Thermal and Thermoelectric Properties of Molecular Junctions

Abstract

Molecular junctions (MJs) represent an ideal platform for studying charge and energy transport at the atomic and molecular scale and are of fundamental interest for the development of molecular‐scale electronics. While tremendous efforts have been devoted to probing charge transport in MJs during the past two decades, only recently advances in experimental techniques and computational tools have made it possible to precisely characterize how heat is transported, dissipated, and converted in MJs. This progress is central to the design of thermally robust molecular circuits and high‐efficiency energy conversion devices. In addition, thermal and thermoelectric studies on MJs offer unique opportunities to test the validity of classical physical laws at the nanoscale. A brief survey of recent progress and emerging experimental approaches in probing thermal and thermoelectric transport in MJs is provided, including thermal conduction, heat dissipation, and thermoelectric effects, from both a theoretical and experimental perspective. Future directions and outstanding challenges in the field are also discussed.

A review of oligo(arylene ethynylene) derivatives in molecular junctions

“…Thermal properties of molecular wires can be determined using modifications to these and other methods. [27][28][29][30] Molecular junctions are widely investigated using computational methods. Charge transport simulations using molecular orbitals derived from density functional theory (DFT) or Hückel (tight-binding) theory are used to calculate transmission functions for molecular junctions.…”

“…91 Notably, the Seebeck coefficient of a molecular junction is independent of the number of molecules present. 28 This means that unlike studies of electrical conductance, comparisons can be made between materials and methods without needing to estimate the number of molecules present in an ensemble junction. Thermal conductance measurements of SAMs are possible, but so far are largely limited to alkane species.…”

“…This section is concerned with the measurement of thermal properties of OAEs in molecular junctions. Molecular wires such as OPEs have been proposed as candidate materials for low-cost, environmentally-friendly thermoelectric generators, [27][28][29] i.e. devices that can harvest (waste) heat and transform it into electricity.…”

Side-group-mediated thermoelectric properties of anthracene single-molecule junction with anchoring groups

“…During the past two decades, the development of experimental techniques made it possible to measure the thermoelectric properties at the level of single molecules, providing new insights into different aspects of structure-function relationship in single-molecule junctions (recently reviewed by Wang et al 7 ). For instance, experimental techniques such as scanning tunneling microscope break junction (STM-BJ) 8 – 11 , mechanically controllable break junction (MCBJ) 12 , 13 and electromigrated break junction (EMBJ) 14 were developed to measure the thermopower of single-molecule junctions connected to metal electrodes—mostly made of gold (Au)—to form a metal-molecule-metal structure.…”

Nearfield trapping increases lifetime of single-molecule junction by one order of magnitude

“…To deliberately supress or switch off the nearfield trapping in the hotspot region (experimental details in Note S8), we defocus the laser in a controlled way or block the laser immediately after a set of experiments (see Figures S12 and 13). The first additional control allows us to exclude far-field effects related to laser illumination, like photocurrent 34 or photo-thermal effects, 52 that could influence the conductance and the stability of the single-molecule junction. Turning off the laser immediately after a power-dependent experiment, on the other hand, allows us to confirm the reversibility of the plasmon-supported enhancement of τ.…”