Control of Dopant Adsorption from Aqueous Solution into Nanoporous Sol-Gel Films

The doping of porous sol-gel films by adsorption of cations onto silica from aqueous solutions is demonstrated. The films are fabricated using the sol-gel method, giving nanometer scale porosity, high surface area, and homogeneity on the scale of optical wavelengths. After deposition by spin coating and initial heat treatment, the films are soaked in a salt solution of the desired dopant, and then given a further consolidating heat treatment.Doping with lead, aluminum and calcium has been demonstrated, and consistent and reproducible processes have been established. Results are presented showing control of doping level through pre-doping temperature and surface treatment, doping time and temperature, and doping solution pH. Potential applications in integrated optics are proposed.