Near-Perfect Absorbing Copper Metamaterial for Solar Fuel Generation
Joel Y. Y. Loh, Mahdi Safari, Chengliang Mao, Camilo J. Viasus, George V. Eleftheriades, Geoffrey A. Ozin, Nazir P. Kherani
Abstract
Metamaterials are a new class of artificial materials that can achieve electromagnetic properties that do not occur naturally, and as such they can also be a new class of photocatalytic structures. We show that metal-based catalysts can achieve electromagnetic field amplification and broadband absorption by decoupling optical properties from the material composition as exemplified with a ZnO/Cu metamaterial surface comprising periodically arranged nanocubes. Through refractive index engineering close to the index of air, the metamaterial exhibits near-perfect 98% absorption. The combination of plasmonics and broadband absorption elevates the weak electric field intensities across the nonplasmonic absorption range. This feedback between optical excitation and plasmonic excitation dramatically enhances light-to-dark catalytic rates by up to a factor of 181 times, compared to a 3 times photoenhancement of ZnO/Cu nanoparticles or films, and with angular invariance. These results show that metamaterial catalysts can act as a singular light harvesting device that substantially enhances photocatalysis of important reactions.