Investigating local oxidation processes in Fe thin films in a water vapor environment by in situ liquid cell TEM

Automated image recognition and analysis techniques were combined with liquid cell transmission electron microscopy to explore the oxidation kinetics of nanocrystalline Fe thin films in a water vapor environment. From in situ microscopy experiments, localized oxidation was observed to initiate in the film then propagate in an unsteady fashion, alternatingly arresting and progressing. The oxidation front propagation occurred via new oxidation sites initiating 10s of nm ahead of the existing front rather than through a continuous expansion mechanism. The oxidation rate was seen to be highly dependent on electron dose rate, with increasing electron dose rate accelerating the oxidation front propagation and increasing the density of oxidation initiation sites. The in situ experiments were also performed in diffraction space where it was seen that Fe₂O₃ was formed during oxidation. Coupling in situ microscopy with automated image analysis creates new opportunities for studying the early stages of localized corrosion by providing direct observation of oxidation propagation as well as quantification of the oxidation rates and rapid identification of byproducts.