ABSTRACT
We first spot the probe beam onto the sample (Fig. 19.1) using an accelerated voltage from the electron source. We can use an electron gun via thermionic emission or field electron emission processes to produce the probe beam. Field electron emission relies on the tunneling effect when we use a strong electric field to induce electrons at the surface of the tip. Thermionic emission is based on the heat effect when we rise the temperature of the filament till the emission of electrons at the surface of the filament. Then a primary electron beam dislocates the secondary electron deep below the surface and the backscattered electron in a deeper region. The electron signals are then converted to SEM images via a CCD camera.
