A comparison of techniques for obtaining convergent beam electron diffraction patterns with a JEOL 200CX

Abstract

Three different techniques for obtaining convergent beam electron diffraction (CBED) patterns using a JEOL 200CX transmission electron microscope will be described and compared. The first technique, described by Goodman, will be shown to yield clear, undistorted patterns, but only with relatively large camera length, and a limited field of view. A second technique, which is a modification of Goodman's technique, will be shown to yield CBED patterns of both large camera length and small camera length with a much larger angular coverage, but the magnitude of the beam convergence is limited by distortion in the pattern. A third technique will then be presented which permits the formation of small camera length, relatively undistorted CBED patterns with large angular coverage and greatly increased beam convergence; high quality large camera length CBED patterns can also be obtained by simply increasing the strengths of the diffraction lenses.