Mapping the three-dimensional structure of faceted gold mesocrystals using coherent X-ray diffraction imaging

Elucidating the structure-property relationship of mesocrystals requires understanding the mutual arrangement of the nanoparticles within their assembly. This, therefore, requires characterization techniques capable of non-destructively distinguishing the shape, position, and orientation of the individual constituent nanoparticles in three dimensions. This detailed structural analysis is achieved here by using coherent X-ray diffraction imaging (CXDI) complemented with angular X-ray cross-correlation analysis (AXCCA) and electron microscopy. Three mesocrystals are examined, each assembled from different-sized gold octahedral nanoparticles and functionalized with ω-thiol-terminated polystyrene (PS-SH) of different molecular weights. AXCCA provides information regarding the ensemble-averaged mesocrystal lattice structure, such as the symmetry, unit cell parameters, and the presence of orientational disorder. CXDI complementarily enables the precise identification of the shape and positions of individual nanoparticles as well as revealing any structural defects. Our results show that each mesocrystal has a nearly perfect lattice structure with minimal defects and exhibits an increased strain toward the surface.