INFLUENCE OF SILICON X-RAY PHOTOELECTRON DIFFRACTION ON QUANTITATIVE SURFACE-ANALYSIS

The problem of XPS quantitative measurements on silicon single crystal surfaces is discussed in relation to the X-ray photoelectron diffraction (XPD). This effect consists in electron emission enhancements in some particular space directions with reference to the polar angle theta and the azimuth phi and originates in the preferential electron scattering in the directions of the interatomic axes (forward scattering). The polar scans I(Si) proportional-to (theta) of the Si2p core level intensities of Si(001) and Si(111) surfaces are given in azimuthal high symmetry directions. The relevant spectra display intensity fluctuations in the emission space up to 40% for angular variations of only 10-degrees around the surface normal. They may induce corresponding inaccuracies in quantitative surface analyses when, by approximate sample positioning, this effect is not taken into account.