Bottom-up synthesis of meta-atoms as building blocks in self-assembled metamaterials: recent advances and perspectives

Abstract

Meta-atoms interact with light in interesting ways and offer a large range of exciting properties. They exhibit optical properties inaccessible by natural atoms but their fabrication is notoriously difficult because of the precision required. In this perspective, we present the current research landscape in making meta-atoms, with a focus on the most promising self-assembly approaches and main challenges to overcome, for the development of materials with novel properties at optical frequencies.

Colloidal Self-Assembly of Silver Nanoparticle Clusters for Optical Metasurfaces

“…33,34 Self-assembly methods have typically contributed to this endeavor by fabricating subwavelength structured composite particles and materials that harbor strong optical magnetism. 14,24,25,35,36 Today, it is clear that artificial optical magnetism is an essential, if not necessary, ingredient for the development of metasurfaces.…”

“…These methods usually yield very large amounts of particles of controlled average sizes and have been proposed for the fabrication − and the assembly − of meta-atoms. They can provide particles of complex structures, e.g., composed of subparticles with a specific arrangement, exhibiting optical scattering and absorption properties that would otherwise be unattainable with homogeneous and simple shaped particles. ,− Although the polydispersity of the meta-atoms assembled with such methods is notably higher than those of top-down fabrication, the sheer number of meta-atoms synthesized in a single batch makes it possible to produce surfaces that are potentially orders of magnitude larger than what is typically achievable by top-down schemes. Furthermore, this also means that there is usually room for particle sorting to increase monodispersity without worrying about the affordability of losing meta-atoms in the process.…”

“…Several types of such devices were successfully produced like metallic dimers, , U-shaped imprints, or fishnet structures, , for which artificial optical magnetism was reported. In order to minimize optical losses, top-down technologies were also applied to silicon-based systems operating in the near infrared. , Self-assembly methods have typically contributed to this endeavor by fabricating subwavelength structured composite particles and materials that harbor strong optical magnetism. ,,,, Today, it is clear that artificial optical magnetism is an essential, if not necessary, ingredient for the development of metasurfaces.…”

Optical Properties of Metacrystals Based on Protein Nanocages

“…[27] With functional nanoparticles as building blocks, it is envisioned that optical metamaterials can be fabricated with fine control over structure and optical properties. [28] However, the assembly of ligand-coated nanoparticles yields mostly closed-packed structures, with little influence on symmetry and order. [29,30] Biomolecules, which are in the same size as nanoparticles, have been suggested to facilitate the self-assembly of functional building blocks.…”

High Q-Factor Plasmonic Surface Lattice Resonances in Colloidal Nanoparticle Arrays

“…An interesting alternative to produce metal arrays with high quality over large areas is the use of colloids . Chemically synthesized metallic colloidal NPs already present a high degree of crystallinity, tunable optical properties, and are compatible with scalable fabrication and solution processability. − Several experimental approaches employed for the fabrication of plasmonic arrays using colloidal particles, including dip coating self-assembly, − capillary-assisted particle assembly (CAPA), − templated-assisted self-assembly, − among others, , are promising alternatives to top-down procedures.…”