The temperature dependence of surface crystal structures of iron passivated at -400 mV SCE was investigated in a borate buffer solution. The size of particle-like structures on the passivated iron surface increases with passivation temperature. Iron surfaces passivated at higher temperature are smoother. Under passivation at 25 and 40degreesC, the terrace is as narrow as less than 2 nm and atomic arrays with 1D order were observed; under passivation at the other higher temperature, terraces appear wider and atomic arrays with long-range 2D order were observed on the 5 nm wide terraces at 60degreesC. At lower temperatures (25 and 40degreesC) defect sites were observed in the 20% region; at higher temperature, defect sites gradually disappeared and a defect-free crystal structure was observed at 60degreesC. After attainment of passivity, the growth of the passive films obeyed Arrhenius law. (C) 2003 The Electrochemical Society.