Of all the analytical techniques in electron microscopy, X-ray energy dispersive spectroscopy (XEDS) is perhaps the most useful. It provides a quick identification of the elements and even with semiquantitative methods; a reasonable composition can be obtained. However, in the scanning electron microscopy (SEM), there are materials systems in which severe peak overlaps of heavier elements L and M lines cannot be easily deconvolved with lighter elements' K lines. In addition, without a sufficient overvoltage in the SEM, even identification of the heavier elements can be difficult. In the analytical electron microscope (AEM), there is always sufficient overvoltage to excite all of the elements' K-lines. However, all of the K-lines might not be able to be detected with commercially available instruments. This is illustrated in Fig.l where the maximum energy of the detector system might be set to 10, 20, or 40 keV.