Optical properties of discontinuous gold films: finite-size effects

The optical constants of discontinuous gold films consisting of both embedded and unembedded spherical particles in the size range 5–14 nm were determined from spectroellipsometric and spectrophotometric measurements. The optical response was modeled with the Yamaguchi anisotropic dielectric function. The energy and width dependence of the surface-plasmon resonance owing to the finite size of the gold particles was determined with a phenomenologically modified metal dielectric function. The expected blueshift and broadening of the resonance with decreasing particle size was observed. The magnitude of the shift suggests that lattice contraction, including its effect on both the free-electron response and the core response, plays an important role in determining the resonant energy. The width dependence on particle size was found to be well described by broadening parameters A=0.15 and A=0.22 for embedded and unembedded particles, respectively.