Abstract:
The dynamic force mode of spectroscopy measurements on the single molecules using soft
cantilevers makes the bending signal easy to detect. But, there are many problems associated
with soft cantilevers.
The aim and the results of this report are focused on one of the major sources of error
when working with a soft cantilever in the dynamic mode of force spectroscopy at the off
Resonance frequencies. When the stiffness of the cantilever and the derivative of the tip-sample
interaction force is of the same order then, the solution of the cantilever dynamics
becomes anharmonic.
Here, to present the anharmonicity in a quantitative manner, I have shown that the power
present at drive frequency gets transferred to the higher harmonics during force mapping on
single molecules. In this report, the power present at 2nd harmonics has been investigated by
demodulating the output signal and then sent to two lock-in amplifiers. The experiment was
also performed in MATLAB and COMSOL software by creating a virtual environment. The
output results agree with the statement made by the experimental results, which suggests
avoiding the use of a soft cantilever for the dynamic mode of force spectroscopy.
