Pore interconnectivity of nanoclustering silica porous films as studiedby positronium time-of-flight spectroscopy

Positronium time-of-flight spectroscopy with improved stability and signal-to-noise ratio, achieved by a developed off-line digital data analysis, was applied to the characterization of three types of nanoclustering silica porous films with different relative dielectric constants and refractive indices. The emission of triplet ortho -positronium ( o - Ps ) from the film surface was examined as a function of incident positron energy ( E in ) . It was found that the o - Ps emission peak energies from two highly porous films with similar total porosities decrease similarly to each other with increasing E in up to 1.50 keV . On the other hand, o - Ps emission intensities from the two films differed considerably in the range between 0.5 keV < E in < 4 keV , which reflects a difference in pore interconnectivity between the two films with different mean secondary particle sizes. Some interconnected pores are expected to be closed by the necking at the particle contacts as calcination proceeds, possibly leading to more necks in the pores for the film with the smaller secondary particle size.