Hints of Growth Mechanism Left in Supercrystals

Supercrystals of DNA-functionalized nanoparticles are visualized in three dimensions using X-ray ptychographic tomography, and their reciprocal spaces are mapped with small-angle X-ray scattering in order to better understand their internal defect structures. X-ray ptychographic tomography reveals various types of defects in an assembly that otherwise exhibits a single crystalline diffraction pattern. On average, supercrystals composed of smaller nanoparticles are smaller in size than supercrystals composed of larger particles. Additionally, supercrystals composed of small nanoparticles are typically aggregated into larger "necklace-like" structures. Within these larger structures, some but not all pairs of connected domains are coherent in their relative orientations. In contrast, supercrystals composed of larger nanoparticles with longer DNA ligands typically form faceted crystals. The combination of these two complementary X-ray techniques reveals that the crystalline assemblies grow by aggregation of smaller assemblies followed by rearrangement of nanoparticles.