Characterization of polyethylene terephthalate films coated with thin Al x Si1− x O y layers using monoenergetic positron beams.

Abstract: Open spaces in polyethylene terephthalate (PET) coated with aluminum silicate (Al x Si1− x O y ) were probed using monoenergetic positron beams. The energy distributions of the annihilation γ rays and the positron lifetime spectra were measured for 60-nm-thick Al x Si1− x O y (x =0–1) deposited on PET using electron-beam evaporation. A clear correlation was obtained between the line-shape S parameter of the annihilation γ rays, water vapor, and oxygen transmission rates. The results suggest that open spaces in the Al x Si1− x O y layers play an important role in water/oxygen diffusion in Al x Si1− x O y /PET, where the concentration/size of such spaces showed its minimum value at x =0.2–0.3. The free volume fraction below the interface between Al x Si1− x Oy and PET (region width=100–400nm) was decreased by the deposition of the coating layer, and this region was also considered to act as a barrier against penetrations of gasses and molecules. [Copyright &y& Elsevier]