Ballistic-Diffusive Phonon Transport and Anderson Localization in Aromatic-Ring Single-Molecule Junctions

We studied the cross-interface heat conduction in a nanodiamond-molecule-carbon nanotube heterostructure by nonequilibrium molecular dynamics simulations, where single-molecule junction is an asymmetric molecular structure of p-phenylenes with NH-C=O as the anchoring group. We found an interesting phenomenon that when the number of phenyls is odd (i.e. n = 1, 3, and 5), interfacial thermal conductance increases with temperature increasing from 100 K to 400 K, and then decreases after temperature greater than 400 K. When the number of phenyls is even (i.e. n = 2, 4, and 6), the interfacial thermal conductance as a function of temperature displays an overall increasing trend in the range 100 to 500 K. Temperature dependence indicates the disordered feature of single-molecule junction in heterojunction systems. The length dependence reveals the ballistic-diffusive phonon transport through single-molecule junctions. Interfacial phonon modes bridge the phonon transport between the dissimilar functional groups, which demonstrate the relationship between phonon localization and other phonons at the interface. Our observations open new perspectives to understand the heat conduction across single-molecule junctions in heterostructure systems and may provide theoretical assistance to applications of phonon engineering in single-molecule electronic devices and electronics thermal management.