Refractive index of Ag nanocrystals composite films in the neighborhood of the surface plasmon resonance

Nanocomposite thin films formed by Ag nanocrystals embedded in an amorphous aluminum oxide (Al2O3) host were prepared by alternating-target pulsed laser deposition. Spectroscopic ellipsometry was used to determine the effective refractive index (n=n+ik). When the Ag volume fraction is over 2%, the linear optical properties of the nanocomposite films differ from those of the pure dielectric host. The extinction coefficient shows a maximum around 435 nm that is related to the surface plasmon resonance. Near this wavelength, the real part of the refractive index undergoes anomalous dispersion, leading to a significant increase of the n value of the composite compared to that of the matrix.