Surface Layer Density of States for Single-Crystal Pt

We will present results from an x-ray photoelectron spectroscopy (XPS) study of the surface atoms' valence density of states for Pt single crystals. The surface sensitivity of XPS is enhanced by detecting photoelectron at near-grazing emission from the sample. A bulk-sensitive spectrum can be subtracted from such a surface- sensitive spectrum to yield a purely surface-atom spectrum. Separating the surface and bulk components in the core spectra taken at two angles determines the correct normalization for obtaining the surface-atom valence band spectrum. This empirical determinization is necessary because the escape depth is not well known and because forward-scattering effects cause oscillations in the surface -to-bulk intensity ratio. Photoelectrons form low-lying core levels are used since they have nearly the same kinetic energy, and hence the same escape depth, as the valence photoelectrons. Symmetry effects on the bulk valence emission require that the two angles are used lie along equivalent crystal axes.