Prof. Andreas Magerl
Chair for Biophysics
Phone: +49 9131 85-25181
Fax: +49 9131 85-25182
Oxide nanoparticles are deliberately introduced to every semiconductor chip to a large extent and play an essential role in guaranteeing long lifetimes. Utilizing dynamical diffraction theory and in particular pendellösungs oscillations (thickness-dependent or energy-dependent), it is possible to get experimental insight to strain fields with greater sensitivity than with any other method. Point defect agglomerates such as oxide nanoparticles introduce such strain fields. With the above mentioned technique, we study the formation, growth and ripening of these particles in-situ at temperatures up to 1200 °C. We focus on the low temperature regime far below 1000 °C and the influence of dopants on the oxygen diffusion.
Morphology and growth of these particles are furthermore investigated on with high-resolution X-ray diffractometry with lab and synchrotron sources as well as with small angle scattering (coherent diffraction imaging). Full goal is determining all relevant quantities such as sizes and number densities of the particles and the interplay precipitate and crystal matrix concerning the growth process.
Ultra-fast in-situ SAXS-WAXS measurements of the nucleation and growth of semiconductor nanoparticles in solution
The formation and growth mechanisms of semiconductor nanoparticles (quantum dots) are a highly interesting research area due to their size dependent optical and electrical properties. Although many synthesis routes have already been developed, the nucleation and growth process of their very early stages is still poorly understood. Therefore a self-developed free jet setup enables us to investigate on these processes in-situ using synchrotron radiation. The accessible reaction times (from 10 µs up to 10 ms) are up to date the fastest X-ray diffraction experiments on quantum dot formation. The combination of Small Angle X-ray Scattering (SAXS), Wide Angle X-ray Scattering (WAXS) and Total Scattering (TS) allows us for getting an experimental insight into the morphology, the crystaline structure and the crystal defects of very early stages of quantum dot formation as a function of time.
These Investigations are partially based on measurements at synchrotron radiation sources (e.g. ESRF in Grenoble, France; APS in Chicago, USA; Spring 8 close to Osaka, Japan; AS in Melbourne, Australia ).
Utilizing surface coatings, it is possible to control the physical, chemical and mechanical properties of materials and surfaces. Self-organizing organic monolayers play a key role in such applications. Thus the understanding of their growth as well as of their ordering and atomic structure is of fundamental yet unexplored interest.
We employ surface-sensitive X-ray diffraction in order to study the interaction of trichlorsilanes, alcohols of different alcane chain lengths and metal porphyrins with amorphous SiO3 (native oxide of Si wafers), crystalline SiO2 and Al2O3 (sapphire). The overall goal is an understanding of the lateral and vertical structures in sub Angström resolution for the control of the above mentioned properties.
Richard Schielein, N.N.
Utilizing backscattering geometry for diffraction, highest energy resolutions are achievable in crystal spectrometers. Key part is a large-scale array of monochromator and analyzer plates made of perfect silicon (~10 m2). Recently, we were able to demonstrate an improvement of one order of magnitude in energy resolution by means of using GaAs crystals instead of silicon.
In collaboration with the Institut Laue-Langevin, Grenoble, France, the world-leading center for research with neutrons and embedded in an international project, we want to implement the first ever backscattering spectrometer utilizing GaAs.