Quantifying Tip-Sample Interactions in Vacuum Using Cantilever-based Sensors: An Analysis

We theoretically and experimentally show that the force law obtained from data acquired under vacuum conditions with dynamic force microscopy may deviate more than previously assumed from the actual interaction when the oscillation amplitude of the probe is of the order of the decay length of the force near the surface, which may result in a non-negligible error if correct absolute values are of importance [1]. However, the related inaccuracies can be effectively suppressed by using oscillation amplitudes sufficiently larger than the decay length of the tip-sample interaction. We also propose a novel technique that includes modulating the drive amplitude at a constant height from the surface while monitoring the oscillation amplitude and phase. Ultimately, such amplitude sweep-based force spectroscopy enables shorter data acquisition times and increased accuracy for quantitative chemical characterization compared to standard approaches that vary the tip-sample distance [1, 2]. In addition, since no feedback loop is active while executing the amplitude sweep, the force can be consistently recovered deep into the repulsive regime.
[1] O.E. Dagdeviren et al., Physical Review Applied 4, 044040 (2018)
[2] O.E. Dagdeviren et al., Nanotechnology 27, 065703 (2016)