Quantifying the Top-Bottom Effect in Energy-Dispersive X-Ray Spectroscopy of Nanostructures Embedded in Thin Films

Summary

Energy-dispersive X-ray spectroscopy is a standard tool for microanalysis in transmission electron microscopy. If the structure to be analysed is much smaller than the sample thickness, it becomes important for quantification whether it is located in the top of the foil, near to the X-ray detector, or at the bottom of the foil, where absorption and fluorescence effects will be stronger. This so-called top-bottom effect is investigated in detail for InGaAsN quantum wells embedded at different depths within a GaAs thin foil specimen by modelling electron scattering and X-ray generation using Monte Carlo simulations. A new procedure is presented to determine the distance of an embedded feature from the top surface of the foil, which is a prerequisite for more accurate quantification of its chemistry.