Nanostructure of pure iron anodically oxidized in borate buffer solution and annealed by infrared radiation.

The behavior of oxide film on pure iron passivated in a borate buffer solution and subsequently radiated by infrared light (IR) was investigated in comparing to that by just IR annealing without passivation, and was evaluated by film structure, etc. The effect of thermal annealing over 250 degrees C was observed with gamma-Fe2O3 grain growth and sharp increase in surface roughness, film thickness and oxygen content. An ellipsometric parameter of tan psi was sensitively reflected by annealing effect, and tan psi curve had a shoulder at 150 degrees C for 5 min and a peak of tan psi was shifted from 350 nm to 450 nm in wavelength. This shift was also caused by the formation of gamma-Fe2O3, because the peak was also observed in tan psi of the bulk Fe2O3 family. Passivation effects at 800 mV prior to IR annealing on thickness and oxygen content changed at 150 degrees C, and decreased tan psi at 350 nm and excessive film growth over 250 degrees C, and increased oxygen content under 100 degrees C and surface roughness at 50-250 degrees C. The terrace width with atomic scale flatness was slightly increase by passivation prior to IR annealing at 50-250 degrees C, and the maximum terrace width reached larger than 10 nm by passivation and IR annealing at 100 degrees C for 30 min.