Control tools for rapid broadband nanomechanical spectroscopy using scanning probe microscope

The identification of frequency dependent material property at nanoscale has been extensively studied and played an important role in the failure analysis of materials, wound healing, and polymer formation mechanism. In this dissertation, the development of a suite of control tools to nanoscale broadband viscoelastic spectroscopy is presented. The combination of novel iterative control techniques with the integration of system identification and optimal input design techniques together can enable rapid measurement of nanomechanical properties of soft materials over a broad frequency band. SPM and nanoindenter have become enabling tools to quantitatively measure the mechanical properties of a wide variety of materials at nanoscale. Current nanomechanical measurement, however, is limited by the slow measurement speed: the nanomechanical measurement is slow and narrow-banded and thus not capable of measuring rate-dependent phenomena of materials. As a result, large measurement (temporal) errors are generated when material undergoes dynamic evolution during the measurement. The low-speed operation of SPM is due to the inability of current approaches to (1) rapidly excite the broadband nanomechanical behavior of materials, and (2) eliminate the convolution of the hardware adverse effects with the material response during high-speed measurements. These adverse effects include the hysteresis of the piezo actuator (used to position the probe relative to the sample); the vibrational dynamics of the piezo actuator and the cantilever along with the related mechanical mounting; and the dynamics uncertainties caused by the probe variation and the operation condition. Motivated by these challenges, this dissertation is focused on the development of novel control and system identification tools for rapid broadband nanomechanical measurement.