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Proper specimen
preparation is an essential factor
in achieving quality electron
microscopy results.
As such, specimen
preparation is an important
consideration for LVEM5 imaging as
well.
TEM:
Typically, the
preparation steps are the same for
traditional TEM and low voltage TEM,
with 2 notable exceptions:
Staining:
Many samples lack
the inherent density differences
necessary to provide adequate
contrast using traditional TEM.
Stains (most often heavy metals such
as uranyl acetate or osmium
tetroxide are used) are added to the
samples in order to enhance the
contrast. The benefit of staining is
increased density gradients to the
extent that traditional TEM can
provide contrasted images. The
drawbacks, aside from the additional
preparation step and the fact that
stains are toxic, are staining
artifacts (features that are not
inherent to the sample but caused by
stains), sample distortion (when
staining leads to undesired changes
in the sample) and may ruin the
sample entirely.
The LVEM5
requires no staining
to achieve highly contrasted
imaging. The reduced accelerating
voltage leads to a greater degree of
electron scattering so that even
small density differences are
measurable at the imaging interface.
Thin-sectioning:
The penetration
ability of a 5 kV beam is less than
that of a higher kV beam. To
facilitate the passage of the beam
through the specimen we encourage
the thinnest sectioning possible.
Many ultramicrotomists (an
ultramicrotome is a equipment that
cuts ultra thin sections of samples)
are comfortable sectioning at 100 nm
or thicker, but the LVEM5 demands
sections in the range of 20 to 50
nm. The specific ideal level – to
achieve the best resolution – is
dependant on the sample material.
For certain, not all materials can
be sectioned at this level but in
our experience most can be. If you
question the ability to cut your
sections at this level, please
contact us so we can share our
experiences with your sample types
and if there is any remaining doubt
we would be happy to receive a block
from you so that we may test the
sectioning and imaging of your
samples.
TEM
Grid support coatings:
In order to keep
the overall penetration volume to a
minimum, we encourage the use of
unsupported grids (sample is laid on
a bare grid) or, where support is
essential, it is provided by a thin
carbon layer (not Formvar which is
less electron transparent than
carbon).
SEM:
Like conventional
SEM, the LVEM5’s SEM mode provides
the best results from conductive
samples or samples that have been
coated with a very thin conductive
layer.
For the LVEM5,
SEM samples must fit into the
standard TEM grid (we have also
fashioned a custom LVEM5 SEM stub)
and be less than 1 mm in height.
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