A sinusoidally varying damped oscillation is shown to be measurable just after the point of contact when an atomic force microscope tip interrogates a sample surface. These oscillations are shown to exist just below the noise in a single measurement. Autocorrelating 20 measurements using the snap to contact feature as the reference mark allows the signal to be clearly visible above the noise. The amplitude of these oscillations is shown to be largely insensitive to the speed with which the sample is brought toward the tip suggesting that the impulse that generates the signal comes primarily from the snap to contact event. It is argued that this sets a lower limit on how softly a sample may be interrogated when seeking mechanical properties in the surface region. The technique is used to create images of a polystyrene/polyethylene sample where the contrast mechanism is stiffness or viscosity.

New method to obtain viscoelastic properties at the nanoscale

254th National Meeting (2017)

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