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Kikuchi Pattern Indexing

Figure1

Figure 1 Kikuchi indexing window.

The toolbar contains tool buttons to:

When an experimental has been loaded these tool buttons are enabled:

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The controls placed in 6 panes allow to:

Figure2a Figure2b Figure2c

Figure 2a Kikuchi bands angles.

Figure 2b Distances to the origin.

Figure 2c Width of Kikuchi bands.

Figure3a Figure3b

Figure 3a Table of crystals.

Figure 3b Microscope and errors settings.

It is necessary to increase the % distance error when narrow bands are used for the indexing.

Figure4a Figure4b

Figure 4a Options.

Figure 4b Scaling.

With option 1 st quadrant solution only solutions in the first quadrant are displayed.

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Indexing the Kikuchi pattern

In order to index a Kikuchi pattern do the following:

  1. Open the Kikuchi indexing window (Fig. 1).
  2. Load the Kikuchi pattern (Fig. 6).
  3. Set the accelerating accelerating voltage.
  4. Set the camera length.
  5. Set the pattern scale (Fig. 4b).
  6. Adjust the origin, pointing arrows and bands(Fig. 7).
  7. Select the crystal to use for the indexing (Fig. 3a).
  8. Start the indexing process using the search search tool button.
  9. When finished a small stereogram with the possible indexing solutions opens (Fig. 8a).
  10. Select one of the solutions of the stereogram (Fig. 8a) or of the table (Fig. 8b).
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The three colored bands must be aligned on experimental Kikuchi bands and the band center positioned on the Kikuchi pattern origin (i.e. transmitted beam position).

Figure6

Figure 6 Loading the Kikuchi pattern.

Figure7

Figure 7 Bands are aligned using the arrows.

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The accelerating voltage and camera length must be set first (before adjustment of the pointing bands) (Fig. 3b). Adjust the error bars according to the measurements precision. When the indexing window is shown for the first time, the default scale is either mm or nm-1 per pixel. The scale is adjusted using the Scale pane (Fig. 4b).

The origin of the Kikuchi bands can be moved on the DP origin (transmitted beam position) using the green arrow or any combination of Alt, Ctrl, Shift and the arrows keys.

The pointing bands are aligned using their small squares and crosses. They must be positionned to 3 intersecting experimental pairs of Kikuchi lines. The red, green, blue bands on experimental Kikuchi pairs of lines of increasing spacing.

Fine adjustment of the alignment of the bands with the Kikuchi lines is done using the red, green and blue dots.

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Figure8

Figure 8 Adjusting the origin and the pointing bands.

The double arrow measures the distance between 2 known features of the pattern. Then the Scale slider is set to 50 nm-1. Push the

button to set the scale.

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Figure9

Figure 9 The origin and arrows are defined and the scale set.

When necessary this step is better performed before aligning the three bands as the red band must be realigned.

After scaling a scale marker appears in the left bottom corner of the SAED area (Fig. 5).

Figure10

Figure 10 A scale marker indicates that the SAED pattern is scaled.

It is possible to drag the scale marker to measure distances on the SAED pattern.

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The tool buttons of the cystals table allows to:

Finally, select the crystal for indexing and click the search tool button to start the indexing.

Figure11

Figure 11 The bands width and angle are provided at the left bottom.

The indexing is performed in dedicated threads that can be stopped (not shown here). The results are displayed on a little stereogram (Fig. 12).

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The poles are plotted on a stereographic projection.

Figure12

Figure 12 The stereogram of the indexing solutions.

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Finally one can display the solutions in a diffraction dialogue.

Figure13

Figure 13 One of the indexing solutions.

It may be necessary to increase the number of Laue zones, and decrease the Kikuchi threshold to make all the bands appear on the drawing. A mouse click on the drawing will index the poles.

Note

The success of the indexing routine depends critically on the accelerating voltage, camera length, error bars settings and adjustment of the bands on the narrowest bands. When no solution is found cross check them, align to new bands.