Polymorphism in nanoparticle-based crystals depending upon their single or polycrystalline character

Abstract

Colloidal single crystals of submillimeter size (colloidal crystal) are built by self-assembly of gold nanoparticles with nearly similar size (ca. 5 nm) but different nanocrystallinities. The external shape of the gold nanoparticles was characterized using electron microscopy and related to their nanocrystallinity. A synchrotron-based experiment is used to collect X-ray diffraction patterns from individual single crystals over the wide q-range relevant to both interatomic and interparticle periodicities. This makes possible a detailed reconstruction of the reciprocal space including diffuse scattering. X-ray diffraction demonstrates that colloidal crystals made up of single-crystal nanoparticles belong to the body-centered cubic system while face-centered cubic single crystals are observed in the case of self-assembly by polycrystalline particles. A remarkable feature is the preferential orientation of the symmetry axes of the single-crystal nanoparticles along those of the colloidal crystal; on the contrary, polycrystalline nanoparticles display random orientation. These results show the importance of the nanocrystallinity for the packing behavior.