Transmission electron microscopy (TEM) uses beams of electrons to image very thinly sectioned samples at high resolutions. TEMs have played important roles in virology, cancer research, materials study, and microelectronics R&D. The first TEM prototype was built in 1931, and the technology was refined over the following decades. Scanning transmission electron microscopy (STEM) was developed in the 1970s, and much of its technology came from advances in TEM. TEMs usually incorporate three lens stages and a vacuum system, sample stage, electron gun, and electronic lens.
Transmission electron microscopy (TEM) is an imaging technology in which beams of electrons pass through very thinly sectioned samples. As electrons are transmitted through the sample and interact with its structure, an image is resolved which is magnified and focused on an imaging medium, such as photographic film or a fluorescent screen, or captured by a special CCD camera. Because the electrons used in transmission electron microscopy have a very short wavelength, TEMs can image at much higher resolutions than conventional light microscopes that depend on light beams. Because of their higher resolving power, TEMs play an important role in the fields of virology, cancer research, materials study, and microelectronics R&D.
The first TEM prototype was built in 1931 and, by 1933, a unit with a greater resolving power than light had been demonstrated using images of cotton fibers as a test sample. In the following decades, the imaging capabilities of transmission electron microscopy were refined, making the technology useful in studying biological samples. After the first electron microscope was introduced in Germany in 1939, further development was delayed by World War II, in which a key laboratory was bombed and two researchers died. After the war, the first electron microscope with 100k magnification was introduced. Its fundamental multistage design can still be found in modern transmission electron microscopy.
As TEM technology matured, a related technology, scanning transmission electron microscopy (STEM), was perfected in the 1970s. The development of the field emission gun and an improved objective lens enabled the imaging of atoms using STEMs. Much of the development of STEM technology has come from advances in transmission electron microscopy.
TEMs usually incorporate three lens stages: the condenser lens, the lens, and the projector lens. The primary electron beam is formed by the condenser lens, while the objective lens focuses the beam as it passes through the sample. The projection lens expands the beam and projects it onto an imaging device, such as an electronic screen or sheet of film. Other specialized lenses are used to correct for beam distortions. Energy filtering is also used to correct chromatic aberration, a form of distortion caused by a lens’s inability to focus all the colors of the spectrum to the same point of convergence.
While various transmission electron microscopy systems differ in their specific designs, they have several components and phases in common. The first of these is a vacuum system that generates the flow of electrons and incorporates electrostatic plates and lenses with which the operator can direct the beam. The sample stage includes airlocks that allow the object to be studied to be placed in the stream. The mechanisms at this stage allow you to position the specimen for optimal viewing. An electron gun is used to “pump” the flow of electrons through the TEM. Finally, an electronic lens, acting similar to an optical lens, reproduces the plane of the object.
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