The adsorption of CO2 and CO on Ca and CaO films studied with MIES, UPS and XPS

Metastable Induced Electron Spectroscopy (MIES), Ultraviolet Photoelectron Spectroscopy (UPS), and X-ray Photoelectron Spectroscopy (XPS) are employed to study the adsorption of CO2 and CO on Ca and CaO films. Ca films are prepared by evaporation of Ca onto clean Si(1 0 0) substrates. CaO films are produced by Ca evaporation in an oxygen atmosphere at a substrate temperature of 670 K. CO2 interaction with the Ca films is initiated by dissociation of the impinging molecules leading to the formation of Ca-O bonds. These Ca-O bonds are subsequently consumed in the formation of a closed CaCO3 layer on top of the surface. CO interaction with the Ca surfaces also leads to the dissociation of the molecule and the formation of Ca-O bonds. We find evidence for the subsequent formation of CO32- complexes on top of the surface. On CaO surfaces, both CO2 and CO lead to the formation of a closed CaCO3 top layer, though displaying very different reaction rates.