Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

Bremsstrahlung photons produced at the superconducting electron accelerator ELBE at the FZ Dresden-Rossendorf will be used for the production of neutron-rich nuclei by photon-induced fission. The properties of such exotic nuclei will be studied by decay spectroscopy. The mass and the charge identifications will be based on a double time-of-flight (TOF) method for both fission fragments. Currently, an experimental TOF spectrometer consisting of two micro-channel plate (MCP) detectors with two-dimensional position-sensitive delay-line anodes has achieved a position resolution of 1.8 (0.3) mm (FWHM) and a time resolution of 240 ps (FWHM) with a foil thickness of 163 mug/cm^2. The spectrometer will also be applied to track beams of exotic nuclei for experiments at the heavy ion synchrotron at GSI, Darmstadt.

The formation of colloids containing U(IV) or U(VI) was studied by experiments simulating colloid formation under unoxic and oxic conditions. It is concluded that both transport-facilitating effects of colloids on “immobile” radiotoxic contaminants such as U(IV) and transport-impeding effects on “mobile” radiotoxic contaminants such as U(VI) can play a part in the surroundings of nuclear waste repositories and abandoned uranium mines. The differences between the two geochemical settings are discussed.

Microbes secrete chelating agents in the surrounding aquifer system. These bioligands, in the case of the ubiquitous fluorescent Pseudomonas spp. pyoverdin-type siderophores, possess a high potential to bind besides Fe(III) also other metals like actinides [1]. The unknown interaction of actinides (U(VI), Cm(III)) with pyoverdin-type bioligands released from the aerobic soil bacterium Pseudomonas fluorescens (CCUG 32456 A) isolated from the aquifers at the Äspö Hard Rock Laboratory, Sweden is the subject of this study. The cells synthesized a bioligand mixture which consists of ferribactin (biogenetic precursors of the pyoverdin) and pyoverdin here in a ratio of 2:1.
The complexation studies were performed at pyoverdin concentrations below 0.1 mM and at an ionic strength of 0.1 M by applying different spectroscopic techniques. Differences in the complexation behavior depending on the nature of the actinide element will be discussed on the basis of the determined complex formation constants.
Two UO22+ -P. fluorescens (CCUG 32456 A) pyoverdin species could be identified due to their individual absorption spectra and molar extinction coefficients.
The Cm(III)-borne pyoverdin species were investigated by fluorescence emission at different excitation wavelengths (360 and 395 nm), i.e. directly at the absorption maxima of Cm(III) or indirectly by energy transfer from the pyoverdin molecule. A strong red shift of the emission signal of app. 7 nm compared to the Cm(III) aquo ion was already observed at low pyoverdin concentrations of 3x10-7 M and at pH 4. Three different Cm- P. fluorescens (CCUG 32456 A) pyoverdin species could be distinguished on the basis of their individual fluorescence emission spectra and lifetimes.
This study helps to improve the understanding of the actinide coordination chemistry with natural pyoverdin-type siderophores in aqueous solution. Such investigations with selected bioligands are essential to explain the overall interaction process of actinides with microbes on a molecular level.

[1] M. Bouby, I. Billard, H.J. Maccordick, Czechoslovak J. Phys. 49, 147-150 (1999).

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

In many cases x-ray absorption spectra measured in transmission mode are degraded by an inhomogeneity in thickness of the samples. As a result, the EXAFS amplitude is decreased and information about the coordination numbers is distorted. To avoid this influence, it is necessary to prepare a homogeneous sample. But, for powder samples, thick inhomogeneous foils, and sputtered films this is not possible. Absorption spectra on these samples should be corrected for the thickness inhomogeneity effect.To correct an absorption spectrum it is necessary to know the sample thickness distribution function. We propose a method of solving an integral equation for a distribution function as an inverse problem. We use and compare the experimental pre-edge absorption behaviour with the theoretical Victoreen function. We apply the Tikhonov regularization algorithm to determine the distribution function. Model calculations are carried out to check the reproducibility of the calculations. This method is applied to preliminary procession of x-ray absorption spectra for high quality foils of crystalline Cu, crystalline Cu powder samples, and an inhomogeneous foil of ordered Ni50Mn50 alloy. We estimate the thickness inhomogeneity effect on the coordination numbers in the cases before and after correcting the spectra.

The radiation source ELBE is based on a superconducting linear accelerator that can be operated in high average power mode (quasi continous wave mode, cw). Electrons are preaccelerated in a 250 keV-thermionic DC electron-gun and prebunched in a two stage RF-buncher section. Main acceleration is accompished in two 20 MeV-superconducting linear accelerator modules operating at 1,3 GHz which are cooled with liquid helium. The RF-power comes from 10 kW clystrons controled by the low level RF-system.

Aim:

The preparation and stability of a new ¹⁸⁸Re-S₄-complex (S₄ = (1-aza-18-crown-6)(O)C-C(SH)-C(SH)-C(O)NH-(CH₂)₃–NH-(CH₂)₃–NHC(O)-C(SH)-C(SH)-C(O)(1-aza-18-crown-6) was studied at therapeutic relevant radioactive concentrations. The results were compared with ¹⁸⁸Re-MAG₃ (MAG₃ = mercaptoacetyltriglycine) and ¹⁸⁸Re-DMSA preparations (DMSA = dimercaptosuccinic acid) performed with the same highly concentrated [¹⁸⁸Re]perrhenate solution (12-15 GBq/ml).

Methods:

The ¹⁸⁸Re complexes were prepared by direct reduction of perrhenate (¹⁸⁸Re-S₄-complex) as well as via the ¹⁸⁸Re-EDTA precursor complex (¹⁸⁸Re-MAG₃, ¹⁸⁸Re-DMSA). The preparations were stabilised with 15 mg of ascorbic acid and analysed after 1, 2, and 24 hours by TLC and HPLC. Additionally, in vitro and in vivo stability studies were performed with the purified complexes. Results: After stabilisation with 15 mg of ascorbic acid, all of the complexes were nearly stable under nitrogen for hours, and only 2-8 % of perrhenate was observed after 24 h. In contrast, only the ¹⁸⁸Re-S₄ complex was completely stable in vitro and in all investigated in vivo samples after separation of ligand excess and reducing agent by HPLC.

Conclusion:

The bridging amine group or free carboxylic groups of the S₄-ligand framework make available reactive positions for coupling biomolecules to the chelate. Thus it appears that the new ¹⁸⁸Re-S₄ complexes offer the possibility of stable and high specific activity labelling of biomolecules for therapeutic application.

We introduce a new wire-mesh sensor based on capacitance (permittivity) measurements. The sensor can be used to measure transient phase fraction distributions in a flow cross-section, such as in a pipe or other vessel, and is able to discriminate fluids having different relative permittivity (dielectric constant) values in a multiphase flow. We designed and manufactured a prototype sensor which comprises two planes of 16 wires each. The wires are evenly distributed across the measuring cross-section, and measurement is performed at the wire crossings. Time resolution of the prototype sensor is 625 frames per second. Sensor and measuring electronics were evaluated showing good stability and accuracy in the capacitance measurement. The wire-mesh sensor was tested in a silicone oil/water two-phase bubbly flow.

Already in the first publications about channeling radiation (CR), it has been declared as a unique quasi-monochromatic photon source. Numerous investigations devoted to the fundamental properties of CR have been carried out up to now at research centers all around the world. New perspectives for the application of CR as a non-conventional intense tunable X-ray source opened with the construction of brilliant superconducting cw electron sources.
At the Radiation source ELBE, systematic measurements of planar electron CR have been performed on diamond crystals. A water-cooled radiation production target has been constructed. The crystal alignment with respect to the beam axis is performed by means of an inventive remotely controlled goniometer.
Intense CR from 14.6 MeV electrons channeled along the (110) plane of a 150 micrometer thick diamond crystal has for the first time been produced at average beam currents of up to 100 microA. On-line monitoring the of CR X-rays at primary counting rates of the order of 10^11 photons per second and per 10% band width was realised by the use of a Compton spectrometer. Applying X-ray diffraction on a HOPG crystal, monochromatisation of CR and bremsstrahlung-background reduction has been investigated.

