Spectroellipsometric characterization of plasma-deposited Au/SiO2 nanocomposite films

Nanocomposite films consisting of metal nanoparticles embedded in a dielect ric matrix were fabricated by simultaneous sputtering of a gold target and plasma-enhanced chemical vapor deposition of hydrogenated SiO2. The optical constants of the films were determined from spectroscopic ellipsometry mea surements and were modeled using the Maxwell-Garnett effective medium theor y. The particle size dependence of the free electron absorption was include d according to the limited electron mean free path effect using a broadenin g parameter A=0.16 determined from the comparison of the measured spectra w ith transmission electron microscopy micrographs. Using bulk interband opti cal constants for gold, very good agreement was obtained between the model and the measured spectra but only in the narrow particle size range similar to 10-20 nm, the latter of which marks the onset of phase retardation effe cts. For smaller particles, the energy of the surface plasmon resonance was progressively blueshifted with respect to the predicted value. This was in terpreted by a size dependence of the interband transitions as a result of strain-induced variation of the lattice constant within the particle. (C) 2 000 American Institute of Physics. [S0021-8979(00)05201-4].