Study of mesoporous silica films by positron annihilation based on a slow positron beam: Effects of preparation conditions on pore size and open porosity

Positron annihilation spectroscopy (PAS) based on an intense pulsed slow positron beam was applied to the study of mesoporous silica films, synthesized using tetraethyl orthosilicate (TEOS) as the network precursor and a triblock copolymer (EO106PO70EO106) as the structure-directing agent. With positron annihilation lifetime spectroscopy (PALS), pore sizes were obtained from ortho-positronium (o-Ps) lifetimes of the films capped with a 20 nm thick SiO2 layer. Influences of preparation conditions such as heating, TEOS vapor infiltration and precursor solution ageing on the pore size were studied. Moreover, the effect of ageing of the precursor solution on film pore interconnectivity/open porosity was investigated through lifetime-energy correlation measurements by observing intrinsic annihilation of o-Ps diffused out from the uncapped film surface.