Die in diesem Bericht dokumentierten Ergebnisse sind vertraulich.

Four-gap Resistive Plate Chamber (RPC) prototypes with silicate glass electrodes (bulk resistivity ~10^8-10^9Ohm cm) were studied for suitability in time-of-flight applications at high rates. These studies were performed using a continuous electron beam of 34 MeV at the FZ Dresden-Rossendorf electron linac ELBE. Time resolutions of about 100 ps and efficiencies larger than 95% were obtained for rate densities up to 20 kHz/cm².

The computer code DYN3D is integrated into the SALOME platform within the NURSIM project. The first phase of implementation were presented. This phase contains the pre processing of a DYN3D calculation by using of SALOME platform.

A nodal expansion method of the multigroup diffusion equation was implemented in the computer code DYN3D. The results were compared with reference results for steady states of international benchmarks. Hexagonal and rectangular geometry of fuel assemblies was considered. The results show a good agreeement with the references.

A fascinating property of micromagnetism comes from the possibility to control the domain and vortex configuration through the sample shape and size. For instance, in a rectangular platelet a configuration containing a stable combination of vortices and an antivortex can be created. Such a single cross-tie wall can be understood as being a coupled micromagnetic system with three static solitons. Here we report on its magnetization dynamics including the vortex-antivortex interactions. The spectrum of eigenmodes is investigated as well as the effect of different vortex core orientations. We show that the vortex dynamics can be used to identify the core configuration which is not directly accessible to x-ray microscopy because of its limited spatial resolution.

Grignard reactions possess considerable hazard potentials due to the spontaneous heat release during the initiation of these strongly exothermic reactions and the high reactivity of the Grignard compounds. To establish an industrially applicable method for an objective real-time detection of the reaction start-up and for the accumulation of the organic halide during the process, a heat/ mass balance-based real-time monitoring approach was developed and tested by miniplant experiments. Additionally to the concentration profiles provided by the approach, the real-time estimation of the safety-relevant parameters, like adiabatic temperature rises and corresponding pressures, enables application of advanced control strategies up to the point of a safety-oriented fully automated control of Grignard reactions. In the same time, such systems can contribute to improve process efficiency by increasing the space-time yield as well as to enhance the inherent process safety.

An overview on benchmarking activities for reactor physics codes for VVER type reactors within the European code platform NURESIM is given. Different levels of benchmarks were calculated - mathematical benchmarks for diffusion codes with given cross section data and with neutron transport reference solutions as well as benchmarks based on experimental data. Benchmarking is performed at different levels - fuel rod lattice and reactor core, static and kinetics calculations. Validation calculations are performed using the codes APOLLO, CRONOS and DYN3D.

We employed high resolution gamma ray tomography to measure radial and axial phase distributions in a laboratory type chemical reactor with a gas inducing turbine stirrer. Therefore, we used a recently developed gamma ray CT system which is operated with a Cs-137 source and a detector that achieves approximately 2 mm spatial resolution. The measured data has been compared to computational fluid dynamics predictions obtained with CFX 10.0.

Conventional annealing processes such as furnace annealing (FA) and rapid thermal annealing (RTA) are compared to the more advanced technique of flash lamp annealing (FLA) regarding the electroluminescence (EL) efficiency, electrical stability, defect formation, and rare-earth nanocluster (RE-nc) creation in metal-oxide-silicon-based light-emitting diodes with Gd implanted SiO2 layers. We observed strong correlation between the electroluminescence efficiency, the nanocluster size, and the annealing technique for Gd implanted oxides. The increase of the annealing temperature and time leads to an increase of the RE-nc size and decreases the EL efficiency. Therefore, short-pulse high-temperature annealing (FLA) has a large advantage over the different annealing techniques (FA and RTA) from the point of view of stable and efficient metal oxide semiconductor light emitters.

This volume contains the proceedings of Symposium U “Si-based Materials for Advanced Microelectronic Devices: Synthesis, Defects and Diffusion” that was held in Nice (France) from the 29th of May to the 2nd of June 2006 during the E-MRS IUMRS ICEM 2006 Spring Meeting. The Symposium was organized by Enrico Napolitani (MATIS – CNR-INFM, Padova, Italy), Andrej Kuznetsov (University of Oslo, Norway), Wolfgang Skorupa (Forschungszentrum Rossendorf, Dresden, Germany), and Majeed Foad (Applied Materials, Sunnyvale CA, USA).
As classical scaling of CMOS devices is slowing down, being progressively replaced by ‘performance engineering’, new approaches are becoming object of more and more intense research, such as strain engineering, new materials, and advanced annealing methods. Topics of the Symposium were new materials such as strained Si, Si1−xGex, concerning issues on defects, diffusion, ion implantation and on their synthesis. But also, and mainly, research on ultra shallow junctions for future Si CMOS devices, spanning from the investigation of new methods for their formation to the fundamental understanding of dopants and defects. 113 contributions were selected from about 30 countries around the world (including Europe, Americas, Africa and Asia). The presentations were organized in 10 oral technical sessions and two poster sessions, including 14 invited speakers, 37 oral presentations and 62 posters.
The organizers of Symposium U would like to thank all participants for their valuable contribution and their active participation, which made the Symposium a very stimulating and lively forum for academic and industrial researchers. Special thanks are due to all the invited speakers for the excellent reviews of their recent work and the state-of-the-art of the actual research activities, and for their brilliant chairing of the sessions. We acknowledge also the significant sponsorship of Applied Materials, which make us capable to provide financial support to some participants and grants to the award winners.

Neben dem Eintrag des Urans durch seine Gewinnung und die Anwendung von Uranmunition, ist auch der Eintrag in die Biosphäre über Industrieprodukte wie Zement, Dünger und Trinkwässer zu berücksichtigen. Durch den erhöhten Umwelteintrag ist eine mögliche Akkumulation des Urans in den Biosystemen in Betracht zu ziehen. Bisher war es nicht möglich, in den notwendigen niedrigen Konzentrationsbereichen, die unterschiedlichen Bindungsformen des Urans zu bestimmen und damit Aussagen über die Abhängigkeit der Toxizität von der Bindungsform abzuleiten. Vor der Problematik des Urangehaltes des Wassers der Nürtinger Heinrichs-Quelle, wird aktuell über erste Ergebnisse der Unterschiede der Bindungsform des Urans im aufgenommenen Wasser und im entsprechenden metabolischen Urin berichtet.

Spektroskopische Methoden erlauben grundsätzlich die Bestimmung der Bindungsform von Schwermetallen, ohne einen chemischen Eingriff in das System selbst vornehmen zu müssen. Je niedriger die Konzentration des Schwermetalls ist, desto komplizierter und spezifischer werden die angewandten Methoden. Im Fall des Urans hilft die besondere Eigenschaft der Lumineszenz, um zu niedrigsten Konzentrationen vorzudringen. Durch die Anregung dieser Lumineszenz mit sehr intensiven Lichtquellen, wie z. B. Lasern, wird eine weitere Empfindlichkeitssteigerung erzielt. An ausgewählten uranhaltigen Wässern werden die heute vorhandenen Möglichkeiten der Bestimmung der Bindungsformen des Urans bis hin zum Spurenbereich erläutert.

There is increasing interest in targeting peptide receptors and their ligands for tumor diagnostics and therapy since there is evidence that various of these receptors are overexpressed in tumors compared to their expression in normal tissues. Among these receptors playing a key role in tumor progression is the neurotensin receptor (NTR) family. The present study investigated the expression of NTR in HT29 cells (human colon adenocarcinoma), in FaDu cells (human squamous cell carcinoma), and in the corresponding HT-29 and FaDu xenografts in nude mice as a well characterized animal tumor model. Quantitative RT-PCR with specific primers for the three NTR subtypes was done to study mRNA expression. Receptor protein expression was analysed by in vitro autoradiography using [³H]neurotensin(8-13) and by immunohistochemistry with specific antibodies against the three neurotensin receptors NTR1, NTR2, and NTR3. Analysis of receptor mRNA revealed a strong expression of NTR3 and a weaker expression of NTR1 and NTR2. Looking at protein levels, strong signals for NTR1 and NTR2 (NTR1 > NTR2) were detected immunohistochemically both in tumor cells and the corresponding xenografts. In contrast, expression of NTR3 revealed only a very weak immunopositive staining in tumors. Because it is the receptor protein that is targeted in vivo, the enhanced expression of NTR1 and NTR2 in these tumor entities could be a useful target for diagnostics, e.g., with radioligands suitable for single photon or positron emission tomography.

