Abstract
In atomic force acoustic microscopy (AFAM) one exploits the contact resonances of the micro-fabricated cantilever, either as an imaging method where the contrast arises from the local variation of elastic and anelastic properties, or for local quantitative measurements. In this work we used AFAM in its spectroscopic mode, where contact-resonance curves are recorded as a function of the loading force P. From such curves the local contact stiffness and the contact damping were determined. The contact damping was found to have a power dependence on the load P when measured on the two different samples quartz-glass and nanocrystalline aluminum. We attribute this effect to micro-sliding of the sensor tip on the sample described by Mindlin for macroscopic contacts. We calculate the friction coefficient from the dissipated energy per cycle in the contact area to be 0.1, while the amplitude of the oscillatory sliding velocity was in the range of 0.05 m/s.