Dielectric-loaded plasmonic nanoantenna arrays: A metamaterial with tuneable optical properties

Abstract

The optical properties of metallic nanorod arrays acting as plasmonic nanoantennas have been studied. Large area arrays consisting of bare Au nanorods of diameter and length tuneable in the range of 20--40 and $200--400\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$, respectively, and spacing of about $40--100\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ have been electrochemically fabricated using templates of anodized nanoporous aluminium oxide. We demonstrate a very strong sensitivity of their resonant optical properties to both the presence of a dielectric load (which is much smaller than the wavelength of the resonant electromagnetic radiation) and modification of the refractive index of this load. This allows us to finely tune the spectral position of the plasmonic resonance of the nanoantenna arrays throughout the visible spectral range from about $550\phantom{\rule{0.3em}{0ex}}\text{to}\phantom{\rule{0.3em}{0ex}}800\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ with a sensitivity better than $3\phantom{\rule{0.3em}{0ex}}\mathrm{\AA{}}$ per $1\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ thickness of the dielectric load. Such dielectric-loaded plasmonic nanoantenna arrays represent a type of anisotropic metallodielectric metamaterials with fully adjustable optical properties for imaging, sensing, and nonlinear optical applications.