SEM In scanning electron microscopy (SEM) an electron beam is scanned across a rectangular area of the sample surface. A variety of different signals are produced by the interaction between the electron beam and a small volume of material (known as the interaction volume) surrounding the point where the electron beam hits the sample surface. The intensities of the different signals produced depend on the charecteristics of the incident electron beam and the material within the interaction volume. Various types of detectors are located inside the scanning electron microscope. Each one detects a different type of signal emanating from the sample. These signals are then sent to computers that process them and display information about the sample, such as images based on sample topography or composition and maps of chemical composition, phase and crystal orientation. Backscattered electron image showing compositional contrast in a rock sample