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How accurate is ALCHEMI for ordering measurements?

Published online by Cambridge University Press:  02 July 2020

Nan Jiang
Nan Jiang*
Affiliation:
Department of Physics and Astronomy, Arizona State University, Tempe, AZ85287
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Abstract

Atom location by channeling-enhanced microanalysis (ALCHEMI) promises a straightforward measurement of ordering in materials. On tilting the electron beam in a transmission electron microscope (TEM) about a superlattice Bragg position the electron channeling changes, weighting X-ray production from each of the sublattices differently. The overall X-ray signal, converted to an apparent composition via a kinematical non-channeling standardization, moves between the composition of the constitute sublattices. However, the accuracy of measurement always bothers many researchers. Results may vary from time to time, and in the worse cases, the composition outputs are nonsense. Table 1 gives an example of a series of ALCHEMIC measurements in a B2 Ti50Al42Mo8 intermetallic alloy.

In general, two major sources cause errors in ALCHEMI: weak channeling and delocalization effects. The later only results in “systematic errors”, which can always be corrected or reduced by theoretical calculations. However, it is difficult to improve the error due to weak channeling.

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. 338 - 339
Copyright
Copyright © Microscopy Society of America 2001

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References

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6. This work was supported by the Overseas Research Scholarships (UK) and NSF DMR 9814055.Google Scholar