Question

There is a collector situated in front of the scintillator in the Back scattered electrons detector. Let us assume that this collector is under a voltage of i) +200 V, ii) 0 V, and iii) –100 V. Explain the differences, if any, in collection of signals by the detector for three above-listed SEM working conditions.

Answer 1

i) for +200V more number of scattered electrons will enter into the detector. These include backscattered and also some of the secondary electrons. A very high number of signals will be obtained.

ii) for 0V less number of scattered electrons will enter into the detector. Here only backscattered electron will entre into collector No secondary electrons will be attacked by collectors. because secondary electrons are having very low energy. Lesser number of signals will obtained

iii) for -100V almost all electrons are repelled by the colletor. Almost no signal will be generated from mode. But some electron may entre into the collector. As backscattered electrons are having very energy.