M. Weisser

Complementary Molecular Dynamics and X-ray Reflectivity Study of an Imidazolium-Based Ionic Liquid at a Neutral Sapphire Interface.

Understanding the molecular-level behavior of ionic liquids (ILs) at IL-solid interfaces is of fundamental importance with respect to their application in, for example, electrochemical systems and electronic devices. Using a model system, consisting of an imidazolium-based IL ([C2Mim][NTf2]) in contact with a sapphire substrate, we have approached this problem using a complementary combination of high-resolution X-ray reflectivity measurements and atomistic molecular dynamics (MD) simulations. Our strategy enabled us to compare experimental and theoretically calculated reflectivities in a direct manner, thereby critically assessing the applicability of several force-field variants. On the other hand, using the best-matching MD description, we are able to describe the nature of the model IL-solid interface in appreciable detail. More specifically, we find that characteristic interactions between the surface hydroxyl groups and donor and acceptor sites on the IL constituents have a dominant role in inducing a multidimensional layering profile of the cations and anions.

Superconductive undulators with variable polarization direction

In the past planar superconductive undulators have been successfully developed and tested with beam. They produce linearly polarized light (X-rays) and allow to tune the emitted wavelength electrically. In this paper a novel type of superconductive undulators is introduced which allows to tune electrically in addition to the wavelength the polarization direction. A short prototype was built and tested in a LHe bath.

A high-energy triple-axis X-ray diffractometer for the study of the structure of bulk crystals

A triple-axis diffractometer for high-energy X-ray diffraction is described. A 450 kV/4.5 kW stationary tungsten X-ray tube serves as the X-ray source. Normally, 220 reflections of thermally annealed Czochralski Si are employed for the monochromator and analyser. Their integrated reflectivity is about ten times higher than the ideal crystal value. With the same material as the sample, and working with the W Kα line at 60 keV in symmetric Laue geometry for all axes, the full width at half-maximum (FWHM) values for the longitudinal and transversal resolution are 2.5 x 10 -3 and 1.1 x 10 -4 for ΔQ/Q, respectively, and the peak intensity for a non-dispersive setting is 3000 counts s -1 . In particular, for a double-axis mode, an energy well above 100 keV from the Bremsstrahlung spectrum can be used readily. High-energy X-rays are distinguished by a high penetration power and materials of several centimetre thickness can be analysed. The feasibility of performing experiments with massive sample environments is demonstrated.

Superconducting In-Vacuum Undulators

During the last years the Research Center Karlsruhe developed novel high-field superconducting in-vacuum undulators with period lengths of 3.8 and 14 mm. The undulators were tested with beam, both in linac type accelerators (Mainzer Microtron MAMI) and storage rings (ANKA). Based on this experience a new generation of superconducting undulators is planned: undulators capable of electrical field error compensation, undulators with electrically variable polarization direction and high brilliance for various accelerators

The Build-Up of Strain Fields in Czochralski-Si Observed in Real Time by High Energy X-Ray Diffraction

The build-up of strain fields caused by the precipitation of oxygen in Czochralski-silicon during annealing up to 1200°C and for process times up to 70 hours has been observed in real time by high energy x-ray diffraction. Five different processes are distinguished in the temperature evolution of the intensity and of the rocking width of the silicon 220-reflection. These features are attributed to different precipitation mechanisms. A fit to part of the data with a diffusion limited precipitation model leads to an activation energy for oxygen diffusion in silicon of 2.2 eV in the temperature range from 700°C to 950°C.

Technical Report: First Beam Tests of a Superconductive Undulator in a Storage Ring at ANKA

In 2005 a test superconductive undulator was installed in the ANKA storage ring. Since then the undulator has been constantly in operation as the first cold-bore, small-gap superconducting undulator ever installed in a storage ring. The aim of this experiment was to demonstrate that such a device can be operated under normal user conditions. Compared with permanent magnet undulators, superconducting undulators have a higher magnetic field strength (for a given period length and a given gap width) and can be tuned electrically. The higher field strength allows the production of photon beams with higher brilliance and higher photon energy.

Operation of the ANKA Synchrotron Light Source with Superconductive Undulators

Following the successful performance of a beam test with a superconductive undulator at the synchrotron light source ANKA there are plans to equip most of the straight sections with superconductive undulators. In this paper the first results of the measurements are presented and future plans are summarized.

One Year Operation of a Superconductive Undulator in the Storage Ring ANKA

In spring 2005 the worldwide first cold‐bore superconductive undulator was installed in the storage ring ANKA. In this paper the obtained results concerning the measured spectra and the heat load from the beam are described. Future developments in the field on superconductive undulators at ANKA are summarized.

Superconductive in-vacuum undulators for storage rings, concept and first operational experience

Superconductive undulators with a small period length are a novel tool in generating X-ray beams with high brlliance. The concept and the first prototype for a s storage ring was developed for ANKA, a 2.5 GeV synchrotron light source in Karlsruhe, Germany.

In-Situ Er-Doping of SiC Bulk Single Crystals

In this work the first PVT grown in-situ erbium doped SiC bulk crystal, to our knowledge, is presented. The crystal was characterised by secondary ion mass spectrometry (SIMS) and photoluminescence measurements. SIMS investigations show erbium concentrations in the range of 1.1 · 1014 cm−3 to 2.9 · 1014 cm−3. Photoluminescence measurements between 1450 nm and 1650 nm were conducted at 19 K, 77 K and 300 K. A distinct luminescence at 1540 nm corresponding to the I13/2 → I15/2 transition was detected even at room temperature. In the investigated temperature range, luminescence intensity shows only a slight decrease of 16 %. Measurements with different laser powers suggest a saturation of erbium related luminescence in our experimental conditions.