Low packing density self-assembled superstructure of octahedral Pt3Ni nanocrystals.

We present a structural study of Pt(3)Ni nanoctahedron superlattice, prepared through both drop-casting and controlled solvent evaporation approaches. In this superlattice system containing ∼10.6 nm side-length Pt(3)Ni nanoctahedra, we observed a body-centered cubic (bcc) packing structure in both local superlattices and statistically averaged superlattice ensembles using transmission electron microscopic tomography and grazing-incidence small-angle X-ray scattering techniques, respectively. Within the superstructure, it was directly observed that nanoctahedra are orientated along the superstructure axes through sharing their vertices. We found that this arrangement of a bcc superstructure with nanoctahedra connecting through their vertices is dependent on neither the processing pathway nor the substrate under our experimental conditions. With such a very low packing density and ultrahigh surface area, this type of self-organized superstructure possesses unique features for future applications.