ZParl Zeitschrift für Parlamentsfragen , Seite 426 - 435

licht, die im Verbund nicht anfallen würden. Auch andere, in diesem Beitrag nicht diskutierte Vorschläge hätten nicht dieselben strukturerhaltend korrigierenden Wirkungen: Das häufi g zitierte Grabenwahlsystem ohne Verrechnung von Direktund Listenmandaten würde, wie auch das einfache Mehrheitswahlsystem, zu Wahlergebnissen führen, die weitab von dem liegen, was Wähler und Parteien in Deutschland gewohnt sind. Ein reines Verhältniswahlsystem mit Fünfprozentklausel würde die Proportionalität des Wahlergebnisses nicht wesentlich verbessern, und selbst wenn man off ene Listen zuließe46, wäre dies auf Landesebene nur ein schwacher Ersatz für die jetzige Personenwahl in Einer-Wahlkreisen. Die einzigartige Struktur des deutschen Wahlsystems hat sich über einen langen Zeitraum bewährt: Das Mischwahlsystem ermöglichte stabile, zumindest 1998 sogar alternierende Regierungsmehrheiten bei gleichzeitiger Wahrung von Parteienund Landesproporz; es sorgte einerseits für die Entstehung geschlossener Parteiverbände mit nationaler Ausrichtung, ohne jedoch andererseits auf volksnahe, direkt gewählte Abgeordnete zu verzichten. Die unterschiedlichen Auswirkungen der Stimmabgabe in beiden Wahlgängen und die Gelegenheit zur individuellen Stimmgebung bieten dem Wähler Möglichkeiten, wie sie kaum ein anderes Wahlsystem bereithält. Seit Ende der achtziger Jahre hat sich das Mischwahlsystem deutscher Prägung zu einem wahren Exportschlager entwickelt. Es ist das meistadoptierte System der jüngeren Vergangenheit, und es vereint nach Ansicht vieler Experten das Beste aus den Welten von Mehrheitsund Verhältniswahl.47 Bei der anstehenden Reform sollte es deshalb vor allem darum gehen, das deutsche Wahlsystem in seiner bisherigen Form zu bewahren. Der Fehler eines möglichen inversen Erfolgswerts von Wählerstimmen ließe sich mit der hier vorgestellten länderweisen Sitzzuteilung beheben, ohne damit das deutsche Wahlsystem in seiner Wirkungsweise grundlegend zu verändern.

Kurzfassung Mikrotomographie erlaubt die hochauflösende Abbildung verdeckter Mikrostrukturen und den Nachweis von Mikrorissen und Mikroporen in vielfältigen Bereichen, darunter die Untersuchung von mikroporösen Materialien und Fasernetzwerken, der Mikrostruktur biokompatibler Materialien (Implantate), der Entwicklung der Struktur von Metallgefügen u.v.m. Synchrotron-Laminographie erweitert das Anwendungsspektrum der 3-D-Methoden auf die zerstörungsfreie Bauteiluntersuchung ohne Probenentnahme bzw. Probenpräparation, und erweitert die hoch auflösende Inspektion z.B. in der Mikrosystemtechnik, der Paläontologie Archäologie etc. Ultraschnelle Radiographie, Computertomographie und Laminographie erlauben die In-situ-Untersuchung von Proben und Bauteilen in Echtzeit und unter betriebsnahen Bedingungen verschiedenster Probenumgebung. Phasenkontrast erweitert die Anwendungsbreite der 2-D und 3-D abbildenden Synchrotronverfahren auf leichte Materialien und führte die Methoden damit in die Leichtbautechnologien und die Lebenswissenschaften. Die Kombination der Techniken mit Röntgenoptiken treibt die Grenzen der Ortsauflösung in den Bereich weniger 10 nm.

Synchrotron radiation imaging methodes have been proven to be highly suitable for investigations in materials research and non-destructive evaluation. The intense flux and partial spatial coherence available at modern synchrotron light sources allows one to work with high resolutions and different contrast modes. This articles gives an overview about different dire ct and indirect imaging methodes for industrial applications, recently available for commercial acces s via the German light source ANKA and its department ANKA commercial services (ANKA COS).

The crystalline quality in epitaxially laterally overgrown (ELO) GaN and the amount of wing tilt is characterized on a local basis, with high spatial and angular resolution. A method of full‐field X‐ray microdiffraction imaging, termed rocking curve imaging, is used to record simultaneously a large set of local X‐ray diffraction profiles originating from sample surface areas of micrometer size. x – ω maps of diffracted intensity allow to quantify the amount of wing tilt in individual lateral ELO periods as well as to monitor the fluctuations of tilt between adjacent periods. Automated shape analysis of the full set of local rocking curves provides a means to quantitatively characterize the local crystalline perfection of GaN. The ELO window and wing regions can be clearly separated; comparison indicates an average improvement of crystal quality by a factor 3–4 due to the lateral overgrowth process. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

We report on recent advances in spatially resolved x-ray diffraction, extending the technique known as rocking curve imaging down to 1-2 mu m spatial resolution. Application to a set of gallium nitride samples grown by epitaxial lateral overgrowth (ELO) shows the potential of the technique. Quantitative information on crystallographic misorientations and lattice quality can be obtained by direct imaging with high lateral resolution. Results from two samples of ELO-GaN grown on different substrates are compared. Tilt in individual lateral periods of the ELO structure can be quantified. Local tilt fluctuations are distinguished from macroscopic variations (curvature). The local lattice quality can be investigated via the peak width of diffraction profiles recorded in individual camera pixels. The peak broadening previously observed in laboratory x-ray diffraction measurements is found to have (at least) two different reasons. In both cases, peak broadening does not indicate a degradation in local crystalline quality.

