The role of structural defects in the growth of nickel oxide films

A transmission electron microscopy investigation was made of the structural defects in nickel oxide films formed at 500° and 600°C on metallographically polished polycrystalline nickel. These films within the thickness range 500–3000 Å were composed of small crystallites. For a given film orientation, the crystallites increased in size with increasing oxidation time. This increase in crystallite size may be considered as a recrystallization reaction occurring during film growth. At later stages of film growth, the preferential migration of some boundaries led to the formation of large oxide grains. These latter films contained dislocations whose distribution varied from a random arrangement to well-defined subboundaries containing dislocations in low energy arrays. All observations were consistent with the conclusion that incoherent boundaries and dislocations in the oxide lying normal to the metal surface acted as short-circuit paths for selective diffusion of nickel. An oxide film model is advanced for correlation of the reaction kinetics to the observed structural defects.