The Influence of Zirconia Stoichiometry on the Morphology of Thin Metal Films Deposited on its Surface After Annealing in Vacuum

Thin metal films deposited on a nonmetallic material can become fragmented in heating. The higher the adhesion in the contact pair, the lower the tendency to fragmentation. Zirconia can lose oxygen to form nonstoichiometric phases; this can influence zirconia-to-metal adhesion. The effect of zirconia stoichiometry on zirconia interaction with thin metal films was studied. Platinum, palladium, nickel, and copper films 100 nm thick were deposited onto substrates of stoichiometric (ZrO₂) and nonstoichiometric (ZrO_2–x) zirconia using the electron-beam method. The single-crystalline substrates with metal films were annealed in vacuum at temperatures 30–10% lower than the melting points of the deposited metals on the absolute scale and then studied with an optical microscope. The metal films became fragmented on the ZrO₂ substrates and interacted with the ZrO_2–x substrates to form new uniform phases. The nickel film interacted with the ZrO_2–x substrate at lower temperatures than those at which it became fragmented on the ZrO₂ substrate. After annealing at 700°C, the copper film on the ZrO_2–x substrate led to texture showing areas with the fragmented and uniform coating probably because the excess zirconium in ZrO_2–x interacted with the copper film resulting in local restoration of the zirconia stoichiometry near the surface. Therefore, the copper film in the adjacent areas was in contact with stoichiometric zirconia and became fragmented. Thus, as expected, the stoichiometry of zirconia influences the morphology of thin metal films deposited on its surface after annealing: the coating metals interact with nonstoichiometric zirconia, promoting adhesion in the contact pair and preventing the film fragmentation observed on stoichiometric zirconia.