Being stable and highly reproducible, this is a standard resolution test for transmission electron microscopes. Graphitised carbon black.
LATTICE PLANE RESOLUTION TESTS
The resolution of crystal lattice planes is a useful test of the performance of an electron
microscope, particularly mechanical and electrical stability. The crystal spacings are known
accurately from X-ray data, and therefore the high magnification used can be calibrated with
accuracy.
The crystal specimens are mounted on perforated carbon films, and wherever possible, thin
crystals which cross one of the holes should be selected, so that interfering structure from
the support film is not encountered.
Good crystals can usually be located by checking the selected area diffraction pattern -
unless a clear single crystal pattern is obtained the lattice planes will not be observed. When
a suitable crystal has been selected, a very high electron optical magnification should be
used, so that the lattice planes can clearly be resolved on the fluorescent screen under the
viewing telescope. The objective lens focus has to be adjusted carefully to optimise the
contrast. The phase contrast of a given crystal lattice spacing is critically dependent on the
amount of objective lens defocusing.
If the contrast is inadequate a significant improvement may be obtained by defocusing the
condenser lens (reduction of illumination semi-angle).
Further improvement may be brought about by tilting the illuminating beam so that the central
beam and first order diffraction spot are symmetrical about the instrument axis (take care that
the objective aperture is large enough to accept the diffracted beams)
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