The image is formed in an SEM by scanning an electron beam across a sample and collecting some signal from the beam-sample interaction, which is used to control the intensity of the spot on a television monitor which is scanning in synchronization with the beam on the sample. The picture produced is often a lot like might be envisioned if the operator were standing above the sample and looking down on it with highly magnified vision. Because the probe used for imaging is an electron beam, some interesting contrast mechanisms (and signals) can be produced. The appearance of the image is usually as though the sample were ''illuminated'' by the detector being used to form the image, up to the point of ''shadows'' and the like. Figure 1 is a low magnification image of a U.S. penny viewed using the E-T detector signal. Dark spots are surface contamination.