Multiband Hypersound Filtering in Two-Dimensional Colloidal Crystals: Adhesion, Resonances, and Periodicity

Area of Science:

• Condensed matter physics
• Materials science
• Acoustics

Background:

• Two-dimensional colloidal crystals offer unique platforms for acoustic wave manipulation.
• Understanding hypersonic phonon propagation is crucial for phononic device applications.
• Spontaneous micro Brillouin light scattering is a powerful, non-invasive technique for probing acoustic properties.

Purpose of the Study:

• To investigate hypersonic phonon propagation in large-area 2D colloidal crystals.
• To identify and characterize acoustic band gaps and their impact on wave propagation.
• To explore the tunability of acoustic properties by material parameters and interface characteristics.

Main Methods:

• Utilized spontaneous micro Brillouin light scattering to probe phonon propagation.
• Analyzed the dispersion relation of thermally populated Lamb waves.
• Employed finite element method (FEM) modeling for mode identification and validation.

Main Results:

• Revealed multiband filtering due to three distinct types of acoustic band gaps (Bragg and hybridization gaps).
• Observed acoustic band gaps in both sub- and superwavelength regimes, influenced by contact resonances and nanoparticle eigenmodes.
• Demonstrated GHz frequency tunability via particle size and contact interface adhesion.

Conclusions:

• The study elucidates the complex acoustic band structure in 2D colloidal crystals.
• The findings enable the design of tunable acoustic filters and phononic devices.
• A contactless method for studying submicrometer particle contact stiffness was developed, revealing size-dependent effects.