In this work 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 nm 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, 9.2 nm) resulted in the most effective plasmonic stamps for hydrosilylation. The thicker stamps had lower efficacy due to the increased fraction of non-spherical particles, which have lower-energy LSPRs that are not excited by green light. Since 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 carried out and the samples 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. File list (2) download file view on ChemRxiv Submission_MaintextMarch21.pdf (8.86 MiB) download file view on ChemRxiv SI_March21_PDF.pdf (7.67 MiB)
Optically transparent PDMS stamps coated with a layer of gold nanoparticles were employed as plasmonic stamps to drive surface chemistry on silicon surfaces. Illumination of a sandwich of plasmonic stamps, an alkene ink, and hydride-terminated silicon with green light of a moderate intensity drives hydrosilylation on the surface. The key to the mechanism of hydrosilylation is the presence of holes at the Si–H-terminated interface, which is followed by attack by a proximal alkene and formation of a silicon–carbon bond. In this study, detailed kinetic studies of hydrosilylation on silicon with different doping levels, n++, p++, n, p, and intrinsic, were carried out to provide further insights into the role of the metal–insulator–semiconductor junction that is set up during the stamping. Moderately doped n-type and p-type silicon are found to have the fastest rate of hydrosilylation, approximately 10 times faster than highly doped n++ and p++ silicon and about 20 times faster than intrinsic silicon. The kinetic studies were correlated with the properties of the moderately doped silicon substrates, and they point to the near-optimal convergence of factors in moderately doped silicon that result in the fastest observed rates of hydrosilylation. Moderately doped silicon has a sufficiently large depletion width and built-in field that result in most photogenerated holes in the bulk being swept to the surface while also being able to separate electron–hole pairs generated by the intense E-field of the gold nanoparticle LSPR. These conditions lead to the highest concentration of holes at the silicon surface and highest rates of hydrosilylation.
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