Imaging of elemental distributions on a fine scale is one of the triumphs of electron microscopy. Compositional imaging frees the operator from the necessity of making decisions about which features contain the elements of interest. Elements in unexpected locations, or in unexpected association with other elements, may be found easily without operator bias as to where to locate the electron probe for compositional data collection. This technique may be applied to bulk or thin specimens using a variety of composition-sensitive signals as shown in Figure 1.Cosslett and Duncumb obtained the first such compositional image in an electron microprobe modified to scan the electron beam and collect a characteristic x-ray signal as a function of beam position. Early images of this type were called x-ray “dot maps” and provided a qualitative indication of the location of elements on a flat polished bulk specimen to a spatial resolution of about 1 μm.
Monitoring of the electron beam position in industrial linacs
