Morphologies of discontinuous gold films on amorphous polymer substrates

Transmission electron microscopy was used to analyze the effects of annealing treatments on the morphologies of discontinuous gold films evaporated onto polystyrene or poly(2-vinylpyridine) substrates. For polystyrene substrates the average size of discrete gold particles increases significantly during a long-term annealing treatment at 179 °C. The size distribution is well approximated by a log normal distribution function, consistent with a coalescence mechanism for particle growth. The fluid character of the polymer substrates at the annealing temperature of interest allows us to control this coalescence rate, thereby providing a unique method for controlling the microstructure of discontinuous metal films. Cross-sectional transmission electron microscopy showed that the coalescence rate for gold particles in a poly(2-vinylpyridine) matrix is much less than the coalescence rate for gold particles in a polystyrene matrix, indicating that polymer/metal interactions play an important role in the determination of the coalescence rate.