Mechanically Tuned Thermopower of Single‐Molecule Junctions

Abstract

In this paper, the tuning of the thermopower with single‐molecule junctions of fullerene (C60), 4,4′‐bipyridine (BPY), and p‐phenylenediamine (PPD) using scanning tunneling microscopy (STM)‐based break junction technique is demonstrated. Single‐molecule junctions are prepared in a nanogap between a Au‐STM tip and a Au(111) electrode. Upon applying a temperature difference across the junction, a thermoelectric voltage is generated across it. By mechanically controlling the tip–electrode separation distance, the thermoelectric voltage of the junction is tuned. The absolute value of the thermopower decreases with decreasing tip–electrode separation distance for BPY and PPD, while it increases for C60. Atomistic simulations of the junction illustrate how this arises from shifts in the conduction orbital energies induced by the mechanical compression of the junctions.

Benchmarking break-junction techniques: electric and thermoelectric characterization of naphthalenophanes

“…We explore first, whether the characteristic coupled behavior of increasing S for reduced G can be explained by decreasing molecule-electrode electronic couplings, Γ. [35][36][37][38][39] We assume that the electronic couplings to the electrodes are reduced in the stretching process towards the point of rupture, where the molecule is fully erected inside the junction. Fig.…”

“…Such molecular energy level shifts and their influence on the thermopower have been reported in the literature for various molecules and models. [35][36][37]40,41 Overall, the four-site tight-binding model offers a framework for elucidating the significant mechanisms, leading to the global trends of S and G in the experimental results. Based on our analysis, a reduction in Γ during the stretching combined with shifts in orbital energies that bring the HOMO level closer to the Fermi energy are responsible for the observed behavior.…”

“…Such molecular energy level shifts and their influence on the thermopower have been reported in the literature for various molecules and models. 35–37,40,41…”

Exploring the Impact of the HOMO–LUMO Gap on Molecular Thermoelectric Properties: A Comparative Study of Conjugated Aromatic, Quinoidal, and Donor–Acceptor Core Systems

“…They can be used in a variety of applications, ranging from power generation in automobiles and industrial processes via the Seebeck effect to cooling of electronics and other devices via the Peltier effect. − Current inorganic thermoelectric materials, such as bismuth telluride (Bi 2 Te 3 ), lead telluride (PbTe), and silicon germanium (SiGe), have been widely studied and utilized, but their applications are restricted due to toxicity and limited availability, as well as a generally low conversion efficiency at room temperature. Also, in most semiconductors, the increase in conductance is accompanied by a decrease of the Seebeck coefficient, which is not desirable and makes improving the thermoelectric efficiency a difficult task. − …”

“…Also, in most semiconductors, the increase in conductance is accompanied by a decrease of the Seebeck coefficient, which is not desirable and makes improving the thermoelectric efficiency a difficult task. 8 − 14 …”