Electric Force Microscopy
In contrast to the atomic forces, the electrical forces arise from the coulomb potential ((q1)/4πe . 1/r).
Their distance dependence is weaker, so they are detectable in distance than the atomic forces. have a different (longer) distance dependence (1/z2) than the conventional atomic forces used for AFM topography imaging (1/z13- 1/ z7). Therefore, a scan in a larger tip sample distance overestimates the electrical forces.
This behaviour is used for the detection of electrical forces in the “Lift” mode.The surface topography of each scan line is measured in a close distance between and sample, so that the electrical forces do not affect the topographical signal. Than,each line is scanned a second time in a flight height above the detected surface topography. During this flight, the tip follows the detected topographical changes, while the cantilever deflection is detected as phase signal.
One possible result is shown here for a sample doped on parallel lines(bias: +8 V, amplitude: 3V) :