ISO 21222:2020

Overview

ISO 21222:2020 - "Surface chemical analysis - Scanning probe microscopy - Procedure for the determination of elastic moduli for compliant materials using atomic force microscope and the two-point JKR method" - provides a standardized AFM-based procedure to determine the elastic modulus of compliant materials. The method uses AFM force‑distance (force‑displacement) curves and a two‑point analysis based on Johnson‑Kendall‑Roberts (JKR) contact mechanics. It applies to compliant materials with moduli from 100 kPa to 1 GPa and typical spatial resolution set by the tip–sample contact radius (~10–20 nm).

Key topics and requirements

• Measurement workflow (Clause 6): steps include measuring cantilever deflection sensitivity, determining the normal spring constant, measuring tip radius, acquiring force‑distance curves, converting raw data and applying the JKR two‑point method for modulus calculation.
• Contact mechanics review: summaries and guidance on relevant models - Hertz, DMT, JKR, Maugis, and COS - and the JKR–DMT transition so users can choose appropriate mechanics for given sample/tip conditions.
• Instrument calibration and uncertainties: requirements for calibrating deflection sensitivity and spring constant (referencing ISO 11775), assessing uncertainties (in deflection, spring constant, tip radius, indentation depth, modulus), and recommended reporting of results.
• Limitations and applicability: targeted at compliant, adhesive materials where JKR assumptions are valid (e.g., soft polymers, organics, adhesive surfaces); guidance on contact radius, indentation depths and model validity is included.
• Supporting material: Annex A (example measurements) and Annex B (inter‑laboratory comparison) assist validation and benchmarking.

Applications and users

ISO 21222:2020 is relevant for:

• AFM/Scanning probe microscopy (SPM) labs performing quantitative nanomechanical mapping and force spectroscopy.
• Materials scientists, polymer researchers, coatings and adhesive engineers needing surface elastic modulus at nanoscale.
• Biomedical and soft‑matter research groups characterizing hydrogels, tissues, biomaterials and thin polymer films.
• Metrology and quality‑control labs, instrument manufacturers and calibration service providers implementing standardized AFM modulus measurement protocols.

Practical benefits include reproducible modulus values for compliant materials, clearer comparison across studies, and validated procedures for AFM-based mechanical property measurement.

Related standards

• ISO 11775 - Determination of cantilever normal spring constants (referenced for calibration).
• ISO 18115-2 - Vocabulary for scanning‑probe microscopy (terminology used throughout ISO 21222).

Keywords: ISO 21222:2020, AFM elastic modulus, JKR two-point method, force-distance curve, scanning probe microscopy, compliant materials, surface chemical analysis.