Infrared spectroscopic study of a γ-mercaptopropyltrimethoxysilane monolayer on a gold surface

Abstract

Reflectance-absorption infrared spectra of γ-mercaptopropyltrimethoxysilane (γ-MPT) adsorbed on Au (111)-oriented films are analyzed on the basis of the calculated vibrational modes of a monomer, a dimer and n-membered rings of SiO ₃ R (R=CH ₂ CH ₂ CH ₂ SAu). The results show that the γ-MPT molecules adsorbed on the Au surface are partially hydrolyzed and that the orientation of the methyl groups and propyl chains are near perpendicular to the surface. After a hydrolysis procedure, the SiO ₃ groups in γ-MPT form a quasi two-dimensional system built predominantly of 6-membered puckered Si-O rings. Additional treatment of the γ-MPT monolayer with a surface-charge-reversing cationic polymer disrupts the connectivity and increases the topological disorder in the silicate system.