In situ scanning tunneling microscopy has been used to study the nucleation and growth mechanisms and the structure of passive films formed on Cu(111) surfaces in 0.1 M berate buffer solution (pH 9.3). A surface topography characterized by terraces with monoatomic steps is obtained after potentiodynamic reduction down to -1.12 V/standard hydrogen electrode (SHE), of the electropolished surface exposed to air. The formation of a single Cu2O passive layer at 0.03 V/SHE proceeds first by a roughening of the steps assigned to a locally blocked step flow process due to a competition between dissolution and preferential nucleation of the oxide at the steps. The observed oxide nuclei are 2-3 nm wide and about one atomic plane high. This process leads to the complete coverage of the terraces by a grain-like structure of the oxide film. The initial terrace topography is completely altered. Thickening of this oxide layer leads to unstable scanning tunneling microscope imaging, despite the presence of a subband in the bandgap of the oxide. Duplex passive films, Cu2O\CuO-Cu(OH)(2), produced at 0.98 V/SHE, are characterized by a grain-like structure with no detectable evidence of crystallinity. The lateral size of the grains ranges from 2 to 5 nm. The measured height difference is less than or equal to 1.5 nm. Stable: imaging occurs via electron tunneling in the conduction band of the passive film. A metal surface topography can be recovered by potentiodynamic reduction of the oxide film down to -0.92 V/SHE. The smallest terraces are eliminated by step coalescence in these oxidation/reduction treatments, which leads to steeper surface profiles.