||Metallic coatings are widely used in various applications for the high reflectivity in a wide wavelength range. However, metallic coatings usually exhibit reflectivity dip due to their interband optical transitions, which can be ameliorated through alloying and breaking the crystalline structure. This investigation takes advantage of thin film metallic glasses (TFMG) to reduce the reflectivity dip of the metallic coating. In this study, the light reflectivity of the thin film metallic glass films is explored in terms of three factors, structure of thin film (electric resistance), surface morphology, and interband optical transition. According to the results, the most major factor is the decrease of electric resistance, which means to improve the structure by decreasing the atomic defects and free volumes via lower Ar working pressure and proper post-sputtering thermal annealing. With the decrease of electric resistance, the light reflection in the visible and infrared regimes would increase. Sub-Tg annealing is considered to be a promising way in improving the reflectivity. However, if the annealing temperature reaches or over Tg, there would be nanocrystalline phases precipitated out from the amorphous matrix, and interband optical transitions made its reflectivity drop in ultraviolet and visible regions.|
The minor factor of film surface morphology should also be considered. A flatter film surface with a lower surface roughness Ra (to a very low level of the order of 0.2-0.4 nm) would lead to higher light reflection. The low surface roughness can be achieved by reducing the film thickness or proper annealing.