Plasmonic Stamps Fabricated by Gold Dewetting on PDMS for Catalyzing Hydrosilylation on Silicon Surfaces

Plasmonic stamps are harnessed to drive surface chemistry on silicon. The plasmonic stamps were prepared by sputtering gold films on PDMS, followed by thermal annealing to dewet the gold and form gold nanoparticles. By changing the film thickness of the sputtered gold, the approximate size and shape of these gold nanoparticles can be changed, leading to a shift of the optical absorbance maximum of the plasmonic stamp, from 535 to 625 nm. Applying the plasmonic stamp to a Si(111)-H surface using 1-dodecene as the ink, illumination with green light results in covalent attachment of 1-dodecyl groups to the surface. Of the dewetted gold films on PDMS used to make the plasmonic stamps, the thinnest three (5.0, 7.0, and 9.2 nm) resulted in the most effective plasmonic stamps for hydrosilylation. The thicker stamps had lower efficacy due to the increased fraction of nonspherical particles, which have lower energy localized surface plasmon resonances (LSPRs) that are not excited by green light. Because the electric field generated by the LSPR should be very local, hydrosilylation on the silicon surface should only take place within close proximity of the gold particles on the plasmonic stamps. To complement AFM imaging of the hydrosilylated silicon surfaces, galvanic displacement of gold(III) salts on the silicon was performed and the samples were imaged by SEM—the domains of hydrosilylated alkyl chains would be expected to block the deposition of gold. The bright areas of metallic gold surround dark spots, with the sizes and spacing of these dark spots increasing with the size of the gold particles on the plasmonic stamps. These results underline the central role played by the LSPR in driving the hydrosilylation on silicon surfaces, mediated with plasmonic stamps.