The study of thermoelectricity in molecular junctions is of fundamental interest for the development of various technologies including cooling (refrigeration) and heat-to-electricity conversion1,2,3,4. Recent experimental progress in probing the thermopower (Seebeck effect) of molecular junctions5,6,7,8,9 has enabled studies of the relationship between thermoelectricity and molecular structure10,11. However, observations of Peltier cooling in molecular junctions—a critical step for establishing molecular-based refrigeration—have remained inaccessible. Here, we report direct experimental observations of Peltier cooling in molecular junctions. By integrating conducting-probe atomic force microscopy12,13 with custom-fabricated picowatt-resolution calorimetric microdevices, we created an experimental platform that enables the unified characterization of electrical, thermoelectric and energy dissipation characteristics of molecular junctions. Using this platform, we studied gold junctions with prototypical molecules (Au–biphenyl-4,4′-dithiol–Au, Au–terphenyl-4,4′′-dithiol–Au and Au–4,4′-bipyridine–Au) and revealed the relationship between heating or cooling and charge transmission characteristics. Our experimental conclusions are supported by self-energy-corrected density functional theory calculations. We expect these advances to stimulate studies of both thermal and thermoelectric transport in molecular junctions where the possibility of extraordinarily efficient energy conversion has been theoretically predicted2,3,4,14.
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P.R. and E.M. acknowledge funding from the Office of Naval Research (N00014-16-1-2672, instrumentation), the Department of Energy (DE-SC0004871, scanning probe microscopy), and the National Science Foundation (CBET 1509691, ECCS 1407967, calorimetry). L.A.Z. and J.C.C. acknowledge funding from the Spanish MINECO (projects MAT2014-58982-JIN and FIS2014-53488-P, and FIS2017-84057-P). J.C.C. also thanks the Deutsche Forschungsgemeinschaft, the research programme SFB767 for sponsoring his stay at the University of Konstanz as Mercator Fellow. We acknowledge the Lurie Nanofabrication Facility and Michigan Center for Materials Characterization for facilitating the fabrication and calibration of devices.
Supplementary Figures 1–10 and Supplementary Table 1.