We report the measurement of the thermal conductivity of a suspended single-layer graphene. The room temperature values of the thermal conductivity in the range ∼(4.84 ± 0.44) × 103 to (5.30 ± 0.48) × 103 W/mK were extracted for a single-layer graphene from the dependence of the Raman G peak frequency on the excitation laser power and independently measured G peak temperature coefficient. The extremely high value of the thermal conductivity suggests that graphene can outperform carbon nanotubes in heat conduction. The superb thermal conduction property of graphene is beneficial for the proposed electronic applications and establishes graphene as an excellent material for thermal management.

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Superior Thermal Conductivity of Single-Layer Graphene

There is intense interest in graphene in fields such as physics, chemistry, and materials science, among others. Interest in graphene's exceptional physical properties, chemical tunability, and potential for applications has generated thousands of publications and an accelerating pace of research, making review of such research timely. Here is an overview of the synthesis, properties, and applications of graphene and related materials (primarily, graphite oxide and its colloidal suspensions and materials made from them), from a materials science perspective.

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Graphene and Graphene Oxide: Synthesis, Properties, and Applications

We present a comprehensive, up-to-date compilation of band parameters for the technologically important III–V zinc blende and wurtzite compound semiconductors: GaAs, GaSb, GaP, GaN, AlAs, AlSb, AlP, AlN, InAs, InSb, InP, and InN, along with their ternary and quaternary alloys. Based on a review of the existing literature, complete and consistent parameter sets are given for all materials. Emphasizing the quantities required for band structure calculations, we tabulate the direct and indirect energy gaps, spin-orbit, and crystal-field splittings, alloy bowing parameters, effective masses for electrons, heavy, light, and split-off holes, Luttinger parameters, interband momentum matrix elements, and deformation potentials, including temperature and alloy-composition dependences where available. Heterostructure band offsets are also given, on an absolute scale that allows any material to be aligned relative to any other.

Band parameters for III–V compound semiconductors and their alloys

Recent years have seen a rapid growth of interest by the scientific and engineering communities in the thermal properties of materials. Heat removal has become a crucial issue for continuing progress in the electronic industry, and thermal conduction in low-dimensional structures has revealed truly intriguing features. Carbon allotropes and their derivatives occupy a unique place in terms of their ability to conduct heat. The room-temperature thermal conductivity of carbon materials span an extraordinary large range--of over five orders of magnitude--from the lowest in amorphous carbons to the highest in graphene and carbon nanotubes. Here, I review the thermal properties of carbon materials focusing on recent results for graphene, carbon nanotubes and nanostructured carbon materials with different degrees of disorder. Special attention is given to the unusual size dependence of heat conduction in two-dimensional crystals and, specifically, in graphene. I also describe the prospects of applications of graphene and carbon materials for thermal management of electronics.

Thermal properties of graphene and nanostructured carbon materials

Graphene’s success has shown that it is possible to create stable, single and few-atom-thick layers of van der Waals materials, and also that these materials can exhibit fascinating and technologically useful properties. Here we review the state-of-the-art of 2D materials beyond graphene. Initially, we will outline the different chemical classes of 2D materials and discuss the various strategies to prepare single-layer, few-layer, and multilayer assembly materials in solution, on substrates, and on the wafer scale. Additionally, we present an experimental guide for identifying and characterizing single-layer-thick materials, as well as outlining emerging techniques that yield both local and global information. We describe the differences that occur in the electronic structure between the bulk and the single layer and discuss various methods of tuning their electronic properties by manipulating the surface. Finally, we highlight the properties and advantages of single-, few-, and many-layer 2D materials in...

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Progress, Challenges, and Opportunities in Two-Dimensional Materials Beyond Graphene

United States. Department of Energy. Office of Science. Basic Energy Sciences (Award Number: DE-SC0001299)

Discovery of ZrCoBi based half Heuslers with high thermoelectric conversion efficiency

We have used an atomistic ab initio approach with no adjustable parameters to compute the lattice thermal conductivity of Si${}_{0.5}$Ge${}_{0.5}$ with a low concentration of embedded Si or Ge nanoparticles of diameters up to 4.4 nm. Through exact Green's function calculation of the nanoparticle scattering rates, we find that embedding Ge nanoparticles in ${\text{Si}}_{0.5}{\text{Ge}}_{0.5}$ provides 20% lower thermal conductivities than embedding Si nanoparticles. This contrasts with the Born approximation, which predicts an equal amount of reduction for the two cases, irrespective of the sign of the mass difference. Despite these differences, we find that the Born approximation still performs remarkably well, and it permits investigation of larger nanoparticle sizes, up to 60 nm in diameter, not feasible with the exact approach.

