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instrumentation particulars) and a backscattered electron
image obtained. These images are sensitive to the crystallogra-
phy of the sample and the grain orientation will determine the
backscatter coefficient leading to beautiful images of the sam-
ple grain structure. In many cases, subsurface scratches and
other sample preparation artifacts will be visible in this type of
image that is not seen in secondary electron images or optical
microscopy.. Figure 29.16 is an example of a high-quality
metallographically polished sample image of a dual phase
stainless steel. Note that the sample as polished with no col-
loidal silica polishing exhibits a large number of subsurface
scratches that limit the EBSD results. After colloidal polishing
for a few hours the difference in surface condition is readily
apparent. Generally, results like these are a good predictor of a
successful EBSD analysis.
Align Sample in the SEM
After the sample is imaged and the sample preparation found
to be of good quality, the sample orientation within the SEM
must be considered. EBSD is often used to determine the tex-
ture or distribution of crystallographic orientations with
respect to some external frame of reference related to the
sample or how the sample was processed. A good example of
this is when metal plates are produced by mechanical rolling.
It is often desired to determine the texture of the sample with
respect to the rolling direction, the transverse direction, or
the plate normal direction. Or for the case where only one
direction of the sample is expected to show a preferred tex-
ture, as in a wire where the preferred crystallographic direc-
tion lies along the wire axis, this axis should be mounted
parallel to one of the primary directions in the SEM. Other
times it is an assessment of the crystallographic growth direc-
tion and thus the sample should be carefully aligned so that
the growth direction corresponds to one of the primary axes
of the scanned image. Thus, the sample must be carefully
aligned in the SEM, and one must be aware of the tilt axis of
the SEM stage and the directions of the x- and y-stage move-
ments (Britton et al. 2016 ).
Once the external reference directions have been set par-
allel to the microscope reference direction, then the sample
still must be tilted for EBSD examination. For the best EBSD
the sample must be tilted to about 70° with respect to the
electron beam. This tilt is best performed with a view of the
inside of the chamber with a video image so that the high tilt
does not result in the sample contacting the microscope pole
piece or other hard expensive components of the micro-
scope. Once the sample is tilted to the appropriate angle and
the area of interest brought under the electron beam then
the EBSD camera must be moved into position. The best
camera position is close to the sample so that the camera
captures about 60–90° of the pattern. Also the brightest part
of the pattern should be located about one third of the total
camera area down from the top of the active area. This posi-
tion will give the best possibility of good patterns being
obtained.Check for EBSD Patterns
Once the sample has been prepared appropriately and posi-
tioned correctly within the SEM, it is sensible to have a quick
collection of a few randomly located points to ensure that
good patterns can be obtained. This is the opportunity to
optimize the SEM parameters for the acquisition. This is also
an excellent opportunity to determine that the phases
selected for indexing are chosen correctly. Correct comple-
tion of these steps will go a long way to ensure that a quality
orientation map can be collected.
The first step is to select correct microscope parameters
for EBSD acquisition. The accelerating voltage is not
extremely critical for success but should be set somewhere
between 10 and 20 kV depending on the sample that is to be
analyzed. The other microscope-critical setting is the current
in the electron beam. In general, the best choice is the highest
beam current that the microscope can generate consistentab. Fig. 29.16 Backscattered electron images of metallographically
polished dual phase steel for EBSD analysis. Short working distance
backscattered imaging results in excellent crystallographic contrast. a
Standard metallographic practice shows numerous fine scratches that
are visible in channeling contrast. EBSD mapping is still possible but
not optimal. b Standard practice plus 4 h of vibratory polishing on col-
loidal silica results in a higher-quality surface finish and optimal EBSD
mapping (Bar = 20 μm)
29.2 · Electron Backscatter Diffraction in the Scanning Electron Microscope