Sideband KPFM is in principle similar to FM KPFM, again using combination of mechanical and electrical oscillation, however the amplitude at frequency which equals to sum of the excitation frequencies (mechanical+electrical) is not evaluated using two step lock-in procedure, but detected directly using the second lock-in. If we use low frequency electrical excitation as in FM KPFM, the amplitude of oscillations is very small and high-speed input bit depth of Gwyscope controller cannot detect it in the large background of the mechanical oscillation. However, if we choose the electrical excitation frequency so, that the sum of the frequencies equals to second resonance frequency of the cantilever, the signal is amplified by resonance and can be detected.
To set up the hardware for FM-KPFM operation with Gwyscope, use the same settings as for AM KPFM.
To set up the operation, first measure the second harmonic resonance frequency using Spectral probe response dialogue. For rectangular cantilevers, the frequency should be about 6 times higher than the base one. Then go back to base frequency and set the Tapping mode operation as usual. Then, pick “Sideband manual” regime in the KPFM tab in the main Gwyscope window and adjust the auxiliary frequency to a difference of the first and second harmonic frequency (e.g. for 50 kHz and 300 kHz resonance frequencies, set the auxiliary frequency to 250 kHz). Make sure that the number of waves to be evaluated by lockin 2 is high enough (e.g. 128 waves).
Then the KPFM dialogue (see AM KPFM description for more details) can be used to select the right signal for feedback by adjusting the phase or altering the excitation frequency.