Dissipation mechanisms associated with atomic force acoustic microscopy

Abstract

The impact of tip‐sample dissipation mechanisms in atomic force acoustic microscopy (AFAM) and other techniques is evident in the width (and corresponding Q‐factor) of the resonances observed. The Q‐factors of resonances while in contact are often several orders of magnitude lower than those for air alone. Dependence on applied load, humidity, and vibration mode have also been observed. Here, two dissipation mechanisms are discussed with application to AFAM. First, frictional losses associated with the tip‐sample oscillations are examined. The cyclic energy loss that accompanies tip vibrations is calculated for the combined normal and shear forces present during AFAM measurements using an extension of a Mindlin contact model. The dependence on mode, applied load and friction coefficient, and other parameters is seen explicitly. Second, the dissipation associated with losses from viscoelastic contact is calculated using simple viscoelastic materials models that are coupled with the vibrating‐beam boundary value problem. In this case, the dependence of the dissipation on sample properties and tip geometry is determined. The role of each of these mechanisms for specific tip‐sample systems is discussed. The results are expected to impact quantitative aspects of nanomechanical characterization techniques. [Work supported by ARL.]