Automated Single-Particle SEM/EDX Analysis of Submicrometer Particles down to 0.1 μm

Abstract

Typically single-particle SEM/EDX analysis of aerosols is done on polycarbonate filters or solid carbon substrates. This has led to a widespread conclusion that EDX provides poor information on carbon, oxygen, and nitrogen content of a particle and usually could not go below 0.5-microm particles. We show that use of grid-supported carbon films of 15-25-nm thickness gives exceptionally low background in the SEM/EDX analysis and allows satisfied automated analysis of particles down to 0.1-microm size, including detection of low-Z elements. In this work, six laboratory-generated 0.1-2-microm aerosols were tested for their elemental composition. The EDX analysis yields reasonably accurate quantitative results featuring all the elements present in the tested compounds, namely, C, O, N, Na, S, Al, Si, and Cl. Furthermore, the carbon film has very low backscattered electron (BSE) yield compared to that from the particle, so in the BSE mode the particle image is seen with very high contrast. This greatly improves quality and speed of the automated mapping of particles by SEM prior to EDX analysis.