Highly reflective silver mirror enhanced by several dielectric films prepared under the low substrate temperature

Abstract

Optical paths in telescopes frequently incorporate silver mirrors for high sensitivity. Unfortunately, silver mirrors without protective coatings are susceptible to sulfurization and oxidation, compromising their quality. Even with protective layers, insufficient adhesion between the coating and the silver film can lead to peeling, exposing the silver to external environments and affecting its quality. This study aimed to identify dielectric materials with superior adhesion to silver, rendering them ideal choices for silver coating applications. By electron gun evaporation, different dielectric layers were deposited on the top and bottom of the silver film under a substrate temperature below 150 °C. These coatings were composed of materials with desired refractive indices, including aluminum oxide (Al2O3), aluminum-doped silicon, magnesium fluoride (MgF2), and other dielectrics. Following the deposition, a tape adhesion test was conducted to evaluate the bond strength of the samples. X-ray photoelectron spectroscopy (XPS) analysis was carried out to investigate the interaction between silver and its neighboring layers. The results revealed that Al2O3 and MgF2 exhibited exceptional adhesion to silver. Moreover, these multilayer coatings can effectively enhance the reflectance of silver in the visible (VIS) wavelength ranges.

Keywords

• Silver mirror
• XPS
• Enhanced silver coating
• Silver adhesion
• Space optics