In situ oxygen-atom erosion study of polyhedral oligomeric silsesquioxane-siloxane copolymer

The surface of a polyhedral oligomeric silsesquioxane-siloxane copolymer film has been characterized in situ by using x-ray photoelectron spectroscopy before and after exposore to incremental fluences of oxygen atoms produced by a hyperthermal oxygen atom source. The data indicate that the atomic oxygen initially attacks the cyclohexyl groups that surround the polyhedral oligomeric silsesquioxane cage, resulting in the formation and desorption of CO2 from the surface. The carbon concentration in the near-surface region is reduced from 65.0 at% for the as-entered surface to 16.3 at% following 63 h of O-atom exposure at a flux of 2 x 10(13) O atoms/cm(2) s. The oxygen and silicon concentrations are increased with incremental exposures to the O-atom flux, but the rates of increase slow with increased exposure. The oxygen concentration increases from 18.5 at% for the as-entered sample to 55.7 at% following the 63-h exposure, and the silicon concentration increases from 16.6 to 28.0 at%. The data reveal the formation of a silica layer on the surface, which serves as a protective barrier preventing further degradation of the underlying polymer with increased exposure to the O-atom Bur.