Photoreactivity of alkylsiloxane self-assembled monolayers on silicon oxide surfaces

We have combined contact angle measurements, Fourier transform infrared spe ctroscopy (FT-IR), and atomic force microscopy (AFM) to investigate the UV photoreactivity of octadecylsiloxane (ODS) SAMs (self-assembled monolayers) in air. Contact angle measurements present evidence that ozone is not the active agent in alkylsiloxane SAM degradation under UV illumination in air. A combination of UV and oxygen is necessary for monolayer degradation to p roceed. AFM measurements on submonolayer coverage SAMs provide direct evide nce of the photodegradation of ODS SAMs and reveal the role of defects in t he degradation process. FT-IR and AFM results suggest that the hydrocarbon chain is the reactive site of the monolayers. A microscopic mechanism of th e photoreactivity involving hydrogen abstraction is suggested based on the mechanism of gas-phase oxidation of alkanes. Our results have implications in clarifying the contribution from the reactivity of alkyl chains during t he photomodification of SAMs. This clarification may provide insight into o ptimization of the SAM photopatterning processes.