Differences

This shows you the differences between two versions of the page.

--- fmkpfm [2025/02/25 10:32] – pklapetek
+++ fmkpfm [2025/02/25 10:43] (current) – pklapetek
@@ Line 3: / Line 3: @@
 In contrast to [[amkpfm|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
+To set up the hardware for FM-KPFM operation with Gwyscope, use the same settings as for [[amkpfm|AM KPFM]]. You don't need to take care for fast input 2 connection in this case as this is handled internally; the only signal that is used is the vertical deflection signal brought to input 1, similarly to a standard tapping mode operation.
 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 [[amkpfm|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.
+To set up the operation, pick "FM manual" regime in the KPFM tab in the main Gwyscope window. Then the KPFM dialogue (see [[amkpfm|AM KPFM]] description for more details) can be used to select the right signal for feedback.
 {{ :fmkpfm_sweep2.png?direct&400 |}}
+Goal is to use signal that is steepest in its response when changing DC bias, here L2y (cosine). This can be mnow chosen in the KPFM tab in the main Gwyscope window and regime can be switched to "FM KPFM" to switch on the KPFM feedback. In contrast to [[amkpfm|AM KPFM]], here we don't bother with any lifts and KPFM feedback is run all the time. Note that the lock-in 2 low pass filter value has to be set to value that is lower than the KPFM frequency, as seen below:
 {{ :fmkpfm_run2.png?direct&600 |}}