So what makes our SEM special?
The conventional type of SEM uses a high vacuum with pressures as low as 10-5
Torr. This means that to get a good image, the specimens to be viewed must be
electrically conductive, and devoid of water and solvents that could vaporize in
the vacuum causing problems in the column. Therefore, biological tissue samples
have to be absolutely dry before they could be put in the conventional SEM. As
you know, being devoid of water is not compatible with living samples!
| To
preserve the 3-D structure of biological samples, the samples have to be
carefully dried using liquid carbon dioxide in a machine called a critical point
dryer. Then the samples have to be coated with a thin layer of metal
such as gold to make the sample electrically conductive. All this takes a lot of
time - many hours. |
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Our SEM is special in that it images the sample under different
vacuum conditions. The JEOL JSM-5800LV scanning electron microscope is called a
Low Vacuum SEM and it can work with a maximum operating pressure of up to 2 - 4
Torr (250 Pascals)! This means that we can look at wet samples quickly in the
SEM. The procedure is that we cut a piece of tissue, stick it down on tape and
it's ready for viewing in the SEM. Our SEM can also view samples
in the conventional mode, but they need to be prepared as for conventional SEMs.
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The low vacuum SEM has a panel on the front which carefully controls
the vacuum pressure. This picture shows the front panel of the SEM. It is set to 80
Pascals using the controller button, and is in the low vacuum mode as evidenced
by the LV button being lit. If the SEM was in the high vacuum mode, the LV
button would not be lit and would read 0 Pascals when under high vacuum.
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SEM
Web Site created and maintained by
David J. Wright and Shirley J. Wright
Department of Biology, The University of
Dayton.
All images and text are copyright protected. All rights reserved.
Copyright © 1999 Shirley
J. Wright (Shirley.Wright@notes.udayton.edu)
