Nanopore structure relevant to the D2O permeation into silica thin films as studied by secondary ion mass spectrometry, ellipsometric porosimetory and positron annihilation

Subnanoscopic pore structure relevant to the water permeation for two types of silica thin films, fabricated by plasma-enhanced chemical vapor deposition (PECVD) and thermal oxidization (TO), were examined by means of dynamic secondary ion mass spectrometry (D-SIMS), vapor-adsorption ellipsometric porosimetry (EP), and low-energy positron annihilation spectroscopy (PALS). The D− secondary ion intensity for the PECVD film, observed using D-SIMS, was much higher than for the TO film, indicative of the higher permeance of D2O molecules in the matrix of the PECVD film. The results from PALS and EP suggest that this is ascribed to the larger pores and the higher open porosity of the PECVD film as compared to the TO film.