damping parameter  increases by a factor of 7. This strong increase is mainly caused by the reduction of the saturation magnetization and the altered sample morphology.

The nuclides 92Mo, 98Mo and 100Mo have been studied in photon-scattering experiments by using bremsstrahlung. Dipole and quadrupole excitations in 92Mo were investigated in photon-scattering experiments at an electron energy of 6 MeV at the ELBE accelerator of the Forschungszentrum Rossendorf. Photon-scattering experiments on 98Mo and 100Mo were carried out at the Dynamitron accelerator of the Stuttgart University at electron energies from 3.2 to 3.8 MeV. Six dipole transitions in 98Mo and 19 in 100Mo were observed for the first time in the energy range from 2 to 4 MeV. Systematics of the magnetic dipole strength in the isotopic chain of the even-mass isotopes from 92Mo to 100Mo are discussed. The experimental results are compared with predictions of the shell model and with predictions of the quasiparticle-random-phase approximation in a deformed basis. The latter show significant contributions of isovector-orbital and isovector-spin vibrations.

This paper discusses the growth of silicon nanostructures on silicon (100), (110) and (111) substrates by electron beam annealing. The nanofabrication procedure involves annealing of the untreated Si substrates at 1100°C for 15 s using a raster scanned 20 keV electron beam. Nanostructuring occurs as a result of kinetic amplification of the surface disorder induced by thermal decomposition of the native oxide. Pyramidal and truncated pyramidal nanocrystals were observed on Si(100) surface. The nanostructures are randomly distributed over the entire surface and square-based, reflecting the two-fold symmetry of the substrate surface. Similar square-based pyramidal structures with four equivalent facets are observed following nanostructuring of Si(110). With Si(111), nanostructure growth occurs preferentially along step-edges formed on the vicinal surface. Significant differences in nanostructure shapes formed on step-edges and terraces are related to the different growth mechanisms on the unreconstructed and 7x7 reconstructed domains respectively.

SiC-surface nanostructures on silicon were produced by 10 keV carbon ion implantation into silicon followed by annealing to 1000°C for 15 s under high-vacuum conditions using a raster-scanned electron beam. Following implantation, an amorphous layer is produced which starts at the surface and extends 65 nm into the substrate. Following annealing, the implanted surface layer remains amorphous but becomes covered with semi-spherical crystalline features up to 300 nm in diameter. The nanocrystals have been confirmed to be SiC which, following nucleation, grow as a result of C and Si diffusion across the oxide free substrate surface during annealing.

High quality single crystals of ZnO in the as-grown and N+ ion-implanted states have been investigated using a combination of three experimental techniques - namely, positron lifetime/slow positron implantation spectroscopy accompanied by theoretical calculations of the positron lifetime for selected defects, temperature-dependent Hall (TDH) measurements and deep level transient spectroscopy (DLTS). The positron lifetime in bulk ZnO is measured to be (151 + 2) ps and that for positrons trapped in defects (257 + 2) ps. On the basis of theoretical calculations the latter is attributed to Zn+O divacancies, existing in the sample in both neutral and single negative charge states, and not to the Zn vacancy proposed in previous experimental work. From TDH measurements the concentrations of negatively-charged and neutral Zn+O divacancies are estimated to lie between 4 × 1015 and 6.3 × 1016 cm-3. DLTS revealed the creation of the defect E1 and an increase in concentration of the defect E3 after N+ ion implantation. Furthermore, a p-conducting layer is formed at the surface after the implantation/annealing procedure that can be used to inject holes during a DLTS measurement. In this way, the acceptor traps A2 and A3 with thermal activation energies of about 150 and 280 meV, respectively, have been detected for the first time by DLTS.

Experimental and numerical investigations of artificial water hammers in a pipe with a bend are presented. At FZR a cold water hammer test facility was used to measure the fluid pressures and the pipe wall stresses occurring during water hammers. The finite element code ANSYS® was used for the numerical analysis of the experiments. The focus was put on the local distributions of pressure and stress. It could be shown that the fluid pressure and pipe wall stress exhibit complex 3-dimensional structures, which is a consequence of the fluid-structure interaction. The highest stresses occur in the pipe bend. The pressure peak is lower than predicted by the extended Joukowsky formula.

