Metallic nanoparticles embedded in a dielectric matrix: Growth mechanisms and percolation

We present a study of the preparation and structural characterization of granular Ag-ZrO2, Co-ZrO2, and Au-ZrO2 thin films grown by pulsed laser deposition ( PLD) in a wide range of volume fraction x of metal ( 0.08 < x(Ag) < 0.28, 0.06 < x(Co) < 0.40, and 0.08 < x(Au) < 0.55). High-resolution transmission electron microscopy ( HRTEM) showed regular distribution of spherical Au, Co, and Au nanoparticles having very sharp interfaces with the amorphous matrix. The structural results are compared aiming to stress the effect of the actual microstructure on the percolation threshold. Two different mechanisms of particle growing as a function of the metal content are evidenced: nucleation and particle coalescence, with their relative significance depending strongly on the type of metal, giving rise to very different values of the percolation threshold (x(c)(Ag)similar to 0.28, x(c)(Co)similar to 0.35, and x(c)(Au)similar to 0.55). Copyright (C) 2008 M. Garcia del Muro et al.