Measurements and Simulations of Surfactant's Impact on the Conductivity and the Noise in Percolation Carbon Nanotube Networks

In this paper, we present a study of 2-D carbon nanotube (CNT) thin films. Conductance and 1/f noise have been experimentally and theoretically investigated. Experimentally, after fabrication and characterization of 2-D films, we have established that the percolation process is the primary physical mechanism influencing the conductance and the noise level in such films, and it strongly depends on the homogeneity of the structure. Theoretically, based on CNT physics and using the Monte Carlo distribution, we have developed a numerical model allowing us to simulate the conductance and 1/f noise in 2-D films. We assume that noise sources are localized at nanotube-nanotube junctions. We use the modified nodal analysis to describe our network and to provide dc and noise characteristics. This model can simulate inhomogeneous structures in good agreement with the experimental results. Nevertheless, for high densities of nanotubes, we have shown that the presence of nanotube clusters in the network affects the noise level in 2-D films. This leads to the conclusion that the noise critical exponent of the percolation power law is not invariant. By comparing the simulations with our experimental results, we have found that our assumptions on the origin of noise generated by tube-tube junctions dominate the total nanotube film 1/f noise despite the presence of nanotube clusters.