A scanning electron microskope (SEM) is a type of electron microscope that produces images of a sample by scanning it with a focused beam of electrons. The electrons interact with atoms in the sample, producing various signals that can be detected and that contain information about the sample´s surface topography and composition. The electron beam ist generally scanned in a raster scan pattern, an the beam´s position is combined with the detected signal to produce a image.
To characterize the chemical composition of smallest areas on samples the SEM uses the characteristic x-ray radiation which is emitted when the electron beam striking out a nucleus near electron. The occurring gap is filled with an electron of a higher energy level and the energy difference is set free as an x-ray quantum. The resulting x-ray radiation is characteristic for the transition and the atom. This radiation is used to determine the composition of the elements for the investigated area.