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which are easier for image analysis software to find. It is

possible to adjust the resolution parameters of the Hough

transform to give higher accuracy results, but again at the

expense of time.

The next step is to compare the angles between the bands

in the patterns with a look up table populated with the calcu-

lated values of interplanar angles from a candidate phase

crystal structure. Once a consistent set of indices are found

the pattern is considered to be indexed. No indexing will ever

be perfect so the deviation between the calculated pattern

and the experimentally measured lines is used as a quality

metric that is stored with the data. The orientation of the

crystal at each pixel can be calculated with respect to the axes

of the microscope and then stored.

It is important to store as much data as possible for each

pixel. Sometimes it may be advantageous to store the com-

plete EBSD pattern at each pixel, particularly when one may

wish to reanalyze the data using a different match unit to help

figure out missing pixels that did not index. The data that

should be stored with each pixel at a minimum should

include the pixel coordinates, the phase match, representa-

tion of the pixel orientation, some sort of pattern quality

metric, and the indexing confidence or error. This procedure

of pattern acquisition, line position identification, pattern

indexing, and data storage is repeated for every pixel in the

map area.

29.2.5 Steps in Typical EBSD Measurements

The conduct of an EBSD experiment in order to collect orien-

tation maps or perform phase identification from a crystalline

sample requires that the user complete a number of steps, as

shown in. Fig. 29.15. These steps consist of the following:

1. Prepare Sample—samples must be free of
   polishing-induced damage


2. Align sample in the SEM—select the optimal sample tilt
   and mounting


3. Adjust SEM and set EBSD parameters—select voltage
   and current and detector settings


4. Check for patterns—make sure patterns are the highest
   quality consistent with the needed speed


5. Run automated map—start the EBSD map and monitor
   quality of map in terms of the number of pixels indexed.

Each step in this sequence is necessary to obtaining high-

quality EBSD results and will be considered separately below.

Sample Preparation for EBSD

As in all materials characterization using the SEM, the prepa-

ration of a sample that is representative of the starting mate-

rial is critical to the success of an EBSD measurement.

Although some samples may not require any sample prepara-

tion at all, such as grown thin films on substrates, naturally

occurring crystals, and others, most EBSD samples will

require preparation. The main requirement of sample prepa-

ration for EBSD is that the sample analysis surface is free from

damage associated with the sectioning and polishing steps. In

most cases, this simply implies standard metallographic pol-

ishing techniques applied carefully to the sample. Standard

preparation techniques include sectioning, mounting grind-

ing and final polishing are the starting point for preparing

samples suitable for EBSD.  It is the final polishing step that

must be conducted in a manner that leaves the surface free of

any sectioning damage. As noted previously, like electron

channeling the EBSD pattern originates from a very thin sur-

face layer of the sample. Final polishing with colloidal suspen-

sions, electro-polishing, and ion polishing are all methods

that have been proven effective for EBSD. Chemical etching is

also sometimes useful but should be applied with caution as

the surface topography and any oxide films should be avoided

for the best EBSD results. It is of course quite useful to assess

the microstructure with optical microscopy prior to attempt-

ing any EBSD measurements.

Once the sample is prepared and placed in the SEM cham-

ber it is often possible to assess the odds of success before any

EBSD measurements are made. One of the most helpful

methods is channeling contrast or grain contrast imaging

using short working distances and a solid state back scattered

electron detector. In this method the sample is moved rela-

tively close to the backscatter detector (4–10-mm working

distance depending on the sample and the SEM

Prepare sample

Align sample in SEM

Adjust SEM and set EBSD collection

parameters

Check EBSD pattern quality

Collect EBSD map data

Select display mode for data

. Fig. 29.15 Steps to accomplishing a successful EBSD map. One of
the most important steps is sample preparation; without good sample
preparation, quality EBSD is difficult to achieve

Chapter 29 · Characterizing Crystalline Materials in the SEM