Roles of vacuum tunnelling and contact mechanics in single-molecule thermopower

Abstract

Molecular junction is a chemically-defined nanostructure whose discrete electronic states are expected to render enhanced thermoelectric figure of merit suitable for energy-harvesting applications. Here, we report on geometrical dependence of thermoelectricity in metal-molecule-metal structures. We performed simultaneous measurements of the electrical conductance and thermovoltage of aromatic molecules having different anchoring groups at room temperature in vacuum. We elucidated the mutual contributions of vacuum tunnelling on thermoelectricity in the short molecular bridges. We also found stretching-induced thermoelectric voltage enhancement in thiol-linked single-molecule bridges along with absence of the pulling effects in diamine counterparts, thereby suggested that the electromechanical effect would be a rather universal phenomenon in Au-S anchored molecular junctions that undergo substantial metal-molecule contact elongation upon stretching. The present results provide a novel concept for molecular design to achieve high thermopower with single-molecule junctions.

Length-dependent Seebeck effect in single-molecule junctions beyond linear response regime

“…Numerous works are focused on exploring properties of the thermopower of single-molecule junctions. It was shown that the thermopower may be affected by molecular vibrations [11][12][13][14][15][16][17], by effects of molecular bridge geometry [18][19][20][21][22] by interactions between electrons participating in transport [23][24][25][26][27][28][29][30] and by photons [31]. Under certain conditions (e.g.…”

“…Length-dependent conductance and thermopower are usually observed and studied in junctions whose molecular linkers are chain-like structures consisting of several identical units (e.g. benzene or phenyl rings) [12,[19][20][21][22][45][46][47][48][49][50][51][52][53]. In the most of experiments, the thermopower appears to be proportional to the molecular bridge length.…”

Control of molecular orientation in a single-molecule junction with a tripodal triptycene anchoring unit: toward a simple and facile single-molecule diode

“…It has been reported that the coupling of the NH 2 group to the Au electrode is as strong as the S group in a molecular junction. 25) ABT is a small conjugated molecule which has a conduction orbital (HOMO) 26) that is delocalized throughout the molecule (Fig. S4 in supplementary data).…”

Thermally induced charge current through long molecules

“…In general, thermoelectric charge transport through molecular junctions is controlled by simultaneous driving by electric and thermal driving forces. The combined effect of these forces depends on several factors including the bridge geometry and the characteristics of its coupling to the leads [13][14][15][16][17][18][19][20][21][22][23][24] and electron-electron interactions [25][26][27][28][29][30][31][32][33][34]. Thermoelectric transport characteristics may be affected due to interaction between transmitting electrons and environmental nuclear motions [35][36][37][38][39][40][41][42][43][44][45][46][47][48][49][50][51][52][53][54] and the effects of quantum interference [55,56].…”