RHEED and XPS study of palladium interaction with cerium oxide surface

In the present studies we investigated structural and electronic properties of Pd nanoclusters deposited on the surface of epitaxial CeO2 thin film grown on Cu(111) single-crystal. The structural and electronic properties were investigated by means of RHEED and XPS methods. The CeO2 thin film with (111) surface orientation prepared by reactive evaporation was used as a substrate for Pd deposition. The RHEED analysis has shown two populations of Pd nanoclusters having FCC structure and (111) epitaxial plane. Intensity analysis of diffraction spots has shown preferential growth of one population. Precise measurement of the position of diffraction spots permits to investigate changes of lattice parameter of Pd during deposition and annealing. A contraction of the Pd lattice with respect to bulk value was observed. The XPS measurement has shown that the deposition of Pd on CeO2(111) surface led to the apparent partial reduction of cerium oxide attributed to the charge transfer given by metal substrate interaction. The interaction peak was found also in the Pd 3d photoelectron spectrum. Thermal stability and deposit-substrate interaction were investigated up to temperature of 600 degrees C. At high annealing temperatures encapsulation of Pd nanoclusters followed by a formation of Pd-Cu bimetallic alloy were observed.