Abstract
Gap plasmon-based optical metasurfaces have been extensively used for demonstration of flat optical elements with various functionalities efficiently operating at near-infrared and telecom wavelengths. Extending their operation to the visible is however impeded by the progressively increased plasmon absorption for shorter wavelengths. We investigate the possibility to improve the performance of gap plasmon-based metasurfaces in the visible by employing monocrystalline gold flakes as substrates instead of evaporated polycrystalline gold films, while using the electron-beam lithography patterning of the evaporated thin gold films for fabrication of top gold nanobricks, which define gap-plasmon resonator elements of the metasurfaces. We demonstrate that the efficiency can be improved by modest but noticeable amount of ≈5% if all other configuration parameters are preserved.
Highlights
Development of the optical metasurfaces [1,2,3] in the recent years allowed to overcome the limitations of the conventional optical components [4,5,6,7]
We investigate the possibility to improve the performance of gap plasmon-based metasurfaces in the visible by employing monocrystalline gold flakes as substrates instead of evaporated polycrystalline gold films, while using the electron-beam lithography patterning of the evaporated thin gold films for fabrication of top gold nanobricks, which define gap-plasmon resonator elements of the metasurfaces
In this work, using numerical simulations and experimental investigations, we study the possibility to improve the performance of beam-steering gap surface plasmon (GSP) metasurfaces in the visible by employing monocrystalline gold flakes as substrates (Fig. 1), while using the widely available and well-established electron-beam lithography (EBL) patterning of the evaporated thin gold films for fabrication of top gold nanobricks defining GSP elements of the metasurfaces
Summary
Development of the optical metasurfaces [1,2,3] in the recent years allowed to overcome the limitations of the conventional optical components [4,5,6,7]. In practice efficiency of the metasurface performance is significantly reduced by fabrication imperfections: in addition to deviations from the nanostructure design dimensions (typical tolerances are ±5 nm), it suffers from roughness and polycrystallinity of the evaporated metal films, that are commonly employed. These intrinsic properties of the evaporated metal films lead to increased surface scattering and greater Ohmic losses that inevitably decrease the quality of fabricated devices and their efficiency. Absorption and scattering losses in typical nanostructures fabricated using the evaporated gold films are so high, that in order to obtain realistic values for the efficiency in numerical simulations, the imaginary part of gold’s refractive index has to be pragmatically increased by a factor of 4 [28]
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