Conductivity Of Graphene Nanoribbons Research Articles

Comparison on thermal transport properties of graphene and phosphorene nanoribbons.

We investigate ballistic thermal transport at low temperatures in graphene and phosphorene nanoribbons (PNRS) modulated with a double-cavity quantum structure. A comparative analysis for thermal transport in these two kinds of nanomaterials is made. The results show that the thermal conductance in PNRS is greater than that in graphene nanoribbons (GNRS). The ratio kG/kP (kG is the thermal conductivity in GNRS and kP is the thermal conductivity in PNRS) decreases with lower temperature or for narrower nanoribbons, and increases with higher temperature or for wider nanoribbons. The greater thermal conductance and thermal conductivity in PNRS originate from the lower cutoff frequencies of the acoustic modes.

Unusual thermal conductivity behavior of serpentine graphene nanoribbons under tensile strain

Thermal conductivity of graphene nanoribbons usually decreases quickly with the increase of tensile strain due to the softened phonon modes and increased lattice anharmonicities. In this work, we present a new design of graphene nanoribbon structures—serpentine graphene nanoribbons (SGNRs) and demonstrate that thermal conductivity of SGNRs increases with the increase of tensile strain through nonequilibrium molecular dynamics (NEMD) simulations. This increase can be held till to as large as 54.7% stretchability of SGNRs. The unusual response of thermal conductivity results from the competition between the elongation of heat transfer path and stress distribution in nanoribbon structures under tension and is closely related with the maximum stretchability of serpentine structures. Both mechanical stress distribution and phonon spectrum of SGNRs are examined to understand the underlying thermal transport mechanism, and show good agreement with simulation findings.

Effect of Stone–Wales defects on the thermal conductivity of graphene

The problem of phonon scattering by strain fields caused by Stone–Wales (SW) defects in graphene is studied in the framework of the deformation potential approach. An explicit form of the phonon mean free path due to phonon-SW scattering is obtained within the Born approximation. The mean free path demonstrates a specific q-dependence varying as q−3 at low wavevectors and taking a constant value at large q. The thermal conductivity of graphene nanoribbons (GNRs) is calculated with the three-phonon umklapp, SW and rough edge scatterings taken into account. A pronounced decrease of the thermal conductivity due to SW defects is found at low temperatures whereas at room temperatures and above the phonon–phonon umklapp scattering becomes dominant. A comparison with the case of vacancy defects shows that they play more important role in the reduction of the thermal conductivity in GNRs over a wide temperature range.

Thermal conductivity of graphene nanoribbons accounting for phonon dispersion and polarization

The relative contribution to heat conduction by different phonon branches is still an intriguing and open question in phonon transport of graphene nanoribbons (GNRs). By incorporating the direction–dependent phonon–boundary scattering into the linearized phonon Boltzmann transport equation, we find that because of lower Grüneisen parameter, the TA phonons have the major contribution to thermal conductivity of GNRs, and in the case of smooth edge and micron–length of GNRS, the relative contribution of TA branch to thermal conductivity is over 50%. The length and edge roughness of GNRs have distinct influences on the relative contribution of different polarization branches to thermal conductivity. The contribution of TA branch to thermal conductivity increases with increasing the length or decreasing the edge roughness of GNRs. On the contrary, the contribution of ZA branch to thermal conductivity increases with decreasing the length or increasing the edge roughness of GNRs. The contribution of LA branch is length and roughness insensitive. Our findings are helpful for understanding and engineering the thermal conductivity of GNRs.

Effect of Chemical Structure on Polymer-Templated Growth of Graphitic Nanoribbons.

Graphene nanoribbon (GNR) is an important candidate for future nanoelectronics due to its high carrier mobility and dimension-controlled band gap. Polymer-templated growth is a promising method toward high quality and massive production of GNRs. However, the obtained GNRs so far are still quite defective. In order to rationally control the crystallinity of the synthesized GNRs, herein we systematically investigate the effect of polymer chemical structure on their templated growth of GNRs. We studied the morphology/dimensions, composition, graphitization degree, and electrical conductivity of GNRs derived from four different types of electrospun polymers. The four polymers polystyrene (PS), poly(vinyl alcohol) (PVA), polyvinylphenol (PVP), and Novolac (a phenolic resin) are chosen to investigate the effect of metal binding and the effect of aromatic moieties. We found that metal-binding functional groups are crucial for obtaining uniform and continuous GNRs. On the other hand, a polymer with aromatic moieties leads to a higher sp(2) percentage in the resulting GNRs, showing a higher graphitization degree and electrical conductivity.

Investigation of carbon dioxide adsorption effects on graphene nanoribbon conductance

A novel method is employed for the derivation of an analytical model for a carbon-dioxide (CO2) gas sensor based on graphene nanoribbon (GNR) conductance variation. The capacitance gradient created between the channel and the gate of a field effect transistor device is employed as an important property in the interpretation. Gas concentration and its effect on capacitance are incorporated as a modelling platform. In another attempt to model the electrical conductance in GNRs, an intelligent artificial neural network scheme is used in the modelling stage. A satisfactory agreement is presented by comparison between the empirical data extracted from a study conducted by Yoon et al. and the proposed models. © The Institution of Engineering and Technology 2015

High Performance Graphene Nano-ribbon Thermoelectric Devices by Incorporation and Dimensional Tuning of Nanopores.

