Transmission Electron Microscopy (TEM)

Basic working principle

TEM is a technique that involves transmitting a high voltage electron beam through an ultra-thin specimen (approximately 100nm), which interacts with the specimen as the electrons pass through it.

An electron gun is positioned at the top of the column and generates electrons. These electrons are then accelerated downward through the vacuum column. Within the column, electromagnetic condenser lenses and an aperture are utilized to focus the electrons into a small, thin, coherent beam. The beam subsequently strikes the ultra-thin specimen, and depending on the properties and thickness of the specimen, some electrons are transmitted through, while others are scattered or diffracted. Optional objective apertures can be employed to enhance contrast by blocking out high-angle diffracted electrons. The transmitted electrons then proceed down the column through intermediate and projector lenses, progressively enlarging and magnifying the image. Finally, the image or transmitted portion of electrons reaches a photosensitive screen, which generates light and enables the user to observe the image. Darker areas in the image indicate areas where fewer electrons have been transmitted, while lighter areas represent areas where more electrons have passed through. The schematic representation of TEM is depicted below.

Conventional TEM	Negative staining	Immuno-gold labelling

Tomography	Energy dispersive X-ray spectroscopy