Figure 5: Frequency noise of the DSFM detection electronics measured as a function of oscillation amplitude for two different bandwidths (50 Hz and 100 Hz). For this measurement, the same cantilever as that used for the previous experiment was utilized (force constant of 0.4N/m). The cantilever was excited by the DSFM electronics with the phase-locked loop enabled, and the frequency output δν ( t ) was fed into a digital lock-in amplifier in order to determine the total noise of the frequency measurement of the DSFM detection unit. For small oscillation amplitude of the cantilever ( a$_{osci}$ < a$_{th}$ , see main text), the frequency noise is independent of oscillation amplitude and for large amplitude the noise decreases linearly (slope 1 in the log − log plot). 23