Achieving Huge Thermal Conductance of Metallic Nitride on Graphene Through Enhanced Elastic and Inelastic Phonon Transmission

Low thermal conductance of metal contacts is one of the main challenges in the thermal management of nanoscale devices of graphene and other two-dimensional (2D) materials. Previous attempts to search for metal contacts with high thermal conductance yielded limited success because of the incomplete understanding of the origins of low thermal conductance. In this paper, we carefully study the intrinsic thermal conductance of metal/graphene/metal interfaces to identify the heat transport mechanisms across graphene interfaces. We find that unlike metal/diamond interfaces, the intrinsic thermal conductance of most graphene interfaces (except Ti and TiNx) is only approximate to 50% of the phonon radiation limit, suggesting that heat is carried across graphene interfaces mainly through the elastic transmission of phonons. We thus propose a convenient approach to substantially enhance the phononic heat transport across metal contacts on graphene, by better matching the energy of phonons in metals and graphene, for example, using metallic nitrides. We test the idea with TiNx with phonon frequencies of up to 1.2 x 10(14) rad/s, 39% of the highest phonon frequencies in graphene of 3.1 x 10(14)/s. Interestingly, we obtain a huge thermal conductance of 270 MW m(-2) K-1 for the TiNx/graphene interface, which is approximate to 140% of the phonon radiation limit. Thus, the huge thermal conductance cannot be fully explained by enhanced elastic phonon transport alone, but may be partially attributed to inelastic phonon transport across the TiNx/graphene interface. Our work provides guidance for the search for good metal contacts on 2D materials and devices.