Substrate and aspect-ratio effects in resonant nanoaperture arrays

Here we discuss the influence of a substrate on transmission through subwavelength holes in metallic films. In particular, we show that in the case of transmission maxima associated with localized resonances of the apertures, that the wavelength at which this maximum occurs are strongly influenced by the presence of a substrate and the aspect ratio of the structure. Furthermore, we show that removing a shallow region of the substrate immediately below the apertures leads to blue-shifting of the resonance and increased transmission compared to that in the presence of a homogeneous substrate.