What do we measure when we record AFM data? In our setup, we drive the tip to oscillate and measure the frequency shift as the tip interacts with the surface. Several methods exist to take this data and convert it back to the more physically-relevant quantities of force and potential energy. But when we tried to use these methods on our lateral force microscopy (LFM) data, they yielded unphysical results. Back to the drawing board!
We focussed on the LFM signal of an isolated adsorbate on a flat terrace. Away from the adsorbate, the signal is zero. This means that it is a periodic signal which can be represented by a Fourier series. The strength of this method is that the coefficients of the Fourier series that represent our data are directly proportional to the coefficients that represent force and energy.