Overview
ISO 11938:2012 specifies procedures for elemental‑mapping analysis by electron probe microanalysis (EPMA) using wavelength‑dispersive spectrometry (WDS). It defines how to plan and perform mapping, compares electron beam mapping (digital beam scanning) with stage/large‑area mapping, and describes five data‑processing approaches: raw X‑ray intensity, k‑value, calibration curve, correlation, and matrix correction methods. The standard also covers measurement procedure, specimen preparation, instrument stability, uncertainty evaluation and reporting requirements.
Key topics and technical requirements
- Mapping setup
- Selection of mapping area, pixel count (spatial resolution) and acquisition mode (beam vs stage).
- Probe size should be comparable to or smaller than pixel spacing; accelerating voltage chosen to excite all elements of interest.
- Specimen preparation
- Clean, flat, conductive specimens; embedding and metallographic polishing as needed.
- Conductive coating recommended (e.g., carbon ~10–20 nm) and same coating on reference and unknown specimens to reduce charging.
- Measurement procedure
- Collect peak and background X‑ray intensities (and optional electron signals) pixel by pixel and store raw data.
- Two background acquisition strategies: pixel‑by‑pixel or separate full peak and background maps - tradeoffs between drift and time.
- Instrument stability and geometry
- Confirm instrument stability over mapping duration (Si wafer suggested for checks).
- Maintain constant working distance and spectrometer geometry to satisfy Bragg diffraction; defocussing effects limit beam mapping for large areas.
- Data display and processing methods
- Five methods: raw intensity (fast, qualitative), k‑value, calibration curve, correlation, and full matrix correction (quantitative).
- Choose method based on required accuracy, element overlaps, and matrix effects (absorption, fluorescence).
- Uncertainty and reporting
- Guidance on evaluating measurement uncertainty and required reporting elements to ensure reproducible results.
Applications and users
ISO 11938:2012 is useful for:
- Materials scientists, geologists and metallurgists performing elemental mapping for phase/particle analysis.
- EPMA laboratory managers and operators setting acquisition parameters for quality control, failure analysis, R&D and industrial inspection.
- Laboratories seeking consistent, comparable EPMA/WDS mapping procedures and compliance with accreditation frameworks (e.g., ISO/IEC 17025).
Related standards
Keywords: ISO 11938:2012, electron probe microanalysis, EPMA, wavelength‑dispersive spectrometry, WDS, elemental mapping, beam mapping, stage mapping, matrix correction, calibration curve.