Thermal conductance and thermoelectric figure of merit of C60-based single-molecule junctions: Electrons, phonons, and photons
Thermal conductance and thermoelectric figure of merit of C60-based single-molecule junctions: Electrons, phonons, and photons
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DOI：
10.1103/physrevb.95.245404
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发表时间：
2017-06-07
影响因子：
3.7
通讯作者：
Pauly, F.
中科院分区：
文献类型：
--
作者：
Kloeckner, J. C.;Siebler, R.;Pauly, F.
最近的实验的动机，我们在这里提出了一个从头算研究的声子输运的热导和热电优值的C-60为基础的单分子结的影响。准确地说，我们结合联合收割机密度泛函理论与非平衡绿色的功能技术来计算这两个数量的连接与C-60单体或C-60二聚体连接到金电极，考虑到电子和声子的贡献。我们的研究结果表明，C-60单体结声子输运中起着次要的作用，在热导，反过来，在品质因数，它可以达到0.1的顺序上的值，这取决于接触几何形状。在C-60二聚体结中，声子的传输效率较低，但它们完全主导热导率，并降低了与单体结相比的品质因数。因此，声称通过堆叠C-60分子可以实现高热电性能，而没有考虑声子的贡献，是不合理的。此外，我们分析了近场热辐射的相关性，这些结的品质因数波动电动力学的框架内。光子隧穿效应是影响热电性能的另一个重要因素，这一点在分子电子学领域一直被忽视。我们的研究说明了至关重要的作用，声子输运和光子隧穿可以发挥，严格评估分子结的性能作为潜在的纳米热电器件。
Motivated by recent experiments, we present here an ab initio study of the impact of the phonon transport on the thermal conductance and thermoelectric figure of merit of C-60-based single-molecule junctions. To be precise, we combine density functional theory with nonequilibrium Green's-function techniques to compute these two quantities in junctions with either a C-60 monomer or a C-60 dimer connected to gold electrodes, taking into account the contributions of both electrons and phonons. Our results show that for C-60 monomer junctions phonon transport plays a minor role in the thermal conductance and, in turn, in the figure of merit, which can reach values on the order of 0.1, depending on the contact geometry. In C-60 dimer junctions, phonons are transported less efficiently, but they completely dominate the thermal conductance and reduce the figure of merit as compared to monomer junctions. Thus, claims that by stacking C-60 molecules one could achieve high thermoelectric performance, which have been made without considering the phonon contribution, are not justified. Moreover, we analyze the relevance of near-field thermal radiation for the figure of merit of these junctions within the framework of fluctuational electrodynamics. We conclude that photon tunneling can be another detrimental factor for the thermoelectric performance, which has been overlooked so far in the field of molecular electronics. Our study illustrates the crucial roles that phonon transport and photon tunneling can play, when critically assessing the performance of molecular junctions as potential nanoscale thermoelectric devices.