In-Vessel-Retention, betrachtetes Stadium, Debrisbett in der Bodenkalotte: Kühlbarkeit/Nichtkühlbarkeit (IKE-Arbeiten), mögliche Schmelzekonfigurationen, Fragestellungen.
Übersicht der Experimente: mechanisches Werkstoffverhalten, Wärmeübergang vom Schmelzepool, Materialwechselwirkung zwischen Corium und Stahlwand, integrale Experimente.
Versagensarten: thermisches Versagen, thermomechanisches Versagen, Versagensort und –form, Auswirkung auf Schmelzeaustrag.
Analysetools: bekannte Modelle, Vorgehensweise im FZR.
Versagenszeitpunkt / mögliche Gegenmaßnahmen
Ausblick: aktuelles Projekt BMWA Nr. 150 1279, weiterführende Fragestellungen.

As a new method of indium tin oxide (ITO) annealing in vacuum, direct electric current flow through the film is proposed. ITO films of about 170 nm thickness were produced by reactive pulsed magnetron sputtering. During annealing at constant electric power, the film resistance, free electron density and structure evolution were monitored in situ. Compared to conventional isothermal annealing, the current annealing is more efficient with a noticeable reduction of the thermal budget and a decrease of the kinetic exponent of the crystallization. Electrical inhomogeneities of the film, which produce locally overheated regions, are discussed as potential reason for the acceleration of the crystallization process.

One of the critical factors in the analysis of in-vessel melt retention is the vessel strength. It is, in particular, sensitive to the thickness of intact vessel wall, which, in its turn, depends on the thermal conditions and physicochemical interactions with corium.
Physicochemical interaction of prototypic UO2-ZrO2-Zr corium melt and VVER vessel steel was examined during the 2nd Phase of the ISTC METCOR Project. Rasplav-3 test facility was used for conducting four tests, in which the Zr oxidation degree and interaction front temperature were varied; in one of the tests, stainless steel was added to the melt.
Direct experimental measurements and posttest analyses were used for determining corrosion kinetics and maximum corrosion depth (i.e. the physicochemical impact of corium on the cooled vessel steel specimens), as well as the steel temperature conditions during the interaction, and finally the structure and composition of crystallized ingots, including the interaction zone. The minimum temperature on the interaction front boundary, which determined its final position and maximum corrosion depth was ~1090°С. An empirical correlation for calculation of corrosion kinetics has been derived.

Es wird ein Überblick zu den Aspekten der Materialsicherheit in der Kerntechnik gegeben. Im Mittekpunkt der Betrachtungen steht der Reaktordruckbehälter von Leichtwasserreaktoren. Im FRZ angwendete Methoden zur Mikrostrukturanalyse und zur Bruchmechanik werden erläutert.

Die Positronen-Emissions-Tomographie (PET) hat sich als bildgebendes Verfahren in der klinischen Routine sowie der medizinischen, biologischen und pharmazeutischen Forschung etabliert.
Daraus ergibt sich die Notwendigkeit, Mediziner sowie Physiker und Ingenieure mit der speziellen Ausrichtung auf multidisziplinäre Forschungsgebiete der Biologie und Medizin bzw. medizintechnischen Anwendungen im Rahmen ihrer Ausbildung möglichst praxisnah mit dieser Technik vertraut zu machen. Zu diesem Zweck soll ein Versuchsplatz für die PET aufgebaut werden, an welchem die allgemeinen Prinzipien der Computertomographie (CT), die Grundlagen der PET sowie die PET als kernphysikalisches Multiparameter-Messverfahren vermittelt werden. Für die Realisierung dieser Aufgabenstellung gibt es folgende Vorgaben:

• Der Tomograph besteht aus zwei kommerziellen, in Koinzidenz betriebenen, ortsempfindlichen Szintillationsdetektoren.
• Zum Gewinnen vollständiger Projektionsdatensätze wird ein Computer gesteuertes Bewegungssystem für die Translation und die Rotation verwendet.
• Die Signalverarbeitung basiert auf Standardmodulen der kernphysikalischen Messtechnik.
• Zur Gewährleistung einer flexiblen, den unterschiedlichen Anforderungen genügenden Auswertung erfolgt die Speicherung der Daten im Listen-Modus.
• Die tomographische Rekonstruktion mittels gefilterter Rückprojektion ist in die laufende Messung (Online-Betrieb) integriert. Daneben besteht

In order to prepare epitaxially oriented Fe nanoparticles embedded below the surface of an oxide single crystalline host material the method of ion beam synthesis has been explored for MgO(001) and YSZ(001). At a fixed implantation energy and fluence the implantation temperature has been varied between *room temperature* and 1273 K. It was found, that for MgO substrates the fraction of metallic Fe increases up to a maximum of 60% (at 1073 K) as a function of implantation temperature, whilst the Fe depth profile remains the same. The Fe nanoparticles are nonmagnetic at room temperature exhibiting fcc structure. They show a mean diameter of 5 nm and an exclusive orientation relationship to the host. In YSZ the fraction of metallic Fe increases with increasing implantation temperature reaching 100% at 1273 K. However, the nanoparticles formed are of bcc structure with a mean diameter of 13 nm located mainly close to the sample surface. The ferromagnetic behavior is reflected by a magnetic hyperfine field of 330 kOe and a hysteretic magnetization reversal. Electron holography measurements have been carried out in order to visualize the stray field of the particles.

