Engineering enhanced thermoelectric properties in zigzag graphene nanoribbons

Abstract

We theoretically investigate the thermoelectric properties of zigzag graphene nanoribbons in the presence of extended line defects, substrate impurities and edge roughness along the nanoribbon's length. A nearest-neighbor tight-binding model for the electronic structure and a fourth nearestneighbor force constant model for the phonon bandstructure are used. For transport we employ quantum mechanical non-equilibrium Green's function simulations. Starting from the pristine zigzag nanoribbon structure that exhibits very poor thermoelectric performance, we demonstrate how after a series of engineering design steps the performance can be largely enhanced. Our results could be useful in the design of highly efficient nanostructured graphene nanoribbon based thermoelectric devices.

Low-dimensional phonon transport effects in ultranarrow disordered graphene nanoribbons

“…Two orders of magnitude reduction in thermal conductivity has been reported for several low-dimensional materials due to roughness compared to the pristine materials, which significantly improve their thermoelectric properties [61,62,14]. Specifically, with regard to GNRs, studies concluded that edge roughness in GNRs can indeed reduce the thermal conductivity by up to two orders of magnitude, depending on the assumptions made about the roughness amplitude and the autocorrelation length.…”

“…Several works have shown that the transports properties of low-dimensional systems are significantly degraded by the introduction of scattering centers and localized states [9,10,22,14,23,24,25]. In the case of electronic transport, even a small degree of disorder can drastically reduce the electronic conductivity (especially in AGNRs rather than ZGNRs), even driving carriers into the localization regime and introduce 'effective' transmission bandgaps [15,26,27,28].…”

“…Graphene nanoribbons (GNR) are onedimensional structures that have attracted significant attention, both for fundamental research as well as for technological applications [1,2,3,4,5,6,7,8,9,10,11,12,13,14]. Ultra-narrow GNRs have been shown to retain at some degree the remarkable thermal properties of graphene.…”

“…Methods to investigate low-dimensional thermal transport vary from molecular dynamics [30,31,32,25,33,34], the Boltzmann Transport Equation (BTE) for phonons using scattering rates based on the single mode relaxation time approximation (SMRTA) [35,36,37,38,39,40,41], the non-equilibrium Green's function (NEGF) method [14,24,20,42,43,44,45,46], and the Landauer method [47,48,49,50], but also even more simplified semi-analytical methods that employ the Casimir formula to extract boundary scattering rates by assigning a diffusive or specular nature to the boundaries [51,52].…”

Phonon transport effects in one-dimensional width-modulated graphene nanoribbons

“…Recent theoretical works even suggest values up to ~6000 W/mK, with a large proportion of phonon mean-free-paths beyond 10μm [41][42][43]. Previous works indicated that under certain conditions, GNRbased channels could provide very high thermoelectric performance as well [44,45]. In addition, GNRs represent the most realistic 1D system available, and studies on this provide fundamental understanding on heat phonon in purely 1D systems.…”