  In the Tapping mode, a variation of the oscillation amplitude and phase as a
function of the tip sample distance is the necessary measurement to access
quantitatively to the properties of the surface. In the present work, we give a
systematic comparison between experimental data recorded on two surfaces, phase
and amplitude, and theoretical curves. With an interaction between the tip and
the surface taking into account an attractive and a repulsive term, the
analytical approach is unable to properly describe the relationship between the
phase variation and the oscillation amplitude variation. When an additional
dissipation term is involved, due to the attractive interaction between the tip
and the surface, the model gives a good agreement with the recorded data.
Particularly, the trends in the phase variations related to the noncontact
situations have been found to be amenable to an analysis based upon a simple
viscoelastic behavior of the surface.