Depressive symptoms are common in patients with neurodegenerative disorders. Imaging studies suggest that a
disruption of frontal–subcortical pathways may underlie depression associated with basal ganglia disease. This pilot study tested the hypothesis that frontal dysfunction contributes to depression associated with multiple system atrophy (MSA) and progressive supranuclear palsy (PSP). Depressed patients with MSA (n = 11), PSA (n = 9), and age-matched controls (n = 25) underwent measures of cerebral glucose metabolism applying positron emission tomography with ¹⁸F-fluorodeoxyglucose. Regional metabolism in the patient groups was compared
to the normal subjects using the voxel-based statistical parametric mapping. Depressive symptom severity (Hamilton Depression Rating) and degree of locomotor disability (Hoehn & Yahr) were assessed in the patient groups. The association between prefrontal metabolism and the occurrence of depressive symptoms and the degree of locomotor disability was investigated. When compared to controls, MSA patients revealed
significant metabolic decreases in bilateral frontal, parietal, and cerebellar cortex and in the left putamen. In PSP
patients, significant hypometabolism was demonstrated in bilateral frontal cortex, right thalamus, and midbrain. Depression severity but not the patients’ functional condition was significantly associated with dorsolateral prefrontal glucose metabolism in both patient groups. The findings of this pilot study support the hypothesis that depressive symptoms in MSA and PSP are associated with prefrontal dysfunction.

The present paper documents the CFD code validation activity carried out at the University of Pisa. In particular, the ANSYS CFX-10.0 code has been used to simulate one of the experiments conducted at the ROCOM mixing test facility (FZD, Germany), that reproduced the injection of a de-borated slug in one cold leg of a pressurized water reactor (simulated by a salt tracer) with all circulation pumps at steady-state operation. The calculations were run on several grids obtained through different meshing strategies and having different sizes. The numerical results, in terms ofnormalized concentration of the transported passive scalar in the downcomer and at the core inlet, were compared against corresponding values obtained through experimental measurements of electrical conductivity in the ROCOM facility. Such comparison resulted in a general good qualitative agreement between simulations and experiments, while some discrepancies were evidenced from a quantitative point of view, mainly due to grid coarseness and low order numerical schemes.

The morphological evolution of surfaces during ion-beam irradiation has attracted significant interest due to possibility of the evelopment and the controlling of self-organization in nanostructures. Pattering and texture on nanometer length scale at metal and semiconductor surfaces has become a topic of intense research. In particular the surface and subsurface ripple formation under 40Ar+ ion-beam irradiation of Si (100) crystal has been studied recently. Based on transmission electron microscopy (TEM), atomic force microscopy (AFM) and x-ray analysis a dramatic effect of the ripple formation was found at an irradiation energy of 60 keV.
Apart from the crystalline part, the amorphization process is very important for understanding the amorphous-crystalline interface and the ripple formation mechanism. The dose of the ion beam was varied in the range from low 3e16 up to high 7e17 ions/cm^2 at an incident angle of 60° and an energy of 60 keV. Keeping the optimized irradiation parameters constant we have measured the degree of amorphization as a function of Ar+ dose by means of x-ray grazing incidence amorphous scattering (GIAS). For irradiated samples we found two broad peaks indicating a short-range ordering of amorphous material which does what with the penetration depth of probing x-ray. GIAS profiles probed at different azimuthal angles display a strong anisotropy of the amorphous scattering. The strong damage of the crystalline structure takes place along particular crystallographic directions. This is for the directional anisotropy: and strongly reveal for low doses, before it becomes completly amorphous and mostly uniform at high doses of implantation.
Such behavior can be explained taking into account the anisotropy of the crystalline material and orientation of the ion beam with respect crystallographic orientation of the substrate material. This work was supported by the DST-DAAD India-Germany Collaborative Program. We are grateful to ID1 beamline staff for the support at ESRF.

Understanding the coupling between conformational changes in the intramembrane domain and at the membrane-exposed surface of the bovine photoreceptor rhodopsin, a prototypical G protein-coupled receptor (GPCR), is crucial for the elucidation of molecular mechanisms in GPCR activation. Here, we have combined FTIR- and fluorescence spectroscopy to address the coupling between conformational changes in the intramembrane region around the retinal and the environment of helix 8, a putative cytosolic surface switch region in class-I GPCRs. Using FTIR / fluorescence cross-correlation we show specifically that surface alterations monitored by emission changes of fluorescein bound to Cys316 in helix 8 of rhodopsin are highly correlated with (i) H-bonding to Asp83 proximal of the retinal Schiff base but not to Glu122 close to the -ionone and (ii) with a MII-specific 1643 cm-1 IR absorption change, indicative of a partial loss of secondary structure in helix 8 upon MII formation. These correlations are disrupted by limited C-terminal proteolysis but are maintained upon binding of a transducin -subunit (Gt -derived peptide, which stabilizes the MII state. Our results suggest that additional C-terminal cytosolic loop contacts monitored by an amide II absorption at 1557 cm-1 play a functionally crucial role in keeping helix 8 in the position in which its environment is strongly coupled to the retinal-binding site near the Schiff base. In the intramembrane region, this coupling is mediated by the H-bonding network that connects Asp83 to the NPxxY(x)F motif preceding helix 8.

Purpose
The purpose of this study was to investigate the potential of [1-¹¹C]acetate (AC) as a metabolic tracer for renal cell cancer in human subjects.
Methods
Twenty-one patients with suspected kidney tumours were investigated with AC and dynamic PET. AC uptake was scored on a five-step scale. Tumour localisation was known from CT/MRI. Histology was available in 18/21 patients. The results in these 18 patients are reported.
Results
AC uptake by the tumour was less than (n=11), equal to (n=5) or higher than (n=2) uptake in the surrounding renal parenchyma. Histological tumour types showed a typical distribution, with a predominance of clear cell carcinomas (n=14) and only a small number of papillary cell carcinomas (n=2) and oncocytomas (n=2). Only the benign oncocytomas were highly positive with AC.
Conclusion
In most kidney tumours the AC accumulation was not higher than in normal kidney parenchyma. Therefore, AC PET cannot be recommend for the characterisation of a renal mass.

Proton recoil detectors for neutron time-of-flight measurements have been developed, which have a good time and position resolution and at the same time a relatively high efficiency for neutrons with kinetic energies of about 30 keV.

Different types of neutron-time-of-flight detectors have been developed and investigated for their applicability for the investigation of astrophysically relevant (gamma,n) reactions.

NiCl2-4SC(NH2)2 (DTN) is a quantum S = 1 chain system with strong easy-pane anisotropy and a new candidate for the Bose-Einstein condensation of the spin degrees of freedom. ESR studies of magnetic excitations in DTN in fields up to 25 T are presented. Based on analysis of the single-magnon excitation mode in the high-field spin-polarized phase and previous experimental results [Phys. Rev. Lett. 96, 077204 (2006)], a revised set of spin-Hamiltonian parameters is obtained. Our results yield D = 8:9 K, Jc = 2:2 K, and Ja;b = 0:18 K for the anisotropy, intrachain, and interchain exchange interactions, respectively. These values are used to calculate the antiferromagnetic phase boundary, magnetization, and the frequency-field dependence of two-magnon bound-state excitations predicted by theory and observed in DTN for the first time. Excellent quantitative agreement with experimental data is obtained.

The relative energy stability of Van de Graaff type ion accelerators is typically limited to some 10^-4. An inexpensive possibility to improve this situation was developed at the Forschungszentrum Dresden-Rossendorf. The method refers to the relatively stable periodic pattern of the acceleration voltage fluctuation in such accelerators. Future values of that fluctuation can be predicted with a high degree of certainty and can taken into account in the belt generator control in spite of the belt convolution caused fundamental reaction delay. The microcontroller based implementation of a ‘‘predictive fluctuation compensation’’ improves the relative acceleration voltage short time stability by a factor of 3–6 to well below 10^-4.

