Question

Question 10 (max 20 points) A) Please explain the difference between drive amplitude and free amplitude. B) Please explain the advantages and disadvantages of static AFM and dynamic AFM

Answer 1

The drive amplitude is the intensity of the external oscillatory signal. The absolute value of the drive amplitude required to achieve a given oscillation amplitude of the cantilever depends on many parameters such as the method of driving (acoustic, photothermal or magnetically) cantilever fixation and parameters (stiffness, geometry) and laser alignment. The exact value of the drive amplitude is therefore not relevant but it is adjusted in each experiment so as to provide an appropriate (and quantifiable) oscillation amplitude of the cantilever.

When the driven cantilever is far away from the sample and no damping of its vibration occurs through tip-sample interactions, its oscillation amplitude is called the free oscillation amplitude. As the vibrating tip nears the surface of the sample, its amplitude starts to decrease. If the feedback is enabled, the z-piezo will constantly re-adjust its extension so that to keel the selected setpoint amplitude, constant. The setpoint value is normally always lesser than the free amplitude.