Observation of guided longitudinal acoustic modes in hard supported layers

Abstract

We report experimental as well as theoretical evidence for the occurrence of a high-frequency acoustic excitation, identified as a longitudinal guided mode, in elastically hard films supported on a soft substrate. While existence criteria related to the transverse and longitudinal sound velocities in the film and substrate argue for strong decay channels into the substrate, the excitation is evident as a clear peak in the Brillouin light scattering spectra. A Green's function formalism accounts for the existence of this excitation and provides insight into its properties as illustrated for diamond-like-carbon layers deposited on silicon.

Surface and interface shear horizontal acoustic waves in piezoelectric superlattices

“…The experimental observation of the surface and interface modes predicted here can be performed by means of Brillouin scattering experiments [24][25][26] and picosecond laser technique. 27 Because many new devices are based on layered structures, 28,29 it is important to understand and characterize propagation of waves in this kind of system.…”

Observation of organ-pipe acoustic excitations in supported thin films

“…4 BLS has been successful in probing a variety of near surface excitations such as Rayleigh, Sezawa, Love, Lamb modes as well as guided acoustic resonances in thin films. [5][6][7][8][9][10][11][12][13][14] Despite an extensive body of BLS experiments, standing acoustic-wave excitations in laminar structures that are characterized only by wave-vector components perpendicular to the thin-film surfaces (K Ќ ) have received little attention. In this case due to the limited film thickness ͑d͒ and applicable acoustic boundary conditions, the allowed values of K Ќ are quantized to a series of discrete values.…”

<title>Elastic properties of cBN films by surface Brillouin scattering</title>

“…This second type of behavior of the dispersion relation has been called the splitting type. The non-splitting type of behaviour has been observed experimentally in an alumina film on aluminium by acoustic microscopy [16], in doped Cr coatings deposited on high speed steel [17], in a titanium film on steel by SBS [18], in diamond-like-films (DCL) [19]. Splitting type of behavior has been observed recently for Si 3 N 4 films on GaAs [9].…”