We measure and compare the electronic transport properties of individual multiwall carbon nanotubes ͑MWNTs͒ and individual single-wall carbon nanotubes ͑SWNTs͒, and SWNT networks of varying thickness. The thinnest SWNT networks, like the individual semiconducting SWNTs, show nonlinear current-voltage ͑I-V͒ characteristics at low temperatures with a current that can be modulated by a gate-source voltage. The overall temperature dependence of conductance in the transparent networks changes systematically as the thickness of the network increases and is consistent with hopping conduction. On the other hand, the thickest SWNT networks ͑freestanding film͒ show more metallic behavior: their I-V characteristics are linear with no gate-voltage effect, and a large fraction of their conductivity is retained at very low temperatures, consistent with tunneling through thin barriers separating metallic regions. We make a comparison with individual MWNTs, which in some cases show even greater retention of conductance at very low temperatures, but ͑unlike the thickest SWNT networks͒ no changeover to metallic temperature dependence at higher temperatures. The temperature dependence of conductance in individual MWNTs is consistent with a model involving conduction in the two outer shells.

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Evolution of a single graphene layer with disorder generated by remote oxygen plasma irradiation is investigated using atomic force microscopy, Raman spectroscopy and electrical measurement. Gradual changes of surface morphology from planar graphene to isolated granular structure associated with a decrease of transconductance are accounted for by two-dimensional percolative conduction by disorder and the oxygen plasma-induced doping effect. The corresponding evolution of Raman spectra of graphene shows several peculiarities such as a sudden appearance of a saturated D peak followed by a linear decrease in its intensity, a relatively inert characteristic of a D' peak and a monotonic increase of a G peak position as the exposure time to oxygen plasma increases. These are discussed in terms of a disorder-induced change of Raman spectra in the graphite system.

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The achievement of low-resistance contact is a key requirement for carbon-electrode electronics. In this study, we have obtained contacts with very low resistance between an individual single-walled carbon nanotube (SWNT) and palladium (Pd) electrodes using electric-current-induced Joule heating without destroying the field effect transistor device that these form. The SWNT is deposited onto Pd electrodes prepatterned on a SiO2/Si substrate, through which an electrical pulse is applied for a microsecond duration. As a result, the source–drain current through the SWNT is greatly increased owing to the elimination of tunnelling barriers between the SWNT and the electrodes. In the case of semiconducting SWNTs, the Schottky barrier is estimated to increase slightly after pulse annealing in some cases, resulting in a relatively high resistance and asymmetrical current–voltage characteristics.

Transparent conducting electrodes (TCEs) are the most important key component in photovoltaic and display technology. In particular, graphene has been considered as a viable substitute for indium tin oxide (ITO) due to its optical transparency, excellent electrical conductivity, and chemical stability. The outstanding mechanical strength of graphene also provides an opportunity to apply it as a flexible electrode in wearable electronic devices. At the early stage of the development, TCE films that were produced only with graphene or graphene oxide (GO) were mainly reported. However, since then, the hybrid structure of graphene or GO mixed with other TCE materials has been investigated to further improve TCE performance by complementing the shortcomings of each material. This review provides a summary of the fabrication technology and the performance of various TCE films prepared with graphene-related materials, including graphene that is grown by chemical vapor deposition (CVD) and GO or reduced GO (rGO) dispersed solution and their composite with other TCE materials, such as carbon nanotubes, metal nanowires, and other conductive organic/inorganic material. Finally, several representative applications of the graphene-based TCE films are introduced, including solar cells, organic light-emitting diodes (OLEDs), and electrochromic devices.

The radio-frequency (RF) electrical response of monolayer graphene is reported. From the measured S-parameter in the range of 10 MHz to 50 GHz, a simple equivalent resistor-inductor-capacitor (R-L-C) circuit is established to analyze frequency impedance. The impedance magnitude shows significant frequency dependence only below 10 GHz and this dispersive behavior is originated from the graphene-metal contact. Above 10 GHz, there is no distinctive change in overall characteristic of impedance due to the absence of the skin effect and low intrinsic kinetic inductance of graphene. These results show that graphene could be a promising candidate for high-speed device application.