diffractogram tableau
diffractogram tableau
"Diffractogram tableau," which is also called "Zemlin tableau," displays two-dimensionally Fourier transform patterns of high-magnification images taken from an amorphous thin film while the azimuthal angle is sequentially changed by a sequential tilt of the incident beam (tilt step: 1 to 2°). Utilizing the degrees of ellipse and symmetries of the patterns, axial astigmatism correction, coma-free axis alignment and three-fold astigmatism correction are executed. When a Rose-Haider-type Cs corrector is installed in a TEM, the use of the diffractogram tableau enables us to correct spherical aberration and four-fold astigmatism and optimize fifth-order spherical aberration. Software that automatically executes these corrections has already been developed.
Figs. (a) and (b) show two diffractogram tableaus without Cs correction and with Cs correction, respectively. The diffractogram tableaus are displayed in the following manner. At the center, a diffractogram obtained without tilt of the incident electron is placed, and around the center, the diffractograms obtained by tilting the incident electron beam are placed according to the tilt angles and azimuth angles.
When the incident beam is tilted, the shapes of the diffractograms are distorted depending on the magnitudes and symmetries of the axial (geometrical) aberrations. In Fig. (a), each diffractogram for the tilted electron beam is largely distorted from a perfect circle, which is caused mainly by the third-order spherical aberration. In Fig. (b), the diffractograms taken at the tilted incident beams keep almost circular shape and show small difference between the patterns of the diffractograms, indicating the aberrations being almost corrected.
Figs. (a) and (b) show two diffractogram tableaus without Cs correction and with Cs correction, respectively. The diffractogram tableaus are displayed in the following manner. At the center, a diffractogram obtained without tilt of the incident electron is placed, and around the center, the diffractograms obtained by tilting the incident electron beam are placed according to the tilt angles and azimuth angles.
When the incident beam is tilted, the shapes of the diffractograms are distorted depending on the magnitudes and symmetries of the axial (geometrical) aberrations. In Fig. (a), each diffractogram for the tilted electron beam is largely distorted from a perfect circle, which is caused mainly by the third-order spherical aberration. In Fig. (b), the diffractograms taken at the tilted incident beams keep almost circular shape and show small difference between the patterns of the diffractograms, indicating the aberrations being almost corrected.
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