Thermoelectric properties of Graphene nano-ribbons (GNRs) with nanopores (NPs) are explored for a range of pore dimensions in order to achieve a high performance two-dimensional nano-scale thermoelectric device. We reduce thermal conductivity of GNRs by introducing pores in them in order to enhance their thermoelectric performance. The electrical properties (Seebeck coefficient and conductivity) of the device usually degrade with pore inclusion; however, we tune the pore to its optimal dimension in order to minimize this degradation, enhancing the overall thermoelectric performance (high ZT value) of our device. We observe that the side channel width plays an important role to achieve optimal performance while the effect of pore length is less pronounced. This result is consistent with the fact that electronic conduction in GNRs is dominated along its edges. Ballistic transport regime is assumed and a semi-empirical method using Huckel basis set is used to obtain the electrical properties, while the phononic system is characterized by Tersoff empirical potential model. The proposed device structure has potential applications as a nanoscale local cooler and as a thermoelectric power generator.

Length, width and roughness dependent thermal conductivity of graphene nanoribbons

This letter reports on the investigation of temperature dependent thermal conductivity along a long free-standing graphene nanoribbon (GNR) by a one-dimensional direction-dependent phonon-boundary scattering in the frame of linearized phonon Boltzmann transport method. It is observed that GNR has highly length and width dependent thermal conductivity due to the difference between in-plane and out-of-plane phonon modes in the phonon dispersion curve. We show that phonon mediated thermal conduction increases with size, while it decreases with increasing edge roughness. These results are relevant for tailoring and engineering of the thermal conductivity of graphene nanoribbons in thermoelectronic and photonic devices.

Fano resonances in the conductance of graphene nanoribbons with side gates

The control of side gates on the quantum electron transport in narrow graphene ribbons of different widths and edge types (armchair and zigzag) is investigated. The conductance exhibits Fano resonances with varying side gate potential. Resonant and antiresonant peaks in the conductance can be associated with the eigenstates of a closed system, and these peaks can be accurately fitted with a Fano line shape. The local density of states (LDOS) and the electron current show a specific behavior at these resonances, which depends on the ribbon edge type. In zigzag ribbons, transport is dominated by intervalley scattering, which is reflected in the transmission functions of individual modes. The side gates induce $p\ensuremath{-}n$ interfaces near the edges at which the LDOS exhibits peaks. Near the resonance points, the electron current flows uniformly through the constriction, while near the antiresonances it creates vortices. In the armchair ribbons the LDOS spreads in areas of high potential, with current flowing near the edges.

237 グラフェンナノリボン電気伝導特性の三次元ひずみ場依存性

237 グラフェンナノリボン電気伝導特性の三次元ひずみ場依存性

The influence of grain boundaries on the low-temperature thermal conductivity of graphene nanoribbons

The low-temperature thermal conductivity of suspended long and narrow graphene ribbon with domain walls is investigated. Three acoustic phonon branches and the torsion mode are taken into account. The influence of domain walls replaces the low-temperature “quantum wire” behaviour of thermal conductivity κ ∼ T with Tn behaviour, where n < 1. The transition from “quantum-wire” to “2D graphene”-like behaviour is shifted to the higher temperature when domain walls are present.

The defect location effect on thermal conductivity of graphene nanoribbons based on molecular dynamics

Abstract The defect location effect on thermal conductivity of single-layer graphene nanoribbons is investigated. The length and width of pristine graphene nanoribbons are 12.3 nm and 5.112 nm in this paper. The results show the defect location has different levels of influence on thermal conductivity in horizontal and vertical directions. In vertical direction, the change of thermal conductivity is smaller than that in horizontal direction. The thermal conductivity of graphene nanoribbons shows some nonlinearity such as periodic trend when changing the defect location. It implies the chirality of zigzag graphene nanoribbons. In addition, phonon spectrum of atoms on the sides of the model is calculated. The results suggest the effect is greatly influenced by boundary scattering.

Thermal transport in folded zigzag and armchair graphene nanoribbons

Thermal conductivities of graphene nanoribbons (GNRs) and carbon nanotubes (CNTs) are systematically investigated by employing nonequilibrium molecular dynamics. It is found that with the same size, the thermal conductivity of armchair GNR (AGNR) is smaller than that of zigzag CNT, while thermal conductivity of zigzag GNR (ZGNR) is larger than that of armchair CNT. The phonon participation ratios and local vibrational densities of states of GNRs (CNTs) demonstrate that the edges of the ZGNR are beneficial to the heat transport, while the edges of the AGNR are completely opposite. All these results are very helpful for us to understand the thermal transport mechanism in carbon-based nanostructures.

