Stick-to-sliding transition in contact-resonance atomic force microscopy

Contact-resonance atomic force microscopy (CR-AFM) has been used to measure the viscoelastic loss tangent of soft materials such as polymers. Usually, the damping is attributed to the dissipation in the contact volume due to internal friction and air damping of the cantilever. However, partial slip or even full sliding can exist in the contact zone under tangential loading, and thus, the accompanying energy dissipation must be taken into account when measuring the damping constant Q l o c − 1. Here, the stick-to-sliding transition of the tip-sample contact in CR-AFM was studied. Amplitude drops were observed in the resonance curves caused by such stick-to-sliding transitions. The results show that the stick-to-sliding transition arises under small contact forces and large excitation amplitudes. Extra energy loss from full sliding induces large contact damping. The critical lateral displacement needed for the stick-to-sliding transition varies linearly with the contact radius.