Application of x-ray cross-correlation analysis for studies of partially ordered systems structure

Start Date
23-11-2017 14:00
End Date
23-11-2017 17:00
03-1-13 ExpHall
Speaker's name
Ivan Zaluzhnyy
Speaker's institute
Contact name
Ewa Wyszynska
Host name
Gilles Renaud
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Ivan A. Zaluzhnyy

Application of x-ray cross-correlation analysis for studies of partially ordered systems structure

Partially ordered systems exhibit intermediate ordering between liquids and crystals. An important parameter that characterizes a structure of partially ordered systems is an orientational order. Angular X-ray cross-correlation analysis (XCCA) is a method that allows one to study the orientational order by analysis of the angular correlations of the X-ray diffraction patterns.

In the focus of our studies were two systems exhibiting different types of orientational order. The first is a hexatic phase in three-dimensional smectic liquid crystals, that is characterized by short-range positional order in distribution of molecule centers of mass and long-range order in orientation of local hexagons formed by neighbouring molecules. Many basic features of the hexatic phase remain unclear, for example, universality class of the smectic-hexatic phase transition, spatial structure of the hexatic phase, temperature dependence of the bond-orientational order parameters, etc.

The second system is a mesocrystal formed by PbS nanoparticles coated by an organic semiconductor. Such assemblies of nanoparticles preserve the optoelectronic properties of quantum confined systems - such as enhanced absorption cross-sections, tunability of the bandgap, the prospects of multi-exciton generation, etc. – but display essentially single-crystalline diffraction patterns. The physical properties of mesocrystals are largely determined by their structural coherence, for which the angular correlation between their individual atomic lattice and the underlying superlattice of nanocrystals is a key ingredient.

Left: Scheme of the X-ray diffraction experiment in transmission geometry.

Right: Polar coordinate system at diffraction pattern to calculate the angular cross-correlation function.

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