  Frequency-modulation atomic force microscopy provides an outstanding
precision of the measurement of chemical bonding forces. However, as the
cantilever oscillates with an amplitude A that is usually on the order of
atomic dimensions or even larger, blurring occurs. To extract a force versus
distance curve from an experimental frequency versus distance spectrum, a
deconvolution algorithm to recover the force from the experimental frequency
shift is required. It has been recently shown that this deconvolution can be an
ill-posed inversion problem causing false force-distance curves. Whether an
inversion problem is well- or ill-posed is determined by two factors: the shape
of the force-distance curve and the oscillation amplitude used for the
measurement. A proper choice of the oscillation amplitude as proposed by the in
ection point test of Sader et al. [Nat. Nanotechnol. 13, 1088 (2018)] should
avoid ill-posedness. Here, we experimentally validate their in ection point
test by means of two experimental data sets: force-distance spectra over a
single carbon monoxide molecule as well as a Fe trimer on Cu(111) measured with
a set of deliberately chosen amplitudes. Furthermore, we comment on typical
pitfalls which are caused by the discrete nature of experimental data and
provide MATLAB code which can be used by everyone to perform this test with
their own data.
