ABSTRACT
Microanalysis in the scanning transmission electron microscopy (STEM) is fundamentally the same as microanalysis in the TEM. Indeed, modern TEMs are achieving a level of micro analytical performance that had been the sole purview of the dedicated STEM. The principal limiting factor in the precision of X-ray microanalysis is statistics. The X-ray photons arrive randomly at the detector; such a process is described by Poisson statistics, but if the number of counts is sufficiently large the use of the more well-known Gaussian statistics is an adequate approximation. A thin specimen must be used if high spatial resolution microanalysis is to be attempted, because the electron beam will spread laterally as it traverses the specimen. In a few microscopes the column vacuum is sufficiently good that the X-ray detector will function well without a window. Such detectors are termed ‘windowless’, and provide the ultimate sensitivity for light element analysis.
