We report surface-initiated thermal radical polymerization from cross-linked monolayers of azo-initiators on Au. Initial attempts to graft polymer layers from initiators attached to alkanethiol monolayers yielded polymer films with thicknesses less than 5 nm. Efficient grafting from such surfaces is not possible because initiator-containing monolayers are somewhat unstable under thermal radical polymerization conditions, and desorbed thiols may serve as efficient chain-transfer reagents that inhibit radical polymerization. In addition, reactive radicals can attack the Au−S bonds that link the initiator monolayer to the surface. To overcome these problems, we employed mercaptopropyltrimethoxysilanes to form an adhesion layer for initiator attachment. Cross-linked poly(siloxane) layers apparently stabilize the initiator layer, allowing well-defined surface radical polymerization to occur from Au substrates. We characterized the grafted polymer layers with ellipsometry, reflectance Fourier transform infrared spectroscopy, and atomic force microscopy.

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Self-assembled monolayers of diphenyldisufide (DDS), naphthalenedisulfide (NDS), and diphenyldiselenide (DDSe) on polycrystalline silver films have been investigated by surface enhanced Raman spectroscopy (SERS) and X-ray photoelectron spectroscopy (XPS). DDS adsorbs on Ag through a homolytic cleavage of the S-S bond and resultant thiolate at the surface decomposes upon prolonged exposure to air. The geometry of the molecule is such that the benzene ring is almost horizontal to the surface. The Raman spectrum has been assigned in the light of ab-initio molecular orbital calculations. In DDSe, the Se-Se bond is retained upon adsorption and the molecule sticks up. In contrast, NDS is highly reactive on the microscopically rough surface so that a stable monolayer could not be prepared. A temperature dependent Raman study of the DDS monolayer shows the absence of any reorientation at the surface as one would expect from the adsorption geometry. XPS study complements the SERS data and shows the presence of Ag 2 S on an NDS exposed surface.