Resonant Diffraction as a tool to probe local chemical and electronic structures in crystals.

Resonant diffraction is a method which combines local information about chemical and electronic properties with the global information about atomic positions. It is, in a sense, diffraction and spectroscopy combined in one technique. We are currently investigating polarization effects and anisotropy of resonant scattering in order to probe chemical and electronic properties in molecular crystals. We are also investigating the macroscopic polarization-dependent X-ray properties of single organic crystals (dichroism, birefringence). Finally, one important aspect of our work is related to characterizing and exploiting anisotropy effects in macromolecular crystallography.

Photo-induced and Radiation-induced structural changes in organic and biological crystals.

We are investigating photo-induced and/or X-ray-induced structural transitions in molecular crystals (i.e. photo- and radiochemical reactions). One of the goals is to set means for studying these transitions in a time-resolved fashion. On a more fundamental aspect, we are also interested in studying the mechanisms by which molecules and molecular crystals undergo degradation when exposed to an intense X-ray beam (radiation damage). This is of some importance in radiation biophysics and is expected to aid in understanding the effects of ionizing radiation on biological molecules. We also use computational techniques and numerical simulations to interpret the experimental data.

The modelling of aperiodic crystal structures

Aperiodic crystals are characterised by discrete diffraction spectra which are incompatible with three dimensional periodicity. Quasicrystals, incommensurate and composite crystals belong to this category.

We are studying aperiodic structures both from the theoretical point of view and also experimentally. In particular, we are interested in the structures of incommensurately modulated crystals. Our methods are essentially based on diffraction and molecular dynamics.

The diffraction spectra of this type of material very often includes diffuse scattering. This is due to defects in the crystalline structures, which are modelled by different approach.

The Swiss Norwegian beamlines (SNBL) at the ESRF in Grenoble

The crystallography laboratory actively participate in the consortium of Swiss and Norwegian partners responsible for the development and management of the two SNBL beamlines at the European Synchrotron Radiation Facility (ESRF).

This facility is producing hard X-rays for a broad spectrum of research studies at the atomic scale. Both beamlines are optimised for single crystal respectively powder diffraction and EXAFS.

Analytical Services