Rayleigh waves, surface disorder, and phonon localization in nanostructures

Abstract

We introduce a technique to calculate thermal conductivity in disordered nanostructures: a finite-difference time-domain (FDTD) solution of the elastic wave equation combined with the Green-Kubo formula. The technique captures phonon wave behavior and scales well to nanostructures that are too large or too surface disordered to simulate with many other techniques. We investigate the role of Rayleigh waves and surface disorder on thermal transport by studying graphenelike nanoribbons with free edges (allowing Rayleigh waves) and fixed edges (prohibiting Rayleigh waves). We find that free edges result in a significantly lower thermal conductivity than fixed ones. Free edges both introduce Rayleigh waves and cause all low-frequency modes (bulk and surface) to become more localized. Increasing surface disorder on free edges draws energy away from the center of the ribbon and toward the disordered edges, where it gets trapped in localized surface modes. These effects are not seen in ribbons with fixed boundary conditions and illustrate the importance of phonon surface modes in nanostructures.

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Cited by in corpus (7)

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• Structure-specific, mode-resolved phonon coherence and specularity at graphene grain boundaries
• Heat current anticorrelation effects leading to thermal conductivity reduction in nanoporous Si
• Impact of dimensional crossover on phonon transport in van der Waals materials: a case study of graphite and graphene
• Thermal conductivity in 1d: disorder-induced transition from anomalous to normal scaling
• Universality of phonon transport in surface-roughness dominated nanowires
• Effect of wave versus particle phonon nature in thermal transport through nanostructures