Signal amplitude and sensitivity of the Kelvin probe force microscopy

When the tip-sample distance is small, Kelvin probe force microscopy is affected by parametric amplification. This is due to the fact that the electric force has two components; the higher one having a frequency exactly twice as high as the lower. The oscillation amplitude may substantially depart from what is usually expected. Those phenomena are analytically modeled and experimentally shown, and the optimal parameter values which must be used for voltage detection are established.