Electron Microscopes

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Electron Microscopes

• What is an electron Microscope?
• How does it differ from an ordinary microscope?
• What can you see with an electron microscope?

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This presentation has slides and animations and
links to other websites. Before proceeding, just
a few notes
Electron Microscopes were developed due to the
limitations of Light Microscopes which are
limited by the physics of light to 500x or 1000x
magnification and a resolution of 0.2
micrometers. In the early 1930's this theoretical
limit had been reached and there was a scientific
desire to see the fine details of the interior
structures of organic cells (nucleus,
mitochondria...etc.). This required 10,000x plus
magnification which was just not possible using
Light Microscopes. ... continued on next slide
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The Transmission Electron Microscope (TEM) was
the first type of Electron Microscope to be
developed and is patterned exactly on the Light
Transmission Microscope except that a focused
beam of electrons is used instead of light to
"see through" the specimen. It was developed by
Max Knoll and Ernst Ruska in Germany in 1931.The
first Scanning Electron Microscope (SEM) debuted
in 1942 with the first commercial instruments
around 1965. Its late development was due to the
electronics involved in "scanning" the beam of
electrons across the sample.
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Click on the button to go to the Museum of
Science, in Boston. there is an animation and a
slide show.
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Theres only a few key facts. The TEM or SEM
uses electrons, not light rays. The beam is
focussed by magnets. Electrons are a lot smaller
than light rays so the resolution is much better.
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A quick recap
The light rays are going upwards, through the
specimen. You can see by reflected light as well,
but illumination is a bit awkward.
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The electron beam is going downwards through the
specimen. The electrons hitting the bottom screen
make it glow like in a TV set, so then visible
light travels up towards the eye.
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This site has some clear diagrams and quite a
good photo gallery of real samples.
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Lets go to the University of Hawaii for some
pictures.
Note I dont think the colours are real. You
dont get coloured electrons. The images must
have been treated somehow to produce false
colour. The owner of this site is probably a
bit flippant. The pictures are impressive though.
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You might find this site a reasonable challenge.
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On this next site, (University of Oxford, dept of
Material Science) only one operator can operate
the SEM at any one time. At the time of writing
this it was too early to book the instrument so
it might be available, it might not.
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OK, for those who have been, well done for
cooperating to get the most from todays
activity. If theres time, take a note of some
of the URLs so you can explore a bit more about
this at home. I can send you details of this (and
all resources used in any lesson) if you would
like. E-mail me on mothi_at_rydehigh.iow.sch.uk