Electrical response of carbon nanotubes under electrolyte

Chemical and electrical properties of carbon nanotubes regarding surface chemistry, carrier transport, current fluctuations, and electron-phonon interactions have been explored by utilizing electrolyte top gated carbon nanotube based devices. Individual semiconducting nanotubes have shown a negative threshold voltage shift at low pHs. The potential offsets induced by surface charges on carbon nanotubes have been considered to explain the observed pH response of nanotube transistors under electrolyte. The noise measurements have been carried out in order to examine effects of potential surface chargeable groups as carrier trapping/scattering sites on electron transport properties. The measured current fluctuations have a distinct dependence on the threshold voltage of nanotube devices. This result suggests non-uniform energy distribution of potential carrier trapping/scattering sites, which may include surface groups on carbon nanotubes. In addition, 1/f noise characterizations have been utilized to investigate intrinsic carrier transport properties of metallic carbon nanotubes. Metallic nanotubes exhibit resonance-like enhancements in current fluctuations only when electrons attain enough energy from applied electric field to emit optical phonons and the Fermi level lies near the band crossing point. The Fermi level dependent enhancements in noise amplitude have been correlated with Raman G-band broadening. These observations suggest that F optical phonons have dominant effects on the rise of current fluctuations rather than K zone-boundary phonons that limit current carrying capacity.