The Mask drawing has the zone axis geometry (Figures 4a, 4b).
The mask is enabled in the Options pane. The mask size can be adjusted and adapted to the SAED
pattern.
It allows to separate reflections from overlapping crystals. It is rotated using the Align pane.
The Microscope pane sets the accelerating voltage and camera length as well as the measurements
errors
of angles and distances.
The Options pane contains checkboxes to change the background color, to show the Mask and to
snap
the arrows at the spots position (when the FindPeak has been
done).
It also allows to reflect the image and to extend the indexing search to all possible zone axes, to use 3
spots
(default is 2) and to filter the indexing by likelihood.
Scaling the arrows and mask drawing requires to point the Double arrow on known features of the
pattern
(SAED spots of known distance or angle, scale marker, ...). This is necessary when the camera length is not
clearly
defined as is very often the case. A precise scaling restricts the indexing to the sets of (hkl)
reflections
in a range of distances to the (000) transmitted beam defined by the accelerating voltage and camera length.
When
not precisely known an extended search option can be set (Fig. 3e). When the
indexing
window is loaded for the first time, the default scale is either mm or nm-1 per pixel.
To index SAED (spots) patterns follow these steps:
-
Set the accelerating voltage, camera length and measurement errors (Fig. 3d).
-
Load the experimental SAED pattern (GaN)(Fig. 2a). Note that HREM images can
also be loaded
and their diffractogram displayed and indexed (Figures 2b, 2c).
-
After processing the SAED pattern, adjust the origin and tips of the pointing arrows (Fig. 4).
-
Set the order of the spots, arrow 0 points to spot 4 and arrow 1 to spot 2 (Fig. 5).
-
Set the diffraction pattern scale (Fig. 4).
-
If necessary set the mask option (Fig. 6).
-
Select the crystals to use for the indexing (Fig. 3b).
-
Start the indexing process using the
search tool button. When finished a small stereogram with the possible indexing will popup (Fig. 8).
-
Select on this stereogram one of the solutions (Fig. 9).
The success of the indexing routine depends critically on the accelerating voltage, camera length, error
bars and spots order
settings. When no solution is found cross check them. When the camera length is unknown use the Extended
search option
(Fig. 3e). This option will display many solutions where the ratio of the arrows and
their angle is
within the measurement range, but mainly with incorrect camera length (Figures 10a,
10b).
PDF documentation: SAED indexing.