Overview
ISO/TS 25138:2019 - Surface chemical analysis - Analysis of metal oxide films by glow-discharge optical-emission spectrometry (GD-OES) - is a technical specification that defines a GD‑OES method to determine the thickness, mass per unit area and chemical composition of metal oxide films. Applicable to oxide layers from 1 nm to 10 000 nm on metallic substrates, the method quantifies metallic film constituents (Fe, Cr, Ni, Cu, Ti, Si, Mo, Zn, Mg, Mn, Zr, Al) and non‑metal elements (O, C, N, H, P, S). The 2019 second edition updates apparatus guidance (including CCD/CID solid‑state arrays) and calibration recommendations.
Key topics and requirements
- Principle: Cathodic sputtering in a DC or RF glow‑discharge, spectral excitation of sputtered atoms, measurement of emission intensity vs sputter time, and conversion to quantitative depth profiles.
- Apparatus: Requirements for glow‑discharge optical‑emission spectrometers and detector types (including solid‑state arrays), and guidance on selecting spectral lines and source types.
- Discharge settings: Procedures for adjusting DC and RF source parameters (current, voltage, pressure, power, bias) and minimum performance targets (repeatability, detection limits).
- Sampling & calibration: Recommended calibration and validation samples by base metal family (iron/steel, stainless, nickel, copper, titanium, silicon, aluminium, etc.), determination of sputtering rates, emission intensity measurement, and calculation/validation of calibration functions.
- Analysis & reporting: Guidance for data acquisition, quantifying depth profiles, expressing results (thickness, mass per unit area, average oxide composition), precision, drift correction and required test report elements.
- Conversion: Quantitative conversion from intensity vs time to mass fraction vs depth using calibrated sputtering rates and calibration constants.
Applications and users
ISO/TS 25138:2019 is intended for laboratories and professionals performing surface chemical analysis and thin‑film metrology, including:
- Materials scientists and researchers characterizing oxide films and passive layers
- Corrosion engineers assessing oxide thickness and composition for failure analysis
- Quality control and process engineers in metal finishing, anodizing, passivation and coating industries
- Semiconductor and wafer processing labs analyzing native and thermally grown oxides
- Test labs validating coating performance and R&D groups developing surface treatments
Practical uses include oxide thickness mapping, depth profiling of multi‑layer oxides, composition analysis for corrosion/passivation studies, and process control where non‑destructive or near‑surface chemical information is required.
Related standards
- ISO 14707 - Introduction to use of GD‑OES
- ISO 16962:2017 - Analysis of zinc‑ and/or aluminium‑based metallic coatings by GD‑OES
- ISO 14284 - Sampling/preparation for chemical composition of steel and iron
Keywords: ISO/TS 25138:2019, GD‑OES, glow‑discharge optical‑emission spectrometry, metal oxide films, depth profiling, oxide thickness measurement, surface chemical analysis.