The method called rocking-curve imaging (RCI) has recently been developed to visualize lattice imperfections in large crystals such as semiconductor wafers with high spatial resolution. The method is based on a combination of X-ray rocking-curve analysis and digital X-ray diffraction topography. In this article, an extension of the method is proposed by which dislocation densities in largescale samples (semiconductor wafer crystals) can be quantified and their variation across the sample surface determined in an instrumentally simple way. Results from a nearly dislocation-free S-doped InP crystal and a semi-insulating GaAs are presented; both display a clearly non-random distribution of dislocations.

Differences in mosaicity between lysozyme crystals grown inside and outside a homogeneous magnetic field of 2.4 T and with and without agarose gel were investigated by X-ray diffraction rocking-curve measurements. High angular resolution was achieved using an Si(113) four-reflection Bartels monochromator. The results show that (i) all crystals were highly perfect, (ii) the mosaicities were clearly anisotropic and (iii) the mosaicities varied more strongly within each group of crystals (grown under identical conditions) than the average values across groups. In particular, the effect of the magnetic field on crystal mosaicity was found to be very small. Finally, the spatial distribution of mosaic blocks inside a protein crystal was visualized with a novel diffraction technique using a high spatial resolution two-dimensional CCD detector.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

We have developed a high-resolution diffraction imaging method for determination of the complete three-dimensional rotational local lattice misorientation of crystalline samples. The method, called synchrotron area diffractometry, is based on recording double-crystal diffraction rocking scans in three mutually non-coplanar scattering planes with a two-dimensional area detector. The subsequent multiple-peak analysis of the rocking curve image series for all pixels and their backprojection to the wafer surface provides local misorientation angles (Euler angles) with spatial resolution up to micrometre range over the wafer surface. We applied this technique to determine the distribution of tilt and twist angles of the lattice misorientation of a macroscopic defect localized in a 6 inch semi-insulating GaAs(001) wafer.

The Ga84R204- [R = N(SiMe3)(2)] species, which represents the largest metalloid cluster entity structurally characterized so far, has been electronically and topologically modified: Via changing the redox potential of the reaction solution, crystals different from those containing the Ga84R204- anion can be isolated, featuring similar Ga84R203- entities. An accurate crystal structure analysis via synchrotron radiation is presented, which might be the first step toward an understanding of the metallic conductivity and superconductivity of the Ga84R204- cluster compound, physical properties which are singular in the field of metalloid clusters so far.

We demonstrate the application of surface sensitive diffuse x-ray scattering under the condition of grazing incidence and exit angles to investigate growth and dissolution of near-surface defects after boron implantation in silicon(001) and annealing. Silicon wafers were implanted with a boron dose of 6×1015 ions/cm2 at 32 keV and went through different annealing treatments. From the diffuse intensity close to the (220) surface Bragg peak we reveal the nature and kinetic behavior of the implantation induced defects. Analyzing the q dependence of the diffuse scattering, we are able to distinguish between point defect clusters and extrinsic stacking faults on {111} planes. Characteristic for stacking faults are diffuse x-ray intensity streaks along 〈111〉 directions, which allow for the determination of their growth and dissolution kinetics. For the annealing conditions of our crystals, we conclude that the kinetics of growth can be described by an Ostwald ripening model in which smaller faults shrink at the expense of the larger stacking faults. The growth is found to be limited by the self-diffusion of silicon interstitials. After longer rapid thermal annealing the stacking faults disappear almost completely without shrinking, most likely by transformation into perfect loops via a dislocation reaction. This model is confirmed by complementary cross-sectional transmission electron microscopy.

In the present work the lattice plane curvature of a nearly dislocation free S:doped InP and a semi-insulating GaAs wafer crystals has been investigated using the method of X-ray rocking curve imaging based on the FRELON CCD area detector with a pixel resolution from 10 to 40 μm at the ID19 ESRF beamline. The geometry of the experiment is based on a vertical Si (111) monochromator and a horizontal sample scattering planes in the Bragg geometry (σ-π geometry). To determine the local lattice inclination, the effect of such dispersive setup on the measured local diffraction peak position has been accurately determined and the equations to determine the lattice plane curvature of the crystals under the condition of isotropic distribution of dislocation Burgers vectors are obtained. The analysis of the data showed that the shift of the Bragg condition is almost completely due to the lattice tilt rather than to the lattice parameter variation. Lattice displacements from the ideal lattice as large as 200 μm are found at the edges of the InP crystal. Non random distributions of dislocation Burgers vectors are observed in both samples.