Anomalous dispersion in nanocomposite films at the surface plasmon resonance

Nanocomposite thin films formed by Cu nanocrystals (NCs) embedded in an amo rphous aluminium oxide (Al2O3) host have been prepared by alternate pulsed laser deposition. Spectroscopic ellipsometry is used to determine the effec tive refractive index (n = n + ik). The extinction coefficient is non-negli gible and shows a broad absorption band related to the surface plasmon reso nance. In the neighbourhood of this wavelength, the real part of the refrac tive index undergoes an anomalous dispersion, leading to a significant incr ease of the n value of the composite compared to that of the host. When the Cu content is low enough, about 2 at. %, the use of an effective medium ap proach combined with a regression method allows us to determine the metal c ontent and film thickness from the ellipsometric measurements. For larger c oncentrations this approach is no longer valid.