Necessary modification to the Oliver-Pharr method for AFM-indentation

• Oliver-Pharr method was successfully applied to deep and shallow AFM indents. • Tilt of the indenter tip was observed during AFM indentation. • Tip area function calibration was performed via hardness measurements. • New β AFM calibration procedure is proposed for AFM indentation. • New calibration successfully captures results on soft and hard materials. Micro-mechanical material properties of materials are essential to be known when designing new devices and applications. This encompasses both standard materials and applications (e.g. metallic materials with measurement of nano-structures or thin films) and non-standard materials such as soft polymers, biological samples or historical/cultural heritage artifacts. One possible measurement method to obtain material hardness and Young’s modulus on the micro–scale is nanoindentation. However, to reach even smaller scales in combination with superior imaging capabilities, without expensive use of in–situ measurements with electron microscopy, the atomic force microscopy (AFM) indentation could be implemented. While several works were already dedicated to AFM-indentation, only two main approaches of results analysis are mostly used – Hertzian contact mechanics and Sneddon theory. These are also combined usually with spherical indenters. However, the use of sharp, pyramidal indenters in combination with Oliver–Pharr analysis offers additional improvements such as the unification of deep and shallow indents and the possibility of more localized deformation. The presented new approach, using modified Oliver–Pharr method combined with tip area calibration through sample hardness and proposed parameter β being a function of cantilever deflection, shows promising results, verified on soft epoxy-silicon and polycarbonate and hard fused quartz and Ni materials.