Numerical Simulation of Nano Scanning in Intermittent-Contact Mode AFM under Q control

TL;DR

This paper uses numerical simulations to analyze and optimize nano scanning in tapping mode AFM under Q control, demonstrating improved image quality and scan speed through adaptive Q control strategies validated by experiments.

Contribution

It introduces a comprehensive simulation approach for entire AFM scan processes under Q control, highlighting the benefits of adaptive Q control for faster, force-limited nano scanning.

Findings

Soft cantilevers with high Qeff improve image quality.

Higher Qeff increases scan speed but raises tapping forces.

Adaptive Q control enables higher scan speeds without increasing forces.

Abstract

We investigate nano scanning in tapping mode atomic force microscopy (AFM) under quality (Q) control via numerical simulations performed in SIMULINK. We focus on the simulation of whole scan process rather than the simulation of cantilever dynamics and the force interactions between the probe tip and the surface alone, as in most of the earlier numerical studies. This enables us to quantify the scan performance under Q control for different scan settings. Using the numerical simulations, we first investigate the effect of elastic modulus of sample (relative to the substrate surface) and probe stiffness on the scan results. Our numerical simulations show that scanning in attractive regime using soft cantilevers with high Qeff results in a better image quality. We, then demonstrate the trade-off in setting the effective Q factor (Qeff) of the probe in Q control: low values of Qeff cause an increase in tapping forces while higher ones limit the maximum achievable scan speed due to the slow response of the cantilever to the rapid changes in surface profile. Finally, we show that it is possible to achieve higher scan speeds without causing an increase in the tapping forces using adaptive Q control (AQC), in which the Q factor of the probe is changed instantaneously depending on the magnitude of the error signal in oscillation amplitude. The scan performance of AQC is quantitatively compared to that of standard Q control using iso-error curves obtained from numerical simulations first and then the results are validated through scan experiments performed using a physical set-up.