Unusual Width Dependence of Lattice Thermal Conductivity\nin Ultranarrow Armchair Graphene Nanoribbons with Unpassivated Edges

Abstract

Low-dimensional\nmaterials attract extensive interest in electronic\napplications since the synthesis of graphene. Understanding the thermal\ntransport in low-dimensional materials with shrinking characteristic\nsize where strong confinement effect occurs is of importance for the\nthermal management of nanoelectronics. Recently, the atomically precise\narmchair graphene nanoribbons (AGNRs) with well-defined edges have\nbeen successfully synthesized. Serving as the fundamental functional\nelements, AGNRs can potentially make novel nanoelectronics realizable.\nHere we systematically investigate the thermal property variations\nof the ultranarrow AGNRs with width without hydrogen termination using\nthe density-functional-based tight binding (DFTB) method, which combines\nthe accuracy of density functional theory and the efficiency of tight-binding\napproximation. The lattice thermal conductivity increases unexpectedly\nfrom 531.7 to 3470.6 W/m-K as the width decreases from 0.97 to 0.35\nnm, different from the width dependence in larger scales; the lattice\nconstants, low frequency phonon group velocities and lifetimes, and\nacoustic phonon contributions also show increasing trends as the width\ndecreases. Such behaviors are attributed to the changes in the lattice\nconstants and the phonon scattering channels of the dominant low frequency\nacoustic phonons. Further DFTB calculations reveal that planar ultranarrow\narmchair BN nanoribbons also show analogous trends in thermal properties\nwith the shrinking width. This study unveils the width-dependent phonon\ntransport behaviors of ultranarrow planar nanoribbons and offers guidelines\nfor the thermal design of potential nanoelectronics.