Metal/ metal oxides have attracted extensive research interesting due to their combination of functional properties and compatibility with industry process. The diffusion and thermal reliability become essential issues that requiring detailed study for developing the atomic scaled functional devices. In this work, the diffusional reaction behaviors are investigated that transformed piezoelectric ZnO into magnetic Fe­₃O₄ at atomic scale. The growth kinetics of metal oxide have systematically studied through macro to micro analysis. The growth rates are evaluated from morphology change, which can realize that the growth behavior is either a diffusion- or reaction- controlled process. Besides, the atom attachment on kink step are observed at atomic scale, which has important implications for thermodynamics in functional metal oxides. The faster growth planes simultaneously become smaller, which results in remaining of low surface energy planes. These results exhibit directly observing the atomic formation process of metal oxide via solid state diffusion. In addition, the nanofabricated method provides a novel approach to investigate metal oxide evolution, and sheds light on the diffusion reaction behavior. More importantly, the results and phenomena of this study provide significant inspiration on materials stability and reliability for the metal/oxide-based devices.