HD SCFM

Scanning Capacitance Force Microscopy
is kind of dynamic EFM. Generally [1] in EFM. the cantilever is biased directly by V_tip=V_dc + V_acsin(wt), where V_ac is referred to as the driving voltage. Scanning is executed on some height h above the sample surface in according with the profile defined during the first scanning in HD mode. The capacitive force F_cap(z) between the tip and a sample surface at potential V_s is F_cap(z) =(1/2) (V_tip - V_s)²(dC/dz)
where C(z) is the tip-surface capacitance dependent on tip geometry, surface topography and tip-surface separation z.
Second harmonic of the capacitive force depends only on (dC/dz) and Vac
F_cap2w(z) =(1/2) (dC/dz)V_ac² sin(2wt) and can be used for acquisition additional information, e.g distribution of the surface capacity over the sample. For maximization of the second harmonic oscillations the ac frequency w is adjusted to be equal to half of cantilever resonance frequency w_r.