Electron-energy-loss-spectroscopy near-edge fine structures in the iron-oxygen system

We report an electron-energy-loss-spectroscopy study of the characteristic oxygen K and iron ${\mathit{L}}_{2,3}$ edges in FeO, ${\mathrm{Fe}}_{3}$${\mathrm{O}}_{4}$, \ensuremath{\alpha}-${\mathrm{Fe}}_{2}$${\mathrm{O}}_{3}$, and \ensuremath{\gamma}-${\mathrm{Fe}}_{2}$${\mathrm{O}}_{3}$ thin films. Data have been processed for quantitative elemental analysis and for detailed comparison of the different fine structures (energy position and width as well as relative intensities). Oxygen edge profiles are sensitive to the local bonding and symmetry properties on the excited anion. The features of the prepeak at the onset are governed by the 3d components in the hybridized unoccupied pd wave functions. They can be described in a molecular-orbital scheme and depend on the first coordination shell. Oscillations at higher energies are interpreted in terms of backscattering from the next coordination shells. The intense white lines on the iron ${\mathit{L}}_{2,3}$ edges are due to strong 2${\mathit{p}}^{6}$3${\mathit{d}}^{\mathit{n}}$\ensuremath{\rightarrow}2${\mathit{p}}^{5}$3${\mathit{d}}^{\mathit{n}+1}$ excitations, and the recorded changes of relative intensity (or branching ratio) are predominantly governed by strong Coulomb and exchange interactions on the excited cation.