Electron Probe Microanalysis of Transition Metals using L lines: The Effect of Self-absorption

Area of Science:

• Materials Science
• Analytical Chemistry
• Physics

Background:

• Quantitative compositional measurement using electron microprobe analysis (EPMA) is crucial for materials characterization.
• Self-absorption of Lα X-ray lines is a known issue affecting the accuracy of EPMA for first-row transition metals.
• Existing matrix correction models do not adequately account for self-absorption effects.

Purpose of the Study:

• To quantify the error introduced by neglecting self-absorption in EPMA of Fe, Ni, Cu, and Zn.
• To evaluate the impact of electron beam energy on self-absorption-induced errors.
• To discuss strategies for mitigating self-absorption in transition metal analysis.

Main Methods:

• Calculation of Lα X-ray intensities from metallic Fe, Ni, Cu, and Zn targets.
• Modeling X-ray line profiles using a Lorentzian function.
• Incorporating energy-dependent mass absorption coefficients near absorption edges.
• Comparison with results from conventional narrow-line, fixed-absorption coefficient approaches.

Main Results:

• Calculated X-ray intensities deviate significantly from conventional methods for Fe and Ni, with errors up to ~10% and ~15% respectively, increasing with electron beam energy.
• Deviations for Zn and Cu were found to be negligible under the studied conditions.
• The study highlights the importance of considering self-absorption for accurate EPMA of certain transition metals.

Conclusions:

• Self-absorption is a critical factor for accurate quantitative analysis of Fe and Ni using EPMA Lα lines.
• The conventional approach leads to substantial errors for these elements, particularly at higher beam energies.
• Further development of EPMA methods is needed to incorporate self-absorption corrections for improved accuracy in transition metal analysis.