Comparison of grazing-exit particle-induced X-ray emission with other related methods

Particle-induced X-ray emission (PIXE) is recognized as a trace analysis method; the Bremsstrahlung background, however, still limits the detection power in the low-energy region of spectrum. The grazing-incidence or grazing-exit arrangements are considered to be useful in order to reduce the background intensity. We measure grazing-incidence PIXE (GI-PIXE) and grazing-exit PIXE (GE-PIXE) using an identical sample vacuum chamber to evaluate the performance of both methods. The sample used is a standard sample (Ca, Fe, Ni and Zn) prepared on Si wafer by the spin-coating method. In GI-PIXE mode, a collimated 2.5 MeV proton beam irradiates the surface of the sample at grazing incident angles. However, it was difficult to reduce sufficiently the background intensity in the GI-PIXE spectra because of the Bremsstrahlung background induced by secondary electrons. In the GE-PIXE mode, proton-induced X-rays are measured at grazing-exit angles. The background intensity is reduced, because only the X-rays emitted from the near-surface layer can be detected in the grazing-exit arrangement. Furthermore, the result obtained for an Au–Cu thin film sample by GE-PIXE method was compared with the result obtained by other related methods: grazing-exit X-ray fluorescence and grazing-exit electron probe microanalysis. Similar results were obtained by different methods, indicating that the same phenomena occur in all grazing-exit X-rays measurements. One of the merits of the grazing-exit microprobe analysis method is in microanalysis using a small diameter electron probe; however, the damage by electron irradiation is more severe than that in GE-PIXE.