Quantitative measurement of elastic constants of anisotropic materials by atomic force acoustic microscopy

In Atomic Force Acoustic Microscopy (AFAM) the cantilever is vibrating in one of its resonance frequencies while the sensor tip remains in contact with the sample surface. The elastic constant which enters in the contact stiffness is the indentation modulus. The contact radius depends on the applied static force, the tip radius, and the elastic constants of the tip and the surface. It ranges between several and up to some tens of nm. Polycrystalline materials which appear elastically isotropic on a macroscopic scale are therefore anisotropic on the scale which is probed by AFAM. When ferroelectric ceramics are imaged, the acoustic images reveal the domains within the grains due to variations in contact stiffness. Furthermore, measurements on thin nanocrystalline films of piezoelectric ceramics have been performed revealing their piezoactivity as a function of annealing temperature are discussed