Fe²⁺/Fe³⁺ Mapping with an Electron Probe Microanalyzer (EPMA)

Abstract

The relative intensities of Fe Lα_{1, 2} and Lβ₁ X-ray emission peaks differ significantly with valance state and bond association. These X-ray emission peaks cannot be distinguished from each other using an energy-dispersive spectrometer (EDS), because the difference in energy between these peaks is smaller than the spectral resolution of EDS (approximately 100-150 eV). However, these emission peaks can be distinguished from each other using a wavelength-dispersive spectrometer (WDS). A crystal whose 2d value is about 60 A is considered to be suitable for analyzing the first order of Fe Lα_{1, 2} and L β₁ X-ray emission peaks. The second order of these peaks can also be analyzed using lead stearate (STE : 2d=100.4 Å) crystal. Although it is difficult to use the ' peak seek' routine for a mapping analysis, the effects of chemical shifts can be suppressed by configuring the spectrometer. The interferences of high orders of Si and Na emission peaks can be suppressed by a pulse height analysis. Applying a mapping technique to measuring Fe Lα _{1, 2} and Lβ₁ emission peaks, Fe²⁺/Fe³⁺ mapping can be obtained using an electron probe microanalyzer.