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3.2 Mounting a Specimen
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3.2 Mounting a Specimen
3.2.1 Precautions Concerning Specimen Preparation
During specimen preparation, observe the following.
(1) Wear clean gloves when exchanging specimens. Holding the specimen or specimen stub
with bare hands should be avoided.
(2) Avoid using an excessive amount of conductive paste to fix a specimen on the specimen
stub. Ensure that the paste has dried before placing the specimen in the chamber. Too
much paste can release a large quantity of gas into the vacuum, which can cause the
vacuum level to decline and result in contamination.
(3) When using double-sided adhesive tape to fix a specimen to the stub, use the least possible
amount so as to minimize out-gassing. The use of double-sided adhesive tape may also
cause specimen drift.
(4) Mounting a specimen containing an excessive amount of water or oil can cause
contamination in the column, which should be avoided.
3.2.2 Specimen Preparation according to Material
The method of specimen preparation varies with different materials. Listed below are typical
preparation methods for various types of specimens.
(1) Conductive specimens such as metals:
These types of specimens can be observed without preparation. However, coating with
heavy metals by using a vacuum evaporator, an ion sputtering or magnetron-sputtering unit
may result in better contrast.
(2) Non-conductive specimens such as semiconductors, fibrous specimens and polymeric
materials:
When imaging a specimen without coating, the recommended procedure is to use either the
low-vacuum mode or a low accelerating voltage. If the specimen needs to be imaged at high
magnification, mount the specimen onto a stub, and then coat the specimen with a metal
coating using a recommended procedure. If a high magnification image is required of micro-
structures, the metal coating may be visible. Care should be taken to avoid this problem.
(3) Biological specimens:
Biological specimens can be observed in the low-vacuum mode without prior treatment. For
high magnification observation, dry the specimen by using a method such as critical point
drying, freeze drying or other drying techniques, then coat the specimen with conductive
material.
(4) X-ray analysis specimens:
Generally, polish the surface of the specimen, then fix it to the specimen stub using carbon
paste. Non-conductive specimens should be coated with carbon using a vacuum
evaporator.