Detection limits of grazing-exit EPMA for particle analysis

In conventional electron probe microanalysis (EPMA), the electron-induced X-rays are measured at large take-off angles of about 45°. In the grazing exit EPMA (GE-EPMA) method, they are measured at small angles (< 1°). X-rays emitted from deep positions can not be detected at grazing exit angles due to refraction effects at sample-vacuum interface; therefore, it is possible to measure X-rays emitted only from near the surface with a low background. GE-EPMA is especially suitable for the analysis of particles deposited on a flat sample carrier. The detection limits of GE-EPMA were investigated for artificial particles (Al₂O₃, Fe₂O₃ and PbO₂, particle sizes: 1 ∼ 18 μm) deposited on flat sample carriers of Au thin films-Si wafers. The detection limits improved with decreasing exit angle. The detection limits for characteristic X-rays at an exit angle of approximately 1.1° were 2-4 times lower than at 45°. A minimum detection limit of ca. 0.1% was obtained for Al in small particles.