XPS ANALYSIS OF PALLADIUM OXIDE LAYERS AND PARTICLES

The thermal reduction of both oxidised palladium foil and SiO2/Si(100) supported palladium oxide particles, ranging in size from 3.5 to 13 n m, was investigated with XPS. Equations were derived for the XPS inten sities, measured at normal emission angles, of the particles which con sisted of a metallic core and an oxidic skin. By applying these equati ons on the spectra measured after each reduction step, the particle si ze and the size of the metallic core were calculated. Measurements on palladium foil showed that the oxide layer thickness decreases linearl y with the reduction time up to the last monolayer oxide. The reductio n rate of the surface oxide is about eight times lower than the reduct ion rate of the bulk oxide. The growth of the metallic core in palladi um oxide particles appeared to be linearly proportional to the surface area. The reduction rate of the smallest particles was comparable to the reduction rate of the surface oxide of the palladium foil. The lar ger particles behave identical to the palladium foil.