1zIUK2Y

DIATOMS UNDER
THE ELECTRON
MICROSCOPE
Diatoms are a great factor in the ecosystem yet
they are too small to be visible with naked eye.
Even with the best optical microscope, we cannot
come near enough. The whole diversity and
richness of complicated structures hidden in the
siliceous skeleton of these algae could be revealed
only by scanning electron microscope (SEM).
There is no doubt SEM is a wonderful tool
covering almost all the needs that appear in the
research work on surface structures of diatoms.
Modern commercial SEM microscopes enable
magnifications from approximately 10 to
1,000,000 times allowing image resolution to
1 nm. However, it must be stressed that real magnification
as well as real resolution of micrograph
depend not only upon the capacity of the microscope
but to a high degree also upon the sample
quality as well as some other factors.
Electronic microscope is sizable and complicated
machine. Along with a number of electric and
electronic complexes it includes also a complicated
vacuum system. In the microscope column
where is also a chamber for the sample, a series
of pumps is maintaining vacuum which enables
forming and managing of the electron beam. That
fore the sample which we will investigate must be
stable in vacuum, resistant to bombardment with
electrons within electron beam and has to have
a clean surface, while high magnifications reveal
even the finest muck.
In this kind of microscope the image doesn’t
appear at a time like we are used in everyday life,
rather it is appearing gradually, step by step. Electron
beam is focused to a spot in the sample surface.
Microscope tilting system scans the electron
beam in a raster fashion over a rectangular area
of the sample surface. The signal emerging from
the collision of the beam with the surface of the
sample investigated is transmitting from detectors
via electronic amplifiers and filters to the
screen where — point after point and row after
row — the picture of the investigated structure is
constituted. We could understand that the quality,
resolution and communication value of the
image are determined by the size of image points
and by the density of the raster along which the
beam is moving; magnification, however, results
from the ratio of the dimensions of the raster on
the specimen and the raster on the display device.
In other words, magnification tells us, how many
times alga, which we are observing is smaller
from its image on the screen.
Dr. Kazimir Drašlar
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