Infrared Photoconductivity of Individual Carbon Nanotubes Using Fourier-Transform Spectroscopy

We have developed a novel infrared spectroscopy technique for studying the photocurrent response of individual semiconducting carbon nanotubes. We use a synchrotron-based, broadband infrared light source coupled to a Fourier-transform spectrometer and microscope to induce currents in electrically biased nanotubes. This approach enables the rapid acquisition of high-resolution photocurrent spectra near the bandgap of the larger diameter ($>$ 1.7 nm) nanotubes commonly produced by synthesis using chemical vapor deposition. We have recorded optical transitions with energies as low as 0.4 eV for individual nanotubes. The structures used in these measurements consisted of isolated nanotubes with well-separated metal contacts on a Si back gate. In addition to describing the experimental approach and results, we will discuss the sensitive dependence of the measured photocurrent on the electrical biasing conditions.