Stigmation And Focus Wobbles; Saving An Image - Zeiss ?IGMA VP-FE-SEM User Manual

1.3.8 Stigmation and Focus Wobble.
Producing well-focused images, especially at higher
magnifications, requires the cross-section of the electron beam to be
circular. The process of circularizing the electron beam is called
stigmation and it is carried out using various electromagnetic coils called
stigmators. Improper beam circularization is referred to as astigmatism
and can most easily be observed as directional fuzziness in the produced
image. Stigmation is performed much in the same way that focusing is,
except the process is done along two orthogonal axes and thus requires
two knobs instead of one. To remedy astigmatism, first magnify and focus
on a part of the sample that has a great degree of contrast. Once selected,
locate the knobs labelled Stigmator X and Stigmator Y at the top left of
the Zeiss SEM Keyboard. While observing areas of high contrast, rotate
these stigmator knobs independently until the image appears to have no
directional fuzziness. Try refocusing the image after correcting for any
astigmatism and observing the results.
Often times the image will appear to move when the operator
attempts to focus it. This phenomenon is referred to focus wobble and
occurs when the various electron beam apertures in the focusing column
are in poor alignment. To correct for focus wobble, find a part of the
image that has a high amount of contrast. Focus upon the selected scene
and correct for any apparent beam astigmatism. Once sufficiently focused,
locate and press the button labelled Wobble on the top portion of the Zeiss
SEM Keyboard. A reduced raster box will appear showing an
amplification of the current focus wobble. Fixing the wobble is done using
the Aperture X and Aperture Y control knobs on the top of the SEM
keyboard. The goal is to use these knobs to stop the image from wobbling.
If done correctly, the image will simply go in and out of focus while
remaining in place. Fixing focus wobble takes a considerable amount of
practice to master.

1.3.9 Saving an Image

Capturing and saving an image involves freezing the scan process
on a single frame, and then exporting that frame to an image file. As
previously stated (Section 1.3.4), the detector scan speed should be fairly
SEM Quick Start
Revision No.2
May 2014
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