The thermal stability of silver-based high reflectance coatings

• Thermal stability of silver-based mirrors is studied using first principle method.
• More diffusion of Cu taking place at higher temperature is confirmed.
• Microstructure change of Ag-Cu alloy film causes reduction of its reflectivity.
• Silver-based mirrors exhibit stable performance at low ambient temperature.

Silver-based highly-reflective coatings are widely used in the manufacture of optical instruments. However, it is still difficult to achieve both high reflectivity and long-term stability of the protected silver-based mirrors simultaneously. Here the thermal stability of silver-based high reflectance coatings is investigated both theoretically and experimentally. Silver-based mirrors are annealed at different temperatures, and then are characterized by X-ray diffraction and UV-VIS spectrophotometer. The microstructure of Ag-Cu alloy film is affected by the annealing temperature, which leads to the decreasing of reflectance of the alloy film with the increasing of annealing temperature obviously.