Optical Transmittance through Ultrathin Gold Films with Subwavelength Hole Arrays

Resonantly enhanced transmission through subwavelength periodic structure in metallic film has received much attention since the phenomenon of extraordinary optical transmission (EOT) was discovered by Ebbesen in 1998. A variety of novel phenomena caused by the interaction of light with metallic film, the surface plasmon polaritons (SPPs) plays a crucial role. The research work about the phenomenon of SPP has been focused on relatively thick metallic films, while ultrathin films with the thickness smaller or comparable to the skin depth are almost neglected. Therefore, a series of ultrathin gold films with hexagonal arrays of subwavelength holes of various hole diameters have been fabricated using nanosphere lithography technique and oxygen reactive ion etching. Their optical transmittances are measured and compared with the simulated results using the FDTD method. The experimental and measurement results demonstrate that the transmittance spectra can be precisely engineered by tuning the geometry parameters of the nanostructures. These investigations provide a guide for the design and fabrication of transparent electrodes based on ultrathin metal films.