Atomic-scale flattening of Ni–Cr alloy surfaces by electrochemical passivation treatments

Ni–Cr alloys were electrochemically passivated in sulphuric acid solutions, generating atomically flat oxide surfaces on the terraces of the resulting passive films. High resolution ex-situ scanning tunnelling microscopy revealed a nanocrystalline structure for the passive film, with a tendency for the grain size to decrease with increasing Cr content in the alloy.