Atomic images of 304SS surface after electrochemical treatments

Sputter-deposited 304 stainless steel was electrochemically treated in 0.1 M H2SO4 aqueous solution, and was observed in air at atomic resolution with a scanning tunneling microscope. After passivation for 15 min at 400 mV (SCE), there was initially little order present, but the diameter of oxide particles (grains or partly ordered domains) increased from about 30 to 200 nm during 3 h after the treatment. Surface atoms of oxygen or hydroxyl gradually become ordered in air and the structure of the substrate surface becomes apparent on the surface of the passive film. This suggests that the surface is covered with a single oxide phase, which is initially rather disordered but crystallizes with time.