Principles of X-Ray Energy-Dispersive Spectrometry in the Analytical Electron Microscope

The solid state x-ray detector or energy-dispersive spectrometer (EDS) was developed in the late 1960s and rapidly found use on electron-beam instruments (Fitzgerald et al., 1968) because of its speed in collecting and simultaneously displaying x-ray data from a wide energy range. Its small size, but relatively large collection angle (see below), also gives it significant advantages over the traditional crystal or so-called wavelength-dispersive spectrometer (WDS), enabling it to interface easily to an AEM despite the severe space constraints of modern TEM stages. The drawbacks to the conventional EDS are its relatively poor energy resolution (∼150 eV) and its inability to detect x-rays from elements below Na (Z = 11) in the periodic table. These limitations, however, are not major practical handicaps in most analyses, and no modern AEM (since the EMMA series in about 1970) has had a crystal spectrometer interfaced to the column. Hence, we will consider the EDS only.