Chapter 14: Spectroscopy of Ground- and Excited-State Charge Carriers in Single-Wall Carbon Nanotubes

A host of both natural processes and man-made technologies rely upon the flow of electronic charge to transport and inter-convert energy over widely varying time scales. Semiconductor-based technologies rely upon careful control over both the ground-state densities of electrons or holes (in n- or p-type semiconductors, respectively) and the dynamic processes that occur for minority and/or majority charge carriers in the excited state. Single-walled carbon nanotubes (SWCNTs) have now been demonstrated as useful elements in a wide range of energy conversion (and other) technologies, including photovoltaics, thermoelectrics, digital logic, and quantum information processing. Elucidating the fundamental mechanisms at play in these technologies hinges upon a deep understanding of the energies and densities of energetic species (e.g. charge carriers, excitons, phonons) and the dynamic processes that define the interconversion between these species when the SWCNTs are exposed to perturbations (e.g. illumination, heat, bias). As such, a large body of work has been devoted to spectroscopic measurements of electrons and holes in SWCNTs over a broad range of energy and timescales. In this chapter, we discuss some critical aspects of using spectroscopic techniques to probe charge carriers in both the ground and excited state of SWCNTs, with a particular focus on recent experiments involving highly enriched semiconducting SWCNTs.