Micro-wear resistance of ultrathin silicon oxide film-covered polymer substrate

An ultrathin silicon oxide film only several nanometers in thickness was prepared on a poly(methyl methacrylate) (PMMA) substrate at the relatively low temperature of 80 °C, which is below the glass transition temperature of PMMA. Our method consisted of three processes. A hydrophobic PMMA substrate was first photochemically hydrophilized using vacuum ultraviolet light of 172 nm wavelength radiated from an excimer lamp. The photochemically treated sample was then exposed to vapor-phase tetoraethoxysilane (TEOS) as a silica precursor. Because of the chemisorbed TEOS layer thus formed, the sample surface again became relatively hydrophobic with a water-contact angle of about 70°. Finally, in order to eliminate the organic phase from the chemisorbed layer, the sample was again irradiated with the same excimer lamp. As confirmed by X-ray photoelectron spectroscopy, the binding energy (BE) of the Si 2p spectra for the chemisorbed TEOS layer shifted from 102.8 to 103.5 eV after photooxidation. This final BE value is consisted with that of amorphous silicon dioxide. The actual thickness of the oxide was estimated to be 3 nm or less by a cross-sectional image acquired by transmission electron microscopy. Furthermore, we investigated the micro-wear resistance of the oxide-covered PMMA substrates based on a micro-scratching test using a nanoindenter. Wear depths on the scratched oxide-covered substrates were markedly reduced by about 60–84% compared with those on bare PMMA substrates.