In-plane X-ray diffraction profiles from organosilane monolayer/SiO ₂ models

The effect of siloxane bonding topology on in-plane X-ray diffraction (XRD) profiles of octadecylsilane self-assembled monolayers (SAMs) on SiO₂ was investigated by large-scale atomistic simulation. Equilibrium structures of the octadecylsilane SAM/SiO₂ systems were obtained by Metropolis Monte Carlo simulations, sampling SAM/SiO₂ structures with different interfacial bonding topologies. Lateral ordering of the octadecylsilane molecules was evaluated by calculating in-plane XRD profiles from the structural models. Analyses of the diffraction profiles revealed that molecules retain a hexagonal order at thermal equilibrium and that the structural order decreases as the number of siloxane bonds increases at the SAM/SiO₂ interface.