Long range order in 3D nanoparticle assemblies

Magnetic nanoparticles and their assembly in highly correlated structures are of great interest for future applications as e.g. spin-based data storage. These systems are not only distinguished by the obvious miniaturization but by the novel physical properties emerging due to their limited size and ordered arrangement, as well. The superstructures are formed from nanometer sized building blocks, ordered like atoms in a crystal, which renders them a newclass of materials. To gain a profound understanding of these systems it is necessary to perform experiments on all length scales. The present work supplies an extensive and novel contribution to the investigation of the structural properties and the self-assembly of iron oxide nanoparticle superstructures. The unique combination of microscopy and scattering techniques allows a new understanding of the structural features of three dimensional structures that develop from the self-organization of these particles. In this thesis, magnetic nanoparticles have been deposited for this purpose using a self organization method to form long range ordered structures, so called mesocrystals. The processof self-assembling has been investigated for the influence of different deposition parameters and these parameters have been optimized. An in-situ study using grazing incidence x-ray scattering during the growth of the mesocrystals allowed the identification of different stages of the mesocrystal growth and its spatial position. From the combination of these different experiments it was possible to establish a model for the growth process governed by a shape and size selective arrangement of the particles. Another highlight of this work is the measurement on a single mesocrystal, which had only a volume of 2.5 $\mu$m$^{3}$, leading to a challenging diffraction experiment. It was possible to extract structural quality parameters from this investigation, as e.g. the mosaicity, which would normally be masked by the distribution of the orientation and lattice parameters generally present in the normal samples that contain a large number of mesocrystals. A detailed analysis of the scattering patterns of different samples with mesocrystal ensembles yielded a refined structure model, which allowed the quantitative analysis of the data collected as well for in-situ created as for already deposited samples. In addition, a new rounded cubes form factor was developed for the modeling of small angle x-ray scattering and the single mesocrystal diffraction data. In conclusion, this work shows the large correlation in these nanoparticle superstructures, the distribution of different structural parameters that can be present in the samples and how much information can be extracted from the scattering patterns