Surface oxygen in the growth of plasma polymerised thin films

Abstract

Three different types of non-oxygen containing monomers were plasma polymerised into thin films and then studied using X-ray photoelectron spectroscopy (XPS) to determine the surface oxygen content. These three monomers were benzene, ferrocene, and octafluorocyclobutane. Depth profiling was also used to investigate the oxygen content into the bulk of the films by analysing the newly formed film surfaces after different amounts of argon ion sputtering. The initial oxygen concentration on the surface of the ferrocene films was the largest of the three (>20 at.%) while octafluorocyclobutane films had only a small concentration at the surface (∼0.4 at.%). The benzene films had an intermediate concentration (∼4 at.%). Affinity for oxygen on the benzene films is due to residual activated species including free radicals and dangling bond sites on the film surface. Depth profiling showed a rapid reduction of oxygen (to ∼0.2 at.%) a short distance into the benzene films, indicating that the oxygen adsorbed on the surface after film deposition and exposure to the ambient. For the ferrocene films, a substantial amount of oxygen remained with depth, indicating that oxygen was incorporated into the film during deposition. Due to the chemical nature of fluorine, the as-deposited octafluorocyclobutane films did not exhibit significant affinity towards oxygen.