Self-consistent method for quantifying indium content from X-ray spectra of thick compound semiconductor specimens in a transmission electron microscope

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Abstract

Summary

Based on Monte Carlo simulations of X-ray generation by fast electrons we calculate curves of effective sensitivity factors for analytical transmission electron microscopy based energy-dispersive X-ray spectroscopy including absorption and fluorescence effects, as a function of Ga K/L ratio for different indium and gallium containing compound semiconductors. For the case of InGaN alloy thin films we show that experimental spectra can thus be quantified without the need to measure specimen thickness or density, yielding self-consistent values for quantification with Ga K and Ga L lines. The effect of uncertainties in the detector efficiency are also shown to be reduced.

Lay description

Energy-dispersive X-ray spectroscopy in an analytical (scanning) transmission electron microscope is routinely used for qualitative chemical microanalysis and mapping of differences in the chemical composition between different alloy phases or nanoparticles with a few nanometers spatial resolution. For quantitative chemical analysis, electron beam broadening by multiple scattering, atomic fluorescence yield, absorption, fluorescence and detector efficiency need to be modeled, and for reliable absorption corrections the foil thickness perpendicular to the electron beam, the detector take-off angle and the atomic density (or mass absorption coefficients) need to be known. ?Based on Monte Carlo simulations of X-ray generation by fast electrons we calculate curves of effective sensitivity factors including absorption and fluorescence effects, as a function of Ga K/L ratio for different indium and gallium containing compound semiconductor alloys. For the case of InGaN alloy thin films we show that experimental spectra can thus be fully quantified without the need to measure specimen thickness or density, yielding self-consistent values for quantification with Ga K and Ga L lines. The effect of uncertainties in the detector efficiency are also shown to be significantly reduced compared to standard approaches so we may be able to determine the indium content of such InGaN alloys more reliably.

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