Light transmission through perforated metal thin films made by island lithography

Transmission spectra of thin metal films perforated by a high density of disordered sub-wavelength diameter cylindrical holes have been measured. The films, consisting of duplex layers of chromium and gold or chromium and silver, were characterised by perforations of mean diameter, d) and fractional area coverage, F: films with (d) and F of 187 +/- 50 nm and 0.2 1, and 340 +/- 67 run and 0.28 were studied. The transmission efficiency of the holes in these films was near unity in the range 340-850 nm. These results are comparable to those found for ordered perforated metal films but without the spectral structure. The sheet resistance of the films, perforated and un-perforated, was measured. The sheet resistance of the un-perforated films was larger than bulk and typical for that found for un-annealed films. The additional resistance of the perforated films is consistent with available spreading resistance calculations. These results suggest that it will be possible to prepare perforated film having comparatively high optical transmission and low electrical resistance. (C) 2004 Elsevier B.V. All rights reserved.