  A method for the separation and quantitative characterization of the
electrostatic and Van der Waals contribution to tip-sample interaction in
non-contact Scanning Force Microscopy is presented. It is based on the
simultaneous measurement of cantilever deflection, oscillation amplitude and
frequency shift as a function of tip-sample voltage and tip-sample distance as
well as on advanced data processing. Data is acquired at a fixed lateral
position as interaction images with the bias voltage as fast scan and
tip-sample distance as slow scan. Due to the quadratic dependence of the
electrostatic interaction with tip-sample voltage the Van der Waals force can
be separated from the electrostatic force. Using appropriate data-processing
the Van der Waals interaction, the capacitance as well as the contact potential
can be determined as a function of tip-sample distance from the force as well
as from the frequency shift data. The measurement of resonance frequency shift
yields very high signal to noise ratio and the absolute calibration of the
measured quantities, while the acquisition of cantilever deflection allows the
determination of tip-sample distance. The separation and quantitative analysis
of Van der Waals and electrostatic interaction as proposed in the present work
results in precise and reproducible measurement of tip-sample interaction that
will significantly improve the interpretation of SFM data and will
substantially contribute to the characterization of nanoscale properties by
SFM.
