Measurement of the Inelastic Mean Free Path by EELS Analyses of Submicron Spheres

Abstract

Accurate measurement of sample thickness is important for analytical electron microscopy (AEM) but is often difficult and tedious. Unlike other thickness measurement methods, with electron energy loss spectroscopy (EELS) thickness may be measured in both amorphous and crystalline specimens and at the same location and orientation at which other data is collected in the electron microscope. Thickness values may be obtained from convergent-beam electron diffraction (CBED) data only if the sample is crystalline with large grains of uniform thickness. Sample thickness may be measured from crystal defects projected through the entire foil, but such defects are not always conveniently located in the area of interest. The distance between contamination spots on the upper and lower surfaces of the specimen may be measured, but this is not considered accurate and contamination is not desirable in microanalysis.Sample thickness t may be determined with EELS by the relation:(1)where It is the total intensity in the EEL spectrum, Iz is the intensity in the zero loss peak, and λ is the inelastic mean free path for energy loss of an incident electron in the sample.