Microscopy 101
image is reconstructed (Image); just like all of the ele- mentary ray diagrams show (see Figure 3).
b. For imaging mode, the projector lens system grabs and magnifies the image plane; while in diffraction mode, the projector lens system grabs the diffraction plane.
6) Lower the screen to protect the camera from the bright transmitted beam, and change the microscope mode to selected area diffraction (SA Diff).
7) Change the camera length to an appropriate value. 8)Te pattern must be focused and the spot checked for astig- matism. Tis is best done with the screen down and using the binoculars. As shown in Figure 3, the diffraction pattern is formed in the BFP of the objective lens. Te projector system must grab that as its object. Te first intermediate lens (IL1) of the projector lens system is adjusted with the diffraction focus control to make the BFP of the objective lens coincide with its object plane. Tis is done by focusing the transmit- ted spot (or any diffraction spot) to the smallest point possi- ble. Te diffraction pattern is now in the calibrated position. a. While focusing the IL1, note whether there is astigmatism in the spot by going through the diffraction focus. If there is, it should be eliminated with the IL1 stigmator controls.
9) At this point, the diffraction pattern may not be centered on the screen or on the camera. If it is not, center the pattern using the projector alignment controls. a. If you are not using a digital camera, simply center the transmitted spot on the center of the phosphor screen.
b. Important!: If using a digital camera, care must be taken to not expose the camera to an intense transmitted beam with a long exposure. Te following procedure is recom- mended for reproducibly in centering the pattern, which can help when using diffraction analysis soſtware. i. With the phosphor screen down, draw two lines from opposite corners of the viewing window as shown in Figure 4A. A simple script to do this is given below:
DM Script: X-MarksTeCenter.s // Tis short script draws two yellow lines from cor- ner to corner to indicate the center of the camera. Image img Number Sx, Sy Img := GetFrontImage () Getsize (Img, Sx, Sy) Component display=
Img.ImageGetImageDisplay (0)
//Draw yellow line from top leſt to bottom right
Nano-Positioning for Microscopy & Imaging PRECISION, SPEED, STABILITY
Component XLine1=NewLineAnnotation(0, 0, Sy-1, Sx-1)
XLine1.componentSetForegroundColor (255, 255, 0)
display.componentAddChildAtEnd(XLine1)
//Draw yellow line from bottom leſt to top right Component XLine2=NewLineAnnotation(Sy-1, 0, 0, Sx-1)
XLine2.componentSetForegroundColor (255, 255, 0)
display.componentAddChildAtEnd(XLine2)
ii. Decrease the exposure of the camera drastically, liſt the phosphor screen, and very quickly center the transmitted beam where the two lines intersect with the projector lens alignment controls as shown in Figure 4B and 4C.
iii. Lower the screen, and restore the exposure.
10) Insert and center the beam block. 11) Raise the screen. 12) Determine the exposure. 13) Record the SAED pattern.
In Part II of this series, to be published in the next issue of
Microscopy Today, acquisition of SAED patterns and optimiza- tion of SAED data will be discussed.
Acknowledgements Te research reported in this document was performed
in connection with contract/instrument W911QX-16-D-0014 with the U.S. Army Research Laboratory. (As of January 31, 2019, the organization is now part of the U.S. Army Combat Capabilities Development Command [formerly RDECOM] and is now called CCDC Army Research Laboratory.) Te views and conclusions contained in this document are
those of the author and should not be interpreted as presenting the official policies or position, either expressed or implied, of the CCDC Army Research Laboratory or the U.S. Government unless so designated by other authorized documents. Citation of manufacturer’s or trade names does not constitute an official endorsement or approval of the use thereof. Te U.S. Government is authorized to reproduce and distribute reprints for Govern- ment purposes notwithstanding any copyright notation hereon.
Reference [1] DigitalMicrograph™, Gatan, Inc., Pleasanton, CA 94588, USA.
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44
www.microscopy-today.com • 2020 March
FSM fast beam steering
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