Exploiting Colloidal Metamaterials for Achieving Unnatural Optical Refractions. Issue 51 (20th October 2020)

• Record Type: Journal Article
• Authors: Huh, Ji‐Hyeok; Kim, Kwangjin; Im, Eunji; Lee, Jaewon; Cho, YongDeok; Lee, Seungwoo
• Is Part Of: Advanced materials. Volume 32:Issue 51(2020)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2020-10-20
• Subjects: capacitive coupling -- colloids -- magnetism -- metamaterials -- self‐assembly; Materials -- Periodicals; Chemical vapor deposition -- Periodicals; 620.11
• DOI: 10.1002/adma.202001806
• Languages: English
• ISSNs: 0935-9648

Abstract

Abstract: The scaling down of meta‐atoms or metamolecules (collectively denoted as metaunits) is a long‐lasting issue from the time when the concept of metamaterials was first suggested. According to the effective medium theory, which is the foundational concept of metamaterials, the structural sizes of meta‐units should be much smaller than the working wavelengths (e.g., << 1/5 wavelength). At relatively low frequency regimes (e.g., microwave and terahertz), the conventional monolithic lithography can readily address the materialization of metamaterials. However, it is still challenging to fabricate optical metamaterials (metamaterials working at optical frequencies such as the visible and near‐infrared regimes) through the lithographic approaches. This serves as the rationale for using colloidal self‐assembly as a strategy for the realization of optical metamaterials. Colloidal self‐assembly can address various critical issues associated with the materialization of optical metamaterials, such as achieving nanogaps over a large area, increasing true 3D structural complexities, and cost‐effective processing, which all are difficult to attain through monolithic lithography. Nevertheless, colloidal self‐assembly is still a toolset underutilized by optical engineers. Here, the design principle of the colloidally self‐assembled optical metamaterials exhibiting unnatural refractions, the practical challenge of relevant experiments, and the future opportunities are critically reviewed. Abstract : The colloidal self‐assembly of optical metamaterials has come to the fore along with recent advances in synthetic strategies of colloids, self‐assembly routes for clusters and superlattices, and effective medium theory for analyzing colloidal assemblies. In particular, unnatural optical refractions such as extremely high and negative refractive indices could be available with colloidal self‐assembly.