Optical response in nanostructured thin metal films with dielectric over-layers

Abstract

Thin metal films which contain nano-size pores yield higher than expected transmittance and larger than expected times for transmission of near infra red radiation. An optically equivalent layer with complex refractive index (n*,k*) can model measured specular transmittance and reflectance, when scattering is weak. The way surface plasmon effects impact on these measured indices is considered. A strongly elevated n* is linked to trad the time for a surface plasmon to re-radiate and hence delay transmission times, and reduced imaginary part k*, to resonant channelling via voids. Measurement of n* thus allows an estimate of trad. The sensitivity of (n*,k*) to surface effects is illustrated using an insulating overlayer to modify the surface states. Resultant measured changes in n*,k* are substantial. Results are for two nanostructured metal systems characterised with 400,000× scanning electron microscopy.