The effect of overlayers on the stability of discontinuous silver films deposited on softened poly(2-vinylpyridine) substrates

Results of studies on the effect of inorganic overlayers on the long-term stability of discontinuous silver films deposited on softened poly(2-vinylpyridine) (PVP) substrates are reported in this paper. Discontinuous silver films were evaporated onto PVP-coated glass substrates held at 425 K in a vacuum of 8 × 10^-6 Torr. The films were coated with overlayers of Al₂O₃, SiO₂ and ZrO₂ prior to exposure to the atmosphere. The stability of the films against exposure to the atmosphere was studied by monitoring the resistance during and after exposure to the atmosphere. The stability was monitored for a period of 120 days and the film's resistance had stabilized by 30 days. Results indicate that overlayers improve the stability considerably and SiO₂ seems to be the best passivator, closely followed by ZrO₂. However, compared to Al₂O₃, ZrO₂ gives better protection even with a smaller overlayer thickness. A stable discontinuous film with a gauge factor of about 30 could be prepared by depositing silver onto softened PVP passivated by an overlayer, after 30 days of ageing.