Adaptive Scan for Atomic Force Microscopy Based on Online Optimisation: Theory and Experiment

TL;DR

This paper introduces an adaptive scan method for Atomic Force Microscopy that optimizes scan speed and image quality in real-time using online extremum-seeking control, validated through simulations and experiments.

Contribution

It presents a novel online optimization scheme for AFM scan rate adjustment based on a performance metric, improving efficiency while maintaining image quality.

Findings

The adaptive scheme reduces scan time compared to fixed-rate methods.

The extremum-seeking approach ensures stability and optimality in real-time.

Experimental results confirm improved imaging performance.

Abstract

A major challenge in Atomic Force Microscopy (AFM) is to reduce the scan duration while retaining the image quality. Conventionally, the scan rate is restricted to a sufficiently small value in order to ensure a desirable image quality as well as a safe tip-sample contact force. This usually results in a conservative scan rate for samples that have a large variation in aspect ratio and/or for scan patterns that have a varying linear velocity. In this paper, an adaptive scan scheme is proposed to alleviate this problem. A scan line-based performance metric balancing both imaging speed and accuracy is proposed, and the scan rate is adapted such that the metric is optimised online in the presence of aspect ratio and/or linear velocity variations. The online optimisation is achieved using an extremum-seeking (ES) approach, and a semi-global practical asymptotic stability (SGPAS) result is shown for the overall system. Finally, the proposed scheme is demonstrated via both simulation and experiment.