Secondary excitation can be a large source of inaccuracy in quantitative X-ray microanalysis of inhomogeneous specimens in the AEM. The size of the secondary excitation component in the measured X-ray spectrum is sensitive to the geometry of the thin foil specimen. Secondary excitation has been examined in a self-supporting disc specimen of composition NiO-20 wt.% TiO2 which has been partially masked by a gold slot washer. The ratio of the intensities of the characteristic Kα peaks of Ti and Ni in X-ray spectra from a periclase-structured phase, of nominal composition NiO, has been measured to be NTi / NNi ≈ 0.005. There is no apparent Ti L2,3 signal in the corresponding electron energy-loss spectrum. The secondary excitation contribution to the characteristic Ti K≈a-peak from all sources can therefore be no larger than 0.5%. It should be possible to reduce this modest level of secondary excitation still further with a better masking arrangement.
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