Resolution of an Electron Microscope
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| Bibliographic Entry | Result (w/surrounding text) |
Standardized Result |
|---|---|---|
| Curtis, Helena. Biology: 5th Edition. New York: Worth, 1989: 96. | "TEM at present afforts a resolving power of about 0.2 nm…. Although the resolving power of the STM is only about 10 nm, this instrument has become a valuable tool for biologists." | 0.2 nm (TEM) 10 nm (STM) |
| Slayter, Elizabeth M. "Electron Microscope." Grolier Multimedia Encyclopedia. Grolier, 1997. | "[TEM] resolutions of 2 nm are common…. Although [STM] resolution is limited to 10 nm, readily interpretable images of surface topography emerge." | 2 nm (TEM) 10 nm (STM) |
| Macmillan Encyclopedia of Physics. New York: Simon & Schuster, 1996: 452-454. | "The smallest distance that can be resolved with a TEM is approximately 0.2-0.5 nm…. A typical [STM] resolution of several tenths of a nm can be achieved." | 0.2–0.5 nm (TEM) ~ 0.1 nm (STM) |
| Kane, Joseph & Morton Sternheim. Physics. New York: Wiley, 1978: 620. | "In practice, the resolution of the TEM is limited to about 0.2 nm." | 0.2 nm (TEM) |
| Robertson, Brian. What are Electron Microscopes? Center for Materials Research and Analysis. University of Nebraska at Lincoln. | "Electron Microscopes were developed due to the limitations of Light Microscopes which are limited by the physics of light to 500x or 1000x magnification and a resolution of 0.2 micrometers." | < 200 nm |
An electron microscope is an instrument that uses electrons instead of light for the imaging of objects. The development of the transmission electron microscope was based on theoretical work done by Louis de Broglie, who found that wavelength is inversely proportional to momentum. In 1926, Hans Busch discovered that magnetic fields could act as lenses by causing electron beams to converge to a focus. A few years later, Max Knoll and Ernst Ruska made the first modern prototype of an electron microscope.
There are two types of electron microscopes: the transmission (TEM) and the scanning tunneling (STM) electron microscope. In a TEM, a monochromatic beam of electrons is accelerated through a potential of 40 to 100 kilovolts (kV) and passed through a strong magnetic field that acts as a lens. The resolution of a modern TEM is about 0.2 nm. This is the typical separation between two atoms in a solid. This resolution is 1,000 times greater than a light microscope and about 500,000 times greater than that of a human eye. The STM is similar to the TEM except for the fact that it causes an electron beam to scan rapidly over the surface of the sample and yields an image of the topography of the surface. The resolution of a STM is about 10 nm. The resolution is limited by the width of the exciting electron beam and by the interaction volume of electrons in a solid.
Resolution is the finest detail that can be distinguished in an image. The resolving power of a microscope is quite different from its magnification. You can enlarge a photograph indefinitely using more powerful lenses, but the image will blur together and be unreadable. Therefore, increasing the magnification will not improve resolution. The minimum separation (d) that can be resolved by any kind of a microscope is given by the following formula:
d = λ/(2n sinθ)
where n is the refractive index (which is 1 in the vacuum of an electron microscope) and λ is the wavelength. Since resolution and d are inversely proportional, this formula suggests that they way to improve resolution is to use shorter wavelengths and media with larger indices of refraction. The electron microscope exploits these principles by using extremely short wavelengths of accelerated electrons to form high-resolution images.
Today, electron microscopy is widely used in metallurgy, biology, material science, physics, chemistry, and many other technological fields. It has been an integral part in the understanding of the complexities of cellular structure, the fine structure of metals and crystalline materials as well as numerous other areas of the microscopic world.
Ilya Sherman -- 2000
| Bibliographic Entry | Result (w/surrounding text) |
Standardized Result |
|---|---|---|
| "Physics Update." Physics Today. June 2000: 9. | "A million-volt field emission transmission electron microscope (FE-TEM) has been built by a team led by Akira Tonomura at Hitachi's Advanced Research Laboratory in collaboration with the Japan Science and Technology Corp…. [T]he new device can image rows of atoms only half an angstrom apart (thus rivaling scanning tunneling microscopes) and can even take pictures fast enough -- 60 per second -- to make movies of fine gold particles changing their shapes." | < 0.05 nm (FE-TEM) |
Editor's Supplement -- 2000