Elastic Properties of Hard Films Multi-Layer Protective Coatings by Light Scattering

摘要

Brillouin light scattering has been successfully applied to investigate the elastic properties of thin films and membranes. Highlights of the project include the first evidence for the existence of 'organ-pipe' type standing waves in supported films (silicon oxynitride and ZnSe) and free- standing membranes (SiN). These harmonics provide a direct means to investigate the longitudinal and transverse sound velocities and thereby to determine the C11 and C44 elastic constants. Evidence for excitations localized within a buried interface offers a previously unexplored approach to non-destructively characterize the elastic properties of sub-surface layers. The role of acoustic barriers offered by AIN in localizing elastic waves in GaN films and studies on amorphous ZrB3 films reveal its transformation to hard nano-crystallites of the boride layer with dramatic enhancement of the elastic properties upon high temperature anneal. Analysis of the results was based on calculating the associated elasto-dynamic Green's tensor enabling the local density of states as well as the acoustic mode dispersion(s) to be determined. The observation of a range of acoustic excitations including dilatational and flexural modes in freestanding membranes, open new opportunities in the non-destructive study of high frequency acoustics of laminar structures and coatings.