3 - The electron microscope family

Summary

Introduction

Just as ‘light microscope’ is a generic term covering a range of instruments for producing magnified images using glass lenses and visible or ultra violet light, so the name ‘electron microscope’ does not refer to a specific design of instrument but to a family of instruments which produce magnified images by the use of electrostatic or electromagnetic lenses with fast-moving electrons as illumination. They all share the ability to give images of high or very high resolution over a very useful depth of field.

Within the electron microscope family there are two well-defined ranges of microscope, corresponding to transmission and reflection (metallurgical) light microscopes, which look directly at the internal structure of translucent specimens and the outside features of bulk material, respectively.

The transmission electron microscope (TEM) is a direct derivative of the compound light microscope, making use of the shorter wavelength electron illumination. In its simplest form its magnification is achieved by exactly the same lens arrangement as in its light counterpart. It has also been developed further to make fuller use of the special properties of electron illumination; principally the higher resolution, but also the ability to carry out various forms of elemental and crystallographic microanalysis. Its variants include higher voltage and higher resolution instruments (HVEM and HREM) and, with the addition of probe-forming and scanning facilities, the very versatile analytical electron microscope (AEM).

The electronic equivalent of the metallurgical or reflected light microscope, used to study the outside of specimens rather than their internal arrangement, is the scanning electron microscope (SEM).