Model-based approach to compensate for the dynamics convolution effect in nanomechanical property measurement

A model-based approach to compensate for the dynamics convolution effect on the measurement of nanomechanical properties is proposed. In indentation-based approaches to measure the nanomechanical properties of soft materials, an excitation force consisting of multiple frequencies needs to be accurately exerted (from the probe) to the sample material, and the indentation generated in the sample needs to be accurately measured. However, when the measurement frequency range becomes close to the bandwidth of the instrument hardware, the instrument dynamics along with the probe-sample interaction can be convoluted with the mechanical behavior of the soft material, resulting in distortions in both the applied force and the measured indentation, which, in turn, directly lead to errors in the measured nanomechanical properties of the material (e.g., the creep compliance). In this article, the dynamics involved in indentation-based nanomechanical property measurement is investigated to reveal that the convoluted dynamics effect can be described as the difference between the lightly-damped probe-sample interaction and the overdamped nanomechanical behavior of the soft sample. Thus, these two different dynamics effects can be decoupled via numerical fitting based on the viscoelastic model of the soft material. The proposed approach is illustrated by implementing it to compensate for the dynamics convolution effect on a broadband viscoelasticity measurement of a Polydimethylsiloxane (PDMS) sample using a scanning probe microscope.