The scanning electron microscope uses high-energy electron beams to create accurate, three-dimensional images of small specimens, such as viruses. Proper sample preparation is crucial, and images are always in black and white.
The scanning electron microscope is a piece of equipment that uses high-energy electron beams to generate information about a microscopy sample. The generated information is then resolved into a sample image. Scanning electron microscopes are up to 250 times more powerful than light microscopes and can magnify images up to 500,000 times.
A standard scanning electron microscope can resolve images of objects as small as five nanometers. A nanometer is one-billionth of a meter, or about four-billionths of an inch. These microscopes can generate accurate images of organisms as small as viruses and even bacteriophages, which are viruses that infect bacteria.
In addition to its ability to magnify such small specimens, another useful feature of the scanning electron microscope is that it can produce three-dimensional images. This is because microscopes have a large depth of field, allowing objects in the background and foreground to stay in focus at the same time. This makes scanning electron microscopy very useful for determining the surface texture and 3D shape of samples.
Because of the way the machine works, proper sample preparation is a vital aspect of scanning electron microscopy. There are two important parts to the preparation. The first is that the samples must be coated with an electrically conductive substance such as gold, platinum or chromium. This is important to reduce the build up of electrostatic charges during the process. The second important aspect is that the samples are examined in a vacuum, which means that they must be completely dry. For this reason, biological samples are chemically fixed with a substance such as formaldehyde to preserve tissue structure.
The operation of the scanning electron microscope involves an electron gun, magnetic lenses and an electron detector. Once the sample is placed on the microscope stage and the process begins, the electron gun starts firing. The gun fires a beam of electrons through an anode, then through two magnetic lenses, and finally the electron detector.
In combination with the microscope’s condenser lens, this process effectively focuses the electron beam so that it can precisely strike the sample. When this happens, the electrons begin interacting with the sample, and detectors in the microscope count the number of interactions that occur. The number of interactions then determines how pixels are displayed on the monitor displaying the images. The more interactions that occur, the brighter the pixels will be. The contrast in the brightness of the pixels makes up the image.
Scanning electron microscope images are generated without the use of light waves; therefore the images are always in black and white. These are highly detailed three-dimensional images, and despite the lack of color, they are extremely accurate. Images can be tinted to make them more vivid and improve contrast.
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