Mechanically affected zone in AFM force measurements — Focus on actual probe tip geometry

• New method to determine AFM probe tip wear from force measurements on known polymers
• Good correlation between the numerical simulation of the test and experimental data
• Determination of the volume of material impacted during a force measurement
• Prediction of spatial resolution during an AFM force measurement on polymers
• Method applicable to interphases characterisation in composites or thin layer systems

The estimation of a mechanically affected zone (MAZ) during AFM force measurements on polymers or composites requires a precise knowledge of the probe tip geometry. A new calibration method is proposed to determine the tip geometry from force measurements on reference materials. The test is then modelled by finite element method in order to validate the probe geometry and to determine the (MAZ) on these materials. The numerical simulation is used to show the influence of test parameters and sample elastic modulus on the impacted volume. The evolution of MAZ diameter and depth with Young's modulus and sample displacement can be correctly described by two analytical models. It is then possible to predict the lateral resolution or depth penetration associated to an AFM force measurement on a given polymer. The aim is to optimize test parameters to characterize mechanical interphases at nanometre scale in multiphase materials and to measure polymer surfaces modulus in thin layer systems.

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