HYDROLYSIS AND CONDENSATION OF SELF-ASSEMBLED MONOLAYERS OF (3-MERCAPTOPROPYL)TRIMETHOXYSILANE ON AG AND AU SURFACES

Self-assembled monolayer films of (3-mercaptopropyl)trimethoxysilane ( 3MPT) and their hydrolysis products on Ag and Au surfaces are characte rized using Raman spectroscopy, FTIR spectroscopy, ellipsometry, X-ray photoelectron spectroscopy (XPS), and electrochemistry. 3MPT monolaye rs are formed through metal-thiolate bonding through the S atom on bot h metals, similar to other alkanethiol chemisorption chemistries. The orientation of 3MPT molecules in these monolayers is similar on both m etals. Prior to hydrolysis, the molecules form an organized monolayer with the methoxy headgroups oriented largely parallel to the surface a nd the propyl chain in a largely trans conformation. When the methoxy groups are hydrolyzed, the 3MPT molecules cross-link through the forma tion of siloxane bonds. Although the surface vibrational spectroscopy indicates the presence of a small number of unreacted silanol groups o n the siloxane surface, cyclic voltammetry of underpotential depositio n of Pb suggests that the Si-O-Si network is highly cross-linked and r elatively free from gross defects. The number of these unreacted silan ols is estimated using XPS to be fewer than 5% of the original Si-O si tes in the 3MPT monolayer.