A photoemission spectroscopy study of the initial oxidation of epitaxial fcc and bcc Fe films grown on Cu(100)

The initial oxidation of Fe is a fundamental issue due to its importance for corrosion and catalysis. In this study, we investigate the initial oxidation of epitaxial fcc and bcc Fe thin films grown on a Cu(100) substrate at room temperature. Fe thin films deposited with two different thicknesses on Cu(100) were prepared by molecular beam epitaxy in order to obtain the fcc Fe(100) and bcc Fe(110) surfaces. The structures and the chemical composition of the Fe films were evaluated by LEED and photoelectron spectroscopy, using the facilities at the TEMPO beamline of the Synchrotron SOLEIL. The Fe 2p and O 1s high-resolution spectra were collected during oxidation at a constant O₂ pressure in order to build the kinetic curves, which are discussed taking into account the Fromhold-Cook theory. Our result revealed the different initial oxidation kinetics of the films and showed that bcc Fe(110) surface has a much higher reactivity with O₂ than the fcc Fe(100). The Fe 2p peak analysis suggests the formation of Fe_1 − xO and an Fe^3 +-rich oxide on the bcc Fe(110) surface and Fe_1 − xO on the fcc Fe(100) surface.