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Apertures

The aperture window is shown in Fig. 1. Its toolbar contains tool buttons to:

Figure1

Figure 1 Aperture window.

This window sets the size of the objective aperture (OA) and the (LACBED/DF) aperture. The OA and LACBED/DF apertures are located in the diffraction and image plane of the objective lens respectively.

It also sets the position of the OA and LACBED/DF apertures as well as the tilt of the incident illumination. Such a tilt corresponds to a translation of the optical axis origin with respect to the diffraction pattern (Fig. 2 ).


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Objective Aperture

Figure2

Figure 2 Optical axis.

By default the OA is centered on the (0,0,0) reflection. It can be moved by clicking on a reflection (Fig. 3a) or by dragging the green cross (Fig. 3b).

Figure3a Figure3b

Figure 3a OA moved to a reflection.

Figure 3b OA dragged.

The OA can also act as a beam stop or phase plate during HRTEM image calculation (Figures 4, 5).

Figure4

Figure 4 OA with beam stop.

Figure5

Figure 5 OA with phase plate.

Note

The Stretch radiobutton can be used to display HRTEM images with maximum contrast (when the OA does not include the transmitted beam).


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LACBED/DF

The LACBED/DF aperture is by default centered on the (0, 0, 0) reflection (Fig. 6). It can be moved by clicking on a reflection or by dragging the green cross. The LACBED/DF also selects the reflection during LACBED calculations.

Figure6

Figure 6 LACBED/DF detector.


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Diffraction

The appearence of the diffraction pattern is modified using the Acceptance/Camera pane where the acceptance angle and/or the camera length>are set (Fig. 7) and the Convergence/Deviation pane where the beam convergence and deviation are adjusted (Fig. 8).

Figure7

Figure 7 Acceptance/Camera pane.

Figure8

Figure 8 Convergence/Deviation pane.

Figure9a Figure9b

Figure 9a OA centered on (000).

Figure 9b HRTEM image.

Figure9c Figure9d

Figure 9c OA moved (2, 2.8, 0).

Figure 9d HRTEM image.