  We perform simulations and experiments on an oscillating atomic force
microscope cantilever approaching a surface, where the intermodulation response
of the cantilever driven with two pure harmonic tones is investigated. In the
simulations, the tip and surface interact with a conservative nonlinear force,
and the parameter space of approach distance and surface stiffness is explored.
Approach experiments are carried out on three surfaces with widely varying
stiffness. Qualitative similarities between simulations and experiment can be
seen, but quantitative comparison is difficult due to the overly idealized
tip-surface force model used in the simulation.
