Direct observation of surface-profile effects on X-ray-photoelectron angular distributions

The first direct observations of surface-profile effects on X-ray-photoelectron angular distributions are reported. Ratios of Al 2p (oxide) and Al 2p (metal) peak intensities were measured at various electron emission angles for two different types of specimens consisting of an aluminum substrate with a surface oxide layer. For triangular-periodic diffraction grating surfaces with 10°, 20°, and 43° blaze angles, pronounced structure was observed in the ratio angular distributions; theoretical calculations based upon the ideal grating geometries furthermore reproduce all of the features found experimentally. For unidirectionally-polished aluminum specimens, ratio angular distributions measured perpendicular and parallel to the polishing grooves were found to be markedly different, with more oxide enhancement being possible at low electron emission angles for the parallel orientation; this finding is also qualitatively consistent with theory.