Self-assembled Au nanoparticle superlattice via a displacement reaction

Long-range order, uniform in size, and regular in shape two-dimensional (2-D) arrays of core-shell structure Au nanoparticles have been synthesized. A reaction involving the displacement of the outer shells from tetraoctylammonium bromide (TOAB) to dodecanethiol (DT) molecules was used to form Au@TOAB-DT nanoparticles at room temperature (RT). The displacement reaction has used both superior size and shape control of Au@TOAB nanoparticles and uniform dispersion capability of Au@DT nanoparticles to achieve an extraordinarily large in extent (3 mum x 3 mum), regular nanoparticle lattice structure. From ultraviolet (UV)-visible spectra, it was inferred that the interaction between the inner core and outer shell of Au@TOAB nanoparticles is weaker than that of Au@TOAB-DT and Au@DT samples. As a result, the ability of the TOAB outer shell to protect the Au@TOAB nanoparticles is weaker so that the system is more prone to agglomerate. On the other hand, the strong interactions between the inner core and outer shell for Au@TOAB-DT and Au@DT nanoparticles led to a predominantly 2-D structure.