Spectral phonon mean free path and thermal conductivity accumulation in defected graphene: The effects of defect type and concentration

TL Feng and XL Ruan and ZQ Ye and BY Cao, PHYSICAL REVIEW B, 91, 224301 (2015).

DOI: 10.1103/PhysRevB.91.224301

The spectral phonon properties in defected graphene have been unclear due to the lack of advanced techniques for predicting the phonon-defect scattering rate without fitting parameters. Taking advantage of the extended phonon normal mode analysis, we obtained the spectral phonon relaxation time and mean free path ( MFP) in defected graphene and studied the impacts of three common types of defects: Stone-Thrower- Wales ( STW) defect, double vacancy ( DV), and monovacancy ( MV). The phonon-STW defect scattering rate is found to have no significant frequency dependence, and as a result, the relative contribution of long-wavelength phonons sharply decreases. In contrast, the phonon scattering by DVs or MVs exhibits a frequency dependence of tau(-1)(p-d) similar to omega(1.1-1.3) except for a few long-wavelength phonons, revisiting the traditionally used similar to omega(4) dependence. We note that although MV-defected graphene has the lowest thermal conductivity as compared to the other two defected graphene samples at the same defect concentration, it has a portion of phonons with the longest MFP. The contribution from the long-MFP and long-wavelength phonons does not decrease much as the vacancy concentration increases. STW defect andMV block more out-of-plane modes than in-plane modes, while DV has less bias for which mode to block. As the MV concentration increases from 0 to 1.1%, the relative contribution from out-of-plane modes decreases from 30% to 18%, while that of the transverse acoustic mode remains at around 30%. These findings of spectral phonon properties can provide more insight than the effective properties and benefit the prospective phononic engineering.

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