The basic idea of Atomic Force Acoustic Microscopy is to excite the cantilever of an atomic force microscope into flexural vibrations when the tip is in contact with the sample [1, 2].
The frequencies of the eigen-modes of the cantilever depends, amongst
other parameters, on the stiffness of tip-sample contact and on the
contact radius, which in turn both are a function of Young's modulus of
the sample and the tip, the tip radius, the load exerted by the tip,
and the geometry of the surface. Such a technique allows one to
determine the Young's modulus from the contact stiffness with a
resolution of a few tens of nanometers. As is shown on the animation
under AFAM Contact Resonance Spectroscopy (CRS) measurements sample is
coupled to the piezoelectric transducer. It emits acoustic waves into
the sample which cause out-of-plane vibrations of the sample surface.
The surface vibrations are transmitted into cantilever via the sensor
tip. The cantilever vibrations are measured by 4-sectioned photo-diode
and evaluated by lock in amplifier. This setup is used to acquire
cantilever vibration spectra. Values of resonance frequencies with
known cantilever and tip parameters allow to determine reduced Young's
module of the sample [3, 4]. The contact-mode topography image is acquired simultaneously with the acoustic one.
