PART IV. Atomic Force Microscopy

A variety of forces act between tip and sample atoms (see Table IV). The potential is Lennard-Jones-like 

Coulomb repulsion (cores) Short range, repulsive 0.1 nm 

The area between approach and retract curves (hysteresis) reflects the energy loss of the cantilever, for example due to deformation of the surface. The shape of force-distance curves changes when repulsive forces dominate (no jump-to and jump-off) or when measuring in liquids. 

The force constants of levers can be calculated from the geometrical dimensions and Young s module. Therefore, force-distance curves allow calibration of the AFM forces with respect to the voltages at the PSD. 

The interaction force versus the tip-sample distance can be calculated partly from force-distance curve. The distance-values are transformed such that the contact line F(z) = -k-z + Fo becomes the ordinate of the interaction force curve. 

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