Stereo Scan 440 - DCU

3-8 Chapter 3 Advanced Operation
Specimen Tilt
Tilting the specimen can greatly affect the SEM image, not only by changing the
area excited but also by altering the zone of secondary electron emission. The
size of this zone varies with the angle at which the primary beam strikes the
specimen. When the specimen surface is perpendicular to the beam, the zone
from which secondary electrons are emitted is smaller than when the specimen
surface is tilted. Since more secondary electrons are emitted. the tilted surface
gives a brighter signal. Tilting in the range 20 to 40° gives the best result. Very
often, a small amount of tilt adds some depth to the final image which gives more
visual appeal than a flat image.
Other Parameters
In addition to the parameters mentioned previously. the following should all be
checked:-
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Electton gun con-ectly aligned
Stigmators correctly adjusted
Aperture centred
Correct film speed selected
Gamma and derivative as required
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Stereoscan 440 Operator Manual
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