The force apply on the surface is directly correlated to the spring constant of the cantilever : lowest spring constant = lowest force
Oscillating mode : A tip vibrating at its resonant frequency sweeps the surface using piezoelectric motors. Laser detection maintains the amplitude of oscillation constant during the measurement. The movements of the vertical piezoelectric motor are recorded to reconstruct the surface. Mapping of mechanical properties is achieved with the offsets of the phase signal. (phase contrast).