Scalable Self-Assembly of All-Dielectric Nanoparticle Metamaterials

We have developed an aerosolized jet spray method to rapidly generate ordered monolayers of colloidal particles over large areas. Particles made of materials with high refractive index with diameters ranging from 100 nm to 1 micrometer can be assembled to generate a range of all-dielectric metamaterials. The colloidal particles are deposited onto a liquid interface using an ultrasonic spray coater to achieve large area (200 cm²) ordered monolayers in less than a minute. Dense hexagonal close-packed monolayers or bidisperse superlattice arrays can be formed and transferred without a loss in structural integrity to a wide variety of solid surfaces, including metal, polymer, and glass, as well as non-planar surfaces. This high-throughput deposition technique could be readily integrated into a commercial spray coat manufacturing process. We further developed a method for controlling the spacing between the high refractive index particles in the monolayers. Uniform polystyrene shells on the primary particles with thickness ranging from 3 to 250 nm can be grown on a range of particles, including those made of titanium dioxide (TiO₂), silica (SiO₂), and amorphous silicon (a-Si). With tight size control and adjusting the ratio between sizes of small and large particles, binary colloidal crystals composed of particles of different refractive index can be generated. By stacking monolayers, three-dimensional films of ordered particles can also be made. Monolayers composed of these high refractive index particles have the potential for application as antireflection coatings, optical metasurfaces, transparent electrodes, or as substrates for biomedical sensing.