The fabrication of diluted magnetic semiconductors (DMS) by transition-metal (TM) doping of ZnO has attracted tremendous interest within the last 3 years. However, there are still vivid discussions if the ferromagnetic state stems from Zener-interaction between diluted TM ions or from magnetic secondary phases. In order to prove or exclude the possible formation of TM-secondary phases in ZnO we have investigated iron doping, since Fe-ZnO (n-type) DMS are theoretically predicted to exhibit ferromagnetism [1].
For these investigations Fe-ions have been implanted with an ion energy of 180 keV (projected range Rp=80 nm) at 250 K and 620 K into ZnO single crystals. Two fluences of either 0.4 or 4x1016 ions per cm2 were chosen which correspond to 0.5 and 5 at%, respectively. The samples were characterized by CEMS (conversion electron Mössbauer spectroscopy), XRD (X-ray diffraction) using synchrotron radiation, RBS (Rutherford back scattering), TEM (transmission electron microscopy) and SQUID (superconducting quantum interference device) magnetometry.
For the as implanted sample a high solubility of Fe was found. The ionic states are 2+ and 3+ but none of the ionic fractions could be clearly determined to occupy substitutional lattice sites. The sample implanted at high fluence and 620 K exhibits ferromagnetic behavior at room temperature as was observed by CEMS and SQUID. However, CEMS and XRD measurements confirm that the origin of the ferromagnetic behavior is due to Fe-nanocluster formation. These nanoclusters show the magnetic moment and hyperfine field of metallic bcc-Fe. For samples implanted at 250 K and a low fluence also a ferromagnetic behavior could be detected at room temperature. No secondary phase formation occurs suggesting the formation of a diluted magnetic semiconductor (DMS)

[1] K. Sato, H. Katayama-Yoshida, Jpn. J. Appl. Phys. 40, L334 (2001)

The static and dynamic magnetic properties of 20 nm thick Ni81Fe19 films have been investigated as a function of Ni ion fluence up to 1x10^16 Ni/cm^2 (5 atom-%). The implantation has been performed at 30 keV in order to implant the Ni ions in the center of the ferromagnetic layer and to achieve a rather homogeneous energy distribution throughout the film. With increasing ion fluence the saturation magnetization and the effective magnetic anisotropies (static and dynamic) are reduced by about 80%. However, the effective magnetic damping is drastically enhanced for higher ion fluences. Starting at a pure permalloy value of alpha= 0.008 a 7-fold increase to alpha= 0.058 is found for a fluence of 0.8x10^16 Ni/cm^2. This increase can be explained mainly by the drop in saturation magnetization in connection with structural changes. In addition ion implantation in an applied magnetic field allows the setting of the uniaxial anisotropy direction irrespective of the initial orientation for fluences as low as 5x10^13 Ni/cm^2.

The interface between ferromagnet (FM) and antiferromagnet (AFM) plays a crucial role for the exchange bias phenomenon. This is mainly because monoatomic steps, islands or point defects give rise to uncompensated spins at the interface which serve as the origin of exchange bias. The number of monoatomic steps and thus the magnitude of the induced uniaxial anisotropy can easily be varied by means of Ar+ ion erosion. Depending on the primary energy and the angle of incidence a rippled surface with a well defined periodicity (20 – 100 nm) and peak to valley height (2 – 5 nm) can be created. On top of this surface the exchange bias system 5 nm Ni81Fe19 coupled to 10 nm Fe50Mn50 has been prepared. The interface corrugation remained throughout the whole layer stack. By means of a field annealing cycle the exchange bias direction has been initialized either along or perpendicular to the ripple direction, which causes to align the uniaxial and unidirectional anisotropy contributions either parallel or perpendicular to each other. For both cases the magnetic easy- and hard-axes remain the same because the uniaxial anisotropy contribution is much larger than the unidirectional one. However, if the exchange bias is initialized along (perpendicular to) the ripple direction the easy-axis (hard-axis) magnetization reversal loop is shifted. In order to evaluate this behavior in more detail a complete angular dependency of the magnetization reversal behavior has been investigated in both cases and compared to simulations based on a Stoner-Wohlfarth coherent rotation model. A good agreement between experimental data and simulations is found.
M. O. L. acknowledges the financial support from the European Communities Human Potential Program NEXBIAS under Contract No. HPRN-CT2002-00296.

