Silicon dioxide film and process for preparation of the same

摘要

A transparent amorphous silicon dioxide film containing many fine voids, characterized in that the refractive index (for light at lambda=500 nm) is in the range of 1.01 to 1.40 and that 80 vol. % or more of the fine voids have a diameter of 5 nm or less, has a low refractive index and excellent physical strength such as high scratch resistance, so that it is advantageously employable as an optical film of an optical device for various uses.