Microstructure and electrical conductivity of plasma deposited gold/fluorocarbon composite films

Abstract

Gold containing plasma polymerized fluorocarbon films have been deposited at room temperature by reactive rf sputtering. The dc electrical conductivity of the films has been measured as a function of gold volume fraction and changes drastically after annealing at about 180 °C. Two phenomena can be distinguished: (1) a contraction of the cross-linked polymer phase in the film due to internal relaxations which results in relative increase of gold volume fraction; and (2) a change of the gold cluster sizes and shapes observed by transmission electron microscopy (TEM). The latter effect is best interpreted by using the effective medium theory of Sheng which accounts for the influence of particle shape on the percolation threshold and the variation of conductivity of a composite material. Before annealing, the films can be described as a statistical mixture of spherical gold particle coated with polymer and very flat platelets (oblate spheroids) of polymer coated with gold, randomly oriented. The effect of annealing can be accounted for by reduction of oblateness of the gold coated polymer inclusions as confirmed by TEM observations.