Electrical and Optical Properties of Carbon Nanotubes Characterized by Terahertz Electromagnetic Pulses

The frequency-dependent optical constants and electrical conductivities of hydrogen-functionalized single-walled carbon nanotubes have been measured from the 0.2- to 1.5-THz region using a terahertz time domain spectroscopy. The indices of refraction and electrical conductivities of the sample after hydrogen functionalization were smaller than those of the sample before hydrogen functionalization. The experimental results were fitted using the Maxwell-Garnett model, and a reduction of plasma frequency was observed. This can be attributed to the fact that the hydrogen functionalization has reduced the number of free carriers with the bonding change from sp²to sp³.