Overview
ISO 18114:2021 specifies a standardized method to determine relative sensitivity factors (RSFs) for secondary‑ion mass spectrometry (SIMS) using ion‑implanted reference materials. The method applies to specimens with a uniform matrix composition where the implanted species peak concentration does not exceed one atomic percent. The RSF enables quantification of an element’s concentration as a function of depth in samples of the same matrix when the detected ion signal is proportional to concentration.
Key Topics
- Principle: An isotopic RSF for an element–matrix pair is derived from a SIMS depth profile of an ion‑implanted external standard. The RSF calculation uses the implanted fluence, integrated analyte signal (background corrected), the reference isotope signal, and the sputtered depth of the analysis crater.
- Applicability limits: Use for uniform matrices and peak implanted concentrations ≤ 1 at.% to avoid strong matrix effects. If detector saturation occurs, intensity correction per ISO 20411 may allow application after correction.
- Reference materials: Prefer certified reference materials (CRMs). If CRMs are unavailable, use reference materials whose implanted fluence has been independently measured (for example by Rutherford backscattering or neutron activation analysis).
- Depth measurement: The sputtered crater depth is typically measured with a calibrated stylus profilometer and assumed constant per measurement cycle when calculating the removed depth.
- Measurement consistency: Analytical and instrument conditions must be the same for the implanted reference and the unknown sample to ensure valid RSF transfer.
Applications
- Calibration of SIMS instruments for quantitative depth profiling of trace elements in homogeneous matrices.
- Routine generation of RSFs for lab reference libraries to support comparison of depth profiles across samples and time.
- Quantitative analysis workflows where ion‑implanted standards provide known fluence and well‑characterized depth distributions.
Practical tips:
- Ensure the implanted peak is at least two times deeper than the onset depth of steady‑state sputtering as indicated by a stable matrix signal.
- Verify the implanted peak intensity is at least 100× the instrument background or detection limit to ensure robust RSF calculation.
- Record and report instrument model, primary beam species/energy/angle, secondary ion species/polarity, spectrometer and analytical conditions, and any deviations from procedure.
Related Standards
- ISO 20411 - Correction method for saturated intensity in single ion counting SIMS (referenced for intensity correction).
- ISO 18115 (all parts) - Surface chemical analysis - Vocabulary (terms and definitions used).
- Wilson R.G., Stevie F.A., Magee C.W., Secondary Ion Mass Spectrometry: A Practical Handbook (useful practical reference cited in ISO 18114).
This standard provides a consistent, practical approach to derive RSFs from ion‑implanted reference materials, improving the reliability and comparability of SIMS quantitative depth profiling.
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