Ripples with a periodicity of 35 nm and a height of 2 nm were formed on a Si(001) substrate
by means of Ar+ ion erosion. The primary energy was 500 eV and the angle of incidence 70° with respect to the surface normal. One of the main characteristics of such a surface is the large step density which is usually only achieved for vicinal miscut substrates. After ripple preparation a 0.5 nm Pt buffer layer and a 5 nm Permalloy (Ni81Fe19) ferromagnetic layer were deposited by means of molecular beam epitaxy. In order to allow for an easy comparison between ferromagnetic layer and exchange biased system on half of the sample a 10 nm Fe50Mn50 antiferromagnetic layer was deposited. Then the whole sample was covered by a 2 nm Cr protection layer. Additional AFM images confirmed that the ripple structure remains throughout the whole layer system.

The magnetization reversal behavior of the ferromagnetic layer and the exchange bias system was then investigated by means of magneto-optic Kerr effect (MOKE). The Permalloy layer itself exhibits already a uniaxial anisotropy of Ku = 3.74×104 erg/cm3 which was determined from the saturation field HS of the hard-axis magnetization reversal curve. This value is already about 20 times larger than the uniaxial anisotropy observed in Permalloy films deposited on flat substrates. Since no field annealing has been performed only a strongly enhanced coercivity with respect to the Permalloy film is found. This is due to the coupling of the ferromagnetic layer to the antiferromagnetic layer. Two additional field annealing procedures have then been performed in order to set the exchange bias direction either along or perpendicular to the ripple direction. Since the uniaxial anisotropy contribution is much larger than the unidirectional one the easy- and hard-axes remain the same. However, if the exchange bias is set along the ripple direction a shift of the easy-axis loop is found. In contrast, if the exchange bias field is set perpendicular to the ripple direction the hard-axis loop is shifted. In order to evaluate this behavior in more detail a complete angular dependency of the magnetization reversal behavior has been investigated in both cases and compared to simulations based on a Stoner-Wohlfarth coherent rotation model. A good agreement between experimental data and simulations is found.

The coordination of the U(IV) and U(VI) ions as a function of the chloride concentration in aqueous solution has been studied by U LIII-edge extended X-ray absorption fine structure (EXAFS) spectroscopy. The oxidation state of uranium was changed in situ using a gas-tight spectro-electrochemical cell, specifically designed for the safe use with radioactive solutions. For U(VI) we observed the complexes UO2(H2O)52+, UO2(H2O)4Cl+, UO2(H2O)3Cl20 and UO2(H2O)2Cl3 with [Cl] increasing from 0 to 9 M, and for U(IV) the complexes U(H2O)94+, U(H2O)8Cl3+, U(H2O)6-7Cl22+ and U(H2O)5Cl3+. The distances in the U(VI) coordination sphere are U-Oax = 1.760.02 Å, Oeq = 2.410.02 Å and U-Cl = 2.710.02 Å, the distances in the U(IV) coordination sphere are U-O = 2.410.02 Å and U-Cl = 2.710.02 Å.

The speciation of Eu complexed with polyacrylic acid (PAA) and alumina-bound PAA
(PAAads) was studied at pH=5 in 0.1M NaClO4. Structural parameters were obtained from 7F0→5D0 excitation spectra measured by Laser Induced Fluoresence ectroscopy as well as from Eu LIII edge Extended X-ray Absorption Fine Structure (EXAFS) spectra. The mode of coordination was also investigated by Infra Red pectroscopy. To elucidate the nature of the complexed species, Eu-acetate complexes were used as references. The spectroscopic techniques show that two carboxylate groups with 2-3 (EuPAA) and 4-5 (EuPAAads) hydration water molecules are coordinated to Eu in the first coordination sphere. For EuPAAads, the coordination between carboxylate groups and Eu appears to be bidendate. A similar coordination is probable for EuPAA but the EXAFS data indicate a sligthly distorted coordination. The results show that the degree of freedom of carboxylate groups is not the same for free or adsorbed PAA. For PAA, the degree of freedom is constrained by the flexibility of the methylene chain. When PAA is adsorbed on alumina, the polymer chains cannot any more be treated as independent chains. One may rather assume formation of aggregates that form an organic layer at the mineral surface presenting a complex arrangement of carboxylate groups.

