Generation of single corrosion pits and in situ monitoring of pit growth on iron exposed to 0.5 M NaCl solution was achieved using combined atomic force - scanning electrochemical microscopy (AFM-SECM). Pits as small as 2.7 μm in diameter were formed at arbitrary locations on the substrate by local generation of highly concentrated nitric acid in the vicinity of the AFM-SECM probe. Addition of nitrite ions to the environment, which act as corrosion inhibitors for iron, ensures passivation of the metal, and hinders metal corrosion despite exposure to the chloride-containing media. Localized acidification was achieved by oxidizing nitrite ions at the probe. Acidification in combination with the high chloride content in the solution leads to a local rapid attack at the surface and pit generation below the AFM-SECM probe. Besides improved spatial resolution and precise control of the pit nucleation site, combined AFM-SECM allows simultaneous imaging of the generated pits by the AFM tip.
