Quantitative force microscopy from a dynamic point of view

We discuss the physical origin and measurement of force between an atomic force microscope tip and a soft material surface. Quasi-static and dynamic measurements are contrasted and similarities are revealed by analyzing the dynamics in the frequency domain. Various dynamic methods using single and multiple excitation frequencies are described. Tuned multifrequency lockin detection with one reference oscillation gives a great deal of information from which one can reconstruct the tip–surface interaction. Intermodulation in a weakly perturbed high Q resonance enables the measurement of a new type of dynamic force curve, offering a physically intuitive way to visualize both elastic and viscous forces.