Using calculations from first principles, we investigate the lattice thermal conductivity of ideal monolayer and bilayer graphenes. Our result estimates that the intrinsic thermal conductivity of both materials is around 2200 W m −1 K −1 at 300 K, a value close to the one observed theoretically and experimentally in graphite along the basal plane. It also illustrates the expected T −1 dependence at higher temperatures. The little variation between monolayer and bilayer thermal conductivities suggests that the number of layers may not affect significantly the in-plane thermal properties of these systems. The intrinsic thermal conductivity also appears to be nearly isotropic for graphene.

Tunneling surface current through a thin ferromagnetic barrier on a three-dimensional topological insulator is shown to possess an extraordinary response to the orientation of barrier magnetization.In contrast to conventional magnetoresistance devices that are sensitive to the relative alignment of two magnetic layers, a drastic change in the transmission current is achieved by a single layer when its magnetization rotates by 90 degrees. Numerical estimations predict a giant magnetoresistance as large as 800 % at room temperature with the proximate exchange energy of 40 meV at the barrier interface. When coupled with electrical control of magnetization direction, this phenomenon may be used to enhance the gating function with potentially sharp turn-on/off for low power applications.

Using calculations from first principles we show how specific interface modifications can lead to a finetuning of the doping and band alignment in epitaxial graphene on SiC. Upon different choices of dopants, we demonstrate that one can achieve a variation of the valence band offset between the graphene Dirac point and the valence band edge of SiC up to 1.5 eV. Finally, via appropriate magnetic doping one can induce a half-metallic behavior in the first graphene monolayer. These results clearly establish the potential for graphene utilization in innovative electronic and spintronic devices.

Using calculations from first principles and the Landauer approach for phonon transport, we study the Kapitza resistance in selected multilayer graphene/dielectric heterojunctions (hexagonal BN and wurtzite SiC) and demonstrate (i) the resistance variability ($50 À 700 Â 10 À10 m 2 K=W) induced by vertical coupling, dimensionality, and atomistic structure of the system and (ii) the ability of understanding the intensity of the thermal transmittance in terms of the phonon distribution at the interface. Our results pave the way to the fundamental understanding of active phonon engineering by microscopic geometry design. V C 2012 American Institute of Physics.

Thermal properties in the metal/graphene (Gr) systems are analyzed by using an atomistic phonon transport model based on Landauer formalism and first-principles calculations. The spe- it is shown that the chemisorbed case provides a generally smaller interfacial thermal resistance than the physisorbed due to the stronger bonding. However, our calculation also indicates that the weakly chemisorbed interface of Pd/Gr may be an exception, with the largest thermal resistance among the considered. Further examination of the electrostatic potential and interatomic force constants reveal that the mixed bonding force between the Pd and C atoms results in incomplete hybridization of Pd and graphene orbital states at the junction, leading effectively to two phonon interfaces and a larger than expected thermal resistance. Comparison with available experimental data shows good agreement. The result clearly suggests the feasibility of phonon engineering for thermal property optimization at the interface.

We demonstrate field emission from an integrated three-terminal device using a suspended planar graphene edge as the source of vacuum electrons. Energy spectra of the emitted electrons confirm the field-emission mechanism. The energy spectra produced by graphene grown by chemical vapor deposition and reduced graphene oxide are compared. The drain-source voltage required to produce a given drain current increases when negative voltages are applied to the gate, confirming field-effect transistor operation. The emission current rises exponentially with inverse voltage over the measured current range from 1 pA to 10 nA. The current-voltage characteristics are consistent with tunneling through barrier potentials calculated numerically from the device geometry.

Graphene is an ideal material for hot-electron bolometers, due to its low heat capacity and weak electron-phonon coupling. Nanostructuring graphene with quantum dot constrictions yields detectors with extraordinarily high intrinsic responsivity, higher than 1×10 9 V W -1 at 3K. The sensing mechanism is bolometric in nature: the quantum confinement gap causes a strong dependence of the electrical resistance on the electron temperature. Here we show that this quantum confinement gap does not impose a limitation on the photon energy for light detection and these quantum dot bolometers work in a very broad spectral range, from terahertz, through telecom to ultraviolet radiation, with responsivity independent of wavelength. We also measure the power dependence of the response. Although the responsivity decreases with increasing power, it stays higher than 1×10 8 V W -1 in a wide range of absorbed power, from 1 pW to 0.4 nW.

The Joule heating effect on graphene electronic properties is investigated by using full-band Monte Carlo electron dynamics and three-dimensional heat transfer simulations self-consistently.A number of technologically important substrate materials are examined: SiO 2 , SiC, hexagonal BN, and diamond. The results illustrate that the choice of substrate has a major impact via the heat conduction and surface polar phonon scattering. Particularly, it is found that the poor thermal conductivity of SiO 2 leads to significant Joule heating and saturation velocity degradation in graphene (characterized by the so-called 1/ √ n decay). Considering the overall characteristics, BN appears to compare favorably against other substrate choices for graphene in electronic applications.