Thermoelectric and Thermionic Transport across van der Waals Heterostructures

The thermoelectric voltage generated at an atomically abrupt interface has not been studied exclusively due to lack of established measurement tools and techniques. We report a novel technique and device structure to probe the thermoelectric transport across Au/h-BN/graphene heterostructures. An indium tin oxide (ITO) transparent electrical heater is patterned on top of this heterostructure, enabling Raman spectroscopy and thermometry to be obtained from the graphene top electrode in situ under device operating conditions. An AC voltage V(w) is applied to the ITO heater and the thermoelectric voltage across the Au/h-BN/graphene heterostructure is measured at 2w using a lock-in amplifier. We report the Seebeck coefficient for our thermoelectric structure to be -215 μV/K. The Au/graphene/h-BN heterostructures enable us to explore thermoelectric transport on nanometer length scales. The thermoelectric voltage generated at the graphene/h-BN interface is due to thermionic emission rather than bulk diffusive transport. As such, this should be thought of as an interfacial Seebeck coefficient rather than a Seebeck coefficient of the constituent materials.