Strain-modulated early stage oxidation of Fe films
YH Wu and WS Yu and SP Shen, JOURNAL OF APPLIED PHYSICS, 125, 245305 (2019).
The way in which external loading influences the oxidation kinetics and oxide structure evolution is important for understanding the initial oxidation of metal surface. Here, we demonstrate that prestrain is capable of modulating the oxidation of Fe (100), (110), and (111) surfaces using molecular dynamics simulations. It is found that oxygen preferentially occupies tetrahedral sites of the Fe lattice during oxidation, leading to a unique BCC-to-FCC transformation of Fe, particularly for the (100) surface. Moreover, whether the ordered-to- disordered oxide structure transformation occurs or not depends on prestrain and surface indices. The prestrain changes the order of oxidation rates among three surfaces. We establish correlations between structure, internal stress, and oxidation kinetics and further validate them by our proposed theoretical models. Finally, the diffusivities of Fe and O in FexOy are found to be extremely low at y:x=1:1. This suggests that the formation of FeO may prevent more oxygen from reaching the unoxidized Fe side, and thus may impede further oxidation of Fe. The findings presented in this work may provide new insights into the nanoscale strain-modulated oxidation of iron.
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