The aim of the present work is to investigate the textural evolution in high-temperature phase (austenite – B2) of Ti-rich NiTi (Ni–51at%Ti) shape memory alloys (SMA). The alloy was subjected to different thermomechanical treatments involving various heat treatments and cold rollings (10% and 40%). The qualitative texture analysis was performed at BM20 (ROBL-CRG) of the European Synchrotron Research Facility (ESRF) using in-situ high-temperature X-ray diffraction (XRD) with a wavelength of 0.154 nm. In-situ high-temperature texture determination has been carried out for the first time for Ni–Ti alloys, by annealing at different temperatures up to 800 °C under a vacuum better than 1e-4 Pa. The discussion highlights the evolution of texture during annealing at high temperatures and the change in the coherency domain size and microstrain.

After a short summary of the achievements made in liquid metal experiment during the last seven years, we try to identify some important points which should be addressed by next generation experiments. These include the role of rotation and precession, the role of large scale and small scale fluctuations on the dynamo threshold, the occurrence of field reversals in highly supercritical states and further studies of the magnetorotational instability in cylindrical, spherical and oblate geometries.

The Metal-Oxide-Silicon (MOS) diode structure containing ion implanted electropositive (M+) and electronegative (M-) ions is one of the most promising candidates for a new type of high-efficiency electroluminescence (EL) devices which can be integrated with standard silicon CMOS technology. The implantation process creates defects in the SiO2 layer. After implantation an annealing process leads to the diffusion of the implanted elements and a broadening of the SiO2/Si interface. The influence of the different implanted ions (Gd, F, K) was investigated by electroluminescence measurements and correlated to different defects in the oxide layer. Implanted electronegative ions (such as F) lead defects comprising O2 molecules and peroxy radicals (POR). On the other hand, the electropositive ions (Gd and K) increase the number of the oxygen vacancy defects.

In the early eighteenth century Johann Friedrich Böttger produced a remarkable type of red stoneware which is extraordinary hard and suitable for surface polishing. Although of considerable value for museums and collectors, surprisingly little is known of the elemental and mineral compositions of this type of stoneware. We have analysed Böttger objects and other red stoneware pieces from the Porcelain Collection of the State art Collections Dresden by non-destructive neutron-diffraction. The neutron analyses of about 20 intact jugs, vases and plates carried out at the spallation source ISIS provides a quantitative overview of the main mineral phase compositions. The data confirm the fine raw material selection by Böttger for the production of his stoneware. The mineral phase composition of Böttger objects, however, is not unique and similar to the also studied Yixing red stoneware.

This paper describes the features of the 3½ cell SRF gun from Rossendorf and the advantages and challenges of superconductivity. One advanced working regime of the SRF photo injectors is to produce short pulses with high bunch charges and low transverse emittance running in cw-mode. The quality of this electron beam is crucially for future FEL's with very short wave lengths. The main challenge is to compensate the growing transverse and longitudinal emittance with increasing bunch charges. Therefore, some procedures for emittance compensation for the 3½ cell SRF gun will be discussed.

Der homogene Dynamoeffekt in stömenden elektrisch leitfähigen Fluids ist verantwortlich für das Auftreten kosmische Magnetfelder, einschließlich des Erdmagnetfeldes. Nach Jahrzehnten ausschließlich analytisch-numerischer Untersuchungen wird der Dynamoeffekt seit 1999 auch in verschiedenen Laborexperimenten untersucht.

Kerne und Sterne - Vom Urknall, der Entstehung der chemischen Elemente und Experimenten im FZR

The design, fabrication and commissioning of a 703.75 MHz SRF photoinjector with a retractable multi-alkali photocathode designed to deliver 0.5A average current at 100% duty factor is the present undertaking of the electron cooling group in the Collider Accelerator Division of Brookhaven National Labs. This photoinjector represents the state of the art in photoinjector technology, orders of magnitude beyond the presently available technology, and should be commissioned by 2007. The R&D effort presently underway, and the focus of this paper, will address the numerous technological challenges that must be met for this project to succeed. These include the novel physics design of the cavity, the challenges of inserting and operating a multi-alkali photocathode in the photoinjector at these high average currents, and the design and installation of a laser system capable of delivering the required 10s of watts of laser power needed to make this photoinjector operational. (c) 2005 Elsevier B.V. All rights reserved.

Multispecies biofilms were cultured on glass slides in a standard culture medium (Sifin; TN 117) under air atmosphere in annular rotating reactors [1] for two months to obtain a thickness of approximately 800 µm. The slides with the grown biofilms were removed from one reactor for microsensor studies in a flow cell. Two other reactors were fed with UO2(ClO4)2 to adjust the total uranium concentration in the culture medium to 1x10-5 mol/l and 1x10-6 mol/l, respectively, i.e. the biofilms in these reactors were exposed to uranium for three weeks before they were removed for additional microsensor studies. Concentration profiles of oxygen versus biofilm depths were measured in each biofilm by electrochemical microsensors with a tip diameter of 10µm. A motor-driven micromanipulator was used for moving downwards through the biofilm in 20 or 50µm steps. The microsensor results clearly showed a significant dependence of the O2 concentration on the presence as well as on the concentration of uranium. In the absence of uranium the O2 concentration in the well aerated biofilm decreased slightly due to the aerophile microbes, dominating this biofilm. In contrast, O2 concentrations in the biofilms, which were exposed to different concentrations of uranium, decreased with increasing uranium concentration. Apparently, uranium acted as a stress factor for the microbes. Since metals have a strong effect on oxygen consumption, decreases in oxygen concentration could be due to changes in microbial activities [2] as well as on the activation of microbial communities induced by the addition of uranium [3]. 16S rDNA gene sequence retrieval and FISH are currently in progress to provide information on the changes occurring in the biofilm community and the resulting influence on the O2 concentration profiles.

[1] Lawrence, J. R. et al., (2000) Journal of Microbiological Methods 42, 215-224.
[2] Viret, H. et al., (2006) Sci Total Environ. 367, 302-311.
[3] Geissler, A. et al., (2005) Geobiology 3, 275-285.

In this work, synchrotron-based X-ray absorption spectroscopy (XAS) and transmission electron microscopy (TEM) studies were carried out to elucidate at molecular scale the interaction mechanisms of Myxococcus xanthus with uranium at different pH values. Extended X-ray absorption fine structure (EXAFS) experiments show that there are significant differences in the structural parameters of the U complexes formed by this bacterium at pH 2 and 4.5. At very low acidic pH of 2, the cells accumulated U(VI) as organic phosphate-metal complexes. However, at pH 4.5, the cells of this bacterium precipitated U(VI) as meta-autunite-like phase. TEM indicated that at pH 2 the uranium accumulates are located mainly at the cell surface. Whereas, at pH 4.5 the uranium precipitation takes place on the cell wall and within the extracellular polysaccharides (EPS) characteristic of this bacterium. Dead/live staining studies showed that 30% and 50% of the uranium-cell treated cell populations are alive at pH 2 and 4.5, respectively. The precipitation of uranium as mineral phase is possibly due to the acid phosphatase activity which was detected at both pH values. Precipitation of U as mineral phase may lead to more stable U(VI) sequestration that may be suitable for remediation uses. These observations, combined with the very high uptake capacity of this bacterium, imply that bacterial cells may significantly influence the fate of uranium in soils where these bacterial groups are mainly found.

• wird nachgereicht

B+ and P+ ions were implanted into Ge wafers covered with an amorphous surface layer of 150 nm. After this, FLA in Ar atmosphere was used in order to realise three objectives:

• recrystallisation of the amorphous region on top of the Ge wafer
• electrical activation of the implanted ions
• reduction of diffusion processes during the FLA.

