Dear Ali, because the thermal stability of NiO is much higher than Ag, it is difficult to avoid the degradation of Ag especially at temperature above 400C. What is the anneal temperature and atmosphere? And also, what is the purpose to use Ag film here? Is it possible to rep;ace it by some other refractory metals such as W, Mo, Ta, and TiN.
Okay. Actually, if you only want to reflect the IR light, you can use Au and Al that are more stable than Ag but have the similar IR reflectance. For higher temperatures, those refractory metal I mentioned above are good choice and they generally have ~95%-98% IR reflectance, especially TiN. Of course, If Ag is necesaary, Al2O3 film may be helpful to act as a interlayer between NiO and Ag.@Ali Raza