Electronic and structural investigations of palladium clusters by x-ray absorption near-edge structure and extended x-ray absorption fine-structure spectroscopies

Palladium metal clusters with an average diameter of 14 Å embedded in a carbon matrix have been studied by synchrotron-radiation x-ray absorption measurements. The data analysis of the $L_{2,3}$ edge ($p-d$ transitions) shows (a) a strong reduction of the absolute value of the absorption compared to the bulk, (b) a shift towards higher binding energies of about 2 eV, and (c) a broadening of the same structures. We explain these effects as mainly due to a change of the $d$ density of states at the Fermi level, since the $L_1$ edge ($s-p$ transitions) does not show similar effects. The extended x-ray absorption fine-structure analysis reveals an important increase of about 3% of the first-nearest-neighbor distance, in contrast with other metals which show a lattice contraction.