New Design Principle of Chemically Tunable Bulk Hyperbolic Metamaterials

Conventional hyperbolic metamaterials are fabricated to form artificial nanoscale structures that are designed to interact with light uniquely. In addition to the difficulty in theoretical prediction of the structures to induce desired properties, their structures had to be realized by technically challenging nanofabrication techniques. Herein, we present a new facile design principle to realize bulk metamaterials with a hyperbolic dispersion tunability. Using two exfoliated inherent hyperbolic materials as a building block, hexagonal boron nitride (h-BN) and graphite/graphene, we developed the facile synthesis method to obtain their heterostructured nanohybrid powders via self-assembly between two functionalized building blocks. Afterwards, the resulting powders were consolidated into dense bulk pellet using spark plasma sintering. The final bulk products comprise the alternating nanoscale layers of h-BN and graphite/graphene. Depending on the mixing ratio and thickness of the constituent building blocks their microstructures were delicately altered, consequently serving as a fine tool to control the hyperbolic responses. Remarkably, embedding a trace of rhombohedral boron nitride (r-BN) also anisotropically changes both type-I and type-II hyperbolic resonance modes and negative permittivities, thus indicating that r-BN acts as a ‘dopant’ in h-BN/graphite metamaterial system. For the first time, our work demonstrates the real bulk metamaterials with finely tunable hyperbolic dispersions by modulating chemical compositions. Negative permittivites are observed for the incident infrared light along both the in-plane and out-of-plane directions. Our achievement can serve a potential platform to rationally design and conveniently realize scalable bulk metamaterials without need of complicated fabrications.