Control of morphology of silica films

A method of forming a silica film coated on a substrate including the steps of:

• producing a silica precursor solution by dissolving in a solvent a hydrolysable silicate oligomer of the form:
• where each X is independently selected from a hydrolysable or non-hydrolysable group with the proviso that at least three X must be hydrolysable groups and wherein n is an integer between 2 and 10 and wherein the hydrolysable silicate oligomer is not silicic acid tetramethyl ester homopolymer;
• forming a coating of the silica precursor solution on the substrate;
• and
• curing the coating of the silica precursor solution by hydrolysing and condensing the coating in a vaporous environment comprising a base, water and a retarder, said retarder retarding hydrolysis of the hydrolysable silicate oligomer to form a film, wherein the concentration of said retarder in the vaporous environment is selected to control the morphology of the film.