Observation of organ-pipe acoustic excitations in supported thin films

Abstract

Brillouin light scattering from supported silicon oxynitride films reveal an extended series of acoustic excitations occurring at regular frequency intervals when the mode wave vector is perpendicular to the film surface. These periodic peaks are identified as distinct standing wave excitations that, similar to harmonics of an open-ended organ pipe, occur due to the boundary conditions imposed by the free surface and substrate-film interface. The surface ripple and volume elasto-optic scattering mechanisms contribute to the scattering cross sections and lead to dramatic interference effects at low frequencies where the surface corrugations play a dominant role. The transformation of these standing wave excitations to modes with finite in-plane wave vectors is also investigated. The results are discussed in the framework of a Green's-function formalism that reproduces the experimental features and illustrate the importance of the standing modes in evaluating the longitudinal elastic properties of the films.

Light-Scattering Study of the Normal Human Eye Lens: Elastic Properties and Age Dependence

“…The Brillouin light scattering technique offers a number of advantages over previously employed indentation and micro bubble techniques [8], [9], [14], which are destructive or at least disruptive to the anatomical structure of the lens tissue. BLS is a non-destructive probe of the elastic properties of the crystalline lens over a microscopic volume (4 to 8 × 10 -4 mm 3 ), a scale over which the properties of these tissues are thought to vary [22].…”

“…The high precision of the method is evident in its application to supported films [14] and free standing, 100 nm thick, membranes [15] to non-destructively measure the sound velocity, and hence the elastic properties of these ultrathin systems. It has also been successfully applied to completely characterize the elastic properties of highly anisotropic laminar structures [16].…”

Acoustic Waves: A Probe for the Elastic Properties of Films

“…Both algorithms refer to the types of waves most frequently measured in Brillouin spectroscopy of films or layered structures: surface acoustic wave, or pseudo surface acoustic waves, which essentially travel parallel to the surface, or however have a significant wavevector component parallel to the surface. It can also be mentioned that it was also possible, by Brillouin spectroscopy, to detect standing acoustic waves trapped within a film, which are reflected back and forth, crossing the film perpendicularly to its surface (Zhang, 2001b). Brillouin spectroscopy lends itself to the characterization of structures other than films or layers.…”

High-frequency acousto-optic effects in Bragg reflectors

“…During the last decade, the field of acousto-optics has progressed to include studies of nanometer scale objects, aimed at exploiting acoustic waves in nano-photonic and opto-mechanical devices. Traditional Brillouin scattering experiments have, so far, provided basic information about the acoustic spectra and the strength of acousto-optical interactions in various nanostructures [1][2][3][4][5][6]. In addition, acousto-optical effects excited in optical fibers provide the possibility of gigahertz (GHz) light modulation [7][8][9].…”