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Nondestructive Evaluation of Thin Film Microstructures by Picosecond Ultrasonics

Published online by Cambridge University Press:  21 February 2011

Humphrey J. Maris
Affiliation:
Department of Physics and Division of Engineering, Brown University, Providence, RI 02912
Holger T. Grahn
Affiliation:
Department of Physics and Division of Engineering, Brown University, Providence, RI 02912
Jan Tauc
Affiliation:
Department of Physics and Division of Engineering, Brown University, Providence, RI 02912
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Abstract

We describe a technique by which ultrasonic measurements can be made in the picosecond time domain. A light pulse (duration of the order of 0.1 psec) is absorbed at a surface, thereby setting up an elastic stress. This stress launches an elastic pulse into the interior. The propagation of this strain, including its reflection at interfaces within a microstructure, is monitored through measurements of the time-dependent changes of the optical reflectivity. These measurements are made using a time-delayed probe pulse. In these experiments the spatial length of the elastic pulses can be as short as 50 Å. We can therefore use this technique to perform a nondestructive ultrasonic evaluation of thin-film microstructures. We describe here results we have obtained which demonstrate the application of the method to the study of the mechanical properties of thin films, the geometry of microstructures, and the quality of bonding at interfaces.

Type
Research Article
Copyright
Copyright © Materials Research Society 1989

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