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Diffraction Channeling and the Production of Secondary Excitation

Published online by Cambridge University Press:  02 July 2020

S.J. Pennycook*
Affiliation:
solid State Division, Oak Ridge National Laboratory, P.O.Box 2008, Oak Ridge, TN37831
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Extract

The pivotal role played by Archie Howie in the development of many areas of electron microscopy is universary acknowledged.Here I would like to highlight his contribution to the quantitative description of secondary excitations, which was an important influence on the development of Z-contrast imaging in zone-axis crystals. Secondary excitations are those such as x-ray emission which occur following a primary scattering event, in this case excitation of inner shell electrons. The first important concept to be realized by Archie was that dynamical diffraction and channeling are different manifestations of the same physical effect, namely, the multiple scattering of electrons within a crystal. Second was the realization that processes which are localized within the unit cell will show a dependence on diffraction conditions, such as incident beam orientation, and could therefore be described quantitatively using dynamical diffraction theory. Precisely the same theory was used to describe the orientation dependence of cathodoluminescence

The development of the STEM for high resolution imaging was of course due primarily to Crewe and coworkers, with an annular detector to allow efficient detection of elastic scattering over a wide angular range.

Type
A. Howie Symposium: Celebration of Pioneering Electron Microscopy
Copyright
Copyright © Microscopy Society of America

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