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Image Periodicities Introduced by Three-Fold Astigmatism in HRTEM Images of α-Al2O3 and Related Materials

Published online by Cambridge University Press:  02 July 2020

D.L. Medlin ,
J.E. Smugeresky  and
D. Cohen
D.L. Medlin
Affiliation:
Materials and Engineering Sciences Center, Sandia National Laboratories, Livermore, CA94550
J.E. Smugeresky
Affiliation:
Materials and Engineering Sciences Center, Sandia National Laboratories, Livermore, CA94550
D. Cohen
Affiliation:
Department of Chemical Eng. and Mat. Science, University of Minnesota, Minneapolis, MN55455
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HRTEM images of α-Al2O3 oriented along [1100] often exhibit a modulation of the basal fringe intensity with a period that corresponds to twice the basal plane spacing. In the example shown in figure 1, note the strong basal fringe contrast in the A12O3 with a period of 4.33 Å. HRTEM image simulations for ideal imaging conditions fail to reproduce this doubling of the lattice fringe period. Instead, simulated images predict that the (0006) fringes (d0006=2.17 Å) should be of equal intensity (e.g., see Figure 3a). Incorrect beam and/or crystal tilt can strongly affect HRTEM image contrast. In particular, anomalous periodicities can arise under beam and crystal tilt conditions for which normally kinematically and dynamically forbidden diffracted beams contribute to the image. More recently, the importance of 3-fold astigmatism on HRTEM imaging has been recognized. As with beam tilt, this lens aberration produces asymmetrical phase shifts in the diffracted beams.

Type
Microscopy of Ceramics and Minerals
Information
Microscopy and Microanalysis , Volume 4 , Issue S2: Proceedings: Microscopy & Microanalysis '98, Microscopy Society of America 56th Annual Meeting, Microbeam Analysis Society 32nd Annual Meeting, Atlanta, Georgia July 12-16, 1998 , July 1998 , pp. 596 - 597
Copyright
Copyright © Microscopy Society of America

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References

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