Radiationless Raman versus Anger behavior at the Cu L3 resonance of CuO and Cu2O

We have investigated the behavior of the 2p3p3p and 2p3s3p Anger lines of CuO and Cu2O scanning the photon energy across the Cu L-3 resonance. For both samples, when the excitation energy is below the L-3 resonance, we observe the 2p3p3p and 2p3s3p peaks at constant binding energy. This behavior is typical of nonradiative resonant Raman scattering. If the photon energy is raised above the L-3 maximum, the two samples behave in different ways. In CuO, the Auger peaks are always observed at constant binding energy, while in Cu2O their kinetic energy first reaches a maximum at correspondence with the absorption threshold, and then stabilizes at a value slightly higher than the off-resonance Auger peaks. These differences are interpreted in terms of the different electronic structure of the Auger intermediate state at resonance. In CuO, the intermediate state corresponds to a single 2p(3/2) core hole, with the Cu 3d band completely filled. On the contrary, in Cu2O the intermediate state is represented by the combination of a 2p(3/2) hole with a 4sp electron in strong interaction with the O-2sp valence band. In CuO, for photon energies higher than 1.5 eV above the L-3-edge maximum, the constant binding energy radiationless Raman peaks are accompanied by constant kinetic energy replicas. These are attributed to the relaxation of the Auger intermediate state through electron-hole pair generation across the band gap of the material. Satellites that could be associated to relaxation precesses involving energies smaller than the band gap are not resolved. No variation of the lineshape of the Anger peaks is observed as a function of the sample temperature, indicating that different densities of thermally accessible excitations do not have a strong influence on the recombination process of the core hole.