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Teoretical Tools for Practical ALCHEMI

Published online by Cambridge University Press:  02 July 2020

L. J. Allen  and
M. P. Oxley
L. J. Allen
Affiliation:
School of Physics, The University of Melbourne, Victoria 3010, Australia
M. P. Oxley
Affiliation:
School of Physics, The University of Melbourne, Victoria 3010, Australia
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Abstract

Precisely known atomic scattering factors are essential for accurate atom location by channelling enhanced microanalysis (ALCHEMI) based on inner-shell ionization.1 For ALCHEMI using energy dispersive x-ray analysis (EDX), first principles calculations of ionization cross sections, realistically modeling the “delocalization” of the ionization interaction, give excellent agreement with experiment.2 Such calculations are complex and computationally intensive. Hence, simple analytic forms are often assumed to describe the ionization potential. However such analytic forms require prior knowledge of the “delocalization” of the effective ionization interaction. Such an approach assumes that the precise shape of the ionization potential is not important but that at least the half width at half maximum (HWHM) should be accurately estimated, for example using estimates of the HWHM from root-mean-square impact parameters for ionization. However this is generally not a good approximation3 and we have provided more realistic estimates (Fig. 1).

Type
Atom Location by Channeling Enhancement of X-Ray and EELS Signals (ALCHEMI)(organized by J.Spence)
Information
Microscopy and Microanalysis , Volume 7 , Issue S2: Proceedings: Microscopy & Microanalysis 2001, Microscopy Society of America 59th Annual Meeting, Microbeam Analysis Society 35th Annual Meeting, Long Beach, California August 5-9, 2001 , August 2001 , pp. 348 - 349
Copyright
Copyright © Microscopy Society of America 2001

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References

1.)Oxley, M. P. et al., Ultramicroscopy 80 (1999) 199–124.Google Scholar
2.)Oxley, M. P. and Allen, L. J.. Phys. Rev. B 57 (1998) 3273–3282.CrossRefGoogle Scholar
3.) Oxley, M. P. and Allen, L. J.. Ultramicroscopy 80 (1999) 125–131.CrossRefGoogle Scholar
4.)Oxley, M. P. and Allen, L. J.. Acta Cryst. A 56 (2000) 470–490.CrossRefGoogle Scholar
5.)Oxley, M. P. and Allen, L. J.. Acta Cryst. A, to be submitted.Google Scholar
6.)Nuchter, W. and Sigle, W., Philos. Mag. A71 (1995) 165–186.CrossRefGoogle Scholar
7.) This research was supported by the Australian Research Council. The authors acknowledge stimulating and helpful discussions with Dr. C. J. Rossouw.Google Scholar