Topological symmetry-induced width dependence of thermal conductance of edge-reconstructed graphene nanoribbons

Using the nonequilibrium Green's function method, we investigate the effects of edge reconstructions on the thermal conductance of graphene nanoribbons (GNRs). For the first time, we show that the thermal conductance of edge reconstructed zigzag GNRs oscillates with the number of dimers along the width direction, N. When N is an odd or even number, the thermal conductance of edge reconstructed zigzag GNRs is about 25 or 85% that of the perfect zigzag GNRs, respectively. For edge reconstructed armchair GNRs, the thermal conductance only decreases slightly and it changes linearly with N. The significant difference in the width dependence of GNR thermal conductance may be attributed to the topological symmetry and edge reconstruction of GNRs. Our results shed light on a new approach to control the thermal conductance of GNRs by reconstructing their edges and controlling their topological symmetry.

Thermal conductivity of graphene nanoribbons with defects and nitrogen doping

Thermal conductivity of defective graphene nanoribbons doped with nitrogen for different distributions around the defect edge at nanoscale is investigated using the reverse non-equilibrium molecular dynamics (RNEMD) method, which explores ways to improve thermal management. In addition, thermal conductivity of graphene nanoribbons with both defects and nearby nitrogen doping is investigated in comparison to that of nanoribbons with defects alone. The simulation results are analyzed from three perspectives: phonon match, concentration of N doping, and distribution of N doping. This approach reveals that a coupling effect is the cause of the observed results. Nitrogen doped graphene nanoribbons (both perfect and defective variants) perform better with thermal management than do graphene nanoribbons with defects alone, which is of considerable interest. Based on these investigations, a guide for graphene-interconnected circuits design is implied.

Thermal conductivity of graphene nanoribbons in noble gaseous environments

We investigate the thermal conductivity of suspended graphene nanoribbons in noble gaseous environments using molecular dynamics simulations. It is reported that the thermal conductivity of perfect graphene nanoribbons decreases with the gaseous pressure. The decreasing is more obvious for the noble gas with large atomic number. However, the gaseous pressure cannot change the thermal conductivity of defective graphene nanoribbons apparently. The phonon spectra of graphene nanoribbons are also provided to give corresponding supports.

Thermal Conductivity of Graphene Nanoribbons with Regular Isotopic Modification

Thermal Conductivity of Graphene Nanoribbons with Regular Isotopic Modification

Characterization of thermal conductivity for GNR based on nonequilibrium molecular dynamics simulation combined with quantum correction

A nonequilibrium molecular dynamics model combined with quantum correction is presented for characterizing the thermal conductivity of graphene nanoribbons (GNR). Temperature effect on graphene nanoribbon thermal conductivity is revealed based on this model. It is shown that different from the decreasing dependence in classical nonequilibrium molecular dynamics simulations, an “anomaly” is revealed at low temperatures using quantum correction. Besides, the conductivity of GNR shows obvious edge and scale effects: The zigzag GNR have higher thermal conductivity than the zigzag GNR. The whole temperature range of thermal conductivity and the slope of thermal conductivity at low temperatures both show an increasing dependence of width. Boltzmann-Peierls phonon transport equation is used to explain the temperature and scale effects at low temperatures, indicating that the model constructed is suitable for a wide temperature range of accurate calculation for thermal conductivity of different chirality and width. Research provides a possible theoretical and computational basis for heat transfer and dissipation applications of GNR.

Edge scattering of electrons in graphene: Boltzmann equation approach to the transport in graphene nanoribbons and nanodisks

We discuss the contribution of edge scattering to the conductance of graphene nanoribbons and nanoflakes. Using different possible types of the boundary conditions for the electron wave function at the edge, we found dependences of the momentum relaxation time and conductance on the geometric sizes and on the carrier density. We also consider the case of ballistic nanoribbon and nanodisk, for which the edge scattering is the main mechanism of momentum relaxation.

Graphene-based Plasmonic Nano-Antenna for Terahertz Band Communication in Nanonetworks

Nanonetworks, i.e., networks of nano-sized devices, are the enabling technology of long-awaited applications in the biological, industrial and military fields. For the time being, the size and power constraints of nano-devices limit the applicability of classical wireless communication in nanonetworks. Alternatively, nanomaterials can be used to enable electromagnetic (EM) communication among nano-devices. In this paper, a novel graphene-based nano-antenna, which exploits the behavior of Surface Plasmon Polariton (SPP) waves in semi-finite size Graphene Nanoribbons (GNRs), is proposed, modeled and analyzed. First, the conductivity of GNRs is analytically and numerically studied by starting from the Kubo formalism to capture the impact of the electron lateral confinement in GNRs. Second, the propagation of SPP waves in GNRs is analytically and numerically investigated, and the SPP wave vector and propagation length are computed. Finally, the nano-antenna is modeled as a resonant plasmonic cavity, and its frequency response is determined. The results show that, by exploiting the high mode compression factor of SPP waves in GNRs, graphene-based plasmonic nano-antennas are able to operate at much lower frequencies than their metallic counterparts, e.g., the Terahertz Band for a one-micrometer-long ten-nanometers-wide antenna. This result has the potential to enable EM communication in nanonetworks.