Characterizing Micro- and Nano-Materials Based on Their Ultrasonic Dispersion Properties: A Feasibility Study

Current methods for characterizing micro- and nano-scale materials (typically based on laser spectroscopy and xray diffraction) are expensive, slow, bulky, and cannot be applied in situ. In contrast with these approaches, this paper explores the use of ultrasonic transduction as an inexpensive tool for in situ material characterization at the micro- and nano-scale. Specifically, we present a technique for characterizing materials based on the analysis of ultrasonic dispersion (i.e., the frequency-dependent wavenumbers) of thin films. Through experimental and simulation results, we perform our technique with silicon and a piezoelectric stack consisting of silicon, molybdenum and aluminum nitride. Simulations are performed in COMSOL Multiphysics. Experimental data is collected from a piezoelectrically transduced nano-acoustic waveguide using a digital holographic microscope, which enables high-resolution measurement of displacement vector over extended regions. Our results demonstrate a near-match between the experimental data and simulations, validating our proposed characterization methodology.