Individual graphene oxide sheets subjected to chemical reduction were electrically characterized as a function of temperature and external electric fields. The fully reduced monolayers exhibited conductivities ranging between 0.05 and 2 S/cm and field effect mobilities of 2-200 cm2/Vs at room temperature. Temperature-dependent electrical measurements and Raman spectroscopic investigations suggest that charge transport occurs via variable range hopping between intact graphene islands with sizes on the order of several nanometers. Furthermore, the comparative study of multilayered sheets revealed that the conductivity of the undermost layer is reduced by a factor of more than 2 as a consequence of the interaction with the Si/SiO2 substrate.

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The realization of high-performance electrical devices incorporating single-wall carbon nanotubes critically depends on the minimization of charge transport barriers in the tubes and at the contacts. Herein we demonstrate photocurrent imaging as a fast and effective tool to locate such barriers within individual metallic nanotubes contacted by metal electrodes. The locally induced photocurrents directly reflect the existence of built-in electric fields associated with the presence of depletion layers at the contacts or structural defects along the tubes.

Confocal optical microscopy was employed to study the effect of surface-enhanced Raman scattering on individual single-walled carbon nanotubes covered with isolated gold particles. The gold particles with diameters between 10 and 120 nm were deposited in low densities on the tubes' sidewalls by an electrochemical method. In the spectra, Raman peaks associated with the nanotubes were found to be superimposed on a broad luminescence background originating from the metal particles. With increasing particle size, both the luminescence intensity as well as the Raman enhancement increased at longer wavelengths. This finding is consistent with a size-dependent broadening of the gold plasmon frequency and a corresponding extension of the energetic range for local field enhancement on the particle surface. In addition, wavelength-dependent experiments revealed a maximum Raman intensity when both nanotube and metal particle were in optical resonance.