Terahertz Transmission Limiters Using Randomly Oriented Carbon Nanotubes Network Near Percolation Threshold

Abstract

We demonstrated a dramatic reduction in the terahertz (THz) transmittance and enhancement in the conductance of the carbon nanotube (CNT) random network system at high radiation intensities near the critical density limit. Amplification of the mesoscopic tunneling and rectification mechanism at the junctions between the adjacent nanotubes into the network induces the macroscopic phenomenon–optical limiting effect. In the percolative networks, the film conductance is dominantly determined by the electron tunneling at the CNT junctions, and the symmetry of the junctions breaks down by the randomness and defects in the network structure. This junction asymmetry enables the optical rectification and reduction of the tunneling barrier height when THz light impinges on the CNT network, and in turn enhancement in the CNT’s and their junctions’ conductance. Consequently, as the radiation intensity increases, the network becomes more conductive and less transparent.