Diffraction and Imaging. Topics. Objective aperture selection BF/DF imaging Relationship of DP to image. BFP. stronger lens - shorter focal length. Image vs. Diffraction. Objective aperture selection. The BFP contains the DP (shows reciprocal space) and the objective aperture.
stronger lens - shorter focal length
No scattered electrons from hole
Large aperture – lower contrast
Small aperture – higher contrast
What you see on screen
How do you center DF beam?
Not in Bragg condition!
If you move diffracted spot into center, it will disappear.
Still in Bragg condition!
If you move direct beam to +g spot, -g will light up.
Beam Tilts in DF mode
DF channel (memory)
Beam Tilt Display
1st intermediate image