Characterization of the thin films and novel materials using resonant ultrasound spectroscopy

Crystalline thin films have become an important area of research in condensed matter and applied physics, electrical engineering, and materials science. There exists fundamental differences between 2 dimensional and bulk physics for many materials; and ever decreasing element sizes in mechanical and electronic devices requires a practical understanding of these differences. With an increased interest in thin films comes a need for new probes, able to gather information on structures with ever decreasing dimensions. This work describes a new extension of the acoustic method resonant ultrasound spectroscopy (RUS) to the measurement of the elastic tensor of a thin film deposited on a substrate. The thin film RUS technique has been successfully applied to various novel materials such as mats of carbon nanotubes, which exhibit novel attenuation effects on small mechanical resonators; and colossal magneto-resistance (CMR) films, for which a previously unreported phase transition has been detected. Typical film thicknesses studied were 100 - 1,000 nm for the CNT films, and 200 and 400 nm for the CMR films. In general, films occupying only 1/1,000 of the substrate can be reliably measured. In addition to thin films, traditional RUS was used to determine a correction to the sign of the c 14 of alpha-alumina, previously measured over 40 years ago; and the first application of RUS to biological materials, specifically human dentin.