Close Btn

Select Your Regional site

Close

selected-area diffraction, SAD

selected-area diffraction

A method for qualitative analysis of crystal structures from a spot diffraction pattern, acquired by illumination of a parallel electron beam on a specimen. By inserting a selector (selected-area) aperture into the image plane of the objective lens, a diffraction pattern is obtained from a specimen area of a several 100 nm diameter. The method enables us to determine the lattice parameters, lattice type and crystallographic orientation of the selected area.

制限視野回折:selected-area_diffraction
Overview of the standard optical ray diagram of the imaging lens system which is composed of the objective lens (OL) and the four-stage imaging lens system (intermediate lenses (IL1, IL2, IL3) and projector lens (PL)).

(a)Image observation mode, in which the magnified image of a specimen is observed on the screen by focusing the imaging lens to the image formed by the objective lens.
In this mode, the selected-area aperture (SA) is inserted into the image plane of the objective lens so that an observation area (field of view) is selected.

(b)Diffraction pattern observation mode, in which the diffraction pattern of a specimen is observed on the screen by focusing the imaging lens to the back focal plane of the objective lens. By switching from the imaging mode to the diffraction mode, the diffraction pattern formed only from the selected area in step (a) is obtained.


 

Related Term(s)