Transmission Electron Microscopy (TEM)

Transmission electron microscopy (TEM) is a microscopy technique that allows the examination of fine details as small as single column of atoms, which is tens of thousands times smaller than the smallest resolvable object in light microscope. TEM forms a major analysis method in a range of scientific fields, in both physical and biological sciences times smaller than the smallest resolvable object in a light microscope. TEM forms a major analysis method in a range of scientific fields, in both physical and biological sciences. TEMs are used in cancer research, virology, materials science as well as pollution, nanotechnology, and semiconductor research.

There are four main components to a TEM: an electron optical column, a vacuum system, the necessary electronics (lens supplies for focusing and deflecting the beam and the high voltage generator for the electron source), and control software. A modern TEM typically comprises an operating console supported by a vertical column and containing the vacuum system, and control panels for the operator. The microscope may be fully enclosed to reduce interference from environmental sources, and operated remotely.

The electron column includes elements analogous to those of a light microscope (Figure 1). The light source of the light microscope is replaced by an electron gun, which is built into the column. The glass lenses are replaced by electromagnetic lenses. Unlike glass lenses, the power (focal length) of magnetic lenses can be changed by changing the current through the lens coil. The eyepiece is replaced by a fluorescent screen and/or a digital camera. The electron beam emerges from the electron gun, and passes through a thin specimen, transmitting electrons which are collected, focused, and projected onto the viewing device at the bottom of the column. The entire electron path from gun to camera must be under vacuum.

Figure 1 – Scheme which illustrates the working setup of TEM system

Resolution of the TEM is limited primarily by spherical aberration, but a new generation of aberration correctors has been able to partially overcome spherical aberration to increase resolution. Hardware correction of spherical aberration for the high-resolution transmission electron microscopy (HRTEM) has allowed the production of images with resolution below 0.5 angstrom (50 picometres) and magnifications above 50 million. The ability to determine the positions of atoms within materials has made the HRTEM an important tool for nano-technology research and development.

Still, there are a number of drawbacks to the TEM technique. Many materials require extensive sample preparation to produce a sample thin enough to be electron transparent, which makes TEM analysis a relatively time consuming process with a low throughput of samples. The structure of the sample may also be changed during the preparation process. Also the field of view is relatively small, raising the possibility that the region analyzed may not be characteristic of the whole sample. There is potential that the sample may be damaged by the electron beam, particularly in the case of biological materials.

Following video demonstrates the TEM operation.