Explain the principle involved in scanning electron microscope (SEM).

Explanation

(i) This is used to obtain three dimensional image and has a lower resolving power than TEM. In this, electrons are focused by means of lenses into a very fine point.
(ii) The interaction of electrons with the specimen results in the release of different forms of radiation (such as auger electrons, secondary electrons, back scattered electrons) from the surface of the specimen.
(iii) These radiations are then captured by an appropriate detector, amplified and then imaged on fluorescent screen.
(iv) The magnification is 2,00,000 times and resolution is 5-20 nm.