accelerating voltage

The accelerating voltage means the potential difference between the cathode and anode which constitute the electron gun. The accelerating voltage for SEM ranges typically from about 500 V to about 30 kV. Electrons emitted from the electron source (cathode) are accelerated by this voltage and pass through a holey electrode (anode) or the exit of the electron gun and are incident on a specimen through the illumination lens system and the deflection system. 
In many cases, the accelerating voltage is equal to the incident (landing) voltage to the specimen. When an extra voltage is applied to the specimen, the landing voltage is different from the accelerating voltage. In this case, the landing voltage is the accelerating voltage minus the specimen voltage. The penetration depth of the incident electrons into the specimen is determined by the landing voltage, not by the accelerating voltage.

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