PALLADIUM ALUMINA INTERFACE - INFLUENCE OF THE OXIDE STOICHIOMETRY STUDIED BY EELS AND XPS

Electron energy-loss spectroscopy (EELS) and X-ray photoelectron spectroscopy (XPS) were used to study the initial stages of the formation of the Pd/alpha-Al2O3(1012BAR) interface. Two kinds of sapphire surfaces were used: (1 x 1) stoichiometric surfaces or reduced and reconstructed surfaces. Depending on the oxidation level, clean surfaces are characterized by specific electronic states located in the band gap. The evolution of the band gap structure during palladium deposition reflects the interaction metal-alumina which appears to be different on the two surfaces. The palladium growth process has been determined by combining Auger parameter (alpha') analysis with EELS measurements. It is found that reduced alumina surfaces induce a stronger electronic interaction with palladium deposit than stoichiometric surfaces do. This difference is confirmed by the Pd growth mode analysis.