UNOCCUPIED ELECTRONIC STATES OF CUO AND CU2O STUDIED BY SECONDARY-ELECTRON EMISSION

The unoccupied electronic states located above the vacuum level of CuO and Cu2O have been studied by means of the secondary electron emissio n technique up to 50 eV above the Fermi level. The results of our meas urements have been compared with bremsstrahlung isochromat data and wi th the calculated unoccupied density of states taken from the literatu re. All the features within 15 eV of the Fermi level coincide with str uctures of the unoccupied density of states. A relaxation mechanism in volving O3d empty levels and O2s core levels has been found to occur i n CuO but not in Cu2O, very probably because of the different strength s of the bonding between oxygen and copper. The predicted Cu4d empty s tates of Cu2O have also been observed.