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    Both types of EM use some sort of metal coating, therefore how do you explain that one type (transmission) produces a two dimensional image and the other type (scanning) produces a three dimensional image?

    © BrainMass Inc. brainmass.com December 24, 2021, 4:54 pm ad1c9bdddf
    https://brainmass.com/biology/cell-structure/scanning-electron-transmission-electron-microscope-14869

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    1. Both types of EM use some sort of metal coating, therefore how do you explain that one type (transmission) produces a two dimensional image and the other type (scanning) produces a three dimensional image."

    Transmission electron microscope (TEM): In the TEM, an electron beam is passed through a very thin (~0.1 micrometres) specimen and the "image" is detected on a phosphorescent screen or on photographic film. In order to achieve such thin specimens, cells are embedded in a plastic and cut on a special cutting device called a microtome. The tiny sections are collected on small mesh grids and "stained" with heavy metal salts. The heavy metal salts are used to give certain biological structures electron opacity or contrast.

    Scanning electron microscope (SEM): In the SEM, electrons are "bounced off" the surface of the specimen. A special type of detector is used to "pick up" the scattered electrons (called secondary electrons) and the "signal" is translated into a "video" image. Most biological specimens are electron-lucent (don't stop or deflect electrons very well) and so the specimens are mounted on a metal "stub" and are coated with a very thin layer of evaporated metal.So, in a nutshell, in the TEM and the SEM the electron detection devices are different and more importantly are located at different positions within the electron microscopes. In the TEM the electrons are passed through the specimen giving you a 2D image and in the SEM electrons are bounced off the surface of the specimen giving you a 3D image. Because cells have only trace amounts of metals, we need to "coat" biological specimens with evaporated metal or "stain" biological specimens with heavy metal salts to give them "reflective properties" in the SEM or "contrast" in the TEM.

    I hope this helps. Take care.

    This content was COPIED from BrainMass.com - View the original, and get the already-completed solution here!

    © BrainMass Inc. brainmass.com December 24, 2021, 4:54 pm ad1c9bdddf>
    https://brainmass.com/biology/cell-structure/scanning-electron-transmission-electron-microscope-14869

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