Thermal stability of mercaptan terminated self-assembled multilayer films on SiO2 surfaces

The thermal stability of mercaptopropyltrimethoxysilane (MPTMS) derived self-assembled multilayer films were investigated as a function of post-deposition anneals (175, 350, 375, 400 and 600 °C) in high vacuum (∼10−6 Torr) for 60 min each. Mercaptan SAMs are of interest to promote the chemisorption of metal–organics and ultimately to improve the wetting, adhesion, structure, and properties of vacuum deposited metals such as copper and palladium. The surface chemistry of the films were investigated using X-ray photoelectron spectroscopy and contact angle goniometry and gas-phase by-products via mass spectrometry. Results indicate that the bonding structure changes as a function of anneal temperature. Evidence exists for C–S bond scission near 350 °C reducing the amount of the desirable disulfide species present at the surface. In contrast, loss of carbon via C–O or C–C bond scission apparently does not take place until higher temperatures ∼400 °C from the XPS C1s spectra. The increase in contact angles for the films at 375–600 °C is correlated well with the loss of sulfur and carbon from the SAMs making the surface more hydrophobic.