On the amorphous and nanocrystalline Zr–Cu and Zr–Ti co-sputtered thin films

In the current study, we examined and compared the mixing and vitrification behavior of the Zr–Cu and Zr–Ti binary systems in the form of co-sputtered thin films with or without post-annealing. The co-sputtered Zr–Cu films are all amorphous under various co-sputtering conditions, suggesting the high vitrification tendency. The amorphous Zr–Cu thin film will start to crystallize into nano-crystalline Zr₂Cu and Zr₇Cu₁₀ phases upon long exposure at temperatures above 350 °C. On the other hand, it is difficult to form amorphous film with the Zr–Ti system, except at a low sputtering power of 30–50 W. The low powers enable the co-sputtered Zr–Ti thin film to exhibit the diffuse hump in the X-ray diffraction. Examination by high resolution transmission electron microscopy reveals numerous fine nano-crystalline phases around 2 nm in the amorphous matrix. Upon exposure at 700 °C, the Zr–Ti films transform into crystalline hexagonal close-packed α and body-centered cubic β phases.