Overview
ISO 18554:2016 - Surface chemical analysis - Electron spectroscopies - Procedures for identifying, estimating and correcting for unintended degradation by X‑rays in a material undergoing analysis by X‑ray photoelectron spectroscopy (XPS) - provides a pragmatic, routine method to detect and correct changes in elemental composition or chemical state that occur while a specimen is being irradiated by X‑rays during XPS. The standard is focused on practical identification, simple estimation and linear correction of X‑ray induced degradation; it does not address degradation mechanisms, depth profiling, or comparisons between different material types.
Key topics and technical requirements
- Scope of correction: The proposed correction procedure is valid only when changes are caused by the X‑rays and lead to less than a 30% reduction or increase in the intensity of a chosen photoelectron peak.
- Time tracking (time zero): Define the moment the specimen is first exposed to X‑rays as time zero and record exposure times throughout acquisition.
- Scan sequence:
- Acquire an initial survey scan (recommended 0.4 eV step interval), record start/stop times and compute mean exposure time.
- Perform detail scans for regions of interest.
- Acquire a final survey scan to compare with the initial survey.
- Recognition and estimation of degradation: Compare first and final scans to identify measurable spectral changes (peak position, intensity or chemical-state shifts). The standard describes deducing the undegraded intensity by linear extrapolation using parameters such as the linear rate of change (parameter A) and references a degradation index (DI) concept.
- Causes to consider: Direct X‑ray interaction, electrons from un‑monochromated sources, photoelectrons, secondary electrons, electron flood guns, low‑energy ion neutralizers, and heating from X‑ray anodes.
- Contamination and reporting: Procedures include assessment and reporting of contamination formation and optional compensation for a surface contamination layer (see informative Annex C). The standard also recommends reporting degradation observations and suggested mitigation steps.
- Limitations: Ion‑beam sputtering, in‑depth mechanisms and specific chemical pathways are outside scope.
Practical applications - who uses ISO 18554:2016
- Surface analysts and XPS operators who need to ensure data integrity for sensitive materials (polymers, organics, thin films, corrosion products).
- Materials scientists and researchers studying X‑ray sensitive samples.
- Quality assurance/quality control labs in electronics, coatings, polymer and surface-engineering industries.
- Instrument vendors and service engineers implementing acquisition sequences, neutralization strategies and user guidance to minimize X‑ray induced changes.
- Accreditation bodies and laboratories documenting measurement uncertainty and traceability for XPS results.
Related standards (if applicable)
- Other standards and guidance produced by ISO/TC 201 (Surface chemical analysis) cover XPS measurement practices and terminology; consult ISO/TC 201 publications and the full ISO 18554:2016 document for complete requirements and annexed examples.