Bombesin (BBN) peptide exhibits high selectivity and affinity for the gastrin releasing peptide receptor (GRPr). The GRPr is over-expressed on many human cancer cell types, thus making BBN a potent delivery vehicle for radionuclide targeting. In this study, the biologically active minimal sequence BBN(7-14) was labeled using the novel Tc ‘4+1’ mixed-ligand system, [Tc(NS₃)(CN-R)], in which Tc(III) is co-ordinated by a monodentate isocyanide linker bearing the peptide and the tetradentate, tripodal chelator, 2,2’,2’’-nitrilotriethanethiol (NS₃). BBN(7-14) was N-terminally modified with Gly-Gly-Gly, ßAla and Ser-Ser-Ser spacer groups (X) and functionalized with 4-(isocyanomethyl)benzoic acid (L1) or 4-isocyanobutanoic acid (L2) resulting in a series of [M(NS₃)(L-X-BBN(7-14))] conjugates (M = ^99mTc, Re). The isocyanides ligand frameworks were introduced using novel bifunctional coupling agents. The spacer groups (X), the monodentate isocyanide units, and a tetradentate NS₃ chelator bearing a pendant carboxylic acid (NS₃COOH) were proposed as pharmacological modifiers. ^99mTc-labeling was performed in a two-step procedure by first preparing ^99mTc-EDTA/mannitol followed by reactions with the isocyanides and NS₃ or NS₃COOH ligand frameworks. The ^99mTc-complexes were obtained with a radiochemical yield of 30 to 80% depending on the amount of the isocyanide (20 to 100 nmol) used. These new conjugates were purified by reversed-phased high performance liquid chromatography (RP-HPLC) to give a radiochemical purity of ≥ 95 %. The ^99mTc-conjugates exhibited high in vitro stability (> 90 %, 24 h). Analogous nonradioactive Re-conjugates were synthesized and characterized by electrospray ionization mass spectrometry (ESI-MS). RP-HPLC analyses of the new Re-conjugates indicated that they exhibited identical retention times to the corresponding ^99mTc-conjugates under identical HPLC conditions, demonstrating structural similarity between the two metallated species. The [Re(NS₃)(L-X-BBN(7-14))] conjugates exhibited GRPr affinity in the nanomolar range as demonstrated by in vitro competitive binding assays using PC-3 human prostate cancer cells. In vitro internalization/externalization assays indicated that ~ 65% of [^99mTc(NS₃)(L2-βAla-BBN(7-14))] conjugate was either surface bound or internalized in PC-3 cells. Cell-associated activity for all other ^99mTc-conjugates was below 20%. Biodistribution studies of [^99mTc(NS₃)(L-βAla-BBN(7-14))], L = L1, L2, in normal, CF-1 mice showed minimal accumulation in normal pancreas (a tissue expressing the GRPr in high density in rodent models) and rapid hepatobiliary elimination. Introduction of a carboxyl group onto the NS₃ ligand framework had only minimal effects to increase renal excretion. Activity distribution and accumulation was highly dominated by the relatively lipophilic ‘4+1’ complex unit.

In explosive nucleosynthesis temperatures are high enough for photodisintegration reactions to occur, e.g. leading to the production of p-process nuclei. In order to understand the reaction rates of element production and element disruption we started an experimental program at the new bremsstrahlung facility of the superconducting electron accelerator ELBE of FZ Dresden-Rossendorf. The bremsstrahlung facility and the detector setup are designed such that the scattering of photons from nuclei and the photodisintegration of nuclei around the particle separation energies can be studied under optimized background conditions. In activation measurements with bremsstrahlung at end-point energy from 10.0 to 16.5 MeV (g ,p), (g ,n) and (g ,a) reactions of 92,100Mo have been studied. Our activation yields can be described within a factor 2-3 or better with calculations using the cross sections from recent Hauser-Feshbach models.

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Hyperon production in the threshold region was studied in the reaction pp→K+Λp using the time-of-flight spectrometer COSY-TOF. Exclusive data, covering the full phase-space, were taken at three different beam momenta pbeam=2.59, 2.68 and 2.85 GeV/c (corresponding to excess energies of var epsilon=85, 115 and 171 MeV). Total cross-sections were deduced to be 7.4±0.5 μb, 8.6±0.6 μb and 16.5±0.4 μb, respectively. Differential observables including Dalitz plots were obtained. From the investigation of the Dalitz plot at pbeam=2.85 GeV/c a dominant contribution of the N*(1650)-resonance to the reaction mechanism was found. In addition the pΛ-final-state interaction turned out to have a significant influence on the Dalitz plot distribution even 171 MeV above threshold.

The amorphized surface of Si(100) sputtered with low energy ions at moderate temperature was found to develop two perpendicular ripple patterns overlaying each other. The evolution of these patterns was studied over a wide range of fluence. Coarsening of both ripple modes was observed, showing a similar time dependence with a coarsening exponent of 1/z ~ 0.08. In the high fluence regime, the surface enters a steady state with both ripple modes still present.

We developed an improved Stillinger-Weber-type potential for Ge by adjusting the three-body parameters in such a manner, that the potential yields the correct lattice constant and the correct cohesive energy, and the melting point and other properties are reproduced satisfactorily. Using this potential, the temperature dependence of equilibrium concentration and diffusivity of vacancies as well as the contribution of vacancies to self-diffusion are investigated by atomistic simulations and thermodynamic considerations. The enthalpies and entropies of formation and migration are calculated. Similar investigations are performed for self-interstitials in order to check whether their contribution to self-diffusion can be neglected, as shown experimentally. Finally, the self-diffusion coefficient and the equilibrium concentration of vacancies determined by the simulations are compared with experimental data from the literature.

P and As are considered the most suitable n-dopants in Ge. However, because of diffusion and deactivation effects it is difficult to achieve highly-n-doped Ge by ion implantation and subsequent annealing. We investigated high fluence P implantation into pre-amorphized Ge and subsequent annealing. The thickness of the amorphous layer was varied by implanting Ge at different energies. In all cases the main part of the as-implanted P profiles is located within this layer. Both RTA and flash-lamp annealing were employed. Considering samples with amorphous layers of different thickness enables detailed investigations of P diffusion in amorphous and crystalline Ge and solid-phase epitaxial regrowth during the post-implantation annealing. The thickness of the amorphous layers and the quality of the regrown crystalline Ge were monitored by RBS/C. The chemical depth profiles of P and the donor depth distributions were measured by SIMS and SRP, respectively. The results indicate that P diffuses much faster in amorphous Ge than in crystalline Ge. It is assumed that the P diffusivity in amorphous Ge shows a concentration dependence similar to that in crystalline Ge. The solid-phase epitaxial regrowth occurs already at the lowest thermal budget used in this work. It causes a considerable P redistribution and, presumably, the incorporation of P into crystalline Ge at concentrations above the equilibrium solubility.

The influence of crystallographic orientation and ion fluence on the shape of damage distributions induced by 500 keV N+ implantation at room temperature into 6H SiC is investigated. The irradiation was performed at different tilt angles between 0 and 4 with respect to the 0001 crystallographic axis in order to consider the whole range of beam alignment from channeling to random conditions. The applied implantation fluence range was 2.5 1014 3 1015 cm 2. A special analytical method, 3.55 MeV 4He+ ion backscattering analysis in combination with channeling technique (BS C), was employed to measure the disorder accumulation simultaneously in the Si and C sublattices of SiC with good depth resolution. For correct energy to depth conversion in the BS C spectra, the average electronic energy loss per analyzing He ion for the 0001 axial channeling direction was determined. It was found that the tilt angle of nitrogen implantation has strong influence on the shape of the induc! ed disorder profiles. Significantly lower disorder was found for channeling than for random irradiation. Computer simulation of the measured BS C spectra showed the presence of a simple defect structure in weakly damaged samples and suggested the formation of a complex disorder state for higher disorder levels. Full-cascade atomistic computer simulation of the ion implantation process was performed to explain the differences in disorder accumulation on the Si and C sublattices. The damage buildup mechanism was interpreted with the direct-impact, defect-stimulated amorphization model in order to understand damage formation and to describe the composition of structural disorder versus the ion fluence and the implantation tilt angle.

