am Dienstag, den 12.06.2012 um 17:00 wird im Hans-Geiger-Hörsaal des Physikzentrums

Prof. Dr. Andreas Stierle (DESY and University of Hamburg)

im Rahmen des Physikalischen Kolloquiums einen Vortrag zum Thema

The Atomic Structure of Nano-Objects: What X-Rays Can Tell

halten. Sie sind herzlich eingeladen.

Abstract:

The atomic structure determination of nano-objects with dimensions in the sub-100 nm regime is a formidable task for today's diffraction,
imaging and scanning probe techniques. Such a detailed structural and compositional analysis is mandatory for a correlation with the
nano-object's functionality e.g. as heterogeneous catalysts, magnetic storage material or light emitting device. In conventional x-ray
diffraction experiments on powder samples the structural analysis is hampered by a random nanoparticle orientation and often by background
scattering from the supporting material. Recently, progress has been made in x-ray diffraction from single nanoparticles in the size regime of a few 100 nm allowing a reconstruction of the particle structure with a few tenth of nm resolution.

Here I will present different ensemble averaging in-situ synchrotron radiation based x-ray diffraction schemes delivering quantitative
information on the nanoparticle size, shape and facet surface structures under varying gas surroundings: first I will discuss high resolution reciprocal space mapping from epitaxial Rh nanoparticles under oxidizing and reducing conditions. As a second approach I will present a combinatorial high energy x-ray diffraction scheme (85 keV photon energy) allowing a systematical screening of particle size or
composition under identical reaction conditions. Finally, I will demonstrate how graphene templated growth of nanoparticles with diameter
< 2 nm opens the door for x-ray diffraction experiments with high crystallographic precision.