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

Abstract

Thin metal films deposited on a nonmetallic material can be 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 the stoichiometry of zirconia on its interaction with thin metal films was studied. Platinum, palladium, nickel, and copper 100 nm thick films were deposited onto substrates of stoichiometric (ZrO₂) and nonstoichiometric (ZrO_2–x) zirconia using the electron-beam method. The single–crystalline substrates with metallic films were annealed in vacuum at temperatures 30–10% lower than the melting points of the deposited metals on an absolute scale and studied by the optical microscope. The metal films 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 temperature than fragmented on the ZrO₂ substrate. After annealing at 700 °С, the copper film on the ZrO_2–x substrate leads to texture showing areas with fragmented and uniform coating probably because the surplus zirconium in ZrO_2–x interacts with the copper film and thus the stoichiometry of the oxide is locally restored near the surface. Therefore, the copper film in the adjacent areas is in contact with stoichiometric zirconia and becomes fragmented. Thus, as expected, the stoichiometry of zirconia influences the morphology of the 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.