Atomistic Study of the Lattice Thermal Conductivity of Rough Graphene Nanoribbons

Karamitaheri, Hossein; Pourfath, Mahdi; Faez, Rahim; Kosina, H.

doi:10.1109/ted.2013.2262049

Cited by 32 publications

(29 citation statements)

References 51 publications

(59 reference statements)

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“…The method is described in detail in our previous work, where we explored the length-dependence of the thermal conductance of GNRs [25,30]. We show that the exponent  is in fact not a single well-defined number, but it takes different values depending on whether the phonon transport is quasi-ballistic ( 1 The 4 th nearest-neighbor force-constant-method that we use (with parameters from [30]) can correctly regenerate the bandstructure of graphene as compared to experimental data [12], and also provides very good agreement with experimental data for rough GNRs with widths up to ~15 nm W [31]. Figure 1a shows for reference a typical phonon spectrum for a GNR channel of width 4 We extract the frequency dependent phonon transmission, ph T , and normalize it by the channel width W .…”

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confidence: 68%

On the channel width-dependence of the thermal conductivity in ultra-narrow graphene nanoribbons

Karamitaheri

Neophytou

2016

Applied Physics Letters

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The thermal conductivity of low-dimensional materials and graphene nanoribbons in particular, is limited by the strength of line-edge-roughness scattering. One way to characterize the roughness strength is the dependency of the thermal conductivity on the channel's width in the form W β . Although in the case of electronic transport this dependency is very well studied, resulting in W 6 for nanowires and quantum wells and W 4 for nanoribbons, in the case of phonon transport it is not yet clear what this dependence is. In this work, using lattice dynamics and Non-Equilibrium Green's Function simulations, we examine the width dependence of the thermal conductivity of ultranarrow graphene nanoribbons under the influence of line edge-roughness. We show that the exponent β is in fact not a single well-defined number, but it is different for different parts of the phonon spectrum depending on whether phonon transport is ballistic, diffusive, or localized. The exponent β takes values β < 1 for semi-ballistic phonon transport, values β >> 1 for sub-diffusive or localized phonons, and β = 1 only in the case where the transport is diffusive. The overall W β dependence of the thermal conductivity is determined by the width-dependence of the dominant phonon modes (usually the acoustic ones). We show that due to the long phonon mean-free-paths, the width-dependence of thermal conductivity becomes a channel length dependent property, because the channel length determines whether transport is ballistic, diffusive, or localized.

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confidence: 68%

On the channel width-dependence of the thermal conductivity in ultra-narrow graphene nanoribbons

Karamitaheri

Neophytou

2016

Applied Physics Letters

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“…Moreover, graphene is a zero-gap material and not suitable to use as thermoelectric material because of its very small Seebeck coefficient. However, theoretical studies revealed that phonon transport is sensitive to defects, strain, sample size and geometry [21] and it is known that by patterning graphene to form nanoribbons or anti-dots one can suppress the phonon contribution to heat transport [3]. This suppression is supported by experimental data, as reviewed in [2].…”

Section: Thermal Properties Of Graphenementioning

confidence: 88%

“…On the one hand efficient thermoelectricity requires a strongly suppressed thermal conductivity (κ) since the performance of thermoelectric devices is inversely proportional to the thermal conductivity. On the other hand, the cooling of local hot spots requires a high thermal conductivity [3]. Thermal conductance in a solid is defined by Fourier's law, where q is the heat flux, κ = κ pl + κ e is the thermal conductance due to phonons (κ pl ) and electrons (κ e ) and is the temperature gradient [1].…”

Section: Introductionmentioning

confidence: 99%

Enhancing the thermoelectric figure of merit in engineered graphene nanoribbons

Sadeghi¹,

Sangtarash²,

Lambert³

2016

Nano Online

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We demonstrate that thermoelectric properties of graphene nanoribbons can be dramatically improved by introducing nanopores. In monolayer graphene, this increases the electronic thermoelectric figure of merit ZT e from 0.01 to 0.5. The largest values of ZT e are found when a nanopore is introduced into bilayer graphene, such that the current flows from one layer to the other via the inner surface of the pore, for which values as high as ZT e = 2.45 are obtained. All thermoelectric properties can be further enhanced by tuning the Fermi energy of the leads.1176

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“…The transmission is significant in the entire energy spectrum and thus the whole spectrum contributes to thermal conductance for both the wide and narrow GNRs [26].…”

Section: B) Effect Of Roughness On Phonon Transmissionmentioning

confidence: 99%

Low-dimensional phonon transport effects in ultranarrow disordered graphene nanoribbons

et al. 2015

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We investigate the influence of low-dimensionality and disorder in phonon transport in ultra-narrow armchair graphene nanoribbons (GNRs) using non-equilibrium Green's function (NEGF) simulation techniques. We specifically focus on how different parts of the phonon spectrum are influenced by geometrical confinement and line edge roughness. Under ballistic conditions, phonons throughout the entire phonon energy spectrum contribute to thermal transport. With the introduction of line edge roughness, the phonon transmission is reduced, but in a manner which is significantly non-uniform throughout the spectrum. We identify four distinct behaviors within the phonon spectrum in the presence of disorder: i) the low-energy, low-wavevector acoustic branches have very long mean-free-paths and are affected the least by edge disorder, even in the case of ultra-narrow W=1nm wide GNRs; ii) energy regions that consist of a dense population of relatively 'flat' phonon modes (including the optical branches) are also not significantly affected, except in the case of the ultra-narrow W=1nm GNRs, in which case the transmission is reduced because of band mismatch along the phonon transport path; iii) 'quasi-acoustic' bands that lie within the intermediate region of the spectrum are strongly affected by disorder as this part of the spectrum is depleted of propagating phonon modes upon both confinement and disorder (resulting in sparse E(q) phononic bandstructure), especially as the channel length increases; iv) the strongest reduction in phonon transmission is observed in energy regions that are composed of a small density of phonon modes, in which case roughness can introduce transport gaps that greatly increase with channel length. We show that in GNRs of widths as small as W=3nm, under moderate roughness, both the low-energy acoustic modes and dense regions of optical modes can retain semi-ballistic transport properties, even for channel lengths up to 2 L=1μm. These modes tend to completely dominate thermal transport. Modes in the sparse regions of the spectrum, however, tend to fall into the localization regime, even for channel lengths as short as 10s of nanometers, despite their relatively high phonon group velocities.

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Atomistic Study of the Lattice Thermal Conductivity of Rough Graphene Nanoribbons

Cited by 32 publications

References 51 publications

On the channel width-dependence of the thermal conductivity in ultra-narrow graphene nanoribbons

On the channel width-dependence of the thermal conductivity in ultra-narrow graphene nanoribbons

Enhancing the thermoelectric figure of merit in engineered graphene nanoribbons

Low-dimensional phonon transport effects in ultranarrow disordered graphene nanoribbons

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