Anisotropic Phononic Bandgap Formation of Nano-Dicolloid Crystals

Self-assembly of colloidal nanoparticles form periodic building blocks and the fabricated crystalline structures exhibit useful photonic and phononic properties because of the periodicity of their structure. Such phononic properties are broadly applicable in technologies such as hypersonic and thermal cloaking materials, heat management systems, and metamaterials. To guide the propagation of acoustic waves to targeted direction, we investigate the potential of self-assembled anisotropic colloidal particles. Colloidal crystals consisted of nano-dicolloids are fabricated using directed self-assembly technique under electric field and their hypersonic phonon spectra are measured by Brillouin light scattering (BLS). The anisotropy of dicolloidal particle shape enables crystals to have different periodicity depending on the direction of phonon propagation. We show that the fabricated crystals have anisotropic phononic bandgaps due to both hybridization and Bragg scattering.