Seedless CTAB mediated growth of anisotropic nanoparticles and nanoparticle clusters on nanostructured plasmonic templates

A seedless method for the synthesis of novel noble metal nanostructures has been developed. The method employs alkanethiol self-assembled monolayer (SAM) functionalized submicron apertures or surface bound colloidal nanoparticles as a template, and it is derived from surfactant mediated anisotropic Au nanoparticle synthesis with cetyltrimethylammonium bromide (CTAB) in solution (M. Grzelczak, et al., Chem. Soc. Rev. 2008, 37, 1783). Nanoparticle nucleation and growth is found to depend on the chain length of the alkanethiol, with short chain SAMs showing little nanoparticle growth. As compared to solution phase nanoparticle synthesis/growth, the addition of Ag+ and I− shape directing ions to the growth solution have a relatively minor effect on the templated growth process. When applied to 80 nm Au nanoparticles immobilized on an ITO surface, this methodology resulted in oligomeric Au nanostructures with asymmetric geometries. To highlight the wide applicability of this approach, Ag and Pd nanoparticles were grown within submicron apertures also, and they displayed features that are distinct from those of Au. The results suggest that the interaction between CTAB and the alkanethiol monolayer template surface is key to the nanostructure growth.