Higher-Harmonic AFM Imaging with a High-Bandwidth Multifrequency Lyapunov Filter
Journal article, Peer reviewed
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Original versionIEEE ASME International Conference on Advanced Intelligent Mechatronics. 2017, 725-730. 10.1109/AIM.2017.8014103
A major difficulty in multifrequency atomic force microscopy (MF-AFM) is the accurate estimation of amplitude and phase at multiple frequencies for both z-axis feedback and material contrast imaging. A lock-in amplifier is typically chosen for its narrowband response and ease of implementation. However, its bandwidth is limited due to post mixing low-pass filters and multiple are required in parallel for MF-AFM. This paper proposes a multifrequency demodulator in the form of a model-based Lyapunov filter implemented on a Field Programmable Gate Array (FPGA). System modelling and simulations are verified by experimental results demonstrating high tracking bandwidth and off-mode rejection at modelled frequencies. Additionally, AFM scans with a five-frequency-based system are presented wherein higher harmonic imaging is performed up to 1 MHz.