The classical theory of Cabrera–Mott describes passivation film formation on metals, where they predicted that this film grows as a uniform layer due to a field-enhanced ionic transport mechanism. Here we present experimental evidence, based onin situtransmission electron microscopy of copper oxidation, that the passivation film nucleates and grows as oxide islands, not as a uniform layer. We propose an alternative phenomenological theory to describe passivation film formation, based on island growth followed by coalescence. ©1998 American Institute of Physics.