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What is...
... A TEM? ...A(n) SEM? ...A cryostat?
What is a TEM?
A Transmission Electron Microscope (TEM) is a very powerful magnifying tool that permits magnification and resolution of images up to 1000 times greater than the best light microscope.
A TEM works very much like a light microscope, except instead of using a beam of light to penetrate a sample it uses a beam of electrons. With an electron beam, images of higher magnification and resolution can be achieved because electrons can travel at much shorter wavelengths than light. This permits up to 1,000 times greater magnification and resolution of images by an electron microscope than the best light microscope. The JEOL 1200X TEM in our facility is capable of magnifications of up to 500,000x.
Biological samples for TEM are usually prepared in resin for being sliced into ultra-thin sections with a glass or diamond knife. After treatment with heavy metal compounds that stain the various microstructures of the specimen, prepared sections are placed into the column of microscope. Images are obtained by permitting a beam of electrons to transmit the section to produce a two-dimensional image on a phosphorescent screen below the specimen. The areas with higher concentrations of heavy metal stains appear electro-dense (darker) compared to the areas with lower concentration of stain (brighter), thus creating contrast in images. The image can be viewed on the screen, recorded on photographic films, or digitally captured for analysis.
What is a(n) SEM?
A Scanning Electron Microscope (SEM) is a very useful tool with applications in various fields, such as biological and material sciences.
The SEM uses a fine beam of electrons to scan the surface of a specimen to generate electrons from its surface. These secondary electrons are then collected by a detector and processed to form images on a monitor for visualization, and to be captured on photographic films or with a digital imaging system.
The secondary electrons are not the only signals generated by beam bombarding a specimen. Backscattered electrons and X-rays are also produced and can be used to gather data about the specimen’s atomic components and the relative location of those components in the sample.
The JEOL JSM 5400 Scanning Electron Microscope in our facility is capable of magnification up to 300,000x. It can perform conventional SEM (signals from secondary electrons), backscatter microscopy (signal from backscattered electrons), and X-ray microanalysis. This microscope is also equipped with cryotrans system, which permits cryo-SEM. The image acquisition is digitized.
What is a cryostat?
A cryostat is a microtome (mechanical knife) used for sectioning frozen tissues. The knife and all accessory parts are maintained inside a chamber at a temperature below freezing point, usually around minus 20 C.