Figure 4.

Amplitude and phase response curves of a cantilever as a function of excitation frequency when the cantilever is freely oscillating (solid line) and when the cantilever tip is influenced by negative force gradient (repulsive regime of tip–sample interaction) without energy dissipation (broken line). This interaction increases the cantilever’s resonant frequency. When the cantilever is excited at frequency f_ex, the resonant frequency shift results in amplitude reduction by ΔA and in phase advance by Δθ.