Extension of Maxwell-Garnett theory for granular surfaces

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Abstract
The Maxwell-Garnett theory is generally used to describe the optical behavior of aggregated metallic films. This theory is, however, restricted to ultrafine particles whose main dimension can be considered very small compared to that of the wavelength. With particle dimensions in experiments generally larger than 10 nm, this approach is no longer valid for many metals. The purpose of the present work is, therefore, to revise the dipole approximation to include frequency-dependent terms. The theory is also extended to quadrupolar terms, in order to assess the relative importance of these latter when the aggregates are no longer very small compared to the wavelength. Applications to real metals are discussed.