VUV-induced optical changes in silicone-based contamination films investigated by simultaneous in situ transmittance and imaging

Abstract The effect of VUV irradiation on polyphenyl-methylsiloxane (PPMS)-coated quartz substrates was investigated by simultaneous in situ measurements of transmittance spectra and sample images. Although unirradiated PPMS was highly transparent, the transmittance of both the thick and thin films initially decreased and then partially recovered during irradiation. The simultaneous in situ observations showed that the initial decrease in transmittance originated mainly from enhanced light scattering rather than visible coloration, as the irradiated region became cloudy without a noticeable color change. The subsequent recovery was attributed to a reduction in scattering, although the recovery process differed between the thick and thin films. Quartz crystal microbalance measurements indicated that mass loss occurred only during the initial stage of irradiation, while X-ray photoelectron spectroscopy suggested the formation of silica-like SiO $$_x$$ x species in the near-surface region after irradiation. These findings demonstrate that simultaneous in situ transmittance and imaging measurements are an effective approach for identifying the mechanisms responsible for both transmittance degradation and recovery in VUV-irradiated silicone contamination films.