Electron energy-loss spectroscopy of UHV-cleaved NiO (100), CoO (100), and UHV-cracked MnO clean surfaces

Electron energy-loss spectra of clean NiO (100), CoO (100), and MnO surfaces have been obtained using primary electrons of 100-900, 30-800, and 300-700 eV, respectively. The observed electronic transitions are interpreted on the basis of the primary electron energy dependence and comparison with optical data. The peaks below approximately 10 eV are due to the O 2- 2p to M 2+ 3d and 4s(M=Ni, Co, and Mn) transitions. It is shown that the onset of the interband transitions is caused by the 2p to 3d charge-transfer excitons. The peaks between 10 and 50 eV are attributed to the one-electron excitations of O 2- 2p to M 2+ 4p and M 2+ 3d to 4p, and to the single- and multiple-bulk plasmon excitations associated with O 2- 2p, M 2+ 3d, and coupled 2p and 3d electrons. The 3p-core excitation spectra are observed beyond 50-60 eV.