MATTER LogoIntroduction to Electron Microscopes

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Scanning Electron Microscope (SEM) > Overview of the SEM

Description of Flash Animation

This animation simulates a Scanning Electron Microscope.

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Is the SEM a real-time instrument? Is it displaying the intensity of one pixel before it moves on to the next?

Assume that the slowest link in the chain of events is the flight of the secondary electron (with kinetic energy of, say, 10eV) from the specimen to the detector (perhaps 30mm).

Is its flight time longer or shorter than the time per pixel when the beam is scanning 1,000 x 1,000 pixels at 50 frames per second?

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An electron gun produces an electron beam of energy of up to 40keV. Several electromagnetic lenses then focus a fine beam (~2nm) in diameter on the specimen. The electron beam is scanned across the specimen by scan coils while a detector measures the radiation emitted from the specimen. At the same time the spot at the cathode ray tube (CRT) is scanned across the screen while the brightness of the spot is modulated by the amplified current from the detector. In this way, a picture is built up of the variation of the detector signal across the specimen.


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