Single layer mesoporous silica thin films as templates for metallic nanoscale arrays

Abstract

Mesoporous silica films have been synthesized as a single pore layer on silicon, germanium, and indium tin oxide substrates. The film structure consists of a hexagonal array of pores approximately 10nm in diameter, with 3nm wall thickness. The film thickness is controlled through ethanol dilution of the precursor solution, while the film structure is controlled through the acid content and relative humidity of the aging environment. Increasing acidity suppresses the condensation and polymerization kinetics in the film, while the water content of the aging environment increases the fluidity of the film prior to condensation and the curvature of the micelles. Higher acidity and relative humidity result in films that develop the thermodynamically stable phase, as would be predicted by the volume fraction of the block copolymer. Gold was sputter deposited onto mesoporous substrates, resulting in gold islands that are thermally more stable compared with those resulting from deposition on the bare substrate. The gold islands that deposit atop the mesoporous film can be easily removed, resulting in an array of isolated gold particles inside the pores. Furthermore, gold films deposited onto mesoporous silica films on germanium substrates show a dramatic increase in thermal stability against coarsening relative to particles on bare germanium. A sputter deposited gold grown and maintained at 550°C for many hours retain a grain size of approximately 10nm, while grains on bare germanium coarsen to larger than 100nm.