Quantitative Nanomechanics on Thin Samples with the Atomic Force Microscope

J. P. Müller, and T. E. Schäffer
Institute of Applied Physics
University of Erlangen-Nuremberg
Erlangen, Germany

One method for investigating the mechanical properties of samples like living cells with an Atomic Force Microscope (AFM) is driving force-curves, i.e. measuring the force applied by the tip of the AFM as a function of the indentation into the sample. By fitting a Hertz-model, which predicts the applied force as a function of the indentation depth, one can infer the elastic modulus of the sample.

Using COMSOL we show that the Hertz-model only works well for thick samples (with respect to the indentation depth). For thin samples on a stiff substrate, like cells on a Petri dish, COMSOL simulations reveal a mismatch between the Hertz-fit and the simulated data points, which becomes more obvious for a decreasing sample thickness.