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Thermal conductivity of graphene isotope superlattices

Graphene has a high intrinsic thermal conductivity and a high electron mobility. The thermal conductivity of graphene can be significantly reduced when different carbon isotopes are mixed, which can enhance the performance of thermoelectric devices. Here we compare the thermal conductivities of isotopic c12/c13 random mixes with isotope superlattices with periods ranging from 46 to 225 nm. Raman Opto-Thermal conductivity measurements of these superlattice structures show an approximately 50% reduction in thermal conductivity compared to pristine c12 graphene. This average reduction is similar to the random isotope mix. The reduction of the thermal conductivity in the superlattice is well described by a model of pristine graphene and an additional quasi-one dimensional periodic interfacial thermal resistance of (2.5\pm 0.5)\times 10^{-11} m^2 K/W for the c12/c13 boundary. This is consistent with a large anisotropic thermal conductivity in the superlattice, where the thermal conductivity depends on the orientation of the c12/c13 boundary.