Effects of higher oscillation modes on TM-AFM measurements

The finite element method and molecular dynamics simulations are used for modeling the AFM microcantilever dynamics and the tip–sample interaction forces, respectively. Molecular dynamics simulations are conducted to calculate the tip–sample force data as a function of tip height at different lateral positions of the tip with respect to the sample. The results demonstrate that in the presence of nonlinear interaction forces, higher eigenmodes of the microcantilever are excited and play a significant role in the tip and sample elastic deformations. Using comparisons between the results of FEM and lumped models, how some aspects of the system behavior can be hidden when the point-mass model is used is illustrated.

Research Highlights
► Tapping the surface leads to an impulse-like force with a broad spectrum (in the frequency domain).
► The lumped model has an inaccuracy due to the excitation of the higher oscillation eigenmodes.
► Amplitude and quality factor reduction lead to intensification of the higher eigenmodes.
► Enhancement of cantilever stiffness slightly reduces the higher modes’ excitation.