Optical properties and microstructure of gold–fluorocarbon-polymer composite films

Abstract

The optical transmittance of plasma-deposited composite gold–fluorocarbon-polymer thin films is analyzed in terms of effective-medium theories. The effect of increasing gold volume fraction is shown to be correctly described by the Sheng model, provided the gold-cluster and polymer-inclusion sizes and shapes analyzed by transmission electron microscopy are properly taken into account. Moreover, good consistency is obtained between the present results and our previous study of the electrical conductivity variation at and above the percolation threshold. An extension of the Sheng model has been developed to deal with three-phase systems and has been applied in this work to test the possible existence of an interfacial carbon layer at the gold-polymer interface. The effects of topological disorder and higher-order multipole interactions between the clusters are discussed. Annealing of the films above the glass transition temperature of the polymer results in a drastic change of the film optical properties which is attributed to an increase of gold volume fraction, due to the collapse of the polymer phase, and above all to a modification of the cluster sizes and shapes by sintering and coalescence of gold particles as confirmed by transmission electron microscopy.