Interaction of oxygen with a Pd(110) surface. II. Kinetics and energetics

Publisher Website
Google Scholar
Abstract
The interaction of oxygen with Pd(110) has been studied by thermal desorptionspectroscopy (TDS), work function change (Δφ), and Auger electron spectroscopy(AES) at 100<T<900 K. Thermal desorptionspectra reveal three major peaks, a low temperature one (α) being from molecular adsorbates and the other two (β1 and β2) from atomic oxygen. The β1 state is believed to be associated with subsurface oxygen. At 100 K, the population of molecular oxygen increases with increasing oxygen coverage. Above 200 K, all adsorbates are present as atomic oxygen. The rate of population of β1 decreases as T increases. This is explained as a kinetic effect due to the formation of the c(2×4) structure which hinders population of the β1 state. The oxygen induced work function change is found to depend strongly on both oxygen coverage and T. At a given T, Δφ is controlled by surface oxygen coverage, surfacestructural changes, as well as the formation of subsurface oxygen. A decrease of the intensity ratio of certain spectral features (I 0 /I Pd ) in the AE spectra is also observed, which might be associated with migration of surface oxygen to the subsurface region. The migration of oxygen to subsurface sites at low temperature is facilitated by the lateral displacements of surface Pd atoms which occurs on oxygen exposure at low T. A physical picture of the interaction of oxygen with a Pd(110) surface is tentatively proposed.