The presentation refers to the application of a spectroelectrochemical cell for X-ray absorption spectroscopy to structure investigations under reduced conditions. The spectro-electrochemical cell will be used at the Rossendorf Beamline in Grenoble/France.

The contribution comprises an introduction in X-ray absorption spectroscopy and several typical examples of speciation and structure analysis. XAFS sectroscopy is a appropriate method to study structure sequences of solution species.

Standardmäßig erfolgt die Datenaufbereitung der Neutronenwirkungsquerschnitte für Reaktorkernrechnungen mit 2D-Zellcodes. Ziel dieser Arbeit war es, einen 3D-Zellcode zu entwickeln, mit diesem Code 3D-Effekte zu untersuchen und die Notwendigkeit einer 3D-Datenaufbereitung der Neutronenwirkungsquerschnitte zu bewerten. Zur Berechnung des Neutronentransports wurde die Methode der Erststoßwahrscheinlichkeiten, die mit der Ray-Tracing-Methode berechnet werden, gewählt. Die mathematischen Algorithmen wurden in den 2D/3D-Zellcode TransRay umgesetzt. Für den Geometrieteil des Programms wurde das Geometriemodul eines Monte-Carlo-Codes genutzt. Das Ray-Tracing wurde auf Grund der hohen Rechenzeiten parallelisiert. Das Programm TransRay wurde an 2D-Testaufgaben verifiziert.
Für einen Druckwasser-Referenzreaktor wurden folgende 3D-Probleme untersucht: Ein teilweise eingetauchter Regelstab und Void (bzw. Moderator mit geringerer Dichte) um einen Brennstab als Modell einer Dampfblase. Alle Probleme wurden zum Vergleich auch mit den Programmen HELIOS (2D) und MCNP (3D) nachgerechnet. Die Abhängigkeit des Multiplikationsfaktors und der gemittelten Zweigruppenquerschnitte von der Eintauchtiefe des Regelstabes bzw. von der Höhe der Dampfblase wurden untersucht. Die 3D berechneten Zweigruppenquerschnitte wurden mit drei üblichen Näherungen verglichen: linearer Interpolation, Interpolation mit Flusswichtung und Homogenisierung. Am 3D-Problem des Regelstabes zeigte sich, dass die Interpolation mit Flusswichtung eine gute Näherung ist. Demnach ist hier eine 3D-Datenaufbereitung nicht notwendig. Beim Testfall des einzelnen Brennstabs, der von Void (bzw. Moderator geringerer Dichte) umgeben ist, erwiesen sich die drei Näherungen für die Zweigruppenquerschnitte als unzureichend. Demnach ist eine 3D-Datenaufbereitung notwendig. Die einzelne Brennstabzelle mit Void kann als der Grenzfall eines Reaktors angesehen werden, in dem sich eine Phasengrenzfläche herausgebildet hat.

Indium tin oxide (ITO) films were grown by reactive middle frequency magnetron sputtering. Postdeposition annealing of transparent and conductive ITO films was performed with an electrical current in vacuum and air. The electrical power released by the current into the film during annealing was maintained at a constant level. The film structure and properties were characterized in situ by synchrotron produced X-ray diffraction, spectroscopic ellipsometry and resistance measurements.
The XRD data demonstrate transformation of the as-deposited amorphous film structure in to
crystalline during annealing. The films annealed in vacuum show two-stage decrease in the film resistance: first in amorphous state and second during crystallization. Increasing the electrical power of annealing hastens the onset of the second stage and reduces its total time. Resistance of the films annealed in air have three-stage behaviour: the resistance decreases at the beginning, then it starts to increase and finally, it decreases again. The experimental results are discussed in the terms of oxygen vacancy generation and tin donor activation.
Comparison of these results with data obtained during annealing of the indium oxide film without tin doping demonstrates significance of tin donor activation on the film resistance during crystallization process.
The mass analysis of the gas fractions escaping the ITO film during subsequent annealing in vacuum of the samples annealed already in air and vacuum was carried out. It is established that the samples annealed in air contain approximately one order of magnitude higher amount of water in comparison to the samples annealed in vacuum. This result shows that the water absorption deteriorates the improvement of the film resistance during annealing in air.