Xenon and krypton adsorption on palladium (100)

Abstract

The adsorption of Xe and Kr on the Pd(100) surface has been studied with thermodynamic, low energy electron diffraction, and work function experiments. Unlike on Ag(111), we observe no 2D island formation for Xe down to 10 K. Quantitative measurements of the liquid-like diffraction pattern show that the diffuse ring of intensity increases in diameter, narrows, and becomes more intense continuously with increasing coverage, suggesting repulsive adatom interactions. The isosteric heat versus coverage gives the average potential energy in the lateral interactions which suggests a steep repulsion at short distances and no attractive well. At high temperatures the results for Kr are similar but there is evidence for island formation near 10 K. The isosteric heat indicates a weak attractive interaction. The XePd vertical spacing is determined. Dipole moments and polarizabilities are estimated from the results of measurements of the work function change versus coverage. The thermodynamic and diffraction results are compared with published simulations for hard and soft disks. It is speculated that the additional interadatom repulsion on Pd is due to the direct overlap of the deformed electron distribution in the substrate.