Patent ID: 8347411

Claim:
A scanning probe microscope for measuring properties of a sample comprising a probe on a mechanical resonator, an oscillator generating a master signal (S) at a frequency f, an actuator driven by said master signal (S) and applying a mechanical force to said mechanical resonator at said frequency f, a DC voltage source applying a DC voltage (Udc) to said probe, an AC voltage source applying an AC voltage (Uac) at said frequency f to said probe, a detector measuring a phase and/or amplitude of a deflection of said mechanical resonator, said scanning probe microscope further comprising a driver controlling said actuator and being adapted to keep a phase and or an amplitude of said deflection constant and a secondary control loop having a setpoint for the frequency or amplitude, respectively, of said master signal (S) and controlling said DC voltage (Udc) to keep said frequency or amplitude, respectively, of said master signal (S) at said setpoint, wherein, if the driver keeps the phase but not the amplitude of the deflection constant, said secondary control loop keeps the frequency at said setpoint, if the driver keeps the amplitude but not the phase of the deflection constant, said secondary control loop keeps the amplitude of the master signal (S) at said setpoint or if the driver keeps the amplitude and phase of the deflection constant, said secondary control loop either keeps the amplitude or frequency of the master signal at said setpoint.