In this paper, we report on the successful preparation and characterization of large Au colloidal crystals using hydrophilic Au nanoparticles as the building units in bulk aqueous solution. Scanning electron microscopy observation shows that the Au colloidal crystals have a clear crystal appearance and well-developed facets. Elemental composition of the Au colloidal crystals is estimated using energy-dispersive X-ray spectroscopy. The crystallographic data are uniquely determined using small-angle X-ray diffraction and transmission electron diffraction. On the basis of the crystallographic data, the stacking behavior of the Au nanoparticles in the colloidal crystals is also discussed. In the three-dimensional superlattices, Au nanoparticles are hexagonal close-packed and interconnected maybe by interparticle chemical bonding thanks to the mercaptosuccinic acid molecules over the Au nanoparticle surface.

Silicon nanoparticles ranging from 2 to 16 nm were synthesized by a facile wet chemical route, in which SiO amorphous powder was annealed at 1000 °C, etched in hydrofluoric acid, and surface modified by alkene. After alkyl-termination of the particle surfaces, size selective precipitation technique was applied to separate the nanoparticles into uniform sized fractions. Transmission electron microscopy showed well-dispersed and highly crystalline silicon nanoparticles after the treatment by alkene. Visible room-temperature photoluminescence in the range 800−500 nm was observed from these nanoparticles. The photoluminescence intensity has significantly been enhanced by the surface functionalization. Moreover, the PL peak energy of the size-selected nanoparticles shifted to blue as the size decreased due to quantum confinement effect. The experimental result was also compared with the theoretical predictions and was found to follow the general trend of the model calculations.