Abstract
AbstractStrong electromagnetic field confinement and enhancement can be readily achieved in plasmonic nanoantennas, however, this is considerably more difficult to realize over large areas, which is essential for many applications. Here, dispersion engineering in plasmonic metamaterials is applied to successfully develop and demonstrate a coupled array of plasmonic–dielectric nanoantennas offering an ultrahigh density of electromagnetic hot spots (1011 cm−2) over macroscopic, centimeter scale areas. The hetero‐metamaterial is formed by a highly ordered array of vertically standing plasmonic dipolar antennas with a ZnO gap and fabricated using a scalable electrodeposition technique. It supports a complex modal structure, including guided, surface and gap modes, which offers rich opportunities, frequently beyond the local effective medium theory, with optical properties that can be easily controlled and defined at the fabrication stage. This metamaterial platform can be used in a wide variety of applications, including hot‐electron generation, nanoscale light sources, sensors, as well as nonlinear and memristive devices.
Highlights
Strong electromagnetic field confinement and enhancement can be readily resulting intensity hot spots can be used for achieved in plasmonic nanoantennas, this is considerably more difficult to realize over large areas, which is essential for many applications
Within the framework of the local effective medium theory (EMT) theory, in the first approximation the optical properties of the nanorod metamaterial do not depend on the particular type of the nanorod arrangement, being defined only by the metal filling factor.[23,24,42]
Gold was chosen as a standard plasmonic material with relatively low losses, which assures high quality factors of the resonances and, high field enhancement
Summary
Split-rod metamaterials were fabricated via sequential electrodeposition of Au (bottom section), ZnO (middle section) and Au (top section) into a nanoporous Al2O3 (alumina, AAO) matrix produced by anodization of an Al film (see the Experimental Section). To study the role of the gap width in the formation of the modes, the length of the metallic segments was fixed to 100 nm, while the thickness of the ZnO layer between them was varied from 20 to 100 nm In this case, the mode spectral positions move to longer wavelengths with the increase of the gap (Figure S6, Supporting Information). The highest field intensity is not observed for the gap position close to the mode-supporting interface (where it is minimal), but closer to the opposite side (Figure 5e) This can be explained by the peculiarity of coupling- and distance-related phase shift between the incident light and the excited surface wave, influenced by the local phase response of the involved metallic segments. To study this aspect and reveal the optimal conditions for maximal field intensity enhancement, the ratio of the field intensities integrated over the gap volume and over the matrix domain was plotted as a function of the wavelength
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