ISO 20411:2018

Overview

ISO 20411:2018 specifies a practical method to evaluate and correct saturated intensity in single‑ion counting dynamic secondary ion mass spectrometry (SIMS). The standard targets pulse‑counting magnetic sector and quadrupole SIMS instruments and provides a test‑and‑correction workflow based on depth profiles of two isotopes in a graded reference material. Using an approximate intermediate extended dead time (a‑IED) model, ISO 20411:2018 enables extension of the detector’s linear intensity range (notably to achieve 95% linearity in validated cases). It does not apply to time‑of‑flight (TOF) mass spectrometers and is only applicable to elements that have minor isotopes (not monoisotopic elements or isotopes with equal abundances).

Key topics and technical requirements

• Scope: Determine maximum acceptable count rate for divergence from linearity in pulse‑counting detector systems (magnetic sector or quadrupole SIMS).
• Reference material: Requires a specimen with a gradual concentration gradient so the minor isotope intensity changes by a factor of 10 over >10 data points; isotopic intensity ratio should differ by 4–500.
• Detector issues addressed: Pulse overlap (saturation), detector dead time, and methods to correct measured intensities using the a‑IED dead time model.
• Instrument setup: Guidance on ion beam, mass analyser, charge compensation, multiplier gain (operating on the gain plateau), and amplifier threshold to minimize background.
• Procedure: Depth profiling of at least two isotopes, interpolation, ratio correction for transmittance/mass fractionation, dead‑time correction, uncertainty assessment and reporting.
• Validation and maintenance: Apply when commissioning a spectrometer, after hardware or detector changes (multiplier replacement, threshold changes), or at roughly 6‑monthly intervals.

Practical applications and users

• Calibration and characterization of SIMS instruments to define safe operating count rates and improve quantitative accuracy.
• Extending usable intensity range so higher count rates can be used while maintaining linearity after validated correction.
• Typical users: surface analysts, SIMS laboratory managers, instrument manufacturers, metrology institutes, materials researchers, and quality assurance personnel involved in surface chemical analysis.
• Use cases: validating new analysis conditions, routine instrument checks, and correcting saturated intensities in measurement results when the a‑IED correction is validated for the instrument.

Related standards and references

• Normative references: ISO 18115‑1 and ISO 18115‑2 (surface chemical analysis vocabulary).
• Prepared by ISO/TC 201 (Surface chemical analysis). Keywords: ISO 20411:2018, Secondary ion mass spectrometry, SIMS, saturated intensity correction, detector dead time, pulse counting, intensity linearity, depth profiling.