This report describes the high regioselectivity of nucleophilic epoxide ring-opening reactions which resulted in two of four possible regioisomers of N-benzoyl- (5a and 5b) and N-fluorobenzoylazaspirovesamicol derivatives (6a and 6b), respectively. Based on structural information obtained from X-ray crystal structure analyses of 5a and 5b the mode of epoxide ring-opening is discussed

We report on the design of the photocathode laser for a superconducting RF gun, which is presently under development at the Forschungszentrum (FZ) Rossendorf. This laser is foreseen to drive the RF gun in CW mode with up to 1 nC bunch charge. It generates pulses of 12...14 ps duration with 500 kHz repetition rate and 0.8 μJ pulse energy at 263 nm wavelength. This should provide sufficient pulse energy for generation of bunches with 1 nC charge using caesium telluride photocathodes. Due to two active modelockers in the laser oscillator, the latter operates in tight synchronism to the RF master oscillator of the linac. The laser consists of a short-pulse oscillator, a pulse picking Pockels cell, a regenerative amplifier and a wavelength conversion unit. The latter converts the infrared laser radiation to the ultra-violet (UV). This unit turns out to be a particularly critical element of such a photocathode laser driving a RF gun in CW mode.

A 3-1/2 cell superconducting RF photocathode gun is being developed at Forschungszentrum Rossendorf to produce a high peak current, low emittance electron beam. This technology is essential to the realisation of many large scale facilities. The gun is designed for CW operation mode with 1 mA current and 9.5 MeV electron energy, and it will be installed at the ELBE superconducting electron linear accelerator. The gun will have a 3-1/2 cell niobium cavity operating at 1.3 GHz. The cavity consists of three cells with TESLA geometry and a specially designed half-cell in which the photocathode will be placed. Typical ERL-based projects require ~100 mA average current, and therefore suitable upgrade paths are required. Simulations have been carried out to evaluate the design and to determine suitable upgrades for higher current operation. Simulations of alternative cathode surface shapes are presented. Several couplers have been identified that can provide higher power to the cavity, whose integration and suitability has been verified. All the investigations that have identified possible solutions to higher current operation are discussed in this report.

Two-phase flow in the primary circuit of a PWR:LOCA scenarios Relevant example of stratified two-phase flow regime for Computational Fluid Dynamics validation:

Slug flow regime characterized by:acceleration of the gaseous phase, transition of fast liquid slugs
Aims of the numerical simulations:
feasibility study of numerical prediction of slug flow with multiphase flow models built in a commercial code (ANSYS-CFX) to prove the understanding of the general fluid dynamic mechanism leading to slug flow

This paper describes the development of a thermal model for flashlamp processing of 3C-SiC on silicon. The model is a numerical solution of the enthalpy equation, using a modified Crank-Nichelson scheme to combine accurate prediction of melt depths with resonable computation times.

Results of an extensive study concerning implantation, annealing and electrical activation of Al and B layers of 6H-SiC are presented. With increasing implantation temperature the implantation induced damage decreased. After annealing dislocation loops are observed in Al implanted layers whereas loops and precepitates are found in B implanted layers. For good electrical properties amorphization must be avoided. Using flash lamp annealing hole concentration is measured for Al doping whereas for B doping a limited hole concentration is observed.

The radiation source ELBE (Electron Linac of high Brilliance and low Emittance) at Forschungszentrum Rossendorf is based on a superconducting linac that produces a high power continuous wave (cw) electron beam up to 40 MeV and 1 mA. The linac is used to drive two free-electron lasers producing infrared radiation from 5 to 150 microns wavelength. Additionally, from several conversion targets MeV-bremsstrahlung (< 20 MeV) and X-rays (10-100 keV) from electron channelling are generated. In the future even neutron and positron beams will be available at ELBE. The used superconducting RF accelerator technology and details of the machine instrumentation, in particular the electron beam diagnosis will be described.

Abstract: Using bulk silicon can be ended for planar 22 nm technological node due to silicon mobility limitation. New type of substrates needs for further scaling in CMOS microelectronics. We speculate that these new type of materials will be semiconductor heterostructure on insulator (HOI) compatible with current silicon planar CMOS technology. In this work an effect of interface mediated endotaxial (IME) growth of thin semiconductor film at Si/SiO2 bonded interface was experimentally observed and investigated for the first time. Joint semiconductor material stack obtained by hydrogen transfer of one layer material (silicon) and second one (germanium or indium antimonide) placed on amorphous silicon dioxide film is presented. First of all thin film dual layer Si-Ge heterostructure properties were considered. Si-Ge HOI structures were obtained using Ge ion implantation in dioxide with followed Ge segregation to the interface between directly bonded silicon and silicon dioxide wafers. The method is also compatible with A3B5 thin film formation, as was shown for InSb film. Thermodynamic, kinetic and lattice mismatch parameter influences on IME process are considered.

4H-(Si1-xC1-y)Gex+y solid solutions with a Ge incorporation on lattice site from 0.7 to 2.5 percent were formed by ion beam synthesis. The concentration was varied from 1 to 20 % by implanting Ge at 600 C. The implanted samples were annealed at 1300 C in a rapid thermal processing equipment.

Using bulk silicon can be ended for 32 nm technological nodes. New type of substrates needs for further scaling in CMOS microelectronics. We speculate that these new type of materials will be semiconductor heterostructure on insulator (SHI) compatible with current silicon planar CMOS technology. Joint semiconductor material stack placed on cheap amorphous dioxide is presented. First of all thin film SiGe heterostructure properties is considered. It was obtain using Ge ion implantation in dioxide with followed Ge segregation to the directly bonded interface between silicon and silicon dioxide wafers. The method is also compatible with A3B5 thin film formation.

A superconducting rf photo electron injector (SRF gun) is under development at the Forschungszentrum Rossendorf. The project aims at several issues: improvement of the beam quality for the ELBE superconducting electron linac, demonstration of feasibility of this gun type, investigation of critical components, and parameter studies for future application (BESSY-FEL, 4GLS). The design layout of the SRF photo-injector, the parameters of the superconducting cavity and the expected electron beam parameters are presented. The SRF gun has a 3+1/2-cell niobium cavity working at 1.3 MHz and will be operated at 2 K. The three full cells have TESLA-like shapes whereas the half-cell has an special form obtained from numerical optimization. In the half-cell a Cs2Te photocathode is situated which will be cooled by liquid nitrogen. In 2005, the main parts for He cryostat like vacuum vessel, cryogenic and magnetic shields were fabricated. Test benches for the cathode cooling system and the cavity tuner were assembled and the measurements performed. The photo cathode preparation lab has been arranged, and the diagnostic beam line has been designed. After delivery of the Nb cavity, its rf properties were measured. The cavity was tuned and its chemical treatment is started.

The paper correlates the growth and structure formation with the properties of indium-tin-oxide (ITO) films fabricated by pulsed reactive magnetron deposition onto amorphous substrates held at elevated temperatures ranging from RT to 510 °C. The evolution of the microstructure is consistent with the well-known structure zone model. The temperature dependence of the film texture is described with consideration of the interplay between the shadowing and surface diffusion processes. It is shown that deposition at elevated temperatures lowers the crystallization threshold and is more effective in reducing resistivity than the post-deposition vacuum annealing at comparable temperatures. The films grown at a substrate temperature of 400 and 510 °C have the lowest resistivity of 1.2*10^-4 Ohm•cm, the highest free electron density of 1.2 - 1.0*10^21 cm^-3, and mobility of 35 - 42 cm^2•V^-1•s^-1 while showing the strongest (222) texture with the largest grain size.

Thermally oxidized SiO2 layers of 100 and 500 nm thickness have been implanted by oxygen and sulfur ions with a dose of 3x1016 and 5x1016 ions/cm2, respectively, leading to an atomic dopant fraction of about 4 at.% at the half depth of the SiO2 layers. The cathodoluminescence spectra of oxygen and sulfur implanted SiO2 layers show besides characteristic bands a sharp and intensive multimodal structure beginning in the green region at 500 nm over the yellow-red region extending to the near IR measured up to 820 nm. The energy step differences of the sublevels amount on average 120 meV and indicate vibration associated electronic states, probably of O2-interstitial molecules, as we could demonstrate by a respective configuration coordinate model.

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Strong decrease in the carrier mobility of the nanometer-thick silicon films imposes a limitation on the application of silicon-on-insulator (SOI) structures in the current silicon planar CMOS technology. The formation of SiGe-heterostructures-on-insulator (HOI) is a way to increase the carrier mobility in the nanometer-scale layers. In this work, we present the results on the interface mediated endotaxial (IME) growth of thin Ge film from the Ge+-ion implanted SiO2 layer of the SOI structure.

