Nanostructure of Pure Iron Anodically Oxidized in Borate Buffer Solution and Annealed by Infrared Radiation

Abstract

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 °C was observed with γ-Fe2O3 grain growth and sharp increase in surface roughness, film thickness and oxygen content. An ellipsometric parameter of tanΨ was sensitively reflected by annealing effect, and tanΨ curve had a shoulder at 150 °C for 5 min and a peak of tanΨ was shifted from 350 nm to 450 nm in wavelength. This shift was also caused by the formation of γ-Fe2O3, because the peak was also observed in tanΨ of the bulk Fe2O3 family. Passivation effects at 800 mV prior to IR annealing on thickness and oxygen content changed at 150 °C, and decreased tanΨ at 350 nm and excessive film growth over 250 °C, and increased oxygen content under 100 °C and surface roughness at 50-250 °C. The terrace width with atomic scale flatness was slightly increase by passivation prior to IR annealing at 50-250 °C, and the maximum terrace width reached larger than 10 nm by passivation and IR annealing at 100 °C for 30 min.