Determination of Young's modulus of thin films by ultrasonic surface waves

: Schneider, D.; Schultrich, B.; Scheibe, H.J.

Abstract
A method has been developed to determine YOUNG'S modulus and thickness of thin surface layers by measuring the phase velocity of ultrasonic surface waves. These are thermoelastically induced by a short laser pulse. From the received pulse form in dependence on measuring distance, the phase velocity is determined over a sufficient wide frequency range by a special measuring and computational procedure. By comparing experimental and theoretical dispersion curves, YOUNG'S modulus and/or the thickness can be obtained without any calibration. The potential of this nondestructive method has been demonstrated for amorphous carbon films of less than 1 micrometer thickness, prepared by vacuum arc deposition. It has been found that the elastic constants responds sensitively to variation of preparation conditions. The ultrasonic method turned out to be a suitable means for characterizing thin films.