Research Article


2019, 12(4): 791–799


Thermal bridging of graphene nanosheets via covalent molecular junctions: A non-equilibrium Green’s functions–density functional tightbinding study

Diego Martinez Gutierrez1, Alessandro Di Pierro1, Alessandro Pecchia2, Leonardo Medrano Sandonas3,4, Rafael Gutierrez3, Mar Bernal1, Bohayra Mortazavi5, Gianaurelio Cuniberti3,4,6, Guido Saracco1, and Alberto Fina1 (*)

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1 Dipartimento di Scienza Applicata e Tecnologia, Politecnico di Torino, 15121 Alessandria, Italy
2 Consiglio Nazionale delle Ricerche, ISMN, 00017 Monterotondo, Italy
3 Institute for Materials Science and Max Bergmann Center of Biomaterials, TU Dresden, 01062 Dresden, Germany
4 Center for Advancing Electronics Dresden, TU Dresden, 01062 Dresden, Germany
5 Institute of Structural Mechanics, Bauhaus-Universitt Weimar, D-99423 Weimar, Germany
6 Dresden Center for Computational Materials Science, TU Dresden, 01062 Dresden, Germany

Keywords: thermal conductance, molecular junctions, Green’s functions, density functional tight-binding (DFTB), graphene, heat transport, phonon transmission function
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Despite the uniquely high thermal conductivity of graphene is well known, the exploitation of graphene into thermally conductive nanomaterials and devices is limited by the inefficiency of thermal contacts between the individual nanosheets. A fascinating yet experimentally challenging route to enhance thermal conductance at contacts between graphene nanosheets is through molecular junctions, allowing covalently connecting nanosheets, otherwise interacting only via weak Van der Waals forces. Beside the bare existence of covalent connections, the choice of molecular structures to be used as thermal junctions should be guided by their vibrational properties, in terms of phonon transfer through the molecular junction. In this paper, density functional tight-binding combined with Green’s functions formalism was applied for the calculation of thermal conductance and phonon spectra of several different aliphatic and aromatic molecular junctions between graphene nanosheets. Effects of molecular junction length, conformation, and aromaticity were studied in detail and correlated with phonon tunnelling spectra. The theoretical insight provided by this work can guide future experimental studies to select suitable molecular junctions, in order to enhance the thermal transport by suppressing the interfacial thermal resistances. This is attractive for various systems, including graphene nanopapers and graphene polymer nanocomposites, as well as related devices. In a broader view, the possibility to design molecular junctions to control phonon transport currently appears as an efficient way to produce phononic devices and controlling heat management in nanostructures.
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Thermal bridging of graphene nanosheets via covalent molecular junctions: A non-equilibrium Green’s functions–density functional tightbinding study. Nano Res. 2019, 12(4): 791–799

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