The growth and chemical structure of thin photonic films formed from plasma copolymerization: I. Effect of monomer feed ratio

Fabrication methodologies of thin, optical quality polymer films are important given the current interest in photonics. Plasma enhanced chemical vapor deposition (PECVD) has been previously investigated as a useful technique to polymerize various organic precursors. In the work presented here, we have studied the simultaneous plasma copolymerization of two monomers, benzene and octafluorocyclobutane (OFCB), and explored the structure of the final films using FTIR and XPS in order to tailor the resulting optical properties. There is a complex relationship between the film structures and the input parameters including monomer feed ratio and feed location. In plasma copolymerization, the gas phase initiation of the monomers is strongly dependent upon the bond dissociation energy of their structural moieties. The change of the monomer feed ratio leads to different trends with respect to various CFn(n=1–3) structural units, resulting in differences in the final film structure. Defluorination of the copolymer films was significantly enhanced by the addition of a small amount of benzene. The main fluorine-containing structural unit was the CF moiety for the copolymerized film, which is different from both homopolymerized OFCB and conventional PTFE polymers where the main fluorine-containing structural unit is CF2. Retention of conjugation and aromaticity in the resultant films was also observed.