Electrons in SEMs (as well as ions in dual beam FIB-SEMs) are accelerated at voltages in the range of a few eV to 30 keV. These charged particles impinge on the surface of the material interacting with uppermost surface layers and, as a result, a cascade of collisions (elastic and inelastic) takes place generating a variety of signals such as secondary electrons (SEs), backscattered electrons (BSEs), and photoemission in the form of X-rays and Cathodoluminescence (CL). In dual beam systems, the secondary ion (SI) signal can also be collected. Each of these signals is emitted as a result of diverse physical processes and from different penetration depths carrying valuable information of the sample.
