Homogenized Lorentz-Drude optical response in highly nanoporous conducting gold layers produced by de-alloying

Elsevier Science Bv
Publication Type:
Journal Article
Optics Communications, 2007, 271 (1), pp. 263 - 268
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Nanoporousgold films produced by de-alloying AuAl2 with void densities between 45% and 65% retain high infra-red reflectance and good conductivity. They act optically like a homogenous Lorentz-Drude metal with a unique wp and an inter-band transition energy unchanged from that of dense gold. The link between wp and wp in dense gold is found using a cimplification of the Bergmann expansio for permittivity valid at infra-red wavelengths. The carrier relaxation time of the effective metal becomes the actual relaxation time in the Au netowork and the complex refractive indices (n.k) found using normal incidence spectrophotometry and oblique incidence ellipsometry agree closely with each other. The single pole approximation for the ratio wp/wp in the infra-red allows estimates of void content and the apparent shift in carrier effective mass. It is then possible to model with no adjustable parameters, the full UV-visible-NR spectral response, giving excellent agreemtn with data. A range of films with these properties are presented.
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