The oscillatory adsorption of self-assembled organosilane films on aluminium oxide surfaces

The time-dependent oscillatory growth mechanism of organosilane film self-assembly on aluminium oxide has been investigated using X-ray photoelectron spectroscopy. While this unusual oscillatory process has been reported for the trifunctional silane, propyltrimethoxysilane, we report here, for the first time, that this oscillatory behaviour is also present during the self-assembly of the difunctional silane propylmethyldimethoxysilane. The presence of multiple oscillations in this growth mechanism is also first reported for propyltrimethoxysilane and propylmethyldimethoxysilane as a function of exposure time. Multiple oscillations indicate that the 3-component model that is used to describe and fit a single coverage oscillation must be reconsidered and contain additional components to account for the multiple oscillations seen experimentally. The absence of such oscillatory behaviour in the growth of the monofunctional organosilane propyldimethylmethoxysilane, which in fact follows a Langmuir-type growth mechanism, indicates that this measurable oscillatory behaviour is because of the ability of multifunctional silanes to oligomerise both on the substrate and in solution.