Optical absorption in discontinuous gold films

Discontinuous gold films with mass thicknesses 1.1–4.0nm were prepared by UHV-deposition onto glass substrates. The islands were accurately represented by randomly oriented prolate spheroids (symmetry axis parallel with substrate plane) with varying sizes and eccentricities. Optical transmittance was recorded for wavelengths 0.3–2.5μm. Extensive computations, based on the Maxwell-Garnett formalism, were carried out for islands surrounded by air. The calculated transmittances were much larger than the experimental ones. The most likely explanation is that local field effects are more prominent than estimated from recent theories.