Transformation of Poly(dimethylsiloxane) into thin surface films of SiOx by UV/Ozone treatment. Part I: Factors affecting modification

UV/ozone treatment of poly(dimethylsiloxane) (PDMS) was used to produce thin surface films of SiOx. Films of PDMS were applied by spin-coating onto gold-coated silicon wafers having (100) orientation. Characterization of the UV/ozone system was performed to map the spatial distribution of intensities of UV radiation. This mapping was used to ensure reproducible modification of films and to aid in the understanding of modification as measured by advancing contact angle using deionized water and x-ray photoelectron spectroscopy (XPS). Rutherford backscattering spectroscopy (RBS) was used to measure thickness of the PDMS films. Treatment reduced the wetting angle, in some cases from a value greater than 100° to a value less than 5°. High resolution XPS spectra were used to study the nature of the modified PDMS film and its relationship to the characteristics of the unmodified PDMS. High resolution XPS spectra in the Si 2p region show that O–Si–C bonds in the siloxane, observed prior to treatment, are converted to SiOx, where x is between 1.6 and 2. Modified films also contain some oxidized carbon components. The time required to reduce the contact angle to a minimum value was greater for the thicker PDMS film samples. The effects of ozone alone (without UV) and UV radiation at 184.9 and 253.7 nm (without ozone) were also investigated. The results of UV/ozone treatment are compared to results achieved by means of plasma surface oxidation.