Generalized
Effective Medium Theory to Extract the Optical Properties of Two-Dimensional
Nonspherical Metallic Nanoparticle Layers
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Abstract
A new
effective medium theory is introduced to describe the optical
properties of a two-dimensional array of metallic nanoislands. This
model which takes into account both the nanoisland orientation and
their shape distribution is successfully used to interpret the ellipsometric
measurements performed on gold nanoislands sputtered on a silicon
substrate. By coupling ellipsometry to atomic force microscopy measurements,
we show that the growth mechanism involves a Volmer–Weber growth
mode. The optical anisotropy of uniaxial films was attributed to in-plane
preferential self-orientation of gold nanoislands. Finally, we demonstrate
that the optical birefringence and dichroïsm of nanoisland
layers can be tuned during the film growth and are due to the splitting
of the plasmon resonance into two modes: the transversal and the longitudinal
modes of gold nanoislands