Experimental evidence for room-temperature intermetallic compound formation at the Pd/Al interface

The growth of Pd films on Al and Pd/Al interface formation were studied with use of ultraviolet photoemission spectroscopy (UPS) and low-energy ion scattering. At room temperature, the deposited Pd intermixes with the Al substrate and forms a thin surface alloy about 5 monolayers (ML) thick. Bulklike Pd states start to build up at $E_F$ when the Pd coverage exceeds 4 ML. More than 8 ML of Pd are needed to completely cover the Al substrate and to fully develop the Pd metallic valence band. A Pd4d–derived band centered at 4 eV below $E_F$ was observed both for monolayer Pd coverage on Al and for thick Al on Pd. It is argued that this deep-lying d band is due to the interaction between Pd and Al through the hybridization of the Pd d and Al s states.