Metallization of a thiol-terminated organic surface using chemical vapor deposition

The deposition and the subsequent decomposition of an organometallic precursor, (η³-allyl)(η⁵-cyclopentadienyl) palladium [Cp(allyl)Pd], on an organic surface exposed by self-assembled monolayers (SAM) was studied using X-ray photoelectron spectroscopy (XPS) and infrared reflection absorption spectroscopy (IRRAS). The interfacial chemical reactions of the vapor-deposited metal precursor with the pendant thiol group of the SAMs made from oligophenyldithiols, which are either prepared directly (terphenyldimethyldithiol, TPDMT) or by a deprotection route from SAMs formed by a monoacylated derivative of biphenyldimethyldithiol (dep. BPDMAc-1) have been studied in detail. When the TPDMT-SAMs were exposed to Cp(allyl)Pd vapor, a Pd²⁺/allyl-terminated SAM surface was obtained (to a lower extent this was also the case for dep. BPDMAc-1 SAMs), which was stable against exposure to H₂ gas. Reduction to Pd⁰ by H₂ was only observed when small amounts of Pd⁰ were already present, for example, after prolonged exposure to the precursor. The catalytic activity of the small Pd⁰ particles also caused a decomposition of the SAMs upon exposure to air.