Compositional mapping by electron energy loss spectroscopy

Abstract

Compositional maps of a thin specimen can be obtained using electron energy loss spectroscopy (EELS) to measure the two-dimensional distribution of inelastic scattering processes. These maps may be acquired both in the energy-filtering transmission electron microscope (EFTEM) and in the scanning transmission electron microscope (STEM). An advantage of EFTEM is that data from large numbers of pixels are collected simultaneously making the technique favorable for detection of high local elemental concentrations. However in the EFTEM images at different energy losses must be acquired sequentially, complicating the analysis of weak spectral features which require careful subtraction of the background intensity. Early attempts to utilize the STEM for EELS mapping were limited by the performance of serial detectors. The availability of parallel detectors and inexpensive PC-type computers with sufficient storage and speed has generated new interest in using the STEM for EELS elemental mapping. In particular the concept of EELSspectrum-imaginghas been introduced by Jeanguillaume and Colliex.