Material-related and various dependences of adhesion force on piezo velocity revealed on an AFM at moderate humidity

ABSTRACT Piezo velocity dependence of adhesion force is contradictory and requires clarification in the literature. The dependence was investigated with the measurements between a silica cantilever and surfaces with different materials in a humid condition on an atomic force microscope (AFM). The results demonstrate that the velocity dependence is correlated with materials. Depending on those surfaces, there are various behaviors: (1) independence below a critical velocity and decreasing above the critical velocity; (2) having large values at low velocities and independence at high velocities; (3) independence in the entire velocity range; (4) independence at low velocities and having large values at high velocities; (5) increasing exponentially. The decrease at high velocities was attributed to the pull-off instability in a water bridge with low viscosity. The large values at high velocities were attributed to the dynamic viscous force with high viscosity. Independence in the entire velocity range was attributed to the compromise between the pull-off instability and viscous force with moderate viscosity. The exponential increase was ascribed to a crack propagation process. The results may add to our knowledge of adhesion forces, propose selection recommendations of AFM parameters, and improve the design of relevant small-scale devices.