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

Abstract

We demonstrated a dramatic reduction in the sub-terahertz (sub-THz) transmittance and enhancement in the conductance of the carbon nanotube (CNT) mats at high radiation intensities near the percolation threshold, i.e. at the CNT concentrations where the mat conductivity as a function of the CNT concentration sharply increases. The CNT mat conductivity near the percolation point is determined by the electron (or hole for p-type CNTs) tunneling between the adjacent nanotubes. The symmetry of CNT contacts is broken by the differences in the positions and the sizes and types of the contacting CNTs enabling the rectification of the THz or sub-THz radiation impinging on the CNT mats. As the consequence of such rectification, the tunneling barrier shape changes to a more triangular share enhance the CNT mat AC conductivity and decrease transmission. One application of this effect is films preventing damage to sensitive THz and sub-THz detectors (such as Schottky diodes or TeraFETs) by limiting the maximum power impinging on the detectors. Since the shape of the tunneling barriers is strongly affected by ambience and/or substrate monitoring limiting CNT transmission near the percolation point transmission as function of intensity, temperature, and frequency could be used for humidity, temperature, gas exposure, strain, and multiple sensors of external stimuli. The nanoscale of CNT contacts and gaps enables high speed THz responses.