Positronium annihilation in mesoporous thin films

Depth-profiled positronium lifetime spectroscopy is used to probe the pore characteristics ~size, distribution, and interconnectivity! in porous, low-dielectric silica films. The technique is sensitive to the entire void volume, both interconnected and isolated, even if the film is buried beneath a metal or oxide layer. Our extension of a simple quantum mechanical model of Ps annihilation in a pore adequately accounts for the temperature and pore size dependence of the Ps lifetime for pore sizes in the range from 0.1 nm to 600 nm. It is applicable to any porous media. @S0163-1829~99!51932-2#