Valence states analysis of Ca and Si in 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). In order to study the reaction process, the reaction was precisely controlled by applying de voltage between Pt electrode and CaSi2 specimen. The Si[2s, 2p, V] Auger spectra of CaSi2 specimen remain unchanged under the applied voltage lower than -15 V relative to the Pt electrode in H2O. At higher applied voltage, 3p components of Si[2s, 2p, V] (V = 3s, 3p) Auger spectra get weak while the 3s components increase drastically. The peak position due to Ca[2p, 3p, 3p] transitions gradually shifted toward the lower energy side by raising the applied voltage. The peak shift is due to the formation of Ca-O bonds in CaSi2. A new peak, which arises from the split of the valence electron states in Ca atoms due to the Ca-O bonds, appeared in Ca[2p, 3p, V] Auger spectra for CaSi2 after the reaction with H2O.