Thermal conductance of single-molecule junctions

Abstract

Single-molecule junctions have been extensively used to probe properties as diverse as electrical conduction1-3, light emission4, thermoelectric energy conversion5,6, quantum interference7,8, heat dissipation9,10 and electronic noise11 at atomic and molecular scales. But a quantity of considerable current interest-the thermal conductance of a single-molecule junction-has eluded direct experimental determination, reflecting the considerable challenge of detecting minute heat currents at the picowatt level. Here we show that, when used in conjunction with a time-averaging measurement scheme to increase the signal-to-noise ratio, the custom-developed probes that enabled thermal conductance measurements of single-metal-atom junctions12 can also quantify the much lower thermal conductance of single-molecule junctions. Our experiments on prototypical Au-alkanedithiol-Au junctions, where the number of carbon atoms was varied from two to ten, 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 conductance13-16 have remained experimentally inaccessible.