Elastic Characterization of Transparent and Opaque Films, Multilayers and Acoustic Resonators by Surface Brillouin Scattering: A Review

TL;DR

This review discusses the use of surface Brillouin light scattering (surf-BLS) for elastic characterization of thin films, multilayers, and acoustic resonators, highlighting recent advancements and potential applications in imaging and metamaterials.

Contribution

It provides a comprehensive overview of surf-BLS methodology, its capabilities for different film types, and introduces recent developments like micro-focused scanning for enhanced imaging.

Findings

Surf-BLS effectively characterizes elastic properties of various thin films.

The technique's information content varies with film transparency and thickness-to-wavelength ratio.

Recent advances enable spatial imaging of acoustic fields in resonators and metamaterials.

Abstract

There is currently a renewed interest in the development of experimental methods to achieve the elastic characterization of thin films, multilayers and acoustic resonators operating in the GHz range of frequencies. The potentialities of surface Brillouin light scattering (surf-BLS) for this aim are reviewed in this paper, addressing the various situations that may occur for the different types of structures. In particular, the experimental methodology and the amount of information that can be obtained depending on the transparency or opacity of the film material, as well as on the ratio between the film thickness and the light wavelength, are discussed. A generalization to the case of multilayered samples is also provided, together with an outlook on the capability of the recently developed micro-focused scanning version of the surf-BLS technique, which opens new opportunities for the imaging of the spatial profile of the acoustic field in acoustic resonators and in artificially patterned metamaterials, such as phononic crystals.