In Situ Ellipsometric Monitoring of Gold Nanorod Metamaterials Growth

An in situ transmission-based system has been designed to optically monitor the ellipsometry constants of a hyperbolic plasmonic metamaterial during electrochemical growth. The metamaterial, made from an array of vertically aligned gold nanorods, has demonstrated an unprecedented ability to manipulate the polarization of light using subwavelength thickness slabs, making in situ ellipsometric data a powerful tool in the controlled design of such components. In this work, we show practical proof-of-principle of this design method and rationalize the ellipsometric output on the basis of the modal properties of the nanorod metamaterial. The real-time optical monitoring setup provides excellent control and repeatability of nanostructure growth for the design of future ultrathin optical components. The performance of the ellipsometric method was also tested as a refractive index sensor. Monitoring refractive index changes near the metamaterial's epsilon near zero (ENZ) frequency showed a sensitivity on the order of 500°/RIU in the ellipsometric phase for a metamaterial that shows 250 nm/RIU sensitivity in its extinction.