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How does Force Mapping work?

Force curve on a stiff sample

A simulated force curve on a stiff substrate without adhesion. The force curve exhibits two linear regions: (1) the deflection is constant as long as the tip does not touch the sample (sample base height > 400 nm in this case) and (2) the deflection is proportional to sample height while the tip is in contact (here for sample base height < 400 nm).

Force curve on a soft sample

A simulated force curve on a soft substrate without adhesion. In contrast to the force curve on a stiff substrate, the deflection is smaller than the movement in sample height, due to indentation of the sample. For typical indenter shapes used in AFM (pyramids or sphere) this results in a non-linear force curve in the contact part.

 

How does force mapping work?

This animation demonstrates how data are collected in force mapping. While the tip is raster scanned over the sample (see lower left panel) from pixel to pixel, a force curve is recorded at each point (lower right panel). To compensate differnet sample heights the range of the force curve is moved up and down accordingly (trigger mode, middle right panel). From the force curve the force vs indentation relation is calculated (upper right panel) and a theoretical curve (Hertz model) fitted to the data.The upperleft panel shows the Young's modulus, which is the result of the fit procedure.