Hierarchical self-assembly of silver nanocluster arrays on triblock copolymer templates

Poly(styrene-b-butadiene-b-styrene) (SBS) triblock copolymer templates which present in-plane cylinders of polystyrene (PS) aligned parallel to the plane of the substrate have been prepared by a solvent-induced order-disorder phase transition method. Silver nanoclusters have been obliquely deposited onto the SBS copolymer templates at low coverage, utilizing the directed low-energy cluster beam deposition (LECBD) method. The morphology of the samples has been characterized by a tapping-mode AFM. It is shown that the silver nanoclusters form ordered linear arrays and the intercluster distance within each individual linear array is comparable to the cluster size. Optical absorption spectra indicate that the surface plasmon resonance (SPR) of the silver nanocluster linear arrays occurs at about 444.5 nm, manifesting a red shift of approximately 21.4 nm compared to the SPR absorption of silver nanoclusters deposited on a fused quartz substrate. This is attributed mainly to the near-field electrodynamic interactions between the silver nanoclusters. This hierarchical approach to create ordered nanostructures transcends the spatial limits of lithography and provides a promising route to achieve well-ordered cluster-based nanostructures.