Scanning
Electron
Microscope
Scanning Electron Microscope
Cornell Materials Science and Engineering
An image taken with the SEM
The JEOL JSM-T330A
Operating Principles
An electron microscope uses a focused beam of electrons to obtain much higher magnification than is possible on a conventional light microscopes (the image above has only 100x magnification, which is well within the reach of light microscopy, however, magnification of thousands of times is possible). This increase in magnification is possible because the wavelength of a high-speed electron is much lower than that of visible light, and so much higher resolution can be obtained.
Of course, optics must be employed to reach this magnification, just like the light microscope. Basic physics explains how a magnetic field will bend the path of an electron, so electromagnets are used to focus the beam. Better lenses can be made out of glass than out of magnetic fields, so there are still challenges for perfecting the optics of an electron microscope.
A scanning electron microscope is similar to a light microscope being used in reflection. The major difference is that instead of imaging the entire specimen at once, the electron beam is scanned back and forth over the specimen, imaging only one point at a time (much like how a television works--there is only one electron beam, but it scans every spot on the screen). The interactions of the electrons with the surface are registered, and from this data an image can be constructed.
Links
More information on electron microscopes:
- Microscopy & Imaging Resources: Electron Microscopy - tons of links
- What are Electron Microscopes? - nice concise explanation of electron microscopes
- S.E.M. Sight - very thorough site, check out the section which compares and contrasts the electron microscope and the light microscope
More information from JEOL:
- www.jeol.com
- JEOL Museum - don't worry, you won't find our model here (yet)
- JEOL's links page - lots of good stuff here!