Probing the electronic response of nanostructures by THz time-domain spectroscopy

THz spectroscopy, by allowing one to measure the frequency-dependent complex conductivity, provides a powerful means of examining the charge transport in solids. The approach is of particular value for investigations of nanoscale systems, for which it is typically difficult to make direct electrical contact to the nanostructures under study. We describe recent applications of THz time-domain spectroscopy to probing nanostructures, including semiconductor nanoparticles and single-wall carbon nanotubes. Because of the pulsed nature of the THz probe radiation in the time-domain spectroscopy approach, the method is readily applicable to photo-excited systems, thus permitting one to examine photo-doped nanostructures and their dynamics. We are consequently able to obtain fundamental information about the charge carriers in nanostructures, including their lifetime and the nature of their response to applied electric fields.