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Z-Contrast Imaging: Quantitative Aspects of the Dynamical Object Function.

Published online by Cambridge University Press:  02 July 2020

B Rafferty
Affiliation:
Oak Ridge National Laboratory, PO Box 2008, Oak Ridge, TN37831-6030, USA.
S J Pennycook
Affiliation:
Oak Ridge National Laboratory, PO Box 2008, Oak Ridge, TN37831-6030, USA.
P D Nellist
Affiliation:
Nanoscale Physics Research Lab., School of Physics and Astronomy, Birmingham University, Birmingham, B17 8DJUK
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Extract

In this paper, we use a Bloch wave approach to show that the elastically scattered electrons from neighbouring atomic columns in a zone-axis oriented crystal contribute incoherently to a Z-contrast image regardless of the fact that we have coherent dynamical scattering from a stationary lattice with no absorption. This incoherent nature of the elastic scattering means that through the filtering of the ls-type Bloch states by the detector geometry we approach the Rutherford Z2 dependence of the column intensity for sufficiently large inner detector angle. Thus, annular dark-field (ADF) imaging provides us with a direct incoherent structure image of the atomic-column positions in a zone-axis oriented crystal.

Bloch wave simulations were carried out at 300 kV for the 〈110〉 orientation of InAs (a = 6.06Å) with full, half and empty columns of In atoms. Calculations including 411-beams were carried out for each of the above structural configurations for a single incident partial plane wave vector parallel to the optic axis.

Type
The Theory and Practice of Scanning Transmission Electron Microscopy
Copyright
Copyright © Microscopy Society of America

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References

References:

1.Nellist, P D, Pennycook, S J, Ultramicroscopy 78 (1999) 111CrossRefGoogle Scholar
2. Supported by Lockheed Martin Energy Research Corp. under DOE Contract No. DE-AC05-96OR22464, and by appointments to the ORNL Postdoctoral Research Associates program administered jointly by ORNL and ORISE.Google Scholar