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

Journal Article · Mon Aug 08 00:00:00 EDT 2016 · Applied Physics Letters

DOI:https://doi.org/10.1063/1.4960528· OSTI ID:22594357

Karamitaheri, Hossein ^[1]; Neophytou, Neophytos ^[2]

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1. Department of Electrical Engineering, University of Kashan, Kashan 87317-53153 (Iran, Islamic Republic of)
2. School of Engineering, University of Warwick, Coventry CV4 7AL (United Kingdom)

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{sup β}. Although in the case of electronic transport, this dependency is very well studied, resulting in W{sup 6} for nanowires and quantum wells and W{sup 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 ultra-narrow 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{sup 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.

• OSTI ID: 22594357
• Journal Information: Applied Physics Letters, Vol. 109, Issue 6; Other Information: (c) 2016 Author(s); Country of input: International Atomic Energy Agency (IAEA); ISSN 0003-6951
• Country of Publication: United States
• Language: English

Related Subjects

71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
COMPUTERIZED SIMULATION
EQUILIBRIUM
GRAPHENE
GREEN FUNCTION
LENGTH
MEAN FREE PATH
NANOWIRES
PHONONS
QUANTUM WELLS
ROUGHNESS
SCATTERING
SPECTRA
THERMAL CONDUCTIVITY
TRANSPORT THEORY
WIDTH