Valence Band Density of States of Cu₃Si Studied by Soft X-Ray Emission Spectroscopy and a First-Principle Molecular Orbital Calculation

Abstract

A systematic study of the valence band structure of Cu₃Si has been performed by soft X-ray emission spectroscopy and a first-principle molecular orbital calculation using the discrete-variational (DV)-Xα cluster model. The existence of Cu 4s, 4p states in the valence band and their important contributions to the valence band as that of Cu 3d are indicated together with previously reported ones. The high-binding energy peak in the Si L_2,3 emission spectrum is considered to originate mainly from the Si–Si 3s bonding state but also have a certain contribution of Si 3s bonding state with Cu 4s, 4p. On the other hand, the low-binding energy peaks in the Si L_2,3 emission band are attributed to both the antibonding states of Si 3s and the bonding states of Si 3d with Cu 4s, 4p and Cu 3d. The bonding states of Si 3s with Cu 4s, 4p and Cu 3d are expected to exist in the lower part of the valence band for η^′-Cu₃Si on the basis of the theoretical calculations. As for Si p states, the high-binding energy peak and the low-binding energy peak in the Si Kβ emission spectrum should be attributed to the Si 3p bonding state and antibonding state with Cu 3d and Cu 4s, 4p, respectively, according to the theoretical calculations. A comparison is made between experimental spectra and theoretical density of states.