Resonant Optical Transmission through Topologically Continuous Films

A continuous thick (≥ 100 nm) Ag film is generally optically nontransparent, but here we show that via a dedicated structuring it can be made transparent. The enhanced optical transmission is realized by preparing metal films with a periodic array of hollow nanocones via an inexpensive and versatile colloidal lithography technique. These topologically continuous films possess the structural feature of sharp top tips and bottom nanoholes, leading to an effective resonance mode of coupling between the surface plasmons around the holes and cone tips. This introduces a resonant optical transmission that is much affected by the thickness and height of the hollow nanocones. Moreover, the topologically continuous films are highly sensitive to the surrounding environment, indicating great potential for plasmonic sensors. The experimental results are in good agreement with numerical simulations. On the basis of the hollow element and enhanced optical performance, hollow nanocone array films can be used as photosensitive microreactors, isolated cell culture bases, etc. This provides a combination of high optical sensitivity and chemistry in microcavities.