The setpoint ratio was shown to be the main parameter controlling the tip-sample force, and consequently the phase contrast.
During tapping mode, the nonlinear tip-sample force activates the internal resonance and thereby amplifies the out-of-phase resonant mode.
The influences of the tip-sample force and of the size of the microelectrode on the electrical properties of the Au microelectrodes were also studied.
This contribution discusses the design of a model-based feedback controller that controls the tip-sample force in dual actuated AFM.
When the tip-sample distance is in the order of inter-atomic spacing, the short-range tip-sample force is usually simulated by the Lennard-Jones model.
The faster control of the tip-sample force reduces the residual tracking error and, thus, reduces the chance of damage or wear of the tip and the sample, and allows for faster imaging.
In Atomic Force Microscopy (AFM), the force between the measurement tip and the sample is controlled in a feedback loop to prevent damage to the tip and sample during imaging, and to convert the measurement of the tip-sample force into an estimation of the sample topography.
Nevertheless, if the ultrasonic excitation amplitude is sufficiently high that the tip-sample distance is modulated within the nonlinear tip-sample force interaction regime, the cantilever experiences a static force during the time that the ultrasonic excitation is acting.
This was connected to a bridge amplifier (model ML112 ADInstruments, Sydney, NSW, Australia) and the output was recorded via a data acquisition system (PowerLab model 8/20, ADInstruments, Sydney, NSW, Australia) programmed to sample force 40 times per second.
Low scan rates (0.3 Hz) further minimised tip sample forces from displacing deposited nanoparticles.
