Early stages of oxidation of the Fe{001} surface: Atomic structure of the first monolayer

The reaction of a clean Fe{001} surface with oxygen gas was monitored with low-energy-electron diffraction (LEED) and Auger-electron spectroscopy. The formation of an Fe{001} 1 ×{} 1-O structure at full monolayer coverage was confirmed, whereas the Fe{001} c(2×2)-O structure reported by three other groups could not be reproduced. A LEED structure analysis of the Fe{001} 1 ×{} 1-O structure revealed that the oxygen atoms are located deep inside the fourfold symmetrical hollows of the substrate surface, with the first substrate interlayer spacing 7.5% expanded with respect to the bulk. The effective hard-sphere radius of the oxygen atom in this structure is 0.78 {}. The results of the structure analysis are consistent with the results of photoemission experiments reported by others.