Bonding interface of SOI structure may be an effective sink for impurity atoms because of higher concentration of vacancies and microvoids on the cleavage planes. The behaviour of ion-implanted Sb and In atoms near the bonding interface of SOI structures was investigated as a function of annealing temperature.

Flash lamp annealing in the millisecond regime of heteroepitaxial silicon carbide on silicon structures involves melting the silicon below the SiC layer, but the deep faceted nature of the liquid-solid interface leads to unacceptable surface roughness. This paper describes a method of controlling melting by implanting a high dose of carbon at a controlled depth below the Si/SiC interface, which significantly alters the melting characteristics of the silicon. This technology has also been applied to SiC and Si multilayer heterostructures. Results confirm the effectiveness of this approach for increasing surface uniformity, making liquid phase processing compatible with standard device fabrication techniques. A thermal model has also been developed to describe this process and results indicate that the theoretical work is consistent with the experimental evidence. The model is a valuable tool for predicting the onset of melting, maximum temperatures, and process windows for controlled liquid phase epitaxy.

This work is a comparative study of the processes of charge trapping in silicon dioxide layers doped with different rare-earth impurities (Gd, Tb, Er) as well as with Ge. Diode structures incorporating such oxide layers exhibit efficient electroluminescence (EL) in the spectral range from UV to IR.
Ion implantation was performed over a wide dose range using doses chosen to provide impurity concentrations of 0.1 to 3 at. % with the implant profiles peaking in the middle of the oxide. Post-implantation anneals were carried out at different temperatures. An ITO layer was employed as the transparent gate electrode for the implanted SiO2/Si light emitting diodes (LEDs).
Charge trapping was studied using an electron injection technique at constant current regime in the range of 1013 to 1021 e/cm2 with simultaneous measurements of the EL intensity. High-frequency C/V characteristics were used to control the net charge in the oxides. The I/V characteristics and the EL intensity vs. applied voltage were also measured.
Analysis of the charge trapping and the variation of the EL intensity during electron injection shows that the current density range can be conveniently divided in three portions: (i) low injection level, where electron/hole capture at traps with a large capture cross-sections and low EL intensity occurs; (ii) medium injection level corresponding to the main operation mode of the LEDs (odd hole trapping depending on the injected current level is observed); and (iii) high injection level (electrical quenching of the EL, which correlates with electron capture at traps of extremely small capture cross-sections of about 10-21 cm2 takes place). The parameters of the hole and electron traps are determined.
The nature of specific electron hole trapping at the medium injection level in RE doped MOSLEDs is discussed. Mechanisms of EL quenching at the high injection level are proposed.

Metal-Oxide-Silicon-based light emitting diodes (MOSLEDs) with Gd and Tb implanted SiO2 layers exhibit strong ultra violet and green electroluminescence (EL) at 316 nm and 541 nm, respectively. If amorphous SiO2 is bombarded with energetic ions, various types of defects are created as a consequence of ion-solid interaction and annealing processes (oxygen deficiency centres (ODC), non-bridging oxygen hole centres (NBOHC), E’-centres, etc.) leading to charge trapping effects during electrical excitation. Elimination or neutralisation of such defects is very important from the viewpoint of electrical stability of MOSLEDs. It will be demonstrated that (i) an additional fluorine implant into SiO2:Gd and SiO2:Tb layers leads to a decrease of E’-centres and ODC´s improving the efficiency of the MOSLEDs; and (ii), an additional potassium implant produces positive ions leading to a compensation effect for the negatively charged electron traps and, hence, to an reduced quenching of the EL efficiency and increased MOSLED lifetime .

This report reviews our recent progress on efficient electroluminescence (EL) from silicon pn junctions and rare earth doped metal-oxide-semiconductor light emitting devices (MOSLEDs) in the infrared to ultraviolet range [1-3]. Silicon pn diodes prepared by boron implantation have shown efficient band edge EL with a high efficiency above 0.15% at room temperature. A detailed study has shown that the anomalous increase of the EL intensity with increasing temperature comes from the release of free carriers by thermal ionization of bound excitons. They are trapped around locally enhanced p-type doping spikes formed by boron clustering at dislocations or fabricated by selective diffusion of boron through a patterned SiO2 mask layer.
Efficient EL from Er, Tb, Gd doped MOSLEDs at 1535, 541 and 316 nm with an high quantum efficiency of 14, 16.5, and 5 %, respectively, has been demonstrated in our MOSLEDs, which is comparable to that of III-V semiconductor devices. The EL properties of efficiency, decay time, and excitation cross-section were studied concerning cross relaxation at concentrations from 0.25 to 9% and clustering of rare earth dopants at annealing temperatures from 800 to 1100°C. Improving of the device stability is achieved by using double-stacked gate oxide layers, charge compensation and elimination of defects in SiO2 layers.
[1] J. M. Sun, W. Skorupa, T. Dekorsy , and M. Helm, J. Appl. Phys. 97, 123513 (2005)
[2] J. M. Sun, W. Skorupa, T. Dekorsy, and M. Helm, Appl. Phys. Lett. 85, 3387 (2004).
[3] J. M. Sun, T. Dekorsy, W. Skorupa, B. Schmidt, A. Mücklich, and M. Helm, Phys. Rev. B 70, 155316 (2004).

In this project we study diffusion and electrical activation in lithium and helium implanted ZnO single crystal wafers with high resistivity using secondary ion mass spectrometry (SIMS), scanning spreading resistance microscopy (SSRM) and scanning capacitance microscopy (SCM), respectively. Li+ ions were implanted with an energy of 837 keV at a dose of 2x1015 cm-2, and He+ were implanted with an energy of 683 keV at a dose of 6x1015 cm-2 to ensure similar implantation depths and damage productions. The samples were then annealed using short 20 ms light flashes corresponding to temperatures of 900°C, 1200°C and 1400°C. After each annealing step the samples were characterized with SSRM/SCM and SIMS. In as-implanted samples, no changes in the initially high resistivity are observed in neither the Li- nor the He-implanted samples but after the thermal treatments a substantial decrease is observed in both sets of samples. This resistivity drop is most likely related to electrical activation of shallow implantation-induced defects or deactivation of compensating defects/impurities, as He in principle should be electrically inactive in any solid state material. No significant redistribution of the implanted ions is observed.

We have investigated flash-lamp annealing (FLA) of germanium wafers doped with phosphorous and boron introduced in the crystal by ion implantation. Annealing was performed by using pre-heating at 400-450 oC in a conventional rapid thermal processing (RTP) unit and a fast (3-20 ms) FLA annealing at 800 oC or 900 oC. Diffusion of P is suppressed during the 800oC-20 ms FLA annealing, while concentration-enhanced diffusion occurs upon 900oC FLA anneals. At this higher temperature the FLA pulse time becomes a fundamental parameter, since the shortest FLA pulse (3 ms) causes less junction deepening and less P dose loss as compared to the longest (20 ms) pulse. Importantly, P activation seems to be enhanced by the FLA process.
The FLA process applied to B-doped pre-amorphized Ge layers does not show advantages as compared to a RTP conventional annealing. B diffusion and activation behavior are indeed similar for the millisecond annealing approach and for a conventional RTP combined with a solid phase epitaxial regrowth of the doped Ge layer.
In summary, the FLA technique holds a potential for the development of P shallow junctions in germanium wafers. However, junction stability following the FLA process is a concern and needs to be further investigated.

We have investigated flash-lamp annealing (FLA) of germanium wafers doped with phosphorous and boron introduced in the Ge crystal by ion implantation. Annealing was performed by using pre-heating at 400-450 oC in a conventional rapid thermal processing (RTP) unit and a fast (3-20 ms) FLA annealing at 800 oC or 900 oC. Diffusion of P is suppressed during the 800oC-20 ms FLA annealing, while concentration-enhanced diffusion occurs upon 900oC FLA anneals. At this higher temperature the FLA pulse time becomes a fundamental parameter, since the shortest FLA pulse (3 ms) causes less junction deepening and less P dose loss as compared to the longest (20 ms) pulse. Importantly, P activation seems to be enhanced by the FLA process. The FLA process applied to B-doped pre-amorphized Ge layers does not show advantages as compared to a RTP conventional annealing. B diffusion and activation behavior are indeed similar for the millisecond annealing approach and for a conventional RTP combined with a solid phase epitaxial regrowth of the doped Ge layer.
In summary, the FLA technique holds a potential for the development of P shallow junctions in germanium wafers. However, junction stability following the FLA process is a concern and needs to be further investigated.

