Deposition of transparent Aluminum Oxide (Al2O3) films on silvered CSP mirrors

This work consists on the improvement of first surface silvered thick glass mirrors. Several types of CSP mirrors based on different Physical Vapor Deposition techniques (PVD) and the presence or absence of the copper protective back layer were prepared: ([Ag Sputtered], [Ag Evaporated], [Cu Sputtered-Ag Evaporated], [Cu Evaporated-Ag Sputtered], [Cu Evaporated-Ag Evaporated] and [Cu Sputtered-Ag Sputtered]). The UV-VIS-NIR measurements have shown that the different combinations of Silvered mirrors have approximately the same Specular Reflectance. The mirrors with the Copper back protective layer were chosen as the optimal mirror combinations since the [Ag-Evaporated] and the [Ag-Sputtered] mirrors presented stability and adhesion problems during the top protective layer deposition process. A transparent Aluminum Oxide (Al2O3) protective layer was deposited on top of the selected mirrors using Dip-coating and Ion Layer Gas Reaction (Spray-ILGAR) deposition techniques. After the deposition of the protective layer, the optical properties, thickness, composition and surface morphology of the mirrors were tested.

The results showed that the Specular Reflectance decreased after the deposition of Al2O3 layer by Dip-coating technique. On the other hand, an improvement in the Specular Reflectance of the [Cu Sputtered-Ag Sputtered] mirror was noticed after the deposition of Al2O3 with the ILGAR technique. An increase in the diffuse reflectance after the deposition of the Al2O3protective layer by ILGAR method was also observed, this can be explained by the presence of some roughness on the surface of the mirror, which was confirmed by the SEM pictures. From these results, it can be concluded that the Al2O3 protective layer deposition by ILGAR technique is a very promising technique since enhances the specular reflectance of the mirrors. The final prepared mirror com- ination is composed of thick glass substrate, covered with a metal back layer of Sputtered Copper (50 nm), a reflective layer of Sputtered Silver (100 nm) deposited on top of the Copper layer, and a top protective layer of Al2O3 deposited by Spray-ILGAR technique.

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