Time-of-Flight Secondary Ion Mass Spectrometry Analyses of Self-Assembled Monolayers of Octadecyltrimethoxysilane on SiO2 Substrate

The self-assembled monolayers (SAMs) of organosilanes formed on an oxide substrate are thought to have a polymerized –Si–O–Si– network due to the homocondensation of silanols of hydrolyzed silane headgroups, which is the most significant difference in the SAMs of organosilanes in comparison with those of alkanethoils and organophsosphonic acids. In order to explore the interface chemistry of organosilane SAMs, surface-sensitive time-of-flight secondary ion mass spectrometry (ToF-SIMS) was used to compare ion fragmentation differences between the SAMs of octadecyltrimethoxysilane (OTMS) formed on a SiO2 substrate and free OTMS molecules, as well as oxide substrate. The ability of ToF-SIMS to verify the hydrolysis of the methoxy groups of OTMS molecules and to assess the polymerized –Si–O–Si– network in their SAMs was demonstrated, which shows that ToF-SIMS provides unique information to help us understand the interface chemistry of OTMS SAMs formed on oxides.