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Microscopy 101


Figure 3: Images for creating a “double-exposed” SAED pattern. A) SAED pattern acquired with a 7 s exposure and the beam block inserted. B) SAED pattern acquired with a 0.003 s exposure without the beam block.


9) Process the image by copying the area of the transmitted beam in the short-exposure recording to the same area in the long-exposure recording and save the image.


10) Follow one of the following procedures to create the “double-exposed” pattern.


Creating the Digital “Double-Exposure” SAED Pattern Tere are several ways to add the transmitted spot to the


long-exposure image with DM. Regardless of the method used, make sure that the image calibrations are correct in the final image. In DM this means making sure that the image and cali- bration tags are the same as the original image taken with the beam block inserted.


1) Te first method is simply to add the two images together. In DM, this can be achieved with the Menu command: Pro- cess-Simple Math – Add – a+b, where “a” and “b” are the two images. Te problem with doing it this way is that if the exposure for the diffraction pattern is short, such as would occur with a two-beam condition, then the background of the resultant summation image may be poor. In addition, the tags from the acquired image must be copied to the


2020 May • www.microscopy-today.com


Figure 4: SAED patterns processed with DiffTools. A) Short-exposure image is used to locate the (000) spot. The center of the transmitted beam is found with sub-pixel resolution and reported in a popup dialog box, as shown. B) Long-exposure image with the ROI of (A) transposed to the same area. The center location of the transmitted beam is saved in an image tag. The size of the ROI in this example was intentionally made larger than needed to show the area transposed.


resultant image. Dave Mitchell’s script, “Copy_All_Tags_ Between_Images.s,” can be used to do this [1]. An alter- native method that preserves the image tags is to write a simple script, such as “SimpleImageSum.s” (Appendix A). Another option, given in the script “ReplaceCenter.s,” is to simply copy a region of interest (ROI) containing the transmitted beam and overlay this in the other image (Appendix B).


2) Te second method uses some of the tools in the latest ver- sion of DiffTools [2, 3] (V6.1) that must be first installed in DM. Tis is done manually in a designated sequence but can be automated with the “ChooseMenuItem” script com- mand. Appendix C presents a short script that can be used to automatically generate images (Figures 5A, 5C, and 5D) from the two images shown in Figure 3. a. Draw an ROI box around the center of the transmitted beam in the image that was taken without a beam block and run the DiffTools menu item, DiffTools – Locate (000) Spot, as shown in Figure 4A.


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