Electronic structure and chemical properties of Pd films supported by MgO

Abstract

Pd films were deposited on MgO-covered Mg substrate by the thermal evaporation method under high vacuum conditions. The electronic and chemical properties of Pd structures with different Pd thicknesses were studied using X-ray photoelectron spectroscopy (XPS) and field emission-scanning electron microscopy (FE-SEM). For relatively low Pd thicknesses (<1 nm), separate Pd particles could be observed. At higher Pd thicknesses, continuous Pd thin films formed by agglomeration of Pd nanoparticles were found. With decreasing Pd thickness, a chemical state with a higher-binding-energy became more pronounced in the Pd core level spectra, demonstrating the electron-deficient nature of Pd atoms in contact with MgO substrate. Very small Pd particles with a pronounced core level shift were shown to be less active toward CO oxidation than thicker Pd films.