In situ oxidation studies on (001) copper-nickel alloy thin films

The (001)-oriented, single crystalline thin films of Cu-3% Ni, Cu-4.6% Ni, and Cu-50% Ni alloy were prepared by vapor deposition onto (001) NaCl substrates. The films were subsequently annealed at around 1100°K and oxidized at 725°K at an oxygen partial pressure of 5×10^–1 N · m^–2 (5× 10^–6 atm). High-resolution transmission electron microscopy was employed to observe the changes in situ. For all the alloy concentrations Cu₂O and NiO were observed to nucleate and grow independently; no mixed oxides were noted. The shape and growth rates of Cu₂O nuclei were similar to those found in previous work on pure copper films. For low-nickel alloy concentrations the NiO nuclei were larger and the number density of NiO was less when compared to the oxidation of pure nickel films. For the Cu-50% Ni films the shape and growth rates of NiO were identical to those for the oxidation of pure nickel films. Low nickel concentrations exhibited a reduced induction period for Cu₂O when compared to pure copper films. Cu-50%Ni films showed surface precipitation and growth of NiO first, followed by Cu₂O in a typical through -thickness growth after a prolonged induction period. The results are consistent with the previously established oxidation mechanisms of pure copper and pure nickel films.This work was performed at the Ames Research Center and funded by NASA Grants NCA2-OP390-403 and NSG-2025.