TEMPERATURE-DEPENDENT EXAFS STUDY ON SUPPORTED SILVER AND PALLADIUM CLUSTERS - COMPARISON OF THEIR INTERATOMIC POTENTIALS WITH THOSE OF BULK METALS

Temperature-dependent Ag and Pd K-edge extended X-ray-absorption fine-structure (EXAFS) spectra were measured for SiO2-supported small Ag and Pd metal clusters and their corresponding bulk metals. The EXAFS analysis using the cumulant expansion technique reveals that the Debye temperature is significantly lower and the thermal expansion coefficient is larger for the small metal clusters compared with the bulk metals. The EXAFS results thus obtained allow us to describe interatomic potential curves of the bulk metals and the metal clusters by use of a Morse potential function. The resultant dissociation energies of the small metal clusters are actually smaller than those of the corresponding bulk metals. It is quantitatively demonstrated that the surface metal atoms of the clusters have shallower and more anharmonic interatomic potentials. © 1990 IOP Publishing Ltd.