Gatan 656, User Manual, Page: 23 / 49

Operation
Dimple Grinder User’s Guide 13
4.2 Preparing the Specimen
Here are some initial criteria that should be met to successfully prepare a speci-
men for dimpling:
• Starting specimens should have perfectly parallel faces prior to dimpling.
• The glue layer should be of uniform thickness.
• The specimen surface in contact with the specimen mount should have a
good finish.
Thickness Issues
Any variation of thickness of the starting disc can easily be determined by visu-
ally noting the change in focus across the disc when observed by the optical
microscope. A deviation of 1° will result in approximately a 25-µm overesti-
mate of the thickness of a 3-mm disc when measured with a micrometer—
clearly unacceptable if attempting to produce a 5-µm dimpled specimen.
Regardless of the dimpling method used, accurate determination of the recom-
mended initial 80-µm thickness is necessary. This thickness will reduce the time
needed for dimpling, yet still provide a sufficiently strong supporting rim that
allows for subsequent ion milling at low angles.
Dimpling Techniques
For normal dimpling, disc grinding can be completed using 5-µm paper but for
thinning of specimens to less than 20 µm, the final stage of disc grinding should
be done with a 3-µm diamond paste.
If mechanically thinning to electron transparency, the disc should be finished on
a polishing cloth with 3-µm diamond paste followed with 0.05-µm alumina.
Alternatively, a good surface finish can be obtained for the flat side using the
dimple polishing technique (see Section 4.8).
4.3 Specimen Mounting
The specimen is normally fixed to the mount with a low melting-point, thermo-
plastic wax. The wax supplied by Gatan is liquid at 130 °C.
Note : If the temperature of the wax is allowed to exceed 130 °C it will begin to
decompose. While this may not appear to affect its adhesive strength, the speci-
men may become detached later, during grinding. (The Gatan Specimen Mount-
ing Hot Plate is recommended.)
Care must also be taken to keep the wax perfectly clean and free from dirt. Par-
ticles as small as a few microns between the specimen and the mount will
adversely affect performance.