Valence-electron spectral change and charge transfer mechanism of CaSi2 during CaSi2-H2O reaction

The changes in the valence electron states of CaSi2 during the chemical reaction with H2O have been investigated by Auger valence electron spectroscopy (AVES), The drastic changes in the valence electron spectra of 3s and 3p states, which are caused by the oxidization of the Si atoms in CaSi2, were observed in Si[2s, 2p, V] spectra for CaSi2 after the reaction. In particular, the Si[2s, 2p, V] spectra of CaSi2 samples reacted with H2O at 60 or 80 degrees C for 3 h were almost similar to that of SiO2. The peak shift of Ca[2p, 3p, 3p] Auger transition toward the lower energy side has been observed, suggesting the formation of bonds between Ca 3p and O orbitals. New peaks due to Ca-O or Ca-OH bonds also appeared in the valence electron region of Ca[2p, 3p, V] Auger transition. The charge transfer and the chemical-bond formation can be well demonstrated by AVES during the CaSi2-H2O reaction.