Electron-exchange processes in bulk and surface d-d excitations in transition-metal oxides

Electron-exchange processes in excitations within the d-multiplet of the TM-ions in NiO(100) and CoO(100) had been examined by spin-polarized electron energy-loss spectroscopy The excitations at surface and bulk ions in NiO show a completely different scattering geometry dependence, providing the possibility of distinguishing between both. In addition to the well-known 0.6 eV surface state, the loss-structure at 2.1 eV excitation energy was identified as surface excitation. In CoO, no surface d-d transitions have been found. Different spin-flip intensities in the excitations of the bulk Co-ions had been used to identify multiplicity changing and conserving transitions definitely. By use of the previously found resonance primary energies and suitable scattering geometries, new d-d excitations had been measured in NiO as well as in CoO. (C) 1997 Elsevier Science Ltd.