Growth, morphology, and optical and electrical properties of semicontinuous metallic films

The growth and optical properties of semicontinuous silver films on insulator substrates were studied experimentally and theoretically. In the experimental studies, films were synthesized by the pulsed-laser deposition technique, characterized by electron microscopy and in situ optical and dc electrical resistance measurements and studied using near-field optical microscopy. The percolation threshold of the films was found to be at similar to65% metal filling fraction, higher than the 50%-60% range of values predicted for two-dimensional (2D) bond or site percolation films and suggesting the importance of grain coalescence and 3D growth in our system. Local optical properties measured by near-field optical microscopy were compared with theoretical results obtained using the block-elimination method, with good agreement. Local-field distributions were found to depend strongly on the metal concentration and wavelength of illumination. The degree of localization was found to increase at metal concentrations both above and below the percolation threshold. At a very high metal coverage, very strong local fields were observed in submicron voids of a metal dielectric film. These fields are likely due to localized surface plasmon polaritons.