Use of monocrystalline gold flakes for gap plasmon-based metasurfaces operating in the visible

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.