Prof. Reinhard Neder
Chair for Crystallography and Structural Physics
Phone: +49 9131 85-25191
Fax: +49 9131 85-25182
The central research topic of our group are disordered crystal structures. We synthesized these and characterize them predominantly with scattering techniques. The diffraction pattern of disordered crystals exhibit strong diffuse scattering in addition to the Bragg reflections. Thus one of our main techniques is the analysis of disordered crystals via the Pair Distribution Function (PDF) techniques.
Currently our work covers:
The DISCUS program is a unique tool to simulate disordered crystals and to calculate the single crystal and powder diffraction data as well as the PDF. A particular strength of the DISCUS program is its ability to simulate nanoparticles including their organic shell. Further tools are under development to improves particularly this last aspect. DISCUS workshops in Erlangen are a regular event.
As the need for PDF measurements is rapidly increasing the BMBF has funded a project to build a dedicated beam line at section 21. This project works in cooperation with the Swedish beam line at PETRA. We indent to build a beam line that will deliver a high intensity beam at 100 keV in order to offer fast measurements by use of an area detector and simultaneously reach a Qmax of 300 nm-1. This will allow fast in-situ experiments and will offer the ability to measure PDF's that are very well resolved in direct space.
Nanoparticles are readily synthesized via a sol-gel techniques in ethanol solutions. We study this synthesis process in order to work out parameters that control the finite size of the nanoparticles. As the nanoparticles are stabilized by a shell of organic molecules, we employ both X-ray and neutron diffraction to determine the size, shape, structure, defect structure of the ZnO core, and the placement of the stabilizing molecules. Recently in-situ studies have been performed to study the nucleation and growth of ZnO nanoparticles.
Metaloxide nanoparticles such as titanium dioxide or zinc oxide (ZnO) are quite frequently produced in sol-gel processes. Although, also by adding organic stabilizers, the final nanoparticle size can be tuned very precisely, little is known about the evolution of the crystalline arrangement during the nucleation in solution. Hence, we conduct wide angle x-ray diffraction experiments on a model system of ZnO in different alcohols to learn more about the structure of precursors, nuclei as well as larger nanoparticles. We measure the currently lowest detectable concentrations of about 30 mM and can observe precursor structures of only 40 atoms. Without the addition of additional precipitation agents, those precursors nucleate and gradually grow on very long timescales of hours to diameters of 3 nm. Such in-situ PDF studies can currently be technically implemented at the ESRF in Grenoble, at Spring-8 in Japan, at DESY in Hamburg or APS in Chicago.
Collaborations: Prof. Dr. Dirk Zahn, chair for theoretical chemistry, Computer Chemistry Center (CCC), FAU Erlangen, Prof. Dr. Jean Geurts, chair for experimental physics III, University Würzburg
The Interactive Teaching pages at the department of cystallography allow you to explore the connection between a structure and its diffraction pattern. You will find simple simulations like a one dimensional row of atoms as well as simulations of shortr range order.