Structure and phase separation of Ag-Cu alloy thin films

We report an in situ electron diffraction study and microscopy observation of phase separation in Ag-Cu solution alloy thin films of different compositions and film thicknesses. The results show that the as-deposited films consist of nanocrystalline Ag- and Cu-rich phases of a few nanometers in size. Upon annealing, two stages of thin-film transitions are observed. In the first stage, the growth of Cu crystallites is responsible for phase separation in Ag₅₀Cu₅₀ or Ag-rich alloy. For the Cu-rich samples, the phase separation process is much slower. The second stage transition involves thin film dewetting. A combination of Z-contrast scanning transmission electron microscopy imaging and electron diffraction reveal grain growth and phase separation between Ag and Cu in both stages. Atomic force microscopy results show the surface morphology of thin films only changes significantly at the late stage of phase separation when the thin film dewets.