Colloidal Plasmonic Nanocubes as Capacitor Building Blocks for Multidimensional Optical Metamaterials: A Review

Localized surface plasmon resonances of colloidal nanostructures are known for their extreme ability to focus light waves onto nanoscale volumes, making the resulting electric fields useful for various applications such as solar energy conversion, sensing, and surface-enhanced spectroscopies. Clusters and arrays of these colloidal nanostructures offer unique platforms to study and develop metaoptical properties that surpass those of naturally occurring materials such as bare metals or semiconductors. The metaoptical properties of these arrays depend on the orientation, geometry, and spacing of each nanostructure. Among various potential building blocks, colloidal nanocubes present a unique opportunity to exploit large capacitive coupling enabled by true nanoscale spacing between adjacent flat facets. In this review, we highlight the metaoptical property engineering of optical metamaterials prepared with colloidal nanocubes as nanocapacitor building blocks. We first discuss the origin of metaoptical properties of nanocube dimers in different geometries including a dimer with an axis perpendicular to the incident wavevector and a nanocube-on-mirror with an incident wavevector normal to the substrate. We then present design principles for achieving distinct optical properties from four different configurations: dilute random, dilute ordered, densely ordered in two or three dimensions, and densely ordered in well-faceted crystals. On the basis of these design rules, we highlight recent developments that focus on experimental demonstrations and conclude with the current challenges and outlook in nanocube-based optical metamaterials research.