Fluid-coupled Lamb waves for self-assembling three-dimensional photonic crystals

Fluid-coupled Lamb waves (LWs) were proposed to facilitate the self-assembling of three-dimensional (3D) photonic crystals (PCs) in this work. Numerical models were constructed for proof-of-concept, and a fabrication set-up was developed for experimental demonstration. LWs were initially generated by a piezoelectric substrate. A couplant altered the propagating direction of these LWs to form the fluid-coupled LWs at a superstrate. The coffee-ring effect (CRE) of a suspension droplet on the superstrate was thus suppressed. The suspended nanospheres formed 3D PCs after the droplet dried out. Diversified PCs were fabricated using the developed set-up. Their transmittance spectra demonstrated the corresponding bandgap clearly. Advantages of utilizing fluid-coupled LWs for self-assembling 3D PCs include flexibility in excitation frequency, fabrication cost-effectiveness, acceptance for a passively oscillating substrate, and enlargement of sample area.