by
Elisabeth Josten(JCNS-2/PGI-4, Forschungszentrum Jülich)
→
Europe/Berlin
BAH1 in bldg. 03 (DESY Hamburg)
BAH1 in bldg. 03
DESY Hamburg
Description
Magnetic nanoparticles and their assembly in highly correlated structures are of great interest for future applications, such as a new generation of magnetic storage media [1]. These systems are distinguished by the novel physical properties emerging due to their limited size and ordered arrangement. The superstructures are formed from nanometer sized building blocks, ordered like atoms in a crystal, which renders them a new class of materials with novel properties as for example magnetic interactions different from conventional solids. To gain a profound understanding of these systems it is necessary to perform experiments on all length scales.
In this talk, after a brief review of the properties of single nanoparticles, I will present a comprehensive investigation of structural properties of well-characterized iron oxide nanoparticles [2] forming an ensemble of highly ordered 3D superstructures (mesocrystals) [3] and how the self-assembly of the mesocrystals occurs. The structural characteristics of the ensemble of mesocrystals were mainly investigated by grazing incidence small angle x-ray scattering (GISAXS) and the kinetics of selfassembly by in-situ GISAXS. These scattering patterns are strongly influenced by the ensemble average. To look beyond the ensemble statistics for extracting the structure properties of a single mesocrystal, I will present a completely new approach performing a diffraction experiment with a microfocused x-ray beam on a single isolated mesocrystal, detached from a sample using an elaborate extraction process with a focused ion beam. This challenging experiment proved the feasibility of the investigation of a single, small mesocrystal of nanoparticles and opens a new field for further investigations of such mesocrystal structures. The differences of properties extracted from the ensemble averaged GISAXS and from the non-averaged single mesocrystal investigations provide viable insight necessary to explain the self-assembly of mesocrystals. The newly developed model of these three dimensional systems explains all different experimental results [4].
References
[1] A. Moser et al., J.Phys 35, R157 (2002).
[2] A. Ahniyaz et al., Proc. Natl. Acad. Sci. USA 104, 17570 (2007).
[3] S. Disch et al., Nano Lett. 10, 799 (2010).
[4] E. Josten et al. in preparation
