Anisotropic optical constants of aggregated gold films by reflection and transmission ellipsometry

Studies of optical properties of aggregated films have usually been perform ed by considering the properties in the direction parallel to the film surf ace and, therefore, information on the films was not complete. The techniqu es of spectroscopic reflection and transmission ellipsometry (RTELL) at var iable incident angles developed by our laboratory were particularly suitabl e for obtaining the anisotropic optical constants for such films with good precision, thus fully characterizing the optical behavior of films. in the present study, aggregated gold films were prepared using solutions containi ng gold nanoparticles, giving films with a very low filling factor. With th e help of an automated RTELL system, the anisotropic optical constants have been determined in the spectral range from 300 to 800 nm. The results obta ined showed a striking difference between the parallel and the perpendicula r optical constants. This difference was well accounted for by using an eff ective-medium theory, approximating the nanoparticle clusters to rotational ellipsoids. (C) 2000 Elsevier Science S.A. All rights reserved.