The influence of different annealing processes (furnace annealing FA, rapid thermal annealing RTA and flash lamp annealing FLA) on the electroluminescence intensity, electric stability and point defect creation in SiO2 layers containing Gd atoms was investigated. The samples were annealed at different temperatures (from 800 to 10000C with the step 1000C for FA and from 10000C to 12000C with the step 500C for RTA and FLA). In the case of the peak at 316 nm which corresponds to Gd3+ the strongest EL intensity was observed from the sample annealed at 11000C after FLA. Increasing of the annealing temperature leads to a decreasing of the luminescence for each of annealing methods. The same effect was observed after increasing of the annealing time. In the case of defect formation under different annealing conditions an inverse situation was observed. Increasing of the annealing temperature and annealing time leads to an increase of the EL from oxygen deficiency centers (ODCs) An increase of the luminescence from defects at a simultaneous decrease of the luminescence from Gd at 316 nm can be explained by Gd-nanocluster creation in a-SiO2 during the annealing process.

The excitation mechanism of electroluminescence (EL) of cerium and erbium ions co-implanted with gadolinium into the SiO2 layer of MOSLEDs was investigated. Ce and Er ions were implanted into SiO2 with a concentration of 1% and 2%, respectively, subsequently implanted by gadolinium ions with concentrations of 0.5, 1.5 and 3%. Silicon dioxide containing cerium co-implanted with Gd exhibits two different excitation mechanisms: direct Ce3+ ion excitation by hot electrons and transfer of energy from 6PJ energy level of Gd to 5d energy state of Ce leading to an increase of the EL of Ce in the blue region. The EL observed from the sample containing 3% of Gd was 5 times higher in comparison with samples implanted only by Ce. The Er implanted SiO2 exhibits the typical peak at 1540 nm and weak luminescence in the green and blue region. Two green peaks correspond to the transitions from 2H11/2 and 4S3/2 to 4I15/2 and blue peaks to those from 2H9/2 and 4F5/2 to 4I15/2. The additional implantation of Gd leads to an increase of luminescence from Er3+ lines in the visible region caused by the energy relaxation from the Gd excited level 6PJ to the higher energy levels of erbium, whereas it has no influence on the infrared luminescence at 1.54 mm.

When amorphous silica is bombarded with energetic ions, various types of defects are created as consequence of ion-solid interaction (oxygen deficient centres ODC, non-bridging oxygen hole centres NBOHC, E’-centres, etc.). Metal-oxide-silicon (MOS) structure contains gadolinium implanted SiO2 layer exhibit strong ultra violet (UV) electroluminescence (EL) at 316 nm from Gd3+ ions and enhancement of luminescence from defects (465 nm, 520 nm and 650 nm corresponds to ODC, Ed’-centre and NBOHC, respectively). Creation and transformation of point defects in bulk SiO2 contains Gd and F atom during constant current injection was investigated. Elimination of such defects is very important from viewpoint of electrical stability of MOS devices. Additional implantation of fluorine in to SiO2:Gd layer leads to decreasing of number of E’-centres and ODC, improves the stability of EL from Gd3+ at 316 nm and lengths working time of MOS structure.

Review of recent work presented at the MRS Spring Meeting at San Francisco

Vortrag anlässlich eines vertraulichen Projekttreffens bei der Creavis-Degussa AG

Vortrag anlässlich der Begutachtung eines japanischen Grossprpojektes

Combining silicon-based electronic circuits with optoelectronic functionality is one of the key challenges for the future semiconductor technology. Such work must not only be devoted to the wavelength of 1.54 µm because there are more applications needing light sources from all the UV to IR wavelength range. In our work we employed ion beam processing to embed different rare earth (RE) luminescent centers (Gd3+, Ce3+, Tm3+, Tb3+, Eu3+, Er3+) into the silicon dioxide layer of a purpose-designed Metal-Oxide-Silicon-based Light Emitting Diodes (MOSLEDs) with advanced electrical performance. Efficient electroluminescence was obtained from UV to infrared with a transparent top electrode made of indium-tin oxide. The distinct differences in efficiency of the various rare earth atoms will be discussed as well as problems of electrical stability of such devices due to hot electron injection and charge trapping phenomena. Several developments for improving the device stability will be proposed related to charge compensation and elimination of the defects in SiO2.

A flash lamp has been proposed for annealing wafers with diameters approaching 100 mm.
The equipment applies a pulse, with duration 0.5 ms to 20 ms, resulting in large transient thermal
gradients in the wafer. In this paper, we present a model for the thermal reaction of this process
and its effect upon the mechanical behaviour, in order to predict stresses, shape changes and to
capture practical phenomenon, such as bifurcation of deformation modes. We then use the
model to follow changes in the expected response consequent on altering process conditions, as
well as exploring important issues associated with scaling to large wafer sizes. The model is
further used to predict material yielding leading to permanent deformations. This work presents
the first description of the thermo-mechanical response of wafers to flash lamp annealing in the
millisecond time regime and is therefore fundamental to the use of this technique in the
fabrication of semiconductor devices.

Flash lamp annealing in the millisecond regime of heteroepitaxial silicon carbide on silicon structures involves melting the Si below the SiC layer, but the deep facetted nature of the solid-liquid interface leads to unacceptable surface roughness. This paper describes a method of controlling melting by implanting a high dose of carbon or germanium at a controlled depth below the Si/SiC interface, which significantly alters the melting characteristics of the silicon. Results confirm the effectiveness of these approaches for increasing surface uniformity, making liquid phase processing compatible with standard device fabrication techniques. A thermal model has also been developed to describe this process and results indicate that the theoretical work is consistent with the experimental evidence. The model is a valuable tool for predicting onset of melting, maximum temperatures and process windows for liquid phase epitaxy.

Thin poly-crystalline silicon films are attractive for the fabrication of active matrix liquid crystal displays. We investigate the use of flash lamp annealing to crystallize amorphous silicon layers on glass substrates as a low cost manufacturing route. In this process amorphous silicon (a-Si) can be crystallized by solid phase crystallization (SPC) or in the super lateral growth (SLG) regime. We present a thermal model incorporating the phase transitions during annealing; providing a valuable tool for optimizing the process conditions. Another consideration is the evolution of stress resulting from the transient thermal loading of the substrate material. Results are presented for various substrate geometries and important scalability issues are addressed.

Li is present in hydrothermally grown ZnO at high concentrations and is known to compensate both n- and p-type doping due to its amphoteric nature. However, Li can be manipulated by annealing and ion implantation in ZnO. Fast, 20 ms flash anneals in the 900–1400 °C range result in vacancy cluster formation and, simultaneously, a low-resistive layer in the implanted part of the He- and Li-implanted ZnO. The vacancy clusters, involving 3-4 Zn vacancies, trap and deactivate Li, leaving other in-grown donors to determine the electrical properties. Such clusters are not present in sufficient concentrations after longer (1 h) anneals because of a relatively low dissociation barrier ~2.6±0.3 eV, so ZnO remains compensated until Li diffuses out after 1250 °C anneals.

Li is present in hydrothermally grown ZnO at high concentrations and is known to compensate both n- and p-type doping due to its amphoteric nature. However, Li can be manipulated by annealing and ion implantation in ZnO. Fast, 20 ms flash anneals in the 900–1400 °C range result in vacancy cluster formation and, simultaneously, a low-resistive layer in the implanted part of the He- and Li-implanted ZnO. The vacancy clusters, involving 3-4 Zn vacancies, trap and deactivate Li, leaving other in-grown donors to determine the electrical properties. Such clusters are not present in sufficient concentrations after longer (1 h) anneals because of a relatively low dissociation barrier ~2.6±0.3 eV, so ZnO remains compensated until Li diffuses out after 1250 °C anneals.