Ballistic-diffusive phonon transport and thermal rectification across single-molecule junctions

CH Diao and Z Yang and Y Dong and YY Duan, INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER, 157, 119851 (2020).

DOI: 10.1016/j.ijheatmasstransfer.2020.119851

We study the interfacial phonon transport across gold (Au) and carbon nanotube (CNT) composite interface that bonded by a carbon chain based single-molecule junction (MJ) using non-equilibrium molecular dynamics (NEMD) simulations. The interfacial thermal conductance is apparently dependent of the length of the molecules, indicating a pattern of ballistic-diffusive phonon transport. Relatively large thermal rectification is also enabled by the system and the rectification ratio is tunable by the molecular length. Detailed analysis on the phonon density of states (PDOS) shows the vibrational mismatch between the S and C-1 atoms in the MJs mainly contributes to the thermal rectification. The change of molecular length causes the variation in the amount of ballistic phonons in the interfacial area, which is the cause for the sensitivity of interfacial thermal conduction to molecular length. Importantly, this sensitivity of thermal transport to molecular length is different upon the heat flowing directions, showing the sophisticated tunability realized by the single molecular structures. This work demonstrates the CNT-metal interface consisting of single- molecule junctions are promising for nanoscale heat management and intelligent heat control. (C) 2020 Elsevier Ltd. All rights reserved.

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