Velocity angular dispersion of surface and bulk modes in LiTaO3 at hypersonic frequencies

Abstract

The existence of two surface acoustic waves, the Rayleigh wave and the second leaky wave, on X-cut LiTaO3 has been detected using Brillouin scattering. Evidence of dispersion between ultrasonic and hypersonic velocities was found for both surface and bulk acoustic waves. Elastic constant values were determined from a simultaneous least-squares fit of the angular dispersion data for the longitudinal and the two transverse bulk acoustic modes.

Determination of LiTaO3acoustic physical constants at hypersonic frequencies from bulk and surface wave velocities

“…The second leaky wave, which is also termed the high-frequency pseudosurface wave, leaks energy into the bulk. Because it suffers severe attenuation, it appears as a Brillouin peak with a large line width [9]. Also displayed in figures 2 and 3 are the theoretical velocities computed using the partial-wave method [14] based on the three sets of ultrasonic acoustic physical constants determined by Kovacs et al [1], Warner et al [2] and Kushibiki et al [3].…”

“…However, published values of these constants [1][2][3][4][5][6][7] are determined mainly by ultrasonic techniques, in the MHz range instead of the desirable GHz operating range for many SAW devices. Investigations [8,9] have revealed that surface and bulk mode velocities measured by Brillouin scattering (GHz range) are systematically lower than the corresponding velocities predicted by theory, which is based on physical constants measured ultrasonically. Because of this discrepancy, and the fact that many types of SAW devices operate in the GHz range, there is a need to find a precise set of acoustic physical constants of LiTaO 3 using, for instance, Brillouin scattering which probes acoustic modes in this frequency region.…”

“…One measurement was performed by Blachowicz and Kleszczewski [10], who determined the elastic constants from measurements of acoustic bulk mode velocities. The other, by Kuok et al [9], yielded a set of effective elastic constants evaluated by a fit to velocity dispersion data on bulk modes.…”

“…Previous fitting procedures [1,4,5,9,10] require, besides measured mode velocities, the measurement of dielectric and/or piezoelectric constants. In contrast, we have been able to determine the complete set of twelve independent constants from a fit to only mode velocities obtained by Brillouin scattering.…”

Sezawa and love modes in Co/Cu superlattices

“…Especially, acoustic phonons frequencies are, from natural reasons, sensitive to elastic anisotropies associated with di®erent crystallographic symmetries of di®erent elementary layers, creating a multilayered structure [4,5,6]. In superlattices grown epitaxially in a very high vacuum { a method of sample preparation known as the Molecular Beam Epitaxy (MBE) { one can control crystallographic order with almost atomic resolution [7,8,9,10,11,12].…”