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Diffraction

High energy electron diffraction patterns, both kinematical and dynamical, are displayed under controls gathered in this window (Fig. 1). In the kinematical approximation the intensity of the spots and lines is proportional to their structure factor. When dynamical calculations are performed the intensity of the reflections is calculated by the Bloch-wave method. All the drawing controls (except the gamma control) are collected in panes.

Figure1

Figure 1 SAED pattern Al14Ca12O33.

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Sections

The toolbar defines tools to:

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An experimental diffraction pattern can be loaded as a background image and the calculated one superposed for comparison (Fig. 2). This offers a good way to figure out the camera length matching the experimental one.

Figure2

Figure 2 GaN (experimental and calculated).


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SAED drawings of Ti5O5 structure (Fig. 3a) will be demonstrated in this help file (Fig. 3b).

Figure3a

Figure3b

Figure 3a 3-D siaplay of Ti5O5.

Figure 3b Diffraction Ti5O5 [001].

The arrows and reset tools are moving the CLC or the position of the transmitted beam (000). (green cross) or the pattern center (blue cross). The drawing can be rotated with the control of the Orientation tabbed pane (Fig. 4a).

Moving the CLC or pattern center is also done by dragging these crosses. The popup menu attached to the drawing allows to switch between the blue and green crosses.

Figure4a

Figure4b

Figure 4a Rotation of SAED drawing.

Figure 4b Pop-up menu attached to the drawing.

The popup menu allows to add Kikuchi (Fig. 5a) or HOLZ (Fig. 5b) lines to the drawing, to index (hkl) reflections and lines (Fig. 6) or to plot double diffraction spots (Figures 7a, 7b) as well as to send or load a drawing to/from the clipboard.

Figure5a

Figure5b

Figure 5a Kikuchi lines.

Figure 5b HOLZ lines (000) spot magnified 10 times.

Figure6

Figure 6 Kikuchi and HOlZ lines with (hkl) indices.

Figure7a

Figure7b

Figure 7a SAED Ti5O5 [001].

Figure 7b SAED Ti5O5 [001] with double diffraction spots.


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Changing the crystal orientation

The crystal orientation is changed by:

The crystal orientation will be [340, 323, 320] i.e. close to [1,1,1]! jems uses always the indices of closest small indices zone axis (here [1,1,1]) and the indices of the CLC (here (8, -7, -1)). Note that the CLC is always perpendicular to the zone axis: [uvw] · (hkl) = 0.

Figure8a

Figure8b

Figure 8a Selecting [111] zone axis.

Figure ba Moving CLC at (8, -7, -1).

For fine adjustment use:

Note that the control (Shift, Ctrl, ...) key actions depend on the operating system.


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Atlas of Zone Axis Patterns

The table of [uvw] zone axes can be one entry at a time. When many rows are selected at once an atlas of SAED pattern can be produced either as a .pdf file (Ti5O5Atlas) or a series of images (Fire).

Figure9a

Figure9b

Figure10a

Figure10b

Figure 10a Selected zone axis.

Figure 10b SAED.


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Indexing [uvw] poles

When several High Order Laue Zones are plotted, the intersection of Kikuchi bands can be indexed with a mouse click on the diffraction pattern (Fig. 11). Then a mouse click on a pole will align the crystal along the selected zone axis (Fig. 12). Note that the reflections are colored (red, green, blue, ...) for ZOLZ = 0, FOLZ = 1, SOLZ = 2, ...

Figure11

Figure 11 Indexing the poles near [2,1,3] with a mouse click.

Figure12

Figure 12 Selecting the [3,1,5] pole.


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Precession

Precession diffraction pattern are simulated by activationg the make tool button after moving the Center of Laue Circle a couple of degrees out of the zone axis direction (Fig. 13). The make tool button also stops the precession.

When the Center of Laue Circle is (000) an SAED pattern image is shown.

The precession electron diffraction technique is able to produce perfectely symmetrical SAED patterns even when the crystal is slightly out of perfect zone axis direction. Dynamical precession diffraction slightly decrease the effects due to dynamical diffraction (multiple scattering). It allows to measure reflections intensities close to those of single scattering (kinematical diffraction). Dynamical precession calculations are possible using the Bloch-wave method. Charge flipping method applied to dynamical precession SAED patterns seems to be able to extract the phase of the reflections and to reconstruct the projected potential of the crystal.

Figure13a

Figure13b

Figure13c

Figure 13a Si [2,1,2], CLC (10.2, 0, -10.2).

Figure 13b Reflections of the precession inside the annulus.

Figure 13b Precession electron diffraction [2,1,2].


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Controls panes

The controls are collected in the follwing panes:

Figure14a Figure14b Figure14c

Figure 14a Avalanche, to create SAED atlas.

Figure 14b Crystal/Matrix, to do dynamical calculations and set the number of Laue zones .

Figure 14b Diffraction, to adjust the diffraction paramters.

Figure15a Figure15b

Figure 15a Lattice, to modify the lattice parameters.

Figure 15b Crystal/Matrix, to boost the intensity of the HOLZ lines.

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Figure16a Figure16b

Figure 16a Options, to set drawing features.

Figure 16b Threshold, to suppress spot and lines weaker than a threshold value.

FOLZ correction is displayed when HOLZ are added to the SAED pattern (Fig. 17).

Figure17

Figure 17 HOLZ voltage correction.


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Figure18a Figure18b

Figure 18a Processing, to process background images.

Figure 18b Variant, to plot diffractions of twinned crystal, variants or epitaxial crystals.

Background images can be enhanced by image processing (Fig. 19).

Figure19

Figure 19 Processed background image with overlapping SAED drawing (GaN [120]).


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The Variant panes are enabled when overlapping crystal is loaded (Fig. 20).

Figure20a Figure20b

Figure 20a Si [1,1,0] FCC twins.

Figure 20b Si [0,1,2] FCC twins.


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Tabular List

Lists of reflections of a the diffraction pattern tabulate the structure factors and other preperties of them including their deviation. The list can be printed.

Figure21

Figure 21 Tabular list of reflections (struture factors).


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Crystal rotation

With the crystalbutton a crystal structure is displayed and rotated when the CLC is dragged (Fig. 22).

Figure22

Figure 22 Rotation of the crystal when dragging the CLC.