The Degradation of Spatial Resolution in Thin Foil X-Ray Microchemical Analysis Due to Plural Scattering of Electrons
Twigg, Mark Erickson
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https://hdl.handle.net/2142/71798
Description
Title
The Degradation of Spatial Resolution in Thin Foil X-Ray Microchemical Analysis Due to Plural Scattering of Electrons
Author(s)
Twigg, Mark Erickson
Issue Date
1982
Department of Study
Metallurgy and Mining Engineering
Discipline
Metallurgical Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Engineering, Materials Science
Abstract
A computer-based Monte Carlo simulation of incoherent plural scattering of electrons has been developed in order to estimate the broadening of an electron probe as it propagates through a solid. By applying this approach to modeling the spreading of a fine (50 (ANGSTROM)) probe focused on a thin foil in a scanning transmission electron microscope (STEM), we have estimated the spatial resolution of the compositional analysis obtainable using energy dispersive x-ray spectroscopy (EDS). Specifically, an attempt has been made to determine how the apparent microchemistry of a feature of finer dimensions than the broadened beam differs from the actual composition of the given feature.
The apparent Ge concentration profile in the vicinity of a 200 (ANGSTROM) wide Ge platelet in a 5000 (ANGSTROM) thick Al foil was measured, using STEM and EDS, and compared with the profile predicted by Monte Carlo calculations. It was found that fairly good agreement existed between experiment and theory when the probe was positioned directly on the platelet. For this reason, it might be expected that the Monte Carlo approach would be successful in compensating for the loss in spatial resolution of x-ray microchemical analysis of thin foils. However, when the probe was positioned just several hundred (ANGSTROM) units off the platelet, a greater value of the apparent Ge concentration was obtained than was predicted by theory.
The source of the apparent discrepancy between the experimental results and theoretical predictions may be due to the relative simplicity of the model employed here, which makes the convenient assumption that all electron scattering is elastic and incoherent. A more accurate model may require the consideration of inelastic and coherent scattering as well. Certainly more experimental and theoretical work is needed before we can confidently apply such a Monte Carlo model to the analysis of precipitates and grain boundaries of unknown composition.
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