Electron Microscopy

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Electron Microscopy
Transmission/Tunnelling Electron Microscope (TEM)
Used to study details of the specimen internal structure
Specimen is dehydrated, sliced with diamond/glass knife, impregnated with heavy metal stain,
electrons pass through lightly/non-stained parts.
Supplies images of even higher magnification than the SEM, but it requires ultra thin sample
specimens. A TEM can show details as small as a single column of atoms.
Sample preparation is longer and more difficult than that for SEM and includes additional steps
Specimen preparation for TEM includes eight major steps: Cleaning, primary fixation, rinsing,
secondary fixation, dehydration, and infiltration with a transitional solvent, infiltration with resin and
embedding, and sectioning with staining.
Scanning Electron Microscope (SE M)
Used to produce 3D images of the specimen surface
Specimen is impregnated with heavy metal stain, electrons reflected from surface
Large depth of field, which means, the area of the sample that can be viewed in focus at the same
time is actually quite large
SEM has also the advantage that the range of magnification is relatively wide allowing the
investigator to easily focus in on an area of interest on a specimen that was initially scanned at a
lower magnification.
The three-dimensional appearing images may be more appealing to the human eye than the
two-dimensional images obtained with a transmission electron microscope. Therefore, an
investigator may find it easier to interpret SEM images.
The number of steps involved for preparing specimens for SEM investigation is lower and thus the
entire process is less time consuming than the preparation of samples for investigation with a TEM.
SEM specimen preparation harbours various risk factors that can easily distort the integrity and
ultrastructure of the sample
The basic steps involved in SEM sample preparation include surface cleaning, stabilizing the sample
with a fixative, rinsing, dehydrating, drying, mounting the specimen on a metal holder, and coating
the sample with a layer of a material that is electrically conductive
David Shaw


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