Converting self-assembled gold nanoparticle/dendrimer nanodroplets into horseshoe-like nanostructures by thermal annealing

A simple and effective nonlithographic method to produce a novel organization of noble metal nanoparticles into horseshoe-like nanostructures via self-assembly is described. The adsorption of Au nanoparticles stabilized with the dendrimer 1,2,3,4,5,6-hexakis[(3′,5′-bis(benzyloxy)benzyl) sulfanylmethyl]benzene (S6G1) on hydrophilic surfaces (native oxide-terminated Si(111)) resulted in the formation of spatially correlated droplet aggregates. Annealing of Au/S6G1 in thin films caused amalgamated droplets to form arrays of horseshoe-like nanostructures with an average size of ∼250 nm and an average height of 13 nm. The mobility and the manner in which the semicapped Au nanoparticles are distributed on the hydrophilic substrate are believed to be the promoters that control the growth of the nucleation to create the horseshoe-like structures. Atomic force microscopy (AFM) measurements demonstrated the changes in height and size of the nanoparticles before and after the annealing process. Oxygen plasma etching was used to remove the S6G1 dendrimer to reveal the orientation of the Au nanocrystals in the nanostructure matrix.