TEM is a method of imaging which involves collimated beam of electrons passing through an ultra thin sample and the interaction of the transmitted electrons with different parts of the sample creates an image in gray scale.

The working principle of a TEM can be divide in to two different mechanisms. (1) Illumination of the sample and (2) Detection and image formation.

(1) Illumination of the sample: The source is a beam of high velocity electrons (~200keV) which is accelerated under high vacuum. The accelerated beam of electron is collimated and focused by condenser lens onto the ultra thin sample.

(2) Detection and image formation: When the sample is illuminated by the collimated beam of electrons it suffers loss and rest of the electrons are scattered by different parts of the sample. Emergent electron beam is focused by objective lens. Final image forms on a fluorescent screen for viewing.