Abstract:
Very thin spongy nanoporous gold films have a unique nanostructure and hence
unusual properties. Our interest in these materials is also due to their wide range of
potential applications [1,2]. An optical study for such nanostructured films is of
fundamental interest for understanding how light interacts with such a spongy
nanoporous structure. In general the gold either percolates or is very closely packed.
Thus surface plasmons, and surface plasmon resonant effects, are expected to play a
key role given the large surface area of metal and the metal backbone of the
nanostructure. The topological complexity of the nano-void network is also expected
to be a major influence. The optical response has, for a metal system, quite unusual
dispersion relations for the effective complex refractive index components n*, k*.
Once these are better understood, new optical engineering possibilities arise.
We are not aware of any optical studies for spongy metal film nanostructures apart
from a brief preliminary report of our own on one such film [3] whose nanostructure
was different to the spongy nanoporous films presented here. We check the internal
consistency and physical acceptability of the results with a Kramers-Kronig analysis
of the spectrum of n*, k* values, because of their unusual spectral character.
