Mapping the Thermoelectric Properties of Noble Transition Metal Dichalcogenides at Atomic Scale

Scanning tunneling microscope (STM) provides a unique platform to characterize electronic, magnetic and thermal properties of atomic scale heterogeneities in 2D materials. Among these properties, the thermoelectric power is particularly interesting due to its high sensitivity to the density of states around Fermi level. Recently, it was predicted that monolayer noble transition metal dichalcogenides (TMDs) with hexagonal lattice structure are high performance thermoelectric materials at room temperature with their pentagonal counterparts promising even better performance due to the in-plane anisotropy of the lattice. However, the thermoelectric properties of these materials can significantly be altered by the heterogeneities in the atomically thin layers. Using a STM, we investigate the thermoelectric properties of both pentagonal and hexagonal noble-TMD monolayers in atomic resolution. We observe that atomic-scale defects like single chalcogenide vacancies and inhomogeneities in 2D layer-substrate interface create a rich thermoelectric landscape which is invisible to mesoscopic scale measurements. Detailed understanding and precise control of these heterogeneities can lead to next-generation thermoelectric materials for energy applications.