Graphene Isotope Superlattices with Strongly Diminished Thermal Conductivity for Thermoelectric Applications

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 synthesize isotopic 12C/13C random mixes and isotope superlattices (SLs) with periods ranging from 46 to 225 nm by chemical vapor deposition. Raman optothermal conductivity measurements of these SL structures show an approximately 50% reduction in thermal conductivity compared to pristine 12C graphene. This average reduction is similar to the random isotope mix. The reduction of the thermal conductivity in the SL is well described by a model of pristine graphene and an additional quasi-one-dimensional periodic interfacial thermal resistance of (2.5 ± 0.5) × 10-11 m2 K W-1 for the 12C/13C boundary. This is consistent with a large anisotropic thermal conductivity in the SL, where the thermal conductivity depends on the orientation of the 12C/13C boundary.