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Resources

Further Reading

If you are interested in finding out more about scanning electron microscopy, or microscopy in general, the following links will serve useful:

Microscopy Society of America
New England Society for Microscopy
Connecticut Microscopy Society
New York Microscopial Society
SEMTech Solutions Inc.
E.Fjeld Inc.

Definitions

Grass Pollen - 25,000X

For those unfamiliar with the scanning electron microscope and X-Ray analysis, here are a few important words to know:

SEM

Short for Scanning Electron Microscope

Scanning Electron Microscope

The SEM is an instrument that scans an electron beam across the surface of an object. The object's surface is bombarded with electrons, causing electrons to be emitted from the object. Depending on the topography of the object, either more or less electrons are emitted at any given instant. This difference in electron density is analyzed by a detector and mapped onto a CRT monitor, thus creating a black and white image. This whole process, by necessity, must occur under vacuum.

The SEM can be divided into three basic parts:

  1. The Gun - a sharp tungsten filament that emits a stream of electrons. These electrons can be accelerated at different voltages
  2. The Column - contains electromagnetic lenses that make the electron "spot" smaller and the coils that scan the beam over the sample
  3. The Chamber - contains the final lens that focuses the electron beam to produce a sharp image. It also holds the sample on a special stage where it can be seen and moved around.

Magnification of an object is created and controlled by a set of magnetic coils that determine the size of the area being scanned. The larger the area being scanned, the lower the magnification. The smaller the area being scanned, the higher the magnification.

X-Ray Analysis or X-Ray Microanalysis

There are two generally used forms of X-Ray Analysis on Scanning Electron Microscopes. In one form, an X-Ray detector sorts out X-Rays according to their wavelength. In the other, X-Rays are sorted out according to their energy.

At PVD Products we utilize the latter type of detector, which is known as an Energy Dispersive X-Ray Spectrometer or EDS. When the electron beam scans over the object being viewed, it emits not only more electrons that go into imaging, but also X-Rays.

If the SEM has a special detector inside the chamber, these emitted X-Rays can be detected and then sorted according to their discrete energies. Each discrete energy represents an element of the atomic table.

Why is SEM and X-Ray analysis a powerful combination?

Simply because the SEM has the ability to magnify objects many times their size and bring the micro-world into our view. With this view we are not only able to see the micro-structure of the unseen world, but discover the elements that make it up with X-Ray Analysis.