A control-based approach to indentation quantification in broadband and in-liquid nanomechanical measurement using atomic force microscope

This paper presents a new control-based approach to achieve accurate indentation quantification in broadband and in-liquid nanomechanical property measurements using atomic force microscope (AFM). Accurate indentation measurement is fundamental to probe-based material property characterization as the force applied and the indentation generated are the fundamental physical variables that must be measured accurately. Large measurement errors, however, occur when the measurement frequency range becomes large (i.e., broadband), or the indentation is measured in liquid environment. Such significant measurement errors are generated due to the inability of the conventional method to account for the convolution of the instrument dynamics with the viscoelastic response of the soft sample, and the distributive hydrodynamic force effects as well as thermal drifts when measuring indentation in liquid. We propose a control-based approach to address these challenges and overcome the limits of the conventional method. The proposed approach is demonstrated through experiments of measuring the indentation measurements on a polydimethylsiloxane (PDMS) sample over a broadband of frequencies in air and with high-speed force load rate in liquid.