In-situ observation of 3D particle assembly

The self-assembly of magnetic nanoparticles has a high potential for future applications [1], as it allows mass production processes of very small structures without the use of expensive equipment. The process itself is complex, including several interactions between nanoparticles, solvent, and substrate. A deeper understanding is the key for a better control of the self-organization process.

The present work adds a novel quantitative contribution to the study of the kinetics in 3D long range ordered nanoparticle superstructures. These superstructures have been investigated in-situ during the self-assembly using an optimized GISAXS setup to explore the dynamic growthmodes during deposition. The nanoparticles investigated are well-characterized γ-Fe2O3 nanospheres [2,3], which have been deposited on a substrate to form an ensemble of highly ordered superstructures (mesocrystals) [4].

The time-dependent GISAXS study of the self-assembly process, carried out at the ID01 beamline at ESRF, resulted in an understanding of how the structures evolve with time and how the evaporation can be controlled by external parameters. The in-situ cell (fig.1), which was developed to monitor the structure as well as the height and shape of the droplet, was employed for additional control of the process parameters and the possibility of an accurate identification of key physical parameters governing the process. The time evolution of the ordering process was analyzed by fitting position and width of multiple peaks for all recorded GISAXS patterns (for example fig.2). New insights into the drying and self-assembly process of an ensemble of 3D highly ordered superstructures were obtained and evaporation time-dependent stages of the mesocrystal growth and their spatial positions were identified [5].