The percolation mechanism of conductivity in nanocomposite a-C:H<Ag+Ti> films

Abstract

The presented work is about percolation mechanism of electrical conductivity of composite a-C:H films. The a-C:H thin films were deposited onto quartz substrates by ion-plasma magnetron sputtering method. High purity argon (Ar) and methane (CH4) gases mixture and combined target of polycrystalline graphite with the purity of 99.99%, silver (99.99%) and titanium (99.99%) were used to produce а- С:Н films. Resistance of the produced films has been measured using «two probe» method to obtain concentration dependence of electrical conductivity. Conductivity of a-C:H films was described theoretically in two ways: using the classical theory of percolation and a general effective medium (GEM) theory. Staircase percolation can be seen from the experimental results. The first percolation threshold occurs at the concentration xc = 0.015 and the second one - at xc = 0.07. This could take place due to the fact that a- C:H composite material consist of two different inclusions, silver and titanium dioxide nanoparticles. The percolation mechanism of a-C:H film conductivity could be described by classical percolation theory and by effective medium model as well.