Transmission electron microscopy (TEM) was historically the first form of electron microscopy to be developed and successfully marketed. The technology represented a true breakthrough in microscopy, as it allowed researchers to achieve resolutions far beyond the capabilities of conventional light microscopes.

Optical microscopes, being dependent on light, are generally limited to resolving features no smaller than the wavelengths of the light being used, on the order of a few hundred nanometers. TEM eschews light in favor of using electrons as the “illumination.” The electrons emitted from an electron gun have a characteristic wavelength, and this wavelength gets smaller as the energy is increased. While the resolution of electron microscopes is also limited by the wavelength of the electrons, this wavelength can be many orders of magnitude smaller than the wavelengths of visible light used in optical microscopes, enabling magnifications well into the millions. TEM microscopes represent the ultimate in resolution; at the high end of the product spectrum, these instruments can resolve individual atoms.

As its name suggests, TEM derives its images from electrons that have been transmitted through the sample. Since electrons typically cannot pass through much solid matter, this requires TEM samples to be extremely thin for the electrons to reach the detectors. This often requires elaborate sample preparation, which is the primary drawback of the technique. TEM measurements are also carried out in a vacuum, which presents further challenges for some samples, particularly in the life sciences.

In the simplest imaging mode, electrons from the electron source pass through the sample. Electrons are more likely to be stopped by denser portions of the sample and by atoms with a high atomic number. The different intensity of electrons emerging from different parts of the sample provides the contrast in the image. Other modes can involve performing energy spectroscopy on the transmitted electrons, or diffraction of the electrons by the sample’s crystal structure.

The difficulties with sample preparation restrict applications to some extent, but TEM is still used in many different academic disciplines from geology and biology to materials engineering and nanotechnology. Life science research and medical science form one of the primary research areas. Samples range from individual viruses and cells to thin sections of tissues. TEM also has some important industrial applications in semiconductors, metals and metallurgy.

The total market for TEM is considerably less than scanning electron microscopy. Nevertheless, demand in 2012 for TEM was a few hundred million dollars. The competitive situation is concentrated among the major electron microscopy vendors. FEI has the greatest market share, followed by JEOL and Hitachi High-Technologies. Another significant competitor is Carl Zeiss. Delong Instruments markets a low-voltage tabletop TEM.

TEM at a Glance:

Leading Suppliers

• FEI

• JEOL

• Hitachi High-Technologies

Largest Markets

• Semiconductors

• Metals

• Academia

Instrument Cost

• $75,000–$6 million