The Physics Factbook™
Edited by Glenn Elert -- Written by his students
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|Bibliographic Entry||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 |
|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 |
|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 |
~ 0.1 nm
|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 |
|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 electronsinstead of light for the imaging of objects. The development ofthe transmission electron microscope was based on theoreticalwork done by Louis de Broglie, who found that wavelength is inverselyproportional to momentum. In 1926, Hans Busch discovered thatmagnetic fields could act as lenses by causing electron beamsto converge to a focus. A few years later, Max Knoll and ErnstRuska 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. Ina TEM, a monochromatic beam of electrons is accelerated througha potential of 40 to 100 kilovolts (kV) and passed through a strongmagnetic field that acts as a lens. The resolution of a modernTEM is about 0.2 nm. This is the typical separation betweentwo atoms in a solid. This resolution is 1,000 times greater thana light microscope and about 500,000 times greater than that ofa human eye. The STM is similar to the TEM except for the factthat it causes an electron beam to scan rapidly over the surfaceof the sample and yields an image of the topography of the surface.The resolution of a STM is about 10 nm. The resolution islimited by the width of the exciting electron beam and by theinteraction volume of electrons in a solid.
Resolution is the finest detail that can be distinguished inan image. The resolving power of a microscope is quite differentfrom its magnification. You can enlarge a photograph indefinitelyusing more powerful lenses, but the image will blur together andbe unreadable. Therefore, increasing the magnification will notimprove resolution. The minimum separation (d) that canbe resolved by any kind of a microscope is given by the followingformula:
d = λ/(2n sinθ)
where n is the refractive index (which is 1 in the vacuumof an electron microscope) and λ isthe wavelength. Since resolution and d are inversely proportional,this formula suggests that they way to improve resolution is touse shorter wavelengths and media with larger indices of refraction.The electron microscope exploits these principles by using extremelyshort wavelengths of accelerated electrons to form high-resolutionimages.
Today, electron microscopy is widely used in metallurgy, biology,material science, physics, chemistry, and many other technologicalfields. It has been an integral part in the understanding of thecomplexities of cellular structure, the fine structure of metalsand crystalline materials as well as numerous other areas of themicroscopic world.
Ilya Sherman -- 2000
|Bibliographic Entry||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 |
Editor's Supplement -- 2000
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