Thermal conductance of single-molecule junctions

Abstract

Single-molecule junctions have been extensively used to probe properties as diverse as electrical conduction^1-3, light emission⁴, thermoelectric energy conversion^5,6, quantum interference^7,8, heat dissipation^9,10 and electronic noise¹¹ at atomic and molecular scales. However, a key quantity of current interest-the thermal conductance of single-molecule junctions-has not yet been directly experimentally determined, owing to the challenge of detecting minute heat currents at the picowatt level. Here we show that picowatt-resolution scanning probes previously developed to study the thermal conductance of single-metal-atom junctions¹², when used in conjunction with a time-averaging measurement scheme to increase the signal-to-noise ratio, also allow quantification of the much lower thermal conductance of single-molecule junctions. Our experiments on prototypical Au-alkanedithiol-Au junctions containing two to ten carbon atoms confirm that thermal conductance is to a first approximation independent of molecular length, consistent with detailed ab initio simulations. We anticipate that our approach will enable systematic exploration of thermal transport in many other one-dimensional systems, such as short molecules and polymer chains, for which computational predictions of thermal conductance^13-16 have remained experimentally inaccessible.