Conversion of Some Siloxane Polymers to Silicon Oxide by UV/Ozone Photochemical Processes

Abstract

A variety of linear and cross-linked polysiloxanes are transformed into silicon oxide (SiO x ) through the application of a recently developed room-temperature UV/ozone conversion process. Ozone and atomic oxygen, produced by exposure of atmospheric oxygen to ultraviolet radiation, remove organic portions of the polymers as volatile products and leave a thin silicon oxide surface film. The conversion rates differ for each polysiloxane studied and are related to differences in their chemical structures. X-ray photoelectron spectroscopy (XPS) measurements of atomic ratios indicate that UV/ozone treatment removes up to 89% of the carbon from the resultant surface film, leading to an overall stoichiometry close to that of SiO 2 . The binding energy of Si(2p) core level photoelectrons shifts from 101.5 eV for the polymer precursors to about 103.5 eV after UV exposure, consistent with the formation of silicon that is coordinated to four oxygen atoms. Ellipsometry measurements of apparent thickness changes during conversion indicate that the SiO x film formed is limited to a thickness on the order of 20−30 nm for poly(dimethylsiloxane) substrates. The results demonstrate that a thin silicon oxide layer can be prepared at room temperature on the surface of polysiloxane films by UV/ozone-induced photochemical reactions.