ASSEMBLY AND SELF-ORGANIZATION OF SILVER NANOCRYSTAL SUPERLATTICES - ORDERED SOFT SPHERES

Hydrophobic dodecanethiol-capped silver nanocrystals ranging from 50 t o 80 Angstrom in diameter were synthesized using arrested growth metho ds. Size-selective precipitation was employed to isolate nanocrystals homogeneous in size and shape which exhibited close-packed structural order after drying on a carbon or mica substrate. Elemental analysis, H-1 NMR and FTIR spectroscopies were used to characterize the composit ional features of the adsorbed thiolate ligands on nanocrystals suspen ded in solution and condensed in nanocrystal films. Small-angle X-ray scattering (SAXS) and transmission electron microscopy (TEM) were used to probe the structure of both individual nanocrystals and superlatti ces, and to estimate the energetic interactions between these sterical ly stabilized particles. In terms of these measurements, the effects o f the capping ligand coverage, particle faceting and shape, and interp article attractions on superlattice formation are elucidated. In parti cular, the concept of nanocrystals as ''soft spheres'' which order wit h an effective hard sphere diameter is introduced. In addition, the wa ys in which nanocrystals deviate from such an ideal model an discussed .