Frequency-dependent phonon mean free path in carbon nanotubes from nonequilibrium molecular dynamics
Frequency-dependent phonon mean free path in carbon nanotubes from nonequilibrium molecular dynamics
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DOI：
10.1103/physrevb.91.115426
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发表时间：
2015-03-20
影响因子：
3.7
通讯作者：
Tulkki, J.
中科院分区：
文献类型：
--
作者：
Saaskilahti, K.;Oksanen, J.;Tulkki, J.
由于其长声子平均自由程 (MFP) 和高导热性，碳纳米管 (CNT) 是电子设备散热等的理想选择。然而，目前尚不清楚本征声子 MFP 如何依赖于非平衡状态下的振动频率。我们根据使用非平衡分子动力学计算的光谱声子传输函数确定了同位素纯碳纳米管中的光谱分辨声子 MFP，通过原子间势能函数的非谐项充分解释了电阻声子-声子散射过程。我们的结果表明，低频声子（f<0.5THz）的有效室温MFP超过10μm，而高频声子（f大于或接近20THz）的MFP在10-100nm范围内。由于确定的 MFP 直接反映能量流阻力，因此可以通过计算单频积分来准确预测任意管长度的热导率。所提出的结果和方法有望显着提高对低维纳米结构中非平衡热传输的理解。
Owing to their long phonon mean free paths (MFPs) and high thermal conductivity, carbon nanotubes (CNTs) are ideal candidates for, e.g., removing heat from electronic devices. It is unknown, however, how the intrinsic phonon MFPs depend on vibrational frequency in nonequilibrium. We determine the spectrally resolved phonon MFPs in isotopically pure CNTs from the spectral phonon transmission function calculated using nonequilibrium molecular dynamics, fully accounting for the resistive phonon-phonon scattering processes through the anharmonic terms of the interatomic potential energy function. Our results show that the effective room temperature MFPs of low-frequency phonons (f < 0.5 THz) exceed 10 mu m, while the MFP of high-frequency phonons (f greater than or similar to 20 THz) is in the range 10-100 nm. Because the determined MFPs directly reflect the resistance to energy flow, they can be used to accurately predict the thermal conductivity for arbitrary tube lengths by calculating a single frequency integral. The presented results and methods are expected to significantly improve the understanding of nonequilibrium thermal transport in low-dimensional nanostructures.