Study of theL23edges in the3dtransition metals and their oxides by electron-energy-loss spectroscopy with comparisons to theory

Excitations of the $2p$ subshell in the $3d$ transition metals and their oxides have been studied by inelastic scattering of 75-keV electrons. The ${L}_{23}$ "white lines" which arise from dipole transitions to unoccupied $d$ states have been investigated in terms of their threshold energies, widths, and intensity ratios. Shifts in the ${L}_{3}$ threshold energy between the metal and oxide are different from the chemical shifts measured by x-ray photoemission spectroscopy and this suggests the importance of relaxation effects. Single-particle calculations for the ${L}_{3}$ spectra are also discussed. Measured ${L}_{3}$ linewidths are generally larger than those predicted by suitably broadened theory. A variation from the statistical ${L}_{3}$-to-${L}_{2}$ white-line intensity ratio of 2:1 has been observed across the $3d$ transition row, with values ranging between 0.8:1 for Ti to 5:1 for FeO. This behavior appears to be associated with the white lines since Cu with a filled $3d$ band exhibits the statistical results. It is suggested that the anomalous ratios may be explained by a breakdown of $j\ensuremath{-}j$ coupling caused by an exchange mechanism. Finally, the extended x-ray absorption fine-structure-type structure extending several hundred eV above the white lines is analyzed for Cr to provide the radial distribution function.