AM-FM is a technique based in tapping mode used for viscoelastic mapping of a sample surface using photothermal actuation or a
specialized probe holder. The cantilever is driven simultaneously at two separate resonance frequencies.

For the higher resonance, changes in frequency are related to sample stiffness and elasticity, whereas changes in amplitude are related to sample dissipation and loss. AM-FM can be used to quantitatively measure viscoelastic properties on a wide range of materials such as polymers, blends, biomaterials, ceramics, and metals.