In contrast to AM KPFM operation, in FM KPFM the mechanical and electrical exicitation frequencies are different, which allows single pass measurements and which also means that the regime evaluates different physical interactions allowing higher spatial resolution.

To set-up the

FM KPFM regime in Gwyscope is implemented as a chain of lock-ins. Probe is excited mechanically at its resonance frequency, using a standard tapping mode operation. The KFPM excitation AC+DC signal comes from fast output 2, similarly to AM KPFM. The electrical excitation has now significantly lower frequency than the mechanical resonance frequency of the cantilever, e.g. few kHz while the resonace frequency is in tens of kHz. The probe vertical deflection signal is fed to lock-in 1 input, similarly to tappping mode and amplitude and phase at the mechanical excitation frequency is detected. On phase, the low frequency electrical signal coming from electrostatic forces is modulated. The lock-in 1 phase output is therefore internally connected to lock-in 2 input and this electrical signal is analyzed.