Index
Plotting the amplitude or intensity and phase of the reflections as a function of crystal thickness
is important for a detailed understanding of dynamical effects in electron diffraction. jems makes that
possible using the Bloc-wave method. As an example the Gjonnes-Moodie lines in BeO are simulated.
Figure 1 shows a SAED pattern (parallel beam illumination) of BeO [110]. Reflections
(00n) with n odd are all missing kinematically (Fig. 1) and dynamically
(Fig. 2) when the incident beam is parallel to [110].
Figure 1 BeO [110] kinematical.
Figure 2 BeO [110] dynamical 100 nm.
A small tilt of the crystal off the zone axis will make the forbidden (00n) reflections visible
(Fig. 3).
Figure 3 BeO off [110] dynamical 100 nm.
A plot of the (001) and (002) reflections is obtained with a mouse click on any reflections
(except the transmitted one) (Fig. 4)
Figure 4 BeO [110] (001) and (002) reflections plot.
Using CBED this dynamical effect is visible as Gjonnes-Moodie black lines along the (00n) reflections.
It can be attributed to destructive dynamical interference of the reflections.
Figure 5 BeO [110], Gjonnes_Moodie lines.
Exporting the plot as a Mathematica notebook allows offers more possibility to display the amplitude or phase of
the reflections as a function of specimen thickness (Fig. 6).
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Figure 6a (000) amplitude and phase. |
Figure 6b (000) constant phase (see Preferences). |
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Figure 6c (200) amplitude and phase. |
Figure 6d (200), (000) phase difference . |
D. Gratias, R. Portier, Time-like perturbation method in high-energy electron diffraction,
Acta Cryst. A39 (1983) 576-584.