Thermal conductance of single-molecule junctions

Single-molecule junctions have been extensively used to probe properties as diverse as electrical conduction 1 – 3 , light emission 4 , thermoelectric energy conversion 5 , 6 , quantum interference 7 , 8 , heat dissipation 9 , 10 and electronic noise 11 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 junctions 12 , 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. The thermal conductance of single-molecule junctions is measured using picowatt-resolution calorimetric scanning probes and is found to be nearly independent of the length of the alkanedithiol molecules studied.