Dr. Travis Rampton, Applications Engineer EDAX
When collecting EBSD data it is important to optimize the detector/camera to obtain the desired information which is usually focused on crystal orientation. However, many factors affect the creation of an EBSD pattern beyond orientation. Some of these are demonstrated in Figure 1. In this blog post we will examine some of those factors. In doing so we will also take advantage of PRIAS imaging to illustrate a few of the different effects.
Figure 1: Examples of EBSD patterns collected under varied conditions. The pattern on the left represents the ideal pattern, while the one in the middle is a mixed pattern and the pattern on the right is an unprocessed image.
A list of a few of the most important factors that affect EBSD patterns is given here. The author recognizes that all effects may not be accounted for and invites your additions in the comments section of this blog.
- SEM kV and beam current
- EBSD camera parameters (gain, exposure, image processing)
- Sample/detector geometry
- Material density
- Surface structures (topography, defects, quality)
- Crystal structure/orientation
- Interaction volume
- Magnetic domains
Not only do the listed factors affect entire EBSD patterns, but some manifest more apparently in certain regions of the image. This is often best manifested in geological samples containing topography, atomic differences, and orientation contrast (see Figure 2).
Figure 2: (Left) PRIAS image taken from the top of the EBSD detector, showing surface topography; (middle) PRIAS image taken from the center for the detector, showing orientation contrast; (right) PRIAS image taken from the bottom of the detector, showing some atomic difference.
Some of the factors that affect EBSD patterns are apparent enough that they can be seen by eye; others are so subtle that they require more sensitive techniques. The final example that will be shown in this post is of magnetic domains. The effect of magnetic domains is not visible by just looking at the EBSD patterns, however, PRIAS imaging makes this effect visible. For this example we will look at a grain oriented electrical steel. Figure 3 shows distinct magnetic regions especially when compared to the SEM image.
Figure 3: (left) SEM image taken of steel and (right) PRIAS image taken from the left side of the detector showing magnetic domains.
The images in Figure 3 give one view of the magnetic domains. An additional set of views is seen in the full 5 x 5 array of PRIAS images shown in Figure 4. A close inspection of all 25 images reveals several varying structures. The differences between all of the ROIs is not fully understood at this time and is the subject of an ongoing study.
Figure 4: 5 x 5 grid of PRIAS images taken from grain oriented electrical steel. Each ROI image shows different structure.
These examples represent just a few of the factors that affect the formation of an EBSD pattern. Often these effects can be seen in the patterns alone, but other times PRIAS imaging is required for clear visualization. While EBSD is a reliable method for measuring crystallographic orientation and phase information there is often much more information in the EBSD pattern. So I pose the question, what’s in your EBSD pattern?