The second part will be focused on a new approach to reconstruction of tip-sample force in TMAFM based on the determination of cantilever acceleration, and thus referred to as scanning probe acceleration microscopy (SPAM). This method utilizes the second derivative of the deflection signal to recover the tip acceleration trajectory. The challenge in such an approach is that with real, noisy data, the second derivative of the signal is strongly dominated by the noise. This problem is solved by taking advantage of the fact that most of the information about the deflection trajectory is contained in the higher harmonics, making it possible to filter the signal by “comb” filtering, i.e. by taking its Fourier transform, and inverting it while selectively retaining only the intensities at integer harmonic frequencies. Such a comb filtering method works particularly well in fluid TMAFM due to the highly distorted character of the deflection signal. The validity of this approach will be demonstrated through numerical simulations and in situ TMAFM experiments on supported lipid bilayer patches on mica.
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