What is a Transmission Electron Microscope (TEM)?
A transmission electron microscope (TEM) generates a beam of electrons which is transmitted
through an ultra-thin (~50 nm) sample. Some regions of the sample will let the electrons
go through, while others will not. The electrons passing through the specimen are
focused into an image that forms onto a fluorescent screen where it can be viewed
and recorded with a CCD camera or photographic film. The image consists of shades
of grey, with darker features corresponding to regions of the sample that have absorbed
the electrons from the beam.
Spatial resolution is how close two features can be within an image and be recorded
as distinct. The best spatial resolution (~0.5 nm) of TEM far surpasses that of light
microscopes (200 nm); and therefore the TEM reveals features of samples that light
microscopes cannot reveal.
TEM’s tungsten filament is the electron emission source and a high tension source
that strips the electrons from the filament. The electrons then travels through the
column under high vacuum. Attached to the column is a port to insert the sample into
the electron beam. Attached to the specimen port are control knobs to move the sample
in the beam path. Electromagnetic lenses focus the electron beam and electrostatic
plates allow the operator to guide the beam as required. Photographic film or CCD
devices are used to record the image from the electrons passing through the sample.
The TEM is used by biologist to investigate cellular features that are not visible
by light microscopy, such as ribosomes and small vesicles. Materials scientists use
the TEM to probe the fine architectures of materials such as nanoparticles.
Major Features of the Jeol JEM-1200 EX II
Tungsten filament and high tension operating between 40 and 120 kV
Magnification range: 50X-500,0000X
Maximum resolution under optimal condition: 0.35 nm
Images can be recorded with an AMT (Advanced Microscopy Techniques Corp.) CCD digital