Surface studies by grazing-exit electron probe microanalysis (GE-EPMA)

Surface analysis was performed by a new analytical method, grazing-exit electron probe microanalysis (GE-EPMA) At grazing-exit (small x-ray take-off) angles, only characteristic x-rays emitted from the near-surface regions are measured because of strong absorption and refraction effects at the surface. The exit angle was carefully determined using a stepping motor (with a minimum step angle of 0.018°), and the emergent x-rays were measured by an energy-dispersive x-ray detector and analyzed with a multi-channel analyzer (MCA). A computer controlled both the stepping motor and the MCA so that the exit-angle dependence of the characteristic x-ray intensities was measured automatically. The angle-dependent curve for a thin cobalt film (5 nm thick) deposited on a silicon wafer indicated that the cobalt x-rays predominated at grazing exit angles, demonstrating that high surface sensitivity was obtainable under these conditions. The results from a polished stainless-steel sample revealed chromium enrichment at grazing exit angles, which corresponds to a thin passivation layer of chromium oxide at the surface. Both sets of data suggest that GE-EPMA is a promising technique for localized surface analysis.