Effect of storage and surface roughness on the SiO₂ thin films adhesion behavior

The thin film elaboration and use, commonly related by the substrate properties and quality, are of great interest in the optical field. Indeed, storage conditions and duration, in addition to the surface quality, can have an effect on the materials and their performances, especially if they are functioning as optical materials. For this purpose, this study aims to contemplate both the storage duration of optical glasses and their surface quality, as well as the adhesion behavior of silica thin film deposition. Therefore, optical glasses were developed and stored for 3 years in the same solution (colloidal silica premixed [CMP] slurry), then they were characterized before the study of their sol-gel thin films adhesion behavior. Furthermore, surfaces were treated with several techniques and their surface quality was measured. The adhesion phenomenon was studied via droplet technique. The results show the influence of the storage duration on the optical properties of the optical glasses (refraction index, Abbe number) and the surface roughness. Moreover, the surface roughness has a great influence on the adhesion of the thin films. In addition to that, sol-gel prepared with 20% TEOS has the highest adhesion of the optical glass when the surface roughness is low.