The contrast mechanism for ferroelectric domain imaging via piezoresponse
force microscopy (PFM) is investigated. A novel analysis of PFM measurements is
presented which takes into account the background caused by the experimental
setup. This allows, for the first time, a quantitative, frequency independent
analysis of the domain contrast which is in good agreement with the expected
values for the piezoelectric deformation of the sample and satisfies the
generally required features of PFM imaging