Electrical and Electronic Engineering - Research Publications

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Author: Manzie, Christopher × Author: Nesic, Dragan × Author: Wang, Kaixiang × End date: 2022 × Start date: 2020 × Type: Journal Article ×

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    Adaptive Scan for Atomic Force Microscopy Based on Online Optimization: Theory and Experiment
    Wang, K ; Ruppert, MG ; Manzie, C ; Nesic, D ; Yong, YK (Institute of Electrical and Electronics Engineers, 2020-05-01)
    A major challenge in atomic force microscopy 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 optimized online in the presence of aspect ratio and/or linear velocity variations. The online optimization is achieved using an extremum-seeking approach, and a semiglobal practical asymptotic stability result is shown for the overall system. Finally, the proposed scheme is demonstrated via both simulation and experiment.
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    Scan Rate Adaptation for AFM Imaging Based on Performance Metric Optimization
    Wang, K ; Ruppert, MG ; Manzie, C ; Nesic, D ; Yong, YK (Institute of Electrical and Electronics Engineers (IEEE), 2020-02)
    Constant-force contact-mode atomic force microscopy (AFM) relies on a feedback control system to regulate the tip–sample interaction during imaging. Due to limitations in actuators and control, the bandwidth of the regulation system is typically small. Therefore, the scan rate is usually limited in order to guarantee a desirable image quality for a constant-rate scan. By adapting the scan rate online, further performance improvement is possible, and the conditions to this improvement have been explored qualitatively in a previous study for a wide class of possible scan patterns. In this article, a quantitative assessment of the previously proposed adaptive scan scheme is investigated through experiments that explore the impact of various degrees of freedom in the algorithm. Further modifications to the existing scheme are proposed and shown to improve the closed-loop performance. The flexibility of the proposed approach is further demonstrated by applying the algorithm to tapping-mode AFM.