  We report a systematic study to determine local elastic properties of
surfaces combining atomic force microscope (AFM) with acoustic waves which is
known as atomic force acoustic microscopy - AFAM. We describe the methodology
of AFAM in detail and interpret the measurement using simple arguments and
other complementary measurements using AFM.We have used a few selected samples
to elucidate the capability of the AFAM technique to map the local elastic
constant of the sample surface. Using the force-distance measurement and the
change in the frequency of resonance peak at various regions we quantitatively
determine the change in the local stiffness (elastic constant) of the sample
surface. We have also shown that AFAM technique can be used to get a better
surface image contrast where contact mode AFM fails.