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Role of light and heavy embedded nanoparticles on the thermal conductivity of SiGe alloys

Recently, using a first principles approach, we predicted that zinc blende boron arsenide (BAs) will have an ultrahigh lattice thermal conductivity, \ensuremath{\kappa}, of over 2000 Wm${}^{\ensuremath{-}1}$K${}^{\ensuremath{-}1}$ at room temperature (RT), comparable to that of diamond. Here, we provide a detailed ab initio examination of phonon thermal transport in boron arsenide, contrasting its unconventional behavior with that of other related materials, including the zinc blende crystals boron nitride (BN), boron phosphide, boron antimonide, and gallium nitride (GaN). The unusual vibrational properties of BAs contribute to its weak phonon-phonon scattering and phonon-isotope scattering, which are responsible for its exceptionally high \ensuremath{\kappa}. The thermal conductivity of BAs has contributions from phonons with anomalously large mean free paths (\ensuremath{\sim}2 \ensuremath{\mu}m), two to three times those of diamond and BN. This makes \ensuremath{\kappa} in BAs sensitive to phonon scattering from crystal boundaries. An order of magnitude smaller RT thermal conductivity in a similar material, zinc blende GaN, is connected to more separated acoustic phonon branches, larger anharmonic force constants, and a large isotope mixture on the heavy rather than the light constituent atom. The striking difference in \ensuremath{\kappa} for BAs and GaN demonstrates the importance of using a microscopic first principles thermal transport approach for calculating \ensuremath{\kappa}. BAs also has an advantageous RT coefficient of thermal expansion, which, combined with the high \ensuremath{\kappa} value, suggests that it is a promising material for use in thermal management applications.

Ab initio study of the unusual thermal transport properties of boron arsenide and related materials

We present a theory for the lattice thermal conductivity ${\ensuremath{\kappa}}_{L}$ of single-walled boron nitride nanotubes (BNNTs) and multilayer hexagonal boron nitride (MLBN), which is based on an exact numerical solution of the phonon Boltzmann equation. Coupling between layers in MLBN and nanotube curvature in BNNTs each break a phonon scattering selection rule found in single-layer hexagonal boron nitride (SLBN), which reduces ${\ensuremath{\kappa}}_{L}$ in these systems. We show that out-of-plane flexural phonons in MLBN and out-of-tube phonons in BNNTs provide large contributions to ${\ensuremath{\kappa}}_{L}$, qualitatively similar to multilayer graphene (MLG) and single-walled carbon nanotubes (SWCNTs). However, we find that the ${\ensuremath{\kappa}}_{L}$'s in BNNTs and MLBN are considerably smaller compared to similar SWCNTs and MLG structures because of stronger anharmonic phonon scattering in the former. A large and strongly temperature-dependent isotope effect is found reflecting the interplay between anharmonic and isotope scattering phonons. Finally, we also demonstrate convergence of BNNTs into SLBN for large-diameter nanotubes and MLBN to bulk hexagonal boron nitride within a few layers.

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Theory of thermal transport in multilayer hexagonal boron nitride and nanotubes

The lattice thermal conductivity of free standing wires is calculated within a Boltzmann equation approach. Diffusive and specular phonon scattering at the wire surfaces are included by appropriate boundary conditions on the phonon distribution. The wire thermal conductivity is found to decrease markedly below the bulk value for narrow wires. We show that this decrease in wires is larger than that which occurs in free standing wells of comparable size.

David Broido

Papers

Discovery of ZrCoBi based half Heuslers with high thermoelectric conversion efficiency

Role of light and heavy embedded nanoparticles on the thermal conductivity of SiGe alloys

Ab initio study of the unusual thermal transport properties of boron arsenide and related materials

Theory of thermal transport in multilayer hexagonal boron nitride and nanotubes

Lattice thermal conductivity of wires