Damping mechanisms in thin-layer materials

In addition to applications in engineering, the intrinsic mechanical damping of materials is important as a research tool. This is a consequence of the astonishing variety of mechanisms that produce damping, many of which provide a means of selectively probing structural features and kinetic processes on the atomic scale. In the study of thin-layer materials, the mechanisms of greatest interest are relaxation processes associated with the thermally-activated motion of defects and that are manifest experimentally as well-defined damping peaks. Examples are given of relaxations that operate on the macroscopic, microstructural, and atomic scales. These are taken from work on long- and short-range diffusion of hydrogen in amorphous alloys, grain-boundary sliding in metallic films, and point-defect reorientation in doped layers of silicon. New experimental approaches using the vibrating-membrane and vibrating-string configurations have been developed, and complexities associated with the mechanics of these arrangements are pointed out.