Mechanical Property and Network Structure of Porous Silica Films

We investigated the relationship between Young's elastic modulus of a series of spin-on sol-gel silica films and the shift of the longitudinal-optical component of the asymmetric stretching vibration mode of Si–O–Si (LO4), by nanoindentation measurements and Fourier transform infrared reflection spectroscopy. With the increase of the annealing temperature from 673–1073 K in air, the position of the LO4 mode reflection peak shifted from 1203 to 1253 cm-1, in parallel with the increase of Young's elastic modulus. The correlation between the LO4 peak position and Young's elastic modulus was also confirmed among a set of silica films in which the preparation conditions and/or the postpreparation treatment conditions were varied. It was concluded that the shift of the LO4 mode peak position is a good measure of the skeletal silica mechanical property of porous silica films.