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4. Interactions occur inside the irradiated sample, affecting the electron beam
These interactions and effects are detected and transformed into an image
The above steps are carried out in all EMs regardless of type. A more specific treatment of the
workings of two different types of EMs are described in more detail:
Transmission Electron Microscope
Scanning Electron Microscope
Transmission Electron Microscope (TEM)
TEMs are patterned after Transmission Light Microscopes and will yield similar information.
Morphology
The size, shape and arrangement of the particles which make up the specimen as well
as their relationship to each other on the scale of atomic diameters.
Crystallographic Information
The arrangement of atoms in the specimen and their degree of order, detection of
atomic-scale defects in areas a few nanometers in diameter
Compositional Information (if so equipped)
The elements and compounds the sample is composed of and their relative ratios, in
areas a few nanometers in diameter
A TEM works much like a slide projector. A projector shines a beam of light through
(transmits) the slide, as the light passes through it is affected by the structures and objects on
the slide. These effects result in only certain parts of the light beam being transmitted through
certain parts of the slide. This transmitted beam is then projected onto the viewing screen,
forming an enlarged image of the slide.
TEMs work the same way except that they shine a
beam of electrons (like the light) through the
specimen(like the slide). Whatever part is transmitted
is projected onto a phosphor screen for the user to
see. A more technical explanation of a typical TEMs
workings is as follows (refer to the diagram below):
1. The "Virtual Source" at the top represents the
electron gun, producing a stream of
monochromatic electrons.
2. This stream is focused to a small, thin,
coherent beam by the use of condenser lenses
1 and 2. The first lens (usually controlled by
the "spot size knob") largely determines the
"spot size"; the general size range of the final
spot that strikes the sample. The second
lens(usually controlled by the "intensity or