Heterogeneity assessment in individual CaCO3-CaSO4 particles using ultrathin window electron probe x-ray microanalysis

In our previous studies, it has been demonstrated that both the excitation interactions between electrons and the atoms of the matrix and the matrix a nd geometric effects of electron-induced X-ray signals can be described by Monte Carlo simulation for low-Z elements, such as carbon, nitrogen, and ox ygen, in individual atmospheric microparticles. In addition, by the applica tion of a quantification method, which employs Monte Carlo simulation combi ned with successive approximations, at least semiquantitative specification of the chemical compositions could be done. This has enlarged the scope of electron probe X-ray microanalysis (EPMA) for the single particle analysis of atmospheric environmental aerosol particles. In this work, we demonstra te that the heterogeneity of individual particles, even of micrometer size, can be characterized by the application of EPMA. X-ray photons obtained wi th different primary electron beam energies carry information on the chemic al compositions for different regions in the particles. Artificially genera ted heterogeneous CaCO3-CaSO4 individual particles were measured at differe nt accelerating voltages, and it was found that the Monte Carlo calculation is a powerful technique to extract the information on the heterogeneity of the particles that is contained in the measured X-ray data. Our approach c an even estimate the thickness of the surface CaSO4 species by the applicat ion of the Monte Carlo calculation. A preliminary result for carbon-coated glass particles is also presented. The complexity involved in the analysis of real world particles is briefly mentioned with a result for heterogeneou s SiO2 particle.