Site-Specific Placement of Au Nanoparticles on Chemical Nanopatterns Prepared by Molecular Transfer Printing Using Block-Copolymer Films

Inexpensive, large area patterning of ex-situ synthesized metallic nanoparticles (NPs) at the nanoscale may enable many technologies including plasmonics, nanowire growth, and catalysis. Here, site-specific localization of Au NPs onto nanoscale chemical patterns of polymer brushes is investigated. In this approach, patterns of hydroxyl-terminated poly(styrene) brushes are transferred from poly(styrene-block-methyl methacrylate) (PS-b-PMMA) block copolymer films onto a replica substrate via molecular transfer printing, and the remaining areas are filled with hydroxyl-terminated poly(2-vinyl pyridine) (P2VP-OH) brushes. Citrate-stabilized Au NPs (13 nm) selectively bind to P2VP-OH functionalized regions and the quality of the resulting assemblies depends on high chemical contrast in the patterned brushes. Minimization of the interpenetration of P2VP-OH chains into PS brushes during processing is the key for achieving high chemical contrast. Large area hexagonal arrays of single Au NPs with a placement accuracy of 3.4 nm were obtained on patterns (similar to 20 nm spots, similar to 40 nm pitch) derived from self-assembled cylinder-forming PS-b-PMMA films. Linear arrays of Au NPs were generated on patterns (40 nm lines, 80nm pitch) derived from lamellae-forming PS-b-PMMA that had been directed to assemble on lithographically defined masters.