Exploring the conversion of heat to electricity in single molecules

May 10, 2017, Osaka University
Exploring the conversion of heat to electricity in single molecules
Figure 1: A schematic model of a single-molecule device. A molecule is interconnected to hot and cold electrodes via chemical bonds. Credit: Osaka University

The direct conversion of a temperature difference into electricity, known as the thermoelectric effect, is an environmentally friendly approach to directly harvesting electricity from heat. The ability of a material to convert heat to electricity is measured by its thermoelectric figure of merit. Materials with a high thermoelectric figure of merit are thus widely desired for use in energy harvesting. Quantum confinement effects in nanomaterials arising from their discrete electronic states may increase their thermoelectric figure of merit. In particular, a single molecule bridging two electrodes displays quantum confinement. Optimization of the electronic states of a single molecule bridging electrodes could yield a large thermoelectric effect. The contact between the molecule and electrodes will also influence its thermoelectric behavior. However, this relationship has seldom been considered because of technical difficulties.

Researchers at Osaka University have recently investigated the influence that the geometry of single molecule– contacts has on the thermoelectric behavior of the molecule. As reported in a recent edition of Scientific Reports, they simultaneously measured the and thermovoltage of with different groups anchoring the molecules to the electrodes at room temperature in vacuum.

The team first fabricated structures consisting of gold electrodes bridged by various single molecules. The distance between the electrodes, which were held under a temperature gradient, was repeatedly increased and decreased while the electrical conductance and thermovoltage of each was measured.

"We investigated the thermoelectric characteristics of various single benzene-based molecules with an emphasis on influence of their junction structures," says corresponding author Makusu Tsutsui. "The molecules displayed different behavior depending on their electrode-anchoring groups, and all molecule types displayed multiple thermovoltage states."

The multiple thermovoltage states of the molecules were investigated by thermoelectric measurements and theoretical analysis. The largest was observed for structures containing a stretched thiol linkage with the gold electrode. The increased thermovoltage of the structures with a stretched gold–thiol bond was attributed to this configuration shifting the energy level of the molecule involved in electron transport to a more favorable position.

"The observed dependence of thermovoltage on the anchoring group in the junction structures reveals a way to modulate the of single-molecule devices," explains Tsutsui.

The group's results expand our understanding of how the geometry of a single-molecule device can influence its thermoelectric figure of merit. These findings should contribute to the development of single-molecule thermoelectric devices that can efficiently derive electricity from heat.

Explore further: Deformable thermoelectric materials add a new twist to the design of energy-scavenging devices

More information: Makusu Tsutsui et al. Roles of vacuum tunnelling and contact mechanics in single-molecule thermopower, Scientific Reports (2017). DOI: 10.1038/srep44276

Related Stories

Theory of thermoelectric properties updated after 23 years

August 24, 2016

Since the Hicks-Dresselhaus publication in 1993, the researchers have focused the low dimensional materials (2D or 1D) for searching the high thermoelectric material according to their theory of the confinement effect on ...

Electricity generating nano-wizards

May 18, 2015

Just as alchemists always dreamed of turning common metal into gold, their 19th century physicist counterparts dreamed of efficiently turning heat into electricity, a field called thermoelectrics. Such scientists had long ...

Recommended for you

Physicist describes the shape of a wormhole

October 17, 2018

A RUDN physicist demonstrated how to describe the shape of any symmetrical wormhole—a black hole that theoretically can be a kind of a portal between any two points in space and time—based on its wave spectrum. The research ...

Physics: Not everything is where it seems to be

October 16, 2018

Scientists at TU Wien, the University of Innsbruck and the ÖAW have for the first time demonstrated a wave effect that can lead to measurement errors in the optical position estimation of objects. The work now published ...

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.