Electron spectroscopy study of NO2 adsorption on the Pd/MgO/Cu system

An evolution of an energy structure of the unoccupied electronic states and of a surface composition during the formation of a Pd/MgO/Cu (polycrystalline) thin layer system and NO2 adsorption was studied using Auger electron spectroscopy, total current spectroscopy (TCS) and work function measurements. All investigations were performed in situ under UHV conditions. A 10nm thick MgO film was prepared via oxidation of a Mg overlayer on a clean polycrystalline Cu substrate. The MgO electronic structure was completely screened after deposition of a few monolayers of Pd and the Pd-related TCS fine structure appeared. We observed an irreversible NO2 adsorption on the Pd layer. A negative charge transfer to adsorbed molecules and appearance of new adsorption-induced unoccupied bands were revealed. These new bands are considered as a result of hybridisation of palladium and unoccupied oxygen orbitals.