The reported thermal conductivity (kappa) of suspended graphene, 3000 to 5000 watts per meter per kelvin, exceeds that of diamond and graphite. Thus, graphene can be useful in solving heat dissipation problems such as those in nanoelectronics. However, contact with a substrate could affect the thermal transport properties of graphene. Here, we show experimentally that kappa of monolayer graphene exfoliated on a silicon dioxide support is still as high as about 600 watts per meter per kelvin near room temperature, exceeding those of metals such as copper. It is lower than that of suspended graphene because of phonons leaking across the graphene-support interface and strong interface-scattering of flexural modes, which make a large contribution to kappa in suspended graphene according to a theoretical calculation.

Tailoring the electronic arrangement of graphene by doping is a practical strategy for producing significantly improved materials for the oxygen-reduction reaction (ORR) in fuel cells (FCs). Recent studies have proven that the carbon materials doped with the elements, which have the larger (N) or smaller (P, B) electronegative atoms than carbon such as N-doped carbon nanotubes (CNTs), P-doped graphite layers and B-doped CNTs, have also shown pronounced catalytic activity. Herein, we find that the graphenes doped with the elements, which have the similar electronegativity with carbon such as sulfur and selenium, can also exhibit better catalytic activity than the commercial Pt/C in alkaline media, indicating that these doped graphenes hold great potential for a substitute for Pt-based catalysts in FCs. The experimental results are believed to be significant because they not only give further insight into the ORR mechanism of these metal-free doped carbon materials, but also open a way to fabricate other new low-cost NPMCs with high electrocatalytic activity by a simple, economical, and scalable approach for real FC applications.

Using low-resistance electrical contacts, we have measured the intrinsic high-field transport properties of metallic single-wall carbon nanotubes. Individual nanotubes appear to be able to carry currents with a density exceeding 10 9 A͞cm 2 . As the bias voltage is increased, the conductance drops dramatically due to scattering of electrons. We show that the current-voltage characteristics can be explained by considering optical or zone-boundary phonon emission as the dominant scattering mechanism at high field. PACS numbers: 73.50.Fq, 72.10.Di, 73.61.Wp The potential electronic application of single-wall carbon nanotubes (SWNTs) requires a detailed understanding of their fundamental electronic properties, which are particularly intriguing due to their one-dimensional (1D) nature [1]. Metallic SWNTs have two 1D subbands crossing at the Fermi energy. In the ideal case the resistance is thus predicted to be h͞4e 2 or 6.5 kV. In early electrical transport experiments, however, the nanotubes typically formed a tunnel barrier of high resistance of ϳ1 MV with the metal contacts [2,3]. Consequently, the bias voltage dropped almost entirely across the contacts, and tunneling dominated the transport. A number of interesting phenomena have been observed in this regime. At low temperatures, Coulomb blockade effects prevail [2,3]. At relatively high temperatures, the transport characteristics appear to be described by tunneling into the so-called Luttinger liquid-a unique correlated electronic state in 1D conductors which is due to electron interactions [4,5].One of the most important questions that remains to be addressed is how the electrons traverse the nanotubes, i.e., whether ballistically or being scattered by impurities or phonons. The unusual band structure of metallic tubes suggests a suppression of elastic backscattering of electrons by long-range disorder [6]. Long mean-free paths for electrons near the Fermi energy have indeed been inferred from regular Coulomb oscillations and coherent tunneling at low temperatures [2,7]. However, there has been no transport study of electrons with significant excess energy above the Fermi energy. It is not clear whether such electrons would experience strong scattering and what type of scattering mechanism would dominate.In this Letter we present electrical transport measurements of individual nanotubes using low-resistance contacts (LRCs). In contrast to the high-resistance contacts (HRCs), a bias voltage applied between two LRCs establishes an electric field across the nanotube which accelerates the electrons, enabling transport studies of high-energy electrons. We find that individual SWNTs can sustain a remarkably high current density of more than 10 9 A͞cm 2 . The current seems to saturate at high electric field. We discuss possible scattering mechanisms and suggest that optical or zone-boundary phonon emission by high-energy electrons can explain the observed behavior. An analytic theory based on the Boltzmann equation is developed which includes both elastic scatteri...

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We fabricate and characterize dual-gated graphene field-effect transistors (FETs) using Al 2 O 3 as top-gate dielectric. We use a thin Al film as a nucleation layer to enable the atomic layer deposition of Al 2 O 3 . Our devices show mobility values of over 8,000 cm 2